Development of a Free-Field Soil Stress Gage for Static and Dynamic Measurements

摘要

The report describes the development of three free-field stress gage types. One gage design, the sand dollar gage, was abandoned early in the investigation, while the other two, the W and SE gages, were subjected to various evaluation tests. Static and dynamic tests in sand and clay were conducted in the Small Blast Load Generator (SBLG). The gages have been used in the laboratory evaluation of a cold gas loader and in two field tests. Evaluation of the performance of the gages in these tests is presented in Appendix A. The gage placement techniques used in the SBLG tests are described in Appendix B. The gages are rugged and relatively easy to place in the laboratory. They may be used for both static and dynamic measurements and have a linear pressure range from 1 to above 1,800 psi. The gages have very low acceleration sensitivity and hysteresis, and have excellent dynamic response capability. Their temperature sensitivity is such that it will be of little consequence in dynamic tests and can be corrected for in long-term static tests. Electrical sensitivity remains essentially constant from -30 to 150F. Of the two gage types discussed, the SE gage is recommended for use. It is much easier to place, is more rugged, and produces a cleaner dynamic signal than the W gage. The gages can be calibrated to compensate for registration errors due to differences in soil and gage modulus; however, gage registration was found to be a function of placement method, depth of burial, input pressure, and conditions of the medium, not simply of modulus ratio. (Author)