Upload
ruhin-yakin
View
216
Download
0
Embed Size (px)
Citation preview
8/8/2019 Equipe 2010 Foundation Design
1/129
Geotechnical Foundation
Design
Peter Reading,
Technical Director
Equipe Training
8/8/2019 Equipe 2010 Foundation Design
2/129
Geotechnical design
8/8/2019 Equipe 2010 Foundation Design
3/129
There is an Intimate LifetimeRelationship
A BUILDING A SITEand
Manufactured to adefined layout using
selected very carefullyspecified materials
Location is selectedbut characteristics are
inheritednotspecified
THE GROUND
The Foundation for
success
Between
8/8/2019 Equipe 2010 Foundation Design
4/129
Reasons for foundation failure
Application of a foundation load whichexceeds the ability of the soil to support
the load
8/8/2019 Equipe 2010 Foundation Design
5/129
Reasons for foundation failure
Shrinkage or swelling of thesoil
8/8/2019 Equipe 2010 Foundation Design
6/129
Reasons for foundation failure
Differential settlement
8/8/2019 Equipe 2010 Foundation Design
7/129
Reasons for foundation failure
Mining subsidence
8/8/2019 Equipe 2010 Foundation Design
8/129
Reasons for foundation failure
Frost action
8/8/2019 Equipe 2010 Foundation Design
9/129
Excavation Failure
Singapore MRT April 30, 2004, 3:15 pm
Failure of excavationstruts
8/8/2019 Equipe 2010 Foundation Design
10/129
Tunnel FailureSao Paulo tunnel collapse (Brazil)
Earth pressure design
miscalculation
8/8/2019 Equipe 2010 Foundation Design
11/129
Reasons for failure
Excavation of basement
Without control of
groundwater
8/8/2019 Equipe 2010 Foundation Design
12/129
With the right information manyproblems can be mitigated
It is essential to carry out a site investigation
The investigation should be made usingappropriate methods and the data obtained,interpreted and evaluated for the proposeddevelopment by someone who is competent andexperienced.
The investigation should be regarded as site-
specific Research and Development
8/8/2019 Equipe 2010 Foundation Design
13/129
Geotechnical Design using Eurocode
The structural eurocodes are a European suite ofcodes for structural designdeveloped over more
than twenty five years. By 2010 they will have effectively replaced the current British
Standards as the primary basis for designing buildings
and civil engineering structures in the UK.
(Institute of Structural Engineers 2004)
8/8/2019 Equipe 2010 Foundation Design
14/129
Design using Eurocode
Conventional design uses allowable stress, this is basedon applying a factor of safety to the ultimate stress .
Allowable Bearing pressure qna = Undrained shear strength x f
factor of safety
Eurocode uses limit state design,
There are basic requirements for limit state design for astructure.
It must sustain all likely actions and influences and mustremain fit for purpose and have adequate structuralresistance ,durability and serviceability for its design life.
8/8/2019 Equipe 2010 Foundation Design
15/129
LIMIT STATE DESIGN
Working state design: Analyse the expected, workingstate, then apply margins of safety.
Limit state design: Analyse the unexpected states atwhich the structure has reached an unacceptable limit.
Make sure the limit states are unrealistic or unlikely.
Limit states can occur in the ground or the structure or acombination of both.
8/8/2019 Equipe 2010 Foundation Design
16/129
Foundation Design
Historically the UK were at the forefront of foundation design.
Designs based on sound mathematical formula, usually theseare ultimate state formula . They calculate the loading which will
cause a catastrophic failure. Depending on the designers confidence in the derived values a
factor of safety can be applied to give working design values.
Typically factors of safety range from 1.2 to 3 or even higher.
Some designs are based on empirical relationships or limitingvalues, these are derived from observational methods which aredeemed to be adequately safe.
8/8/2019 Equipe 2010 Foundation Design
17/129
The SPT test
This is a field test and isthe number of blowsfrom a 63.5kg hammerfalling 760mm used todriver a 30 degree coneor split spoon of 50.8mmdiameter.
Blows required to drive
the tool for 300mm arecounted, The number ofblows is referred to asthe penetration
resistance N value.
8/8/2019 Equipe 2010 Foundation Design
18/129
Cone Penetration Tests (CPT)
Rigs are: 20tonne trucks (as shown) Lighter crawlers Demountable units
A cone is pushed into the ground ona rod string using hydraulic rams Cone resistance and side friction
continuously recorded electronically Piezocone also measures pore
water pressure
Provides a plot records againstdepth which can be interpreted
to give an indication of soil type
8/8/2019 Equipe 2010 Foundation Design
19/129
.
Cone Penetration Tests (CPT)
8/8/2019 Equipe 2010 Foundation Design
20/129
Cone Penetration Tests (CPT)
8/8/2019 Equipe 2010 Foundation Design
21/129
Empirically derived bearing pressure
The graphs here werederived by Terzaghi andPeck from SPT N values.The allowable bearingpressures are forfoundations placed on sandand presume a limitingsettlement of 25mm.
8/8/2019 Equipe 2010 Foundation Design
22/129
Factors affecting foundation design
We intend to construct a foundation which
will not cause shear failure by
overstressing the ground. Will not suffer distress from excessivesettlement.
