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

在地面已开挖的钻孔中受到爆炸荷载的情况下，井壁周围的土体会突然被压缩，然后在地面上形成一个空洞，被压缩的土墙包围。将这一思想应用到隧道或基础的施工中，可以用最少的堵塞和减少的衬砌来创造地下空间。在项目期限的第一年，我们研究了爆破引起的波在地面中的传播特性。确定了爆破可以有效扩孔，并建立了模拟地面冲击扩孔现象的程序。第二年，通过研究土的种类、含水率、钻孔初始直径等实验条件与波传播的关系，进一步讨论了波传播的细节特征。…用高速摄像机也观察到了更多的冲击性土壤压缩的NA。研究结果表明：1)地面波传播的衰减由土体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。对于类似粘土的压缩土，其内部衰减明显。2)在粉剂用量不变的情况下，虽然膨胀孔直径受初始直径的影响较大，但爆破压缩土域的体积受初始直径的影响不大。这意味着膨胀孔的直径可以通过孔的初始直径和粉剂的量来控制。3)虽然可以用每0.1ms拍摄一次的高速摄像机来监测爆破对土壤的冲击压缩现象，但爆破过程中产生的气体干扰了任何清晰的照片。一些解决这一问题的装置有望被开发出来，并根据研究结果做了技术报告。较少

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