1、The Process of the Cut and Cover Method,Subway Construction Technology,Investigation of the underground utilitiesTransplanting trees and shrubs Relocation of the underground utility linesRelocation of the roadside facilitiesReduction of sidewalk space,Column-type diaphragm Wall-type diaphragm Settin
2、g H shape Steel,The Process of the Cut and Cover Method,Subway Construction Technology,Excavation The placement of waling and strutting,The Process of the Cut and Cover Method,Subway Construction Technology,Placing reinforcement bar Forming work Casting in concrete,The Process of the Cut and Cover M
3、ethod,Subway Construction Technology,The Principle of the Slurry Shield Method,Subway Construction Technology,Types of Shield Tunnels,Subway Construction Technology,Single Track,Double Track,Triple Track,Eyeglass-Type Station,Removable Triple-Faced Shield,Triple-Faced Shield (island platform),New Sh
4、ield Methods Removable Triple-Faced Slurry Shield,Subway Construction Technology,Removable Triple-Faced Slurry Shield Machine,New Shield Methods Nested Parent-Child Slurry Shield,Subway Construction Technology,Nested Parent-Child Slurry Shield Machine,Construction of Station Using the Cut and Cover
5、Method,Subway Construction Technology,Introduction,Structurally controlled instability in tunnels,Falling wedge,Sliding wedge,Determination of average dip and dip direction of significant discontinuity sets. Identification of potential wedges which can slide or fall from the back or walls. Calculati
6、on of the factor of safety of these wedges, depending upon the mode of failure. 4. Calculation of the amount of reinforcement required to bring the factor of safety of individual wedges up to an acceptable level.,Identification of potential wedges,Structurally controlled instability in tunnels,The t
7、hree structural discontinuity sets are entered into the program UNWEDGE, together with the cross-section of the tunnel and the plunge and trend of the tunnel axis. The program then determines the location and dimensions of the largest wedges which can be formed in the roof, floor and sidewalls of th
8、e excavation.,Support to control wedge failure,Structurally controlled instability in tunnels,A characteristic feature of wedge failures in blocky rock is that very little movement occurs in the rock mass before failure of the wedge. This dictates that movement along the surfaces must be minimized.
9、Consequently, the support system has to provide a stiff response to movement.,Rockbolt support mechanisms for wedges in the roof and sidewalls of tunnels,F1.3 to 1.5W,1m,Rock bolting wedges,Support to control wedge failure,Structurally controlled instability in tunnels,Shotcrete support for wedges,R
10、avelling of small wedges in a closely jointed rock mass. Shotcrete can provide effective support in such rock masses.,Consideration of excavation sequence,Structurally controlled instability in tunnels,Deformation around an advancing tunnel,Tunnels in weak rock,Vertical section through a three-dimen
11、sional finite element model of the failure and deformation of the rock mass surrounding the face of an advancing circular tunnel.,The plot shows displacement vectors as well as the shape of the deformed tunnel profile.,Deformation around an advancing tunnel,Tunnels in weak rock,Pattern of deformatio
12、n in the rock mass surrounding an advancing tunnel.,Tunnel deformation analysis,Tunnels in weak rock,A circular tunnel subjected to a hydrostatic stress field; The surrounding rock heavily jointed; Rock mass behaves as an elastic-perfectly plastic material; Failure involving slip along intersecting
13、discontinuities; Zero plastic volume change.,Analytical model,Tunnel deformation analysis,Tunnels in weak rock,Definition of failure criterion,Tunnel deformation analysis,Tunnels in weak rock,Analysis of tunnel behavior,Failure of the rock mass surrounding the tunnel occurs when the internal pressur
14、e provided by the tunnel lining is less than a critical support pressure pcr , which is defined by:,If the internal support pressure pi is greater than the critical support pressure pcr, no,failure occurs, the behaviour of the rock mass surrounding the tunnel is elastic and the inward radial elastic
15、 displacement of the tunnel wall is given by:,where Em is the Youngs modulus or deformation modulus and is the Poissons ratio.,Tunnel deformation analysis,Tunnels in weak rock,Analysis of tunnel behavior,When the internal support pressure pi is less than the critical support pressure pcr, failure oc
16、curs and the radius rp of the plastic zone around the tunnel is given by:,For plastic failure, the total inward radial displacement of the walls of the tunnel is:,Dimensionless plots of tunnel deformation,Tunnels in weak rock,Relationship between size of plastic zone and ratio of rock mass strength
17、to in situ stress.,This plot shows that the plastic zone size increases very rapidly once the rock mass strength falls below 20% of the rock mass strength. Practical experience suggests that, once this rapid growth stage is reached it becomes very difficult to control the stability of the tunnel.,Di
18、mensionless plots of tunnel deformation,Tunnels in weak rock,Tunnel deformation versus ratio of rock mass strength to in situ stress.,Once the rock mass strength falls below 20% of the in situ stress level, deformations increase substantially and, unless these deformations are controlled, collapse o
19、f the tunnel is likely to occur.,Dimensionless plots of tunnel deformation,Tunnels in weak rock,Ratio of plastic zone to tunnel radius versus the ratio of rock mass strength to in situ stress for different support pressures.,Dimensionless plots of tunnel deformation,Tunnels in weak rock,Ratio of tun
20、nel deformation to tunnel radius versus the ratio of rock mass strength to in situ stress for different support pressures.,Tunnels in weak rock,Relationship between support pressure and tunnel deformation for different ratios of rock mass strength to in situ stress.,Dimensionless plots of tunnel deformation,
