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

如果在地面上挖掘的钻孔中承受爆炸载荷，钻孔壁周围的土壤将突然压缩，然后在地面上产生一个空腔，被压缩的土壤壁包围。当我们将这一思想应用于隧道或基础的施工时，可以用最少的出碴量和减少的衬砌来创造地下空间。在项目期的第一年，我们研究了由于爆破引起的波在地面中的传播特性。在证实了爆破扩孔的有效性的基础上，建立了模拟冲击扩孔现象的程序。第二年，通过对土的种类、含水量、初始孔径等试验条件与波传播的关系的研究，探讨了波传播的具体特征， 关于我们 用高速摄影机观察了冲击土压缩的NA。研究结果表明：（1）波在地下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共同组成。2）初始直径对扩孔孔径影响较大，但当药量一定时，初始直径对扩孔后土体压缩体积影响不大。这意味着可以通过钻孔的初始直径和粉末的量来控制扩大的钻孔的直径。3）虽然通过爆破对土壤的冲击压缩现象可以用高速照相机（其可以每0.1ms拍摄一张照片）来监测，但是在爆破期间引入的气体干扰任何清晰的照片。希望能研制出一些解决这一问题的装置，并将研究结果作了技术报告。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