Open cut tunnel plain concrete pile composite foundation and construction method

Abstract

The invention belongs to the field of open-cut tunnels, and particularly relates to an open-cut tunnel plain concrete pile composite foundation and a construction method, the composite foundation comprises a stratum reinforced by a plurality of plain concrete piles, and a broken stone cushion layer and a C20 concrete cushion layer laid on the top of the plain concrete piles; the plain concrete piles are arranged in a matrix mode, and the width of the plain concrete pile matrix is larger than that of the tunnel structure. The uniform transition of the foundation rigidity between the filling section and the excavation section is realized by changing the pile length of the plain concrete pile; the construction method is the construction method of the composite foundation, the plain concrete pile is subjected to hole forming through a rotary drilling machine and then backfilled with soil, and then a long spiral drilling machine is matched with a ground pump for pouring. The composite foundation is simple in structure and reasonable in design, and the tunnel structure foundation difference is reduced; compared with a traditional underwater steel guide pipe pouring method, construction of the plain concrete pile is higher in construction speed, small in turnover material consumption, low in cost and good in pile body integrity.

Description

Technical Field

[0001] The invention belongs to the technical field of open-cut tunnel construction, and in particular relates to an open-cut tunnel plain concrete pile composite foundation and a construction method. Background Art

[0002] Cut-and-cover tunnels are tunnels built using the open-cut method. The open-cut method is an underground engineering construction method that first digs the ground, builds the lining in the open air, and then covers and backfills. It is mostly used for shallow buried tunnels; it is also the most basic and most commonly used construction method in soft soil underground engineering construction. Generally, open-cut tunnels do not require special foundation treatment. Most of them use foundation pit support or ground-connected walls, then carry out the main construction, and finally backfill.

[0003] A certain project is to build an open-cut tunnel under the airport. The tunnel is constructed by open-cut construction, and then the airport is built on the surface. The thickness of the backfill soil layer is about 20 to 30 meters. If the foundation of the open-cut tunnel under the airport is not treated, settlement will occur, affecting the safety of the tunnel structure. The open-cut tunnel under the airport is 2489 meters long. The survey area is hilly with large fluctuations. The ground elevation is 25 to 130 meters. The maximum burial depth of the tunnel is about 80 meters. The longitudinal slope of the tunnel entrance and exit slope is 15° to 25°. According to the relationship between the elevation of the open-cut tunnel under the airport and the elevation of the planned airport field, the tunnel is divided into several excavation sections and filling sections. At the same time, the tunnel passes through multiple strata, such as W3 stratum (strongly weathered metamorphic sandstone, which is soft rock), W4 stratum (fully weathered metamorphic sandstone, which is medium-hard soil), and Quaternary stratum. For the open-cut tunnel foundation treatment of this project with both excavation and filling sections, there are few similar projects and the existing open-cut tunnel base treatment methods are difficult to directly apply here. Therefore, it is necessary to provide a foundation treatment technology for deep buried open-cut tunnels that targets the above-mentioned situation. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an open-cut tunnel plain concrete pile composite foundation and a construction method.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A composite foundation of plain concrete piles for an open-cut tunnel is applied to a fill-to-cut transition section of a deep-buried open-cut tunnel, comprising a stratum reinforced by a plurality of plain concrete piles and a crushed stone cushion layer and a C20 concrete cushion layer laid on the tops of the plain concrete piles; the plain concrete piles are arranged in a matrix, and the width of the plain concrete pile matrix is ​​greater than the width of the tunnel structure; and a uniform transition of foundation stiffness between the fill section and the cut section is achieved by changing the length of the plain concrete piles.

[0007] Furthermore, the diameter of the plain concrete pile is 0.6m, the length is not less than 3.0m, and the depth of the pile end into the bearing layer is not less than 1m; the horizontal pile spacing in the plain concrete pile matrix is ​​1.70-2.35m, and the longitudinal pile spacing is 2-2.5m; the maximum particle size of the gravel in the gravel cushion layer on the top of the pile does not exceed 50mm, the mud content is not more than 5%, and the dynamic deformation modulus after compaction E vd Not less than 40MPa.

[0008] Furthermore, the plain concrete piles are arranged in a plate every 10 meters in the mileage direction. Depending on the geological conditions, the lengths of the plain concrete piles in each plate are the same or different; depending on the geological conditions, the length of the fill-excavation transition section is 10 to 50 meters.

[0009] Furthermore, the excavation section adopts plain concrete piles, CFG piles, steel pipe grouting and closed cushion reinforcement measures according to the geological conditions; for the filling section, reinforced concrete bored piles are used for foundation treatment.

[0010] Furthermore, deformation joints with a width of 2 cm are set in the transition sections of sections where different foundation treatment measures are adopted; the length of the foundation treatment piles and the thickness of the cushion layer in the transition section are gradually transitioned and changed, which plays a role in reducing the longitudinal differential settlement of the tunnel structure; for the cross-sectional direction, the same foundation treatment measures are adopted within the influence range of the tunnel structure to reduce the lateral differential settlement of the structure.

[0011] Furthermore, the diameter of reinforced concrete bored cast-in-place piles is determined comprehensively according to the pile foundation form, force analysis and construction conditions; for sections with soil cover less than 10m, a 1.25m diameter pile foundation is used, and for sections with soil cover greater than 10m, a 1.5m diameter pile foundation is used. The pile type selection in the cavern of the fill section is the same as the open-cut structure of the same section; 4 piles are arranged in the cross-sectional direction of the bored cast-in-place piles, respectively arranged under the side walls of the open-cut structure, the center distance of the bored cast-in-place piles is 2 times the pile diameter, and the net distance from the edge of the structural bottom plate to the outermost row of piles is 0.5 times the pile diameter; the arrangement of bored cast-in-place piles along the line direction should be considered to be unified with the casting modulus of the open-cut structure, the longitudinal spacing of the pile foundation is 5m, the single casting length of the open-cut structure is 10m, the pile foundation is arranged in the center, the center is 2.5m away from the structural construction joint, the top of the pile foundation is consolidated with the open-cut bottom plate structure, and extends 100mm into the structural bottom plate.

