Construction methods for deep-water bare rock geological pile foundations in mountainous areas

Abstract

This invention discloses a method for constructing underwater pile foundations in deep-water exposed rock geology for highways in mountainous areas. The method involves first placing a large-diameter steel casing at a corresponding location on the riverbed bottom, then using a drilling rig guided by the large-diameter steel casing to construct the underwater pile holes. After construction, a standard-diameter steel casing is inserted into the upper end of the large-diameter steel casing, with adjacent standard-diameter steel casings fixedly connected, ensuring the last standard-diameter steel casing extends above the water surface. Then, the reinforcement and concrete pouring of the underwater pile foundation are carried out sequentially. This invention improves construction safety and is characterized by safety, economy, and environmental protection. It offers significant economic, progress, and social benefits and has good potential for widespread application.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, specifically to a method for constructing pile foundations in deep-water, bare rock geological conditions on mountainous highways. Background Technology

[0002] Our company recently completed a highway bridge project, including a key bridge construction phase. The bridge's location is described below: Situated in a mountainous area, the Liuchi River has long isolated the two banks, preventing direct bridge access and causing significant inconvenience for residents of both towns who must detour or travel by boat. Local hydrological data indicates that the water depth at the bridge piers exceeds 30 meters, and the water level cannot be lowered due to downstream hydropower station impoundment. Based on comprehensive load calculations under construction and operational conditions, the underwater pile foundations must penetrate at least 20 meters into the rock. Survey data from the design and survey unit reveals a significant vertical drop in the riverbed, dense gullies, and a bed primarily composed of rock deposits (layer 2) or large rock bands (layer 3). This indicates a lack of soft soil or other soft geological features on the riverbed surface, and the bottom is extremely uneven with significant elevation differences, typical of deep-water bare rock geological conditions. Preliminary assessments indicate difficulties in deep-water pile foundation anchorage and significant challenges in underwater tie beam construction.

[0003] Based on the above description, the main technical challenges in the design of this project are as follows:

[0004] Firstly, there is the issue of anchoring the pile foundations for the underwater pier bridge. Due to the typical deep-water, bare rock geological conditions, the design unit plans to use a multi-pile underwater foundation model (no less than four piles). These underwater piles must be firmly connected to the riverbed to avoid disturbance caused by the river or geological conditions. There are two main construction methods for underwater pile foundations: 1. If the bottom is primarily soft soil, a steel casing is pre-stressed at a designated location, and then a drilling rig is used to drill holes along the direction of the casing to form the pile holes (4) for the underwater pile foundation. The steel casing serves as a permanent structure, reinforced with steel bars and grouting to form the underwater pile foundation. 2. If the bottom is primarily hard rock and requires a relatively flat bottom, an impact drill is used to initially break up the rock at a designated location to create a preliminary hole. Then, a steel casing is pre-stressed at the broken area. Further breaking up and deepening the rock is then performed using an impact drill, and the steel casing is pre-stressed again, repeating this process. Ultimately, the entire steel casing is installed within the pile holes (4) of the underwater pile foundation, serving as a permanent structure to form the underwater pile foundation. Both of the above methods share a common problem: the cast-in-place underwater pile foundation (in this project, the underwater pile foundation is over 20 meters deep) is surrounded by a steel casing. The structural material of the steel casing is completely independent of the geological material of the waterbed and does not interfere with it. At the same time, the concrete poured later cannot produce any physical or chemical reaction with the waterbed geology during the solidification process. Also, due to the presence of the steel casing, the underwater pile foundation is completely independent of the waterbed (i.e., the underwater pile foundation is directly inserted into the waterbed). However, in the early stage, because the steel casing needs to be inserted into the pile hole 4 of the underwater pile foundation, there is a gap between the steel casing and the waterbed foundation, which may cause the underwater pile foundation to deflect due to water flow or geological changes later. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing pile foundations in deep-water exposed rock geological conditions for mountain expressways. This method is suitable for hydrogeological environments where the water level is deep, the riverbed is covered with hard bedrock, or there is a layer of large-diameter pebbles. By raising the high pile cap to the water surface, it solves the problem that steel caissons and tie beams must be constructed underwater to complete the bridge. It is also suitable for situations where the stability of underwater piles is difficult to guarantee under gravity loads, thus overcoming the shortcomings of existing technologies.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing deep-water bare rock geological pile foundations for mountain expressways. This method involves first placing a large-diameter steel casing at a corresponding position at the bottom of the riverbed, then using a drilling rig guided by the large-diameter steel casing to construct the pile holes for the underwater pile foundation. After construction is completed, a standard-diameter steel casing is inserted into the upper end of the large-diameter steel casing, with adjacent standard-diameter steel casings fixedly connected, ensuring that the last standard-diameter steel casing extends above the water surface. Then, the reinforcement construction and concrete pouring of the underwater pile foundation are carried out sequentially.

