5:15 PM - 7:15 PM
[MIS20-P04] Evaluation test of strength and drilling resistance of soil simulating methane hydrate-bearing ground
Keywords:methane hydrate, simulated soil, unconfined compression test, drilling test
In order to develop drilling technology for shallow methane hydrate (MH), it is necessary to properly evaluate the strength of the ground containing MH. So far, in order to develop a drilling method using a large-diameter drill, drilling tests have been conducted in ground simulating MH containing ground to evaluate the strength of the simulated ground. The drilling tests were conducted in ice ground simulating 100% MH and soil-mixed ground simulating 20% MH, but the MH content of actual ground varies, and in order to develop drilling technology, it is necessary to evaluate the strength of the ground according to various MH content states.
In this study, unconfined compression tests were conducted on ice specimens simulating methane hydrate, and soil specimens containing layered or chunky ice in soil to which salt was added to prevent freezing even at low temperatures. As a result, it was found that the strength of ice was slightly higher than that of natural MH, and that when the ice content was low, the strength of the simulated soil was equivalent to that of clayey soil without ice. In addition, the strength of the simulated soil was about 1/50 of that of ice. This result was equivalent to the strength of actual sedimentary soil containing MH, and it was found that the strength of MH-containing ground can be evaluated by using the simulated soil. On the other hand, the difference in drilling resistance between ice ground simulating 100% MH and soil-mixed ground simulating 20% MH was only several times, and it became clear that compressive strength and drilling resistance do not necessarily correlate. Therefore, in order to evaluate the drilling resistance more accurately, a small-scale drilling test was conducted using the simulated soil. As a result, the drilling resistance of ice was several times higher than that of the simulated soil, and a similar trend was obtained as the previous results of the drilling test using the large-scale simulated soil. This suggests that the drilling resistance in real ground can be evaluated by conducting tests with a mechanism similar to that of actual MH excavation.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).
In this study, unconfined compression tests were conducted on ice specimens simulating methane hydrate, and soil specimens containing layered or chunky ice in soil to which salt was added to prevent freezing even at low temperatures. As a result, it was found that the strength of ice was slightly higher than that of natural MH, and that when the ice content was low, the strength of the simulated soil was equivalent to that of clayey soil without ice. In addition, the strength of the simulated soil was about 1/50 of that of ice. This result was equivalent to the strength of actual sedimentary soil containing MH, and it was found that the strength of MH-containing ground can be evaluated by using the simulated soil. On the other hand, the difference in drilling resistance between ice ground simulating 100% MH and soil-mixed ground simulating 20% MH was only several times, and it became clear that compressive strength and drilling resistance do not necessarily correlate. Therefore, in order to evaluate the drilling resistance more accurately, a small-scale drilling test was conducted using the simulated soil. As a result, the drilling resistance of ice was several times higher than that of the simulated soil, and a similar trend was obtained as the previous results of the drilling test using the large-scale simulated soil. This suggests that the drilling resistance in real ground can be evaluated by conducting tests with a mechanism similar to that of actual MH excavation.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).