红层地区城市地下空间膏盐富集层探测新方法——以成都市国际生物城为例

含膏盐岩体是红层地区城市地下空间利用过程中常见的不良地质体。提前获知基岩内膏盐富集地层的埋深及空间展布规律，对城市地下空间资源的开发利用以及地基承载力、持力层、基础选型等参数的确定具有重要的参考意义。本文以成都市天府新区国际生物城为研究区，选择了一种快速、无损、抗干扰能力强的全新瞬变电磁法——等值反磁通瞬变电磁法（OCTEM），对白垩系灌口组红层内膏盐富集层进行探测研究。首先根据研究区内不同地层的电阻率特征，建立了三层、四层、五层3种地电模型，分别进行OCTEM正演响应分析，结果表明该方法能够有效地识别出与围岩电阻率差异明显的膏盐富集层；然后对2 km²的试验区开展了网度为100 m×10 m的实测扫面工作，通过反演计算建立了研究区200 m以浅的三维电性结构，结合钻孔结果综合验证与分析，成功推断出膏盐富集层的空间展布形态，证明了该方法对红层地区城市地下空间膏盐富集层探测的有效性。

A new method for detecting gypsum mineral salt enriched layer of urban underground space in red bed area: A case study of Chengdu International Biological City

Gypsum mineral salt enriched layers are common bad geological body in the process of utilizing urban underground space in the red beds area. The detection of the burial depth and spatial distribution of gypsum-salt enriched strata in advance is of great significance for the development of urban underground space resources, the determination of foundation bearing capacity, bearing stratum and foundation type selection. Taking the International Biological City of Tianfu New District of Chengdu as the experimental area, the authors chose a fast, non-destructive and anti-jamming new transient electromagnetic method, opposing coils transient electromagnetic method (OCTEM), to detect and study the gypsum-salt enriched layer in red mudstone of Cretaceous Guankou Formation. Firstly, according to the resistivity characteristics of different strata in the study area, the authors established geoelectric models such as three-layer model, four-layer model and five-layer model, and carried out OCTEM forward response analysis for these models, respectively. The forwarding calculation shows that, with OCTEM method, the gypsum salt enriched layer can be effectively identified from surrounding rocks with obvious resistivity difference. Then, the authors took the practical measurement in the test area covered about two square kilometers, and swept the field with a network of 100m×10 m. Finally, the authors obtained the inversion results and established the three-dimensional electrical structure of strata in the depth greater than 200 m in the study area. With the comprehensive verification and analysis of drilling results, the spatial distribution pattern of gypsum mineral salt enriched layer was successfully inferred, which proves that this method is effective for the detection of gypsum-salt enrichment layer in urban underground space of the red bed area.