[0007] As a further aspect of the present invention, the method for placing the large-diameter steel casing is as follows: if the bottom of the riverbed consists of an upper layer of rock deposits and a lower layer of large rock blocks, the large-diameter steel casing is first inserted into the upper layer of rock deposits through pre-compression to form the initial guide groove for the drilling rig, and then the drilling rig constructs the pile holes for the underwater pile foundation.

[0008] As a further aspect of the present invention, the method for placing the large-diameter steel casing is as follows: if the bottom of the riverbed is composed entirely of large rock layers, firstly, a large-size impact drill bit is installed at the end of the drilling rig. By breaking the rock at the bottom of the riverbed and forming a shallow trench borehole of a certain depth, a large-diameter steel casing is installed in this borehole through pre-loading. Then, a normal-size impact drill bit is replaced, and the drilling rig constructs the pile holes for the underwater pile foundation, thereby forming a pile hole structure with an annular clamping platform by the shallow trench borehole and the pile holes for the underwater pile foundation.

[0009] As a further aspect of the present invention: the surface area of ​​the large-diameter steel casing covered by the bottom of the riverbed is not less than 1 / 4 of the total surface area of ​​the large-diameter steel casing.

[0010] As a further aspect of the present invention: an annular card is provided inside the upper connecting end of the large-diameter steel casing. The net size enclosed by the annular card is smaller than the outer size of the standard-diameter steel casing, and the net size of the large-diameter steel casing is larger than the outer size of the standard-diameter steel casing, so that the standard-diameter steel casing can be clearance-fitted with the large-diameter steel casing and locked on the annular card.

[0011] As a further aspect of the present invention: a sealing strip is provided above the large-diameter steel casing, and the sealing strip is in transition fit with the connection end of the standard-diameter steel casing to achieve a seal between the standard-diameter steel casing and the large-diameter steel casing.

[0012] As a further aspect of the present invention: the inner surface of the pile hole of the underwater pile foundation is made of rock material with high roughness, and the large-diameter steel casing, the standard-diameter steel casing in the water and the standard-diameter steel casing extending out of the water surface constitute the steel cofferdam structure of the pile hole of the underwater pile foundation.

[0013] As a further aspect of the present invention: the underwater pile foundation structure includes a deep section located within the pile hole of the underwater pile foundation, the deep section completely filling the pile hole of the corresponding underwater pile foundation and fully contacting the high-roughness rock material inside the pile hole, the upper part of the deep section being a transition section wrapped by a large-diameter steel casing, the transition section being partially embedded in the bottom of the riverbed; the upper part of the transition section being a main body section wrapped by a standard-diameter steel casing, the upper end of the main body section extending out of the water surface.

[0014] As a further aspect of the present invention: the size of the transition section is larger than the size of the penetration section and the main body section, and the transition section as a whole is a convex pillar structure, or a convex pillar structure of a lower annular insert.

[0015] The design principles of this invention, its technical differences from existing technologies, and its effects:

[0016] 1. The pile foundation construction of this invention is particularly suitable for typical deep-water bare rock geological conditions (the riverbed is basically composed of hard geological layers such as rock layers, the riverbed surface is uneven and has a large drop, the river is deep and the flow is rapid, and the river drop is significant, etc.).

[0017] 2. In this invention, the surface of the pile hole of the underwater pile foundation is a high-roughness rock layer material and is completely exposed. The large-diameter steel casing and other standard-diameter steel casings form a steel cofferdam structure for the pile hole of the underwater pile foundation. This allows the concrete to fully contact and mix with the high-roughness rock layer material when it enters the pile hole during the later pouring of the underwater pile foundation, which greatly improves the compactness and connection strength.

