Objective Updating of Design Predictions for Supported Excavations Using Construction Monitoring Data

在城市环境中进行深开挖时的一个主要问题是与施工相关的地面运动对邻近建筑物和公用设施的影响。考虑到与移动预测相关的不确定性，通常包括监测程序来记录施工期间发生的地面移动。 理想情况下，这些记录的运动可以用于控制施工过程，并在施工早期阶段根据测量的变形更新运动预测。 然而，如果不是不可能的话，也是相当困难的，以足够及时的方式将观察到的运动用于这些目的，以用于对承包商来说时间至关重要的典型项目。 为了提高预测和控制与支护开挖相关的地面移动的最新技术水平，本项目开发了以下方法：（1）使用施工期间获得的监测数据客观地更新粘土中支护开挖变形的设计预测，以及（2）评估设计中性能预测的关键输入。 采用自动化过程，例如逆建模技术，其中通过迭代地改变模型输入值直到模拟输出值与测量数据匹配来校准给定模型。 这些程序将与有限元程序相结合，以自动更新对地面运动的预测。 客观措施的关键输入支持开挖的有限元分析提供定量信息的相对重要性的各种输入参数。 基础设施技术研究所提供了资金，以帮助支持这一努力。 该方法的开发和测试使用详细的地面和建筑物的运动数据从13米深的开挖通过软粘土的地铁改造项目在芝加哥。在Wiss，Janney，Elstner Associates通过芝加哥交通部的资助下，西北大学收集并分析了地铁开挖时的地面变形和邻近建筑物的运动。 由业主代表和岩土工程及结构设计师组成的咨询委员会通过定期审查工作进度为项目提供投入。 咨询委员会的成员还从他们的项目文件中提供详细的案例研究，用于检查最初根据芝加哥项目的数据开发的方法。

A major concern when performing deep excavations in urban environments is the impact of construction-related ground movements on adjacent buildings and utilities. Given the uncertainties associated with making movement predictions, it is usual to include a monitoring program to record the ground movements that develop during construction. Ideally, these recorded movements can be used to control the construction process and update predictions of movements given the measured deformations at early stages of constructions. However, it is quite difficult, if not impossible, to use the observed movements for these purposes in a timely enough fashion to be of use in a typical project where time is of the essence to a contractor. To improve the state-of-the-art of predicting and controlling ground movements associated with supported excavations, this project develops methods to (1) objectively update design predictions of deformations for supported excavations in clay using monitoring data obtained during construction, and (2) to evaluate critical inputs to performance predictions in design. Automated procedures, such as inverse modeling techniques, are adopted wherein a given model is calibrated by iteratively changing model input values until the simulated output values match the measured data. These procedures will be coupled with a finite element program to automatically update predictions of ground movements. Objective measures of the critical inputs to a finite element analysis of a supported excavation are developed to provide quantitative information concerning the relative importance of various input parameters. The Infrastructure Technology Institute has provided funding to help support this effort. The methodology is developed and tested using detailed ground and building movement data from a 13 m deep excavation through soft clays for a subway renovation project in Chicago. With funding from Wiss, Janney, Elstner Associates through the Chicago Department of Transportation, Northwestern University collected and analyzed ground deformations and adjacent building movements at the subway excavation. An advisory committee comprised of an owner's representative and geotechnical and structural designers provides input to the project via periodic reviews of the progress of the work. Members of the advisory committee also contribute detailed case studies from their project files that are used to check the methodology initially developed based on the data from the Chicago project.