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

本文通过室内试验、现场试验和现场观测资料的综合分析，以及各种方法所得刚度值的比较，研究了一种现场估算岩土非线性刚度的实用方法。首先，开发了一种独特的方法，在压缩试验中，可以从局部轴向压缩沿着试样的侧表面连续测量约0.0001%至约10%的非常宽范围的非常精确的应变。结果表明，对于包括沉积软岩在内的刚性几何材料，用常规方法（即应变法）得到的轴向应变值与实测值相比，存在较大的误差。例如，从加载活塞或样品盖的轴向位移）大大低估了真实刚度，因此是完全不可靠的。结果发现，上述因素以及在目前的实验室试验实践中，刚度被定义在相对较大的值， ...更多信息 应变是引起许多现场情况两个主要原因，在这些情况下，估计的位移远大于观测的位移。然后，人们发现，从软粘土到软岩石的广泛范围的地质材料的共同点是，在应变小于约0.001%时的变形特性实际上是线性的和弹性的。也就是说，在实验室测试中，在该小应变水平下定义的杨氏模量在静态单调和循环加载测试以及动态测试中是相同的。此外，通过任何实验室测试精确确定的弹性杨氏模量可以非常接近从相应的现场剪切波速度测量确定的值。另一方面，由于现场载荷试验中应变水平大得多，因此，用传统的测压试验和平板载荷试验方法确定的现场刚度比弹性杨氏模量小得多。即，首先，从现场剪切波速度测量获得弹性杨氏模量（或剪切模量）。接下来，在相对大的应变水平下的刚度值从压力计测试获得。此外，从0.0001%的应变范围内的峰值（约10%）的连续的应力-应变关系是从一个精确的实验室单调加载试验（或测试）使用高品质的原状样品。必要时，进行循环加载试验。结合以上信息，估计作为应变的函数的刚度的场值。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