掘削に伴つて変動する岩盤内応力の新しい測定法について
圧力セルを用いた地圧変化測定法に関する研究 (第1報)
1987 年 103 巻 1195 号 p. 543-547
詳細
1987 年 103 巻 1195 号 p. 543-547
Determination of in-situ stress change in rock mass during excavations is most important for security of underground constructions or mining excavations. However, monitoring of displacement or strains is mainly conducted for the purpose because there is not a simple and reliable method for measuring the change of in-situ stresses especially for the wide range of rock masses.
In this paper, a new method is proposed for measuring two-dimensional change of in-situ stresses, and the results of laboratory tests under both uniaxial and biaxial compression are described.
The new method uses a cylindrical pressure cell with eight strain gauges glued tothe inner wall of thecell, which is inserted in a borehole with non-contraction type of grouting material. A special merit of this method lies in the internal pressure test, which is carried out prior to the measurement of in-situ stress change, using the measuring instrument itself in order to know the mechanical interaction between the measuring system and the rock mass. Utilizing the information on the deformation modulus of the rock mass obtained in the internal pressure test, two-dimensional change of in-situ stresses in the rock mass is measured with least squares method on the circumferential strain distribution around the inner wall ofthe pressure cell as in equation (12).
Results of laboratory tests both in uniaxial compression and in biaxial compression are summarized in Tables 1 and 2, respectively. These results are almost satisfactory from the practical view point. However, non-linearity between compressive strains and applied stress at the lower levels of stress and poor increase of tensile strains at the larger levels of stress lower the precision of the predicted stresses. Although these points could be improved by increasing initial internal pressure as in the in-situ measurements, it is still necessary to conduct a systematic investigationon the mechanical properties of various grouting materials in order to choose the most suitable one.
