Civil Insight: A Technical Magazine Volume 3 | Page 59
Gautam A. et al.
Civil Insight (2019) 57-63
springs were placed starting from 2.5m below the base of the pile cap to the end of the pile at an interval of
1m. End bearing springs were placed at the bottom tip of the piles. Then, a point load was applied at the
center of the pile cap.The spring modeling of soil-pile interaction is shown in Fig. 2.
Fig. 2. Spring modeling of soil-pile interaction and the application of load
To find the soil spring stifness, Elastic Modulus (E) and Poission’s Ratio of soil were estimated using
Bowles (2001).
Table 1. Estimation of properties of soil using Bowles (2001)
Depth (m)
0-3
3-6
6-9
Below 9
Type of Soil
Sand Medium
Sand and Gravel (Medium-Dense)
Dense Sand
Sand and Gravel (Dense)
N-Value
50
50
50
50
E (kN/m 2 )
32500
67200
32500
67200
Q
0.25
0.30
0.35
0.35
Using the values of Table 1, the spring stiffness of the soil were calculated.
The skin friction in pile was modeled using frictional stiffness values provided by Randolph (1978), as
expressed in Eqn (2).
ሺ݇ ௦ ሻ ௧ ൌ
ܩ
ݎ ቀ
ݎ ሺʹሻ
ቁ
ݎ
where G is the shear modulus of soil, r 0 is the radius of the pile, r m is the radial distance at which shear
become negligible. Randolph and Wroth (1979) suggested r m using Eqn (3).
ݎ ൌ ʹǤͷ݈ߩሺͳ െ ߥሻሺ͵ሻ
where ݈ is the pile embedment depth, Q is the Poisson's ratio of soil, and U is the factor of vertical
homogeneity of soil stiffness, as expressed in Eqn (4).
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