Structures & Walls FAQs
1. How much settlement can MSE wall structures tolerate?
MSE walls are constructed with discrete facing panels with ¾” open joints on all sides, making them very flexible structures that can accommodate differential settlements up to 1% along the wall face. Where foundation soil conditions result in greater estimated settlements, the use of precast slip joints may be used to provide even more flexibility to the system.
2. Can MSE wall structures be used in locations where walls will be submerged due to permanent or temporary flooding in front of the wall?
MSE walls are constructed with ¾” open joints backed with geotextile around all panel edges, making them free-draining and accommodating to partially submerged and rapid drawdown conditions. To facilitate the free-draining nature of the walls, open-graded stone backfill, #57 or #3 stone, which has a very high permeability is typically used as wall backfill which allows for rapid relief of pore pressure for walls subjected to rapid drawdown conditions. Hydrostatic pressures and effective unit weights are considered in the internal and external design of submerged MSE wall structures subject to rapid drawdown so the number and lengths of reinforcing strips are designed to accommodate both static and rapid drawdown design conditions.
3. For MSE wall structures supporting pile or drilled shaft-supported bridge abutments, at what distance from the wall facing should the piles or shafts be located?
It is generally recommended to maintain a minimum 1.5 ft of clearance between the edge of bridge abutment piles and the back-face of the MSE wall facing panels. Where drilled shafts are utilized, the greater of 3 ft or one shaft diameter of minimum clearance is recommended. These criteria provide the necessary clear space to achieve proper compaction of the reinforced backfill in this area, and adequate distance to skew the soil reinforcing strips around the deep foundations.