- Open Access
- Authors : Anuja Pradeep, Jaseena A. Rasheed
- Paper ID : IJERTCONV10IS06015
- Volume & Issue : ICART – 2022 (Volume 10 – Issue 06)
- Published (First Online): 21-06-2022
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License: This work is licensed under a Creative Commons Attribution 4.0 International License
Feasibility Study of Pyramidal Shell Foundation of Varying Embedded Depth on Sandy Soil
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
Keywords- Sandy soil; Pyramidal shell foundation; Ultimate bearing capacity
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.
OBJECTIVES OF STUDY
To examine the behaviour of pyramidal shell foundations on sandy soil
To identify the influence of different embedded depth on the performance of foundation models.
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.
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.
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
LABORATORY TESTING The properties of sandy soil is shown in Table I.
Flat foundation (a=25mm)
TABLE I. PROPERTIES OF SANDY SOIL
Uniformity coefficient, Cu
Coefficient of curvature, Cc
Field density (g/cm3)
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.
RESULTS AND DISCUSSION
The particle size distribution curve of soil sample from sieve analysis is shown in fig 4.
0.01 0.1 1 10
Particle size (mm)
Fig 4. Particle size distribution curve of soil sample
Bearing capacity (kN/m2)
0 5000 10000 15000
Flat foundation (a=35mm)
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.
Embedded depth (mm)
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.
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.
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