48-Building a University on Liquiable Soils

8/17/2019 48-Building a University on Liquiable Soils

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BUILDING A UNIVERSITY ONLIQUEFIABLE SOILS USING DYNAMIC

COMPACTION

Ravi Sundaram, Sanjay Gupta, Sorabh GuptaCENGRS GEOTECHNICA PVT. LTD.


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Project Details

Gautam Budh University at Greater Noida,

Uttar Pradesh Covers an area of about 511 acres

, ,cover

Site in the flood plains of the River Yamuna,

about 2 km from river

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Vicinity Map

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The Project 2007..

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The Project Today..

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.. And what it will be.

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Site Conditions

Site is in Earthquake Zone IV - IS 1893: 2002

Loose alluvium - fine sand (Yamuna Sand)

Groundwater met at shallow depth

an o - m ep s prone o que ac on Ground Improvement by Dynamic Compaction

carried out for all buildings planned at site

Each structure was individually assessed

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Benefits achieved

Dynamic compaction successfully mitigated

liquefaction potential Greater stability during earthquake

Need for piling was eliminated and the buildings

were supported on open foundations Substantial savings achieved – foundation cost was

less than 50% of what would be required if piling

was done Savings also achieved in time required to complete

foundation construction

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Investigations Before CompactionInvestigations Before Compaction

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Investigations After CompactionInvestigations After Compaction

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Plethora of Data..

Over 700 boreholes and200 static cone penetration

es s comp e e n eUniversity area over a

period of 3 years

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This Paper Presents..

Ground Improvement by

DYNAMIC COMPACTIONDYNAMIC COMPACTION done for

FACULTY BLOCKFACULTY BLOCK

as an ustrat ve examp e o t e woras an ustrat ve examp e o t e wordone and extent of improvementdone and extent of improvementachievedachieved

The need for piling was eliminatedThe need for piling was eliminatedresulting in substantial savingsresulting in substantial savings

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Faculty Block Location

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Scope of Work- Faculty Block

At Faculty Block:

Before Compaction:

4 boreholes – 15 m

1 SCPT

After Compaction: 4 boreholes – 15 m

1 SCPT

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Before Compaction

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After Compaction

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Borehole Data – Before Compaction

SPT values

typically 10-15 to

8 m depth

5-10 %

Groundwater at 4-

5 m depth, mayrise to GL

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Liquefaction Assessment

Seed & Idriss (1971) method – NCEER

Summary Report

Cyclic Stress Ratio (CSR)

Maximum Credible Earthquake (MCE)

Design Earthquake Magnitude: 6.7

Peak Ground Acceleration: 0.24g

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Liquefaction Assessment

Cyclic Resistance Ratio (CRR) determined

from SPT & SCPT As per the analysis, the fine sands to 8 m

liquefaction in the event of the designearthquake

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Dynamic Compaction

Dropping a heavy

weight can compact

loose sands to

substantial depth Effective for sands

only

Done on a grid pattern

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Conceptual Illustration

The maximum depth of improvement

(Df ) at the project site was estimated

using Mitchell & Katt i, 1981:

where

n = modification factor (taken as 0.7)

W = weight of pounder, and

H = height of drop

n= n=

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Compaction Details

Conventional Crane –

TLC 955A Compaction in 3 Phases:

Ironing Phase

1 week time lag in

between – to allow porepressures to dissipate

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Compaction Phase

Area divided into 4 x 4 m grids

11.65 T pounder falling from

height of 14 m

Energy Imparted: 1600 kN-m

Corresponding depth of

improvement: 9 m

2nd Phase staggered 2 m

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Ironing Phase

Craters filled with GSB Grade II

material

Hammer weight: 11.65 T

No. of drops: 5

Energy: 2114 kN-m

Area graded with 10 passes

of 10 T vibratory roller

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SPT before compaction

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SPT before & after compaction

75 % Improvement to

about 4 m depth

25~30 % Improvement to

about 10 m depth

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SPT & SCPT before & after

compaction

75 % Improvement to

4 m depth

25~30 % Improvement to

10 m depth

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SPT & SCPT before & after

compaction

50-170 % Improvement

to 4 m depth

25~50 % Improvement

to 10 m depth

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Extent of Improvement Achieved

After Compaction, N>20, qc > 50 MPa

Peak Improvement: Between 1 and 5 m

Improvement below 10 m depth is

marginal

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CRR Evaluation (Before Compaction)

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CRR Evaluation (After Compaction)

After Compaction, CRR > CSR After Compaction, CRR > CSR

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FOS against Liquefaction

(based on SPT & SCPT)

f i a b l e

Z o n e

L i q u e

No LiquefactionLiquefaction to

8m depth

Before Compaction After Compaction

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Liquefaction Mitigation

Untreated ground (before compaction) is

susceptible to liquefaction to 8 m depth After compaction, Factor of Safety against

>

Susceptibility to liquefactionSusceptibil ity to liquefaction

successfully mitigatedsuccessfully mitigated

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Foundation Selection

For unimproved ground, pile foundations transferringthe loads below the liquefiable zone would benecessary. Pile lengths would be on the order of 15to 20 m

O en foundations on im roved round: Isolated

footings with connecting beam Design Net Bearing Pressure: 175 kPa175 kPa

RESULTED IN SUBSTANTIAL SAVINGSRESULTED IN SUBSTANTIAL SAVINGSIN COST AND CONSTRUCTION TIMEIN COST AND CONSTRUCTION TIME

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Concluding Remarks

Case Study demonstrates successful

mitigation of liquefaction potential by use ofdynamic compaction

Field trials are necessary to confirm feasibility

Sufficient in-situ testing before and after

improvement should be done to confirmefficacy of the improvement

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Thank You!Thank You!

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48-Building a University on Liquiable Soils