试验反压对深海能源土宏观力学特性影响的离散元分析

Influence of back pressure on macro-mechanical properties of methane hydrate soils by DEM analyses

在饱和土体三轴试验中,反压常被用于提高试样饱和度,其对常规土体强度特性无影响已广为认同,而已有试验资料表明反压对深海能源土强度、弹性模量等宏观力学参数均存在一定影响,成为困扰国际岩土界的一个难题。首先探讨了试验反压对能源土力学特性的影响机理,通过引入能源土微观接触模型的离散元双轴试验检验上述机理的合理性;然后结合20组离散元双轴试验,进一步探究能源土宏观力学特性随反压的变化规律。结果表明:试验反压对能源土力学特性的影响与水合物作用相关;反压能提高能源土强度,使应变软化和剪胀特性更加明显,并对其弹性参数有一定的影响;试验反压较大时,反压变化对能源土强度参数的影响难以忽略,但对弹性参数的影响可忽略。

Back pressure is extensively applied in triaxial tests to improve sample saturation and has been identified irrelevant to the strength of saturated soils. However, the influence of back pressure on macro-mechanical properties of methane hydrate soils has been shown by other researchers. This paper aims to further investigate the geotechnical paradox. Firstly, the mechanism of the back pressure effect on mechanical properties of methane hydrate soils is studied according to its microstructure. Secondly, DEM biaxial tests incorporating the micro contact model of methane hydrate soils are performed to examine the proposed mechanism. Finally, 20 DEM biaxial tests are simulated to discuss the specific influence of back pressure on macro-mechanical properties of methane hydrate soils. The results show that the influence of back pressure is related to the properties of methane hydrate. The back pressure improves the shear strength, increases the tendency of strain softening, and dilatancy and affects the elastic parameters of methane hydrate soils. In addition, when the back pressure is high, the influence on strength parameters can not be ignored while the influence on elastic parameters of methane hydrate soils is negligible.