Foundation design on poor soil

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TECHNICAL PAPER

A systematic approach to the design and

construction

of

single storey residential

masonry structures on problem soils

By R B WATERMEYER Member) and B E TROMP Member )

Synopsis

A site classification system relating differential move ment of problem soil

horizons in non-dolomitic areas to foundation design and building procedures

for single-storey residential structures of masonry construc tion is presented.

Servicea bility criteria as well as a systematic approach to the implem entation of

the technology described are formulated.

Samevatting

n Klassifiseringstelselwat die verb and tussen diffensiIle bewegings van prob-

leemgrond in nie-dolomitiese gebiede en fondamentontwerp en bou-

prosedures ten opsigte van enkelverdieping-woningstrukture uit m esselwerk-

konstruksie daarstel, word beskryf. Diensbaarheidskriteria asook n stelsel-

matige benadering tot die implementering van die tegnologie wat beskryf is,

word ge formuleer.

Introduction

Problem soils in South Afrlca

Problem soils and unstable soils In non-dolomitic areas, wh~ chmay

detrimentally affect the structures that they support, are widely dls-

Ronald B Watermeyer

PrEng graduate d in

civil engineering from the University of the

Witwatersrand in 1978. As a bursar, he

entered employment with Transnet and was

involved n the civil and building construction

of the service depots at the Sentrarand

Marshalling Yard complex. In 1984 he was

transferred from the central yard construc-

tion office to the Chief Civil Engineer s struc-

tural design office, where he held the pos t of

District Engineer (Structures). InJuly

l988

he oined the flrm of consult-

ing engineers, Soderlund and Schutte Inc, becomin g a director of the

firm in March 1990.He currently serves on the masonry committees of

the SABS a nd SAICE.

Bryan Trornp

PrEng was born in 1949. He

obtained a BSc (Eng) (Civil) degree at the

University of the Witwatersrand in 1972 and

worked for the Johannesburg City Engineer s

Department from 1972 to 1974 gaining ex-

perience in the planning, design and con-

struction of municipal roads and services.

After three years as a project geotechnical

engineer with a buildi ng concern, he joined

Steffen Robertson an d Kirsten Inc, where he

was extensively involved ~nal l aspects of c ivil an d mrnlng geotechnrcs.

In July 1980he co-founded the firm of Schwartz TrompandAssociates.

His main fields of interest are site investigation a nd the design of spe-

cial foundations in the civil and mining ndustries and the evaluation of

materials for use in road and earthworks construction.

Thls paper was submitted to Independent referees for scrutlny prior to accep-

tance for publication.

tributed throughout South Africa, as shown in Fig 1 Horizons with

potentially collapsible fabrics are commonly encountered across the

southern, south-western and central parts of the Transvaal, in the

Bloemfontein and Durban environsand in acorr idor in theorange Free

State north of Bloemfontein stretching to the Vaal River. Expansive

soils, on the other hand, are more widely distributed across South

Africaand have been reported tooccu r in most partsof thecountry with

the exception of the Little Karoo, the extreme northern Cape, the far

northern Transvaal and the extreme eastern Transvaal regions. The

areas most affected by expansive soils include the OFS gold fields, the

western Transvaal and the PWV complex, which are some of the most

densely populated areas in South Africa.

Pioneering work in identifying, establishing and predicting basic

parameters for expansive soils was undertaken by Jennings and

others fro m as early as 1947 . By the early 1960s practical structura l

procedures and techniques for building construction on these soil

horizons as well as a site classification system had been formulated

and successfully ~rnple mented, hich resulted in a table being com-

piled by Jennings and Kerrich2 relating structural solutions (building

practices) to a range of to tal estimated heave movements. At about the

same time, the phenomenon of collapsing soils was mvestigated by

Knight, who developed a theory explaining the mechanism of collapse

and a laboratory p rocedure for predicting collapse settlement3.

In the field of expansive clays, ongoing South African research has

made advances in pred icting the total and differential heave move-

ments that astructure may experience and the development of an ade-

quate design method for stiffening the foundations of residential

structures to tolerate these movements. On the other hand, no signifi-

cant research in to the field of structures founded on collapsible soils

has been undertaken since the early 1960s. To date, there is no South

African code of practice for the construction of structures founded on

prob lem soils, despite the obvious necessity for such acode. Neither is

there a uniform classification system nor a standardized approach to

build ing procedures for the range of problem soil horizons that may be

encountered in this country.

Existing legislation

The existing South African legislation makes provision for

1. The general investigat ion of soil conditions prlor to the establish-

ment of a township in some of the provinces (eg theTransvaal Town

Planning and Township Ordinance (Ordinance 15 of 1986)).

2 The submiss~on f plans for approval by the local author~ ty rlor to

the construction of structures on problem soil horizons (National

Building Regulations and Building

Standards Act (Act 103 of

1977)).

According to the National Build ing Fiegulations4 (NBR) the foun-

dations of all structures must comply with the functional requirements

contained in Regulation HI, namely The foundation of any building

shall be des igned to safely transmit all the loads from such building to

the ground. Empirical rules that are deemed to satisfy this regulation

are contained in SABS 04005. However, these empirical rules do not

apply to foundations supporting walls founded on heaving soils, shrink-

able clays or soils with a collapse fabnc, in wh ~c h ase the appolnt-

ment of a professional engineer to design such foundations In ac-

DIE SlVlELE INGENIEUR in Suid-Afrika Maar t 1992



cordan cewi th Regula t ion B1 s requ i red ; s uch app o~ n t m e n tonst i tutes

wi th changes in mois ture content :

comp l iance wi th Regula tion H1

In terms of Part A of the Reg ulat ions, local authori t ies are em -

powered to requ i re that an app l i ca t ion to erec t a bu i ld ing be accom-

pan led by adequate in format ion regard ing the subso i l o f t he s i te .

Fur thermore, hey areen t i t l ed o presc r ibethe form at and ex tent o f any

add i t i ona l documentat ion to b e submi t ted together wi th an app l i ca t ion

to erec t a bu i ld ing on a pr ob le m so i l hor izon.

Terminology

The terms used to de sc r~ be eotechn ica l cond i t i ons and s t ruc tura l

so lut ions apper ta in ing to prob lem so i l s are genera l l y i l l -de f ined and

may vary f rom one pu b l i ca t ion to another . A go od exa mple o f t h i s may

be found in the term s t i f f ened ra f t6 . Th is te rm i s common ly use d in

S ou t h ~ f r i c a . o des c r i be a founda t i on t echn i que on ex pansi v e so i ls

~ nv o l v i nghe

construction

of a gr id o f re in force d conc re te beam s cas t

integral ly wi th the f loor s labs, which by v l r tue of thei r s t i f fness r educe s

the d i f fe rent ia l moveme nts to a level t ha t can b e to lera ted by the

masonry supers t ruc ture wi thout s ign i fi cant s t ruc tura l d i s t ress occur -

r i ng. I n t he US A , t he s am e f oun da t ~ on y s tem i s s om e t ~ m es es c r i bed

as a waf f le s labg O o r a s t i f fened m a t 12 whi ls t i n Aus t ra l~a he terms

s tandard ra f t and gr i l l age ra f tg , depe nding o n the wid th o f t he beam s

and the excavat ion techn ique e mploye d, are a lso used. Recent l y, i n

South A f r i ca , t he term waf f le s lab was in t roduce d to desc r ibe s t i ff ened

raf ts wi th n ar row c lose ly spaced beams that d i f f e r i n geome t ry (as

oppos ed t o f unc t i on ) f r om t he A m er i c an s y s t em bea r i ng t he s am e

nam e . T he t e rm i no l ogy IS f u r ther con fused by the use o f s t i f f ened ra f t

as a foun dat~ on echn iqu e on co l laps~ ng o i l s i tes3. where, a l though

there are s im i la r i ti es in the geo met r i c layout , t he in tended func t ion o f

t he f ounda t ion d~ f f e r s ons i de rab ly f r om t he f unc ti on ~ t s r eq u~ redo

perform in the case of expans ive soi ls .

De f in i ti onsand ~ n t e rp re t a t i on s o fe rm s and ex p res s i ons ape r t a i n i ng

t o p rob l em s o i l s i n S ou th A f r~ c a av e been f o rm u l a ted and a re c on -

ta ined in Appe ndix A . The words a nd express ions used in th i s paper

have the same meaning as ass igned to them in Appen dix A .

The problem

T he na t u re o f m ov em en t s o n p rob l em s o i ls

Foundat ion mo veme nts on prob lem so i l s are normal l y assoc ia ted

1 Expans ive so i ls undergo vo lume chang es upon the wett ing and dry -

ing o f t he so i l h or i zons . The natura l wet t ing up o f t he so i l hor i zon

be low the s t ruc ture may b e suf fi c ien t to deve lop a m oun d pro f i l e

undern eath the s t ruc ture . A l te rnat ive ly, a change In mols ture con-

tent due to the e f fec ts o f c l imat i c cond i t i ons and vegeta t ion (evapo-

t ransportat ion) or a lowering of the water table may resul t In

shrmkage movements .

2 . Co l laps ib leso il s w i l l exper ien ceset t leme nt upon satura t ion f rom an

externa l source. This set t lemen t wi ll take p lace rapidly i f the soil is

f ree-dra ining a nd grad ual ly i f i t is not free-dra ining.

Uni form heave, shr inkage, co l lapse set t lements or conso l ida t ion

set t lements genera l ly do not cause dam age to s t ruc tures , but may det -

r imenta l l y a f fec t serv ice (water and sewerage) p lp e ent r~e s t t he

per imeter o f s t ruc tures . Non-un i form or d i f f e rent ia l movem ents cause

s t ruc tura l d i s t ress , deformat ion s and overs t ress ing o f s t ruc tura l com-

ponents , resu l t ing in the occu r rence o f da mage to the s t ruc tures .

Tendenc ies in damage

Dam age caused by heave/shr inkage movements d i f f e rs f rom that

due to col lapse or consol idat ion set t lements . General ly , i f no pre-

caut ions are taken to reduce d i f f e rent ia l movements or to prevent con-

di t ions promoting potent ia l movements f rom occur r ing , such m ove-

rnents wi ll re sul t in the fol lowing:

1 On expansive soi ls :

Damage wi l l occur throughout the s t ructure, the severi ty of the

dama ge be ing greates t i n the ex terna l wa l ls , o r i n terna ll y in the

cent ra l por t ions o f t he s t ruc ture , depending on the mois ture con-

tent o f t he so il p rec ed ing cons t ruc t ion ; an d

Crack s wi l l a l ternately ope n and c lose as a resul t of seasonal and

c l imat ic changes in the water content of the soi l .

2 . O n com pre ss~b le o i ls :

Dam age w~ l l an i fes t ~ t s e l fn a par t~cu la r or t lon o f t he s t ruc ture ,

eg a long a l i ne through the s t ruc ture ; and

Cracks wi l l open in t ime as subsequent se t t l ement occurs

Fig

:

istribution of expansive clays and collapsing sands

SITES WHERE HE VING

IS

KNOWN

TO OCCUR

84

DIE S lV lELE INGENIEUR in Su id -A f r~ ka Maar t 1992



3.

On col laps ib le sol ls :

Damage wi ll be conf ined to p or t ions o f t he s t ruc ture as and when

co l lapse set t lement occurs , eg beneath foun dat ions ad jacent to

leak ing p lpes or ad jacent to areas o f poor dra inage where pond-

~ n gf rainfal l occurs .

