1、Practical example,Tunnels in weak rock,Estimate of rock mass properties,This shows that the size of the plastic zone and also the induced deformations will be negligibly small. Furthermore, no permanent support should be required for the tunnel.,Practical example,Tunnels in weak rock,Estimate of roc
2、k mass properties,Practical example,Tunnels in weak rock,Estimate of rock mass properties,Top hat section steel sets,Assembly of a friction joint in a top hat section steel set,Installation of sliding joint top hat section steel sets immediately behind the face of a tunnel being advanced through ver
3、y poor quality rock.,Practical example,Tunnels in weak rock,Estimate of rock mass properties,1 Forepoles typically 75 or 114 mm diameter pipes, 12 m long installed every 8 m to create a 4 m overlap between successive forepole umbrellas. 2 Shotcrete applied immediately behind the face and to the face
4、, in cases where face stability is a problem. Typically, this initial coat is 25 to 50 mm thick. 3 Grouted fiberglass dowels Installed midway between forepole umbrella installation steps to reinforce the rock immediately ahead of the face. These dowels are usually 6 to 12 m long and are spaced on a
5、1 m x 1 m grid.,4 Steel sets installed as close to the face as possible and designed to support the forepole umbrella and the stresses acting on the tunnel. 5 Invert struts installed to control floor heave and to provide a footing for the steel sets. 6 Shotcrete typically steel fiber reinforced shot
6、crete applied as soon as possible to embed the steel sets to improve their lateral stability and also to create a structural lining. 7 Rockbolts as required. In very poor quality ground it may be necessary to use self-drilling rockbolts in which a disposable bit is used and is grouted into place wit
7、h the bolt. 8 Invert lining either shotcrete or concrete can be used, depending upon the end use of the tunnel.,Full face 10 m span tunnel excavation through weak rock under the protection of a forepole umbrella.,Practical example,Tunnels in weak rock,Estimate of rock mass properties,Spiling in very
8、 poor quality clay-rich fault zone material.,Installation of 12 m long 75 mm diameter pipe forepoles in an 11 m span tunnel top heading in a fault zone.,Engineering rock mass classification,Rock mass classification,Introduction,Most of the multi-parameter classification schemes (Wickham et al (1972)
9、 Bieniawski (1973, 1989) and Barton et al (1974) were developed from civil engineering case histories in which all of the components of the engineering geological character of the rock mass were included. In underground hard rock mining, however, especially at deep levels, rock mass weathering and t
10、he influence of water usually are not significant and may be ignored. Different classification systems place different emphases on the various parameters, and it is recommended that at least two methods be used at any site during the early stages of a project.,Engineering rock mass classification,Ro
11、ck mass classification,General factors,intact rock strength,fracturing intensity,shear strength of fractures,geometrical relationship between fracture patterns and the excavation,groundwater,Engineering rock mass classification,Rock mass classification,Terzaghis rock mass classification,Intact rock
12、Stratified rock Moderately jointed Blocky and seamy rock Crushed but chemically intact rock Squeezing rock Swelling rock,by Terzaghi (1946),Engineering rock mass classification,Rock mass classification,Classifications involving stand-up time,Lauffer (1958) proposed that the stand-up time for an unsu
13、pported span is related to the quality of the rock mass in which the span is excavated. Lauffers original classification has since been modified by a number of authors, notably Pacher et al (1974), and now forms part of the general tunneling approach known as the New Austrian Tunneling Method. The s
14、ignificance of the stand-up time concept is that an increase in the span of the tunnel leads to a significant reduction in the time available for the installation of support. For example, a small pilot tunnel may be successfully constructed with minimal support, while a larger span tunnel in the sam