[0012] Furthermore, the steel flower pipe used for grouting has an outer diameter of 76mm and a wall thickness of 3.5mm. It is arranged at intervals of 100cm×100cm, vertically laid on the base, and has a depth of 2.5m. The steel flower pipe is made of seamless hot-rolled steel pipe, and grouting holes are drilled at the front with a hole diameter of 6mm and a hole spacing of 20 to 30cm. It is arranged in a plum blossom shape, and the front end is processed into a cone. The tail is not drilled for a length of not less than 100cm, which serves as a grouting stop section. Cement slurry is used for grouting with a water-cement ratio of 1:1 (weight ratio) or determined on site, and a grouting pressure of 0.5 to 1.0MPa. The slurry viscosity is 80s to 90s.

[0013] Furthermore, the excavation section is reinforced with CFG piles with a diameter of 500mm and the depth of the pile end entering the bearing stratum is not less than 0.5m; a 0.3m thick gravel cushion layer and a 0.15m thick C20 concrete cushion layer are set on the top of the pile, and the upper layer of the C20 concrete cushion layer is the bottom surface of the tunnel lining structure; the filling section is reinforced with reinforced concrete bored piles, and a 0.2m thick C20 concrete cushion layer is set on the top of the pile; the filling-excavation transition section is reinforced with plain concrete piles with a diameter of 600mm, and a 0.2m thick gravel cushion layer and a 0.15m thick C20 concrete cushion layer are set on the top of the pile; temporary drainage is carried out during the construction of the excavation section cushion layer, and C20 concrete is used to backfill the foundation pit at unequal heights of the structure.

[0014] The present invention also proposes a construction method for a composite foundation of open-cut tunnel plain concrete piles, comprising the following steps:

[0015] S1. According to the relationship between the tunnel elevation, the current ground elevation and the airport planned field elevation, and taking into account the influence of the thickness of the soft soil layer at the bottom of the tunnel, the boundary between the filling and excavation sections is determined, and the filling section, excavation section and filling-excavation transition section are divided;

[0016] S2. According to the tunnel stratum conditions, select reasonable foundation treatment measures to reduce structural differential settlement;

[0017] Different foundation treatment measures are selected for the excavation section according to different strata; for the fill section, reinforced concrete bored cast-in-place piles are used for foundation treatment, and the pile diameter, pile length, reinforcement and other parameters are determined by calculation; for the fill-excavation transition section, plain concrete piles are used for foundation treatment, and uniform transition of foundation stiffness between the fill section and the excavation section is achieved by changing the pile length.

[0018] Furthermore, the plain concrete pile is made by drilling a hole, backfilling the hole with soil, and then pouring plain concrete using a long spiral drill and a ground pump;

[0019] After the rotary drilling is completed, the existing plain concrete piles are backfilled to prevent the hole from collapsing. The backfill material is the clay produced during the drilling process;

[0020] The downward drilling speed of the long spiral drill is 1.8 to 2.2 m / min. When the long spiral drill is drilling, observe the depth of the drill rod. When the maximum depth is reached, continue drilling for 3 minutes to ensure that the hole reaches the designed hole depth. After the long spiral drill has drilled to the designed depth, lift the drill rod to open the drill bit slide and start pouring concrete through the ground pump. Pour while lifting the drill rod, with a drilling speed of 1.2 to 1.5 m / min, and ensure that the drill bit tip is always buried in the slurry mixture for 0.8 to 1.1 m to prevent pile breakage. When pouring concrete to the top of the pile, it should appropriately exceed the designed elevation of the pile top by not less than 50 cm.

[0021] The beneficial effects of the present invention are:

[0022] The composite foundation of the present invention has a simple structure and a reasonable design. The foundation of the filling-excavation transition section is reinforced by dry plain concrete piles and a crushed stone cushion layer is provided. The foundation stiffness between the filling section and the excavation section is uniformly transitioned by changing the length of the plain concrete piles, thereby reducing the difference in the foundation of the tunnel structure.

[0023] The method of the present invention performs reasonable foundation reinforcement treatment on the excavation section, the filling section and the excavation-filling transition section according to the tunnel stratum conditions, thereby reducing the differential settlement of the tunnel structure caused by different geological conditions and ensuring the long-term stability of the open-cut tunnel under the airport;

[0024] The plain concrete piles in the present invention are backfilled with soil after a hole is drilled by rotary drilling, and then poured with a long spiral drill in cooperation with a ground pump. Compared with the traditional underwater steel pipe pouring method, the plain concrete piles of the present invention have a faster construction speed, less consumption of turnover materials, low cost, and better integrity of the pile body. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0026] Figure 1 This is a cross-sectional layout diagram of CFG pile reinforcement according to an embodiment of the present invention.

[0027] Figure 2 This is a cross-sectional layout diagram of reinforced concrete bored cast-in-place pile reinforcement according to an embodiment of the present invention.

[0028] Figure 3 This is a vertical layout diagram of the steel bars of a reinforced concrete bored pile according to an embodiment of the present invention.

[0029] Figure 4 This is a cross-sectional layout diagram of the grouting of the steel flower tube according to an embodiment of the present invention.

[0030] Figure 5 This is a grouting arrangement diagram for a steel flower tube according to an embodiment of the present invention.

