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SYNOPSIS Post-failure deformation experiments were carried out for rocks and coal having compressive strength varying from 24 MPa to 366 MPa and analyzed for the two classes of post-failure behavior i.e.Class-1 and Class-II as reported in the literature. All the experiments were conducted under uniaxial compressive stress conditions using an MTS compression testing machine. Depending on the rock type, either lateral strain or displacement control was used as the feedback signal. Post-failure deformation was recorded for all the rocks and coal samples. Based on the post- failure deformation pattern and the fracture mode of the failed samples, three types of post-deformation patterns were identified. Type-1 is characterized by a steep fall in stress with tensile cracks, Type-2 showed a typical pattern of rise and fall in stress with a combination of tensile and shear cracks, while Type-3 showed a gradual decrease of stress with shear cracks. The Class-II failure as reported in the literature was not observed even for rocks having strength of 366 MPa. Based on this study it is inferred that all the rocks may undergo post-failure deformation, the amount of deformation depends on the failure mechanism which is a combination of tensile and shear cracks. 1. INTRODUCTION The concept of Class-I and Class-II post-failure behavior was originally proposed by Wawersik and Fairhurst(1,2) to classify the shape of the complete stress-strain curve for a particular rock according to its strain beyond the peak strength. If the strain increases monotonically throughout the failure process, the curve is designated as Class-I, and other curves as Class-II. Class-I behavior is characterized by ‘stable’ fracture propagation. But rock that exhibit Class-II behavior, the failure is unstable and the fracture of rocks cannot be controlled. The dividing line between Class-I and Class- II behavior is defined by the dashed line as shown in figure 1. In the present study six different rocks including coal having strength from 24 MPa to 366 MPa were investigated for the two types of post-failure behavior. 2. SAMPLE PREPARATION A total of six rock types including coal were investigated, table 1 gives their uniaxial compressive strength, Young's modulus and Poisson's ratio. Except for coal remaining samples were collected in the form of drilled cores. Coal samples were drilled from the blocks perpendicular to bedding plane to obtain NX size cylindrical cores. The diameter of the samples varied from 37 mm to 54 mm. The length to diameter ratio was maintained at 2.0. Samples were cut to the required length and the end faces were ground using surface grinder. 3. EXPERIMENTAL METHODOLOGY MTS rock mechanics system was used along with their extensometers for conducting post-failure experiments. As reported in the literature (3, 4, 5, and 6) three feedback controls are commonly used for the post-failure tests and they are:Lateral strain control Axial strain control Displacement control or also called as stroke control Load control is not used as a feed back as it produces sudden failure of the sample beyond the peak stress.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Abstract: Geotechnical instruments are integral part at power house cavern (PC) of Kiah Boshes project. Instrumentation data are collected during and after excavation and concreting period. Absolutely, extensometer is the main instrument in large underground spaces which install as soon as possible in excavation phase. Pressure cell, pedometer and linear displacement transducer are main instruments applied in concreting period. Two extensometer In order to achieve total displacement are installed before starting of PC excavation. We are analysis instrumentation data for powerhouse cavern of Kiah Boshes project to determine amount of omitted data which help to back analyzing and achieve actual rock mass properties. About 5 cm Styrofoam board in order to damping future rock mass displacement to concrete wall is installed between concrete and shotcrete surface. Also some opening anticipate for future ground anchor. According instruments data, stable condition achieve after concreting period. 1- INTRODUCTION Kiah Lishe pumped storage power plant is the first pumped storage project at Iran with capacity of 1000 MW. Power house cavern (PC) with 131m high, 24m width and 47m high is adjacent of guard gate and transformer caverns. PC is located in a sedimentary layers (Quartzite Sandstone and red Shale) and igneous masses (intrusive rock). Thickness of sedimentary layers is from some centimeter to about 1 meter. Some shear bands and two major joint set are affected rock mass [1]. 2- PC EXCAVATION PC has excavated and supported generally according to the New Austrian Tunneling Method (ATM). Vault admit exists on upstream side of PC which help to install two extensometer (E10 and E15) before starting of PC excavation. PC has excavated at two parts: top and benching. PC crown divided to three parts: upstream, center and downstream (figure 1). PC benching was started after installation of roof ground anchor (mono bar). PC invert lowering about 3 m in each sequence of benching, figure 2. PC's volume was 117700 cubic meters which excavated from Oct. 2004 until Feb. 2007 and concreting from July 2006 until July 2010. 2- MONITORING SYSTEM PC monitoring system consists of six instrumentation sections (figure 3). Two extensometer (E10 and E15) are installed before starting PC excavations (figure 4) and other instruments (extensometer, load cells and convergence meters) are installed during the excavation period. Therefore, for more extensometer installation delay cause omits some of actual displacement which is related to PC excavation. Concrete instruments such as pedometer, pressure cell and linear displacement transducer are installed during concreting period. 3- DATA INTERPRETATION According E15 date-displacement curve (figure 5) and sequence of PC excavation (figure 1 and 2): More than 15 percent of total movement wall occurred before that invert reach to elevation of extensometer. About 23 percent of total movement of PC wall occurred before that invert reaches to 1.3 m below of extensometer elevation. 4- ROCK-CONCRETE INTERACTION Some geotechnical instruments such as Pressure cell(figure 6-a), Liner displacement transducer(figure 6-b), Pedometer and Strain gage are installed in concreting phase of PC in order to monitoring rock concrete interaction [2].
- Asia > Middle East > Iran (0.37)
- Asia > India (0.30)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.55)
- Geology > Rock Type > Igneous Rock (0.55)