Capacities and Deflections of Laterally Loaded Shafts behind Mechanically Stabilized Earth Wall

Abstract

Current practice for designing laterally loaded shafts that pass through a mechanically stabilized earth (MSE) wall often involves isolating the shaft from the MSE mass and anchoring the shaft into rock with a rock socket. Sizeable cost and time savings could be realized, along with continued effective performance and reliability, if a method were available to evaluate the lateral load capacity of a shaft supported by the MSE mass alone without a rock socket. The Kansas Department of Transportation assembled a team to develop such design methods: the construction, instrumentation, and loading of multiple 36-in. (0.914-m) diameter shafts supported within the reinforced mass of a 20-ft (6-m) tall MSE block wall designed according to existing FHWA procedures without consideration of lateral loads. The design and construction of the wall and the shafts, which were designed as drilled shafts, and the results from the lateral load tests of four shafts are described. These shafts had lengths equal to the full height of the wall and had spacings from the back of the wall facing to the center of each shaft of one, two, three, and four shaft diameters. Results for both load and displacement of the shafts, the width of shaft influence, and the relative displacements of the shafts and the wall facing during loading are presented, along with design recommendations.

Modelling of laterally loaded drilled shaft group in mechanically stabilised earth wall

“…The completed study by Pierson (2007) and Pierson et al (2009b) involved designing, constructing and testing drilled shafts within an MSE wall that was 43 m long and 6 m high. The wall was divided into six test sections with one wing wall at each end, as shown in Figure 1(a).…”

“…4.1 Parameter determination and validation of capyield model The data from the gradation and triaxial tests along with the numerical back-analysis were utilised to determine the required Interface Properties MSE wall facing blocks Horizontal (Pierson, 2007). The shape factor, AE, was assumed to be 1 to make the compression yielding surface circular.…”

“…In addition, the interactions among the shafts or piles are also ignored, regardless of their spacing. As a result, the shafts or piles as well as the MSE wall are often not designed with appropriate factors of safety (Huang et al, 2011;Pierson, 2007).…”

Lateral Load Capacity of Cast-in-Place Shafts behind an MSE Wall

“…Movement of telltales installed within the fill and attached to the geogrid, as well as targets attached to the wall facing, was monitored using a digital camera and a photogrammetric process. Additional details on construction and instrumentation are located in Pierson (2008Pierson ( , 2009.…”

Effect of Lateral Cyclic Loading on Drilled Shaft within an MSE Wall

“…Under this circumstance, the existing p-y curves are not applicable. Due to lack of information, Pierson et al [11] performed a study to assess the behavior of drilled shafts in an MSE wall and provided a threshold lateral deflection of the drilled shaft that a MSE wall can tolerate. Rollins et al [12] then studied driven pile in an MSE wall and suggested additional load to be considered in the drilled shaft and MSE wall design during a seismic event.…”