海洋土取样应力释放三轴模拟试验研究

Using triaxial unloading tests to simulate the marine soil sampling process

基于海底现场取土样,利用GDS高压三轴试验仪重塑不同压力条件下的海洋土,在此基础上通过三轴加卸载试验,模拟研究高压海洋土在非保真取样过程中的卸荷响应特性,即围压-土样体积变化规律。饱和土样总体积变化一般可用反压体积变化近似描述,本文进一步考虑了高压水可压缩性的影响。通过不同加卸载循环次数以及卸载时间等的试验,表明其对高压试验结果影响很小,不同初始围压与孔压土样的卸荷试验则表明了孔压越大土样体积变化越明显等特点。卸载试验总的特征为:高压卸载过程中土样体积膨胀开始慢,发展逐渐变快,至尾段变化最快;不同作用因素对卸载中间阶段影响明显,而对初始段和末尾段影响不明显,这与中低压卸载特性存在一定区别。

To simulate the unloading sampling process of marine soil, laboratory triaxial tests are carried out with the marine soil from the seabed, and the advanced GDS triaxial test instrument is employed to remold the marine soil sample under the same initial pressure conditions as those of the field soil, thus the properties of marine soil, e. g. , cell pressure vs soil volume change, are investigated. In general, the saturated soil sample volume change is approximately measured by the volume change of the back pressure controller; the correction of volume change due to compressibility of high-pressed water is also taken into consideration in this study. The test results with different test conditions, such as different loading and unloading cycles, as well as different unloading times, show that the high-pressure test results are not sensitive to these conditions. The unloading tests on different initial confining and pore pressures show that soil volume change increases with the initial pore pressures, etc. The general test features of the unloading sampling process are concluded in this study. The high-pressed soil sample swells slowly in the early unloading process, and then becomes steadily quicker, and the quickest in the end. The results of all the test conditions only differ from each other in the middle stage of the unloading process, not at the beginning or at the end stages, which is somewhat different from that of low-pressed soils.