W
ill take account of the site constraints. Will be economically viable.
8/8/2019 Equipe 2010 Foundation Design
23/129
Factors affecting foundation design
Changes in total stress will not causedeformation of an element of soil.
Deformation is the result of changes ineffective stress.
8/8/2019 Equipe 2010 Foundation Design
24/129
Definitions
Ultimate bearing pressure (qt) Is the value of the bearing pressure at which the
ground will fail in shear
Maximum safe bearing pressure (qs ) Is the intensity of the applied pressure that thesoil will safely support without the risk of shearfailure
qs = qt / F
F depends on our confidence of the soil properties and canrange from 1.75 to 3. This approach may be fine under Eurocode. The factor can be
applied to the assessed part of the formula.
8/8/2019 Equipe 2010 Foundation Design
25/129
Ultimate Bearing capacity
The three components of the Terzaghi (1943) bearingcapacity equation are:
gross qult = cNc+poNq+1/2 KBN K
where:cNc is due to cohesion and friction in the soilpoNq is due to surcharge and friction in the soil1/2 KBN K is due to self-weight and friction in thesoilpo = total overburden pressure at foundationlevel around the foundation (see fig 8.14)
K = bulk unit weight of soilB = width of foundationNc,Nq andN K are termed bearing capacity factorsand are related to the J value only.
8/8/2019 Equipe 2010 Foundation Design
26/129
Adaptation of the basic Terzaghiequation
The Terzaghi solution can be applied to cases wherethe groundwater table is very deep, in this case totalstress is equal to the effective stress.
The solution can also apply to the undrained totalstress situation using cu and u .
For free draining soils such as sand where theexcess pore pressure under the footing is zero once
the load has been applied the Terzaghi equation canbe modified to
q = Nc +p'(Nq -1) + B K N K + p Where p = initial effective overburden pressure at the foundation level
p = initial total OBP and K = submerged unit weight
8/8/2019 Equipe 2010 Foundation Design
27/129
Skemptons Bearing capacity equation
Skempton derived an equation from theTerzaghi method for clay soils
Qf = Su Ncu + q0
Where Ncu is Skemptons bearing capacityfactor and is equal to Nc.sc .dc
Where s is a shape factor = 1+ 0.2(B/L)
d is a depth factor =1+(0.053D/B) Nq = 1 N K = 0 and Nc = 5.14
8/8/2019 Equipe 2010 Foundation Design
28/129
Skemptons Bearing capacity equationfor clay soils
8/8/2019 Equipe 2010 Foundation Design
29/129
Bearing capacity in practice Cohesivesoils
It is necessary to consider the
ground condition within which the
foundation is to be placed .
If the soils are predominantly clay
pore pressure will increase as
the load is applied. Because permeability is lowdissipation will take a long time. There will be little gain
in strength therefore the condition is undrained. Theanalysis can be made in terms of total stress.
Overtime pore pressure will dissipate and there will bea gain in strength.
8/8/2019 Equipe 2010 Foundation Design
30/129
Bearing capacity in practice Cohesivesoils
Where foundations are placed in a free draining soil such assand and gravel, pore pressure will dissipate as the load isapplied.
The soil will consolidate and gain in strength as constructionproceeds such that all
settlement is completed by the
time construction is complete.
In this situation a drained analysis can be made using effective
stress parameters.
8/8/2019 Equipe 2010 Foundation Design
31/129
Bearing Capacity Factorsfor Foundations
The factors Nc, Nq andN K are dependant onthe angle of shearing resistance J.In cohesive soils J = 0 and c = SuThe total stress condition
therefore the N K term is = 0The Nq = 1In drained soils the calculation is in terms ofeffective stresses.
Nc,NqandN K > 0
8/8/2019 Equipe 2010 Foundation Design
32/129
Use of the bearing capacity factors
Ultimate bearing pressure qult is dependant on the initialeffective overburden pressure at the foundation leveltherefore as foundation depth is increased then qult alsoincreases.
If groundwater is absent again p' is increased andhence qult is increased. Where the groundwater table isconsidered to lie at least 2B below the base of thefooting and will remain so then p' is equal to p, this willalso increase qult .
Caution must be used where J'is high because highvalues ofNq andN K will be obtained for small changesin J'
8/8/2019 Equipe 2010 Foundation Design
33/129
Bearing capacity factors
Following on from the work of Terzaghi severalresearches modified the values of the factors Nc, Nq andN K and also took account of the footing depth andshape.
Terzaghi proposed a shape factor to be applied to theterms
Strip Circular Square
Sc 1.0 1.3 1.3
SK 1.0 0.6 0.8
8/8/2019 Equipe 2010 Foundation Design
34/129
Variation of Shear strength with depth
In most cases the undrained shear strength increaseswith depth.
In soils made up of layers of different properties the
stress at each stratum needs to be checked to ensurethat the stratum is overstressed.
This is particularly important where softer soils underliefirmer soils. In these cases the load is taken to spread atan angle of 30o down to the weaker soil and bearing
capacity is checked in the usual way.
