مقاله انگلیسی تحقیقات زمین شناسی و ژئوفیزیک از خصوصیات یک سایت مهندسی
Abstract
Introduction
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Abstract
Characterizing subsurface site conditions and understanding main geological features are critical components of any safety assessment for any construction, particularly defining subsurface flow paths and weakness (i.e. fracture and fault) zones. Poor definition of flow paths and weakness zones may lead to serious hazards during construction. This study, integrating geophysical and geological investigations, is undertaken to enhance the understanding of both surface and subsurface complexities of an engineering site characterization located in western Saudi Arabia near Red Sea. Two geophysical investigations, Electrical Resistivity Tomography (ERT) and Transient Electromagnetic (TEM), were carried out to characterize the subsurface of the study area. A total of three ERT profiles and sixteen TEM sounding measurements was conducted in the study area. Geological investigation was mainly focused to understanding geological features and bedrock conditions of the two opposite river's abutments at the study site. Geophysical results show NNE-SSW and NNW-SSE fault zones which were confirmed by in-situ geological inspections and by satellite images. The results also reveal the presence of geothermal fluids validated by the observation of hot water flowing in the river along the measurements. This study demonstrates that the integrated geophysical and geological investigations provide means to infer geothermal fluids, locate fractures, and fault zones. This study enabled us to characterize and locate the geological structural framework as well as possible geothermal fluids existence in the study area.
Introduction
Site characterization is an important step in civil engineering study or design. In order to devise a design for an engineering project such as urban development, a range of conceptual factors need to be assessed. An important factor that should be taken into account is the geological situation at the site. Therefore, a geological assessment should be implemented prior to any constructions. A proposed site in the western part of Saudi Arabia, near the Red Sea (Fig. 1), was planned by the government to be developed. For that reason, the subsurface characterization of the local geological and tectonic conditions (Fig. 2) were needed and a geophysical survey was suggested. Thus, detailed geological and geophysical studies were carried out to conduct full assessment of the under-development site. Geophysical survey at the study area suggests that the site has been affected by almost E-W fault system that resulted in two depressions (Al-Homoud et al., 1995), which extended in the form of buried structural channels filled with porous alluvium and fractured greenstone rocks (Moustafa et al., 2013). These depressions are considered permeable zones and represent a favorable pathway for groundwater flow. Consequently, further geological and geophysical surveys are necessary to better characterize the site (Wang et al., 2019). Therefore, we carried out detailed geological and geophysical investigations to define the tectonic geological features, such as the existence of main faults, and to better understand the subsurface geological conditions. Detailed geological studies have been conducted at the exposed rocks of the two abutments of the site in order to identify rock types as well as the delineation of the tectonic features, especially those related to faulting at the proposed site. Geophysical survey has been conducted using electrical resistivity tomography (ERT) and transient electromagnetic (TEM) methods to characterize the subsurface geological elements such as geological structures and identify different subsurface fault zones.