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. We carried out some laboratory experiments and field ones, where small boreholes were expanded by blasting. The results of the experiments gave us some knowledge on the possibility of the underground space construction by this idea.