Consulting: Civil Engineering

Retaining Structures

Itasca has provided analysis of nearly all types of retaining structures, including slurry-supported reinforced concrete diaphragm walls, sheet pile walls, soil-nailed walls and tieback walls. As with dams, water pressure acting within the soil mass is often a key issue. The ability to predict water pressures is an important element in understanding the behavior of retaining structures. FLAC is used to study the flow through soil and uses the resultant pore pressures to determine effective stresses used in constitutive relations.

Itasca has worked with a number of unique retaining structures. As soil-nailed walls were just being introduced into the U.S. in the early 1990s, Itasca performed analysis of a test wall. Cable-bolt support elements were used to represent the soil nails. The analysis showed good agreement between loads in the cable bolts and actual loads measured in the soil nails. For the U.S. Forest Service, Itasca developed analysis procedures to help design rockeries (stacked rock blocks used as a soil retention system) and performed analysis of patterned soil nails/rock bolts to retain an excavation adjacent to and existing powerhouse on the Swan River in Idaho. (The existing powerhouse is on the National register of historic places.)

Many of the retaining structures Itasca has studied are associated with port facilities, including the Port Said project in London, the North Charleston port, 33 South Wharf (Melbourne) and the Port of Long Beach container wharf. For the Port of Long Beach, the busiest port on the west coast of the United States, Itasca developed a FLAC model for Kleinfelder, Inc. that was used to perform detailed seismic deformation of a dike, pile and wharf system. The FLAC model provided deformations, pile rotations, and an estimate of shear and moment for each row of piling as a function of elevation. Plots of lateral displacement of piling, pile curvature and shear stress for various earthquake assumptions were also generated. The information was used to check the adequacy of the piles supporting the wharf.

Itasca developed models for The Port and Harbor Research Institute (Tokyo) to study the liquefaction of soils and their effect on support structures in harbors. The material model used to model liquefaction is the same one used to study liquefaction potential of tailings dams. These material models generate pore pressures as soil structure collapse under cyclic shear. The soil collapse increases pore pressures leading to liquefaction when effective stresses vanish. The FLAC model developed for the Port and Harbor Research Institute included representation of a massive concrete block used to retain soil adjacent to the waterfront. Dynamic simulation showed the behavior of the massive concrete blocks during earthquake loading and subsequent liquefaction of retained soil.