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Underpinning Of Structures Jamani Mohammedabbas R (SD0510) Faculty Guide : Prof R.J.Shah School Of Building Science And Technology CEPT University , Ahmedabad

Underpinning

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Underpinning Of Click to edit Master subtitle Structures styleJamani Mohammedabbas R (SD0510)

Faculty Guide : Prof R.J.Shah School Of Building Science And Technology CEPT University , Ahmedabad4/16/12 underpinning of structures

Contents

Introduction is underpinning of underpinning and disadvantages is underpinning required

What Why

Methods

Advantages Case

study22

conclusion4/16/12 underpinning of structures References

IntroductionThe

construction industry over the years has faced many problems right from the time of its inception problems related to the construction can be classified under two major categories i.e. i) superstructure.

The

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ii) substructure. underpinning of structuresstructures underpinning of

33

ContinueSeveral

techniques have been developed in order to deal with these types of problems by the engineers but the feedback obtained from the engineers is the problems related to superstructure can be solved and rectified much easily as compared to the substructure

is one of the engineering underpinning of structures deal with solutions 4/16/12 underpinning of structures to 44

Underpinning

What is underpinning ????????The

word underpinning is used in foundation engineering to denote the process of transferring the weight of an existing structure from its original foundation to temporary supports and from them to a new permanent substructure.

may also denote the construction of new foundation under the structureunderpinning of structures intermediate without the 4/16/12 55

It

ContinueWhen This

the work is completed, the structure is said to be underpinned. may be necessitated occasionally by the inadequacy of original foundations or by their harmful settlements.

most cases, however, it is caused by the fact that the new work in the immediate vicinity of the structure or even in the building itself, 4/16/12 underpinning of structures 66

In

ContinueSuccessful

underpinning requires a knowledge of the state of balance of a building, its foundation and of the ground conditions. of load transfer need to be fully investigated within any structure to be underpinned.

Paths

will help us in knowing the probable concentrations of stress the 4/16/12 underpinning of structures 77 building is subjected to.

It

Why underpinning ????Some of the construction modifications and

Likely to make underpinning of existing Structures necessary are the following.Provision

of a basement in a building that had none before. of tunnels , sewers under or near columns or walls. tanks, wells 88

Installations

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Construction of ofpits, underpinning structures

Continueof subways. Lowering of water table by adjacent excavations that endanger the safety of footings on piles. Increase of loads on columns or walls that requires replacement of present foundations. The construction of deep foundations in positions that endanger present ones. Loweringunderpinning ground surface by the of structures 4/16/12 99Construction

General PrinciplesThe process of underpinning involves great care and patience as conditions are likely to differ for every job and every job is special in its own way. The load has to taken off the existing footing and held by temporary means while a new support is provided. The load is then has to be 4/16/12 underpinning of structures 10 transferred to the new bearing.

.ContinueIt

is important to do all this in a manner that does not require or produce raising or lowering of the structure sufficiently to cause cracking or other harm to it. are several means to achieve the above mentioned objective but the common ones are use of wedges and screw jacks, hydraulic jacks etc.underpinning of structures 11

There

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Methods Of UnderpinningSeveral methods used for underpinning are as Follows:Conventional Micro Angle

concrete underpinning.

piles. piles piles. beams. of structures underpinning12

Bracket4/16/12

Needle

ContinuePiled

R.C. Raft. piles. grouting. pipe piles.

Sheet Steel

Pressure

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underpinning of structures

13

Conventional Concrete Underpinning Conventional

concrete underpinning is accomplished from small, sheeted and braced pits constructed beneath the foundationunderpinning of structures 14

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Traditional Underpinning This

method stabilizes existing wall foundations by digging under the present foundation in sequenced bays to a depth where firm strata exists and replacing the excavated material with mass concrete. loading capabilities are based upon the strata encountered.underpinning of structures 15

The

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ContinueIn

some circumstances when the existing footing is adequate to span between supports, intermediate piers can be used to reduce cost, i.e miss out piers 2 and 4 as shown on the diagram below.

suitable bearing stratum is assessed by the Supervising Officer or Building Inspector upon completion of thestructures sequence of 4/16/12 underpinning of first 16

A

ContinueTraditional

Underpinning is usually applied when the existing foundations are at shallow depth. are excavated generally 1.0m 1.2m in length, 0.6m wide, and up to 2.5m from ground level. However a mini-piled solution would be more economical over depths of 1.5m.underpinning of structures 17

Bays

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Continue

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Traditional underpinning underpinning of structures

18

Advantagessimple

engineering understood. for heavy loads.

and

easily

Suitable

Occupants

can remain in the property as work is under taken from outside. can be used in restricted access areas. Suitable underpinning of structures new cellars for formation of 19

Method 4/16/12

Needle Beam MethodThis

method stabilises existing wall foundations by the use of piles installed either side of the wall. A small pocket is broken out below the ground level and a reinforced concrete needle beam is cast in-situ connecting the piles and supporting the walls.

the span between needle 4/16/12 underpinning of structures 20 beams can accommodate very high

Reducing

..ContinueHowever,

the bearing capacity of the underlying strata will determine the number, diameter and spacing of piles used.

system is used where traditional underpinning is not appropriate due to the existing foundations being deep, or that good-bearing strata is so deep that it is uneconomical to dig. (Depths greater than 1.5m) . 21 4/16/12 underpinning of structures

This

AdvantagesSuitable Needle

for restricted access.

beam constructed at a higher

level if the existing foundation is too deep.Faster High More4/16/12

than tradition underpinning.

load capability. economical at greater depths. disruption, less spoil generated underpinning of structures 22

Less

Continue

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Needle beam underpinning of structures method

23

Piled R.C. RaftThis

method stabilizes existing wall foundations to whole rooms. Mini-piles are installed within the property and capped with an integral reinforced concrete raft. Needle beams project from the slab into to the walls below ground level.