8/8/2019 Equipe 2010 Foundation Design
35/129
Before Eurocode 7
Factor of Safety of 3 limits settlement to a controllable level.
For granular soils, ultimate bearing capacity is usually higher than for clays butthey derive the allowable bearing capacity on density (often from SPTs).
8/8/2019 Equipe 2010 Foundation Design
36/129
Partial factors
Under the Eurocode factors of safety will be applied tovarious components.
The weighting of the factor is dependant on confidence
in the parameter and if the effect is favourable or not. There are three possible design approaches.
It is most likely the UK will adopt design approach 1.This has two combinations of factors both need to bechecked to ensure the design is adequate.
The final methods will not be confirmed until the Nationalannex has been published.
A work in progress....
8/8/2019 Equipe 2010 Foundation Design
37/129
Some examples of partial factors
Partial factor
Design approach 1
Combination 1 Combination 2
K G 1.35 1.0
K G,fav 1.0 1.0
K 1.0 1.25
K cu 1.0 1.4
KRh 1.0 1.0
K G,fav /(KRh x K ) 1.0 0.8
KG /(KRh x K ) 1.35 0.8
1 /(KRh x Kcu ) 1.0 0.71
8/8/2019 Equipe 2010 Foundation Design
38/129
Foundation design
Once we establish the allowable bearing pressure, thesize of the foundation can be obtained this is based onthe actual loads applied to the footing including factors ofsafety for the structure.
This may need to be an iterative process.
It may be found that a solution is not possible ie ourloads exceed the allowable load which may be applied. Ifthis is the case an alternative foundation solution may berequired.
8/8/2019 Equipe 2010 Foundation Design
39/129
Settlement
Some soils reach failure at relatively small strains forexample stiff clays.
Others do not reach their failure stress until relatively
large strains have been developed. It is thereforeimportant to check that strain is not so large that it willcause structural distress.
In addition clay soils will dissipate pore pressures at a
slow rate whilst this will develop an increase in strengththe resulting consolidation may be undesirable.
Therefore once the foundation size and bearing pressurehas been obtained the footing needs to be checked toensure that settlement is not excessive.
8/8/2019 Equipe 2010 Foundation Design
40/129
Stress strain relationship for soils ofvarious types
8/8/2019 Equipe 2010 Foundation Design
41/129
The Behaviour of the Ground
The most significant
behaviour for most structures
Settlement
Total
Settlement
Differential
Settlement
Rate
8/8/2019 Equipe 2010 Foundation Design
42/129
Settlement Depends on...
- Actual not maximum loads
- Distribution and duration of loading
- Area stressed and stress distribution- Strata thicknesses and compressibility's
- Strata levels relative to applied stress
- Strata type and stress history- Collapse of voids unrelated to applied
stress
8/8/2019 Equipe 2010 Foundation Design
43/129
Stress Distributions BeneathFoundations
On SandOn Clay
Flexible foundationOn Clay
8/8/2019 Equipe 2010 Foundation Design
44/129
Settlement calculation
Settlement prediction based
on Consolidation tests.
Settlement proportional to:
- mv co-efficient of volume decrease
- Stress applied
- Thickness of soils stressed
8/8/2019 Equipe 2010 Foundation Design
45/129
Boussinesq equation
Distribution of stress with depth due to theapplication of a load at ground surface(Boussinesq)
8/8/2019 Equipe 2010 Foundation Design
46/129
Distribution of vertical stress
Within Allowable Stress Levels
8/8/2019 Equipe 2010 Foundation Design
47/129
Total settlement calculation
There are several basic formula used tocalculate total settlement
c = e H 1+ e
c = mv .H.p
c = Cc H log10 p'0
+p
1 + e0 p'0
8/8/2019 Equipe 2010 Foundation Design
48/129
Calculation of settlement in amultilayered system
Using the distribution of stress with depthgraphs the effect of the stress applied by each
strata can be derived in proportion. Therefore by using the mv derived for each
layer the total settlement attributed to eachlayer can be calculated.
The total settlement should be less than thesettlement considered to be acceptable forthe structure.
8/8/2019 Equipe 2010 Foundation Design
49/129
consolidation testing derivation of
parameters.
geotechnical laboratory testing awareness
8/8/2019 Equipe 2010 Foundation Design
50/129
Consolidation testingVoids ratio load curves
geotechnical laboratory testing awareness
8/8/2019 Equipe 2010 Foundation Design
51/129
Calculation of Mv
The coefficient of volume compressibilityis derived from consolidation tests and is
defined as mv = V P
V
In the oedometer test a change in volumeis proportional to the change in heightthus
mv = H P
8/8/2019 Equipe 2010 Foundation Design
52/129
Consolidation testingTaylor analysis forCv
geotechnical laboratory testing awareness
8/8/2019 Equipe 2010 Foundation Design
53/129
Oedometer consolidationCassagrande analysis forCv
geotechnical laboratory testing awareness
8/8/2019 Equipe 2010 Foundation Design
54/129
Consolidation testing
To relate test to voids ratio it is necessary to measurethe particle density.
Often assumed as 2.65 or 2.70
The choice of cv values should be determined from thebest fit analysis Taylor or Casagrande.