[0031] Figure 6 This is a cross-sectional layout diagram of a plain concrete pile foundation treatment according to an embodiment of the present invention.

[0032] Figure 7 This is a plan view of the plain concrete piles according to an embodiment of the present invention.

[0033] Figure 8 It is a schematic longitudinal section diagram of a fill-cut transition section according to an embodiment of the present invention.

[0034] Fig. 9 It is a schematic diagram of the reinforcement application of the fill-cut transition section according to an embodiment of the present invention.

[0035] Fig.10 for Fig. 9 Foundation plan of the fill-cut transition section.

[0036] Fig.11 It is a schematic longitudinal section diagram of the full weathering-strong weathering transition section of an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0038] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0039] like Figures 1 to 10 As shown, the present invention proposes a composite foundation of plain concrete piles for open-cut tunnels, which is applied to the fill-to-cut transition section of deep-buried open-cut tunnels, including a stratum reinforced by a plurality of plain concrete piles and a crushed stone cushion layer and a C20 concrete cushion layer laid on the tops of the plain concrete piles; the plain concrete piles are arranged in a matrix, and the width of the plain concrete pile matrix is ​​greater than the width of the tunnel structure; and a uniform transition of the foundation stiffness between the fill section and the cut section is achieved by changing the length of the plain concrete piles.

[0040] The present invention also proposes a construction method for a composite foundation of plain concrete piles of an open-cut tunnel, which is used for the construction of the above-mentioned composite foundation of plain concrete piles of an open-cut tunnel, and comprises the following steps:

[0041] S1. According to the relationship between the tunnel elevation, the current ground elevation and the airport planned field elevation, and taking into account the influence of the thickness of the soft soil layer at the bottom of the tunnel, the boundary between the filling and excavation sections is determined, and the filling section, excavation section and filling-excavation transition section are divided;

[0042] S2. According to the tunnel stratum conditions, select reasonable foundation treatment measures to reduce structural differential settlement;

[0043] Different foundation treatment measures are selected for the excavation section according to different strata; for the filling section, reinforced concrete bored pile measures are adopted for foundation treatment, and the pile diameter, pile length, reinforcement and other parameters are determined according to the requirements of meeting the bearing capacity of the composite foundation; for the filling-excavation transition section, plain concrete pile treatment measures are adopted for foundation treatment, and the foundation stiffness between the filling section and the excavation section is uniformly transitioned by changing the pile length, so that the filling-excavation transition section meets the composite foundation bearing capacity requirements in the relevant specifications ("Technical Code for Foundation Treatment of Railway Engineering" (TB 10106-2023)). The principle of the foundation treatment of the present invention is: along the line direction, according to the changes in the strata at the bottom of the tunnel, the foundation treatment measures are selected by category, and deformation joints are set for the section transition section using different foundation treatment measures. At the same time, the foundation treatment pile length and cushion thickness in the transition section are gradually transitioned and gradually changed, which plays a role in reducing the longitudinal differential settlement of the tunnel structure; for the cross-sectional direction, the same foundation treatment measures are adopted within the influence range of the tunnel structure to reduce the lateral differential settlement of the structure.

[0044] Furthermore, the excavation section adopts plain concrete piles, CFG piles, steel pipe grouting and closed cushion measures according to the stratum conditions. Specifically, for the open-cut tunnel construction under the airport in the background technology of the present invention; for the excavation section, when the tunnel bottom is located in the W3 stratum, the foundation treatment adopts closed cushion measures, when the tunnel bottom is located in the W4 stratum, steel pipe grouting reinforcement (unloading section) or CFG pile composite foundation (loading section) is adopted; when the tunnel bottom is located in the Quaternary stratum, CFG pile composite foundation is adopted.

[0045] Furthermore, the diameter of the reinforced concrete bored pile is determined based on the pile foundation form, force analysis and construction conditions; for sections with soil cover less than 10m, a 1.25m diameter pile foundation is used, and for sections with soil cover greater than 10m, a 1.5m diameter pile foundation is used. The pile type selection in the cavern of the fill section is the same as the open cave structure of the same section. Figure 2 As shown, four bored piles are arranged in the cross-section direction, respectively arranged under the side wall of the open hole structure. The center distance of the bored piles is 2 times the pile diameter, and the net distance between the edge of the structure bottom plate and the outermost row of piles is 0.5 times the pile diameter. The arrangement of bored piles along the line direction should be considered to be consistent with the casting modulus of the open hole structure. The longitudinal spacing of the pile foundation is 5m, and the single casting length of the open hole structure is 10m. The pile foundation is arranged in the center, with the center distance of 2.5m from the structural construction joint. The top of the pile foundation is consolidated with the open hole bottom plate structure and extends into the structure bottom plate by 100mm. Figure 3As shown in the figure, the reinforced concrete bored pile has a full-length steel cage, the main reinforcement of the pile foundation extends into the structural base plate at 15°, the anchorage length is 1.5m, and reinforced stirrups are set. The steel cage is equipped with spiral stirrups, which are spot welded and fixed on the main reinforcement. The vertical spacing of the spiral stirrups is 200mm. For the top and bottom of the pile, the reinforcement is increased within 5D, and the spacing is 100m. A reinforcing hoop is set every 2m along the direction of the steel cage. The reinforcing hoop is a closed hoop and welded to the main reinforcement. The reinforced concrete bored pile body adopts C40 reinforced concrete (impermeability grade P10), the thickness of the steel protection layer is 70mm, and the steel bars are HRB400 and HPB300.

