Study on embedded square footing resting on … on embedded square footing resting on geotextile reinforced sand Shailendra kumar et al International Journal of Civil and Structural

INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING

Volume 5, No 3, 2015

© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0

Research article ISSN 0976 – 4399

Received on December, 2014 Published on February 2015 243

Study on embedded square footing resting on geotextile reinforced sand Shailendra kumar 1, Solanki C.H 2, Bhaskar D. Wabhitkar 3

1-Assistant Professor, S.V. National Institute of Technology, Surat, Gujarat, India

2-Professor, S.V. National Institute of Technology, Surat, Gujarat, India

3- P.G. Student, S.V. National Institute of Technology, Surat, Gujarat, India

[email protected]

doi:10.6088/ijcser.2014050023

ABSTRACT

This paper presents the results of laboratory model tests carried out on embedded square

footing supported on geotextile reinforced sand bed. The model steel tank of size 120 cm x

50 cm x 50 cm and square footing of 10 cm are used. Locally available fine sand is used for

experimental purpose. The constant uniform settlement is applied to footing with the help of

hand operated gear arrangement system and settlement is measured using two LVDT (Linear

variable differential transformer) placed opposite to each other and corresponding load is

measured with the help of load cell. The study highlights the effect of size of geotextile and

placement of geotextile below footing on load-settlement characteristics. The study also

highlights the improvement in bearing capacity ratio and settlement reduction ratio.

Keyword: Bearing Capacity Ratio, Settlement Reduction Ratio, Embedded Square Footing,

Geotextile.

1. Introduction

Geosynthetics soil reinforcement such as geotextiles, geogrides and geocomposites have

beneficial effects on bearing capacity and settlement of shallow foundations. Considerable

experimental research has been reported to study the behaviour of footing resting on

geosynthetics reinforced bed (Guido et al., 1985; khing et al.,1993; adams and Colin, 1997;

Hataf and baziar, 2000; Boushehrian and Hataf, 2003; Sitharam and Sireesh, 2004; Basudhar

et al., 2007; Latha and Somwanshi,2009; Yasrobi et al.,2009; Lovisa et al.,2010; Tafreshi and

Dawson,2012)

From the studies reported in the literature, it has been observed that there is a substantial

increase in bearing capacity of foundation reinforced with geosynthetics and settlement of

foundation also decreases. For the maximum improvement of bearing capacity, different

researchers have given different view about following design parameter.(a) u= depth of first

layer of reinforcement below footing base. Value of u/B reported in literature varies from

0.175 to 0.5 (B= width or Dia. of footing) (b) z = vertical spacing between reinforcement

layer. Value of z/B varies from 0.2 to 0.46 ( c) b= width of reinforcement layer. Value of

b/B varies from 2.5 to 4.0. (d) N= No. of reinforcement layers. Value of N varies from 3 to 5.

Thus there is a necessity to conduct such studies further to have better understanding.

2. Experimental investigation

The experimental program reported herein, that involves small scale model test, was carried

out using a test facility in the Geotechnical Laboratory of Applied Mechanics Department at

SVNIT Surat, India. Details of the experimental test program, material used, test procedure

Study on embedded square footing resting on geotextile reinforced sand Shailendra kumar et al

International Journal of Civil and Structural Engineering 244

Volume 5 Issue 3 2015

and analysis of the test results of model studies on load bearing capacity and settlement

behavior of embedded square footings resting on geotextile-reinforced sand bed are presented

below.

2.1 Materials

In the present work, fine sand has been selected as a foundation medium and geotextile as a

reinforcing material. The properties of sand and geotextile are shown in Table 1 and table 2

respectively.