Note that permeability is given by
k= cv mv x 0.31 x 10-9 m/s
Thus as load is increased permeabilitydecreases
ie cv x mv must decrease.
geotechnical laboratory testing awareness
8/8/2019 Equipe 2010 Foundation Design
55/129
Consolidation testing
Organic soils
Low Particle Density so need to measure this to
calculate true voids ratios which can be very high
Need to measure the coefficient of secondaryconsolidation this is consolidation which continues
to occur after pore pressures have equilibriated. Thiscontinues for a very long time (longer than primaryconsolidation).
geotechnical laboratory testing awareness
8/8/2019 Equipe 2010 Foundation Design
56/129
Consolidation testing
Limitations Sample thickness is only 19mm.
Results may not reflect true soil structure
Drainage is in vertical direction.
Can only be carried out on fine grained soils.
Difficult not to smear drainage paths duringpreparation
geotechnical laboratory testing awareness
8/8/2019 Equipe 2010 Foundation Design
57/129
Differential settlement
Differential settlement will occur if
The foundations are not uniformly loaded
The strata is variable beneath thestructure
Shrinkage or swelling occurs associatedwith trees or vegetation
With careful design all these factors canbe eliminated or catered for in the design.
8/8/2019 Equipe 2010 Foundation Design
58/129
Some examples of partial factors
Partial factor
Design approach 1
Combination 1 Combination 2
K G 1.35 1.0
K G,fav 1.0 1.0
K 1.0 1.25
K cu 1.0 1.4
KRh 1.0 1.0
K G,fav /(KRh x K ) 1.0 0.8
KG /(KRh x K ) 1.35 0.8
1 /(KRh x Kcu ) 1.0 0.71
8/8/2019 Equipe 2010 Foundation Design
59/129
Example foundation design Spreadfoundation - Pad on clay
K s:k characteristic weight,density of soil = 20kN/m3
K c;k density of concrete
=24kN/m3
Cu:k characteristic value ofundrained shear strength= 60 kPa
Determine the width B of thefooting
ie Vd < Rd
0.5m
500kN
B
1.50m
8/8/2019 Equipe 2010 Foundation Design
60/129
Example - pad foundationDesign approach 1 combination 1
1. Imposed vertical load = 500kN
2. Weight of foundation
Wt of concrete (1x0.5x0.5x24) +(2x2x0.5x24) = 54kN
3. Weight of backfill (2x2x1) (0.5x0.5x1) x
20 =
75kN
Total permanant load Vk =
8/8/2019 Equipe 2010 Foundation Design
61/129
Example - pad foundation
design strength cudi = cuk /K cu = 60 /1.0
= 60 kPa Soil surcharge , design value adjacent to
footing
q di = q k x K G = (1.5 x 20) x 1.0
q di = 30kPa
8/8/2019 Equipe 2010 Foundation Design
62/129
Example - pad foundation
Design bearing resistance
Rd1 = Rk / KRh
= Rk / 1.0 Rd1 = Rk After Terzaghi
Rd1 = 4 [ ( + 2) x 1.2 x60 +30]
Rd1 = 1601kN
Check ifV
d1 < Rd1 849kN
8/8/2019 Equipe 2010 Foundation Design
63/129
Example - pad foundationDesign approach 1 combination 2
Design load Vd2 = 1.0 x 629
Vd2 = 1.0 x 629
Vd2 = 629 kN Design strength
Cud2 = 60 / 1.4
= 43kPa
Soil surcharge
qd2 = qd2 x K G = (1.5 x 20 ) x 1.0
= 30 kPa
8/8/2019 Equipe 2010 Foundation Design
64/129
Example - pad foundationDesign approach 1 combination 2
design bearing resistance
Rd2 = R/ R K v
= R /1.0 Again after Terzaghi
Rd2= 4 [ ( + 2) x 1.2 x 43 +30]
= 1181kN Check if Vd2 < Rd2 629 < 1181
footing 2m x 2m is acceptable
(design app. 1 comb.1)
8/8/2019 Equipe 2010 Foundation Design
65/129
What if......
Bearing Capacity is too low? or Settlement is too great?
or Ground is too variable?This may, and often does apply to
natural deposits on Greenfield
Sites but it is often the case on
Brownfield Sites where there aresubstantial deposits of Made
Ground or Fill and we need to look
for Solutions
8/8/2019 Equipe 2010 Foundation Design
66/129
Fill and Phil are very similar
Character Profile
- Inconsistent
- Unreliable
- Generally weak
- Dodgy history
- Variably dense- Variably thick
- Sometimes smells
- Unpredictable
- Can take time to settle
- Can be aggressive
- Hangs around cities
- Doesnt recognise
normal laws- Operates under cover
- Can collapse suddenly
Phil
8/8/2019 Equipe 2010 Foundation Design
67/129
We could try to improve Phil
.Use some method to increase the grounddensity and hence improve its loadcarrying capacity and reduce the effect of
settlement Compaction
Surcharging
Grouting
Stone columns (or similar)
Dynamic consolidation
8/8/2019 Equipe 2010 Foundation Design
68/129
We could try to improve Phil
We can compact the ground will a heavyroller
Solutions Excavation and
8/8/2019 Equipe 2010 Foundation Design
69/129
Solutions - Excavation andRecompaction
AdvantagesSimple technologyCan be used on sites of all
sizesCan be cost effectiveTreats all of the soil to the
required depthsCan closely control
treatment
DisadvantagesRequires storage areas on
siteCannot treat ground below
groundwater level without
lowering itRequires support of
excavation sides or batteredslopes
Exposes operatives topotential contamination
8/8/2019 Equipe 2010 Foundation Design
70/129
Width > 2 x d
h = height of surcharge fill toapply stresses well inexcess of foundation, raft,floor or long term fillstresses.
