First of all, when you plan to do a PSI analysis or plan to do a pile foundation design the users should do some basic checks about their engineering analysis.  It is because most of the analysis error come from the input data.  For example,

1. Does my pile foundation have sufficient capacity, especially both axial and lateral pile capacities? Or overall capacities?
2. Did I enter my soil input correctly? Did I check my T-Z and P-Y curves?  Do I have too many extremely thin soil layers, do they make sense?
3. Do I have my PSI analysis run with extremely light loads but got errors with larger applied loads? Or do I have errors with even a very small load?  Why?
4. Do I have my pile unreasonably too long? Is the pile length even possible to drive into the seabed/foundation?

Below are some engineering analyses that SACS users should perform and troubleshoot the common analysis error associated with pile stiffness matrix errors or some other PSI analysis issues.

1. Run ‘Basic Static’ analysis.
2. Look at the vertical reaction.
3. Create a pile capacity plot.
4. Now, compare the jacket vertical reaction at the base fixity and pile capacity. Check for compression/tension capacity adequacy.
5. Run a single pile analysis. Look at the lateral deflection and lateral load capacity.  Now, compare the single pile's lateral load capacities with the maximum lateral reaction force at the base of the jacket.  
6. Please refer to the website below for a Single Pile analysis sample.

Single Pile Analysis - MAXSURF | MOSES | SACS - Wiki - MAXSURF | MOSES | SACS - Bentley Communities

7. After all the pile capacities are sufficient, check if there are sharp slope discontinuities in the T-Z or P-Y curves.  The user can generate soil plot.   If there exist, enter TABR input lines to overcome error with stiffness matrix with non-positive definite.  Refer to the website below on Communities for detailed information about entering TABR input data.

Error message with **ERROR-STIFFNESS MATRIX IS NON-POSITIVE DEFINITE FOR LOAD CASE# - MAXSURF | MOSES | SACS - Wiki - MAXSURF | MOSES | SACS - Bentley Communities

8. Please also check convergence tolerance in the PSIOPT input line. Depending on the PSI input data the user may need a larger convergence tolerance or a bigger number of pile increments.
9. Ensure that the soil data are entered correctly. Please create a soil plot to see if the soil curves look correct.  Please also check that some of the soil layers are not too thin which is not practical.
10. Ensure that the pile length is not too long which can significantly reduce the pile’s stiffness and hence cause the pile stiffness error. For example, the stiffness of the pile in Section 4.5 Equivalent Pile Stub in the PSI manual was given by AE/L.  So, the longer the pile length, the lesser the pile’s stiffness will be.
11. The users should also countercheck these with the PSI manual, especially with Section 7 Troubleshooting Common Problems.