Pressuremeter Test Application for Large Monoshaft Foundation Design: Fid-Bau Portal

Pressuremeter Test Application for Large Monoshaft Foundation Design

Huang, Ellen / Liu, Xiteng / Noble, Kyle

Large 2.5 m diameter drilled cast-in-place concrete monoshafts were used to support an elevated guideway for the light railway transit in Edmonton. The monoshafts were generally 20–35 m in length and installed at about 30 m spacing. Besides large vertical loads, the monoshafts will be subject to significant lateral load, especially at vehicle stop or turning locations. Due to the low redundancy of the monoshaft system, it is critical to accurately determine the load deformation response of the surrounding soil/rock for the foundation design. As a supplement to the conventional geotechnical field investigation, the pressuremeter test (PMT) was introduced to better evaluate the soil/rock strength and compressibility for the foundation design. The PMT is a stress–strain test performed on the wall of a borehole using a cylindrical probe, which is an advanced geotechnical tool to measure soil and rock properties. The behavior of soil and very weak rock and their stiffness vary with both strain and confining stress over the location and depth. For improving deformation prediction, advanced soil/rock models were employed to simulate the nonlinear stress–strain behavior of the soil/rock. In addition, the undrained shear strength of soil and uniaxial compressive strength of bedrock were established from field and laboratory test results and further calibrated with PMT results. The validated soil parameters were applied for the monoshaft settlement analysis and lateral load design. This paper describes the PMT execution, soil parameter evaluation, model calibration, and validation for the applications. The PMT combined with numerical modeling were successfully used on this project for improving the accuracy of deformation predictions, which reduced risk and decreased the design uncertainty.