阅读说明：本技术 明洞接长泡沫混凝土回填结构的施工方法 (Construction method of open cut tunnel extension foam concrete backfill structure ) 是由 王新泉 刁红国 崔允亮 魏纲 于威 齐昌广 于 2021-07-02 设计创作，主要内容包括：本发明涉及明洞接长泡沫混凝土回填结构的施工方法,包括步骤：先明洞接长段两侧场地整理,打设拉森钢板桩止水施工,再明洞接长段两侧基础施工,接着吊装预制侧板,做好下部陡坡的防水作业以及支撑杆、斜向杆的安装施工,然后在明洞接长段外侧整平区内多道凹沟和竖向插筋并边斜侧向支模进行第一泡沫混凝土填充区施工,之后进行预制钢拱板的吊装工作和第二泡沫混凝土填充区施工,布置好预留的排水盲沟和排水管后进行第三泡沫混凝土填充区施工,最后进行顶部和侧边的排导槽施工。本发明的有益效果是：本发明的整个施工过程中能够保证明洞接长段内部既有路线的正常运营,实现了无封道明洞接长作业,对社会交通的影响极小,因此具有较好的社会效益。(The invention relates to a construction method of a open cut tunnel extension foam concrete backfill structure, which comprises the following steps: the construction method comprises the steps of firstly arranging sites on two sides of a connecting section of the open cut tunnel, constructing Larsen steel sheet pile water stop construction, constructing foundations on two sides of the connecting section of the open cut tunnel, then hoisting prefabricated side plates, performing waterproof operation on a steep slope on the lower portion and installation construction of a supporting rod and an oblique rod, then conducting first foam concrete filling area construction on a plurality of concave ditches and vertical inserting ribs in a leveling area outside the connecting section of the open cut tunnel and obliquely supporting a formwork, then conducting hoisting work and second foam concrete filling area construction on a prefabricated steel arch plate, conducting third foam concrete filling area construction after arranging reserved drainage blind ditches and drainage pipes, and finally conducting top and side drainage groove construction. The invention has the beneficial effects that: the invention can ensure the normal operation of the existing route in the open cut tunnel extension section in the whole construction process, realizes the open cut tunnel extension operation without a closed road, and has little influence on social traffic, thereby having better social benefit.)

1. A construction method of a open cut tunnel extension foam concrete backfill structure is characterized by comprising the following steps:

1) the two sides of the open cut tunnel extension section (21) are arranged, the ground on the outer side is leveled, the side slope on the inner side is properly excavated to form a lower steep slope (6), and the foundation position of the open cut tunnel extension section (21) is determined by measuring and paying off;

2) constructing a Larsen steel sheet pile (13) on the inner side of the open cut tunnel extension section (21): driving a Larsen steel plate pile (13) for water stop, and filling saw dust powder, fiber-rich cotton wool and expansion cement into a locking gap of the Larsen steel plate pile in a matched manner;

3) foundation pits are respectively dug on two sides of the open cut tunnel extension section (21), steel bars are bound to pour concrete, slots (33) are reserved, a cast-in-place T-shaped foundation (12) integrated with the Larsen steel sheet pile (13) is formed on the inner side of the open cut tunnel extension section (21), a cast-in-place wedge-shaped foundation (22) is formed on the outer side of the open cut tunnel extension section (21), and meanwhile, the prefabricated side plates (32) and the prefabricated steel arch plates (17) are manufactured in a prefabricated field;

4) protection construction of a lower steep slope (6) on the inner side of the open cut tunnel extension section (21): anchor rods (11) are arranged on the lower steep slope (6) at intervals, anchor cables (7) are arranged at corresponding positions, then a hanging net (5) is installed on the anchor rods (11) and the anchor cables (7), after the anchor rods and the anchor heads (10) and the anchor heads (8) are fixed, concrete is sprayed to form a spraying and mixing layer (4), the spraying thickness does not cover the anchor heads (8), then anchor head supports (9) are welded and installed on the anchor heads (8), and foundation supports (23) are bolted and installed on the cast-in-situ wedge foundation (22);

5) hoisting construction of prefabricated side plates (32) on two sides of the open cut tunnel extension section (21): the prefabricated side plates (32) are transported to a construction site, and the prefabricated side plates (32) are hoisted by a crane through lifting lugs (15) pre-buried and installed on the side faces of the prefabricated side plates (32) and are respectively installed in slots (33) in the tops of a cast-in-place T-shaped foundation (12) and a cast-in-place wedge-shaped foundation (22);

