基于电阻率法的沿海地区浅表富气土层含气特征探测试验分析

Experimental analysis on gas-bearing characteristics detection of shallow gas-rich soil layer in coastal area based on resistivity method

我国东南沿海及长江三角洲地区浅部软土层中赋存大量生物质气体,给地下工程建设带来严重影响。为查明其分布和响应特征,通过数值模拟方法构建地电模型,对不同条件下富气土层的含气特征进行模拟,并基于模拟结果在杭州某地进行现场探测验证。结果表明,土层富气后地电场响应特征明显,表现为高电阻率异常,随富气土层所在深度增大其地电场响应特征变弱。试验场地存在多处浅层气疑似富集区,电阻率一般分布在40~300Ω·m间,以15~25 m长带状、透镜状富集在埋深6~30 m的粉砂夹黏土层、砂质粉土夹淤泥质粉质黏土层以及淤泥质粉质黏土夹粉土层中。采用电阻率法对富气土层含气特征探测具有一定的可行性,可为工程探查气层分布、气层评价等研究提供依据。

There are a lot of biomass gases in the shallow soft soil layer along the southeastern coast of China and the Yangtze River Delta region,which have a serious impact on underground engineering construction.In order to find out its distribution and response characteristics,the geoelectric model was constructed by numerical simulation method to simulate the gas-bearing characteristics of gas-rich soil under different conditions.Based on the simulation results,field detection and verification were carried out in a certain place in Hangzhou.The results showed that the response characteristics of geoelectric field were obvious after the soil layer was rich in gas,showing high resistivity anomaly,and which became weaker with the increase of depth of gas-rich soil layer.There were several suspected enrichment areas of shallow gases in the test site,and the resistivity values were mostly distributed in the range of 40~300Ω·m.It was enriched in the silty sand interbedded clay layer,the sandy silt interbedded muddy silty clay layer and muddy silty clay layer interbedded silty clay layer in the depth of 6~30 m in the shape of 15~25 m bands and lenses.It was feasible to use resistivity method to detect the gas-rich soil layer,which could provide the basis for the engineering exploration of gas layer distribution and evaluation effect.