h
d
Surcharge Fill
Soft, loose orvariableground
Competent Stratum
Solutions - Surcharge
8/8/2019 Equipe 2010 Foundation Design
71/129
Advantages Treats all of the loaded area
uniformly Treats the full depth of problem
soils Proves the treated area Provides parameters for future
predictions Can rapidly treat unsaturated fills Does not require sophisticated
plant Simple concept
Surcharge - Simple Concepts
8/8/2019 Equipe 2010 Foundation Design
72/129
Surcharging
Disadvantages Requires large quantities of fills requiring later disposal For saturated natural soils consolidation can be slow without
vertical drains Requires detailed monitoring of settlement patterns
8/8/2019 Equipe 2010 Foundation Design
73/129
Load Settlement Data
Surcharging
8/8/2019 Equipe 2010 Foundation Design
74/129
Speeding up the surcharging process
8/8/2019 Equipe 2010 Foundation Design
75/129
Solutions - Vertical Drains
8/8/2019 Equipe 2010 Foundation Design
76/129
Vertical Drains
Accelerates consolidationof layered soft cohesive
soilsAllows gain in strengthresulting fromconsolidation to be usedin stage loadingprogramme beneath
embankments / structuresQuick to installProvides control of
consolidation rates
AdvantagesDisadvantages
Requires working platform forrelatively high plant
Requires surface drainage layer
(usually)Requires surcharge to addresslong term settlements
Does not, of itself, strengthen orincrease density of treated soils
Requires instrumentation to
monitor pore water pressuresand settlement
Can provide linkages betweenpollutants and groundwater orgases
8/8/2019 Equipe 2010 Foundation Design
77/129
Solutions - Vibrocompaction
8/8/2019 Equipe 2010 Foundation Design
78/129
Vibro-compaction
Advantages Suitable for compacting loose
granular soils Can be adapted to treat made
ground by incorporatingcompacted stone columns
Known depth of treatment Accelerates consolidation rates
by providing drainage to linknatural preferential drainagepaths
Can treat foundation and floorslab areas
Reduces total and differentialsettlement
Helps unify ground conditions Avoids contact between site staff
and contaminated soils Can treat materials below water
table
Disadvantages Causes ground vibration which
can adversely affect localinstallations
Creates pathways for flows ofpotentially contaminated water
Can create pathways formigrations of ground bornegases
Requires import of granular soils Treats discrete vertical columns
rather than the whole area
Unsuitable for small sites Can be costly May require surcharge to deal
with settlements
8/8/2019 Equipe 2010 Foundation Design
79/129
Vibro-compaction
8/8/2019 Equipe 2010 Foundation Design
80/129
Variations on a theme
Vibro replacement and vibro
concreted columns
S C
8/8/2019 Equipe 2010 Foundation Design
81/129
Solutions - Dynamic Compaction
S l ti D i C ti
8/8/2019 Equipe 2010 Foundation Design
82/129
Solutions - Dynamic Compaction
D i C ti d t
8/8/2019 Equipe 2010 Foundation Design
83/129
Dynamic Compaction - advantages
Applies high impact stresses much greater than foundation loadsCauses any voids to collapse and reduces risk of collapse settlementCan treat to 8m depthDoes not create preferential drainage paths
Reduces permeability of compacted soilsDoes not require disposal of soilsTreats the whole areaReduces post-construction settlementSimple technology
Suitable for uncompacted Made GroundCan treat floor and foundation areasCosts can be favourable in relation to piling
Avoids contact between contaminated soils and site personnel
8/8/2019 Equipe 2010 Foundation Design
84/129
Disadvantages Causes substantial vibratory loads to adjacent properties and installation Requires import of fills to form working platform and fill voids Depth of effect can only be demonstrated by comparing pre and post treatment
investigation data
Requires large plant, considerable headroom and stable access and working area Adverse affects from disturbance of soft alluvial deposits Cannot be used in natural organic ground Unsuitable for small sites Can be costly
8/8/2019 Equipe 2010 Foundation Design
85/129
Ground improvement by grouting
8/8/2019 Equipe 2010 Foundation Design
86/129
Drilling and Grouting
Jet Grouting and Soil Mixing
These processes both disturb the soil and introduce grout intothe soil melange.
