UNDER THE GUIDANCE OF

T GNANANANDA RAO Assistant Professor

CASE STUDIES ON DIFFERENTIAL SETTLEMENTS ByG SAI SRAVYA (14071D1204)

Department of Civil Engineering VNR Vignana Jyothi Institute of Engineering &Technology,Bachupally, Nizampet (S.O), Hyderabad-500090, AP

CONTENTS:1. INTRODUCTION2. OBJECTIVES 3. LITERATURE REVIEW4. CASE STUDIES5. CONCLUSION6. REFERENCES

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1.INTRODUCTIONSETTLEMENT:

Settlementin a structure refers to the distortion or disruption of parts of a building due to:a) Unequal compression of its foundationsb) Shrinkage due to changes in moisture contentc) Undue loads being applied to the building after its initial construction.

TYPES OF SETTLEMENT:Uniform settlement Non-uniform settlement

Tilting

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2.OBJECTIVES:The present project will investigate theoretically , the behavior of soil under long term loading.This project includes :What are the causes of settlements.How differential settlement takes place.How to overcome settlements in structures.

CAUSES OF SETTLEMENTS:Weak soil strataPoor compactionChanges in moisture contentMaturing trees and vegetationSoil consolidationWetting and softening of soils*

REPAIR TECHNIQUES:Foundation underpinning

Polymer injection

Grout pumping*

DIFFERENTIAL SETTLEMENT:The settlement of a structure is the amount the foundation sinks during and after construction. If that settlement takes place unevenly it is said to be undergoing Differential settlement.

Generally the foundations which rest on weak soil strata undergo uneven settlement.

Due to differential settlement the foundation sinks unevenly and cracks are formed in the structure and there is a danger of collapse of a structure.

*FIG: DIFFERENT FORMS OF SETTLEMENT

LITERATURE REVIEW:Xiaoming Yuan, Rui Sun, Meng Shangjiu et.al: The irregular character of the seismic waves themselves may have a significant contribution to the differential settlement of subsoil and buildings and should be considered in evaluation for the differential settlement and other problems relating to the soil deformation due to earthquakes.

Kyung Nam Kim, Ki-Seok Kim, Choong-Ki Chung, Myoung Mo Kim, Hae Sung Lee et.al: This paper presents an optimal pile arrangement scheme for minimizing the differential settlements of piled raft foundations. The optimization is performed with respect to the locations of the piles.

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Jaeyeon Cho, Sangseom Jeong, Jaehwan Lee et.al: The settlement behaviour of a square piled raft in clay soil was investigated. The emphasis was on quantifying the reduction of the average and differential settlements in soft and stiff clay soils. It is found that the required pile group-raft area ratio (Ag/Ar) for minimizing differential settlement in soft clay was slightly larger than that of stiff clay in the same pile array.

Ernesto Cascone, Giovanni Biondi et.al: The method of preloading associated with prefabricated vertical drains was used to accelerate the consolidation process and anticipate the long-term settlements of the foundation soil of two cylindrical oil tanks founded on an alluvial deposit mainly consisting of silty clays.

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4 CASE STUDY ON DIFFERENTIAL SETTLEMENT: 4.1 LEANING TOWER OF PISA ITALY: Leaning tower of Pisa which was in Italy has considered one of the seven wonders in ancient times as it was leaned towards south with an angle of 3.97.

FIG: LEANING TOWER OF PISA ITALY

CAUSES OF SETTLEMENT:

Inadequate foundationWeak soil strata fluctuating water table

REMEDIAL MEASURES:Drilling a network of holes into the foundation and then filling them with a cement grout mixture.

Braced with steel tendons, to relieve the strain on the vulnerable masonry

Underground steel anchors, to invisibly yank the tower northwards. Installation of helical drills surrounded by hollow steel casings to remove soil from below the high north side of the tower*

FIG: MEASURES ADOPTED TO REDUCE TILT*

4.2 G+2 INSTITUTIONAL BUILDING WHICH HASUNDERGONE DIFFERENTIAL SETTLEMENT:

The foundation work was complete and the Superstructure construction was in progress, when cracks were noticed in the plinth Beams.

* FIG: CRACKS IN PLINTH BEAM

CAUSES OF FAILURE:

Some foundations were located above the natural ground at a depth of 2m in unconsolidated filled up ground of an abandoned laterite stone quarry, where SPT was found to be less than12,which resulted in differential settlement.

This differential settlement was observed towards the front left corner of the Building which was lying on the filled up ground*

REMEDIAL MEASURES:

In order to avoid the transfer of stresses in the connecting components, the affected beams were separated from sinking columnsExpansion joints were provided between this portion and the rest of the intact part of the structure.

*FIG: BEAMS SEPARATED FROM COLUMNS

5 CONCLUSIONS:

Generally differential settlement is predominant in weak soils and it leads to failure of structure.

Non homogeneous soil strata, poor compaction and water table level are the main causes of differential settlement in structures.

Remedial measures such as ground improvement techniques, removal of excess soil on high side of the structure, grout pumping are mostly adopted.

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6. REFERENCES:Effect of asymmetry and irregularity of seismic waves on earthquake- induced differential settlementof buildings on natural subsoil by Xiaoming Yuan, Rui Sun, Meng Shangjiu et.al.

Optimal pile arrangement for minimizing differential settlementsin piled raft foundations by Kyung Nam Kim, Ki-Seok Kim, Choong-Ki Chung, Myoung Mo Kim, Hae Sung Lee et.al

Thesettlementbehavior of piled raft in clay soils by Jaeyeon Cho, Sangseom Jeong, Jaehwan Lee et.al.

A case study on soil settlementsinduced by preloading and vertical drains by Ernesto Cascone, Giovanni Biondi et.al.

THANK YOU. . *

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