Static and Seismic Instrumentation of Soil Nails in a Complex Geologic Setting

土钉用于开挖和边坡的临时和更重要的永久性支撑的使用正在迅速增加，特别是用于公路拓宽项目。它是一项非常有吸引力的新技术，可以在各种应用和地质环境中提供临时和永久的开挖支护。然而，虽然经验总体上是相当积极的，但由于缺乏可验证的性能数据，土钉支护系统的设计水平落后了。当涉及到抗震设计时，这种情况尤其严重，因为地震事件很少，土钉技术相对较新。本研究项目的目的是在加州大学伯克利分校的混合岩石和崩积层的深基坑中测量土钉。该挖掘紧邻海沃德断裂带，距离活动断层迹200米以内。海沃德断层被认为是未来30年旧金山湾区最有可能发生6.7级地震的地方，而且小地震发生得非常频繁。该项目的目标是使用应变计和加速度计测量挖掘面的一部分和7个土钉的垂直阵列。土钉长度可达70英尺，每隔10英尺安装一对应变计（顶部和底部）进行测量。此外，双轴MEMS加速度计将安装在开挖面和仪器钉的嵌入端，以测量开挖面与岩体之间的地面运动差值。双轴加速度计将配对，在每个仪器位置提供3个运动轴，从而允许将地面运动分解为断层-正向，断层平行，垂直分量。除了这种电子仪器外，还将使用激光测量仪器对开挖工作面进行持续监测，测量开挖过程中和开挖完成后的开挖工作面变形情况。然后，组合数据将提供将观察到的变形与钉子中产生的载荷相关联的机会，并将观察到的性能与设计载荷进行比较。因此，这个地点提供了一个独特的机会来测量土钉和整个挖掘支撑系统在极端载荷下的反应。基坑工程的地震反应是岩土地震工程中主要的未解问题之一，因为该问题难以在实验室中进行测量，而且没有完整的现场记录数据。特别是，斜坡和挖掘附近的地面运动放大问题的理解非常少，并且基于非常有限的轶事和纯粹的分析证据。因此，关于这一主题的新数据对研究界来说应该是无价的。

The use of soil nails for temporary and, more importantly, permanent support of excavations and slopes is rapidly increasing, particularly for highway widening projects. It is a very attractive new technology for providing temporary and permanent excavation support in a variety of applications and geologic environments. However, while the experience has been generally quite positive, the state of art of design of the soil nail support systems has lagged behind due to a lack of verifiable performance data. This situation is particularly acute when it comes to seismic design, since seismic events are rare and the soil nail technology is relatively new.The aim of this research project is to instrument soil nails in a deep excavation in mixed rock and colluvium on the Campus of the University of California, Berkeley. The excavation is immediately adjacent to the Hayward Fault zone and within 200 m of the active fault trace. The Hayward Fault has been assigned the highest probability of generating an earthquake with magnitude 6.7 in the next 30 years in the San Francisco Bay Area, and small events occur very frequently.The objective of the project is to instrument a section of the excavation face and a vertical array of 7 soil nails using strain gauges and accelerometers. The soil nails, up to 70 feet in length, will be instrumented with paired strained gauges (top and bottom) installed every 10 feet along the length of the soil nail. In addition, dual axis MEMS accelerometers will be installed at the face of the excavation and at the embedded end of the instrumented nails in order to measure the difference in ground motions between the excavation face and the rock mass at depth. The dual axis accelerometers will be paired to provide 3 axes of motion at each instrument location, thus allowing the resolution of the ground motions into fault-normal, fault-parallel, vertical components. In addition to this electronic instrumentation, the excavation face will be continuously monitored with laser surveying instruments to measure the excavation face deformation during excavation and following its completion. The combined data will then provide the opportunity to correlate observed deformations with the loads developed in the nails and to compare the observed performance with the design loads.Thus, this site provides a unique opportunity to measure the response of the soil nails and the entire excavation support system under extreme loading. The seismic response of excavations is one the major unanswered questions in geotechnical earthquake engineering because the problem is difficult to scale in a laboratory, and the well documented field data does not exist. In particular, the issue of amplification of ground motions in the vicinity of slopes and excavations is very poorly understood, and based on very limited anecdotal and purely analytical evidence. Hence, new data on this topic should prove invaluable to the research community.