[0046] Further, such as Figure 6 , Figure 7 As shown, the diameter of the plain concrete pile is 0.6m. The determination of the pile diameter is based on the requirements for the diameter of solid plain concrete piles in the "Technical Code for Foundation Treatment of Railway Engineering" (TB 10106-2023) and is obtained through bearing capacity calculation, while taking into account economic efficiency; the cross-sectional pile layout range is not less than 2m outside the tunnel floor structure, the pile length is not less than 3.0m, and the depth of the pile end into the W3 stratum bearing layer is not less than 1.0m. Considering economic efficiency, the depth of the pile end into the W3 stratum is 1m, which meets the bearing capacity requirements. The horizontal pile spacing is 1.70~2.35m, the longitudinal pile spacing is 2~2.5m, the excavation side is treated to 2m outside the structure, and the filling side is treated to 5m outside the structure. The body of the plain concrete pile is made of C35 concrete, and the cubic compressive strength at 28 days is not less than 35Mpa; a 0.2m crushed stone cushion is set on the top of the pile. The crushed stone is hard, not easy to weather and well-graded gravel or crushed stone, with a maximum particle size of no more than 50mm and a mud content of no more than 5%. The dynamic deformation modulus after compaction is E vd Not less than 40MPa. When the pumping performance of the plain concrete mixture meets the construction requirements, no pumping machine is required. When the cement content is relatively low and the temperature is high, a pumping agent can be appropriately added to the plain concrete raw materials.

[0047] Further, such as Figure 1 As shown, the diameter of the CFG pile is 0.5m, the length is not less than 3.0m, and the depth of the pile end into the W3 bearing stratum is not less than 0.5m. The excavation side is treated to 2m outside the structure, and the filling side is treated to 5m outside the structure. The pile body is made of C35 concrete, and the mix ratio should be determined through indoor tests before construction. The cubic compressive strength at 28 days is not less than 35MPa. A 0.3m thick crushed stone cushion layer is set on the top of the pile. It uses hard, non-weathered and well-graded gravel or crushed stone. Its maximum particle size should not be greater than 50mm, the mud content should not be greater than 5%, and the dynamic deformation modulus after compaction is E vdNot less than 40MPa. The CFG pile construction process can be followed in accordance with the conventional CFG pile construction process. Note that the drill rod should be lifted statically, and the lifting speed should generally be controlled at 1.2m-1.5m / min, and continuous lifting should be ensured. Overspeed lifting is strictly prohibited during construction.

[0048] Further, such as Figure 4 , Figure 5 As shown in the figure, the outer diameter of the steel tube used for grouting is 76mm, the wall thickness is 3.5mm, the spacing is 100cm×100cm, the vertical base is set, and the depth is 2.5m; the steel tube is grouting to 2m outside the structure. Grouting uses cement slurry, the water-cement ratio is 1:1 (weight ratio) or determined according to the site, and the grouting pressure is 0.5~1.0MPa. The steel tube is made of seamless hot-rolled steel pipe, and the grouting hole is drilled in the front part, with a hole diameter of 6mm and a hole spacing of 20~30cm. It is arranged in a plum blossom shape, the front end is processed into a cone, and the tail is not drilled for a length of not less than 100cm, which serves as a grouting stop section. The viscosity of the slurry should be 80s~90s, and the compressive strength of the 70.7mm×70.7mm×70.7mm cubic test block after sealing the slurry for 7d should be 0.3MPa~0.5MPa. Ordinary Portland cement is suitable for slurry. Fly ash can be partially added during grouting, and the amount of addition can be 20% to 50% of the weight of cement. According to the needs of the project, quick-setting agent, water-reducing agent and anti-water precipitation agent can be added when mixing the slurry. The installation of steel flower pipes generally adopts the drilling method. The diameter of the drill hole is 3 to 5 mm larger than the diameter of the steel pipe. Then the small catheter is passed through the steel frame and pushed in with a hammer or a drill. The length of the push-in is not less than 90% of the length of the steel pipe, and the sand and gravel in the steel pipe are blown out with high-pressure wind. Before grouting the steel flower pipe, a water pressure test should be carried out to check whether the mechanical equipment is normal and whether the pipeline connection is correct. In order to speed up the grouting speed and maximize the efficiency of the equipment, group pipe grouting (3 to 5 pipes each time) can be used. After the grouting volume reaches the designed grouting volume or the grouting pressure reaches the designed maximum grouting pressure and the grouting flow rate is not more than 1L / min, the grouting can be stopped after continuing for 30 minutes. During the grouting process, the changes in the grouting pressure and the grouting pump discharge volume should be observed at any time, and the grouting situation should be analyzed to prevent pipe blockage, grouting, and leakage. Keep good grouting records in order to analyze the grouting effect.

[0049] like Figures 8 to 10The figure shows the foundation treatment schematic diagram of the fill-excavation transition section; the excavation section is reinforced with CFG piles, the diameter of the CFG piles is 500mm, and a 0.3m thick gravel cushion and a 0.15m thick C20 concrete cushion are set on the pile top. The upper layer of the C20 concrete cushion is the bottom surface of the tunnel lining structure; the fill section is reinforced with reinforced concrete bored piles, and a 0.2m thick C20 concrete cushion is set on the pile top; the fill-excavation transition section is reinforced with plain concrete piles, the diameter of the plain concrete piles is 600mm, and a 0.2m thick gravel cushion and a 0.15m thick C20 concrete cushion are set on the pile top. The number of piles in the figure is for reference only. During construction, the lining type should be selected, and the transition section lining structure should be equipped with deformation joints; during the construction of the lining structure, the low-to-high order should be followed, with the excavation section being constructed first and the fill section being constructed later; temporary drainage should be done during the construction of the excavation section cushion, and C20 concrete should be used to backfill the foundation pit at the unequal height of the structure.