Typ ica l ranges o f cos ts o f remedia l work requ i red to rehab i l i ta te

s t ruc tures that were bu i l t w i thout p recaut ions on norm al s t r ip foot ings

are given in Table 113.

Prevent ion versus repair

Notwi ths tand ing the fac t t ha t the NBR conta in m anda tory requ i re-

ments for the des ign o f f oundat ions on p rob lem so i ls , t he ques t ion

ar i ses as to whether or not prevent ion o f c rack lng i s pre ferab le to

remedia l measures. In a t tem pt ing to answer th i s ques t ion, the fo l low-

ing fac tors shou ld be taken in to account :

1 . The cost o f repa i r o r abno rmal main tenance cos ts (see Tab le 1 for

order of magni tudes).

2. The ini t ia l con struc t ion cost ' . l (see Tab le 2 for est imates).

3 The impac t o f s t ruc tura l damage on the resa le va lue o f t he

st ructure.

4 The cost of inconvenience associated wi th repa i rs .

5. Emo t ional ef fects .

6.

Englne ering factors such as s tabi l i ty , safety and s t ructural in-

tegrity.

7 . Env i ronmenta l f ac tors such as whether or not the s t ruc ture i s

habitable.

8 The r isk of the predic te d potential move men t be lng rea l ized.

I r respec t ive o f whether or n ot ~ t s mo re economical t o a llow damage

than to prevent damage , the leg is la tors have determ ined that preven-

t ion i s requ i red. I t wou ld appear f r om Regula t ion B1 o f t he NBR that the

in tent ion o f t he law-makers i s to address the above-ment ioned

engineer ing and env i ronmen ta l ac tors wi th , perhaps , theem phas is on

stabi l ity a nd safety .

Shor t com ings ~n the ex is t ing leg is la t ion an d admin is t ra t ion pro -

c edu res

A l though loca l author i t ies , i n erm sof the NBR, areap poin ted toc on-

t ro l and to approv e the erec t ion o f s t ruc tures o n a l l so i l hor i zons , they

se ldom exerc ise the i r powe rs to ca l l f o r f oundat ion re por t s and to

enforce the NBR desp i te the i r knowle dge o f the presence o f prob lem

soi l hor i zons in par t i cu lar areas under the i r cont ro l . The genera l

approach o f mos t loca l author i t i es i s to d is tance themselves f rom

invo lvement in s t ruc tures fou nded on p rob lem so i ls . The onus o f

detec t ing such hor i zons and com pl iance wi th the regu la t ions i s p laced

on the owner a nd the su i tab i li t y of t he cons t ruc t ion so lu t ions on a p ro-

fess iona l eng ineer appo in ted by the owner . A l te rnat i ve ly , a loca l

author i t y may approve a p lan for the cons t ruc t ion o f a s t ruc ture that i s

t o be ounded on a p rob l em s o il ho r iz on , p rov i ded theowne r ge t s a p ro -

fessiona l eng ineer to s lgn ' fo r t he s t ruc ture . Deta l ls o f any des lgn pro -

posa ls are rare ly ca l led for or

examined.

The wisdom of th i s approa ch i s ques t ionab le . Rep or t s abound in the

news media o f t ownsh ips and hous ing schem es cons t ruc ted wi thout

any , or w i th inappropr ia te , precaut ions hav ing been taken aga ins t

ground movement , now suf fer ing the inev i tab le consequences o f

ex tens ive c rack ing and s t ruc tura l d i s t ress . F requent l y , where the s ta te

or local government is involved, these pro blems becom e pol i t ic ized.

The record o f t he co nduc t o f p ro fess iona l eng ineers in th i s f ie ld o f

eng ineering i s fa r f rom be ing above re proach . An examinat ion o f t he

South A f r i can C ounc i l f o r P ro fess iona l Eng ineers ' (SACPE) annual

reports over the past few years indicates that the major i ty of the dis-

c ip li nary e nqu i r ies in to des ign inadequac ies re la ted to foundat ion

des ign on uns tab le an d expans ive so i l s. I n the 1986-1987 annual

repor t , t he Counc i l recorded the fo l lowing when rep or t ing on the Code

of Profess ional Conduct and contravent ions of the Act : 'A number of

compla in ts invo lved the unde rdes ign o f f oundat ions in areas o f expan-

s ive so il s . Counc i l i s concerned that pro fess iona l eng ineers tend to

underest imate the level of expert ise req uire d. ' In i ts Newslet ter N o

4

(Ju ly 1989) SACPE at temp ted to addre ss th i s i ssue by br ing ing to the

at tent ion of profess ional engineers the fact that the 'des ign of foun-

dat ions in areas of expa ns ive so i ls is a mat ter wh ich requ i res spec ia l

ex pe r ti se ' and by u rg i ng p ro fes s iona l eng i nee rs t o a c ~ u i r e he

Table 1: Typical repair costs of masonry single-storey residential structures

founded on problem soils with normal construction and no pre-

cautions

Site class Dffferen tial

(See Table 3 movement

Type of

movement

Shrinkage1

heave

Settlement

Approxfmate range of eshmats

repair cost*

( of present-day new house

construction cost)

On sltes

subject

to

collapse settlement

thls

f ~ g u r e o u ld

r r p r e s e n t the repal r

cost to

repa l r

one

localved area

of collapse

settlement

Table

2:

Typical initial costs of s tructural solutions for single-storey residential

masonry structures founded on problem soils

Site class

l Differen tial Type of

(See Table

3

movement

I

movement

C , H. R and

S

<2 , 5

I

C1 and S1 2.5 7.5 Settlement

C2 and S2

>T

H1

H2

H2 and H3

H 2 a n d H 3

Construchon

type

Normal constructlon

[inte rna l walls foundec

on strip footings)

2.5 7.5

7,5

15

> l

> l 5

Estimated

addftional

CO

(

of

inftfal

house con-

structfon cos

O

Heave/

shrinkage

Modified normal

Split constructlon

St~ffenedaft

Piled constructlon

Modified normal 1 3

Piled or pler 5 1Soo

:onstruction

Stiffened strip foot~ngs

3r stiffened ra ft

5 10

necessary capa b l l l t ~es ' o under take such des ign w ork , l e by keep ing

up oda t ew i t h m ode rn ec hno log i c al adv anc es s o as t oens u re an ade -

quate and economlc des ign. '

Des ign inadequacies are exacerbated by the fact that no des lgn

s tandards or co des o f prac t i ce ex ist ~nSouth A f r i ca for the des ign and

cons t ruc t ion o f s t ruc tures on p rob lem so l ls . Th ls

shortcoming

engen-

ders er ron eous expec ta t ions of s t ruc tura l per formance and m lsun-

ders tand ings between owner and professional engineer ; f u r thermore

serv iceab i li t y s tandard s tend to be owered in he pursu i t of a reduc t ion

In ini t ia l construct ion costs by developers.

ddressmg the problem

A

hypothes is

Observations

of repo rted fal lures In res ldent lal masonry s t ructures

founde d on prob lem so l l s In non-do loml t l c areas have led to thefo llow-

Ing hypothes ls P rov lded that a reasonably

appropriate

cons t ruc t lon

so lu t lon IS adopted s lgn l fl cant dama ge will not occur

I f thls hypothes ls IS ado pted as the bas ls for des lgn a system of

c lasses of s ltes serv lceab l l l ty cr l ter la and accepta ble construct lon

prac t l ce IS r equ l red t o de f lne and I n te rp ret t he t e rm s app ro p r~ a t e on -

s t ruc tlon so lu t ions an d s lgn i f lcant dam age

A pro po sed s i te c lass if i ca tion sys tem

Table

3

conta ins a propo sed universal slte classif ication system for

residential s i tes where the found ing hor i zons may be described as sta-

ble, expans ive, compress ible or potent ial ly col laps ible in character.

Th is tab le IS not intended for dolomit ic areas unless addi t ional inves-

t igat lons are carr ie d out to veri fy the s tabi l i ty of the dolomlt ic for mat ion

(ie the r lsk of s inkholes a nd dol in e format ion is accep table). S imi lar ly ,

areas o f l andf i ll , where the com pac t ion h as not been adequate ly co n-

t ro l led , or areas under la in b y sha l low mine work ings do n ot fal l w i th in

the scope o f Tab le

3

The des ign at ion of s i te c lasses is based on the assum pt ion that the

magn i tude o f d if f e rent ia l movements exper ienced by single-storey

res ident ial s t ructures, expressed as a percentage of the total soi l

movements , are approx imate ly

50

per cent in the case of soi ls that

exh ib i t expans ive or com press ive charac ter i s t ics and 75 per cent in he

DIE SlVlELE INGENIEUR in Suid-Afr ika Ma art 1992



Fine-grained solls

with moderate to

very hlgh plastic~ty

(clays, silty clays,

clayey s~l ts nd

sandy clays)

Table

3:

Residential site class designations

Silty sands, sands, Compressible

sandy and gravelly and potent~ally

soils collapsible soils

Fine-grained so~ls Compressible

(clayey silts and soils

clayey sands of

low plasticity),

sands, sandy and

gravelly soils

Typical founding

material

Rock (excluding mud

rocks that

exhib~t welling

to some depth)

case of soils that exhibit both compressive and collapse characteris-

tics. Where this assumption is incor rect or inappropriate , the site class

should be determined on the basis of the resultant differential move-

ment read from the table being equal to that expected in the field.

In some instances, it may be more appropriate to use a composite

designation to describe a site more fully, eg Cl /H 2 or S1 and/or H2.

Composite site classes may lead to higher differential movements and

result in design solutions appropriate to a higher range of differential

movement, eg a class RIS1 site may be described as a class S2 site.

Alternatively, a further site investigation may be necessary, as the final

design solution may depend on the location of the structure on a par-

ticular site with variable soil conditions.

Proposed serviceability criteria

The NBR (see Regulation Bl (1 ) of Part B) prescribe that 'any build-

Ing and any structural element or component thereof shall bedes igned

to provide strength, stability, serviceability and durability, in accor-

dance with accepted principles of structu ral design

.'

The 'deemed-

to-satisfy rulescontained in SABS 0400donotcontain any guidanceor

definitions of acceptable serviceability and durability criteria; they

merely refer the reader to the South African codes of practice or struc-

tural design.

The South African codes of practice, on the other hand, offer com-

prehensivegu idance on assessing thestrength, stability and structural

integrity of structures and, with the exception of the masonry code,

offer some useful guidelines, based on allowable deflection ratios, to

restrict deformations, distortions and structural distress arising from

applied loads to within acceptable lim its. SABS 0160q5 General pro -

cedures and oadings to be adop ted for the design of buildings) states,

in subclause 3.1.3, that 'the deforma t~on f a building or any part of it

should not adversely affect the appearance or proper function ing of the

building'. In SABS 0161' (The design of foundations for buildings), in

regard to ground movements that are independent of the applied load

(see subclause 5.1.2). ~t s stated that 'the designer should decide, hav-

ing regard to the user's requirements and the design of the building,

whether the effects of such movements can be tolerated'. Apart from

these two general references to serviceability considerations, the

structural codes are silent on serviceability criteria relating to, or that

may be adopted for, residential structures founded on problem soil

horizons.