6) and (2) waterproof construction of a lower steep slope (6) at the inner side of the open cut tunnel extension section (21): paving a waterproof layer (3) on the outer side of a sprayed and mixed layer (4), paving a layer of geotextile (2), attaching the bottom ends of the waterproof layer (3) and the geotextile (2) to the top of a cast-in-place T-shaped foundation (12), embedding the top ends of the waterproof layer (3) and the geotextile (2) into a lower steep slope (6), bolting and installing a support rod (16) between an anchor head support (9) and a lifting lug (15) of a prefabricated side plate (32) on the upper part of the cast-in-place T-shaped foundation (12), and installing a plurality of inclined support rods (20) between the lifting lug (15) of the prefabricated side plate (32) on the upper part of the cast-in-place wedge-shaped foundation (22) and a foundation support (23);

7) excavating a plurality of concave ditches (24) in the leveling area at the outer side of the open cut tunnel extension section (21), and installing vertical dowel bars (25) in the ditches;

8) an inclined lateral formwork is erected at the edge of a leveling area on the outer side of a open cut tunnel extension section (21), a plurality of lateral connecting ribs (14) are installed on the outer sides of prefabricated side plates (32) on two sides, then foam concrete is poured, and the filling height is poured to the top ends of the prefabricated side plates (32) on two sides to form a first foam concrete filling area (31);

9) laying small gantry cranes (36) at the tops of two sides of a first foam concrete filling area (31), hoisting the prefabricated steel arch plate (17), fixing two ends of the prefabricated steel arch plate (17) on wedge-shaped surfaces (35) of prefabricated side plates (32) by using positioning bolts (19), then installing angle-shaped water stop strips (18) on contact surfaces, and well taking anti-corrosion measures of the prefabricated steel arch plate (17);

10) continuously pouring foam concrete above the first foam concrete filling area (31) to form a second foam concrete filling area (30), reserving positions of a drainage blind ditch (26) and a drainage pipe (28) at the top of the second foam concrete filling area (30) during construction, paving a waterproof coiled material on the reserved drainage blind ditch (26), filling graded broken stones inside, covering geotextile on the top, wrapping a plurality of layers of geotextile by the pre-buried drainage pipe (28), communicating one end of the geotextile with the drainage blind ditch (26), and communicating the other end of the drainage blind ditch with the outer side of the open cut tunnel extension section (21);

11) and continuously pouring foam concrete above the second foam concrete filling area (30) to form a third foam concrete filling area (29), then constructing the drainage grooves (27) at the top and the side edges of the foam concrete filling area, and communicating the pre-buried drainage pipes (28) with the drainage grooves (27) at the side edges, thereby completing the construction operation of the open cut tunnel lengthening foam concrete backfilling structure.

Technical Field

The invention relates to the technical field of road traffic safety, in particular to a construction method of a open cut tunnel lengthening foam concrete backfill structure.

Background

The open cut tunnel is usually composed of a roof structure and side walls, depending on the terrain, geology and backfill conditions. When the bottom stratum may be squeezed into the hole, an inverted arch is required. When the top structure is made into an arch, the structure is called an arch-type open cut tunnel. The open cut is mainly used for tunnel openings or cutting sections which are damaged by collapse, falling rocks or flowing rocks and flowing mud, and is sometimes used as an effective means for treating diseases such as falling rocks and landslides of cutting. A tunnel is a necessary measure taken by a line passing through a mountain area or a complex terrain area. Many tunnel approaches are mostly in the form of shallow buried single-pressure or bias voltage in mountainous areas. Over time, shallow single-pressure or bias tunnels can create safety hazards for lines due to natural disasters. In order to avoid the situation, the protection of the lines among the tunnel groups by adopting the open cut tunnel lengthening mode is more reasonable and economical.

