Hi Richard Ay, Please can you give an insight on this situation?

For spool analysis, the interaction between the pipe & seabed soil (friction say 0.7) and the pipe to mattress (friction say 0.5) are represented.
We model the mattress on the pipe as a pseudo (imaginary) pipe while stripping off the pipe properties. That is the pseudo pipe density is deleted and the modulus is reduced significantly, thus eliminating the pseudo pipe stiffness. Hence it can only act as a dummy.
Premise:
- Typically, for a spool configuration at node 160 with soil friction of 0.7; mattress to pipe friction of 0.5; and pseudo pipe connection of node 1160 as mattress with UDL (uniformly Distributed Load) of 600 N/mm on it, we have:
- node 160 (Restraint, +Y; Mu 0.7); node 1160 (Restraint, Y cnode 60 ; Mu 0.5; Restraint X, Guide; Restraint Z, LIM). The pseudo pipe has a uniform load of 600 N/mm.
- Where the Guide and the LIM restraints are only keeping the pseudo pipe, with lost stiffness, in place.
Query:
- The restraint loads extended output at node 160 (green highlight) gives the expected lateral friction loads i.e vertical load * mu(0.7) and displacement but that at node 1160 (orange highlight) does not give the required lateral friction and displacement. It appears that the mattress does not move given the 0 displacements at X and Z.
- Why is the 0.5 friction coefficient between pipe & mattress not utilised as per the output?
A representative example is shown in the spread sheet below;

Node Load Case FX N FY N FZ N MX N.m MY N.m MZ N.m DX mm DY mm DZ mm
160 Rigid +Y
1(OPE) -1182 -2170 953 0 0 0 -1.50 0 1.211
1160
Rigid Y; Rigid GUI; Rigid LIM
1(OPE) -9 -1866 6 0 0 0 0 0 0