Feasibility Study of Pyramidal Shell Foundation of Varying Embedded Depth on Sandy Soil

Feasibility Study of Pyramidal Shell Foundation of Varying Embedded Depth on Sandy Soil

Anuja Pradeep

M. Tech Research Scholar Department of Civil Engineering

Sarabhai Institute of Science & Technology Thiruvananthapuram, Kerala, India

Jaseena A. Rasheed Assistant Professor

Department of Civil Engineering Sarabhai Institute of Science & Technology

Thiruvananthapuram, Kerala, India

Abstract Shell foundations are better alternatives to conventional flat foundations which transmits heavy super structural loads to poor soil. In this paper, Pyramidal shell foundations were designed and compared with flat foundations of same dimensions. A series of reduced scale plate load tests were carried out on sandy soil for investigating the behaviour of Pyramidal shell foundations and flat foundations of varying embedded depth. Four types of foundation models made up of mild steel having same thickness (3 mm) and different embedded depth (25 mm and 35 mm) were used in this study.

A. Sandy soil

1. MATERIALS USED

   Keywords- Sandy soil; Pyramidal shell foundation; Ultimate bearing capacity

   1. INRODUCTION

      Due to the vital function of Foundations on the stability of structures, a number of investigators studied the utilization of safer and more economical foundations like shell foundations. Shells can obtain the stability and bearing capacity from their specified geometrical shapes. This characteristics of shells helps them to generate maximum structural efficiency with minimum materials. In geotechnical engineering, the specific behaviour of shell foundations have been directly linked with different geometrical shapes including pyramidal, triangular and conical.

      The main aim of this paper is to examine the overall geotechnical performance of pyramidal shell foundation resting on sandy soil. The ultimate load of corresponding foundation models made up of mild steel were obtained by conducting a series of reduced scale plate load tests and the results were compared with traditional flat foundations of same counter parts.

   2. OBJECTIVES OF STUDY

1. To examine the behaviour of pyramidal shell foundations on sandy soil

2. To identify the influence of different embedded depth on the performance of foundation models.

3. To compare the pyramidal shell foundation with conventional flat foundation of same dimensions

Fig.1. Sandy soil sample

The sandy soil was collected from Achencovil river basin, Kollam district, Kerala at a depth of 5 m from the ground surface. The soil was poorly graded sandy soil.

1. Foundation models

   Fig.2. Foundation models

   The load tests were conducted on pyramidal shell and flat foundation models made up of mild steel having thickness 3 mm. Also, investigated the effect of varying embedded depth (25 mm and 35 mm) of foundation models on the ultimate load.

2. Test tank

Fig.3. Test tank

A test tank made up of mild steel were used in this study for conducting plate load tests. The dimension of the tank was 40 cm x 40 cm x 40 cm.

Bearing capacity (kN/m2)

0 5000 10000 15000

1. LABORATORY TESTING The properties of sandy soil is shown in Table I.

   0

   0.5

   1

   1.5

   2

   2.5

   3

   3.5

   Pyramidal shell

   foundation (a=25mm)

   Flat foundation (a=25mm)

   TABLE I. PROPERTIES OF SANDY SOIL

   Sl. No.	Property	Dredged Soil
   1	Specific Gravity	2.676
   2	Moisture Content	0 %
   3	Uniformity coefficient, Cu	2.12
   4	Coefficient of curvature, Cc	1.14
   5	Field density (g/cm3)	1.433 g/cm3

   soil.

   Settlement (mm)

   The soil sample is classified as poorly graded sandy

   A number of load tests were carried out on both pyramidal shell and flat foundation models of different embedded depth such as 25 mm and 35 mm. The ultimate load and settlement of each foundation were obtained from the load versus settlement curve from the load test.

2. RESULTS AND DISCUSSION

The particle size distribution curve of soil sample from sieve analysis is shown in fig 4.

100

% Finer

80

60

40

20

0

0.01 0.1 1 10

Particle size (mm)

Settlement (mm)

Fig 4. Particle size distribution curve of soil sample

Bearing capacity (kN/m2)

0 5000 10000 15000

0

0.5

1

1.5

Pyramidal shell

foundation (a=35mm)

Flat foundation (a=35mm)

2

2.5

3

Fig 5. Load – Settlement curve (t = 3mm, a =25 mm)

Fig 5. Shows the load settlement curve of both pyramidal shell and flat foundation models having equal thickness (t=3mm) and embedded depth (a=25mm). From the figure, the ultimate bearing capacity of pyramidal shell foundation is 6000 kN/m2 and that of flat foundation is 3500 kN/m2.

Fig 6. Load – Settlement curve (t = 3mm, a =35 mm)

Ultimate Bearing capacity (kN/m2)

Fig 6. Shows the load settlement curve of both pyramidal shell and flat foundation models having equal thickness (t=3mm) and embedded depth (a=35mm). From the figure, the ultimate bearing capacity of pyramidal shell foundation is 7000 kN/m2 and that of flat foundation is 4500 kN/m2.

8000

7000

6000

5000

4000

3000

2000

1000

0

PS

FF

0

20

Embedded depth (mm)

40

Fig 7. Ultimate Bearing capacity v/s embedded depth

The ultimate bearing capacity of foundation models versus embedded depth is shown in fig 7. From the figure, we can understand that the ultimate bearing capacity increases with increase in embedded depth.

CONCLUSION

The results of this study proves that the pyramidal shell foundation shows better performance than conventional flat foundation of same dimension on sandy soil. The ultimate bearing capacity of pyramidal shell foundation increased by

71.42 % than flat foundation of equal embedded depth. The ultimate bearing capacity increases with increase in embedded depth from 25 mm to 35 mm as in the range of

16.66 % for pyramidal shell foundation and 28.57 % for flat foundation. The settlement decreases with increase in embedded depth as in the range of 25 % for pyramidal shell foundation. Also, the settlement of pyramidal shell foundation decreased in the range of 68 % for embedded depth 25 mm and 50 % for embedded depth 35 mm.

REFERENCES

[1] A. Hanna and M. A. Rahman (1990), Experimental investigation of shell foundations on dry sand, Canada geotechnical engineering journal, ppno:847- 857, volume (35)

[2] Hassan Sawsan A., Al-Soud Madhat S. and Mohammed Shahad A (2018), Behaviour of Pyramidal Shell foundations on Reinforced sandy soil, Geotech Geol Eng, ppno: 2437-2452, volume (37)

[3] M. Kazemi, J. Bolouri Bazaz (2017), Ultimate Bearing Capacity of Composite Shell Annular Foundations in Cohesionless Soil, Amirkabir journal of civil engineering, volume (50), issue 4, ppno: 243-246

[4] M. Ramesh and B. M. Joy (2015), Experimental Study on Conical Shell Footing, International Journal of Engineering Research & Technology, volume (4), issue 6, ppno: 167- 171

[5] R. Rinaldi, .A. Rahman and A. Hanna (2018), Experimental Investigation of Shell footing models Employing High- Performance Concrete, Springer International Publishing, ppno: 373-390

[6] S.A. Ghaffari, A. Hamidi and G.T. Meherjardi (2021), Bearing Capacity of Triangular Shell Foundations Adjacent to the Reinforced sandy slopes, Journal of Engineering Geology, volume (14)

[7] T. Jose and J. G. Philip (2017), Experimental and Numerical Analysis of Conical Shell Strip Footing Reinforced in Multi- Layered Soil, International Journal of Engineering and Management Research, volume (7), Issue 2, ppno: 340-344