Practical Approach of the Underground Space Construction by Explosive Loading in a Borehole

在地下已开挖的钻孔中施加爆炸载荷时，钻孔壁周围的土壤会被突然压缩，在地面上形成一个空腔，被压缩的土壁包围。当我们将这一理念应用于隧道或地基的建设时，可以用最少的淤泥和减少的衬砌来创造地下空间。在项目的第一年，我们研究了由于爆破引起的波在地面上的传播特性。通过对爆破扩孔效果的验证，建立了模拟冲击扩孔现象的程序。第二年，通过研究波浪传播与土壤种类、含水量、钻孔初始直径等实验条件的关系，对波浪传播的详细特征进行了探讨。高速摄像机还观察到更多的冲击土压缩现象。通过研究得到以下结果：1)波在地下传播的衰减由土壤压缩引起的内部衰减和二维波传播引起的空间衰减两部分组成。黏土等压缩性土的内部衰减明显。(2)爆破后扩孔直径受初始直径影响较大，但在粉量一定的情况下，爆破压缩土域体积受初始直径影响不大。这意味着扩大钻孔的直径可以由钻孔的初始直径和粉末的量来控制。3)高速摄像机每0.1 ms拍摄一张照片，虽然可以对爆破对土体的冲击压缩现象进行监测，但爆破过程中产生的气体会干扰任何清晰的照片。一些克服这一问题的装置有望被开发出来。研究结果作了一份技术报告。少

In the case that an explosive load is subjected in a borehole which has been excavated in the ground, the soil around the borehole wall will be abruptly compressed and then a cavity will be created in the ground, being surrounded by the compressed soil wall. When we apply this idea to the construction of tunnels or foundations, the underground space can be created with the minimum mucking and the reduced lining.In the first year of the project term, we investigated the characteristics of the wave propagation in the ground due to the blasting. We confirmed that the borehole can effectively be expanded by blasting and then built the code to simulate the phenomena of the impact expansion in the ground. In the second year, the detail characteristics of the wave propagation was discussed in succession by investigating the relationship among the wave propagation and other experimental conditions such as the sort and water content of soil and the initial diameter of borehole, etc. The phenome … More na of the impact soil compression were also observed with a high-speed camera. The following results have been obtained through the research.1)The attenuation of the wave propagating in the ground is composed with both of the internal attenuation due to the soil compression and the spatial one due to the two-dimensional wave propagation. The internal attenuation is remarkably observed for the compressive soil like clay.2)Although the diameter of the expanded boreholes was much affected by their initial diameter, the volume of the soil domain compressed by the blasting was not much affected by the initial diameter when the amount of the powder is constant. It means that the diameter of the expanded borehole can be controlled by the initial diameter of the borehole and the amount of the powder.3)Although the phenomena of the impact compression of the soil by blasting can be monitored with a high-speed camera which can take a photograph every 0.1 ms, the gas inducted during blasting disturbs any clear photograph. Some devices to overcome this problem are expected to be develop.A technical report was made with the results of the research. Less