Burland et all on the other hand, have suggested that there are

three basic criteria that ought to be satisfied when limiting movements

are considered, viz:

Character of

founding materfal

(mm)

Stable

1. Visual appearance

2. Serviceability or function

3. Stability

Experience has shown that deviations from the vertical or horizontal

in excessof l/ 25 0 and local slopes in floors in excessof l /lO Oar e likely

to be noticed and will often cause subjective feelings that are unplea-

sant and possibly alarmingt6.Excessive movementscan also affect the

function of a struc ture by causing service pipes to fracture and win-

dows and doors to jam. Crac k~ng f the masonry itself, rom an owner's

poin t of view, is generally aesthetically unacceptable and of great

concern.

The attainment of a completely crack-free masonry structure, on the

other hand, even on the most stablesoil horizon, isvirtually imposs~ble.

Masonry is a b rittle construction material and as such is susceptible to

cracking. In addition to foundation movements, cracking in residential

structures may arise from one or a combination of the following1':

1 .

Thermal movements (expansion and contraction).

2. Moisture movements in masonry units (wetting and drying, and

shrinkage in concrete and calcium silicate units).

3. The absorption of water vapour on a molecular level In burnt clay

units (moisture expansion).

4. Corrosion of wall ties and brick reinforcement .

5. High-strength morta rs rich in cement.

6. Structural overload.

7.

Shrinkage of concrete roof or floor slabs.

8. Deflection of the supporting structure under load.

In residential structures:

1. Thecauses of cracking in masonry are not always related to applied

loads or displacements.

2. Excessive deflections are unlikely to occur from applied lateral

loads such as wind.

3. Deflections and distor tions in walls leading to the fracturing of ser-

vice pipes and the jamming of windows and doors will occur only

after cracking has taken place in the masonry.

4. The structural codes of practice offer no quantifiable guidance on

serviceability criteria .

It would therefore be useful to formulate performance-oriented ser-

viceability criteria in order to classify ranges or degrees of damage to

which a structure may be subjected.

A proposed performance-oriented classification system describ-

ing the level of damage with respect to walls and floors is contained in

Table (masonry walls) and in Table 5 (concretefloo rs). Table4, which

classifies the degree of damage in terms of ease of repa ir, crack width.

impairment of function and visible (aesthetically unacceptable)

damage, is based on the work of Jennings and Kerrich2,Burland et all6

and G i ~ e s ' ~ . ' ~ a n dn the Australian Standard AS 28 70~. able 5, on the

other hand, is similar to a table contained in AS 2870.

Tables and 5 are divided into two degrees of damage, namely

minor damage and significant damage. Minor damage describes vis-

ible damage relating to relatively isolated, narrow cracks that can

generally be repaired when redecoration of the wall finishes is under-

taken and distortionsin thewallsand w~ndow sthat re notobviousand,

at worst, only cause doors and windows to stick slightly. Significant

damage, on the other hand, describes damage relating to wide cracks

or groups of narrow cracks that can generally be effectively repaired

only by rebuilding portions of the walls, effecting improvements to the

foundations and/or cutting articulation joints mto the walls, and to

not~ceable istortions in the walls and floors causing doors to jam, ser-

vice pipes to fracture and floor finishes to crack or tear1'.

It must be stressed, however, that in assessing the category of

expected damage, account must be taken of the locat~onn the struc-

ture of the damage, and of the function of the structure. Likewise, the

width of cracks should not be seen in isolation when the category of

expected damage is decided upon; it is only one factor and should not

be used by itself in classifying damaget6.

In terms of Regula tion B1 of the NBR, categories of expected

damage with a valueequal to or greater than four are considered t o fall

outside the perm issible strength and stability limits, whilst those with a

value equa l to or greater than three are considered to fall short of the

serviceability and durability requirements of the regulations, when

read as a whole.

It is therefore proposed that significant damage (category 3 and

higher) should not be permitted. Categories of minor damage would

then constitute a range of performance-oriented serviceability criteria

Expected

range of total

movements

at surface

of soil

Negligible

DIE SlVlELE INGENIEUR in Suid-Afrika Maart 1992

Assumed

different~al

movement

(

of total)

Site

class

R



appropriate for res ident ial s tructures rangi ng from low-cost to

Appropr ia te cons t ruc t ion so lut ions

Tables

6

t o 8 conta in deta i ls o f foundat ion des ign, bu i ld ing pro-

cedures and precautionary measures m respect of s ingle-storey

res ident ial s tructures of masonr y construct ion located o n s ites as

c lass if ied in Table

3.

The words and express ions conta ined in these

tables have the meanings and in terpretat ions g iven in Appendices A

and B as appl icable.

The cons t ruc t ion so lut ions propose d n hese tab les may be d ivided

into two categories, v iz s tructural an d geotechnical solut ions. Geo-

technical solut ions el iminate or reduce th e unacceptable total soi l

movements b y means of on e of the fo l low ing:

1 Removal of the soi l hor izons giv ing r ise to unacceptable dif ferent ial

movemen ts and rep la cement of these hor izons w i th iner t mater ia l

suitably compacte d or t he re-use of the excavated mater ial as

founding mater ia l in

a

compac ted form.

2. Found ing of the wall foot ings at a deeper level than IS commonly

associated w i th no rmal cons t ruc t ion, ie on a competent founding

hor izon be low the proble m hor izon.

3. Densif icat lon of the soi l hor izons giv ing r ise to unacceptable dif-

Table 6: Foundation design, build ing procedures and precautionary measures

for single-storey residential structures founded o n expansive soil

superior s tandards

Table : Classification of damage w ith refe rence to masonry walls

Approximate

maximum crack

width in walls

(mm)

Category

an d degrs

of expects

damage

Description of damage in terms of ease of

repair and typical effects

Minor damage -

Categories

0 o 2

horizons

Hairline cracks less than about

0,l

mm

width are classed as negl ig~bl e.

Fine internal cracks that can easily be

treated dur ~n g ormal decoration. Cracks

rarely visible in external masonry.

Internal cracks easily filled. Redecoration

probably required. Recurrent cracks can be

masked by su~tableinings. Cracks not

necessarily visible externally. Doors and

windows may stick slightly.

stimate

otal

leave

mm)

Construction

type

<0,1

<

<5

Foundat~on esign and building procedures

(Expected damage limit ed to Category 1)

0

Negligible

Very

slight

2

Slight

Significant damage Categories 3 to 5

Normal

Cracks can be repaired an d possibly a

small amount of masonry may have to be

replaced. Art~culationo~ntsmay have to

be cut in some of the walls. Doors and

wmdows sticking. R ig ~d ervice pipes may

fracture. Weather-tightness often Impaired.

Up to 10 mm gap between ceiling cornices

and walls.

Foundations

to SABS 0400 Part H.

Site drainage and serwce/plumbing prc

cautions recommended.

xtensive repair work that includes

breakmg out and replacing sectlons of

walls, especially over doors and

wmdows, cuttlng of

articulation

joints

in walls, and the construction of

moisture trenches and apron slabs

around the structure, or the jack~ng f

foundations, depending on the type of soil

movement. Window and door frames

distorted,

floor sloping noticeably. Walls

lean~ ng r bulging

noticeably,

some

loss of bearing in beams. Service pipes

probably disrupted. Up to

20

mm gap

between ce~l ino ornices and walls.

5 o 15

(or a number of

cracks 3 to

5

in one group)

l5

to

25

(depending also

on number of

cracks In a

group)

3

Moderate

4

Severe

Modified

normal

Soil raft

Lightly reinforced strip footings.

Articulation joints at all internallexterna

doors and openings

Light reinforcement in masonry.

Site drainage and plumb~ng/service

precautlons

Remove all or part of expansive

hor~zono 1,Om beyond the perimeter

of the structure and replace with inert

backfill compacted to 93 per cent MOD

AASHTO density at 1 per cent to

2 per cent of optimum moisture

content.

Normal construction w~th~ghtly

reinforced strlp footmgs and hght

reinforcement in masonry ~f esidual

movements are <5 mm or construction

type approprlate to residual movements

Site drainage and plumb~ng/service

precautlons.

Major repair work required, involving

Usually

partial rebuildmg and the above-

greater than

mentioned repair techniques. Beams lose

25 (depending

bearing, walls tilt badly and require

also on number

shoring. Windows broken and distorted.

of cracks in a

Danger of ~nstability. group)

Very

severe

Table 5: Classification of damage with reference to concrete floors

Stiffened

or cellular

raft

Piled

construction

Split

construction

So11 aft

Stiffened or cellular raft with articulation

joints or sohd lightly reinforced

brickwork/blockwork

Site drainage and plumbing/service

precautlons.

Piled foundations with suspended floor

slabs wlth or without ground beams.


precautions.

Combmation of reinforced brickwork/

blockwork and full movement joints.

Suspended floors or mesh

reinforced

ground slabs acting independently from

the structure.


precautions.

As for HI.

Description of typical damage

Stiffened or

cellular raft

Soil raft

P~ led

construction

Significant damage - Categories 3 to

5

As for

H2.

As for HI.

As for

H2.

~ p p r o x

maximum

crack width

in floor

(mm)

Wide cracks. Obvlous curvature

or change in level local

deviation of slope from the

horizontal slope may exceed

1.100.

Gaps in floor. Disturbing

curvature or change In level.

DIE SlVlELE INGENIEUR in Suid-Afr ika Maart

1992

Mmor damage - Categories 0 o 2

Maximum

deviation of

any joint

from a

3

m

straight edge

(mm)

Hairline cracks, insignificant tilt

of floor or change In level.

Fine but noticeable cracks.

Floor reasonably level.

Distinct cracks. Floor noticeably

curved or changed in level.

2

o

4

>

Category

and degree

of expected

damage

<0,3

<1,0

<2,0

15

o

25

>25

Moderate

o 5

Severe to

v -ry severe

<

<l0

<l5

0

Negligible

Very sllght

2

Slight



ferent ial movements by means of surface compaction

site c lasses, s ince they are based on on e or mor e of the fol lowing:

Structural solut ions, on the other han d, employ techniques to

improve f lex ibi l i ty /s t~ffness n d strength, which redu ces the effects of

1. Well docume nted casestudie sof s tructuresan d design procedures

in South Afr ica.

2.

Rational design methods.

3. Published research f indings that have been proved on South

African so11profiles.

4 Current, w~d el y ccepted, South African state-of-the-art practice.

dif ferent ial soi l movements o a level that can be olerated by hestru c-

ture without s ignificant damage .

The select ion of either a geotechnical or a s tructural solut ion

depen ds on the pract icabi l i ty an d economy of the solut ion in

question.

The solut ions presented in Tables

6

t o

8

are cons idered to be

appropria te for the range and type of movement cor responding to the

Although these ables have been ormulated for acategory of expec-

ted d amage with a value of one, they ma y nevertheless be adapted for

Table

8:

Foundation design, building procedures and precautionary measures

for single-storey residential structures founded on horizons subject to

Table 7: Foundation design, build ing procedu res and precautionary measures

for single-storey residenti al structures founded on horizons subject to

both consolidatio n and collapse settlement

consolidation settlement

/te

lass

istima ec

otai

:ettiemen

mm)

lite

lass

;

1

;2

:stlmatec

otal

ettlemen

mm)

15

Construction

type

Normal

Modified

normal

Compaction

of In s~tu

soils below

~ndlv~dual

foot~ngs

Deep strip

foundat~ons

So11 aft

St~ffened

strlp

foot~ngs.

stiffened or

cellular raft

Deep strlp

foundations

Compact~on

of In sltu

soils below

tnd~v~dual

footlngs

So11 aft

P~led r

pler

foundat~ons

E d a t l o n design and building procedures

(Expected damage lim ited to Category 1)

Foundat~on esign and build~ng rocedures

(Expected damage limited to Category l )

Foundat~onso SABS 0400 Part H

Foundat~on earing pressure not to

exceed 50 kPa.