[0050] Further, such as Figures 8 to 10 As shown in the figure, the open-cut structure is equipped with deformation joints at the places where the structural section changes, the places where the foundation treatment measures change, the boundary between the open-cut tunnel and the roadbed structure, and the places where the strata change significantly. The width of the deformation joint is 2cm, and the deformation joint can be designed in a conventional way. The construction joints (excluding deformation joints) are arranged at intervals of 10 or 20m on the bottom plate of the open-cut structure, and the construction joints (excluding deformation joints) are arranged at intervals of 10m on the open-cut arch wall.

[0051] Furthermore, the site is leveled before pile foundation construction. If there are plants, the plant roots need to be dug out and the site is leveled. The leveling elevation = designed pile top elevation + 1.0m.

[0052] Next, the pile foundation construction process of the present invention is specifically described by taking the open-cut tunnel under the airport in the project in the background technology as an example. The overburden in the design area of ​​the open-cut tunnel under the airport is the Quaternary Holocene (Q4) and Pleistocene (Q1+2+3); the underlying Tertiary Miocene (N1), Lower Tertiary (E), Cretaceous (K), Jurassic (J), Triassic (T), Carboniferous (C), Devonian (D), Ordovician (O), Cambrian (∈) strata. The intrusive rock is mainly Yanshanian (γ5) granite. The lithology of each rock and soil layer is, from top to bottom and from new to old, metamorphic sandstone W4 stratum and metamorphic sandstone W3 stratum; metamorphic sandstone W4 stratum is a fully weathered stratum with a basic bearing capacity of 180kPa; metamorphic sandstone W3 stratum is a strongly weathered stratum with a basic bearing capacity of 450kPa. The concrete materials, mix proportions and durability indicators used in foundation treatment should meet the requirement of a design service life of 100 years.

[0053] Specifically, the foundation treatment process of the tunnel filling section is as follows:

[0054] The first step is to build construction fences, level the site, and build drainage ditches around the foundation pit; if there is a pond, drain the pond in the tunnel area and treat the surface silt texture;

[0055] The second step is to carry out the first phase of earth backfilling, fill the soil to the tunnel bottom elevation, and perform tamping treatment;

[0056] The third step is to construct the reinforced concrete bored pile foundation;

[0057] The fourth step is to construct the tunnel bottom cushion, lay the bottom slab waterproof layer, and pour the open hole bottom slab concrete; after the bottom slab concrete reaches the designed strength, the open hole arch wall structure can be constructed;

[0058] In this embodiment, the length of the reinforced concrete bored pile is 16m to 86m.

[0059] Specifically, the foundation treatment process of the tunnel excavation section is as follows:

[0060] The first step is to build construction enclosures, level the ground, and construct an open excavation pit; set up a water interception ditch on the top of the slope, and set up a brick retaining wall outside the slope line; excavate the soil layer with a slope, and the excavation height should not exceed 1.0m each time, and hang a net and spray mix in time, and apply soil nail support. Only after completion can the excavation continue;

[0061] The second step is to excavate the foundation pit to the first-level slope platform, carry out the second-level slope excavation, and excavate to the design elevation of the foundation pit bottom according to the method in the first step, implement slope protection measures and drainage ditches at the bottom of the pit;

[0062] The third step is to implement foundation treatment measures at the bottom of the foundation pit; for the excavation section, when the tunnel bottom is located in the W3 stratum, the foundation treatment adopts closed pad measures; when the tunnel bottom is located in the W4 stratum, steel flower pipe grouting reinforcement (unloading section) or CFG pile composite foundation (loading section) is adopted; when the tunnel bottom is located in the Quaternary stratum,

[0063] Use CFG pile composite foundation;

[0064] The fourth step is to construct the tunnel bottom cushion layer, lay the bottom slab waterproof layer, and pour the open hole bottom slab concrete; after the bottom slab concrete reaches the designed strength, the open hole arch wall structure can be constructed.

[0065] The foundation treatment process of the fill-excavation transition section refers to the fill section process and excavation section process.

[0066] In the present invention, CFG piles and reinforced concrete bored piles adopt conventional construction steps, and plain concrete piles do not adopt conventional underwater steel pipe pouring method, but innovatively adopt rotary drilling, long spiral drilling machine and ground pump pouring construction scheme. Specifically, the construction method of plain concrete piles in this embodiment includes the following steps:

[0067] (1) Construction preparation: On the basis of three connections and one leveling, the drilling platform site is leveled, and it must be leveled and compacted. Site leveling requires that the original ground elevation must be 1m higher than the pile top elevation before the drilling rig enters the site.

[0068] (2) Determine the hole position: According to the control points provided in the design drawings, use the total station to arrange the control network on site and check it. According to the coordinate value of the central axis of the pile foundation, use the coordinate method to lay out the center line and center point of the pile foundation, and drive in the standard stakes. The stakeout error of the center line is controlled within 1 cm. A cross-shaped control stake is set in a safe area about 2 m away from the center of the pile for easy verification, and the pile number is marked on the pile.

[0069] (3) Digging and burying casing: The casing is made of 10mm thick steel plate; its bottom is buried 3.5m below the ground surface, and the top of the casing is 0.5m above the ground. The casing is buried by digging and burying method, and the burial is accurate, horizontal, vertical and stable. The surrounding of the casing is backfilled with clay and compacted. The center line of the drill bit and the center line of the casing are kept in the same straight line, and the deviation shall not exceed 50mm. The verticality deviation of the steel casing is less than 1%, ensuring that the drilling rig can work smoothly along the vertical direction of the pile position. After the casing is in place, the excavated seam on its outside is backfilled and compacted in layers.

[0070] (4) Positioning of drilling rig: The drilling rig can be put into position only after the pile position has been verified to be correct. After the rotary drill is in place, adjust the verticality of the drill frame, align the center of the drill bit with the center of the cross line of the pile guard, and inject mud.