[0018] 3. The underwater pile foundation structure obtained by this invention includes a deep section located within the pile hole of the underwater pile foundation. This deep section completely fills the corresponding pile hole and is in full contact with the high-roughness rock material within the pile hole. The upper part of the deep section is a transition section encased in a large-diameter steel casing, which is partially embedded in the riverbed bottom. The upper part of the transition section is a main body section encased in a standard-diameter steel casing, with its upper end extending above the water surface. That is, the deep section of the underwater pile foundation is in full contact with the underwater geology (without gaps, and the concrete can completely fill the gaps in the underwater geology), preventing disturbance from water flow. The large-sized transition section in the middle can be partially embedded in the underwater surface, achieving complete connection between the underwater pile foundation and the underwater surface to form a whole. The transition section can also serve as an independent support for the main body section (at this time, the size of the transition section is larger than the size of the main body section, allowing the transition section to form a new foundation). The transition section is a convex column structure, or a convex column structure with a lower annular embedded body, which improves the stability and firmness of the underwater pile foundation located at the underwater surface.

[0019] This invention, designed for unique geographical and geological environments, creatively solves the problems of weak stability and firmness in underwater pile foundation construction based on existing construction technologies. It also addresses the need to install tie beams underwater and provides a relatively objective solution for the rapid installation and dismantling of pile cap formwork. This invention overcomes challenges such as hard riverbed rock strata, large vertical drop, difficulties in underwater pile foundation construction, difficulty in effectively fixing the foundation, high environmental pressure, and difficulty in ensuring stability under load. It accumulates valuable technical experience for pile cap construction in deep-water bare rock geology under similar hydrogeological conditions. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 This invention describes the installation location of a large-diameter steel casing in a riverbed with a double-layer geological structure.

[0022] Figure 1.1 Diagram showing the connection relationship between large-diameter and standard-diameter steel casings when the riverbed geology is a double-layered geological structure;

[0023] Figure 1.2 This is a schematic diagram of the underwater pile foundation after cast-in-place construction when the riverbed has a two-layer geological structure.

[0024] Figure 1.3 A schematic diagram of a concrete structure for underwater pile foundations when the riverbed has a two-layer geological structure;

[0025] Figure 1.4 for Figure 1.2 Enlarged view of part A in the diagram;

[0026] Figure 1.5 for Figure 1.1 Enlarged schematic diagram of part B

[0027] Figure 2 The installation location of the large-diameter steel casing is as follows: The riverbed geology is a single layer.

[0028] Figure 2.1 Diagram showing the connection relationship between large-diameter and standard-diameter steel casings when the riverbed geology is a single layer.

[0029] Figure 2.2 This is a schematic diagram of the cast-in-place pile foundation in water when the riverbed has a single-layer geological structure.

[0030] Figure 2.3 Schematic diagram of a concrete structure for underwater pile foundations when the riverbed geology is a single layer.

[0031] Figure 3 This is a schematic diagram showing the overlapping installation positions of the main crossbeam and longitudinal and transverse beams in the bearing platform of the present invention.

[0032] Figure 4 This is a schematic diagram of the installation of the bottom mold of the pier in this invention;

[0033] Figure 5 This is a schematic diagram of the demolding gasket structure in this invention;

[0034] Figure 5.1 This is a schematic diagram of the pad plug in this invention.

[0035] The numbers in the diagram are as follows: 1. Water flow; 2. Rock accumulation layer; 3. Large rock band layer; 4. Pile hole; 5. Large diameter steel casing; 5.1. Ring card; 5.2. Sealing strip; 6. Standard diameter steel casing; 7. Underwater pile foundation; 7.1. Deep section; 7.2. Transition section; 7.3. Main section; 7.4. Annular insert; 8. Demolding gasket; 8.1. Base; 8.2. Gasket block; 8.3. Plug structure; 8.4. Fine sand; 8.5. Threaded hole; 8.6. Threaded rod plug; 8.7. Crossbeam slot; 8.8. Flexible retaining ring; 9. Annular mounting platform; 10. Main crossbeam; 11. Longitudinal and transverse beams; 12. Square timber; 13. Bamboo plywood; 14. Corbel. Detailed Implementation

[0036] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0037] Referring to the figure, this embodiment applies to a newly built bridge. The superstructure of the newly built bridge adopts prestressed concrete (post-tensioned) T-beams (3x40m), which are initially simply supported and then become continuous. The total length of the bridge is 132.04m, and the center pile number is K0+125. The substructure uses U-shaped abutments and single rectangular column piers. The piers and abutments are pile foundations, with 4 piles under each pier and abutment. The pile caps are 2 high-pile rounded rectangles above water.