Traditional open cut tunnel is backfilled and is generally adopted the mode of thick high fill of filling, and high fill tunnel open cut tunnel is because self load structure limits, and the too big problem of ubiquitous vertical load arouses the structural deformation increase of portal and open cut tunnel structure easily, and overall stability reduces to influence the operation safety in tunnel. Meanwhile, when the open cut tunnel extension section is constructed, traffic needs to be interrupted, traffic control is carried out, and normal operation of traffic lines is influenced

Therefore, the construction method for the open cut tunnel lengthening foam concrete backfilling structure which is stable in structure, high in construction speed, effective in load reduction and settlement prevention and small in traffic influence is needed to be found out very importantly.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a construction method of a open cut tunnel growing foam concrete backfill structure.

The open cut tunnel lengthening foam concrete backfilling structure comprises a cast-in-place T-shaped foundation, Larsen steel sheet piles, lateral connecting ribs, supporting rods, prefabricated steel arch plates, positioning bolts, inclined supporting rods, a cast-in-place wedge-shaped foundation, foundation supports, grooves, vertical inserting ribs, drainage blind ditches, drainage channels, drainage pipes, a third foam concrete filling area, a second foam concrete filling area, a first foam concrete filling area and prefabricated side plates, wherein the Larsen steel sheet piles are arranged at the bottom of the cast-in-place T-shaped foundation, the cast-in-place T-shaped foundation is arranged at the bottom of the inner side edge of an open cut tunnel lengthening section, the foundation supports are arranged at the top of the cast-in-place wedge-shaped foundation, the cast-in-place wedge-shaped foundation is arranged at the bottom of the outer side edge of the open cut tunnel lengthening section, the prefabricated side plates are respectively arranged on the cast-in-place T-place wedge-in-place foundation and the prefabricated wedge-in-place foundation, the prefabricated steel arch plates are arranged between the prefabricated side plates through the positioning bolts, the supporting rods are arranged between the steep slopes at the lower parts of the inner sides of the prefabricated side plates and the open cut tunnel lengthening section, the inclined support rod is arranged between the prefabricated side plate and the cast-in-place wedge-shaped foundation, lateral connecting ribs are arranged on the outer side of the prefabricated side plate, vertical inserting ribs are arranged in the concave groove, the concave groove is arranged in the ground on the outer side of the cast-in-place wedge-shaped foundation, the first foam concrete filling area is arranged in the area below the top end of the prefabricated side plate, the second foam concrete filling area is arranged above the first foam concrete filling area, the drainage blind groove is arranged at the top of the second foam concrete filling area and is close to the steep slope at the lower part, the drainage pipe is communicated with the drainage blind groove and the drainage groove at the side edge of the foam concrete filling area, the third foam concrete filling area is arranged above the second foam concrete filling area, and the drainage groove is arranged at the top and the side edge of the foam concrete filling area.

Preferably, the method comprises the following steps: and the top parts of the cast-in-situ T-shaped foundation and the cast-in-situ wedge-shaped foundation are provided with slots for mounting prefabricated side plates.

Preferably, the method comprises the following steps: the prefabricated steel arch bar is formed by welding an arch frame and a steel plate.

Preferably, the method comprises the following steps: the top of the prefabricated side plate is a 45-degree wedge-shaped surface, and the bottom of the prefabricated side plate is provided with a plug.

Preferably, the method comprises the following steps: the prefabricated steel arch bar and the prefabricated side plate contact surface are provided with angle-shaped water stop strips.

Preferably, the method comprises the following steps: the lower part abrupt slope of open cut tunnel extension section inboard is equipped with stock and anchor rope, and the hanging net passes through stock anchor head and anchor rope anchor head to be fixed on the abrupt slope of lower part, the hanging net outside is equipped with spouts and mixes the layer, spout and mix the layer outside and set gradually waterproof layer and geotechnological cloth.

Preferably, the method comprises the following steps: the anchor cable anchor head is provided with an anchor head support, the outer side of the prefabricated side plate is provided with a lifting lug and a lateral connecting rib, the support rod is arranged between the anchor head support and the lifting lug of the prefabricated side plate on the upper portion of the cast-in-situ T-shaped foundation, and the inclined support rod is arranged between the lifting lug of the prefabricated side plate on the upper portion of the cast-in-situ wedge-shaped foundation and the foundation support.

Preferably, the method comprises the following steps: and small gantry cranes are arranged at the tops of two sides of the first foam concrete filling area.

