The measurement of underground medium variation using a repeated artificial source has gradually become an important goal to pursue. In recent years,we have developed and improved a technology system with large capacity airguns excited in land reservoirs by transplanting marine seismic exploration technology. The excitation effect has a close relationship to airgun capacity,water environment,and excitation conditions. In view that large capacity airgun must be excited without a water environment,we expand the system to use in downhole. Based on the BHS-2200 LL downhole airgun with a capacity of250in3,this paper carries out a comparative analysis on the characteristics of an airgun source excited in 0. 2m- and 5. 0m-diameter wells,and the results show that:( 1) The dominant frequency of the airgun signal excited in a 5. 0m well is mainly from 10 Hz to40Hz,lower than that in a 0. 2m well,and the larger body of water is good for bubble oscillation.( 2) In terms of exciting energy,the signal excited in a 5. 0m well has stronger energy than in a 0. 2m well,with a difference of 1 order in magnitude,and the signal can be detected up to 9km excited in a 5. 0m well with a single shot.( 3) The airgun signal has good repeatability in both excitation wells. The downhole airgun excitation technology system has potential application in dynamic monitoring near a fault zone with a small scale range, exploration of oil and mineral resources, and modern urban geophysical environment.
Yang WeiWang BaoshanLiu ZhengyiYang JunLi XiaobinChen Yong
为有效评价青荣城际铁路桃村跨线断裂带的地基稳定性,提出采用断层测龄、地基加固处理和路基沉降变形监测等技术,来保障铁路工程设计建设。通过对桃村断层泥中石英形貌测龄和宏观特征研究,判断其最晚活动时间分布在更新世早、中期,是非活动断层。采用强夯施工对断裂带地基进行加固处理,检测结果显示,1 200 k N·m的强夯夯击能明显提高断裂带5 m以内地基的压实程度和力学性能,消除跨线断裂带地基的不均匀沉降。对跨线断裂带上路基沉降变形的长期监控结果表明,断裂带线下工程的沉降趋于稳定,具备铺轨条件。
