EXPERIMENTAL AND NUMERICAL STUDIES OF SAND SLOPES LOADED

WITH SKIRTED STRIP FOOTING

BY: SHIVARAJA.N

UNDER THE GUIDANCE OF:Dr.L. Govindaraju

CONTENTS INTRODUCTION

LITRETURE REVIEW

EXPERIMENTAL STUDY

EXPERIMENTAL RESULT

NUMERICAL STUDY

NUMERICAL RESULT

CONCLUSION

REFERENCES

INTRODUCTION Foundations are sometimes

located either on a slope surface or near to the crown of a slope .These cases arise due to the limitation of available space or according to architectural needs.

The use structural skirts for a strip footing located near to a sand slope crest has a significant effect in improving the bearing capacity.

This technique can be consider as a good method to control the horizontal movement of the subgrade and for decreasing the slope deformation.

Prototype Skirted Foundation

Depth, Z

Su0

kz

contd If shallow foundation could be used instead of deep foundations to

support such structures or if the allowable bearing capacity can be increased using an appropriate soil improvement technique.

From an economical point of view it is more advantageous in case of bridges to locate the footing near to the edge of the slope and to make the slope as steep as possible but in such case the ultimate bearing capacity shall be reduced as the footing is more adjacent to a slope crest.

Shallow skirted foundations are now considered to be a viable foundation option for a variety of offshore application.

Depth, Z

Su0

kz

LITERATURE REVIEWDE BEER and WALLAYS in 1970, reported the success of using piles as a vertical reinforcement in many situations in order to improve slope stability .

SELVADURAI and GNANENDRAN in 1989, have carried out studies on the use of slope reinforcement to improve the load bearing capacity of a footing on the slope.

M. Y. AL- AGHBARI in 2002,have conducted series of tests on foundation models to study the factors that affect the bearing capacity of foundations with skirts. Several factors including foundation base friction, skirt depth, skirt side roughness, skirt stiffness and soil compressibility were studied and incorporated in the equation.

W.R.AZZAM et al in 2010, have carried out model tests and numerical study on the behaviour of a strip footing with structural skirts adjacent to a sand slope .

CASE STUDY ON

EXPERIMENTAL AND NUMERICAL STUDIES OF SAND SLOPES LOADED WITH SKIRTED STRIP FOOTINGS

W .R Azzam and A.Farouk (2010)

MODEL TANK AND FOOTING

MATERIALS USED SAND:

PROPERTY VALUE

COEFFICIENT OF UNIFORMITY 26

EFFECTIVE DIA. 0.33

COEFFICIENT OF CURVATURE 1.33

SP.GRAVITY 2.65

MAX.DRY DENSITY 19.50 kN/m3

MIN.DRY DENSITY 15.6kN/m3

RELATIVE DENSITY 86%

MAX.VOID RATIO 0.699

MIN.VOID RATIO 0.471

GRAIN SIZE DISTRIBUTION CURVE

EXPERIMENTAL SETUP

Slope geometry and parameters used are

The ratio of the skirted depth to the footing width (L/B).

The ratio of the distance from the slope crest to the footing width (b/B).

The slope angle β.

EXPERIMENTAL RESULTS

NUMERICAL MODELLING

Numerical analysis was conducted using the commercial finite element program PLAXIS to verify the laboratory model tests results and to identify the

deformation behaviour and failure pattern

MATERIALS USED

PARAMETER VALUE

TYPE OF MATERIAL BEHAVIOUR

DRAINED

YOUNG’S MODULUS 50000kN/m2

POISSON’S RATIO 0.3

COHESION 0

FRICTION ANGLE 41

ANGLE OF DILATANCY 11

INTERFACE REDUCTION FACTOR

0.67

AXIAL STIFFNESS FOR STEEL SKIRTS EA

31500

COMPARISION B/W EXPERIMENTAL AND NUMERICAL RESULTS

CONCLUSIONS Stabilizing the earth slope using structural skirts with adequate depth in the conjunction of strip footing adjacent to slope crest has a significant effect in improving the soil bearing capacity.

The optimum skirts depth which produces the maximum ultimate bearing capacity was about two times of footing width.

The ultimate bearing capacity of a strip footing with structural skirts increases with increasing the distance from the footing to the edge, while it decreases when angle of slope increases. However, at edge distance more than the footing width, the ultimate bearing capacity is effectively increased.

CONTINUED..The finite element analysis helped in better understanding the failure patterns of the skirted footing-soil system adjacent to a slope. In addition, it confirmed the load transfer mechanism and illustrates how skirts can protect the slope from collapse by decreasing the slope deformation.

The main role of the skirts is to reduce the distortion rate in the sheared zone and reduced the ultimate shear stress generated in the shear zone hence, the bearing capacity failure can be modified to punching shear failure under the footing and at end of skirts the general bearing

capacity failure was formed.

The existence of the skirts along each side of footing mitigates the vertical settlement, controls the horizontal soil movement underneath the footing and decreases the slope deformation.

REFERENCE

Debeer and wallays (1970)- Experimental and numerical studies of sand slopes loaded with skirted strip footing.Selvadurai and Gnanedran (1989)- Experimental and numerical study of strip footing supported on stabilized sand slopes . M Y Aghbari (2002) – Bearing capacity of strip foundation with structural skirts.EI Sawwaf (2005) – Experimental and numerical study of strip footing resting on stabilized sand slopes.W R Azzm et al (2010)- Experimental and numerical studies of sand slopes loaded with skirted strip footing .

rimental and numerical studi sand slopes loaded with skirted strip footings

Selvaduari and Gnanadran (1989) – an experimental study of a footing located on a sloped fill influence of a soil reinforcement layerM Y Aghbari (2005) – Bearing capacity of strip foundation with structural skirtsEI Sawwaf (2005) – Experimental and numerical study of strip footing resting on stabilized sand slopesW R Azzam et al (2010) – Experimental and numerical studies of sand slopes loaded with skirted strip footing

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