SGER: Geotechnical Site Characterization for Instrumented Excavation Sites

在本次SGER中，佐治亚理工学院（GT）将使用现场地震压电锥（SCPTu）和地震平板膨胀仪测试（SDMT）执行岩土场地表征程序，以捕获三个地点的地质地层、土壤特性和小应变刚度。两个地点包括西北大学校园的福特设计中心和芝加哥市中心的普伦蒂斯妇女医院的特殊仪器大型挖掘。第三个地点是位于密歇根湖西岸的国家岩土试验基地（NGES）。这些项目是与西北大学和伊利诺伊大学厄巴纳-香槟分校的美国国家科学基金会联合项目合作选定的，旨在开发新的综合工具，以预测、监测和控制与支撑挖掘施工相关的地面运动。自2002年9月以来，nuu - uiuc的活动集中在收集和分析芝加哥地区几个挖掘的详细现场性能数据，开发和评估跟踪挖掘进度的新方法，以及开发自动更新挖掘支持系统性能预测的数值技术。收集了块和活塞样品，使用内部安装的局部应变传感器进行实验室测试，以捕获软粘土的非线性应力-应变-强度行为。特别的优点是在数值方案中包含了小应变剪切模量（Gmax = G0）作为关键的初始状态参数，以便真实地模拟开挖周围土体内的诱发应变和应力。目前可用的商业软件包（例如，PLAXIS， CRISP， FLAC, SV-Solid）不包括任何内置算法来从初始基本G0刚度开始土区域的本构非线性应力-应变-强度曲线。然而，天然土壤沉积物和地层都起源于由其原位孔隙比（e0），垂直应力（svo），静水孔隙水压力（uo），侧向应力系数（K0）和小应变刚度（G0 = rT Vs2）指定的初始状态条件。虽然实验室测试（如共振柱和弯曲单元）可以提供G0的评估，但只能获得离散值，并且经常出现样品干扰问题。因此，需要现场土壤参数和性质，特别是通过计划的SCPTu和SDMT测深集和导出的剪切波速剖面进行地球物理测试。由于Evanston NGES位于附近，GT团队将在SDMT部署中校准新的真间距井下地震阵列，并使用NGES已有的标准化测试数据进行校准。在三个试验点中的每一个，将执行一系列3至6次SCPTu和SDMT探测，以优化数据场收集。根据先前的信息，这些地点的下面是沙子和/或填充物，上面覆盖着软粘土粉砂、较硬的粘土和土墩（Finno, 1989 GSP 23; 2000, GSP 93）。在选定的探测中，可以通过频繁的真间隔测量获得详细的横波剖面。与NU的Rich Finno教授和UIUC的Yousef Hashash教授合作，对相关参数(例如：g ? ?f', su， OCR, K0， E', Eu)将被评估为数值模拟的输入。就智能价值而言，预期目标包括使用混合测试（SCPTu和SDMT）优化特定地点的数据收集，该混合测试将穿透型探头与地球物理方法相结合，以确定一次探测中的多个测量结果。在NU-UIUC更新的有限元算法中，原位剪切波剖面将允许对土层应力-应变-强度曲线的初始部分使用小应变刚度。就更广泛的影响而言，该SGER旨在建立NU-UIUC-GT之间的合作努力，以实现一个完全集成的实验室和现场测试系统，数值有限元模拟，以及在施工期间受控挖掘中的嵌入式无线现场传感器的持续反馈。利用小应变刚度对于反映施工作业的真实预期响应是至关重要的。实验室测试和锥体/膨胀仪/剪切波测试的互补性，在挖掘和详细建模期间校准墙壁和支架的全尺寸现场性能，可以使美国未来的城市项目和基础设施重建受益。最后，在对北大和UIUC校园进行实地考察期间，GT团队将向研究生和感兴趣的人士展示原位技术。

In this SGER, a geotechnical site characterization program will be performed by Georgia Tech (GT) using in-situ seismic piezocone (SCPTu) and seismic flat plate dilatometer tests (SDMT) to capture the geostratigraphy, soil properties, and small-strain stiffness at three sites. Two sites involve specially-instrumented large excavations at the Ford Design Center on the Northwestern University campus and the Prentice Women's Hospital in downtown Chicago. The third site is the National Geotechnical Experimentation Site (NGES) on the western shore of Lake Michigan. These projects are selected in collaboration with a joint NSF project by Northwestern University (NU) and the University of Illinois at Urbana-Champaign (UIUC) to develop new integrated tools to predict, monitor and control ground movements associated with construction of supported excavations. Since September 2002, the NU-UIUC activities have focused on collecting and analyzing detailed field performance data at several excavations in the Chicago area, developing and evaluating new methods to track excavation progress, and developing numerical techniques to automatically update predictions of performance of the excavation support system. Block and piston samples have been collected for laboratory testing using internally-mounted local strain sensors to capture the nonlinear stress-strain-strength behavior of the soft clay soils. Of particular merit is the inclusion of the small-strain shear modulus (Gmax = G0) in the numerical scheme as a key initial state parameter in order to realistically model the induced strains and stresses within