ABSTRACT:

Fracture mapping at exposed rock faces is one of important approaches to investigate the influence of fractures on mechanic and hydraulic behavior of fractured rock masses. The objective of this study is to apply non-reflector geodetic total station and close range digital photogrammetry to characterizing fracture geometry at exposed rock faces. Total station was used for establishing a local co-ordinate system and capturing control points for transformation of target points from the image co-ordinate systems into an object co-ordinate system. Photogrammetric techniques aim to take 3-D fracture mapping from digital images of the rock face. In this contribution, a theoretical background of the presented method is presented. A case study was carried out at exposed rock faces for measuring trace length, dip angle and dip direction of fractures. Methodology and results of the case study are presented and discussed.

INTRODUCTION

Fracture geometry is one of the most influential factors for the effect of single fracture or fracture systems on the hydromechanical behavior of fractured rock masses. In-situ fracture mapping is often conducted in rock engineering projects to capture and quantify the geometrical features of fractures from exposed rock faces. In rock engineering, fracture geometry can be characterized by several parameters, such as orientation (dip angle and dip direction), spacing, trace length and roughness. These geometrical features of fractures are traditionally measured at exposed rock faces by using simple equipment such as a compass-inclinometer, a measuring tape and a roughness profile gauge. Although these techniques are easy to operate and observe the fracture geometry from exposed rock faces, some drawbacks (they are time-consuming, labor-intensive, and require physical touching of the rock face) inherent in these techniques might affecthe reliability and accuracy of the mapping results. One of challenging tasks in rock engineering is to apply new techniques for improving the quality of in-situ fracture mapping. The objective of this study is to develop a method by using close range photogrammetry and geodetic total station measurements for 3-D semi-automatic mapping of fracture geometry at exposed rock faces.

Photogrammetry is a technique for 3-D mapping by measuring images of the object based on the principle of triangulation. By taking pictures or images from at least two different positions and measuring the corresponding images points of the same target points in each image, the target points of an object can be intersected from the two (or more) corresponding image points, and then triangulated to produce 3-D co-ordinates of the targets in a reference object co-ordinate system. Close range photogrammetry is the technique when the extent of the target object to be measured is less than about 100 meters (Cooper & Robson, 1996). This technique has been applied in rock engineering for characterizing fracture geometry (Ross-Brown et al., 1973, Harrison, 1993, Beer et al., 1999) and for investigating rock mass deformation (Siebrits et al., 1997, Zhang, 2000). A geodetic total station (TS) is an electronic tacheometer (Kavanagh & Glenn Bird, 1992), which is often used in engineering survey for measuring the position of target points in space. This technique has been applied for measuring trace length, dip angle and dip direction of fractures at exposed rock faces (Bulut & Tades, 1996, Feng, 1999).

In this study, both geodetic total station and close range photogrammetry were applied for measuring and characterizing the fracture geometry. A nonreflector total station was used for control survey in combination with photogrammetric mapping. It can quickly measure co

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