Hi all,
In the retaining system in sloping ground, the sloping angle is included in the soil pressure through the lateral coefficient and the depth is considered from the top of the retaining system not the top of the sloping ground.
My question here is how the water pressure is considered if the ground water table is flowing through ground surface which means the water table also make the slope as the sloping ground (let assume no seepage)?
Thanks.
PLAXIS is based on the effective stress principles, the total stress at a stress point is computed as the summation of the effective stress and the pore pressure. So if the ground surface and water surface are sloping, PLAXIS will calculate the total stresses on the wall using the actual geometry of the soil surface. The horizontal and vertical stresses on the wall will differ as it is based on the coefficient of earth pressure at rest and/or the gravity loading. The pore pressures are also calculated on the wall based on the depth of the point below the water table but water pressure is applied equally in all directions. Plaxis offers a few options for defining the water condition (given in the water tabsheet): head, hydrostatic, interpolate, dry, and user-define. (Please refer to page 55 of the reference menu for detailed information about defining water conditions.)
When computing the total lateral force of the retaining wall, pore pressure component should be taken into account. For the steady state flow condition (no groundwater flow), if the water level is defined and activated in the model, pore pressure distribution will directly be generated based on the unit weight of water and the depth with respect to the water level. Pore pressure value at the depth below the water level is taken to be negative, and it is taken to be positive as suction for the soil layers above the water level (suction can be ignored using the settings).
Mr. Faseel,
Thanks for the reply.
My question is not based on the Plaxis, but the general one. As you see, when calculating the soil pressure, the slope effect of the backfill is included in the lateral coefficient, but for water pressure it is not and the water pressure acts all the direction same. That's why I brought that question here for the discussion (which is indicated in the screenshot above).
Dear Nitharshan,
As your question goes beyond PLAXIS I will leave it open to our fellow geotechnical engineers to check and share their thoughts.