Abstract
A soil sample goes through stress changes during and after sampling. Sensitive clays are affected by sample disturbance and stress changes have a great effect on the quality. The reduction of in-situ total stresses to zero causes the soil sample to develop a negative pore pressure, which is also referred to as residual effective stresses. In an ideal situation, a block sample shall retain its residual effective stress during sampling and storage, which prevents it from swelling. To study this, an attempt was made to monitor the pore pressure variations inside a block sample of soft, sensitive, low-plasticity clay during and after sampling. The pore pressure was measured continuously during the storage period of 3 days and the results were compared with a similar work. The findings suggest that the residual effective stress in block samples may be reduced in a matter of minutes after sampling. Testing performed on reference samples corroborate these storage effects.
Highlights
Sampling of sensitive clays is a challenging task as their engineering properties, such as undrained shear strength, stiffness and preconsolidation stress, are affected by sample disturbance
Extensive studies have shown that block sampling is among the best methods of collecting high-quality samples of soft clays (e.g. DeGroot et al, 2005; Karlsrud & Hernandez-Martinez, 2013)
It has become more common to use Sherbrooke block sampling (Lefebvre & Poulin, 1979) in sensitive clays as this method ensures that the soil remains unaffected by shear distortions during sampling (e.g. Lacasse et al, 1985; Tanaka et al, 2001)
Summary
Sampling of sensitive clays is a challenging task as their engineering properties, such as undrained shear strength, stiffness and preconsolidation stress, are affected by sample disturbance. Significant development has taken place to overcome sample disturbances. Extensive studies have shown that block sampling is among the best methods of collecting high-quality samples of soft clays DeGroot et al, 2005; Karlsrud & Hernandez-Martinez, 2013). It has become more common to use Sherbrooke block sampling (Lefebvre & Poulin, 1979) in sensitive clays as this method ensures that the soil remains unaffected by shear distortions during sampling Lacasse et al, 1985; Tanaka et al, 2001). One of the issues that is challenging with block sampling is the stress relief.
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