SGER: Geotechnical Site Characterization for Instrumented Excavation Sites

在本SGER中，佐治亚理工学院(GT)将使用现场地震压电锥(SCPTu)和地震平板膨胀仪试验(SDMT)执行岩土场地表征计划，以获取三个场地的地质地层、土壤特性和小应变刚度。有两处遗址涉及西北大学校区福特设计中心和芝加哥市中心的Prentice女子医院的特殊仪器大型挖掘。第三个地点是密歇根湖西岸的国家岩土工程试验场(NGES)。这些项目是与西北大学(NU)和伊利诺伊大学香槟分校(UIUC)的NSF联合项目合作选择的，目的是开发新的集成工具来预测、监测和控制与支撑挖掘施工相关的地面移动。自2002年9月以来，NU-UIUC的活动主要集中在收集和分析芝加哥地区几个挖掘现场的详细现场性能数据，开发和评估跟踪挖掘进度的新方法，以及开发数值技术来自动更新挖掘支持系统的性能预测。利用内部安装的局部应变传感器采集了块体和活塞样本用于实验室测试，以捕捉软粘土的非线性应力-应变-强度行为。特别值得注意的是，在数值方案中加入了小应变剪切模数(Gmax=G0)作为一个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导应变和应力。当前可用的商业软件(如PLAXIS、CRISP、FLAC、SV-Solid)不包括任何内置算法，以从初始基本G0刚度开始计算土体区域的本构非线性应力-应变-强度曲线。然而，天然土体和地层都起源于由其原地孔隙率(E0)、垂直应力(Svo)、静水孔压(Uo)、侧向应力系数(K0)和小应变刚度(g0=rt vs2)指定的初始状态。虽然共振柱和折弯器元件等实验室测试可以提供G0的评估，但只能获得离散值，而且经常会出现样品干扰问题。因此，需要现场的土壤参数和性质，特别是通过计划的SCPTU和SDMT测深和导出的剪切波速剖面进行地球物理测试。由于埃文斯顿NGE位于附近，GT团队将在SDMT部署中利用NGE已有的标准化测试数据和文件来校准他们新的真间隔井下地震阵列。在三个试验点中的每个试验点，将进行一系列3至6次SCPTU和SDMT探测，以优化数据现场收集。根据先前的信息，这些地点由沙子和/或填充物覆盖，上面覆盖着软粘土粉土、更硬的粘土和碎石(Finno，1989年GSP 23；2000，GSP 93)。在选定的测深处，可以通过频繁的真井距测量获得详细的横波剖面。与国立大学的Rich Finno教授和UIUC的Yousef Hashash教授合作，将评估相关参数的解释--例如g？？F‘、su、OCR、K0、E’、Eu)，以便输入到数值模拟中。就智力价值而言，预期目标包括使用混合测试(SCPTU和SDMT)优化收集特定地点的数据，这种测试将穿透型探头与地球物理方法相结合，以确定在一次探测中进行多项测量。在NU-UIUC更新的有限元算法中，原位剪切波剖面将允许将小应变刚度用于土层应力-应变-强度曲线的初始部分。在更广泛的影响方面，本SGER寻求在NU-UIUC-GT之间建立一个重大倡议的合作努力，以建立一个完全集成的系统，包括实验室和现场测试、数值有限元模拟以及施工期间控制挖掘内嵌入式无线现场传感器的持续反馈。小应变刚度的利用对于反映施工作业的真实预期反应至关重要。实验室测试和锥形/膨胀仪/剪切波测试在校准过程中与挖掘和详细建模期间墙和支撑的全尺寸现场性能相辅相成，可以为美国未来的城市项目和基础设施重建提供帮助。最后，在对南大和加州大学校园进行实地考察期间，GT团队将向研究生和感兴趣的各方提供现场技术演示。

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.