[0038] According to local hydrological data, the maximum water depth at the two underwater pier locations exceeds 30 meters. Due to the downstream hydropower station's water storage and power generation, the water level cannot be lowered. Furthermore, considering the comprehensive load calculations under construction and operational conditions, the underwater pile foundations must ensure a rock penetration depth of at least 20 meters. Survey data from the design and survey units revealed a significant vertical drop in the riverbed, dense gullies, large exposed silty rocks, and an extremely uneven bottom layer, typical of deep-water bare rock geological conditions. Preliminary assessments indicated difficulties in deep-water pile foundation anchorage and significant challenges in underwater tie beam construction. Through repeated discussions and demonstrations with the design and owner, a proposed solution was to raise the pier cap elevation above the waterline to avoid underwater tie beam construction, reducing safety risks and costs associated with underwater steel caisson construction. To avoid construction difficulties during the rainy season and minimize construction costs and risks, the pier cap construction must be completed during the dry season.

[0039] The construction process is as follows:

[0040] Step 1: Underwater pile foundation construction; Underwater pile foundation 7 is constructed using underwater drilling and grouting piles, while the underwater portion is constructed using steel casing for fixed-shape grouting pile construction;

[0041] Specifically, firstly, a large-diameter steel casing 5 is placed at the corresponding position at the bottom of the riverbed. Then, the pile hole 4 of the underwater pile foundation is constructed under the guidance of the large-diameter steel casing 5. After the construction is completed, a standard-diameter steel casing 6 is inserted into the upper end of the large-diameter steel casing 5. Adjacent standard-diameter steel casings 6 are fixedly connected, and the last standard-diameter steel casing 6 extends out of the water surface. Then, the steel reinforcement construction and concrete pouring construction of the underwater pile foundation are carried out in sequence.

[0042] The above construction requires further differentiation based on the geological conditions of the riverbed. If the riverbed bottom consists of an upper layer of rock deposits 2 and a lower layer of large rock blocks 3, firstly, a large-diameter steel casing 5 is inserted into the upper rock deposits 2 through preloading to form the initial guide groove for the drilling rig. Then, the drilling rig constructs the pile holes 4 for the underwater pile foundation (see...). Figure 1-Figure 1.2 and Figure 1.4 If the riverbed bottom is composed entirely of large rock layers, 3, firstly, a large-size impact drill bit is installed at the end of the drilling rig. This breaks up the riverbed bottom rock and forms a shallow trench borehole of a certain depth. Then, a large-diameter steel casing 5 is installed in this borehole using a pre-loading method. Next, a normal-size impact drill bit is replaced, and the drilling rig constructs the pile holes 4 for the underwater pile foundation. This results in the shallow trench borehole and the underwater pile hole 4 forming a pile hole structure with an annular clamping platform 9 (see...). Figure 2-Figure 2.2 In this project, about 1 / 3 of the underwater pile foundation is composed of a large rock layer 3, and the rest is composed of a rock accumulation layer 2 on the upper layer and a large rock layer 3 on the lower layer. The surface area of ​​the large-diameter steel casing (5) covered by the bottom of the riverbed is not less than 1 / 4 of the total surface area of ​​the large-diameter steel casing 5.

[0043] See Figure 1.5 An annular clip 5.1 is installed inside the upper connecting end of the large-diameter steel casing 5. The net size enclosed by the annular clip 5.1 is smaller than the outer size of the standard-diameter steel casing 6, while the net size of the large-diameter steel casing 5 is larger than the outer size of the standard-diameter steel casing 6. This allows the standard-diameter steel casing 6 to fit with the large-diameter steel casing 5 with a clearance and be secured to the annular clip 5.1. A sealing strip 5.2 is installed above the large-diameter steel casing 5. The sealing strip 5.2 and the connecting end of the standard-diameter steel casing 6 are in a transition fit to achieve a seal between the standard-diameter steel casing 6 and the large-diameter steel casing 5. The inner surface of the pile hole 4 of the underwater pile foundation is made of high-roughness rock material. The large-diameter steel casing 5, the standard-diameter steel casing 6 in the water, and the standard-diameter steel casing 6 extending above the water surface constitute the steel cofferdam structure of the pile hole 4 of the underwater pile foundation.