Jet grouting is carried out by jetting the soil with the grout inorder to break the soil down and produce a grout soil mix
Soil mixing uses a drag bit to break to soil up. Rigid blades on
the drill string mix in the Grout which is introduced through thedrill string
8/8/2019 Equipe 2010 Foundation Design
87/129
Jet Grouting
This technique was invented in the UK, anddeveloped in Japan
The method uses a high pressure jet of waterto erode the soil.
the soil residue is then mixed with grout toform a soil grout mix often formed into
columns. The process can be used for a variety of
geotechnical solutions, it does not requirelarge plant and is therefore ideal for areas
where access is restricted.
8/8/2019 Equipe 2010 Foundation Design
88/129
Jet Grouting
Jet Grouting
8/8/2019 Equipe 2010 Foundation Design
89/129
Has been used to carry out works such as ;-
Embankment stabilisation
Underpinning of foundation
To provide foundation for new structures
In curtains to provide a barrier to fluid flows
Remedial works to dams cut off curtains and cofferdams
Solidification of contaminated soil or as a cut off.
Jet Grouting
8/8/2019 Equipe 2010 Foundation Design
90/129
Can be carried out using either single jet; double jetor triple jet systems
Single jet Uses a 5 to 10 mm diameter nozzle on a hollow stem
grout tube the grout jet is used to erode the soil to createa slurry mix of grout and soil
Double jet Similar to the single jet method but the grout jet is
shrouded in a jet of air this improves cutting of the soil
Triple jet This uses an air shrouded water jet to erode the soil
grout is injected by a lower jet
Jet Grouting
8/8/2019 Equipe 2010 Foundation Design
91/129
8/8/2019 Equipe 2010 Foundation Design
92/129
Compaction Grouting
1. Compaction Grouting
This is carried out by injecting a stiff grout or paste into theground in order to cause displacement of the soil mass.
The method is used to increase
the compaction of loose soils and
improve their ability to carry loads.
8/8/2019 Equipe 2010 Foundation Design
93/129
Compaction Grouting
1. Compaction Grouting
This is carried out by injecting a stiff grout or paste into theground in order to cause displacement of the soil mass.
The method is used to increase
the compaction of loose soils and
improve their ability to carry loads.
8/8/2019 Equipe 2010 Foundation Design
94/129
Compensation Grouting
Compensation Grouting is aspecialist form of hydrofracture.
It involves injecting grout intothe ground during tunnelling to
reduce or eliminate the effects of surface settlement which alwaysoccurs when tunnelling is beingcarried out.
The process was developedduring the 90s and was used in
London tunnels for the jubilee lineextension were constructed, beneathmany important structures.
In order to ensure the buildingswere not damages compensationgrouting was carried out
A new underground station was builtclose to the tower of Big Ben
(The Clock Tower that is as Big Ben is the name of the bell !!)
Amazing Fact eh?
8/8/2019 Equipe 2010 Foundation Design
95/129
Compensation grouting uses permeation, hydrofracture;intrusion and compaction grouting methods to minimise the effectsof tunnelling.
The difference between this and other forms of grouting is thatthe grouting takes place as the tunnel is advanced to preventsettlement.
Usually an initial injection is carried out to stiffen the ground .
Compensation Grouting
8/8/2019 Equipe 2010 Foundation Design
96/129
Compensation Grouting
As the tunnel or excavation proceeds very accurate surfacemeasurements are made. Grout injection starts when apredetermined settlement is recorded.
Grouting and monitoring are carried out simultaneously to ensure settlements are not exceeded.
It may be necessary to carry on grouting for some time after the tunnel
face has passed a particular point.
The process is complex and is normally controlled by computerised systems.
8/8/2019 Equipe 2010 Foundation Design
97/129
Solutions - Piling
8/8/2019 Equipe 2010 Foundation Design
98/129
Solutions - Piling
AdvantagesEasiest way to form a deep foundationConvenient way to bypass soft variable soils
and use strength/density of underlyingdepositsWide variety of proprietary driven and bored
techniques available
Wide range of diameter and hence loadcapacitiesCan use in groups to take heavy loadsConsiderable experience in their use
Can enhance lateral stabilit of foundations
8/8/2019 Equipe 2010 Foundation Design
99/129
Pile Support is achieved via:
8/8/2019 Equipe 2010 Foundation Design
100/129
Pile Support is achieved via:
a shear strength mobilised on the surface
of the shaft of the pile, the contribution ofeach stratum depending on its strength,
density and frictional characteristics.
bearing capacity at the base of the pile,
called end bearing.
8/8/2019 Equipe 2010 Foundation Design
101/129
Pile design
Shaft resistance and base
resistance are mobilised at
different amounts of
settlement.
The full shaft resistance is
mobilised at a pile head
settlement of about 1-2% of
the pile diameter. To mobilise the full base
resistance the pile must be
pushed down about 10-
20% of the diameter.
Pile classification
8/8/2019 Equipe 2010 Foundation Design
102/129
their method of installation i.e. driven, bored, jacked
their material type i.e.. timber, steel or concrete, pre-cast
or cast in situ, full length or segmental
the plant used to install them such as driven, tripod,auger, under-reamed, continuous flight auger
their size i.e.. small diameter bored, large diameter bored,
under-reamed, mini-piling
their effects during installation i.e.. displacement orreplacement
the way they provide load capacity i.e.. end bearing, friction
piles, uplift piles, raking piles.
