Construction method for entering shallow-buried multi-arch tunnel under water-rich geological conditions

Abstract

A construction method for a shallow-buried multi-arch tunnel under water-rich geological conditions includes the following steps: cleaning a grouting ground surface; marking a grouting reinforcement scope; performing survey setting-out; drawing a cross-section diagram to scale; calculating out coordinates and angles of anchor points that need to be set; marking drilling positions; nailing small wooden piles at the drilling positions for identifying; determining a setting depth of the anchor rods according to ground elevation; drilling holes, cleaning bottom of hole, grouting, performing construction preparation, performing long pipe shed construction at the entrance after an earth-rock of a tunnel entrance and an open cut tunnel is excavated to flush with a springing line of the tunnel. A down-the-hole drill is used for drilling in construction. Long pipe shed grouting is designed based on solidifying a soil mass in limited scope around a consolidation pipe shed.

1 . A construction method for entering a shallow-buried multi-arch tunnel under water-rich geological condition, comprising:
 a cleaning step for cleaning a ground surface to be grouted, comprising removing debris that obstruct grouting from the ground surface of a slopes to be grouted, without destroying vegetation on the ground surface of the slopes as far as possible;   a marking step for marking a grouting reinforcement range, comprising:   
       performing analysis and calculation to obtain the grouting reinforcement range at the entrance of the tunnel that is characterized by:
 a longitudinal length of the tunnel of 18 m; 
 a width extending leftward from a center line of a left main hole of the tunnel is 5 m; 
 a width extending rightward from a center line of a right main hole of the tunnel is 5 m; and 
 a depth of 0.5 m distanced from a top of arches of the tunnel, wherein a length of a pipe shed is 16 m;
 a surveying and setting out step, configured for performing surveying and setting out at corresponding positions on the ground surface of a top of the tunnel according to a circumferential position spacing 100 cm and a longitudinal position spacing 60 cm of radial anchor rods at the entrance of the tunnel in a design drawing, wherein a cross-section diagram is drawn to scale, coordinates and angles of the positions at which the anchor rods are to be driven are calculated, the positions are marked; small wooden piles are nailed at the positions for identifying; and a depth of a portion of the anchor rods to be driven into is determined according to ground elevation; 
 a drilling holes step, configured for drilling at circulation break by using an engineering drilling rig, wherein the drilling is performed at the positions by using a down-the-hole drill, a drilling angle is adjusted before drilling, and the drilling angle is checked frequently during drilling; 
 a sweeping the holes step, configured for sweeping the holes, wherein grouting is performed in a manner of sweeping each hole twice and grounding the hole sectionally so as to ensure a effect of the grouting, after the hole is drilled, the hole is swept once by way of withdrawing a drill pipe to clean the hole, then the drill pipe is inserted to the bottom of the hole to sweeping the hole once again; 
 a grouting step, configured for grouting the ground surface, wherein several representative field tests are performed on performance of slurries with various mix proportions so as to select an optimal mix proportion suitable for the grouting of the tunnel, and setting time, tensile strength, and flexural strength are compared mainly among the tests; 
 a construction preparation step, configured for constructing drainage systems at the entrance after the grouting is completed, wherein the intercepting ditches at tops of the slopes are arranged not less than 5 m away from tops of the slopes comprising side slops and front slopes, slope ratios of the intercepting ditches are set according to terrain, and a drainage slope ratio is not less than 3%, so as to avoid sedimentation; 
 a cover arch construction step configured for constructing the cover arch, wherein a long pipe shed construction at the entrance after earth rocks at the entrance and an open cut tunnel is excavated to flush with a springing line of the tunnel, the cover arch adopts a 2 m long C25 concrete cover arch for orientation of the pipe shed, a base of the cover arch is placed on a stable foundation, a concrete guide wall of the cover arch is construed outside a profile of the open cut tunnel; four sections of I16 I-steel beam are arranged in the guide wall, the I-steel beam sections are bent into arcs according to design sizes, and adjacent sections are connected by using bolts to form a semicircle steel frame; orifice pipes of Φ114 are mounted and fixed at the steel frame after the I-steel beam sections are erected and fixed at the entrance; an internal framework and an external framework are erected for pouring concrete, the cover arch is 60 cm thick; 
 a driving step is configured for driving steel pipes into a surrounding rock at an angle of 1° greater than an angle of longitudinal slope of the tunnel along a periphery of the tunnel, wherein the down-the-hole drill is adopted to drilling and the circumferential spacing of the steel pipes is 40 cm, a vertical axis direction of the down-the-hole drill is controlled accurately to ensure correct hole direction at the orifice, and one steel pipe is driven once one hole is drilled; 
 a long pipe shed grouting step configured for performing long pipe shed grouting according to a design of a soil mass in a limited range around a pipe shed being consolidated, wherein a diffusion radius of the slurry is not less than 0.5 m; grouting is performed sectionally; single fluid grouting is adopted for grouting; a test for single fluid grouting is performed before grouting; a grouting ending standard is that a slurry amount grouted into a single pipe reaches a predetermined grouting amount; when the slurry amount grouted does not reach the predetermined grouting amount after the grouting pressure has reached a predetermined final pressure for 10 minutes, the grouting is ended. 
 
