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

使用土钉作为开挖和斜坡的临时和更重要的永久支撑的情况正在迅速增加，特别是在公路拓宽项目中。 它是一种非常有吸引力的新技术，可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，虽然经验一般是相当积极的，由于缺乏可验证的性能数据，土钉支护系统的设计技术水平已经落后。 这种情况是特别严重的，当涉及到抗震设计，因为地震事件是罕见的，土钉技术是相对较新的，本研究项目的目的是仪器土钉在深基坑混合岩石和崩积层校园的加州大学伯克利分校。 开挖紧邻海沃德断层带，距离活动断层痕迹200 m以内。 海沃德断层被认为是未来30年内在旧金山弗朗西斯科湾区发生6.7级地震的最高可能性，并且小事件发生非常频繁。该项目的目标是使用应变计和加速度计对开挖面的一部分和7个土钉的垂直阵列进行测量。 最长为70英尺的土钉将配备成对的应变仪（顶部和底部），沿土钉长度沿着每10英尺安装一个应变仪。 此外，双轴MEMS加速度计将安装在开挖面和仪器钉的嵌入端，以测量开挖面和岩体深度之间的地面运动差异。 双轴加速度计将配对，以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常、断层平行和垂直分量。 除此电子仪器外，还将使用激光测量仪器对开挖面进行持续监测，以测量开挖期间和完工后的开挖面变形。 综合数据可将观测到的变形与土钉产生的荷载相关联，并将观测到的性能与设计荷载进行比较。因此，该工地提供了一个独特的机会，可以测量土钉和整个开挖支护系统在极端荷载下的响应。 基坑的地震反应是岩土地震工程中一个主要的未解决的问题，因为这个问题很难在实验室中进行标定，并且没有有据可查的现场数据。 特别是，在斜坡和开挖附近的地面运动放大的问题是非常不了解，并根据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.