pseudo-static analysis & kinematic load

Question

I am analyzing a steel pipe pile quay with PLAXIS 2D. How to check the earth pressure acting on the pile after pseudo-static analysis? Is it &sigma;'_xx? 
 Does &sigma;'_xx include kinematic load caused by earthquakes?

Dennis Waterman · Accepted Answer

Dear Poongsik Kim, A dynamic analysis it's taken into account that the soil has movement in terms of acceleration and velocity and those velocities and accelerations change in time and have spatial variation. A pseudo-static analysis on the other hand gives the soil has a constant increase of stresses due to the constant acceleration that is applied.Hence, the chance that those two completely different concepts would give similar results is quite small. Furthermore, the results of a pseudo-static analysis depend on the size of the soil mass taken into account for the calculation. Originally pseudo-static analysis was used for calculating slope stability problems (including dams and embankments) and the size of a dam or embankment is of course predetermined by the design of the dam or embankment. However, when using pseudo-static analysis for piles, tunnels, excavations the size of the soil mass is the size of subsoil, and that is not predetermined by design but a user choice: it depends on where the user puts the left and right boundary of the model. So for these kind of calculations the results of the pseudo-static analysis depend on the size of the geometry and one can obtain any result wanted just by playing around with the width of the model. Therefore it's impossible to say whether the results of pseudo-static analysis are conservative compared to dynamics analysis as the results depend on the geometry size. 
 With kind regards, 
 Dennis Waterman

Dennis Waterman · Answer

Dear Poongsik Kim, 
 For earth pressure you could check indeed sig_xx since it's a vertical pile here. Alternatively if the pile has an interface you could check in the interface the normal stress sig_N. If you do a pseudo-static analysis then the stresses do not include a dynamic load since there is no dynamic load, only a static load. That's the principle of pseudo-static analysis: to model dynamic effects using a static acceleration. 
 If you would do a real dynamic analysis then sig_xx would indeed contain the effect of dynamic loading. 
 With kind regards, 
 Dennis Waterman

pseudo-static analysis & kinematic load

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