SITE INVESTIGATIONS for HIGH RISE BUILDINGS.pptx

Prof. Samirsinh P Parmar
Asst. Prof. Dept. of Civil Engg.
Dharmsinh Desai University, Nadiad,
Gujarat , Bharatvarsh.
Prof. S.P.Parmar, DoCL, DDU, Nadiad, Gujarat, Bharatvarsh.
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Content of the presentation
Introduction
Definition of tall buildings
Structural aspect of soil investigation
Stages of foundation design
Various in-situ tests
Case study- Burj Khalifa
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INTRODUCTION
 The accommodation for migrated and existing population in big cities and
shortage of land needs vertical development in form of tall buildings.
 The construction of tall building has exponentially increased across the
world in last few decades.
 Super Structure and sub structure design of High rise buildings are
challenges for the structural and geotechnical engineers and also for civil
engineers to execute with proper quality control.
 The foundation design of high rise buildings are not limited to traditional
design methods such as bearing capacity with an applied factor of safety.
It shall be important to consider the soil structure interaction (SSI).
 Geotechnical Uncertainty of sub profile is one of the major risk in
foundation design. So it is vary important to carry out site investigation
precisely to establish accurate knowledge of ground condition which shall
be used to design economical foundation design.
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DEFINITION OF TALL BUILDING
 As per IS 16700 : 2017
• T
all Building: Height > 50m and < 250m.
• Super T
all Building: Height >250m.
 The Council of T
all Buildings and Urban Habitat Chicago, USA
define
• Height > 100 m as sky scrapper
• Height > 300m as Super T
all Height building
• Height > 600m as Mega T
all building
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SOME STRUCTURAL ASPECTS
WHICH AFFECT THE SITE INVESTIGATION
 Construction Machinery
 Height of building
 Density of building
 Wind and seismic effect
 Dynamic Analysis
 Selection of reinforced material and grade of concrete
 Designer’s considerations in foundation design
 Other special consideration for tall structures which effect
the Geotechnical design.
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STAGES OF FOUNDATION DESIGN
1. PRELIMANARY STUDY
2. SITE INVESTIGATION
3. GEOTECHNICAL MODEL
4. DETAIL DESIGN
5. MONITORING OF THE BUILDING PERFORMANCE
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 PRELIMANARY STUDY
• Preliminary study involves review of overall layout of structure, geology,
topography and hydrogeology, ravines, quarries, evidence of erosion or
land slides, behaviour of existing structures near the site, water bodies,
natural vegetation, drainage pattern etc… which can influence design
and performance of the foundations.
• This helps to decide
• Future programme of field investigations,
• Determining the scope of work,
• Method of exploration to be adopted,
• Field tests to be conducted
• Administrative arrangement required for the investigation.
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 SITE INVESTIGATION
• Site investigation includes a comprehensive field and lab testing by various
routine
methods to characterize strength and stiffness properties of the sub-
surface condition and geophysical methods to overcome limitations of drilling
and other routine investigation methods.
Advantage of geophysical methods
 They provide a means of identifying the stratigraphy between
boreholes/cone penetration test
 Help to identify localized anomalies in the ground profile, for example
cavities, sinkholes or localized pockets of softer or harder material;
 They can identify bedrock levels;
 They provide shear wave and compression wave velocities.
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 GEOTECHNICAL MODEL
• Based on the findings of the site investigation, the geotechnical
model and associated design parameters are developed for the site
and then used in the foundation design.
• In some cases a series of models may be necessary if ground
conditions are variable across the building footprint.
• Preliminary assessment of foundation requirements, based on
relatively simple methods of analysis and design.
• Refinement of the design, based on more accurate information of the
structural layout, applied loadings and the ground conditions.
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 DETAIL DESIGN
• During detailed design, the foundation system shall be modified
based on loads computed by the structural designer and a
compatible set of loads and foundation deformations developed
through an iterative process.
• In situ foundation testing is essential to better predict the foundation
performance under loading.
• Usually initial test piles are constructed and tested and if the tested
behavior deviates from expected, the foundation design may need
to be revised. This could result in either an increase or decrease in
foundation requirements prior to construction.
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MONITORING OF THE BUILDING PERFORMANCE
Monitoring of foundation performance during and after
construction like observation of settlements around the
foundation, and load sharing between the raft and the
piles shall be useful.