Good site drainage.

Normal

Foundat~onso SABS 0400 Part H.

Foundatlon bear ~ng ressure not to

exceed 50 kPa.

Good site drainage.

Retnforced strlp footlngs

Arttculat~onotnts at some Internal and

all external doors

Llght relnforcement In masonry

Stte dralnage and servtcelplumb~ng

precautlons

Foundat~on ressure not to exceed 50

k Pa

Modlf~ed

normal

Compaction

of In sltu

so~ls elow

~ndtv~dual

foot~ngs

Deep strip

foundatlons

Sod raft

Remforced strlp footlngs

Arttcu lat~o n olnts at some Internal and

all external doors

Light re~nforcement n masonry

Stte dralnage and se rv~celp lumb~ ng

precautlons

Foundat~on ressure not to exceed 50

kPa

Remove In s~ tumater~al elow

foundat~ons o a depth and w~ dt h f

1

5

times the foundat~on ldth or to a

competent hor ~zon nd replace wlth

mater~ al ompacted to 93 per cent MO[

AASHTO den s~ty t

1

per cent to 2

per cent of optlmum molsture content

Normal constructlon w~thtghtly

re~nf orced trlp foundat~onsand hght

relnforcement In masonry

Normal constructlon wlth precautlons

Found ~ng n a competent ho r~zo n elob

the problem hor~zon

Remove In s~tumatertal to 1 0 m beyon,

perimeter of butldlng to a depth of 1 5

ttrnes the w~d est ounda t~on r to a

competent hor~zo n nd replace w~th

mater~ al ompacted to 93 per cent MO[

AASHTO den s~ty t

1

per cent to 2

per cent of optlmum motsture content

Normal constructlon wtth l ~ghtl y

re~nf orced trlp footlngs and llght

re~nforcement n masonry

Remove In s~tumater~ al elow

foundatlons to a depth and wldth of 1 5

tlmes the foundatton wldth or to a

corpetent horlzon and replace w~ th

materlal compacted to 93 per cent MO1

AASHTO de ns~ty t

1

per cent to 2


Normal constructlon w~ th ghtly

re~nf orced trip foundat~ons nd light


Normal constructlon w~ th recautlons.

Founding on a competent h or~zo n elo\

the problem horizon.

Remove In sltu materlal to 1,O m beyond

perimeter of bulldmg to a depth of 1,5

tlmes the w~destoundatton or to a

competent h or~zon nd replace w~th

mater~al ompacted to 93 per cent MOO

AASHTO denslty at 1 per cent to

+2


Normal constructlon w~th~ghtly

re~nforced trp foot~ngs nd hght


St~ffened trlp footlngs or st~f fene d r

cellular raft wlth arttculatlon Iolnts or

solid lightly re~nforced r~ckwor kl

blockwork

Mesh relnforcement In floor slabs

Bearmg pressure not to exceed 50 kPa

S~te ra~nage nd serv~celplumb~ng

precautlons

As for S1 but w~ thmesh re~nforceme ni

In floor slabs

As for S1

St~ffened

strlp

footlngs,

stiffened or

cellular raft

Deep strlp

foundations

Cornpactlon

of In s~t u

so~ls elow

~ n d ~ v ~ d u a l

foundat~ons

So11 aft

Piled or

pier

foundations

Stiffened strlp fo ot~ng s r stiffened or

cellular raft wlth arttculatton Iolnts or

solid Itghtly reinforced br tckwork l

blockwork.

Bearing pressure not to exceed 50 kPa

Mesh qe~nforceme ntn floor slabs.

Site dra~na ge nd service/plumbing

precautlons

As for

C1

but with mesh relnforcement

In floor slabs.

As for C1

As for C l .

Retnforced concrete ground beams or

solid slabs on p~ le d r pier foundations

Ground slabs with mesh re~nforcement

Good site drainage.

As for S1

Remforced concrete ground beams or

solid slabs on p~ le d r pler foundat~ons

Ground slabs with mesh re~nforcement

Good slte drainage.

DIE SlVlELE INGENIEUR in Suid-Afr ika Maart

1992



category 2 l evels o f expec ted dama ge wi th some m inor modifications.

An Inc rease in the degree o f da mag e p ermi t ted im pl ies that the s t ruc -

tures in ques t ion wil l be pr ov ~d ed l t h less s ti ff f oundat ions or less f lex -

~ b l eupers t ruc tures . Thus the cons t ruc tlon d eta l l s as opposed to the

construct lon type) wi l l change. Accordm gly , the am ount of s teel rein-

forcement In both the m asonry and foundat ions re fer red to in these

tab les may be e i ther reduc ed or omi t ted. In the case o f sp l i t cons t ruc -

t lon . t he l lm i t o f d~ f fere nt la l eave that may b e to lera ted may b e ra ised

to 40 mm , whi l s t i n modi f ied norm al cons t ruc t ion the numb er o f

art lculat lon jolnts may be reduced

I m p l em en t i ng a s y s t em a t i c app roac h t o des i gn a nd c ons t ruc t i on

Class i f icat ion of erven

At the outset o f a townsh ip deve lopment pro jec t , a geotechn lca l

inves t igat ion com pr is ing a s tab i l~ t ynves t lgat lon of t he s i te i f unde r lam

by do lomi tes ) and an investigation i n to the foundat ion charac ter i st i cs

of the near -sur face so i l hor izons i s requ i re d:

1. As a p lann ing a id In the determinat ion o f app ropr ia te land use.

2.

To en ab le the loca l author i t y to assess the suitability o f t he s ~ t eor

the proposed deve lopment .

3. To prov id ethe oca l author i t y w i th information i n o r d e r t o e n a b l e i t t o

enforce the requ i re ments o f t he NBR.

4 .

To prov ide a prospec t i ve deve loper or owner wi th in format ion

regard ing found ing cond i t i ons .

T h ~ snves t igat ion shou ld cu lm ina te in the pre parat ion o f a so i l map

~ n d ~ c a t l n goun dar ~es f a reas wi th comm on s i te c lasses des ignated in

accordance wi th Tab le

3,

t ogether wi th a repor t conta in ing the

fol lowing:

1.

A desc r ip tion o f the s ite , ~ t socat ion and the nature o f t he in -

vestigation.

2.

Deta il s o f the s i te geo logy and en g lneer lng prope r t ies o f the found-

Ing hor i zons .

3. A geotechn ica l eva luat ion of f ound ing con d i t~o ns ,nc lud ing recom -

m enda t i ons on f ound i ng dep t hs.

4 .

Deta il s of any pro b lem s tha t may have been ident i fi ed and that may

have a bearing o n the des ign and construct ion of the s t ructures.

5.

Ful l part iculars of al l boreholes, t r ia l holes and test pi ts and the

resul ts of al l f le ld and laboratory tests .

A f ter the town sh ip layout has been f ina l ized an d thee rven have been

physically

pegged. but be fore cons truc t ion o f t he s t ructures comm en-

ces , a fu r ther inves t igat ion i s p ropose d to es tab l i sh the s i te c lass in re-

s pect o f eac h m d l v idua l e r f. T h ~ s dd~ t l ona l oun da t ~ on nves t igat ion

would b e a imed a t conf i rm ing and am ending , as necessary , the pre -

v ious ly determined boundar ies o f areas wl th common s i te c lasses .

General ly , this invest igat ion wi l l no t necessari ly entai l addi t ional tes t ing

and m ay requ l re no m ore han t he excavation of tes t p l t s to conf i rm the

p r e v ~ o u s l ydent i f ied pro f i l es and s i te c lass bound ar ies . Aga in , t h i s

inves t igat ion sh ou ld cu lm inate in a repor t conta in ing any add i t i ona l

pertinent l n format lon and a so i l m ap by m eans o f wh lch the s l te c lass

designation

f o r eac h ~ nd l v l d ua l r f m ay be ascertained.

The two above-ment ioned repor t s , t ogether wi th the s i te c lass

des ignat ions for each er f , shou ld b e submi t ted to the bu i ld ing inspec -

torate of the appl icable local authori ty in order to enable i t to:

1 Sys temat i ca l l y cont ro l t he erec t~on of s t ruc tures on prob lem

soils.

2

Furn ish in teres ted par t ies wi th comprehens ive geotechn ica l i n -

format ion.

3. Cont ro l t he rec lass i fi ca t ion o f any ind iv idua l s i t es th i s may be

requ i red in the case o f erven s i tuated on the border o f two

zones).

Where undeve loped s tands in ex is t ing townsh ips are to be de-

ve loped and so i l maps are not ava i lable , e~ th erhe loca l author i ty , t he

developer or the owner would be requ i red to appo in t a p ro fess iona l

englneer to des ignate the s i te c lass in terms of Table 3

Cont rol l ing the des ign a nd co ns t ruc t ion o f s t ruc tures

The bul ldlng inspectorate of the local authori ty has s tatuatory

author it y to mo n~ tor nd con t ro l the erec t ion o f s t ruc tures . I n order to

fac i l i tate this funct ion, however, i t is cons idered important that a

manual be made ava i lab le to the inspec tora te set ting out ax ep ta b l e

s tandards and o ther re qu i rem ents apper ta in ing to the des ign and con-

s t ruc t ion o f f oundat ions and s t ruc tures on prob lem so i l s . Such a

m anua l wou l d p rov ide :

1

A c l a s s ~ f ~ c a t ~ o nrocedure for the determlnat lon of s l te c lasses,

gu ldan ce on ra t lona l des lgn concepts and acceptab le serv lceab l ll ty

l ~ m l t s

2 Standard deta l l s In respec t o f p lu mb ~n g erv lces and dramage see

Appe ndlx B ) , a r tl cu la t lon joints joints associated wlth spht con-

s t ruct lon and sets of rules

governing

the s tabl l l ty of certam

jointed wal ls

3 Maintenance and pe r forman ce ln format lon for use by owners

4 Procedures for the sub mls s~o n f p lans for approva l by the loca l

authority

The manu al cou ld a lso Inc lude ru les and i ll us tra t ive sketches re la t-

ing cons t ruc t ion so lu t ions appropr ia te for the lower range o f so i l

move ments eg to mod i f ied normal cons t ruc tion) so as to reduce the

numb er o f s i tes that wou ld requ i re the appo in tment o f a pro fess iona l

eng ineer . Ru les app l i cab le to m odi f ied norm al cons t ruc tion cou ld , f o r

example , be dra f ted on the b as ls o f F igs 2, 3 and 4 , A ppend i x B and

Table 9 . The benef i t s o f a manua l wou ld inc lude the fo llowing:

1 P ro f es s ~ ona lengineers wou ld be prov lde d wl th an adequate

d e s ~ g n r le f

2

Prospec twe owners would be In formed o f t he maintenance re-

qu l rem ents and the expec ted per form ance charac ter ls t l cs o f

thew Investment

3 The b u l ld lng Inspec tora te wou ld b e prov lde d wl th suf f lc len t deta l l t o

enab le ~ t o

re ognize

and ldent l fy the cons t ruc t lon

technique

p ro -

pos ed by t he

applicant

or

professional

englneer

4

T hedes l gne r w ou l d be f u rn l s hed w l th gene ra l l n f o rm a t ~ o n nd c on -

ceptua l or where applicable deta l led des lgn ln format lon wl th res -

pec t to the preparation a n d s u b m ~ s s ~ o nf plans

The above-ment ioned ob jec t i ves cou ld b e ach ieved i f the manual

were wr l tt en on the bas ls o f Tab les to 9 and Appendices A and

B

Definitions of the var ious cons t ruc t ion techn iques cou ld b e ampl i f ied

by me ans of i l lus t rat ive sketches such as that shown in Fig

2

f o r mod-

i f ied n ormal cons t ruc t ion . T yp ica l cons t ruc tion deta i l s cou ld a lso be

