A study on the mechanical properties of Neogene sedimentary rock; A particular reference to the effect of the geological process and the elapsed time on its mechanical properties after coring

Ishijima, Yoji*

Coring of rock from the strata induces various changes in the cored sample such as change from deoxidation circumstance to oxidation, change from water saturated condition to transpiration, change from virgin rock stress state to stress relieved condition etc. In accordance to these changes, rock suffers weathering, which in tern induces change of mechanical properties. This change could advance quickly in newly deposited sedimentary rock of relatively large porosity. From standpoint of development of underground for various purpose, it is important to know the in-situ mechanical properties of rock. This information is also important to give precise evaluation of rock stresses measured based on the overcoring method. First purpose of this study is to develop a measuring method which gives precise evaluation of strength and deformability of in-situ rock. For this, a measuring system has been developed to conduct the uniaxial compression test, in the field, by using light-weight loading apparatus for the specimen quickly prepared from the core. It has been proved that the test can be completed in less than 1 hour after the core is obtained. It has also been cleared that the values such as Young's modulus, compressive strength and tensile strength evaluated by the newly developed system are almost same as those obtained in the laboratory by using the servo-controlled testing machine. Second purpose of this study is to test two different methods to preserve the core: one is to wrap the grease-coated core by the polyethylene film and another is to keep the core in submerged condition. Compression tests have been conducted four times during three months. Neither the change of strength with elapsed time nor the difference of strength between the two storing conditions has been detected. This could be attributed to the fact that the sandstone that is used receives little weathering effect. Third purpose of this study is to investigate the influence of the geological ...