An Attempt to Image Um El-Adam Cavity Structure in the Karst Terrain at Hit Area, Western Iraq

Ali Abed

doi:10.46717/igj.54.1a.5ms-2021-01-26

Abstract

Um El-Adam cavity is one of the well-known cavities inside gypsum rocks in the Hit region, western Iraq, where this was chosen as a case study to evaluate 3D resistivity imaging technique detection and imaging of this type of cavity in complicated lithology. 3D view fulfilled by collating four 2D resistivity-imaging lines. The 2D resistivity imaging survey was carried out by Dipole-Dipole array with (n) factor and electrode spacing (a) of 6 and 2m, respectively. Both conventional inversion methods obtained the 2D and 3D models: standard least-squares and robust constrain options. The two options were able to define clearly the cave, but the second was more accurate, the dimensions of the cave in the inverse model closer to the actual dimensions. Horizontal slices displayed the final 3D model to reveal a 3D resistivity distribution with depth. The effect of Um El-Adam cavity appears after 1.5 m on the model slices, which is represented by increasing resistivity contrast compared to surrounding sediments. At the seventh and eighth slices, it was found that the size of the cavity exceeded compared with the actual dimensions. The results of this study indicated the high potential of this method for the detection and delineation of subterranean caves.

Highlights

The heading of the karst phenomenon refers to all cavities, voids, karst and pits in the subsurface (Owen, 1983)
The inverse model produced by the standard least-squares option has a gradational boundary for the cavity (Fig. 5)
The inverse model produced by the standard least-squares option has a gradational boundary for the cavity, While the inverse model produced by the robust constrain option shows the boundaries of the cavity sharper and straighter

Summary

Introduction

The heading of the karst phenomenon refers to all cavities, voids, karst and pits in the subsurface (Owen, 1983). Karst features developed due to the dissolving of limestone or gypsum (Ulugergerli and Akea, 2006). In limestone, the shape of the sinkholes is uniform and larger in comparison to those developed in gypsum. In the Southern Desert, Iraq, the diameter of some old karsts may reach few kilometers, with depth ranges 10–15 m (Hamza, 1997; Sissakian et al, 2005). When planning the construction of civil engineering installations, subsurface cavities should identify under the construction area. These cavities could cause undesired effects at the ground surface such as subsidence of collapse (Walthamand et al, 2005).

Objectives

Methods

Results

Conclusion