关于在土层中进行钻孔应变观测的可行性问题

DISCUSSION ON FEASIBILITY OF BOREHOLE STRAIN OBSERVATION IN SOIL

在土层中开展钻孔应变观测实验是地球动力学以及地震预报研究的需要。能否观测到固体潮对该实验的成功与否起决定作用。土层与岩层的主要区别是其疏松性。由此造成的压密永久变形问题,可以通过在适当深处以下安装探头来解决。同时,因为土在小变形动态载荷下呈现弹性,而固体潮应变变化量级为10-8左右,所以探头并不需要安装在太深的地方。理论分析的结果是,虽然钻孔应变仪在土层中观测应变变化的灵敏度小于岩层,但是因为在相同的应力下,土层弹性变形比岩层大得多,所以在整体效果上是有利于在土层中观测到固体潮的。孔隙水的变化会给钻孔应变观测带来严重干扰,钻孔应变探头的深度应该避开地下水位变动范围。如何能在土层中观测到固体潮,最终需要通过实验来说明。

Tests for observing strain changes in soil with borehole strainmeters are needed in researches of earthquake forecast as well as geodynamics. The observation ognized. The difference of observation in soil from in rocks can be testified if solid earth tides will be clearly reclies on the looseness of the medium. Therefore, the strainmeter should be placed significantly deeper in order to solve the problem of permanent deformation. Meanwhile, since soil responds elastically to small dynamic deformation, and the tides of strain are on the order of 10^-8, the placement may not be necessarily very deep. Results of theoretic analysis indicate that, although resolution of borehole strainmeter for observation in soil is lower than in rocks, soil deforms much larger than rocks for same stress changes will benefit the observation of tides in soil Existence of pore liquid will bring about disturbance to borehole strain observation and the sensor should be placed beyond the depth close to water table. It will eventually be checked through practical tests. Whether the present borehole strainmeters can record earth tides.