Table 1: Properties of sand

Parameter Value

Grain size distribution

Gravel

Sand

Silt & Clay

Uniformity coefficient , Cu

Coefficient of curvature, Cc

0 %

98.5 %

1.5 %

1.78

1.03

Specific gravity 2.60

Maximum dry unit weight 17.3 kN/m³

Minimum dry unit weight 14.2 kN/m³

Dry unit weight of sand bed 17.0 kN/m³

Table 2: Properties of geotextile

Property Test method SEPC. Result

Physical properties

Mass / unit area ASTM D 5261 >140 g/m² 147

Mechanical properties

Tensile

Strength

WARP IS 1961 >28 kN/m 33

WEFT >26 kN/m 29

Elongation at specified

tensile strength

WARP IS 1969 < 25% 20

WEFT < 25% 16

Trapezoid tear strength WARP ASTM D 4533 >300N 612

WEFT >300N 475

Index puncture strength ASTM D 4833 >250N 637

2.2 Experimental set-up and test procedure

Experimental works were carried out on model square embedded footing at 0.5B (B= width of

footing) on reinforced and unreinforced sand bed. Geotextile reinforcement is used below the

base of the footing at predetermined depth to improve the bearing capacity of reinforced sand.

The model tests were carried out in a steel tank (120cm x 50cm x 50cm). The model square

footing of 10 cm was used. The schematic view of test set-up and arrangement of load cell and

LVDT are shown in Figure 1 and Figure 2 respectively. The sand was placed in tank in layers

of 5cm using sand raining technique to achieve required density of sand in each layer.

Geotextiles of size 2Bx2B, 3Bx3B and 4Bx4B (B=width of footing) was placed in sand layers

below footing at the depth of 0.1B, 0.2B, 0.3B, 0.4B and 0.5B.




Figure 1: Schematic view of test set-up

Figure 2: The arrangement of load cell and LVDT

Square footing of size 10cm x 10cm is embedded at depth of 0.5B from surface. A constant

strain rate of 1 mm/min was given to footing with the help of gear arrangement system

supported against reaction frame. Load was measured with the help of load cell and settlement

(S) of footing was measured at two points with the help of LVDT to check the differential

settlement of footing.

3. Results and discussion

Pressure v/s normalized settlement (S/B %) graph for unreinforced sand and reinforced sand

with geotextiles of size 2Bx2B, 3Bx3B and 4Bx4B placed below footing at depth 0.1B,

0.2B, 0.3B, 0.4B & 0.5B are shown in Figure 3, Figure 4 and Figure 5 respectively.




Figure 3: Pressure v/s normalized settlement graph for unreinforced and reinforced sand with

geotextiles of size 2Bx2B


geotextiles of size 3Bx3B.


geotextiles of size 4Bx4B.




Figure 3 shows that optimum depth of placement below footing for 2Bx2B size of geotextile is

0.2B. Figure 4 shows that optimum depth of placement below footing for 3Bx3B size of

geotextile is 0.3B. Figure 5 shows that optimum depth of placement below footing for 4Bx4B

size of geotextile is again 0.3B. Pressure v/s normalized settlement graph with geotextiles of

size 2Bx2B, 3Bx3B and 4Bx4B placed below footing at same depth of 0.1B, 0.2B, 0.3B,

0.4B & 0.5B are shown in Figure 6 to Figure10 respectively.

Figure 6: Pressure v/s normalized settlement graph for geotextiles placed at 0.1B depth.











From Figure 6 to Figure 10, it may be concluded that optimum size of geotextile is 2Bx2B up

to 0.2B depth below footing and 3Bx3B up to 0.4B depth below footing thereafter 4Bx4B size

of geotextile observed as maximum improvement in bearing capacity. Bearing capacity

improvement occurs significantly due to the application of geotextile. Without geotextile,

footing takes a pressure of 245 kPa at 10 mm settlement. So, taking this pressure at 10 mm

settlement, as a reference, improvement in bearing capacity and settlement reduction were

calculated by equation mentioned below

Bearing capacity ratio = (Pressure taken by footing with geotextile at 10 mm settlement) /

(Pressure taken by footing without geotextile at 10 mm settlement)

Settlement reduction ratio= (Settlement of footing without geotextile at 245 kPa) /

(Settlement of footing with geotextile at 245 kPa)

Bearing capacity ratio (BCR) and settlement reduction ratio (SRR) for geotextile size 2Bx2B,

3Bx3B & 4Bx4B placed at depth 0.1B to 0.5B below footing are shown in Figure 11 & Figure

12 respectively.