[0071] The drilling mud is made by a mixer, that is, the clay is first placed in the mud making tank and then stirred to form mud. The mud is circulated and precipitated through the sedimentation tank and the slurry storage tank to purify the mud. The mud circulation sequence is: new mud → mud tank → pile hole → sedimentation tank → mud tank → pile hole. The relative density of the mud tested in the laboratory is 1.05~1.15g / m 3 , viscosity 16~22s, sand content not more than 4%.

[0072] (5) Drilling (drilling construction): Different drill bits are selected according to soil conditions and drilling methods; rotary drill bits can be used for clay, silt, fill, and sandy soil layers with medium density or above; rock-embedded drill bits can be used for crushed stone soil, medium-hard rock and weathered layers. The selection of the drill bit diameter of the rotary drilling rig must ensure that the hole diameter is not less than the designed pile diameter. The rotary drilling rig should be operated with light pressure and slow advance, and the drill bit speed should not exceed 10r / min. After the active drill rod has completely entered the hole, it can be gradually accelerated for normal drilling.

[0073] The rotary drilling rig can use mud wall protection or dry drilling according to the operation mode and geological conditions; during the drilling process of the rotary drilling rig, the drill speed should be selected according to the geological conditions of the soil layer and the operation mode. The lifting speed should be strictly controlled during the drilling process to reduce the disturbance of the drilling bucket to the hole wall and avoid the collapse of the hole. The hole position must be accurate, and the hole wall of the initial hole should be vertical, round and solid.

[0074] During the drilling process, the geological changes should be checked and recorded frequently, and compared with the geological column chart; each drilling rig on site must be equipped with a slag sample box to fill in the drilling records in time. Sampling should be carried out at every 1m of footage, and slag samples should also be retained when different rock layers are converted. The retention of slag samples is the main basis for judging the design of the final hole. In this embodiment, the slag sample is used to determine whether the W3 bearing layer has been drilled. At the same time, the drilling records should also be carefully recorded, and the drilling depth is generally recorded every 2 meters. During the drilling process, the hole position, hole diameter and inclination should be checked frequently, and deviations should be corrected in time when found. After the hole reaches the designed depth, the hole should be inspected in time. Check the hole position, hole diameter, hole depth and hole shape, and keep records.

[0075] When constructing plain concrete piles, verified steel measuring ropes are used, and the construction team is required to over-drill by about 20 cm to ensure that the hole depth is qualified and the length of the plain concrete pile is controlled to meet the requirements.

[0076] In this embodiment, after the rotary drill enters the W3 stratum 1.0m deep, the rotary drill finishes drilling and the existing plain concrete piles are backfilled to prevent the hole from collapsing. The backfill material is the clay produced during the drilling process.

[0077] (6) Long spiral drilling rig with ground pump injection:

[0078] Due to the inclination of the existing ground line or weathering surface, the plain concrete piles are arranged in a plate every 10m along the mileage direction of the tunnel. The lengths of the plain concrete piles of different plates are the same or different, and the lengths of the plain concrete piles in each plate are the same or different. The pile length is specifically determined according to the position of the W3 stratum. In the composite foundation of the open-cut tunnel under the airport in this embodiment, there are multiple fill-excavation transition sections, and the length of the fill-excavation transition section is 10 to 50 meters. After the rotary drill completes a plate of drilling operations, the backfilled plain concrete piles are poured. Use a long spiral drill with a ground pump for pouring.

[0079] Before the pouring operation, it is necessary to mark out the existing pile positions on the plain concrete pile working surface that has been backfilled. After the drilling rig is in place, the position should be corrected with the help of vertical benchmarks on the front, back, left and right sides of the drilling rig tower so that the drill rod is vertically aligned with the center of the pile position.

[0080] When the long spiral drill starts drilling, close the drill valve, move the drill rod downward until the drill bit touches the ground, and start the motor to drill. Start slowly and then speed up, and check the deviation of the hole and correct it in time. If the drill rod is found to be shaking or difficult to drill during the process, the drilling footage should be slowed down to prevent the pile hole from being deflected, displaced, and the drill rod and drilling tools from being damaged. The long spiral drill drills at a constant speed, and the normal drilling speed is about 2m / min. At the same time, the drilling depth is controlled according to the markings on the drilling tower.

[0081] After the long spiral drill drills to the designed depth, the on-site commander should notify the drill to stop drilling and lift the drill rod 30cm to open the drill bit slide, and at the same time notify the pump driver to start pouring concrete and maintain continuous pouring. When pouring concrete to the top of the pile, it should exceed the designed elevation of the pile top by not less than 50cm to ensure that the pile top elevation and the quality of the concrete at the top of the pile meet the design requirements. The driller and the pump operator work closely together to control the drilling speed according to the amount of mixed material pumped in, which should be controlled at about 1.2 to 1.5m / min to ensure that the drill bit spearhead is always buried in the mixture for about 1m to prevent broken piles. When the mixture does not reach the designed elevation of the pile head, it should be handled in time, and the pump pipe should be inserted 50cm below the mixture to supplement the material. Before pouring concrete, check whether the pipeline is smooth and stable; before pouring the first pile of each shift, the pipeline should be moistened with cement mortar. When pouring concrete, the height of the drill should be less than 25cm at a time, and the height of the drill buried in the concrete should be greater than 1.0m. A dedicated person should be assigned to check the quality of concrete pouring and the handling of unexpected situations on site. Concrete should be poured immediately after entering the site (within 2 hours), and it is strictly forbidden to leave it for a long time. Ensure that the pile body concrete is maintained for at least 24 hours to avoid disturbance. During the construction process, the construction records should be filled in carefully, and every 100m per shift 3 A set of 3 concrete mixture test blocks (150×150×150mm) are prepared and the compressive strength test of the 28-day standard curing test pieces is carried out. After the piles are cast, the top of the piles is capped with wet clay for protection. The pouring volume of each pile and mixture shall not be less than the designed pouring volume.

