A combined support structure suitable for deep foundation pit excavation in aeolian sand strata

Abstract

The invention discloses a deep foundation pit excavation combined support structure suitable for aeolian sand formation, wherein the upper half is an open excavation slope, and a plurality of slope anchor rods are driven into the slope; the lower half is provided with jet grouting piles and bored cast-in-place piles in sequence from the slope foot to the inside to form retaining piles, the inner side of the retaining piles is a foundation pit, the bottom of the foundation pit is a base jet grouting pile, the base jet grouting piles are provided with base concrete, the inside of the foundation pit is a tunnel lining, and the tunnel lining is backfilled. The deep foundation pit excavation combined support structure of the invention is more reasonably designed, has lower cost, and is safer and more efficient to construct.

Description

Technical Field

[0001] The invention belongs to the field of supporting structures for railway tunnel construction, and in particular relates to a combined supporting structure suitable for deep foundation pit excavation in aeolian sand strata. Background Art

[0002] Aeolian sand is a deposit formed by wind transport. It is widely distributed in my country, mainly in the northwest region (mainly Inner Mongolia, Gansu, Xinjiang and other places) and parts of Tibet. Its structure is loose and its shear strength is poor. After tunnel excavation, if the support is not timely, the surrounding rock will undergo significant deformation. Traditional construction generally adopts the method of partial excavation + advance support to build tunnels. The construction process is cumbersome, and after excavation using this method, the stability of the heading face is poor, and it is prone to vault collapse and roof falls (roof falls are manifested as: vault collapse, extending all the way to the surface, forming pits on the surface), which causes great trouble to the safe and efficient construction of tunnels.

[0003] In Tibet, my country, aeolian sand is also shallowly buried, generally not exceeding 40m, and is mostly located at the entrance and exit of tunnels. When tunnels pass through such strata, the arch may even collapse, such as the Deji Tunnel on the Lhasa-Nyingchi section of the Sichuan-Tibet Highway. This not only threatens the safety of construction workers, but also requires landfilling of the collapsed area later, which will increase construction costs. Summary of the invention

[0004] Aiming at the problem of railway tunnel construction in shallowly buried aeolian sand strata, the present invention provides a combined supporting structure for deep foundation pit excavation suitable for aeolian sand strata.

[0005] The invention discloses a combined supporting structure for deep foundation pit excavation in aeolian sand strata, wherein the upper half is an open-cut slope, on which a plurality of slope anchor rods are driven; the lower half is a retaining pile formed by sequentially arranging jet grouting piles and bored cast-in-place piles from the toe of the slope inward, the inner side of the retaining piles is a foundation pit, the bottom of the foundation pit is a base jet grouting pile, the base jet grouting piles are provided with base concrete, the inside of the foundation pit is a tunnel lining, and the tunnel lining is backfilled.

[0006] Furthermore, lateral supports are provided between the retaining piles of the foundation pit.

[0007] Furthermore, the slope gradient and slope anchor distribution are determined based on the shear strength of aeolian sand.

[0008] Furthermore, the bored piles extend below the invert.

[0009] Furthermore, a certain thickness of aeolian sand is filled into the invert position of the foundation pit to ensure the bearing capacity of the foundation.

[0010] The beneficial technical effects of the present invention are:

[0011] 1. The upper part of the tunnel is cut open with slope, and the toe of the slope is located at a certain position above the tunnel, rather than directly placing the toe of the slope at the bottom of the invert. The excavation volume is relatively small, saving construction costs.

[0012] 2. The foundation pit adopts retaining piles (consisting of bored cast-in-place piles and rotary jet piles). The bored cast-in-place piles are used to prevent the foundation pit from overturning, and the rotary jet piles are used to stop sand, which will not cause sand leakage.

[0013] 3. The horizontal cross braces are set on the retaining piles to hinder the horizontal displacement of the surrounding rock and ensure that the horizontal displacement of the surrounding rock is small. And due to the effect of the cross braces, the bending moment generated by the soil pressure of the retaining piles can be redistributed, resulting in a smaller bending moment than when no cross braces are set, thus enhancing the bending resistance of the retaining piles.

