Finite element analysis of braced excavation with jet grouting

Abstract

Braced excavations are becoming prevalent in an increasingly urbanised world. For excavation in soft clays, jet grout piles (JGP) are often used as a ground improvement technique to reduce the wall deflections and increase the factor of safety with respect to basal heave stability. This project studies and reports on the effects of jet grouted piles on the performance and behaviour of a typical deep braced excavation in soft clay.

In this study, finite element analyses were carried out to examine the effects of JGP parameters, namely JGP thickness, undrained shear strength, and elastic modulus on the basal heave factor of safety (FS), maximum lateral wall deflection, maximum wall bending moments and maximum strut forces. These parameters are often dictated by quality assurance and quality control during the jet grouting process. The design implications of the findings are also discussed.

A total of 33 cases were considered in this report. The result shows that the elastic modulus of the JGP has minimal effects on the basal heave factor of safety. Increasing JGP shear strength or thickness increases the basal heave factor of safety and reduces the lateral wall deflection and strut forces. Increasing JGP shear strength beyond an optimal point results in large wall bending moments being developed. Careful consideration based on the project requirements must be taken as there is a trade-off between maximum wall bending moments and wall deflections.