The construction method of the open cut tunnel extension foam concrete backfill structure comprises the following steps:

1) the two sides of the open cut tunnel extension section are arranged, the ground on the outer side is leveled, the side slope on the inner side is properly excavated to form a steep slope on the lower portion, and the foundation position of the open cut tunnel extension section is determined by measuring and paying off;

2) construction of Larsen steel sheet piles at the inner side of the open cut tunnel extension section: driving a Larsen steel plate pile for water stopping, and filling saw dust, fiber-rich cotton wool and expansion cement into a locking gap of the Larsen steel plate pile in a matched manner;

3) the method comprises the following steps of respectively digging foundation pits dug at two sides of a open cut tunnel extension section, binding reinforcing steel bar pouring concrete and reserving slots, forming a cast-in-place T-shaped foundation integrated with a Larsen steel sheet pile at the inner side of the open cut tunnel extension section, forming a cast-in-place wedge-shaped foundation at the outer side of the open cut tunnel extension section, and simultaneously carrying out manufacturing work of prefabricated side plates and prefabricated steel arch plates in a prefabricated field;

4) protection construction of a lower steep slope on the inner side of the open cut tunnel extension section: anchor rods are arranged on the steep slope at intervals, anchor cables are arranged at corresponding positions, then the hanging net is installed on the anchor rods and the anchor cables, the anchor heads of the anchor rods and the anchor cables are fixed and then sprayed with concrete to form a sprayed layer, the sprayed layer does not cover the anchor heads of the anchor cables, anchor head supports are welded on the anchor heads of the anchor cables, and foundation supports are bolted on a cast-in-place wedge foundation;

5) hoisting construction of prefabricated side plates on two sides of the open cut tunnel extension section: transporting the prefabricated side plate to a construction site, hoisting the prefabricated side plate by using a crane through a lifting lug pre-embedded and installed on the side surface of the prefabricated side plate, and respectively installing the prefabricated side plate into a slot at the top of a cast-in-place T-shaped foundation and a slot at the top of a cast-in-place wedge-shaped foundation;

6) and (3) waterproof construction of the lower steep slope on the inner side of the open cut tunnel extension section: paving a waterproof layer on the outer side of the sprayed concrete layer, paving a layer of geotextile, attaching the bottom end parts of the waterproof layer and the geotextile to the top part of the cast-in-place T-shaped foundation, burying the top end parts of the waterproof layer and the geotextile into a steep slope on the lower part, then bolting an installation support rod between an anchor head support and a lifting lug of a prefabricated side plate on the upper part of the cast-in-place T-shaped foundation, and installing a plurality of inclined support rods between the lifting lug of the prefabricated side plate on the upper part of the cast-in-place wedge-shaped foundation and a foundation support;

7) excavating a plurality of concave ditches in the leveling area outside the open cut tunnel extension section, and installing vertical dowel bars in the ditches;

8) obliquely and laterally erecting a formwork at the edge of a leveling area at the outer side of a connecting section of the open cut tunnel, installing a plurality of lateral connecting ribs at the outer sides of the prefabricated side plates at two sides, then pouring foam concrete, and pouring filling height to the top ends of the prefabricated side plates at two sides to form a first foam concrete filling area;

9) laying small gantry cranes at the tops of two sides of a first foam concrete filling area, hoisting the prefabricated steel arch bar, fixing two ends of the prefabricated steel arch bar on a wedge-shaped surface of a prefabricated side plate by using positioning bolts, then installing an angle-shaped water stop strip on a contact surface, and taking anticorrosion measures of the prefabricated steel arch bar;

10) continuously pouring foam concrete above the first foam concrete filling area to form a second foam concrete filling area, reserving positions of a drainage blind ditch and a drainage pipe at the top of the second foam concrete filling area during construction, paving a waterproof coiled material on the reserved drainage blind ditch, filling graded broken stones inside the drainage blind ditch, covering geotextile on the top, wrapping a plurality of layers of geotextile by the pre-buried drainage pipe, communicating one end of the geotextile with the drainage blind ditch, and leading the other end of the drainage blind ditch to the outer side edge of the open cut tunnel extension section;

11) and continuously pouring foam concrete above the second foam concrete filling area to form a third foam concrete filling area, then performing the construction of the drainage grooves at the top and the side edges of the foam concrete filling area, and communicating the pre-buried drainage pipes with the drainage grooves at the side edges, thereby completing the construction operation of the open-cut tunnel lengthening foam concrete backfilling structure.

