Optimization of gas explosion subsoiling parameters based on soil fissure trace equation and soil disturbance model

Abstract: Soil subsoiling is currently the most widely used method for soil loosening, which can break the hard bottom of soil. At present, soil subsoiling operations mainly use shovel subsoiler, which has common problems like poor subsoiling effect, uneven soil disturbance and high energy consumption. In this context, a new subsoiling technology, gas explosion subsoiling, is studied in this paper, which injects high pressure gas into the soil to cause fissures, thereby breaking the bottom soil and achieving the purpose of subsoiling. In order to clarify the subsoiling effect of gas explosion on soil, an orthogonal test with the gas explosion parameters like pressure, depth and volume was designed. The soil block used in test was in standard size of 100 cm × 50 cm (diameter × height). The soil fissures and disturbance situation on the soil section were observed through the cross-sectional treatment method, and the influence of gas explosion parameters on soil fissure extension was analyzed. Then, the soil fissure trace equation and soil disturbance model were established based on the 9 orthogonal test results calculated by OriginPro software and Auto2Fit software. The effect of soil damage form on the impact of soil subsoiling was discussed based on Mohr-Coulomb soil strength theory and Rankine's earth pressure theory. The orthogonal experiment results showed that the greater the gas explosion pressure, the deeper the gas explosion depth; the more the gas volume, the better the soil subsoiling effect. The soil fissure trace equation was a quadratic function and the soil disturbance area was parabolic. This research provided a model and method for studying the soil fissure trace equation, and the soil hardness in the equation could be used as a variable for the soil type, so the soil fissure trace equation was applicable to most types of soils. The soil was mainly subjected to pulling damage when the gas explosion depth was less than 25 cm, the soil surface tended to rise at the gas splitting force of 0.17 MPa and the disturbance coefficient of 50%, and the center of soil fissure was the gas explosion center. The soil was mainly subjected to shear damage when the gas explosion depth was more than 25 cm, the soil surface elevation was not obvious at the gas splitting force of 0.39 MPa and the soil disturbance coefficient of more than 50%, and meanwhile the center of soil fissure moved downward, and the downward displacement increased with the increase of gas explosion pressure. What was more, the effect of shear damage on soil subsoiling was better than that of pulling damage. Therefore, soil shear damage should occur as much as possible in design of gas explosion technological parameters, which played a significant role in promoting the expansion of soil fissures and increasing the degree of soil loosening. When the gas explosion depth was 25 cm, the soil damage would be the joint action of pulling and shear, and the degrees of these 2 kinds of damages were equivalent, which was conducive to the horizontal expansion of soil fissures. In addition, the gas explosion pressure was not as high as possible, and higher pressure gas source had a higher technical requirement on gas storage and booster device, and also a longer time for gas collection, which was not conducive to long-term working operation. The data optimization results showed that 1 MPa gas explosion pressure and 30 cm gas explosion depth were more appropriate, and under the condition the soil subsoiling effect was remarkable with the soil disturbance coefficient of 79.5%. The results can provide theoretical basis for the optimization of gas explosion subsoiling parameters.