A block sample goes through stress changes during and after sampling. Sensitive clays are affected by sample disturbance and stress changes have a great effect on sample quality. Reduction of the in-situ total stresses to zero causes a soil sample to develop a negative pore pressure. In an ideal situation, a block sample retains its negative pore pressure during sampling and storage, preventing it from swelling. To study this, five in-situ tests were conducted in which the pore pressure variations inside block samples were monitored during and after sampling. The pore pressure was measured continuously during a storage period of several days and the results were compared with tests on reconstituted clay in an attempt to simulate the same stress conditions as those in situ. Similar to the in-situ tests, the pore pressure inside the reconstituted samples was measured throughout the test. The findings suggest that the negative pore pressure in mini-block samples may be reduced in a matter of minutes or hours after sampling. Parallel testing on mini-block and reconstituted clay samples indicated that pore pressure dissipation had a negative effect on the preconsolidation pressure, constrained modulus and sample quality.

中文翻译：

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在敏感粘土块状样品中卸荷引起的应力释放的现场和实验室研究

块状样品在取样期间和之后经历应力变化。敏感粘土会受到样品干扰的影响，应力变化对样品质量有很大影响。将原地总应力减小到零会导致土壤样品产生负孔压。在理想情况下，块状样品在采样和存储期间会保持负孔隙压力，从而防止其膨胀。为了研究这一点，进行了五个原位测试，其中在采样期间和采样之后监测块状样品内部的孔隙压力变化。在几天的存储期间连续测量孔隙压力，并将结果与​​在再生粘土上的测试进行比较，以模拟与原位相同的应力条件。与原位测试类似，在整个测试过程中都测量了重构样品内部的孔隙压力。研究结果表明，小块样品中的负孔压可能会在采样后几分钟或几小时内降低。对小块和重构粘土样品的并行测试表明，孔隙压力耗散对预固结压力，约束模量和样品质量具有负面影响。