The top of the first section of steel pipe is made into a conical shape for jacking.
(3) In order to ensure that the drill pipe joint has sufficient strength, stiffness and toughness, the material of the drill pipe connecting sleeve shall be consistent with that of the drill pipe, the internal threads shall be processed at both ends (matched with the external thread at the first end of the drill pipe), and the wall thickness of the connecting sleeve shall be ≥ 10mm.
(8) The diameter of the guide hole is 15 ~ 20mm larger than the outer diameter of the pipe shed steel pipe, and the hole depth is more than 0.5m longer than the length of the pipe.
During construction, each section shall be overlapped for 3M, and 10mm small holes shall be drilled on the steel pipe according to the quincunx shape with a spacing of 15cm.
(2) Pipe fitting fabrication: pipe shed adopts Φ 108 seamless steel pipe, the steel pipe is lengthened by 3M and 6m pipe joints section by section, and the connecting joint is made of thick wall hoop with full screw thread, and the screw thread length is 15cm; In order to ensure the uniformity of stress, the steel pipe joints shall be staggered longitudinally.
1、 Scope of application: construction mechanism of advanced large pipe shed: considering the shallow buried depth and easy collapse in the concealed excavation section of the portal, the design mainly adopts advanced large pipe shed for protection.
The odd holes are made of seamless steel pipe, and the even holes are made of plum blossom steel pipe.
(7) When the first section of drill pipe is drilled into the rock stratum, stop drilling when there is 20 ~ 30cm left at the tail, manually clamp the drill pipe with two pipe tongs, reverse the drill at low speed and disconnect the drill pipe.
The general method of entering the tunnel is: first excavate the arch part of the open tunnel section, and support the side and front slopes according to the design, then construct C20 concrete arch, and then construct the advanced long pipe shed, and finally enter the tunnel safely under the support of the pipe shed.
When reaching the height of the excavation contour line of the arch crown of the concealed excavation section, dig vertically down to the bottom of the set upper half section, and temporarily spray concrete to close the tunnel face.
construction requirements of large pipe shed (1) in order to ensure the hole forming quality and prevent the hole forming collapse in front when drilling adjacent holes, the drilling shall be carried out at intervals.
The open excavation section shall be excavated layer by layer from top to bottom, and the side and front slopes shall be protected by shotcrete along with the excavation.
4、 The process flow of tunnel pipe shed is shown in Figure 1.
Cut along the excavation contour in a circular direction, install 2 steel frames (the size of the steel is according to the design documents), and pour concrete to prepare for the excavation of the concealed tunnel.
The even first section shall be 3M, the odd first section shall be 6m, and all subsequent sections shall be 6m.
3、 According to the technical requirements, the earth excavation at the portal must avoid the construction in rainy season.
Fig.
Fixing Socket Cross Pin Nail Plate
(6) The drilling speed of the drilling rig should be low, and turn to the normal drilling speed after drilling 20cm.
Steel pipes must also be installed immediately after even holes are formed to prevent hole collapse.
After the odd number of holes are formed, the steel flower pipe or non porous steel pipe shall be installed in time, and the cement slurry shall be injected.
The steel pipes are connected by sleeves.
In order to prevent the drill pipe from vibrating up and down under the dual action of thrust and vibration force, resulting in non straight drilling, the straightener shall be sleeved on the drill pipe and translated forward with the drill pipe.
Before excavation, construct intercepting ditch, gutter and other drainage systems, and then excavate the portal.
Reset the drill along the guide rail, and then install the second drill pipe.
The buried length of pipe shed is 24m.
Drill odd holes first and then even holes, with the diameter of φ 140mm for smooth installation φ one hundred and eight × 6mm steel flower tube.
1 drilling process flow chart of long pipe shed v.
During drilling, a measuring instrument shall be often used to measure the deviation of steel pipe drilling.
(4) The vertical shaft direction of the drilling rig must be accurately controlled, and the hole position and hole number shall be marked on the poured sleeve arch.
(3) After the hole cleaning inspection and drilling are qualified, the steel pipe shall be installed.
1.
2、 The construction of pipe shed shall be completed by installing the arch frame and guide steel pipe in the arch, erecting the formwork and pouring the arch concrete, and then drilling, pipe jacking, grouting and sealing.
(5) During drilling, the trolley boom must be pressed against the face of the tunnel to prevent excessive vibration from affecting the drilling accuracy.
(2) When constructing long pipe shed（ φ one hundred and eight × 6mm), the drilling angle of the hole section is 1 ° ~ 3 °, the circumferential spacing is 40cm, and each section is 40m long (each section is 9m long and is connected with a 89cm long casing).
One steel pipe shall be jacked after each hole is drilled.
The front section of the first steel pipe shall be welded with alloy steel sheet hollow drill bit to prevent top bending or splitting at the end.
(4) Pipe jacking: after placing the steel pipe on the boom of the trolley, align the rock drill with the drilled guide hole and push the steel pipe at low speed, with the impact force controlled at 18 ~ 20MPa and the pushing pressure controlled at 4.0 ~ 6.0MPa..
The lengthened pipe fittings shall meet the stress requirements of the pipe shed, and the joints of adjacent pipes shall be staggered from front to back to avoid stress on the same section.
Pipe jacking construction of long pipe shed (1) pipe jacking process: according to the requirements of rapid construction, it is decided to adopt the process of combining large guide hole and shed pipe drilling, and first drill the guide hole larger than the outer diameter of the steel pipe, and then use the impact and thrust of the drill (the rock drill does not use rotary pressure and does not produce torque when jacking into the pipe shed) to Jack the shed pipe with working pipe head along the guide hole, Lengthen the pipe shed section by section until the hole bottom.
The hole number is divided into odd holes and even holes.
When the pipe shed is extended, the previous steel pipe shall be jacked into the drilled guide hole before connection.
φ one hundred and eight × 6mm steel pipe adopts two specifications of 4.0m and 6.0m, the first of odd holes is 4.0m, the first of even holes is 6.0m, and the rest are 6.0m, so as to avoid steel pipe joints on the same section.
At the same time, the construction of even holes can check the grouting quality of odd holes on the one hand, and supplement grouting on the other hand to improve the effect of grouting reinforcement of surrounding rock.
The process method is applicable to the tunnel project of Chengdu Chongqing passenger dedicated line.
If the deviation exceeds the design requirements, it shall be corrected in time.
That is, large guide hole construction is adopted to overcome the difficulty of pipe delivery in pipe jacking construction to the greatest extent.
