Seismic Subsidence of Loess Induced by a Short Delay Blasting

Abstract eng:
As viewed from concept, seismic subsidence of loess is an abrupt settlement of soil due to earthquake loading in non-saturated and low moisture conditions. In laboratory testing, it has been proved that seismic subsidence of loess is an existing thing. There is nothing, however, to discover a convictive proof of loess seismic subsidence in before investigations of seismic hazards, because an earthquake is always so far that not enough energy to destroy the microstructure of loess and to induce seismic subsidence in a flat loess field. Here the authors introduce a field testing to observe the characteristics of loess seismic subsidence at a loess site (Q3) by means of a series of explosion, or a short delay blasting, simulating an earthquake event. In order to understand the seismic subsidence of loess better, there are 140 observation points to be arranged in the testing field; at the same time, 4 observation points of different layer subsidence are placed near the center of the site, monitoring soil subsidence with the depth of 4m, 8m, 12m, and 16m respectively. Ground motion in the loess field caused by the explosions, otherwise, is recorded by 24 accelerographes. After the explosions, observation data shows that all points developed an obvious subsidence in the testing field. The maximum seismic subsidence of loess ground in testing site reaches 33mm approximately, and this point stands at the south of the field, whereas the maximum seismic subsidence of soils around the site attains to 26mm. It could be disclosed that, furthermore, just after explosion the seismic subsidence of loess is almost 50 percent to the maximum observation value of loess subsidence; that is to say, during the blasting process, seismic subsidence of loess increases rapidly. But in sequent stages, the development of loess subsidence becomes tardy and tardy. This development of seismic subsidence of loess fits an exponential function.

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