 
     
     
         2 . The construction method according to  claim 1 , wherein in the marking step, materials are prepared,
 the anchor rods in the tunnel are Φ25 hollow grouting anchor rods;   the anchor rods outside the tunnel are replaced by grouting pipes, wherein the grouting pipes are Φ50 mm hot pressed seamless steel pipes with the wall a thickness of 3.5 mm;   apertures are drilled on bodies of the steel pipes at the spacing of 15 cm to form a quincunx; a diameter of each aperture is 8 mm; the steel pipes are arranged in a quincunx shape at a longitudinal spacing of 1 m and a circumferential spacing of 0.6 m;   a Φ6 reinforcement stiffening hoops are welded at tails of the steel pipes; a length of the steel pipes is determined according to actual situations on site;   front ends of the steel pipes each are processed into a cone;   four rows of Φ8 mm grouting apertures are drilled in a periphery of a portion of the grouting pipes located in the grouting reinforcement range;   no aperture is drilled in other portion of the grouting pipe located out of the grouting reinforcement range, to serve as slurry guide pipe for grouting.   
     
     
         3 . The construction method according to  claim 1 , wherein in the grouting step,
 a material for grouting adopts single-fluid cement slurry;   cement of the single-fluid cement slurry adopts ordinary portland cement above 42.5 R with high activity, and a manufacture date of the cement does not exceed 3 months;   in order to allow the grouting to be performed without a break, a condition of a grouting pump, accessories, raw materials for preparing the slurry, and quality of the raw materials is checked before grouting, and a water-cement ratio is 0.5 and is adjusted properly according to actual situations.   
     
     
         4 . The construction method according to  claim 1 , wherein in the grouting step,
 drilling and grouting are performed in a construction sequence of from both sides to a center in a transverse direction of the tunnel, and from low to high in a longitudinal direction of the tunnel;   an interval construction method is adopted in a same row to prevent the slurry from channeling between adjacent construction holes.   
     
     
         5 . The construction method according to  claim 1 , wherein in the cover arch construction step,
 specification of the steel pipes in the pipe shed is that:   the pipe shed is made by adopting hot rolled seamless steel pipes with an outside diameter Φ of 108 mm and a wall thickness of 6 mm;   front ends of the steel pipes are tip cones;   Φ10 stiffening hoops are welded at tails of the steel pipes;   four rows of Φ12 mm grouting apertures are drilled in a periphery of a pipe wall of each steel pipe;   drilled apertures are spaced apart at a spacing of 15 cm and are arranged in quincunx;   the steel pipes are driven into the surrounding rock at an extrapolation angle of 1° along the periphery of the tunnel;   a total length of the steel pipes is 18 m, and a portion with a length 4.5 m at the tail end of each steel pipe has no aperture drilled therein;   a length of the tip cone is 10 cm;   the steel pipe comprises a plurality of pipe segments, a length of each segment is 3 m or 6 m, both ends of each segment of the steel pipe are preprocessed into external threads;   a number of joints of the pipe segments in a same cross section does not exceed 50% of a total number of the steel pipes;   a first segment of each odd-numbered steel pipe adopts a 3 m perforated steel pipe segment, and a first segment of each even-numbered steel pipe adopts a 6 m perforated steel pipe;   each of segments following the first segment adopts a 6 m perforated steel pipe;   a last section of each steel pipe driven into the surrounding rock is intercepted according to a length of the cover arch, so that a length of the steel pipe in soil is a predetermined length 16 m.