[0082] When pouring is almost finished, the amount of concrete poured should be checked to determine whether the concrete pouring height is correct. The top of the bored pile after pouring should be more than 50cm higher than the designed pile top to ensure good quality of concrete at the cross section.

[0083] In the composite foundation of the open-cut tunnel under the airport in this embodiment, the diameter of the plain concrete pile is 600mm, and the length of the pile body is adjusted according to the working conditions, and it is required to enter the W3 bearing layer 1m, which is specifically determined according to the rock slag sample drilled on site. Due to the inclination of the existing ground line or weathering surface, the length of the plain concrete pile in the open-cut tunnel project under the airport varies from 3 to 26m. The following table shows the length of the plain concrete piles in some excavation-filling transition sections.

[0084] Table 1 Length of plain concrete piles in some cut-fill transition sections

[0085]

[0086] Note: When drilling with a long spiral drill, observe the depth of the drill rod. When the maximum depth is reached, continue drilling for 3 minutes to ensure that the hole reaches the designed hole depth. When pouring concrete, keep pouring continuously and strictly control the concrete pouring speed. The long spiral drill lifting speed is controlled at 1.2-1.5m / min to reduce the possible minor defects of the pile body after the pile is formed.

[0087] To ensure the quality of concrete, cement, sand, and stone raw materials can only be used after all indicators are tested and qualified. Concrete mixture should have good workability and should be able to maintain sufficient fluidity during pouring. The slump should be measured in real time. The slump should be controlled within 180-220mm, and the loss of slump caused by the influence of temperature, transportation distance, and construction time should be fully considered. The water-cement ratio should be strictly controlled to ensure the strength index of concrete. Before pouring, the slump and air content of concrete should be tested, and pouring can only be carried out if it meets the requirements of the specifications.

[0088] (7) Chiseling pile head: After the concrete pile is poured, the pile head is chiseled by the ring cutting method. After chiseling, the pile head should be dense and without loose layers.

[0089] Compared with the underwater steel conduit pouring method, the plain concrete pile construction method of the present invention has a faster construction speed, consumes less turnover materials, has a low cost, and has better integrity of the pile body.

[0090] For the open-cut tunnel under the airport in this embodiment, due to geological factors, the transition section includes a full weathering-strong weathering transition section in addition to the fill-cut transition section in the same rock layer. Fig.11 The figure shows the longitudinal section of the transition section from fully weathered to strongly weathered. In the W4 stratum section, CFG piles are used for reinforcement, and a 0.3m thick gravel cushion layer and a 0.15m thick C20 concrete cushion layer are set on the top of the piles. In the W3 / W4 stratum transition section, plain concrete piles are used for reinforcement. The diameter of the plain concrete piles is 600mm, the length of the plain concrete piles is not less than 3m, and a 0.2m thick gravel cushion layer and a 0.15m thick C20 concrete cushion layer are set on the top of the plain concrete piles. In the W3 stratum section, a 0.15m thick C20 concrete cushion layer is used for reinforcement. The longitudinal differential settlement of the structure is reduced by the gradual transition of the cushion thickness.

[0091] The beneficial effects of the present invention include:

[0092] 1. Ensure the quality of the project: Reasonable foundation treatment allows the foundation to meet the requirements of bearing capacity and stability, provide solid support for railway projects and other structures, ensure the bearing and stability of the composite foundation, and ensure safe use. Effectively control settlement and deformation. After relevant verification, it can reduce track and structural problems caused by settlement and ensure the normal performance of the project.

[0093] 2. Optimize construction: The design follows the principle of adapting measures to local conditions, considering multiple factors and comparing the options, determining economically reasonable and feasible options, avoiding unreasonable investment, and ensuring the economy of the project.

[0094] 3. Reduce uneven settlement: Take transition measures such as using plain concrete piles to reinforce the strata in relevant sections and joints to ensure a smooth transition of foundation characteristics, ensure close connection and coordinated force of the projects, reduce uneven settlement of tunnel foundations caused by different geological conditions, and improve integrity and continuity.

[0095] 4. Improve construction quality: strengthen quality control and effect detection, carry out settlement and deformation observation and evaluation according to specifications, make timely remedial measures, and strictly control construction points to ensure the quality of foundation treatment and long-term effects.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A composite foundation of plain concrete piles for open-cut tunnels, applied to the fill-cut transition section of deep-buried open-cut tunnels, characterized by: It includes a stratum reinforced by a plurality of plain concrete piles and a crushed stone cushion layer and a C20 concrete cushion layer laid on the top of the plain concrete piles; the plain concrete piles are arranged in a matrix, and the width of the plain concrete pile matrix is ​​greater than the width of the tunnel structure; and a uniform transition of foundation stiffness between the filling section and the excavation section is achieved by changing the length of the plain concrete piles.

2. The open-cut tunnel plain concrete pile composite foundation according to claim 1 is characterized by: The diameter of the plain concrete pile is 0.6m, the length is not less than 3.0m, and the depth of the pile end into the bearing layer is not less than 1m; the horizontal pile spacing in the plain concrete pile matrix is ​​1.70~2.35m, and the vertical pile spacing is 2~2.5m; the maximum particle size of the gravel in the gravel cushion layer on the top of the pile shall not exceed 50mm, the mud content shall not exceed 5%, and the dynamic deformation modulus after compaction is E vd Not less than 40MPa.

