Fumio Sugimoto

Simulation Model for Spontaneous Combustion in Coal Seam by Coal Seam Gas Containing Oxygen

In order to clarify a phenomenon of spontaneous combustion in coal seam, we propose a simulation model based on two assumptions:(a) Coal powder, which exists in cracks of coal seam, is a heat source.(b) Coal seam gas is a supply source of oxygen to oxidize coal.In addition, we assume that the oxidative reaction of coal at normal temperature occurs mainly by volatile matter in coal, and that the calorific value of the coal powder is theoretically obtained from its combustion enthalpy. By using the proposed model, we simulate a process of spontaneous combustion in coal seam after mining coal.From the results of the simulation, we found that two conditions for igniting coal seam have to be satisfied if coal contains volatile matter of approximately 40% by weight. The conditions are as follows:(1) To ignite a coal powder layer of 1cm thickness, if coal seam gas contains an oxygen concentration of 1%, its flow rate is required to be 4-14cm/s.(2) The width of the crack filled with coal powder is more than 2cm.

The Charpy Impact Test of Rock (2nd Report)-Dynamic Fracture Toughness-

In this study, we investigated dynamic fracture toughness and crack propagation velocity of rocks by using Charpy impact test.The results of the experiments showed that crack propagation velocity of the rocks depends on impact energy applied to it, and Q (impact energy/crack propagation velocity) correlates with static strengths of the rocks. Also, the dynamic fracture toughness of the rocks, which is calculated from the dynamic fracture energy obtained by using Charpy impact test, was found to depend on the impact energy applied with it, and correlates with crack propagation velocity and static compression and tensile strengths of the rocks.

Shear Displacement Behavior of Rocks in Shear Fatigue Process. Experimental study on cyclic fatigue process of rocks under direct shear test (2nd Report).

In this study, the behavior of upper and lower (permanent) shear displacements was investigated with cyclic shear loading tests for two kinds of rocks. The behavior of shear displacement obtained in this study may be classified into two processes. In one process, shear displacement is induced mainly by the closure of pores and cracks, the deformation within grains and sliding. In the other one, it is induced mainly by the growth of cracks. In case of neglecting the effect of normal stress, the slope of the equation expressing the relationship between the minimum rate of upper shear displacement and the number of cyclic loading on log-log graph is -1.02 for Kimachi sandstone and -0.92 for Tohoku marble. It is -1.09 for Kimachi sandstone and -1.00 for Tohoku marble when the rate of lower shear displacement is minimum. Upper shear displacement where the rate of upper shear displacement increases rapidly corresponds to shear displacement at the peak shear stress in the convenient direct shear test. Similarly, lower shear displacement where the rate of lower shear displacement increases rapidly corresponds to the permanent shear displacement at the peak shear stress.

AE Monitoring for Estimating Shear Strength of Rock Mass

In in-situ block shear tests, shear stress-shear displacement curve, shear stress-normal displacement curve etc. are usually obtained. Because characteristic points in these curves are not always distinct except failure point, it is difficult to estimate shear strength of rock mass for designing rock structure only from these curves. From these points of view, it is attempted to estimate shear strength in both in-situ block shear test and laboratory direct shear test by monitoring AE (Acoustic Emission). Consequently, it is found that shear strength which is estimated by monitoring AE in in-situ block shear test takes a lower value, and shear strength estimated by monitoring AE in laboratory direct shear test takes a higher value than peak shear strength obtained in in-situ block shear test. Also, shear strength estimated by monitoring AE in in-situ block shear test shows a tendency to be nearly equal to residual shear strength obtained in laboratory direct shear test.