Table 9: Summary of differences in m odified norma l construction for different

site classes and lor ca tegories of expe cted damage

Gutter~ng ot perm~tted

Apron slabs to be prov~ded

Art~culat~onolnts to be p rov ~de d t all Internal and

external doors and openlngs

Two 5 6

m m

d~ameterhard drawn wlre rods to be

prov~ded elow wlndows

Alternat~ve oundat~on eta~l ot permitted

Gutter~ng pt~onal

Apron slabs to be prov~ded f guttering

IS

om~tted

Art~culat~on

oints

to be p rov ~de d t all Internal and

external doors

Br~ckforcen two courses ~mm ed~a telybove floor

slab may be om~tted

Alternat~ve oundat~on e ta~l ot perm~tted

Gutter~ng ot perm~tted

Apron slabs to be prov~ded

Art~culat~onolnts to be pr ov~ ded t most Internal

and all external doors Where two ~nternal oors

are ~m med~atelydjacent to each other an

artlculatlon jolnt need only be pro v~ded t one doo

openlng )

One add~ t~onal

12

remforc~ng ar to be prov~ded

In external wall strlp footlngs

Gutter~ng pt~onal

Apron slabs to be prov~ded f guttering IS om~tted

Art~culat~onolnts to be prov ~de d t external doors

only

Br~ ckfo rce n two courses lmm edlately above floor

slab may be omltted

3te

:lass

DIE S lV lELE INGENIEUR in Su id-A f r i ka Maar t 1992

Adjustments to basic modified normal constructlon

shown in Fig 1

Standard format brick structures only)



CMEE

D IN lYE /

m 1 c E s

PLUWING PECAVIIWARY EASUilES APPLY

ig

: Modified normal construction

h TC

BE

CONSTRUCTEL

M NGE

F l N I M D

LWR

LEKL EETUW ALJACENT

ROOE TO EXCEED m m

LEGEN

4

U N

L1 - JOINTS M ppIIW;S

-

FIGURE 3

D1

- JOINTS GW6 FIGURE

ALTERNATIVELY FULL HEIGHT D M R S

TO

BE

SECT

ION

POLYn€N€

STEP HEIGHl TO

E

A W T I P L E

OF MXRSE HEIGtil

FXlT

LESS

THAN4m-I Yl2

ALTERNATIVE FOUNDATION DET iL STEPPED STRIP FOUNDATION DETAIL

DIE SlVlELE INGENIEUR in Suid Afrika Maart

1992



W -

I l l

ig

3:

Details of ar ticulation oints at doors and openings

DIE SlVlELE INGENIEUR in Suid-Afrika Maart 1992

included in asimila rform at tothat

adopted in Fig

3

in order toclarif y

some of the design concepts and

to standardize details.

In terms of the proposed

manual the local authority would

require that a professional en-

gmeer be appo~nte d o de s~g n

and supervise theconstruction of

the foundat~ons nd associated

superstructures and to specify

and supervise any ground im-

provement techniques that may

beempl oyed for structureserect-

ed on site classes other than

H

C

S and

R

or whereconstruction

methods do not comply w~thhe

e m p ~r ~c a lr regu latory rules that

may be prescribed. The pro-

fess~onal ngineer in turn would

be required to prepare a struc-

tural design or to spe c~f y geo-

technical solution in accordance

with those descr~bedor each site

class designation in Tables

6 7

and 8 read in conjunction with

the definitions and inter-

pretatlons of the ter ms contained

~n Appendix A and w~ th any

amp l~f ylng ketches contained In

the proposed manual. Further-

more the professional engineer

would be responsible for ensur-

~ n ghat any design prepared by

him would equal or exceed the

performance criteria relatmg to

the specified expected category

of damage contained in Tables 4

and 5.

Where a professional engineer

elects to employ a construction

technique other than those des-

cribed in Tables

6

7 and 8 the

local authority could call upon the

professional engineer to furnish

the following additional par-

t~c ular s so as t o enable it to

evaluate and approve the design

in question:

1.

A deta~ledationale In support

of the proposed design.

2

Full particulars of structures in

which the proposed design

has previously been imple-

mented with deta~ ls f post-

construction performance.

3

A written statement granting

the local author~t y ermission

to have the design reviewed

by another profess~onalen-

gineer nominated by it.

4 . Professional mdemnity ~ n -

surance cover in an amount

determined by the local

authority in its absolute dis-

cretion the amount of indem-

nity not to exceed the estim-

ated replacement cost of the

design structures.

5. A

written statement by the

developerlowner indemnify-

ing the local authority and its

agents from any liabilities.

91



Procedures :

The

sys temat i c cont ro l o f s t ruc tures o n pro b le m sods

The f low char t shown in F ig 5 s um m ar i z es he p ropos ed p rocedu res

cons t i tu t ing thesys temat i c cont ro l o f bu l ld lng cons t ruc t ion on pr ob le m

soi ls f rom the t lme o f t he es tab l ishment o f t he townsh ip u p to the com -

p le t~o n f t he s t ruc tures . To fac l li t a te the examlnat lon and appro va l o f

bu i ld ing p lans , the loca l author l ty w ou ld requ i re the fo l lowing a d-

di t ional

information

t o s upp l em en t t ha t r equ i red t o b e f urn i shed i n

terms of Clause A7 of the NBR:

1

Sec t lons In two d l rec t lons through the s t ruc ture showing d eta ~ ls f

t he proposed foundat lons and re in force ment , where app l i cab le

2 Work ing drawmgs o f t hes t ruc ture a nd found at ionsshow ing a l l re le-

vant dimensions.

3 The locat ion and d eta l l s o f a l l j o~ nt s n the supers t ruc ture .

4.

The s ize and locat ion o f a l l m asonry re in forcement .

5 . A l l no tes re la t ing to spec i fi c cons t ruc t ion proced ures .

In order to enab le the loca l author i t y to eva luate the des ign pro-

posa ls submi tted a nd to prov ide a pe rman ent reco rd o f the des ign, the

fo llowing in format ion shou ld b e nser ted on the draw ings immedia te ly

above the t i t le block.

1.

Site class.

2.

Construction t ype.

3 . Category o f expec ted damage.

4. T he p ro f es si ona l engm eer s nam e , reg~ s t ra t l on um ber a nd s i gna -

ture , where a pp l i cab le .

By re ference to the above-mentioned ~ n f o rm a t i on , he bu l l d i ng

Inspec tora te wou ld be ab le to m oni tor and cont ro l t he cons t ruc t ion o f

s t ruc tures on pro b lem so l l s and p lay a m ore e f fec t ive ro le in the

~ r n ~ l e m e n t a t i o nnd enforcement o f t he N R

D CONCERTINA TIES

WENING

W C

NrEFWAL

s

RICK

WALLS

u r n

PENINGS

98

,D WR F R ME

M M .

FFL

W

NOT S :

LATERAL SUPPORT TO WALL PANELS TO BE PR WI DE D I N ACCORDANCE

WITH SABS 486 PART K CLAUSE

KKS.

INTERSECTING WALLS TO BE BONDED TO EACH OTHER AS FOLLOWS :

K R E R S TO M F U L M Y B OW .

INTEWlEDIATE INTERSECTIONS TO

BE

EITHER FULL MWtFlY

BON OR

TO

BE

BUILT FLUSH

LP

AGAINST THE M I N WALL

AM

TIED IN WITH

788 mm

LONG GALVANIISED

1 6 X 88 m HOW

IRON

STRAPS AT

458 m V U X W l t l

VERTICAL CENTRES.

E W S

DF

U)NCER TINA TI ES TO BE BENT. TO SUI TE BRICK VOW(.

The advantages of a systematic approach

The advantages o f a dopt ing a sys temat i c approach in the cont ro l o f

budding cons t ruc t lon on prob lem so i l s may be summar ized as

fol lows:

The loca l author l ty wou ld be In a pos l tl on to enforce In a prope r

m a n n e r a n d as a s er v lc e to ~ t sommunity, the prov ls lons of the

NBR thus mln lm lz lng dam age to st ruc tures

The deve loper wo uld be prov lded wl th deta l led ln format lon on the

f o u n d ln g c o n d l t ~ o n s n d foundation d e s ~ g n

olutions

together

wl th the prob ab le ass oc~a ted os ts In the ear l y stages o f townsh lp

dev e l opm en t enabhng dec l s ~ on so b e ma de o n the v lab lh ty o f the

p ro j ec t t he ty pe o f ho us ~ nghat IS envisaged, the eff lc lent ut l l lza-

t lon of land etc

The loca l author l t y , t he deve loper , t he prospec t l ve owner an d the

hous e des ~ gne r ou l d hav e de t a ll ed l n f o rm a t l on on f oundm g c on -

d l t l ons once the to wn sh~ p ayouts had been f lna l lzed and the

e rv en pegged

In new

townships,

sav lngs In ge otec hn~ ca l nves tlgatlon cos ts

would b e e f fec ted par t~ cu la r l y here severa l deve lopers deve lop

erven scat tered ac ross the townsh lp

The s tandard lza t lon o f cons t ruc t lon deta l l s w~ l l l t ~ma te ly educe

the des lgn an d cons t ruc t lon cos ts assoc~a ted l t h the var lous s lte

c lass des lgnat lons

l n f o rm a t l on rega rdm g t he des l gn o f f ounda t ~ ons ,

maintenance

requ l rem ents the expec ted leve ls of s t ruc tura l per form ance and

degree o f damage would be a va~ lab le o the prospec t lve owners

A c lear br le f wou ld be g lven to pro fe ss~o nal ngineers adequate ly

de f l n l ng t he own e rs expectations of s t ruc tura l per form ance and

the loca l author l t y requ l rements

The pro b lems lnvo lved In the des lgn an d cons t ruc t lon o f res lden-

MTERNAL 228 RICK WALL

PANn

WITH WWOW OPENINGS

CGUAR JOINT

B E M E N

LEAKS TO

BE

ML ID L Y F IL LE D U I M MORTAR

886 M X .

OPENING

W2488

3588 I U X . OPENING

M>2588

MTOFW

228

BRICK

WALL WITH LARGE WWOW OPENING

WWOWS

SI ING

w s

sr

w s WrH SI E LIGHTS)

88

- 5 - 86

1 2 mm

THICK

GALVANIZED SHEET

WNCERTINA

TIE

Fig 4rStability of wall panels with

joints

at doors and openings

DIE S lV lELE INGENIEUR In Su ld-A f r i ka Maar t 1992



t i a l s t ruc tures located on prob le m so i l s wou ld be bet ter unde r-

deve lopers and governm ent agenc ies to establish statlst lcs on actual

s t ood by t he c om m un i t y .

construct ion costs in respe ct of the various des ign solut ions, s ite c lass

9. Prope r records o f the bu i ld lng procedure s that were ado pted for des ignat ions and categor ies o f expec ted damage. Discounts or sub-

eac h and ev e ry s t ruc t u re wou l d be k ep t .

s idies on the s tand pr lces of erven in order to comp ensate for vary ing

10.

