The sand hypoplastic model has been used to simulate the interaction between soil and pile. However, there is a bad convergence in the process of calculation. When I try to set 0.5m displacement loading on the top of pile, the calculating will end with very small increment. After checking the messages files, I find there is the key tip, as following:
THE SYSTEM MATRIX HAS 7 NEGATIVE EIGENVALUES.
NEGATIVE EIGENVALUES MEAN THAT THE SYSTEM MATRIX IS NOT
FOR EXAMPLE, A BIFURCATION (BUCKLING) LOAD MAY HAVE BEEN EXCEEDED.
Could anyone kindly help me solve this problem? Thanks a lot!