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 GEOTECHNICAL INVESTIGATION
• Geotechnical Investigation shall be includes
• Depth wise stratifications
• Engineering properties of sub strata,
• Liquefaction potential analysis,
• Soil spring constants and modulus of sub grade reaction
 Minimum requirement given for geotechnical investigation by IS 16700: 2017
 Borehole shall be spaced at max. 30m within building footprint
 Minimum 3 BH per tower
 Depth of investigation shall be 1.5 times of estimated smaller width of foundation subject
to minimum 20m in soil and 15m in rock.
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 VARIOUS IN-SITU TEST FOR SITE
INVESTIGATION
• STANDARD PENETRATION TEST:
SPT conducted using an auto-trip hammer shall be use for evaluate soil
capacity of soil strata by various correlation formula where not suitable
to collect undisturbed sample.
• STATIC CONE PENETRATION TEST:
SCPT can give a continuous profile of soil resistance with depth and
may be used for bearing capacity and settlement analysis.
• PRESSURE METER TEST:
Pressuremeter data in soils can provide very useful results to evaluate E-
values of soil strata at test depth. The test provides deformation properties at
various strain levels which commensurate with ground subjected to service
loads from the building.
However, in sands below water table where ground may get disturbed due to
collapse during drilling could result in reporting lower values of deformation
modulus.
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VARIOUS IN-SITU TEST FOR SITE
INVESTIGATION
• GEOPHYSICAL METHODS:
 Cross-hole or down-hole seismic test usually gives a good assessment
of shear and compression wave velocity with depth.
 This may be supplemented with seismic refraction test to assess the
lateral variation of the ground characteristics.
 This information can be used to estimate the in situ values of soil
stiffness at small strains which provide a basis for estimating the
deformation properties of the soil strata.
 But E-value for small strain cannot be applied directly to foundation
analysis since ground strains under dead, live and wind or earthquake
loads are significantly higherthan those experienced during seismic
testing.
 The influence of the strain level should be taken into account in the test
interpretation. Haberfield suggests dividing the E values from cross-hole
seismic test by a factor of 5 to obtain the static E value for settlement
analysis.
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VARIOUS IN-SITU TEST FOR SITE INVESTIGATION
• IN-SITU PERMEABILITY
 In-situ permeability tests may be required in areas of shallow water table for
design of dewatering system. Since tall buildings may usually have at least
2-3 basements, substantial dewatering could be required in areas of
shallow water table. In sands, dewatering could be a challenge due to the
high inflow.
 Field permeability tests are usually done in boreholes by falling head
method or constant head method. Pump-out test can give a more realistic
assessment of the hydraulic parameters for the design of the dewatering
system.
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 LABORATORY TEST FOR SITE INVESTIGATION
 SOFTWARE MODELING
• Plaxis, Midas, Geostudio, Abaqus, FLAC etc…
• Test on Soil samples
• Particle size analysis
• Atterberg limit;
• Field density and natural water content
• Specific gravity;
• Consolidation test
• Tri-axial test (UU, CU & CD method) to
evaluate c, phi and E value
• Uni-axial compressive strength
• Chemical analysis of soil and ground
water
Test on rock samples
• Uni-axial compressive
strength
• Point load Index strength
• Brazillian test
• Porosity
• Density
• Specific Gravity test
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 FOUNDATION PERFORMANCE TESTING
• STATIC PILE LOAD TEST
:
 It is conventional method used to verifiy pile capacity.
• CYCLIC PILE LOAD TEST
:
 This test is used to separate out end bearing and side friction
of pile shaft.
 The pile under the tall building suffering from the cyclic loading
due to seismic and wind load.
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 FOUNDATION PERFORMANCE TESTING
• HIGH STRAIN PILE LOAD TEST
:
This testing method is largely adopted in our country because of time
saving and quick ready analysis by software. The suitable heavy
hammer is allow to fall on strong pile head, which generate high strain
compression wave in pile shaft. From the acceleration, strain and
imposed load the outputs generated by software are capacity,
settlement and profile of pile shaft.
• BI-DIRECTIONAL TEST :
A circular row of jack is cast near the pile base, and pressure is
applied. The base is jacked down wards while the shaft provide
reaction and is jacked upwards. The test can continue until the element
with the smaller capacity reaches its ultimate resistance.
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19

CASE STUDY:
SITE INVESTIGATION FOR THE BURJ KHALIFA, DUBAI, UAE
 BRIEF OVER VIEW OF BURJ KHALIFA
The BurjKhalifa in Dubai is a 163 storey, 828 m high, mega tall
tower, with podium at its base, including 4 to 6 storey garage. The
foundation system is a piled raft.