The cos t o f t he serv ices o f a pro fess iona l eng ineer would be

found ing cond i t i ons cou ld a lso be o f fered so as to ach leve un i form

avoided in the case of s l tes exhibit ing low or der soi l m ovements.

house pr i ce s in any g iven

township.

The sys tem co u ld then be used to

ensure that the ind iv idua l deve lopers prov ide s t ruc tures com-

The imp lemen ta t ion o f t he prop osed sys tem would a lso a l low large

mensurate wl th the subs idy or

discount of fered and of such a

standard that the purchaser is not

disadvan taged In terms of s t ruc-

tura l per formance. The sys tem

can also be use d as a spec i flca-

t lon for compet i t i ve des lgn-and-

construct tenders.

NEW TOWNSHIPS

EXISTING TOWNSHIPS

OTECHVICAL ENGINEER CLASSIF IES TOWNSH CHVICAL ENGMER APPOINTED BY MJNER

FOR

P L N I N G

REPORT FOR TOWNSHIP

WER

OR LOCAL AUTHOAITY INER TAK ES

ESTABLISmEKT PURPOSES IL S MS TI GA TI ON S AND CLASSIFIES

Implementing a systematic pro

cedure in Ennerdale

The commit tee of consul t ing

eng lneersadv ls lng the Ennerda le

GEOTECHVICAL W IN E E R CLASS IFIES

IMI IVI UJ AL ER KN AFTER TOCMSHIP

H S BEEN PEGGED

Loca l Deve lopment Commi t tee

(EPOK) recogn ized both the need

for and the advantages of fered by

a systemat ic appro ach to control

DESIONER SUBnITS

PLANS

TO LOCAL AUTHORITY I

t he des ign and cons t ruc t ion o f

res ident ia l s t ruc tures on prob lem

sol ls Wl th av lew to lmplement ing

such a systematic procedure,

UILDING

INSPECTORATE

I

CHECKS SITE CLASS

consul t ing engineers wi th whom

the authors are assoc iated were

ins t ruc ted to pr epare a M anual o f

s tandards an d o ther requ i re-

SIGN CM lPL IES OlrMER/MVELOPER TO

WITH STANDARO APPOINT PROFESSIONAL

DESIGNS ENGINEER

ments appe r ta in ing to the des ign

an d cons t ruc t ion o f s ing le-storey

residential s t ruc tures o f masonry

construction f o u n d e d o n p r o -

b lem so i l sz8.

The manual cons is ts of two

volumes. Volume I contains

e s

inter al ia:

1.

The def ini t ions and inter-

pretat ions as per Appendix A.

2.

Tables

1

to

9.

LOCAL AUTHORITY

1

3.

Procedures and requ i rements

for s i te c lass i f icat ion, the d e-

s ~ g n f foundat ions and s t ruc -

tures , and bu i ld ing Inspec -

OWKR DNELOPER

TO

APPOINT PAOFESSIONAL

DESIGN IN

t o ra te approva l .

4.

Commentary and notes ap-

pertaining to the varlous pro-

cedures and requirements.

ORMAL APPRWAL

TABLES

6

TO 8

PAOCUXlRES

CALL FOR FURTHER

AFTER REVIEW

5. P ro formas for the appo in t -

ment o f a pro fess iona l en-

gineer a nd the not i f icat ion of a

chang e in s i te c lass i f icat ion.

6

Typical general notes.

7 . An owner s gu ide to p er for -

mance requ i rements and

foundat ion maintenance.

CONSTRUCTION OF STRUCTURES

8. A prospec t i ve deve loper s

URING ND AFTER

guide to the pro tec t ion o f

s t ruc tures aga ins t damage

due t o g round m ov em en t s.

Volume I I cons ls ts of draw-

lngs that :

1. Ampl i f y def in i t i ons and ~nter -

pretat ions relat lng to the

various construct ion types.

2. Prov lde s tandard articulation

and fu l l movement jo in t de-

tai ls In respect of br ick

COrPLETION

CERTIFICATE

Fig

5: Appr vat procedures for residential structures

founded on problem soils

DIE S lV lELE INGENIEUR In Su id-A f r l ka Maar t

1992



structures.

3. Provide details of water pipe entries and free-standing walls.

4. Contain full details of modified normal construc tion for new and

incremental brick structures founded on Class Cl , H1 and S1

sites.

5 Specify limiting dimensions of brick wall panels that contain art-

iculation joints at door openings.

The design concepts presented in Volume II relate largely to brick

structures, as distinct from blockwork, because of:

Relatively complex details required to adequately reinforce

block walls.

The inherently weak flexural tensile strength characteristics of

blockwork, which results in inadequate lateral resistance of wall

panels to lateral loading requirements (wind and imposed loads to

SABS 0160) when articulation joints are formed at doors, or when

full height/fan-light doors are provided.

Additional complexities that occur as a result of joints provided to

control shrinkage and thermal and moisture movements within the

blocks themselves.

In termsof the manual, the appointment of a professional engineer is

mandatory on all sites other than Class C, H, S and R sites where the

foundations comply with the requirement of SABS 0400, and on Class

Cl , H1 and S1 sites where the developerlowner elects to utilize the

standard modified normal construction details set out in the manual.

The manual permits a professional engineer to adopt:

1. Ageotechnical solution in accordancewith the tablesand additional

requirements set out in the manual

2. A structural solution in accordance with current technology and

proven practice and consistent with the definitions, descriptions

and illustrative drawings contained in the manual, or

3

Adesign solution not described in the manual, further particulars of

which he must furnish to the local authority.

The approach adopted in the manual differssignifican tly from that of

the Australian Standard 2870-1 986. AS 2870 provides a wider range of

empirical solutions and only requires the appointment of an engineer

to design foundations on prob lem sites (areas of mining subsidence,

uncontrolled fills, landsl ip conditions, soft soil conditions and collaps-

ing sands) and extremely reactive sites with predicted surface move-

ment in excess of 70 mm. Furthermore, engineers are requi red to

design foundations within prescribed parameters and methods on

reactive sites. However, the standard does state that the expected

damage could be as high as category

2

and assumes that the builder is

experienced in the construction of foundations and licensed in terms of

state legislation.

EPOK intends implement ing the system on all new townships, com-

mencing with Ennerdale Ext 8, adevelopment managed by the Depart-

ment of Local Government, Housing and Agriculture in the Adminis-

tration of the House of Representatives. Accordingly, the individual

erven have been classified in terms of Table 3 and the erection of

residential structures will be controlled by way of the provisions of the

above-mentioned Manual of standards and other requirements.

onclusions

Appropriate solutions for the construction of single-storey residen-

tial structures of masonry construction for the range of problem soil

sites in non-dolomitic areas encountered in South Africa can be for -

mulated. Design criteria on the basis of serviceability can be est-

ablished todefine acceptable levels of expected damage. However, he

implementation of this technology is the aspect that requires address-

ing in order to ensure that the provisionsof the NBR relating to thecon-

struction of structures founded on problem soils arecompl ied with and

appropriate solutions are adopted so as to ensure the satisfactory per-

formance of such structures.

It is our opinion that the engineering profession as well as the com-

munities served by the profession would benefit from the int roduction

of a code of practice or a manual of standards and other requi rements

appertaining to the design and construction of foundat ions and struc-

tures on problem soils based on the material presented in this paper.

Furthermore, we propose that acommit tee be established to draft such

a code to ensure that the current technology is properly an:

effectively implemented.

Future research in South Africa should focus on refining design

solutions, on reducing the increments in differential movements that

define the class of site and on the development of empi rical rules or

regulations with aview to extending the range of solutions not requi ring

professional input.

Acknowledgements

We wish to thank Dr A A B Williams and Messrs E L Giles, K Schwartz. T K

Ralph,

C

R Ringler and W K Schutte for their valuable comments on various

aspects of the material presented in this pa per. The paper is published by kin d

permission of the Department of Local Government, Housing and

Agriculture

In

the Administration of the House of Representat~ves.

References

1. Williams, A A B , Pidgeon, J T, and Day. P W Expans~ve olls. Cfv Eng S Afr,

Vol 27, No 7, July 1985.

2 Jennings J E, and Kerrich, J

E

The heaving of buildm gs and the associated

economic consequences, with particular reference to the Ora nge Free State

goldfields. Civ Eng S Afr, Vol 5 No

5

May 1963.

3. Schwartz, K. Collapsible s o~ ls . fv Engr S Afr, Vol 27, No 7, July 1985

Natlonal Bu~ldingRegulat~ons.Government Gazette, Not~ceNo 8743. 8

Sept 1987.

SABS. Code of pract ice for the application of the Natfonal Bufldfng

Regulations: SABS 0400- 1987.

Standards Assoclation of Austral~a.Residential slabs an d footings. Aus-

trahan Standard 2870-1986.

SABS. Code of practice for the design of foundatfons for buildings: SABS

0161-1980.

Pidgeon, J T. The lnteract~on n expanslve so ~l s nd a st~ffene daft founda-

tion. Proc, South Afr~ca nGeotechnical Conference, Sllverton, Nov 1980.

organwed by SAICE.

Fargher, B E. A summary of developments in the technology of footlngs in

expansfve clay soils. Miscellaneous Publica t~on o 2, Cement and Concrete

Association of Australia 1971

Dawson,

R F

Modern practices used on expanslve soils. Colorado Schoolof

Mines Quarterly V54, No 4. Oct 1959.

Lytton, R L, and Kirby, T. Stiffened mats on expanslve clays. Journal of the

Soil Mechanics and Foundations Div, ASCE, May 1971

Lytton, R L. Des~gn ethods for concrete mats on unstable so~ls. roc. Th~r d

Inter-Amer Conf on Materials Technology. Rio de Jane~ ro, razil. 1972.

G~les,E L. Repa~rof SATS houses damaged by ground movements

associated w ~t hheaving clays and collapsi ng sands Personal com-

munlcatlons, Feb 1990

K~tcher. S D Bu ~ ld ~n gouses on heavlng clay: Countlng the cost. SA

Buflder, Jan 1983.

SABS. Code of prachce for the general procedures and oadings to be adop-

ted for the desfgn of bufldfngs. SABS 0160- 1980.

Burland. J B. Broms, B B, and De Mellow, V

F

B. Behav~our f foundations

and structures. Proc, Ninth Int Conf on SM and FE, Tokyo. 1977

Watermeyer. R B Movement in masonry Chapter 12, Structural Handbook.

E l . CCE s Department. SATS, June 1986.

Giles, E L. Remedial measures for cracked houses bu ~l t n heav~ng lays.

Proc, State of the Art Sympos~um,Geotechnic al DIV, SAICE, 1985

SABS. Code of practice for the structural use of masonry SABS 0164

Part 1980

Watermeyer, R B. The des ~gn f laterally loaded unrei nforced walls. SAICE

lecture for Durban Branch. June 1989

Holland. J E. The desfgn performance and repafr of housing foundations.

Swinburne Institute of Technology, Melbourne. Nov 1981.

Holland, J E. Behav~our nd des~g n f housing slabs on f~lling. roc, Th ~r d

Australia-New Zealand Conf on Geomechanics. Wellhngton, 1980.

Yates. J R C, and Tromp. B E. Supplementary geotechnical ~nvestfgatfonor

Ennerdale Extensfon 8 township presentfng typfcal foundatfons des ~gns.

CED flle no 105111 Report DC-0111-01-00-0986, Johannesburg, 1986.

BSI. Britfsh standard code of practice for the use of masonry: Part

2

Struc-

tural use of reinforced and prestressed masonry BS 5628: Part 2: 1985.