[0044] A type of underwater pile foundation structure obtained by the above process (see...) Figure 1.3 and Figure 2.3The underwater pile foundation 7 structure includes a penetration section 7.1 located within the pile hole 4 of the underwater pile foundation. The penetration section 7.1 completely fills the corresponding pile hole 4 of the underwater pile foundation and is in full contact with the high-roughness rock material within the pile hole 4 (see...). Figure 1.4 The upper part of the deep section 7.1 is a transition section 7.2 wrapped by a large-diameter steel casing 5, and the transition section 7.2 is partially embedded in the bottom of the riverbed; the upper part of the transition section 7.2 is a main body section 7.3 wrapped by a standard-diameter steel casing 6, and the upper end of the main body section 7.3 extends out of the water surface. The size of the transition section 7.2 is larger than that of the deep section 7.1 and the main body section 7.3. The transition section 7.2 is a convex column structure as a whole, or a convex column structure of the lower annular embedded body 7.4.

[0045] Step 2: Foundation construction;

[0046] 1. Installation of fixed supports for the bottom formwork of the foundation: Support structures are installed on both sides of each standard diameter steel casing 6 exposed on the horizontal plane, with all support structures at the same height. The support structure is either a corbel 14 structure symmetrically arranged on both sides of the corresponding steel casing, or a support beam structure penetrating the central axis of the corresponding steel casing (corbel 14 is used in this embodiment). The corbel assembly materials are first uniformly processed and formed by the steel processing plant according to the design drawings. After the corbel steel plates have passed the processing and acceptance, they are transported to the site for welding with the steel casing. During welding, they are symmetrically arranged along the axis of the casing, and the elevation is controlled according to the design elevation. The welding of the corbel and the casing is a full weld, and the weld width and height meet the specifications. The elevation of the top surface of the corbel must not be higher than the design elevation.

[0047] 2. Installation of the foundation bottom formwork; see Figure 3 and Figure 4 The main crossbeam 10 of the foundation bottom formwork is erected between the supporting structures corresponding to the position. The longitudinal and transverse beams 11 perpendicular to the main crossbeam 10 are laid at equal intervals on the main crossbeam 10. Then, square timber 12 and bamboo plywood 13 are laid on the longitudinal and transverse beams 11 in sequence to form the foundation bottom formwork.

[0048] Specifically, after the welding is completed, demolding pads are installed on the corbels of the steel casing. Then, double-span I40a I-beams are erected on the demolding pads as the platform support frame, with the beams perpendicular to the bridge direction. Nine long double-span I20a I-beams are laid on top, with each side welded in parallel. To ensure the relative stability of the longitudinal and transverse beams, two 50*50*16mm steel plates are welded at the contact points between the main longitudinal beams and the transverse beams as limiters. At the same time, 10*10cm square timbers are fully laid on top of the I-beams of the distribution beams, spaced 20cm apart. 15mm bamboo plywood is then fully laid on the square timbers as the construction platform plane and the bottom formwork of the pier.

[0049] After the foundation formwork is installed, to ensure the safety of personnel, a safety protection fence needs to be set up around the platform. The fence is constructed using φ48mm steel pipes and fasteners. The uprights are 1.2m high and the spacing between the uprights is no more than 2m. There are two layers of horizontal bars, with the upper horizontal bar 1.2m from the platform surface and the lower horizontal bar 0.6m from the platform surface. The base of the uprights is welded to the horizontal distribution beams, and an 18cm high kickboard is installed at the bottom.

