Analysis of Wedges for Underground Excavations - Coursework Example

Rock mechanics work: design study Professor Institution Course Date Rock Mechanics Coursework: Design Study Insitu stress 1 Project Settings Project Title: Stability Analysis of Wedges for Underground Excavations Wedges Computed: Perimeter and End Wedges Units: Metric, stress as tonnes/m2 General Input Data Tunnel Axis Orientation: Trend: 80° Plunge: 0° Design Factor of Safety: 1.500 Unit Weight of Rock: 26.000 t/m3 Unit Weight of Water: 0.981 t/m3 Seismic Forces Direction: Sliding Seismic Coefficient: 0 Scale Wedges Settings Not Used Joint Orientations Joint 1 Dip: 55° Dip Direction: 088° Joint 2 Dip: 72° Dip Direction: 225° Joint 3 Dip: 78° Dip Direction: 157° Joint Properties Water Pressure Constant: 0 tonnes/m2 Waviness: 0° Shear Strength Model: Mohr-Coulomb Phi: 35° Cohesion: 0 tonnes/m2 Tensile Strength: 0 tonnes/m2 Bolt Properties Bolt Type: Mechanically Anchored Tensile Capacity: 10 tonnes Plate Capacity: 10 tonnes Anchor Capacity: 10 tonnes Shear Strength: Unused Bolt Orientation Efficiency: Used Method: Cosine Tension/Shear Shotcrete Properties Shear Strength: 200.00 t/m2 Unit Weight: 2.600 t/m3 Thickness: 10.00 cm Insitu stress 2 Project Settings Project Title: Stability Analysis of Wedges for Underground Excavations Wedges Computed: Perimeter and End Wedges Units: Metric, stress as tonnes/m2 General Input Data Tunnel Axis Orientation: Trend: 0° Plunge: 90° Design Factor of Safety: 1.500 Unit Weight of Rock: 26.000 t/m3 Unit Weight of Water: 0.981 t/m3 Seismic Forces Direction: Sliding Seismic Coefficient: 0 Scale Wedges Settings Not Used Joint Orientations Joint 1 Dip: 55° Dip Direction: 088° Joint 2 Dip: 72° Dip Direction: 225° Joint 3 Dip: 78° Dip Direction: 157° Joint Properties Joint Properties 1 Water Pressure Constant: 0 tonnes/m2 Waviness: 0° Shear Strength Model: Mohr-Coulomb Phi: 35° Cohesion: 0 tonnes/m2 Tensile Strength: 0 tonnes/m2 Bolt Properties Bolt Property 1 Bolt Type: Mechanically Anchored Tensile Capacity: 10 tonnes Plate Capacity: 10 tonnes Anchor Capacity: 10 tonnes Shear Strength: Unused Bolt Orientation Efficiency: Used Method: Cosine Tension/Shear Shotcrete Properties Shear Strength: 200.00 t/m2 Unit Weight: 2.600 t/m3 Thickness: 10.00 cm Insitu stress 3 Project Settings Project Title: Stability Analysis of Wedges for Underground Excavations Wedges Computed: Perimeter and End Wedges Units: Metric, stress as tonnes/m2 General Input Data Tunnel Axis Orientation: Trend: 170° Plunge: 90° Design Factor of Safety: 1.500 Unit Weight of Rock: 26.000 t/m3 Unit Weight of Water: 0.981 t/m3 Seismic Forces Direction: Sliding Seismic Coefficient: 0 Scale Wedges Settings Not Used Joint Orientations Joint 1 Dip: 55° Dip Direction: 088° Joint 2 Dip: 72° Dip Direction: 225° Joint 3 Dip: 78° Dip Direction: 157° Joint Properties Water Pressure Constant: 0 tonnes/m2 Waviness: 0° Shear Strength Model: Mohr-Coulomb Phi: 35° Cohesion: 0 tones/m2 Tensile Strength: 0 tonnes/m2 Bolt Properties Bolt Type: Mechanically Anchored Tensile Capacity: 10 tonnes Plate Capacity: 10 tonnes Anchor Capacity: 10 tonnes Shear Strength: Unused Bolt Orientation Efficiency: Used Method: Cosine Tension/Shear Shotcrete Properties Shear Strength: 200.00 t/m2 Unit Weight: 2.600 t/m3 Thickness: 10.00 cm While ensuring the uniaxial compressive strength of the tunnel rocks is properly defined, the means used should be the best and easy for this application. The coordinates makes it possible to incorporate clay materials in the characterization by utilizing the undrained and unconfined compression strength. The clay infill in weakness and fault zones where the blocks may or may not have contacts can in this manner be characterized by the clay material strength. In the case of granular soil materials like sand, silt and gravel the strength is always hard to calculate and is therefore mostly estimated. The Uniaxial compressive strength always undergoes a test that is frequently used to define the tunnel rock behaviour. The test is principally open to misinterpretation, due to the structure and the breakdown mechanism of the tunnel rock. There are also a probability of sources of error in the sample preparation and sampling. The methods employed for determining the uniaxial compressive strength takes many factors into consideration. For example, the point load strength is an easy and quick method for identifying the strength of rocks in the tunnel, and it is known to provide more reliable outcome than compression tests on machined cylindrical samples. It’s fundamentally clear that the floor of the circular tunnel allows heaving of the floor or upward displacement. The smooth surface all around the tunnel creates low stress concentrations and generate les bending moments in any lining installed in the railway tunnel. The failure of the floor basically introduced at these surfaces. The floor heave is significantly reduced by the concave curvature of the tunnel floor. In borderline cases any modification to the circular shape may be adequate to limit or minimize the type of damage. Nevertheless in very severe circumstances, a circular tunnel is invariably the best form of modification any tunnel as indicated by the smooth strength factor contour. The roof wedge will not fall as a result of gravity loading and, due to its circular shape, which shows restraint from the three linking discontinuities. This indicates that the factor of safety of the wedge, upon it is release by the excavation of the ramp outlet, is 1.5. In most circumstances, the sliding on one plane or along the line of intersection of four planes may occur in a roof wedge and this will eventuate in an infinite value for the factor of safety. The surfaces of the circular tunnel are all interconnected and are approximately the same shape as well as disposed of the in space similarly. The factors of safety are equal as shown in the analysis result, sliding occurs on all the surfaces. The floor wedge is absolutely stable and doesn’t require further consideration (Zhang, Xu, Kulatilake , Huang, 2012). Rock mass classification Description Value Rating Point load index 8 MPa 12 RQD 70% 13 Spacing of discontinuities 300mm 10 Condition of discontinuities Note 1 22 Groundwater Wet 7 Adjustment for joint orientation Note 2 -5 Total 59 As indicated in the RMR table, Note 1 for slightly rough and changed discontinuity surfaces of < 1mm, the table 4.A.4 provides a rating of 25.With all the detailed information available, the table 4.E is used to provide a more refined rating.Therefore,in this circumstances ,the ratings is the aggregate of : 4 (1-3 m discontinuity length), 4 (separation 0.1-1.0 mm), 3 (slightly rough), 6 (slightly rough) and 5 (slightly rough) = 22. In the Note 2, table 4.F provides a statement of “fair” for the circumstance adopted where the tunnel is to be driven against the dip of a set of joints at 60o.Employing this statement for the tunnels in table 4. B presents an adjustment rating of -5 These set the guidelines published by Bieniawski for the choice of support in tunnels in the rock for which the RMR value has been determined. These guidelines are further recreated in table 4 and published to be utilized on 10mm span of circular shaped tunnel ,constructed using drill and blast procedures in a rock mass prone to vertical stress < 25MPa (Equivalent to a depth below surface of Read More