15、e rock mass may not be stable without the immediate installation of substantial support.,Engineering rock mass classification,Rock mass classification,Rock quality designation index (RQD),RQD is defined as the percentage of intact core pieces longer than 100 mm (4 inches) in the total length of core
16、 (Deere et al 1967).,The suggested relationship for clay-free rock masses is (Palmstrm,1982):,where Jv is the sum of the number of joints per unit length for all joint (discontinuity) sets known as the volumetric joint count.,Engineering rock mass classification,Rock mass classification,Rock Structu
17、re Rating (RSR),RSR = A + B + C,Parameter A, Geology: a. Rock type origin. b. Rock hardness. c. Geologic structure.Parameter B, Geometry: a. Joint spacing. b. Joint orientation (strike and dip). c. Direction of tunnel drive.Parameter C: Effect of groundwater inflow and joint condition. a. Overall ro
18、ck mass quality on the basis of A and B combined. b. Joint condition. c. Amount of water inflow.,Engineering rock mass classification,Rock mass classification,Rock Structure Rating (RSR),Rock Structure Rating: Parameter A: General area geology,Engineering rock mass classification,Rock mass classific
19、ation,Rock Structure Rating (RSR),Rock Structure Rating: Parameter B: Joint pattern, direction of drive,a Dip: flat: 0-20; dipping: 20-50; and vertical: 50-90,Engineering rock mass classification,Rock mass classification,Rock Structure Rating (RSR),Rock Structure Rating: Parameter C: Groundwater, jo
20、int condition,b Joint condition: good = tight or cemented; fair = slightly weathered or altered; poor = severely weathered, altered or open,Geomechanics Classification,Rock mass classification,Rock Mass Rating (RMR) system,The following six parameters are used to classify a rock mass using the RMR s
21、ystem:1. Uniaxial compressive strength of rock material. 2. Rock Quality Designation (RQD). 3. Spacing of discontinuities. 4. Condition of discontinuities. 5. Groundwater conditions. 6. Orientation of discontinuities.,Geomechanics Classification,Rock mass classification,Rock Mass Rating (RMR) system
22、,Rock Mass Rating System (After Bieniawski 1989).,Geomechanics Classification,Rock mass classification,Rock Mass Rating (RMR) system,Rock Mass Rating System (After Bieniawski 1989).,Geomechanics Classification,Rock mass classification,Rock Mass Rating (RMR) system,Guidelines for excavation and suppo
23、rt of 10 m span rock tunnels in accordance with the RMR system (After Bieniawski 1989).,Rock Tunnelling Quality Index, Q,Rock mass classification,where RQD is the Rock Quality Designation Jn is the joint set number Jr is the joint roughness number Ja is the joint alteration number Jw is the joint wa
24、ter reduction factor SRF is the stress reduction factor,Definition (Barton et al, 1974),(RQD/Jn) Block size; (Jr/Ja) Inter-block shear strength; (Jw/SRF) Active stress.,Rock Tunnelling Quality Index, Q,Rock mass classification,Parameters used in the Tunneling Quality Index Q,RQD & the joint set numb
25、er Jn,Rock Tunnelling Quality Index, Q,Rock mass classification,Parameters used in the Tunneling Quality Index Q,Joint Roughness Number Jr,Rock Tunnelling Quality Index, Q,Rock mass classification,Parameters used in the Tunneling Quality Index Q,Joint Alteration Number Ja,Rock Tunnelling Quality Ind
26、ex, Q,Rock mass classification,Parameters used in the Tunneling Quality Index Q,Joint Alteration Number Ja,Rock Tunnelling Quality Index, Q,Rock mass classification,Parameters used in the Tunneling Quality Index Q,Joint Water Reduction Jw,Rock Tunnelling Quality Index, Q,Rock mass classification,Par
27、ameters used in the Tunneling Quality Index Q,Stress Reduction Factor SRF,Rock Tunnelling Quality Index, Q,Rock mass classification,Parameters used in the Tunneling Quality Index Q,Stress Reduction Factor SRF,Rock Tunnelling Quality Index, Q,Rock mass classification,Estimated support categories based on the tunnelling quality index Q,ESR- Excavation Support Ratio,