The invention has the beneficial effects that:

1. the invention can ensure the normal operation of the existing route in the open cut tunnel extension section in the whole construction process, realizes the open cut tunnel extension operation without a closed road, and has little influence on social traffic, thereby having better social benefit.

2. According to the open cut tunnel, foam concrete is backfilled layer by layer, so that the dead weight is effectively reduced, the vertical load is reduced, the stable structure of the open cut tunnel is ensured, and meanwhile, the first foam concrete filling area provides an operation platform for hoisting the prefabricated steel arch slab, so that the construction is facilitated.

3. According to the open cut tunnel foundation, the bearing capacity of the open cut tunnel foundation is effectively improved by adopting the cast-in-place T-shaped foundation and the cast-in-place wedge-shaped foundation, the prefabricated side plates and the prefabricated steel arch plates are used for rapid installation, the supporting structures are arranged, the structural stability and the construction efficiency are effectively improved, and the construction period is shortened.

4. According to the invention, lateral connecting ribs are arranged on the side surface of the prefabricated side plate, and grooves and vertical inserting ribs are arranged on the stratum, so that the ground gripping force of foam concrete is enhanced, and the integrity and stability of the open cut tunnel extension section are improved.

Drawings

FIG. 1 is a schematic view of a open cut tunnel extension foam concrete backfill structure;

FIG. 2 is a cross-sectional view of a cast-in-place T-footing;

FIG. 3 is a cross-sectional view of a cast-in-place wedge foundation;

FIG. 4 is a cross-sectional view of a prefabricated side panel;

FIG. 5 is a schematic view of the structure of the lower steep slope protection;

FIG. 6 is a schematic view of the installation of prefabricated side panels;

FIG. 7 is a layout view of the grooves and vertical dowels;

FIG. 8 is a schematic view of the hoisting of the prefabricated steel arch slab;

FIG. 9 is a layout view of a drain blind and a drain pipe;

FIG. 10 is a flow chart of construction process of open cut tunnel extension foam concrete backfill structure.

Description of reference numerals: 1-upper steep slope; 2-geotextile; 3-waterproof layer; 4-spraying the mixed layer; 5, hanging a net; 6-lower steep slope; 7-anchor cable; 8-anchor cable head; 9-anchor head support; 10-anchor rod and anchor head; 11-anchor rod; 12-cast-in-place T-foundation; 13-Larsen steel sheet pile; 14-lateral connecting ribs; 15-lifting lug; 16-support bar; 17-prefabricating a steel arch plate; 18-angle water stop bar; 19-positioning bolt; 20-diagonal brace rod; 21-open cut tunnel extension section; 22-cast-in-place wedge foundation; 23-base support; 24-groove; 25-vertical dowel bars; 26-drainage blind ditch; 27-a drainage groove; 28-a drain pipe; 29-third foam concrete filled area; 30-second foam concrete filled area; 31-first foam concrete filled area; 32-prefabricated side panels; 33-slot; 34-plug; 35-wedge surface; 36-Small gantry crane.

Detailed Description

The present invention will be further described with reference to the following examples. The following examples are set forth merely to aid in the understanding of the invention. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Example one

