We are running a shallow foundation with a highly eccentric V-H loading. There will be a separation between foundation and soil near the edge of foundation. In order to simulate the separation of soil and foundation, we have used tension zero cut-off (no tensile strength) for the soil, and set an interface with Rint = 0.65. My question is for the area where foundation-soil separation is expected, whether the sliding resistance still exists? Ideally, I would expect that once the contact is lost, there should be no sliding resistance provided at interface. The undrained model B and C are used, with undrained shear strength as inputs.
The above question is for the soil-structure interface. Similar question can be to soil-soil condition. For example, at the top of slope failure, a tension crack may occur. Along the tension crack, obviously it is a separation between soils. Will the shear resistance still exist at the crack area?
Hope anybody can help. I could not find a clear answer in the manual. Thanks!
Dear Stefanos,
Many thanks for your reply.
I have read through the manual. Based on what you say, if we use the third option "Manual with residual strength", if I set the residual strength equal to zero, then once the interface strength as defined by Rinter is reached, the interface strength will soften down to zero, regardless whether there is soil-structure contact or not.
However, this only satisfies one criterion that we need to follow. I would like to follow two criteria in one analysis (undrained C with su as input, assuming Rinter = 0.65):
1. If there is still a soil-structure contact (normal stress is compressive), the interface strength should reduce to Rinter * su-soil = 0.65 su-soil;
2. If the soil-structure contact is lost (normal stress is zero due to the tensile strength cut-off at zero), the interface strength should reduce to zero, NOT 0.65 su-soil.
Through the manual, I could not figure out how to satisfy these two criteria at the same time. Hope to get your inputs. Great thanks!
Regards,
Yi
Dear Yi Xie,
The interface allows for simulating the sliding and gapping behaviour. At failure, the behaviour is typically (for most models) according to the Mohr-Coulomb failure criterion.If the strength determination is set to Manual there is no residual strength. In such case, you can select the third option which is Manual with residual strength.
You can read all the details on how Rinter affects strength and stiffness in our Reference manual (sections 6.1.7.1 and 6.1.7.2, PLAXIS 2D 2023.1).