Jenn~ngs, E, and Evans, G A. Pract~cal roceduresfor bu~l dingsn expan-

slve so11areas. R/Bou 130, NBR1, 1962

Webb. D L. Foundation and structural treatments for bu~ld~ngsn heaving

subs011 Proc, Second Int Research and Eng~neer~ngonf on Expans~ve

Clay So~l s, exas, 1969.

Pidgeon, J T, and Pellissi er, J P The behaviour of an L-shaped raft subjected

to non-uniform support conditions. R/Bou 1451, NBR1, 1987.

Soderlund and Schutte Inc in collab orat ~on lth Schwartz Tromp and Assoc.

Manualofstandardsandother requirements ppert infng to the design and

constructfon of single-storey resfdential structures of masonry constructfon

found ed on prob lem sofls. Ref 323R11190, Ennerdale Local Development

Committee. Aug 1990.

DIE SlVlELE INGENIEUR in Suid-Afr ika Maart 1992



Appendix A Definitions and interpretations

The words and express ions sha l l ha ve the fo l low ing mean ings

A r t ~ c u l a t ~ o no m t s Jo in t s i n m a so n ry p ro v id e d a t su l t a b le l o ca ti o n s a n d in t e r -

vals taktng cogniz ance of the lateral stabil i ty and structural integrity of

i n d ~ v ~ d u a lane ls , enab l ing wa l l pane ls to mov e In harmony w i th the foun-

da ttons w i thou t deve lop ing s ign i f lcan t s t ress c racks o r s t ructu ra l d is t ress

Note.

1 . Wal l pane ls shou ld be designed in accordance w i th SABS 0164 Part l1 9 t o

safely resist lateral loadsz0.

2 . Jo in ts shou ld be designed to acc omm odate movem ents tha t a re p re -

dominant ly In the p lane o f the wa l l .

3 A r t lcu la t ton jo ln ts may a lso be fo rme d a t door open ings

B r~ ck f o rce i g ht w e ld e d f a b ri c co m p r i s in g t w o h a rd -d ra w n w i re s o f d ia m e t er

not exceeding 3 55 m m, he ld apar t by cross w ires, bedded in sound hor izon tal

mortar jo ints

Buddfng Inspecto ra te The bu i ld ing inspecto rste o f the loca l au thor i ty hav ing

sta tu to ry powers to con t ro l the de s~ gn nd the const ruct ion o f

buildings

Cel lu lar ra f t A foundat lon system tha t comp r ises two hor izon ta l re tn fo rced

concre te s labs in te rconnected by a ser ies o f web beams tha t by v i r tue o f

its st if fness

1

Enab les a s t ructu re to to le ra te d i f fe ren t ia l movements o r loca l tzed loss o f

suppor t (so f t spo ts3 o r

2 Reduces the d i f fe ren t ia l heave movem entsto a leve l tha t can be o le ra ted by

the superst ructu re1

wt thou t s ign i flcan t damag e

o urring

Note

1 A ce l lu la r ra f t foundat ion system has been deve loped and pa ten ted by the

CSlR and is mark e ted unde r the name 'Bouce l l Ra f t ' .

2

Th e d e s ig n m e t h o d a d o p t e d f o r h e a ve p ro f i l es sh o u ld b e b a se d o n a ' p la t e -

on-mound ora swell-under-load approachl

tha t has been proved in South

~ f r i c a ' su ch a s t h a t t n co rp ora t e d I n :

a ) The f in i te e lement p rogramme

FOCALS '

b ) L y t t o n' s m e t h o d '

C) The D iv is ion o f Bu i ld ing Techno logy S (C S I R ) M S -D OS co m p u t e r p ro -

g ram fo r s t t f fened ra f t des ign

3

Genera l ly the masonry s uperst ructu re is p rov ided w i th e i ther a r t icula t ton

jo ln ts o r l igh t re in fo rcement in o rder to fu r ther reduce crac k ing and st ruc

tural d istress

Co l lapse se t t lement The sudden se t t lement tha t occu rs when a po ten t ia l ly

co l laps ib le so i l under load IS wet ted

C o l l a p s ~ b l e s o ~ lso i l w i th a co l laps ib le so i l s t ructu re (open extu red w i th a low

d e n s~ t y ) h a t w h e n su b je c t e d t o a co m b in a t io n o f a n a p p l~ e do a d a n d a n

Increase tn so11 mo lstu re con ten t w i l l exper ience sudde n or rap id se t t le -

ment

C o m p re ss~ b le so f lA so11whose bu lk vo lum e ma y gradua l ly decrease w l th t ime

when sub jected to an app l ied load

Note A l l so i ls a re compress ib le under load However the degree o f com pres-

s ion depends on the so i l t ype and st ructu re and the magn i tude o f the

app l ied load

C o n s o l ~ d a t ~ o net t lement The ver t ica l se t t lement o r decrease in so i l vo lume

tha t occurs In a so i l under an ap p l ied s ta t ic load owing to the s low t ime-re la ted

reduct ion in the vo lume o f the vo ids

Deep strip t o u n d a t ~ o nNorm al const ruct ton w i th p recaut ions where the foun-

da t ions a re found ed a t a g rea te r dep th than norm a l on a competen t hor izon

b e lo w t h e p ro b le m so i l h o r~ zo n

Deve loper Person o r o rgan tza tton responsib le fo r the deve lopment and con-

s t ru c tl o n o f th e s t ru c t u re a n d ~ t soundat ions

D e s f g n e r P e rso n (s) a p p o in te d b y t h e o w n e r ld e ve lo p e r t o p re p a re a n d su b m i t

d rawings to the loca l au thor i ty fo r approva l

D ~ f f e r e n t ~ a leave The expected re la t ive sur face d isp lacement be tween

1. The cen t re and edge o f the mo und fo rm ed by heave movem ents

(domtng) , o r

2 . The cen tre and edge o f the d ish fo rmed by heave movements (edge heave

or dtshtng)

o f the so i l beneath a s t ructu re be fo re a l lowances fo r heave suppress ion due o

loads a re made

D~t te renba lse t t lement The re la t tve d~s p lac em ent ue to uneven se t t lement o f

d i f fe ren t por t lons o f a s t ructu re

Expanswe so f ls A f ine g r a~ ne d o i l (genera l ly w i th a h igh c lay con ten t ) tha t

changes in vo lume to vary lng degrees In response to changes in motstu re con-

tent, le th e so11may Increase in vo lume (heave o r swe l l ) upon wet t lng and de-

crease In vo lume (shr tnk) upon dry ing ou t

E xp e c t e d d am a g e A n a p p ro x im a t io n o f t h e p ro b a b le d a m a g e t h a t m a y o ccu r

in the masonry wa l ls and co ncre te f loors o f a res iden tia l s t ructu re

N o t e

1 The ranges o f damage tha t may be exper ienced are de f ined in Tab les

4

a n d 5

2 Occastona l damage in loca l ized a reas mor e severe than tha t env isaged a t

the design s tage may deve lop

3 Crack w id th is on ly one facto r in assess ing damage and shou ld no t be used

on i ts own as a d i rect measure o f damage In assessing the degree o r

sever i ty o f damage account m ust be taken o f the po in t in the s t ructu re a t

whtch i t occurs a nd a lso o f the funct ion o f the s t ructu re

F o u n d m g h o r ~ z o n sA so i l layer o r s t ra tum

exhibiting

simllar geotechnical and

eng ineertng p roper t ies and characte r is t tcs tha t suppor ts a s t ructu re

Fu l l m o ve m e n t l o f n t s Articulation jo tn ts tha t a re designed to accomm odate

movemen ts bo th in and ou t o f the p lane o f the wa l l

Ge o t e ch n ~ ca le n g m e e rA pro fess iona l eng ineer competen t in he d isc ip l ine of

so11mechan ics appo in ted b y e l ther the loca l au thor t ty o r the owner ldeve loper

to c lass i fy the s i te

Heave/shr fnkage The anticipated su r f a ce m o ve m e n t p ro d u ce d b y a n e xp a n -

s ive so i l hor izon caused by mo lstu re changes w i th in the hor izon

Increm enta l hous e Any res lden t ta l s t ructu re tha t fo r reasons o f a f fo rdab i lt t y

IS

to be c onst ructed In s tages in such a manner tha t in i t s in te rmed ia te s tages

the st ructu re can be occup ied by i t s owner

L ~ g h t l ye ~ n t o rc e d lo ckw o rk B lo ckw o rk h a v~ n g o ri zo nt a l r e in fo r ce m e n t

L ~ g h t l yemfor ced bnck work B r ickwork having hor izon ta l bed o in t re in fo rce-

m e n t n o t e xce e d in g 6 m m n d ia m e t e r b e d d e d n so un d m o r t a r j o in t s i n a d d

t io n t o b r i ck f o r ce

Masonry Anas semb lanceo f s t ructu ra l un i ts la id ins i tu inwh ic h hest ructu ra l

un i ts a re bonded and so l id ly pu t toge ther w i th mor ta r o r g rou t

N o t e

1 Masonry may be re in fo rced o r unre in fo rced

2 Masonry un i ts may be descr ibed as b r icks o r b locks depend ing on

t h e i r d im e n s~ o n s

3

A b lock is a masonry un i t tha t when used in i t s norma l aspect is more than

300 m m l o n ~ 5 0 m m w id e o r 1 2 0 m m h ig h

4 S t a n d a rd f o rm a t b r i cks a re 2 2 2 m m lo n g l0 6 m m w id e a n d 7 3 m m

high

o d ~ f ~ e d n o rm a l c o n s t r u c t ~ o n

orma l const ruct ion w i th

precautions

art icula-

t ion jo ln ts a t doors and open lngs l tgh t re in fo rcement in masonry and re~ nfor -

cement In concre te s t r ip foo t ings

N o r m a l construction Unre in fo rced conc re te s t r ip foo t ings w i th p la in masonry

superst ructu res bu i l t in accordancewl th the empir ica l ru les con ta ined in SABS

0400 Par ts H a n d K

N o r m a l c o n s tr u c t fo n w ~ t h re ca u t f o n s N o rm a l co n s t ru ct i o n e xc lu d ing t h e u se

of th ickened f loor s lab foundat ions under ~n te r na l a l ls w i th mandatory s i te

dra inage and p lumbing insta l la t ion p recaut ions

Owner Person in whom the lega l t i t le o f the p roper ty

IS

vested and who is re -

sponsib le fo r the m a in tenance o f the bu i ld ing and the s i te

P fer o undat lon Masonry re in fo rced concre te o r mass concre te co lum n w i th

or w l thou t a pa d foo t ing designed to t ransfer s t ructu ra l loads to a su itab le

f o u n d in g h o r i zo n

P ~ l e A re in fo rced concre te co lumn shaped member des igned to t ransfe r

s t ru c tu ra l l o a d s t o a su ~ t a b leoundtng hor izon

P ro b le m soils Found ing hor tzons tha t possess one o r more o f the fo l low-

ing charactertst lcs

1 Expansive

2 Compress ib le

3

Col laps ib le

N o t e O t h e rg e o te ch n ica l p ro b le m s m a y b e e n co u n t e re d e g in a re as u n d e r la m

by do lomites and sha l low m in ing work ings o r where uncont ro l led land f tl l has

been p laced

Pro fessfona l engmeer A c lv i l eng ineer who is reg is te red in te rms o f the p ro

vts tons o f sect lon 18 o f the Pro fess iona l Eng ineer

S

Act 1968 (Act 81 o f

1968)