the soil mass surrounding the excavations. Current available commercial packages (e.g., PLAXIS, CRISP, FLAC, SV-Solid) do not include any built-in algorithms to start the constitutive nonlinear stress-strain-strength curves of the soil regions from the initial fundamental G0 stiffness. Yet, natural soil deposits and formations all originate from an initial state condition specified by their in-place void ratio (e0), vertical stress (svo), hydrostatic porewater pressure (uo), lateral stress coefficient (K0), and small-strain stiffness (G0 = rT Vs2). While laboratory tests such as resonant column and bender elements can provide evaluations of G0, only discrete values are obtained and sample disturbance issues often arise. Therefore, in-situ soil parameters and properties are desired, particularly using geophysical tests via the planned sets of SCPTu and SDMT soundings and derived shear wave velocity profiles. Since the Evanston NGES is located nearby, the GT team will calibrate their new true-interval downhole seismic array in a SDMT deployment with standardized test data already available and documented at the NGES. At each of the three test sites, a series of 3 to 6 SCPTu and SDMT soundings will be performed to optimize data field collection. Based on prior information, the sites are underlain by sand and/or fill overlying soft clayey silts, stiffer clays, and tills (Finno, 1989 GSP 23; 2000, GSP 93). At select soundings, detailed shear wave profiles can be obtained by frequent true-interval surveys. Working with Professor Rich Finno of NU and Professor Yousef Hashash of UIUC, the interpretation of relevant parameters ?e.g., g??f', su, OCR, K0, E', Eu) will be evaluated for input into the numerical modeling. In terms of Intellectual Merit, the intended goals involve the optimized collection of site-specific data using hybrid tests (SCPTu and SDMT) which combine penetration type probes with geophysical methods to ascertain multiple measurements in a single sounding. In-situ shear wave profiles will allow the utilization of small-strain stiffness for the initial portion of the stress-strain-strength curves of soil layers within the updated FEM algorithms by NU-UIUC. In terms of Broader Impacts, this SGER seeks to establish a collaborative effort between NU-UIUC-GT on a major initiative towards a fully-integrated system of laboratory and in-situ testing, numerical finite element simulation, and continued feedback from embedded-wireless field sensors within the controlled excavations during construction. The utilization of small-strain stiffness is paramount to reflecting the true anticipated response of the construction operations. The complementary nature of the laboratory testing and cone/dilatometer/shear wave testing in calibration with full-scale field performance of walls and supports during excavation and detailed modeling can benefit future urban projects and infrastructure redevelopments in the US. Finlaly, during field visits to the NU and UIUC campuses, the GT team will offer demonstrations of in-situ techniques to graduate students and interested parties.