[0014] 4. Since a larger space is formed after foundation pit excavation, the tunnel lining can be completed in one go, with high construction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional view of the combined support structure of the present invention.

[0016] Figure 2 It is a plan view of the combined support structure of the present invention.

[0017] Figure 3 Schematic diagram of slope anchor arrangement.

[0018] Explanation of the numbers in the figure: 1-ground line; 2-slope; 3-tunnel centerline; 4-slope anchor; 5-jet grouting piles; 6-lateral support; 7-tunnel lining; 8-base jet grouting piles; 9-bored cast-in-place piles; 10-base concrete; 11-heading face; 12-slope toe position. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0020] The present invention is suitable for deep foundation pit excavation combined support structure of aeolian sand strata. Figure 1 , Figure 2 As shown, the upper half is an open-cut slope 2, on which a number of slope anchor rods 4 are driven; the lower half is composed of jet grouting piles 5 (jet grouting piles are used to stop sand) and bored piles 9 arranged in sequence from the toe position 12 of the slope 2 to form retaining piles, the inner side of the retaining piles is a foundation pit, the bottom of the foundation pit is a base jet grouting pile 8, on the base jet grouting pile 8 is base concrete 10, inside the foundation pit is a tunnel lining 7, and the tunnel lining 7 is backfilled.

[0021] Furthermore, transverse supports 6 are provided between the retaining piles of the foundation pit according to different burial depths.

[0022] Furthermore, the slope of the slope 2 and the distribution of the slope anchors 4 (such as Figure 3 (Figure 2) shows an example of slope anchor distribution, which is determined based on the shear strength of aeolian sand.

[0023] Furthermore, the bored piles 9 extend below the invert to ensure that the pile has sufficient anti-overturning capability.

[0024] Furthermore, a certain thickness of aeolian sand is filled into the invert position of the foundation pit to ensure the bearing capacity of the foundation.

[0025] The implementation method of the deep foundation pit excavation combined supporting structure of the present invention is as follows:

[0026] 1. Before construction, the side slope 2 is firstly sloped, and the side slope anchor rods 4 are driven while the slope is sloped. The slope gradient is determined according to the shear strength of the aeolian sand, and the slope foot 12 is located above the tunnel.

[0027] 2. After the slope is cut, the jet grouting piles 5 and bored cast-in-place piles 9 are constructed.

[0028] 3. When the retaining piles reach the designed strength, the foundation pit is excavated from top to bottom, and the rotary jet grouting piles are constructed at the same time.

[0029] 4. When the foundation pit is excavated to the designed depth, the base jet grouting piles 8 and base concrete 10 are constructed.

[0030] 5. When the base jet grouting piles 8 and base concrete 10 reach the designed strength, the tunnel lining 7 is constructed.

[0031] 6. When the tunnel lining 7 reaches the designed strength, backfill the foundation pit.

Claims

1. A combined support structure for deep foundation pit excavation in aeolian sand strata, characterized in that: The upper part is an open-cut slope (2), and a plurality of slope anchor rods (4) are driven into the slope (2); the lower part is a retaining pile formed by jet grouting piles (5) and bored cast-in-place piles (9) arranged in sequence from the slope foot position (12) of the slope (2), the inner side of the retaining pile is a foundation pit, the bottom of the foundation pit is a base jet grouting pile (8), the base jet grouting pile (8) is provided with base concrete (10), the inside of the foundation pit is a tunnel lining (7), and the tunnel lining (7) is backfilled; Transverse supports (6) are arranged between the retaining piles of the foundation pit; and the bored piles (9) extend below the invert arch.

2. The combined support structure for deep foundation pit excavation in aeolian sand strata according to claim 1 is characterized in that: The slope of the side slope (2) and the distribution of the side slope anchor rods (4) are determined according to the shear strength of the aeolian sand.

3. The combined supporting structure for deep foundation pit excavation in aeolian sand strata according to claim 1 is characterized in that: A certain thickness of aeolian sand is filled into the invert position of the foundation pit to ensure the bearing capacity of the foundation.

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