The open cut tunnel lengthening foam concrete backfilling structure comprises geotextile 2, a waterproof layer 3, a spraying and mixing layer 4, a hanging net 5, an anchor rope 7, an anchor rope anchor head 8, an anchor head support 9, an anchor rod anchor head 10, an anchor rod 11, a cast-in-place T-shaped foundation 12, a Larsen steel sheet pile 13, lateral connecting ribs 14, lifting lugs 15, supporting rods 16, prefabricated steel arch plates 17, angle-shaped water stop strips 18, positioning bolts 19, inclined supporting rods 20, a cast-in-place wedge-shaped foundation 22, a foundation support 23, a concave ditch 24, vertical inserting ribs 25, drainage blind ditches 26, drainage channels 27, drainage pipes 28, a third foam concrete filling area 29, a second foam concrete filling area 30, a first foam concrete filling area 31 and prefabricated side plates 32, wherein the Larsen steel sheet pile 13 is arranged at the bottom of the open cut tunnel lengthening section 21, the foundation support 23 is arranged at the top of the wedge-shaped foundation 22, the concrete-filled open cut tunnel is arranged at the bottom of the outer side edge of a open cut tunnel lengthening section 21, prefabricated side plates 32 are respectively arranged on a cast-in-place T-shaped foundation 12 and a cast-in-place wedge-shaped foundation 22, a prefabricated steel arch plate 17 is arranged between the prefabricated side plates 32 through positioning bolts 19, angle-shaped water stop strips 18 are arranged on the contact surfaces of the prefabricated steel arch plate 17 and the prefabricated side plates 32, an anchor rod 11 and an anchor cable 7 are arranged on a lower steep slope 6 on the inner side of the open cut tunnel lengthening section 21, a net 5 is fixed on the lower steep slope 6 through an anchor rod anchor head 10 and an anchor cable anchor head 8, a spraying and mixing layer 4 is arranged on the outer side of the net 5, a waterproof layer 3 and a geotextile 2 are sequentially arranged on the outer side of the spraying and mixing layer 4, an anchor head support 9 is arranged on the anchor cable anchor head 8, lifting lugs 15 and lateral connecting ribs 14 are arranged on the outer side of the prefabricated side plates 32, a support rod 16 is arranged between the anchor head support 9 and the lifting lugs 15, an oblique support rod 20 is arranged between the lifting lugs 15 and a foundation support 23, vertical joint bars 25 are arranged in the concave ditch 24 and are arranged in the ground outside the cast-in-place wedge-shaped foundation 22, the first foam concrete filling area 31 is arranged in the area below the top end of the prefabricated side plate 32, the second foam concrete filling area 30 is arranged above the first foam concrete filling area 31, the drainage blind ditch 26 is arranged at the top of the second foam concrete filling area 30 and is close to the lower steep slope 6, the drainage pipe 28 is communicated with the drainage blind ditch 26 and the drainage groove 27 on the side edge, the third foam concrete filling area 29 is arranged above the second foam concrete filling area 30, and the drainage groove 27 is arranged at the top and the side edge of the foam concrete filling area.

The top of the cast-in-place T-shaped foundation 12 and the top of the cast-in-place wedge-shaped foundation 22 are both provided with slots 33 for mounting prefabricated side plates 32.

The prefabricated steel arch bar 17 is formed by welding an arch frame and a steel plate.

The top of the prefabricated side plate 32 is a 45-degree wedge-shaped surface 35, and the bottom of the prefabricated side plate is provided with a plug 34.

The upper steep slope 1 is located above the lower steep slope 6.

And small gantry cranes 36 are arranged at the tops of two sides of the first foam concrete filling area 31.

Example two

The construction method of the open cut tunnel lengthening foam concrete backfill structure comprises the steps of firstly arranging the fields on two sides of the open cut tunnel lengthening section, driving a Larsen steel sheet pile for water stop construction, then constructing foundations on two sides of the open cut tunnel lengthening section, well performing protection construction on a steep slope on the lower portion of the inner side of the open cut tunnel lengthening section, then hoisting prefabricated side plates, performing waterproof operation on the steep slope on the lower portion and installation construction of a supporting rod and a diagonal rod, then performing first foam concrete filling area construction on a plurality of concave ditches and vertical inserting ribs in a flattening area on the outer side of the open cut tunnel lengthening section while supporting a formwork in an inclined side mode, then performing hoisting operation and second foam concrete filling area construction on a prefabricated steel arch plate, performing third foam concrete filling area construction after arranging reserved drainage blind ditches and drainage pipes, and finally performing guide groove construction on the top and the side edges, and completing backfill construction of the open cut tunnel lengthening foam concrete system. The method specifically comprises the following steps:

1) the two sides of the open cut tunnel extension section 21 are arranged in a field mode, the ground on the outer side is leveled, the side slope on the inner side is properly excavated to form a lower steep slope 6, and the foundation position of the open cut tunnel extension section 21 is determined by measuring and paying off;

2) constructing the Larsen steel sheet pile 13 at the inner side of the open cut tunnel extension section 21: driving the Larsen steel sheet pile 13 for water stopping, and filling water stopping materials such as sawdust powder, fiber-rich cotton wool, expansion cement and the like into a locking gap of the Larsen steel sheet pile in a matched mode, so that the water stopping effect of the Larsen steel sheet pile 13 is enhanced;