A 3.7 m thick raft supported on 1.5 m diameter bored piles
extending up to 50 m below the raft base.
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The geotechnical investigation was carried out in four phases as follows:
 PHASE 1 (MAIN INVESTIGATION)
 23 boreholes with in situ SPT’s,
 40 pressure meter tests in three boreholes,
 Installation of four standpipe piezo meters,
 laboratorytesting, specialist laboratory testing
testing
and contamination
CASE STUDY:
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 PHASE 2 (MAIN INVESTIGATION)
 Three geophysical boreholes with cross-hole
 T
omography geophysical surveys carried out between three new
boreholes and one existing borehole;
CASE STUDY:
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 PHASE 3 (ADDNL INVESTIGATION)
 Six boreholes with in situ SPT’s,
 20 pressuremetertests,
 installation of two standpipe piezometers
 laboratory testing
CASE STUDY:
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CASE STUDY:
 PHASE 4 (CONFIRMATORY INVESTIGATION)
 One borehole with in situ SPT
s,
 Cross-hole geophysical testing in three boreholes
 Down-hole geophysical testing in one borehole
 Laboratory testing.
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 The drilling was carried out to depths between 30 and 140 m below
ground level.
 The quality of core recovered in some of the earlier boreholes was
somewhat poorer than that recovered in later boreholes, and, therefore,
the defects noted in the earlier rock cores may not have been
representative of the actual defects present in the rock mass.
 Phase 4 of the investigation was targeted to assess the difference in core
quality and this indicated that the differences were probably related to the
drilling fluid used and the overall quality of drilling.
CASE STUDY:
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 Disturbed and undisturbed samples and split spoon samples were
obtained from the boreholes.
 Undisturbed samples were obtained using double tube core barrels (with
Core liner) and wire line core barrels producing core varying in diameter
between 57 and 108.6 mm.
 Standard Penetration T
ests (SPT
s) were carried out at various depths in
the boreholes and were generally carried out in theoverburden soils, in
weak rock or soil bands encountered in the rock strata.
CASE STUDY:
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 Pressuremeter testing, using an OYO Elastmeter, was carried out in
five boreholes between depths of about 4 and60 m below ground level
within T
ower footprint.
 The geophysical survey comprised cross-hole seismic survey, cross-
hole tomography and down-hole geophysical survey. The main purpose
of the geophysical survey was to complement the borehole data and
provide a check on the results obtained from borehole drilling, in situ
testing and laboratory testing.
 The cross-hole seismic survey was used to assess compression (P)
and shear (S) wave velocities through the ground profile.
CASE STUDY:
27

 Cross-hole tomography was used to develop a detailed distribution of P-
wave velocity in the form of a vertical seismic profile of P-wave with depth,
and to highlight any variations in the nature of the strata between
boreholes.
 Down-hole seismic testing was used to determine shear (S) wave
velocities through the ground profile.
CASE STUDY:
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CONVENTIONAL TESTS:
 Moisture content,
 Atterberg limits,
 Particle size distribution,
 Specific gravity,
 Unconfined compressive
strength,
 Point load index,
 Direct shear tests,
 Carbonate content tests.
SOPHISTICATED TESTS:
 Stress path tri-axial,
 Resonant column,
 Cyclic un-drainedtriaxial,
 Cyclic simple shear
 Constant normal stiffness (CNS)
direct shear tests
CASE STUDY:
The geotechnical laboratory testing program consisted of two broad classes
of test and undertaken by a variety of commercial, research and university
laboratories in theUK, Denmark and Australia. :
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REFERENCES:
 IS 16700: Criteria for structural safety of tall concrete buildings
 IS 1892: Sub surface investigation for foundaitons
 IS 12070 : Shallow foundations on rock
 IS 8009 : Calculation of settlement of foundations
 IS 1904: Code of practice for design and constructions of foundations in soil
 Geotechnical parameter assessment for tall building foundations by H G Poulos
and F
. Badelow
 T
all building foundations: design methods and applications by H G Poulos
 Foundations for T
all Buildings on Alluvial Deposits – Geotechnical Aspects by Ravi Sundaram,
Sanjay Gupta, and Sorabh Gupta
 CTBUH : Council for T
all Buildings and the Urban Habitat, website www.ctbuh.org.
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