Figure 11: Bearing capacity ratio with geotextile placed at depth 0.1B to 0.5B below footing

Figure 12: Settlement reduction ratio with geotextile placed at depth 0.1B to 0.5B below

footing




From Figure 11, maximum value of BCR are observed as 1.52, 1.62 & 1.47 with geotextile

size 2Bx2B, 3Bx3B & 4Bx4B placed at depth 0.2B, 0.3B and 0.3B respectively. From Figure

12, maximum value of SRR are observed as 1.60, 1.72 & 1.51 with geotextile size 2Bx2B,

3Bx3B & 4Bx4B placed at depth 0.2B, 0.3B and 0.3B respectively. From Figure 11 & 12, we

may conclude that for maximum improvement in bearing capacity and settlement reduction,

the optimum size of geotextile is 3Bx3B and optimum depth of placement is 0.3B below

footing.

4. Conclusion

On the basis of the present investigation and discussion made on results, the following

conclusions are drawn

1. For geotextile size 2Bx2B, the maximum improvement in bearing capacity and

settlement reduction are 1.52 & 1.60 times respectively when placed at 0.2B below

footing.



footing.



footing.

4. Optimum size of geotextile is 2Bx2B up to 0.2B depth below footing and 3Bx3B up to

0.4B depth below footing thereafter 4Bx4B size of geotextile observed as maximum

improvement in bearing capacity.

5. For maximum improvement in bearing capacity and settlement reduction, optimum

size of geotextile is 3Bx3B when placed below footing at depth of 0.3B.

5. References

1. Adams, M. T. and Collin, J.G., (1997), Large Model Spread Footing Load Tests on

Geosynthetic Reinforced Soil Foundations, Journal of Geotechnical

Geoenvironmental Engineering, 123 (1), pp 66-72.

2. Basudhar, P. K., Saha, S. and Deb, K., (2007), Circular footings resting on

geotextile-reinforced sand bed, Geotextiles and Geomembranes, 25, pp 377-384.

3. Boushehrian, J. H. and Hataf, N., (2003), Experimental and numerical investigation

of the bearing capacity of model circular and ring footing on reinforced sand,

Geotextiles and Geomembranes, 21, pp 241-256.

4. Guido, V.A., Biesiadecki, G.L. and Sullivan, M.J.(1985), Bearing capacity of

geotextile reinforced foundation, Proceedings of the 11th International conference on

Soil Mechanics and Foundation of Engineering, San Francisco, CA, pp 1777-1780.




5. Hataf, N. and Baziar, A., (2000), Use of tire shreds for bearing capacity improvement

of shallow footings on sand, Proceedings of the 3rd International conference on

Ground Improvement Technique, Singapore, pp 189-194.

6. Khing, K.H., Das, B. M., Puri, V.K., Cook, E.E. and Yen, S.C., (1993), The bearing

capacity of a strip foundation on geogrid reinforced sand, Geotextiles and

Geomembranes, 12, pp 351-361.

7. Latha, G. M. and Somwanshi, A., (2009), Bearing capacity of square footing on

geosynthetic reinforced sand, Geotextiles and Geomembranes, 27, pp 281-294.

8. Lovisa,J., Shukla, S. K. and Sivakugan, N., (2010), Behaviour of prestressed

geotextile-reinforced sand bed supporting a loaded circular footing, Geotextiles and

Geomembranes, 28, pp 23-32.

9. Sitharam, T. G. and Sireesh, S., (2004), Model studies of embedded circular footing

on geogrid-reinforced sand beds, Ground Improvement,8, No-2, pp 69-75.

10. Tafreshi, S.N.M and Dawson, A.R.,(2012), A comparison of static and cyclic loading

responses of foundations on geocell-reinforced sand, Geotextiles and Geomembranes,

32, pp 55-68.

11. Yasrobi, S. S., Rahmaninezhad, S. M. and Eftekharzadeh, S. F., (2009), large

physical modeling to optimize the geometrical condition of geotextile in reinforced

loose sand, GeoHunan International Conference 2009,ASCE, pp 53-59.

Documents

Study on embedded square footing resting on … on embedded square footing resting on geotextile reinforced sand Shailendra kumar et al International Journal of Civil and Structural