Central project of the researchers group FOR 1136 with demonstrator experiments

在中心项目第二阶段，将进行实验室试验，作为岩土边界值问题数值模拟的基准。这些测试适用于合作伙伴的每个子项目（TP）。在项目第二阶段，已经完成了有关测试方法的重要前期工作，特别是涉及密封概念、应力测量和数字图像相关（DIC）。界面测试盒的主要部分是一个仪器化的壁，分为四个部分，可以相对于相邻的砂体移动。在该试验配置中，可以在平面应变条件下观察砂与具有不同表面粗糙度的结构（桩、墙）之间的接触区。各种配置的壁段允许调查的发展的表面摩擦和桩状结构的端部阻力。在试验箱的两侧，通过玻璃窗可以观察到土壤和墙壁的位移，以便使用数字图像相关技术（DIC）评估土壤变形。后处理软件的几项改进现在允许对测试结果进行定量而不仅仅是定性解释。现有试验箱的结构和仪器也得到了扩展和升级。现在可以进行循环测试，除了壁段上的切向应力外，还可以捕获法向压力。这是对试验进行定量评估和与模拟进行比较的一个重要要求。由于这些改进，计划在第二阶段进行进一步的、主要是周期性的接口试验箱试验。硕士和学士学位论文将被用来给学生的机会，在这个主题介绍作为学生助理后，工作在这个问题上。在第二阶段的中心项目的主要任务将是在饱和土壤中的测试。振动箱试验的结果显示了饱和土壤在正弦基础激励下的行为，这些结果已经准备好供项目合作伙伴进行模拟。在第二阶段，计划进行额外的桩基试验，但大多数试验将集中在饱和土壤中的桩贯入度上。因此，一个新的测试箱准静态（单调/循环）和动态测试，以下的旋转对称空腔膨胀的想法，正在建设中。将在该新试验箱中进行准静态（单调/循环）和动态试验。在土体中，孔隙水压力和总应力的演变将被捕获。将研究由基底和表层引起的桩力。对于饱和，干的雨洪砂体将被抽空到非常低的压力水平。这一程序在小样本上进行了试验，并将被转移到更大的规模上，特别注意确定土体的初始状态（密度分布和初始应力）。在砂土充填过程中，将捕获应力，并将DIC应用于评估土壤变形。中心项目的另一个主题是TP 1和TP 2中开发的本构律的参数估计。这些参数将用于其他子项目中，对已完成的实验室试验和边界值问题进行数值模拟。

In project phase II of the central project laboratory tests will be performed as a benchmark for numerical modelling of geotechnical boundary value problems. These tests are adapted for each subproject (TP) of the collaborating partners. In project phase II important preliminary work concerning the test methods has been performed, especially dealing with the sealing concept, the stress measurement and the Digital Image Correlation (DIC).The main part of the interface-test-box is an instrumented wall, divided into four segments, which can be moved relative to an adjacent sand body. In this test configuration the contact zone between sand and structures (piles, walls) with different surface roughnesses can be observed under plane strain conditions. Various configurations of the wall segments allow the investigation of the development of skin friction and tip resistance of pile-like structures. On both sides of the testbox the displacements of soil and wall are observable through glass windows for the evaluation of the soil deformations with the Digital Image Correlation technique (DIC). Several improvements of the post-processing software allow now a quantitative and not only a qualitative interpretation of the test results. Also the construction and the instrumentation of the existing test-box was extended and upgraded. Cyclic tests can now be performed and in addition to the tangential stresses on the wall segments the normal pressures can be captured. This turned out to be an important requirement for quantitative evaluation of the tests and comparisons with simulations.Due to these improvements, further, mainly cyclic, tests in the interface-test-box are planned for the second phase. Master and bachelor theses will be used to give students the opportunity to work on this subject after being introduced in the topic as student assistants.The major task of the central project in the second phase will be the tests in saturated soil. The results of shake-box tests showing the behaviour of saturated soil under sinusoidal base excitation have been prepared for simulations of the project partners. In the second phase additional shakebox tests are planned, but the majority of the tests will focus on the pile penetration in saturated soils. Therefore a new test-box for quasi-static (monotonic/cyclic) and dynamic tests, following the ideas of the rotationally symmetric cavity expansion, is under construction. Quasi-static (monotonic/cyclic) and dynamic tests in this new test-box will be performed. In the soil body the evolution of the pore water pressure and the total stresses will be captured. The pile forces resulting from base and skin will be investigated. For the saturation the dry pluviated sand body will be evacuated to a very low pressure level. This procedure was tested on small samples and will be transferred to the larger scale.Particular attention is paid to the determination of the initial state (density distribution and initial stresses) of the soil mass. During the sand pluviation the stresses will be captured and DIC will be applied to evaluate the soil deformations. Another topic of the central project is the parameter estimation for the constitutive laws developed in TP1 and TP2. These parameters will be used in the other subprojects for numerical simulations of the performed laboratory tests and boundary value problems.