Rem forced b lockwo rk B lockwork having hor izon ta l and ver t ica l g rou ted s tee l

re in fo rcement in accordanc e w l th BS 5628 Par t 2

Refn fo rced bnckwork B r ickwork having s tee l re in fo rcement bo th in the bed

jo in ts and In g rou ted cav i t ies in accordance w i th BS 5628 Par t 2

S ~ g n ~ h c a n tamage Damage in masonry wa l ls and concre te floors equa l to o r

g rea te r than ca tegory

3

dama ge as re fe r red to in Tab les 4 and 5

S i te c lass The ca tegor iza tion o f a s i te by a geo techn ica l eng ineer in te rms o f

Tab le 3

S p l f t co n s t ru c t ~ o nA const ruct ion techn ique2

26

in wh ich thest ruc tu re o f the

b u i l d in g i s p ro v id e d w ~ t h u ff i c ie n t f l e x~ b t l i t yo a cco m m o d a t e t h e d l ff e re n t ~ a l

m o ve m e n t s o f t he f o u n d m g h o r i zo n b y m e a n s o f a co m b ~ n a t t o n f f u ll m o ve -

ment jo in ts re in fo rced b r ickw ork lb lo ckwo rk s t i f fened st r tp - foo t ings and

f lo a t i n g / su sp e n d e d fl o o rs w i t h o u t s ig n i f ~ ca n t a m a g e o ccu r r i n g

DIE SlVlELE INGENIEUR

in

Suid-Af r ika

Maart 1992



S t ~ f f e n e d ra f tA f o u n d a t ~ o n ys t e m t h a t comprises a g r ~ df r e ~ n f o r c e d oncre te

b e a m s ca st ~ n t e g ra l l y ~ t h h e fl o o r s la b w h lch b y v i r t ue o f ~ t s t l f fness

1

E n a ble s a s t ru c tu re t o t o le ra t e d ~ f f e re n t ~ a lo ve m e n t s o r l o ca l~ ze doss o f

suppor t (so f t spo ts3 o r

2

R e d u ce s t h e d l f f e re n t ~ a l eave movements to a leve l tha t can be o le ra ted by

the superst ructu re7

w ~ t h o u t i g n ~ f ~ c a n ta m a g e o ccu r r ln g

Note.

S t i ffened ra f ts a re a lso des cr~ bed n s o m e p u b l ~ c a t ~ o n ss waff le slabsg. 1°

s t ~ f f e n e d a t s1 ' . . ra f ts2 ' , g r~ l lageaf tss, s tand ard ra f ts9 , deep stnp foo t -

~ n gr i l lages21 and r ig id s labs2 ' .

Th e d e s~ g n e t h o d a d o p t e d fo r h e a ve p ro f ~ le s h o u ld b e b a se d o n a ' p la t e -

on-m ound ' o r a 'we l l -under- load ' approach1 tha t has been proved In South

~ f r ~ c a ' .

.

su ch a s t h a t ~ n co rp o ra t e d n:

a ) Th e f ~ n l t e le m e n t p ro g ra m m e FOCALS'

b) Lyt ton 's method ' l

C ) T he D lv ts io n o f B u ~ l d ~ n ge ch n o lo g y' s (C S I R ) M S -D OS co m p u t e r p ro -

g r a m f o r s t ~ f f e n e d a f t d e s ~ g n .

S t ~ f f e n e d a ft f o u n d a t ~ o n sm a y c o m pr l se e ~ t h e r 0 0 m m t o 4 50 m m w ~ d e

beams a t

2

5 0 0 m m t o 4 00 0 m m c e n tr e s o r 1 50 m m w ~ d e e a m s a t

c loser cen t res

Beams on heave p ro f l les a re norma l ly no t sha llower than 600 m m ~ndepth

a n d a re d o u b ly re ~ n f o rce d

Genera l ly the masonry superst ructu re IS p r o v ~ d e d ~ t h ~ t h e r r tl c u la t lo n

p n t s o r l t gh t r e ~ n f o rce m e n t n o rd e r to f u r t he r r e d u ce c ra ck~ n g n d s t ru c

t u ra l d s t re s s

S t ~ f f e n e d s t n po o t in gs . A f o u n d a t ~ o n ys t e m t h a t b y m e a n s o f r e ~ n f o rce d tl f -

f e n ~ n g e a m e le m e n t se n a b le sa s t ru c tu re to t o lera t e d ~ f f e re n t ~ a lo ve m e n t so r

loca l tzed loss of foun dat ~on uppor t (so f t spo tsH1

23

without s lgn l f lcan t

damage occurr lng

N o t e

1 Genera l ly the masonry superst ructu re IS p ro v~ d e d l t h e ~ t h e r rt l cu la t l o n

j oi nt s o r l ~ g h te~nfo rcem ent n rder to fu r ther reduce cracktng and struc-

t u ra l d ~ s t re ss

2 T h e f o u n d ~ n g e p t h IS n o t n o rm a l l y l e ss th a n 6 0 0 m m

S t r i p f o o t ~ n gA re c t a n g u la r p la ~ n o r g h tl y r e ~ n f o rce d o n c re t e f o u n d a t lo n su p -

por t lng the wa l ls o f a masonry s t ructu re

Appendix B General notes applicable to mod

ified normal construction

A d e q u a t e su r f a ce d ra t n a g e t o b e p ro v ~ d e do p re ve n t an y su r f ace ru n -o f f r o m

p o n d ~ n g r o u n d s t ru c tu r e s

T h e g r o u n d ~ m m e d ~ a t e l yd jacen t to the s t ructu re to fa l l 75 m m over the

ftrst 1 5 m

F lo we r b ed s t r ee s a n d sh ru b s n o t t o b e p la n t ed w ~ t h ~ n5 m o f t h e

st ructu res

E ~ t h e r l a w n o r a

l

m ~ m p e r m e a b l e p r o n t o b e p r o v ~ d e d r o u n d t h e s tr u c -

t ur e to p r o v td e a u n ~ f o r m u rf ac e f ~ n ~ s h

S e r v ~ c e s n d p l u m b ~ n g r e c a ut i o n s

N o p l u m b m g a n d d r a ~ n a g e o be p laced u nder f loor s labs.

L e a ks In p l u m b ~ n g n d d r a ~ n a g eo b e re p a l re d p ro m p t l y

A l l wa te rp lpe en t r ies In to s t ructu res to be In accordance w l th Fig B1

A l l se we r a n d d ra ~ n ip e s to b e u P V C t o S A B S 7 9 1 a n d 9 6 7 a s a p p ro p -

r ia te

Sof t boar d packtng to be p laced be tween gu l leys and superst ructu re wa l ls

A l l se rv l ce tr e n ch e s to b e 1 . 5 m (m t n ~ m u m ) le a r o f t h e s t ru c t u re a n d b a ck f ~ l l e d

w ~ t hn s~ t u a t e r~ a l s o m p a c t e d t o 9 0 p e r ce nt M o d A A S H TO d e n s tt y

A n m p e rm e a b le a p ro n t o b e p ro v ld e d a ro u n d t h e e n tt r e s t ru c t u re wh e re n o

guttering IS p r o v ~ d e d

1,O m b y 1,O m co n c re te a p ro n s t o b e p ro v ~ d e d t al l d o w n p ~ p e s

M a so n ry

Morta r to b e c lass I I (SABS 0164) C lass I mor ta r no t to be used.

A l l w lng wa l ls , ya rd wa l ls , s teps, e tc . to be separa ted f rom maln s t ructu re by

means o f ver t ica l m ovement jo in ts .

Masonry un t ts to have nomina l he igh t . w ~ dt h n d le n g t h d im e n s~ o n s f 7 5 m m ,

1 0 6 m m a n d 2 2 2 m m

ln te rse ct~ng a l ls to be bonded to each o ther as fo l lows:

C o rn e rs t o h a ve fu l l m a so n ry b o n d

l n t e r m e d ~ a t en t erse ct l on s t o b e e ~ t h e r u l l masonry bo nd or bu l l t f lush up

a g a tn s t th e m a in w a ll a n d t ~ e dn w l t h 7 0 0 m m lo n g g a lva n ~ ze d t r a p s a t

4 5 0 m m maximum) ver t lcal ce n t res

C o n c re t e l hn te ls t o b e p ro v ~ d e d b o ve a l l w ~ n d o w s e x t e rn al d o o rs a n d

o p e n ln g s B r t ck fo r ce t o b e p ro v~ d e dn t he t w o c o u rs e s ~ m m e d ~ a t e l ybove the

l tn te ls and to extend 600 mm bey ond open lngs

B r ~ c k f o r c eo consls t o f hard d rawn w lres 3 5 m m I n d ~ a m e t e rma ln w lres and

2

5 m m d ~ a m e t e r r o ss w l re s w e ld e d a t 3 0 0 m m ce n t re s

R e ~ n f o rc e m e n t o b r ~ c k w o r k o b e

5

8 m m d ~ a m e t e r h a rd d ra w n p re -

s t ra ~ g h t e n e d i r e w t th a m ln lm u m p ro o f st r ess o f 48 5 N / m m 2 as supphed by

t h e m a n u f a c tu re r o f a w e ld e d s t e e l f a b r ~ c e ~ n f o rce m e n t Th e

following

shall

a lso app ly

R e ~ n f o rce m e n t o b e w e l l b e d d e d ~ n morta r

M ~ n ~ m u ma p le n gt h t o b e 6 0 0 m m

C u t a n d b e n d t o su ~ t n s l te

C o ve r to r e ~ n fo r ce m e n t 0 m m ( m ~ n ~ m u m )

Bed o ln tso n n on-p laste red exte rna l wa l ls to be we l l too led a t leve l of re ln fo r -

ce m e n t (To p re ve n t r~ sk f s t a ln ln g of b r~ ck w o rk

corrosion

pro tect lon

sh o u ld b e co n s t d e re d

)

R e ~ n f o r c em e n t n d b r c k f o r c e to b e d ~ s c o n t ~ n u o u st all art lculat lon lo lnts

F re e -s t a n d in g w a l l s t o b e p ro v~ d e dw ~ t hmovement jo ln ts a t 4 m to 5 m

centres.

Roof t russes

Roof t russes to h e suppor ted on ly on exte rna l wa l ls

Wh e re t ru ss ssu p p o r t e d d ~ re c t l y b o ve d o o rs , p ro v l s lo n o b e m a d e t o t ra n s f e r

loads to ad jacent t russes by mea ns o f a bearer .

Wa l l p la te to b e cu t a t a r t ~ cu la t ~ o no m t s

C e ~ l ~ n go rn l ce t o b e t ~ m b e r g yp su m co rn i ce s t en d t o cu r l )

Ce ihng corn ices to be f ixed to wa l ls on ly .

C e ~ h n g o rn l ce s t o b e cu t a t a r t i cu la t io n j o ~ n t s .

Foundat ions

PIPE ENTRY INTO

STRUCTURE

HOLDERBAT (NOT

FULLY TIGHTENED)

Grade 25 concre te

Three N o Y12

R 6 t l e b a rs a t 1 0 0 0 c l c

Concre te cover 50 mm.

Pad foo t~ ngs uppor t ing Iso la ted co lum ns no t permt t ted

F i g

B :

Wa t e r p ip e e n t r y d e t a i l s

POLYPROPYLENE

HOLDERBAT

D E T I L

FOR ST L

PIPING

k

DETAIL

FOR P O L Y A a P Y l

/ LIPPER P I P N

Documents

Foundation design on poor soil