Multi-directional shear loading

[Rain]

Hi everyone,

I want to simulate an undrained simple shear test of soil under multi-directional shear loading(2D shaking). But there is something wrong with the pattern code:

...
timeSeries Sine 1 0 $FTime $period -factor 9.81 ;# FTime is the end time
timeSeries Sine 2 [expr $period/4.0] $FTime $period -factor 9.81
pattern UniformExcitation 1 1 -accel 1 ;# acc in X-dir
pattern UniformExcitation 2 2 -accel 2 ;# acc in Y-dir
# "[expr $period/4.0]" in the timeSeries 2 could provide a phase difference of 90°.
...

As the code goes like this, there is little pore water pressure can be observed in the result. This is against the real laboratory test. However, the result goes well with the real test when I replace "[expr $period/4.0]" with zero.

How can I fix this problem? Thank you.