Pile classification
8/8/2019 Equipe 2010 Foundation Design
103/129
8/8/2019 Equipe 2010 Foundation Design
104/129
Various uses of pile groups
The zone of the soil stressed around a single
pile is much smaller than around and beneath a
8/8/2019 Equipe 2010 Foundation Design
105/129
p
pile group
the installation method has lesseffect on group behaviour thanon single pile behaviour
compressible layers existingbeneath the base of a pile group
will produce settlement of thegroup while they may not effectthe result of a single pile loadtest
extrapolation from theperformance of a single pile load
test to the behaviour of a groupmust be treated with caution.
8/8/2019 Equipe 2010 Foundation Design
106/129
Background to Eurocode
HISTORICAL CONTEXT
8/8/2019 Equipe 2010 Foundation Design
107/129
HISTORICAL CONTEXT
1957: EEC Treaty of Rome 1975: Commission of the EC - Eurocodes 1981: European national geotechnical societies
1987: First draft EC7 1989: Comit Europen de Normalisation
(CEN/TC250/SC7)
1994/5: ENV1997 (European Vornorm) 2004 : EN1997-1 + National Annex (2006)
2006 : EN1997-2 + National Annex (2007)
LEVELLING THE FIELD - MOBILITY
8/8/2019 Equipe 2010 Foundation Design
108/129
STATUS OF THE STANDARDS
The BS EN ISOs have supremacy over existingnational standards, eg BS 5930 & 1377
To comply with the principle of supersession, nationalstandards must not conflict with BS EN ISOs
For example BS 5930 & 1377 will be progressively superseded
and revised as Eurocode related standards arepublished
Progress to date: 5930 Section 6, ie soil and rock description, has been
revised to accommodate changes and is with BSI forpublication (early 2008?)
1377 Part 9 already published in revised form (July 2007), iewith DP and SPT covered purely by onward referral to the BS
EN ISOs
8/8/2019 Equipe 2010 Foundation Design
109/129
THE EUROCODE SYSTEM
BS EN 1990 Eurocode 0 Basis of design BS EN 1991 Eurocode 1 Actions on structures BSEN 1992 Eurocode 2 Concrete structures BS EN 1993 Eurocode 3 Steel structures BS EN 1994 Eurocode 4 Composite structures BS EN 1995 Eurocode 5 Timber structures BS EN 1996 Eurocode 6 Masonry structures BS EN 1997 Eurocode 7 Geotechnical design BS EN 1998 Eurocode 8 Design of structures for
earthquake resistance
BS EN 1999 Eurocode 9 Aluminium alloystructures
8/8/2019 Equipe 2010 Foundation Design
110/129
EN 1990 2002
8/8/2019 Equipe 2010 Foundation Design
111/129
EN 1990 :2002
Describes the Principles and requirements for safety,serviceability and durability of structures.
It is based on the limit state concept used in conjunctionwith a partial factor method.
For the design of new structures, EN 1990 is intended tobe used, for direct application, together with EurocodesEN 1991 to 1999
EUROCODE 1997: GEOTECHNICAL
8/8/2019 Equipe 2010 Foundation Design
112/129
EUROCODE 1997: GEOTECHNICALDESIGN (EC7)
EC7 is in two parts
BS EN 1997-1: General Rules
BS EN 1997-2: Ground Investigation and Testing
EC7 Part 2 calls up several other series of BS EN ISO standards
14688: Identification and classification of soil
14689: Identification and classification of rock
22475: Sampling by drilling and excavation andgroundwater measurements
22476: Field Testing
These are normative references, ie they are mandatory
Eurocode 1997 or EC7
8/8/2019 Equipe 2010 Foundation Design
113/129
Eurocode 1997 or EC7
Part 1 published. National Annex in preparation
Part 2 published. National Annex to be prepared thisyear
As a special concession 1997 has been allowed tocoexist with National Standards until 2010
Other Standards no concession - implementationrequired within 6 months of publication
National Foreword to set out rules and no more
EC 1997 P t 1
8/8/2019 Equipe 2010 Foundation Design
114/129
EC 1997 Part 1
Comprises 12 sections and Annexes A to J
Section 1 General
Section 2 Basis of Geotechnical design
Section 3 Geotechnical data
Section 4 Supervision of construction,monitoring and maintenance
Section 5 Fill, Dewatering, groundimprovement and reinforcement
Section 6 Spread Foundations
Section 7 Pile foundations
EC 1997 P t 1 ( t)
8/8/2019 Equipe 2010 Foundation Design
115/129
EC 1997 Part 1 (cont)
Section 8 Anchorages
Section 9 Retaining structures
Section 10 Hydraulic Failure
Section 11 Overall Stability
Section 12 Embankments
Annex A Recommended partial factors of safety
Annexes B to J supplementary information and guidanceincluding internationally applied calculation methods
EC 7 Part 1
8/8/2019 Equipe 2010 Foundation Design
116/129
EC 7 Part 1
Section 2 deals with Geotechnical design
2.1 Design requirements
2.2 Design situations2.3 Durability2.4 Geotechnical design by calculation2.5 Design by prescriptive measures2.6 Load tests and tests on models
2.7 Observational method2.8 Geotechnical Design Report
PARTS OF EUROCODE 7
8/8/2019 Equipe 2010 Foundation Design
117/129
PARTS OF EUROCODE 7
EN 1997-1
General Rules
EN 1997-2
Geotechnical Investigation and Testing
TC 341
Test Standards
TC 288
Execution of geotechnical works
Design using Eurocode
8/8/2019 Equipe 2010 Foundation Design
118/129
Design using Eurocode
Conventional design uses allowable stress, this is basedon applying a factor of safety to the ultimate stress .
