美国地质工程assignment作业：mapping of the extent of quick clay deposits by 2D electrical resistivity tomography (ERT) was demonstrated
In this article, the accurate mapping of the extent of quick clay deposits by 2D electrical resistivity tomography (ERT) was demonstrated. As highly sensitive marine clay, quick clay needs to be mapped in detail since it is regarded as an indicator for geo-hazards. Nevertheless, it has been proved that small resistivity contrast near large anomalies cannot be resolved by conventional ERT methods. Therefore, constraints were involved in theinversion of ERT data to achieve delineation of quick clay extent. The experimental results revealed that this constrained inversion models exhibit sharper resistivity contrasts and enhanced consistence with the results ofin situ measurements.
1. Synthetic method合成方法
快速粘土网站综合模型。该模型用于具有不同电阻率的几个地质单元。在地表附近，三导电体ofmarineclay（ρ= 3Ω•m）被放置在一个ρ= 50的Ω•M.片麻岩电阻的背景（ρ= 1000Ω•m），在35–45米深处的bedrocklies。此外，海洋粘土深体（ρ= 3Ω•m）的基岩之上是位于模型的中心部分。As an illustration of theapplication of ERT investigationsin quick clay mapping, a synthetic model resembling typical Norwegian quick clay sites is introduced.This model consists of several geological units with differentresistivities.In the vicinity of the surface, three conductive bodies ofmarineclay (ρ = 3 Ω•m) are placed within a resistive background with ρ = 50 Ω•m. Made of gneiss (ρ = 1000 Ω•m),the bedrocklies at 35–45 m depths. In addition, a deep body of marine clay (ρ = 3 Ω•m) lies on top of the bedrock locatedin the center of the model section. Byperturbing the theoretical solution of the forwardproblem with 5% Gaussian noise using the software mentioned above, we can obtain a syntheticdataset. The noise added is calculated based on the potentials with a multiple-gradientarray consisting of 81 electrodes at 4 m spacing. Themultiple-gradient array has been designed for use in multi-channel systemsand is optimal for the instrument weused. Afterwards, the synthetic dataset obtained is invertedwith RES2DINVusing standard parameters.
2. Case study案例学习
In this part, the proposed method was applied in two real-life cases.
The first case suggested that interpolation between soundings quick clay investigations usingdiscrete rotary pressure soundings can be significantly enhanced byusing ERT profiles to interpolate. In this case, the resistivities inverted from theERT data were perfectlyaligned with the data provided byin situmeasurements,indicating excellent resolutionof the ERT method.
The second case showed thatthe threshold resistivityfor the quick clay zoning should be adjustedaccording to theRCPT soundings of each case/site. In this case, however, ERT imaging of layers of homogeneous materialrequiredfor the calculatio