3) as shown in fig. 2, 3 and 4, foundation pits are respectively dug on two sides of the open cut tunnel extension section 21, steel bar pouring concrete is bound, slots 33 are reserved, a cast-in-situ T-shaped foundation 12 integrated with the larsen steel sheet pile 13 is formed on the inner side, a cast-in-situ wedge-shaped foundation 22 is formed on the outer side, and meanwhile, the prefabricated side plates 32 and the prefabricated steel arch plates 17 are manufactured in a prefabricated field;

4) as shown in fig. 5, the protection construction of the lower steep slope 6 inside the open cut tunnel extension section 21: anchor rods 11 are arranged on the lower steep slope 6 at intervals, anchor cables 7 are arranged at corresponding positions, then a hanging net 5 is installed on the anchor rods 11 and the anchor cables 7, an anchor rod head 10 and an anchor cable head 8 are used for fixing and then concrete is sprayed to form a spraying and mixing layer 4, the spraying thickness does not cover the anchor cable head 8, then an anchor head support 9 is welded and installed on the anchor cable head 8, and a foundation support 23 is bolted and installed on the cast-in-place wedge foundation 22;

5) hoisting construction of the prefabricated side plates 32 on two sides of the open cut tunnel extension section 21: transporting the prefabricated side plates 32 to a construction site, hoisting the prefabricated side plates 32 by using a crane through lifting lugs 15 pre-embedded and mounted on the side surfaces of the prefabricated side plates 32, and respectively mounting the prefabricated side plates into slots 33 in the tops of the cast-in-situ T-shaped foundation 12 and the cast-in-situ wedge-shaped foundation 22;

6) as shown in fig. 6, the waterproofing work of the lower steep slope 6 inside the open cut tunnel extension section 21: paving a waterproof layer 3 on the outer side of a sprayed and mixed layer 4, paving a layer of geotextile 2, attaching the bottom end parts of the waterproof layer 3 and the geotextile 2 to the top part of a cast-in-place T-shaped foundation 12, embedding the top end parts of the waterproof layer 3 and the geotextile 2 into a lower steep slope 6, then bolting and installing a support rod 16 between an anchor head support 9 and a prefabricated side plate 32 lifting lug 15 on the upper part of the cast-in-place T-shaped foundation 12, and installing a plurality of inclined support rods 20 between the lifting lug 15 of the prefabricated side plate 32 on the upper part of a cast-in-place wedge-shaped foundation 22 and a foundation support 23;

7) as shown in fig. 7, a plurality of concave ditches 24 are dug in the leveling area outside the open cut tunnel extension section 21, and vertical dowel bars 25 are installed in the ditches;

8) obliquely supporting a formwork on the edge of a leveling area outside the open cut tunnel extension section 21, installing a plurality of lateral connecting ribs 14 on the outer sides of the prefabricated side plates 32 on two sides, then pouring foam concrete, and pouring filling height to the top ends of the prefabricated side plates 32 on two sides to form a first foam concrete filling area 31;

9) as shown in fig. 8, small gantry cranes 36 are arranged at the tops of two sides of the first foam concrete filling area 31 to hoist the prefabricated steel arch bar 17, two ends of the prefabricated steel arch bar 17 are fixed on wedge-shaped surfaces 35 of side plates by using positioning bolts 19, then angle-shaped water stop bars 18 are installed on contact surfaces, and anti-corrosion measures for the prefabricated steel arch bar 17 are taken;

10) as shown in fig. 9, foam concrete is continuously poured above the first foam concrete filling area 31 to form a second foam concrete filling area 30, positions of the drainage blind ditch 26 and the drainage pipe 28 are reserved at the top of the second foam concrete filling area 30 during construction, a waterproof coiled material is laid on the reserved drainage blind ditch 26, graded broken stones are filled inside, the top is covered with geotextile, the pre-buried drainage pipe 28 wraps multiple layers of geotextile, one end of the geotextile is communicated with the drainage blind ditch 26, and the other end of the drainage blind ditch is communicated with the outer side edge of the open cut tunnel extension section 21;

11) as shown in fig. 1, foam concrete is continuously poured above the second foam concrete filling area 30 to form a third foam concrete filling area 29, then the construction of the drainage grooves 27 at the top and the side of the foam concrete filling area is carried out, and the pre-buried drainage pipes 28 are communicated with the drainage grooves 27 at the side, so that the construction operation of the open cut tunnel extension foam concrete backfill structure is completed.