Abstract:

The mechanical behavior of rock masses is significantly affected by the deformation modulus. Several parameters such as confining stress and the angle o anisotropy and direction of loading affect the deformation modulus. The dilatometer is one of the most versatile instruments used for determining the in-situ modulus of deformation and has been used extensively in a site investigation program that was carried out near railway station on the Bakhtiary Dam site in Lorestan province, southwest of Iran. This paper discusses the effect of confining stress and the angle between anisotropy and loading direction on the deformation modulus obtained from dilatometer tests carried out at Bakhtiary dam site.

1.
INTRODUCTION

Rock is a discontinuous medium with fissures, fractures, joints, bedding planes, and faults. The strength and deformability of rock masses depends on the behavior of these discontinuities or planes of weakness. The frequency of joints, their orientation with respect to the engineering structures and the roughness of the joint have a significant importance from the stability point of view. Reliable characterization of the strength and deformation behavior of jointed rocks is very important for safe design of civil structures such as arch dams, bridge piers and tunnels. The deformability is one of the most important properties that represent the mechanical behavior of rock masses and is used in various rock engineering projects including underground and surface structures [1]. Rock mass deformation modulus can be measured by different methods including field testing and laboratory testing by considering the relation between the applied load and resulting deformation. It should be noted that a rock mass usually contains discontinuities and its mechanical behavior is different to that of small rock specimen tested in the laboratory. Hence large scale techniques offer advantages by testing at a more reasonable scale. It should be noted however, that several parameters such as confining stress and the angle between anisotropy and direction of loading affect the deformation modulus [2]. Dilatometer testing has been used extensively in a site investigation program that was carried out near the city of Khoramabad in Lorestan province south-west of Iran. The effect of confining stress and the angle between anisotropy and direction of loading on the obtained deformation modulus will be discussed in the following this paper.

2.
SITE INVESTIGATION PROGRAM

A site investigation program was carried out near the city of Khoramabad, which has previously been reported. It is proposed to construct a dam at this location on the Bakhtiary River in order to provide water for drinking and agricultural purposes. The investigations are aimed to provide geotechnical parameters in order to analyze the suitability of this location and also to obtain required design parameters. The dam site is located on the Bakhtiary river bank, one of the Dez river's headstreams, 5 km upstream of the confluence of the Sezar and Bakhtiary rivers, amid the Zagros mountains and almost 50 km to the upstream of the Dez dam and Hydropower Plant, constructed about 45 years ago [3].

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