Study into stiffness of geomaterials for a wide range of strain under static and dynamic loading conditions

通过一系列综合的室内试验、现场试验和现场观测分析，以及对上述各种方法所得刚度值的比较，研究了一种实用的现场岩土非线性刚度估计方法。首先，开发了一种独特的方法，在压缩试验中，可以沿着试件的侧表面连续测量从局部轴压到约0.0001%至约10%的极宽范围内的非常精确的应变。结果表明，对于包括沉积软岩在内的刚性几何材料，传统方法（即从加载活塞或试样帽的轴向位移）获得的轴向应变大大低估了真实刚度，因此是完全不可靠的。研究发现，上述因素和在目前的实验室试验实践中，刚度定义在一个相对较大的应变，是导致许多现场情况下的估计位移远大于观测位移的两个主要原因。然后，人们发现，从软粘土到软岩石的各种地质材料，在小于0.001%的应变下，变形特性实际上是线性的和弹性的。即在室内试验中，在此小应变水平下定义的杨氏模量在静态单调循环加载试验和动态试验中是相同的。此外，任何实验室测试精确确定的弹性杨氏模量都可以非常接近相应的现场剪切波速测量值。另一方面，由于这些现场加载试验中涉及的应变水平要大得多，因此，从传统的压力表试验和板加载试验方法确定的现场刚度要比弹性杨氏模量小得多。基于上述研究结果，提出了以下方法：即，首先，弹性杨氏模量（或剪切模量）是由现场横波速度测量得到的。接下来，从压力计测试中获得相对较大应变水平下的刚度值。此外，通过使用高质量的未扰动样品进行精确的实验室单调加载试验，获得了从0.0001%到峰值（约10%）的连续应力-应变关系。必要时，进行循环加载试验。结合上述信息，估计刚度作为应变函数的场值。少

A practical methed to estimate the non-linear stiffness of soils and rocks in the field was studied by means of a comprehensive series of laboratory tests, field tests and analyses of field observations and the comparison of the stiffness values obtained from the above-mentioned various methods. First, a unique method was developed with which in a compression test, a very precise strain for an extremely wide range from about 0.0001% to about 10% can be continuously measured from the local axial compression along the lateral surface of specimen. It was revealed that for stiff geometerials including sedimentary soft rocks, the axial strain obtained by the conventional method (i. e., from the axial displacement of loading piston or the specimen cap) considerably underestimates the true stiffness and is, therefore, is totally unreliable. It was found that this factor mentioned above and the fact that in the current practice of laboratory tests, the stiffness is defined at a relatively larg … More e strain are two major causes for that many field cases have been reported where the estimated displacement be much larger than the observed ones. Then, it was found, common for a wide rage of geomaterials from soft clays to soft rocks, that the deformation properties at strains less than about 0.001% are virtually linear and elastic. Namely, in the laboratory tests, the Young's modulus defined at this small strain level is the same among static monotonic and cyclic loading tests and dynamic tests. Further, the elastic Young's modulus precisely determined by any laboratory test could be very close to the value determined from the corresponding field shear wave velocity measurement. On the other hand, the field stiffness determined from the conventional methods of pressuremeter tests and plate loading tests are much smaller than the elastic Young's modulus, because of much larger strain levels involved in these field loading tests.Based on the above-mentioned findings, the following method was proposed. Namely, first, the elastic Young's modulus (or shear modulus) is obtained from field shear wave velocity measurements. Next, the stiffness values at relatively large strain levels are obtained from pressuremeter tests. Besides, a continuous stress-strain relation from a strain range from 0.0001% to that at the peak (at about 10%) is obtained from an accurate laboratory monotonic loading test (or tests) using high-quality undisturbed samples. When needed, cyclic loading tests are performed. Combining the above information, the field value of stiffness as a function of strain is estimated. Less