Experimental Study On Detection And Identification Of Gas-rich Soil Layer

A large amount of biogas is present in the shallow soft soil layer in the southeast coast and the Yangtze River Delta of China.Because of its irregular distribution,it will have a serious impact on the construction of underground engineering.Therefore,it is necessary to accurately detect the distribution law of gas-rich soil layers and gas-bearing characteristics,and provide an important basis for engineering construction exhaust,thus ensuring construction safety.This shows that the shallow gas high precision test research work is of great significance.In this paper,physical simulation,numerical simulation and on-site comprehensive test research are carried out for the gas-rich soil layers.Based on the geological conditions of a subway construction in Hangzhou,the paper carries out physical simulation tests and analyzes the feasibility and effectiveness of resistivity method for testing gas-rich soil layers.Based on the field geological data,the geoelectric model is established by EarthImager2 D numerical simulation software.Numerical simulation of gas-bearing characteristics of gas-rich soil layers under different parameters was carried out.The results of physical simulation show that after the soil is rich in gas,the resistivity value increases and is mostly distributed in the range of 80~160 ?·m,which illustrates the feasibility of the experimental study.The numerical simulation results show that the electric field response characteristics of the gas-rich soil layer are obvious,which is characterized by high resistivity anomaly;the increase of the depth of the gas-rich soil layer and the decrease of the resistivity of the surrounding medium will cause the geoelectric field response characteristics to weaken;The electric field response characteristic of the soil layer with increasing gas content is more obvious.Based on the results of the simulation test,the comprehensive detection experiment of the rich gas layer is carried out by using the resistivity method in combination with the geological radar and seismic wave method to explore an effective method for testing shallow gas.The results of parallel electric survey show that the 3m electrode spacing test system is more suitable for this field test according to the test depth and accuracy requirements.The field electric field response characteristics of the rich gas-bearing soil layer are obvious,and the band-like and lenticular enrichment is mostly 15~25m.It has obvious high resistivity anomaly,and the resistivity value is mostly distributed in40~300?·m.There are many shallow gas suspected enrichment areas in the test area,which are mainly distributed in silt contains clay layer,sandy silt contains muddy silty clay layer and muddy silty clay layer with buried depth of 6~30m.In the geological radar test analysis,some gas-rich regions show obvious electromagnetic wave anomalies,which can correspond to electrical response characteristics.In the seismic wave test analysis,the seismic wave has a weak response to the rich gas region,but it has a good performance for the stratum resolving ability,and can clearly show the stratigraphic distribution,which corresponds to the geoelectric response characteristics.Combined with the analysis results of the three test methods and the results of the previous survey report,it is shown that the resistivity method is effective for the detection of rich gas layers.At present,due to the limitations of engineering site conditions and testing methods,the relevant experimental research content is not rich enough,such as more reasonable construction of physical models,more comprehensive numerical simulation and optimization of field test system,etc.Figure [51] Table [12] Reference [96]...