Central project of the researchers group FOR 1136 with demonstrator experiments

在中央项目的项目第二期，将进行实验室测试，作为岩土工程边界值问题数值模拟的基准。这些测试适用于协作伙伴的每个子项目（TP）。在二期工程中，对测试方法进行了重要的前期工作，特别是密封概念、应力测量和数字图像相关（DIC）。接口测试箱的主要部分是一个仪器化的管壁，分为四个段，可以相对于相邻的砂体移动。在此试验配置中，可以观察到在平面应变条件下，砂与不同表面粗糙度的结构（桩、墙）之间的接触区。墙段的各种配置允许研究类桩结构的表面摩擦和顶端阻力的发展。试验箱两侧通过玻璃窗观测土体和墙体的位移，利用数字图像相关技术（DIC）对土体变形进行评价。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的解释。同时对现有测试箱的结构和仪器进行了扩展和升级。现在可以进行循环测试，除了壁段上的切向应力外，还可以捕获正常压力。事实证明，这是对测试进行定量评估并与模拟进行比较的重要要求。由于这些改进，进一步地，主要是循环的，在第二阶段计划在接口测试盒中进行测试。硕士和学士学位论文将被用来让学生在作为学生助理被介绍到这个主题之后，有机会研究这个主题。二期中心工程的主要任务是饱和土试验。振动箱试验的结果显示了饱和土在正弦基底激励下的行为，并为项目伙伴的模拟准备。在第二阶段，计划进行额外的振动箱试验，但大多数试验将集中在饱和土中的桩突。因此，一个新的准静态（单调/循环）和动态试验箱，遵循旋转对称腔膨胀的思想，正在建设中。准静态（单调/循环）和动态测试将在这个新的测试箱中进行。在土体中捕捉孔隙水压力和总应力的演变过程。桩基和桩皮所产生的桩力将被研究。在饱和状态下，干燥的雨淋砂体将被抽离到一个很低的压力水平。该程序在小样本上进行了测试，并将转移到更大规模。特别注意的是确定土体的初始状态（密度分布和初始应力）。泥沙淤积过程中的应力将被捕获，DIC将被用于评估土壤的变形。中心项目的另一个主题是在TP1和TP2中开发的本构律的参数估计。这些参数将在其他子项目中用于对已进行的实验室试验和边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.