Allowable Bearing pressure qna = Undrained shear strength x f
factor of safety
Eurocode uses limit state design, There are basic requirements for limit state design for a
structure.
It must sustain all likely actions and influences and must
remain fit for purpose and have adequate structuralresistance ,durability and serviceability for its design life.
Basis for design
8/8/2019 Equipe 2010 Foundation Design
119/129
Basis for design
Design Working life is defined as:-
the period for which a structure or part of it is to be usedfor its intended purpose with anticipated maintenance butwithout major repair being necessary. [EN1990
1.5.2.8]
Design working life for most structures is 50 years,
Temporary structure are generally 10 to 15 years andsignificant structures 120years
LIMIT STATE DESIGN
8/8/2019 Equipe 2010 Foundation Design
120/129
LIMIT STATE DESIGN
Working state design: Analyse the expected, workingstate, then apply margins of safety.
Limit state design: Analyse the unexpected states at
which the structure has reached an unacceptable limit.
Make sure the limit states are unrealistic or unlikely.
Limit states can occur in the ground or the structure or acombination of both.
Limit States
8/8/2019 Equipe 2010 Foundation Design
121/129
Limit States
Ultimate limit states are concerned with the safety ofpeople and the structure [EN 19903.3pt1]
There are three limit states concerned with structures
Limit state EQU dealing with static equilibrium
Limit state STR dealing with excessive deformationloss of stability
Limit state FAT dealing with fatigue mechanismsand time related effects
Limit States geotechnical
8/8/2019 Equipe 2010 Foundation Design
122/129
Limit States - geotechnical
There are three geotechnical Limit states referred to inthe code,
Limit state GEO relates to or excessive movement
of the ground Limit state HYD relates to hydraulic heave erosion
and piping in the ground caused byhydraulic gradients
Limit state UPL relates to loss of equilibrium due touplift by water pressure or othervertical actions.
Ultimate limit state
8/8/2019 Equipe 2010 Foundation Design
123/129
Ultimate limit state
This is derived from a combination of thesix limit states
EQU STR FAT
GEO HYD URL
Design to Eurocode
8/8/2019 Equipe 2010 Foundation Design
124/129
Basic requirements - limit state
The structure must be able to withstanddisproportionate damage which might be caused byadverse events such as Explosion
Impact
Human error
In addition the design must be sufficient to avoidor limit the potential for damage by avoiding or
eliminating hazards. Avoiding sudden collapse (employing redundant
members)
Designing for accidental removal of members
Basic Design Requirements of
8/8/2019 Equipe 2010 Foundation Design
125/129
BS EN 1997
For each and every geotechnical situation thestandard requires that no relevant limit state conditionis exceeded.
The following factors need to be taken into account:-
Site conditions considering groundmovements and stability
Surrounding influences ( adjacent
structures, vegetation, contamination etc) Ground conditions
Groundwater
Environmental influences (hydrology,
BS EN1997th t
8/8/2019 Equipe 2010 Foundation Design
126/129
assumes that.
Data is collected, recorded and interpreted by appropriatelyqualified personnel;
Structures are designed by appropriately qualified andexperienced personnel;
Continuity and communication exists between thepersonnel involved in data-collection, design andconstruction;
Supervision and quality control are provided; Execution is carried out according to the relevant standards
and specifications by personnel having the appropriate skill
and experience; Construction materials and products are used as specified; The structure will be adequately maintained; The structure will be used for the designed purpose.
OBTAINING PARAMETERS
8/8/2019 Equipe 2010 Foundation Design
127/129
OBTAINING PARAMETERS
Field or laboratory test result
Derivation Derived values of geotechnical
parameter
Characterisation Characteristic value
Factorisation
Desi n Value
CHARACTERISTIC VALUES
8/8/2019 Equipe 2010 Foundation Design
128/129
CHARACTERISTIC VALUES
The selection of characteristic values for geotechnicalparameters shall take account of the following:
geological and other backgroundinformation.
the variability of the measured propertyvalues.
the extent of the field and laboratory
investigation. the type and number of samples. the extent of the zone of ground governing
the behaviour of the geotechnical structureat the limit state being considered.
CHARACTERISTIC VALUES
8/8/2019 Equipe 2010 Foundation Design
129/129
CHARACTERISTIC VALUES
Bear in mind that
soil and rock structure may play a different rolein the test and in the structure;
many geotechnical parameters are not trueconstants but depend on stress level and modeof deformation;
time effects;
the softening effect of water on soil or rockstrength;
the brittleness or ductility of the soil and rock