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Geocentrix Repute - Onshore pile design and analysis

3 x 3 pile group for railway viaduct in North London

This benchmark describes the design of a 3x3 pile group subjected to a combination of vertical loads, horizontal loads and moments, and embedded into the stiff London Clay [1].

The bored cast-in-situ reinforced concrete piles are 17m long, 0.9m in diameter, with a centre-to-centre spacing of three pile diameters, and with the underside of the pile cap assumed at the top of the London Clay. A profile of undrained shear strength (Cu) of 50 + 9.4z kPa has been adopted, where z is the depth in m below the top of the London Clay.

For the axial response, the profile of soil modulus has been derived from the correlation Es = 400Cu for the linear analyses and from Es = 1500Cu for the non-linear analysis. For the lateral response, the profile of soil modulus has been assumed to increase linearly with depth from a value of zero at the top of the London Clay at a rate of 4.14MN/m3 for the linear analyses and 6.15MN/m3 for the non-linear analysis.

The applied vertical loads (V) result from the combined effect of live and dead loads, whereas the horizontal loads (H) and moments (M) are generated by the high-speed trains braking and accelerating. The loads acting on the cap have been estimated as V = 14200kN, H = 470kN and M = 3200kNm.


Results from Repute

The results from Repute are given in the table below.

Comparison with benchmark

The table below summarizes results obtained from various programs. In the linear elastic range, there is a reasonably good agreement between the group deformations and axial load distribution predicted by the different codes.

Variable MPILE DEFPIG Repute
linear non-linear
Group centre settlement (mm) 9.0 11.3 11.6 4.0
Group deflection (mm) 3.2 4.3 3.9 2.7
Axial load at top of corner piles of leading row (kN) 2220 2210 2230 2100
Axial load at top of corner piles of trailing row (kN) 1700 1670 1640 1520
Lateral load at top of corner piles of leading row (kN) 66 62 94 76
Lateral load at top of corner piles of trailing row (kN) 66 62 23 35
Bending moment at top of corner piles of leading row (kNm) 120 177 225 179
Bending moment at top of corner piles of trailing row (kNm) 120 177 87 124

Comments

If the effects of soil non-linearity are considered using Repute, we obtain lower group deformations (due to the higher value of soil modulus adopted) and a decrease of predicted loads on the most heavily loaded row of piles (i.e. the leading row), thereby resulting in a more uniform load distribution between the piles.

Reference

[1] Basile F. (2003). Analysis and design of pile groups. In Numerical Analysis and Modelling in Geomechanics, E & FN Spon (eds J. W. Bull), Chapter 10, in press.

Downloads

Repute linear project for this example
Repute non-linear project for this example

 

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