August 15, 2022
Scope of Application of Pipe Shed Support
According to the construction practice at home and abroad, combined with the actual cases of the application of pipe roof support in underground engineering in China, pipe roof support can be applied to the construction of underground structures with rich geological and groundwater conditions, such as soft sandy soil stratum, sandy gravel stratum, expansive soft flow plastic, and hard plastic silty clay stratum, fractured rock mass, mud, and water inrush section, fault fracture zone, collapse section, broken soil and rock pile section, shallow buried and large bias, and the excavation support of tunnel entrance and exit section. It is also applied to the excavation pre-support of underground engineering such as subway crossing the urban area. It can be used as an auxiliary method for tunnel construction under existing buildings, highways, railways, and underground structures; as an auxiliary method for the construction of tunnel portal sections and large section tunnels, and as an auxiliary method for other constructions, it is also commonly used in projects with special requirements for construction settlement when there are buildings on the surface or when the tunnel is close to the underground structure in the case of shallow buried but not suitable for open excavation or shallow buried tunnel.
Pipe Shed Layout Form
According to the topography and geology as well as different loading conditions, usually, the tube shed can be arranged in the following forms:
(1) Fan-Shaped Layout: used in tunnel sections where the stratigraphy is relatively stable, but the stratigraphy near the arch is not stable.
(2) Semi-Circular Layout: it is used when the stratum in the lower half of the tunnel is stable, but the stratum above the arch line is unstable. In addition, even if the stratum is relatively stable, but the surface, there are structures around, buried at a very shallow depth also use this layout form.
(3) Door-Shaped Layout: the tunnel in addition to the bottom, is arranged as a semicircle, sidewall door-shaped. Used for tunnel foundation is stable, the section of the stratum and the upper stratum is not stable occasions.
(4) Full Circumferential Layout: used for weak stratum or expansion, extrusion surrounding rock, and other very poor occasions.
(5) All-Round Layout and Upper Side Layout: when there are highways, railroads, important structures, protection or slope terrain may form deviations on the side of the tunnel.
(6) Double-Layer Layout: used in the upper part of the tunnel with important facilities, the arch stratum is collapsible, unstable or subway stations and other large section of tunnel construction or break through the river bottom section construction occasions.
(7) One-Line Layout: used in the construction of railroads, and highways directly underneath or underneath certain structures.
Pipe Shed Drilling Trajectory Control Method
Once the pipe shed steel pipe drilling hole slant or exceeds the design allowable deviation, it will prevent the drilling of adjacent steel pipes, resulting in the uneven shape of the hole, poor support effect, and other results; if the steel pipe sinks to a certain extent, the excavation also needs to be removed, resulting in increased spacing and easy collapse. For this reason, drilling can take medium pressure to feed, medium speed, and medium circulation fluid drilling; drilling plane error radial should be controlled within 20cm, the angle error is less than 1 ° so as not to cause the pipe shed steel pipe skew and downward bending due to excessive hole diameter. In actual construction, it is generally difficult to avoid the bending of horizontal drilling, so in addition to improving the positioning accuracy of the pipe shed, an appropriate amount of upward lift can be given (according to the site geological conditions) to compensate for part of the sagging amount of drilling.