[0050] See Figure 5 and Figure 5.1 A demolding pad 8 is provided between the main crossbeam 10 and the supporting structure; the demolding pad 8 includes a base 8.1 with a cavity structure, the cavity of the base 8.1 being a cylindrical or square cavity structure, and a plug structure 8.3 being a conical or multi-faceted conical structure. The base 8.1 is fixed to the corresponding supporting structure. A pad block 8.2 is provided above the base 8.1, the upper part of the pad block 8.2 being consistent with the cavity structure of the base 8.1 and being clearance-fitted with each other, and the lower part of the pad block 8.2 being a conical plug structure 8.3; the cavity of the base 8.1 is filled with fine sand 8.4 with good fluidity, and multiple threaded holes 8.5 are evenly provided at the lower end of the base 8.1 to facilitate the outflow of fine sand 8.4, and a... There is a corresponding threaded rod plug 8.6; the upper part of the gasket block 8.2 is embedded in the cavity of the base 8.1 and the end of the plug structure 8.3 forms a gap H with the bottom side of the cavity structure of the base 8.1. The upper surface of the gasket block 8.2 is provided with a main crossbeam slot 8.7. A flexible retaining ring 8.8 is embedded in the upper part of the cavity of the base 8.1. The flexible retaining ring 8.8 and the upper tail of the gasket block 8.2 are transitionally fitted to prevent fine sand 8.4 from overflowing from the base 8.1. All bases 8.1 are filled with an equal amount of fine sand 8.4. After the gasket block 8.2 is embedded in the corresponding base 8.1, it is pressed flat. Then the corresponding main crossbeam 10 is inserted into the corresponding main crossbeam slot 8.7. Then the other parts of the base bottom mold are installed to form the base bottom mold structure.

[0051] The demolding pad is 200mm high and is made of Q238B steel plate. During the welding of the node box, full penetration welds are required, and the weld height must not be less than 8mm.

[0052] 3. Reinforcement processing and installation of the pier cap: The reinforcement of the pier column above the bridge pier and the reinforcement of the pile column in the underwater pile foundation are tied together with the reinforcement of the pier cap; they are fixed together with the reinforcement of the pier cap by spot welding. In order to ensure the position of the pier column reinforcement and prevent the displacement of the pre-embedded reinforcement of the pier column, a channel steel bracket is welded around the pier cap to support and stabilize the pier reinforcement. When pre-embedding the pier reinforcement, it is necessary to check it with the longitudinal and transverse axes of the pier, and at the same time ensure sufficient anchorage length.

[0053] Step 3: Installation of the foundation support formwork; the foundation formwork uses standardized steel molds. The formwork must have sufficient strength, rigidity, and stability, with tight, leak-proof joints, and be able to withstand various loads that may occur during construction. The formwork dimensions are customized according to the foundation dimensions.

[0054] Before installation, the formwork should be thoroughly sanded and coated with a dedicated release agent; waste engine oil or similar substances must not be used as a substitute. Ensure that the flatness of each individual formwork panel is less than 1mm, and that the flatness is less than 2mm when checked with a 3m straightedge. The misalignment between formwork panels should be controlled to less than 1mm.

[0055] The formwork is supported on a solid base using temporary scaffolding. Tie rods are installed at the top and bottom of the formwork for support.

[0056] The internal and external support and reinforcement system for the side formwork must consider the concrete pouring sequence and the impact of vibration load on the side formwork. Therefore, channel steel is used for horizontal and longitudinal reinforcement of the formwork, and fasteners are used to connect the formwork sections. M20 tie bolts are used for reinforcement of the front, rear, and side formwork. Four sets of combined channel steel are used for transverse reinforcement at 75cm intervals, and channel steel is used for longitudinal reinforcement at 55cm intervals. Before installation, release agent should be evenly applied to the inner surface of the formwork. During installation, the design drawings must be strictly followed to ensure the verticality of the formwork and control the centerline position and elevation to meet the design specifications. The formwork joints must be horizontal and vertical, with double-sided adhesive strips inserted between the joints. Tie rod holes are sealed with rubber rings or foam sealant to ensure no grout leakage during concrete pouring.

[0057] After the formwork is installed, its planar position, top elevation, and longitudinal and transverse stability should be checked. The design elevation of the foundation top should be measured and marked on the inner wall of the formwork to facilitate control of concrete pouring. Concrete can only be poured after the inspection is passed and the supervising engineer has inspected and signed off on it.

[0058] Step 4: Transportation and pouring of foundation concrete;

[0059] 1. Concrete mix proportions and temperature control measures

[0060] To reduce the heat of hydration in large-volume concrete and avoid its early concentrated release, which could lead to shrinkage cracks, the following measures will be taken during the construction of the foundation concrete:

[0061] (1) The proportion design should appropriately reduce the amount of cement, and add a certain proportion of finely ground fly ash and high-efficiency water-reducing agent to increase the workability, early strength and reduce the heat of hydration of concrete.

