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

土钉用于临时和更重要的挖掘和斜坡的永久支撑的使用正在迅速增加，特别是在高速公路拓宽项目中。它是一种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撑。然而，虽然经验总体上是相当积极的，但由于缺乏可核实的性能数据，土钉支撑系统的设计水平一直落后。在抗震设计方面，这种情况尤其严重，因为地震事件很少发生，而且土钉技术相对较新。本研究项目的目的是在加州大学伯克利分校校园内的混合岩石和崩塌地层中进行深挖土钉测试。开挖工程紧邻海沃德断裂带，距离活动断裂带不到200米。海沃德断层被认为是旧金山湾区未来30年内最有可能发生6.7级地震的地区，而且小地震经常发生。该项目的目标是使用应变计和加速计测量一段挖掘面和一组由7个土钉组成的垂直阵列。长达70英尺的土钉将安装成对应变计(顶部和底部)，沿土钉的长度每隔10英尺安装一次。此外，双轴MEMS加速度计将安装在开挖工作面和仪表钉的嵌入端，以测量开挖工作面和深部岩体之间的地面运动差异。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辨为断层正常、断层平行的垂直分量。除了这种电子仪器外，还将利用激光测量仪器对开挖工作面进行连续监测，以测量开挖过程中和完成后的开挖工作面变形。合并后的数据将提供机会将观测到的变形与钉子中产生的荷载相关联，并将观测到的性能与设计荷载进行比较。因此，该场地提供了一个独特的机会来测量土钉和整个开挖支撑系统在极端荷载下的反应。开挖的地震反应是岩土地震工程中尚未解决的主要问题之一，这是因为这一问题在实验室中很难衡量，而且缺乏良好的现场记录数据。特别是，人们对斜坡和挖掘附近的地面运动放大问题知之甚少，而且是基于非常有限的轶事和纯粹的分析性证据。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.