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underpinning of structures

24

.ContinueReducing

the span between projecting needle beams and increasing pile numbers can accommodate highly loaded structures. However, the bearing capacity of the underlying strata will determine the number, diameter and spacing of piles used.underpinning of structures Load Capabilities using mini-piles: 25

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ContinueThis

system is used where whole rooms or whole structures are to be underpinned and includes the provision of a new internal floor slab. is appropriate when existing foundations are deep, or that goodbearing strata is so deep that it is uneconomical to dig. (Depths greater than 1.0m).underpinning of structures 26

It

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ContinuePiles

are installed at determined by loadings.

centers

Pockets

are then broken out and reinforced needle beams are placed to pick up the walls. A ring beam is constructed linking the needles, mesh is laid and the whole structure poured.underpinning of structures 27

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Continue

Piled R.C raft method4/16/12 underpinning of structures 28

Continue

Piled R.C raft method4/16/12 underpinning of structures 29

AdvantagesProvides

lateral and traverse ties throughout the structure. new completion. 1.0m. floor slab upon

Provides

Economical No4/16/12

at depths greater than

need for external access.underpinning of structures 30

Cantilever Beam Method

This method stabilises existing wall foundations either internally or externally whichever the most appropriate. mini-piles are installed, one compression and one tension.

Two A

pocket is broken out into the existing wall and a reinforced concrete beam is cast linking the 4/16/12 underpinning of structures 31 two piles.

.Continue This

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system is used where traditional underpinning is not appropriate due to the existing foundations being deep, or that good-bearing strata is so deep that it is uneconomical to dig. (Depths greater than 1.5m). Orunderpinning of structures 32

.ContinueReducing

the span between cantilevers can accommodate high loads. However, the bearing capacity of the underlying strata will determine the number, diameter and spacing of piles used.

are installed at approximately 1.0m 1.5m centers and 1.2m apart 4/16/12 underpinning of structures 33 determined by loadings.

Piles

ContinueThen

pockets are broken out and reinforced beams are placed to pick up the walls. Beams are usually cast alternate. Capabilities using mini-piles: i) 105mm dia SWL 60KN . ii) 150mm dia SWL 80KN.

Load

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underpinning of structures

34

..Continue

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Cantilever method underpinning of structures

35

..Continue

Cantilever method4/16/12 underpinning of structures 36

AdvantagesFaster

than traditional underpinning. one side only.

Access

from Occupants can

stay in the property during construction.Economical

at depths greater than

1.5m.Suitable4/16/12

for restricted access.underpinning of structures 37

Micro-pilesMicro-piles

are small diameter (100 to 300 mm in diameter), reinforced load transfer elements capable of supporting design loads in excess of 200 tons. Micro-piles can be installed through almost any type of subsurface condition, from sands to clay to bouldery soils to rock.underpinning of structures 38

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ContinueMicro-piling

is accomplished using low-vibratory drilling techniques, a critical consideration when working around sensitive structures. The micro-piles can readily be installed in confined space and low headroom situations.

Often installation can be accomplished without disrupting 4/16/12 39 normal underpinning of structures operations. facility

ContinueVertical

.

and/or inclined micro-piles can be installed to provide additional foundation support needed to withstand increased structural loading, underpin existing shallow foundations during adjacent new construction, arrest ongoing settlement, and for seismic retrofit.underpinning of structures 40

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Case StudyImperial Location

College. : London

Considered

as a major centre for teaching and research in science and engineering. of structure :- load bearing brick walls. in the beginning of the41

Type

Constructed4/16/12

19th century underpinning of structures

.ContinueMethod Soil

used :- needle beam with the help of concrete stools. profile:- soil consisted of gravels overlyed by clay. table was at approx 2m below the existing basement level.

Water

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underpinning of structures

42

.ContinueThe

first stage was to excavate a very deep basement at the rear of the main building. walls of main building comprised of a series of heavily loaded piers each of 1m thick* 2m wide. most heavily loaded pier carried at load of 4000 KN and the staircase wall loading was 250 KN/m.underpinning of structures 43

The

The

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ContinueThe

depth of basement excavation was required to be 9 m below the existing basement floor level and walls were underpinned to a depth of 11m. beam method was used to underpin the wall.

Needle

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underpinning of structuresstructures underpinning of

44

.Continue

Intial stage of beam construction4/16/12 underpinning of structures 45

.Continue

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Reinforcement between stoolsunderpinning of structures

46

.Continue

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Placing of stools underpinning of structures

47

.Continue

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Final stool underpinning of structures positions

48

Continue

Schematic view4/16/12 underpinning of structures 49

ConclusionUnderpinning

of a structure is a complex and a time consuming process. is necessary to study in detail the pre-requites before taking the underpinning process.

It

should be allocated to the consultants who have already worked on similar nature of projects 4/16/12 underpinning of enough to achieve 50 and are confident structures

Work

ReferencesUnderpinning FoundationDr. K .R. Arora

and retention

S .Thorburn and G. S. Littlejohn

engineering and framing

UnderpinningJ.F.S Pyrke

Differential

movement of domestic51

buildings4/16/12 underpinning of structures

Experience

along with expertise is necessary to deal with any kind of structural problems and the aim of the construction should be to carry out the work with all the strength and quality required along with skill and economy.

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underpinning of structures underpinning of structures

52

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4/16/12

underpinning of structures