3. The open-cut tunnel plain concrete pile composite foundation according to claim 1 is characterized by: Plain concrete piles are arranged in a group of 10 meters along the mileage direction. Depending on the geological conditions, the length of the plain concrete piles in each group is the same or different. Depending on the geological conditions, the length of the fill-excavation transition section is 10 to 50 meters.

4. The open-cut tunnel plain concrete pile composite foundation according to claim 1 is characterized by: The excavation section adopts plain concrete piles, CFG piles, steel pipe grouting and closed cushion reinforcement measures according to the geological conditions; for the filling section, reinforced concrete bored piles are used for foundation treatment.

5. The open-cut tunnel plain concrete pile composite foundation according to claim 4 is characterized by: Deformation joints are set for the transition sections of sections with different foundation treatment measures, and the width of the deformation joints is 2cm; The length of the foundation treatment piles and the thickness of the cushion layer in the transition section gradually transition and change, which plays a role in reducing the longitudinal differential settlement of the tunnel structure; in the cross-sectional direction, the same foundation treatment measures are adopted within the influence range of the tunnel structure to reduce the lateral differential settlement of the structure.

6. The open-cut tunnel plain concrete pile composite foundation according to claim 4 is characterized by: The diameter of bored reinforced concrete piles is determined comprehensively according to the pile foundation form, force analysis and construction conditions; for sections with soil cover less than 10m, a 1.25m diameter pile foundation is used, and for sections with soil cover greater than 10m, a 1.5m diameter pile foundation is used. The pile type selection in the cavern of the fill section is the same as that of the open-cut structure in the same section; 4 piles are arranged in the cross-sectional direction of the bored piles, respectively arranged under the side walls of the open-cut structure, the center distance of the bored piles is 2 times the pile diameter, and the net distance from the edge of the structural bottom plate to the outermost row of piles is 0.5 times the pile diameter; the arrangement of bored piles along the route direction should be considered to be unified with the casting modulus of the open-cut structure, the longitudinal spacing of the pile foundation is 5m, the single casting length of the open-cut structure is 10m, the pile foundation is arranged in the center, the center is 2.5m away from the structural construction joint, the top of the pile foundation is consolidated with the open-cut bottom plate structure, and extends 100mm into the structural bottom plate.

7. The open-cut tunnel plain concrete pile composite foundation according to claim 4 is characterized by: The steel flower pipe used for grouting has an outer diameter of 76mm and a wall thickness of 3.5mm. It is arranged at intervals of 100cm×100cm, vertically laid on the base, and has a depth of 2.5m. The steel flower pipe is made of seamless hot-rolled steel pipe, and grouting holes are drilled at the front with a hole diameter of 6mm and a hole spacing of 20 to 30cm. It is arranged in a plum blossom shape, and the front end is processed into a cone. The tail is not drilled for a length of not less than 100cm, which serves as a grouting stop section. Cement slurry is used for grouting with a water-cement ratio of 1:1 (weight ratio) or determined on site, and a grouting pressure of 0.5 to 1.0MPa. The slurry viscosity is 80s to 90s.

8. The open-cut tunnel plain concrete pile composite foundation according to claim 4, characterized in that: The excavation section is reinforced with CFG piles with a diameter of 500mm and the depth of the pile end entering the bearing stratum is not less than 0.5m. A 0.3m thick gravel cushion and a 0.15m thick C20 concrete cushion are set on the top of the pile. The upper layer of the C20 concrete cushion is the bottom surface of the tunnel lining structure. The filling section is reinforced with reinforced concrete bored piles, and a 0.2m thick C20 concrete cushion is set on the top of the pile. The filling-excavation transition section is reinforced with plain concrete piles with a diameter of 600mm and a 0.2m thick gravel cushion and a 0.15m thick C20 concrete cushion are set on the top of the pile. Temporary drainage is carried out during the construction of the excavation section cushion, and C20 concrete is used to backfill the foundation pit at uneven heights.

9. A construction method for a composite foundation of open-cut tunnel plain concrete piles, characterized in that: The following steps are involved: S1. According to the relationship between the tunnel elevation, the current ground elevation and the airport planned field elevation, and taking into account the influence of the thickness of the soft soil layer at the bottom of the tunnel, the boundary between the filling and excavation sections is determined, and the filling section, excavation section and filling-excavation transition section are divided; S2. According to the tunnel stratum conditions, select reasonable foundation treatment measures to reduce structural differential settlement; Different foundation treatment measures are selected for the excavation section according to different strata; for the fill section, reinforced concrete bored cast-in-place piles are used for foundation treatment, and the pile diameter, pile length, reinforcement and other parameters are determined by calculation; for the fill-excavation transition section, plain concrete piles are used for foundation treatment, and uniform transition of foundation stiffness between the fill section and the excavation section is achieved by changing the pile length.

10. The construction method of open-cut tunnel plain concrete pile composite foundation according to claim 9, characterized in that: The plain concrete pile is made by drilling holes, backfilling with soil, and then pouring plain concrete using a long spiral drill and a ground pump; After the rotary drilling is completed, the existing plain concrete piles are backfilled to prevent the hole from collapsing. The backfill material is the clay produced during the drilling process; The downward drilling speed of the long spiral drill is 1.8 to 2.2 m / min. When the long spiral drill is drilling, observe the depth of the drill rod. When the maximum depth is reached, continue drilling for 3 minutes to ensure that the hole reaches the designed hole depth. After the long spiral drill has drilled to the designed depth, lift the drill rod to open the drill bit slide and start pouring concrete through the ground pump. Pour while lifting the drill rod, with a drilling speed of 1.2 to 1.5 m / min, and ensure that the drill bit tip is always buried in the slurry mixture for 0.8 to 1.1 m to prevent pile breakage. When pouring concrete to the top of the pile, it should appropriately exceed the designed elevation of the pile top by not less than 50 cm.

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