Understanding the stiffness of soils in Singapore from pressuremeter testing

Abstract

The stiffness of soil is an important parameter that affects the prediction of ground deformation and impact on adjacent structures due to construction activities such as deep excavations and tunnelling. Whilst constitutive models and analytical methods have been derived to predict soil deformation from its stiffness, engineers face a difficult task of identifying soil stiffness from routine site investigations. This paper discusses the use of pressuremeter testing in site investigations to estimate the soil modulus for design.

In recent years, an intensive regime of pressuremeter testing was implemented along with conventional soil investigation works for the land transportation infrastructure construction in Singapore. These include the investigations in the Downtown Line project on Kallang Formation and the Old Alluvium soils, investigations in the North-South Expressway and Thomson Line projects on the Bukit Timah Granite Formation, and investigations in the Tuas West Extension project on the Jurong Formation. This paper reports on the use of various types of pressuremeter testing in Singapore – namely the Menard pressuremeter, the OYO pressuremeter and the self-boring pressuremeter – in terms of the practical experience and the interpretation of pressuremeter test results to understand the stiffness of local soils.

The paper begins by summarising the applications and limitations for various types of pressuremeters in in-situ testing, before discussing the lessons learned from using these pressuremeters in Singapore. Some of the improvements include relating the pressuremeter modulus to the corresponding strains from which they are derived, as well as developing guidance for operators on when to start the unloading cycle. Empirical relationships using SPT-N correlations would also be recommended based on the pressuremeter tests for the various local soils. Other than its elastic modulus, the small strain stiffness of soil has also been investigated to various extents depending on the type of pressuremeter test...