地铁与隧道施工力学2

書式設定,*, 書式設定,第,2,第,3,第,4,第,5,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.,For the granodiorite,GSI = 55,m,i,= 30 and,ci,= 100 Mpa,cirm,= 23 MPa.,Rock mass strength,In situ stress,=5,Practical example,Tunnels in weak rock,Estimate of rock mass properties,For the altered porphyry and fault material,GSI = 15,m,i,= 12 and,ci,= 10 Mpa,cirm,= 0.4 MPa,.,Rock mass strength,In situ stress,if,r,0,=2 m, then,r,p,=9.3 m and,U,=0.4 m,substantial support is required.,=0.1,Experience suggests: U/r,0,= 0.02,Support pressure,In situ stress,=0.35,Support pressure=1.4Mpa,Shotcrete,Concrete lining,Closely spaced steel sets,Sliding joint top hat section sets.,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 very 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, 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 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,shotcrete,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 with 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 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),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 the 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,Rock 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,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 unsupported 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 significance 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 same 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 (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 Structure 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 rock 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 classification,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, joint 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,system:,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,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 support 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,J,n,is the joint set number,J,r,is the joint roughness number,J,a,is the joint alteration number,J,w,is the joint water reduction factor,SRF,is the stress reduction factor,Definition,(Barton et al, 1974),(,RQD,/,J,n,),Block size;,(,J,r,/,J,a,),Inter-block shear strength;,(,J,w,/SRF,),Active stress.,Rock,Tunnelling,Quality Index,Q,Rock mass classification,Parameters used in the Tunneling Quality Index,Q,RQD &,the joint set number,J,n,Rock,Tunnelling,Quality Index,Q,Rock mass classification,Parameters used in the Tunneling Quality Index,Q,Joint Roughness Number,J,r,Rock,Tunnelling,Quality Index,Q,Rock mass classification,Parameters used in the Tunneling Quality Index,Q,Joint Alteration Number,J,a,Rock,Tunnelling,Quality Index,Q,Rock mass classification,Parameters used in the Tunneling Quality Index,Q,Joint Alteration Number,J,a,Rock,Tunnelling,Quality Index,Q,Rock mass classification,Parameters used in the Tunneling Quality Index,Q,Joint Water Reduction,J,w,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,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,