[0062] (2) Concrete raw materials must be inspected upon arrival at the site to ensure they are qualified.

[0063] (3) The concrete slump should be controlled at 160-200mm (adjusted according to the actual pumping effect during construction).

[0064] (4) Before construction, temperature control design and temperature monitoring design should be carried out based on factors such as raw materials, mix proportions, environmental conditions, construction plan and construction technology. After pouring, the temperature of the inside and surface of the concrete should be monitored and controlled according to the design requirements. When controlling the temperature of large-volume concrete, the maximum internal temperature should not exceed 75℃, the internal surface temperature difference should not exceed 25℃, and the temperature difference between the concrete surface and the ambient temperature should not exceed 20℃.

[0065] (5) Temperature control of large-volume concrete should follow the principle of "internal cooling and external insulation". Cooling water pipes should be installed inside the concrete for circulating water cooling, and heat storage or water storage should be used to insulate the outside of the concrete. When cooling water is circulated inside the concrete, the temperature difference between the inlet and outlet water should be less than or equal to 10℃, and the temperature difference between the water and the inside concrete should not be greater than 20℃. The cooling rate should not be greater than 2℃ / d. When the cooling water discharged from the cooling water pipes is used to store water on the top surface of the concrete for heat preservation and curing, the temperature difference between the curing water and the concrete surface temperature should not be greater than 15℃.

[0066] Step 5: Demolding of the side formwork of the foundation and curing of the foundation concrete;

[0067] Geotextile fabric should be used for water-retaining curing. Water should be slowly poured into the concrete after the surface has initially set, utilizing the raised portion of the formwork; forceful pouring is strictly prohibited. The water-retaining curing time should be determined based on actual strength gain and heat of hydration release. Water-retaining curing should cease when the temperature of the cooling water and the top surface curing water approaches the air temperature. Simultaneously, temperature monitoring chips should be pre-embedded during concrete pouring to monitor the internal temperature of the concrete. Formwork removal is only permitted when the temperature difference between the internal and surface temperatures does not exceed 25°C.

[0068] The curing work should not be affected or interrupted during demolding, and the newly exposed concrete surface should be kept moist and cured in a timely manner.

[0069] When removing formwork, it is strictly forbidden to damage the concrete. Do not pry it forcefully to avoid large sections collapsing and injuring people. Removed formwork must not be piled up on the platform and should be hoisted and stacked neatly outside the factory area in a timely manner.

[0070] Step Six: Removal of the Foundation Bottom Formwork; After the foundation is poured, to ensure the reuse of materials, the foundation bottom formwork needs to be recycled. First, simultaneously unscrew the threaded rod plug 8.6 on the base 8.1 of the demolding shim 8, allowing the fine sand 8.4 inside the base 8.1 to gradually flow out and be recycled through the threaded hole 8.5. As the fine sand 8.4 flows out, the shim clip 8.2 will gradually move downward along the axis of the cavity of the base 8.1. Due to the shape of the conical plug structure 8.3, under the weight of the foundation bottom formwork, the conical plug structure 8.3 will push the fine sand 8.4 inside the base 8.1 evenly outward in a downward and outward manner, thereby pushing the fine sand 8.4 to gradually flow out through the threaded hole 8.5. The corresponding shim clip 8.2 will also move downward until the plug structure 8.3 of the shim clip 8.2 reaches the bottom side and stops, with a movement distance of H. The foundation bottom formwork will also move downward by a corresponding distance H. Then, the various parts of the foundation bottom formwork are pulled out and recycled from top to bottom using a pulling method.

[0071] Step 7: Construction of bridge piers and columns.

[0072] Compared to traditional construction methods, this embodiment necessitates the initial construction of underwater tie beams in deep water to ensure the overall stability of the bridge's two columns. This underwater tie beam construction requires the use of steel caissons, incurring significant costs for safety measures and coordination, as well as coordination with upstream and downstream hydropower stations, resulting in substantial safety and environmental pressures. In contrast, the high-pile pier construction method only requires raising four piles above the water surface to construct the pier, successfully avoiding the safety risks of underwater construction and eliminating the need for steel caissons. This method is simpler, less costly, and provides valuable technical experience for deep-water pier construction in similar hydrogeological conditions.

[0073] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing pile foundations in deep-water exposed rock geological conditions for highways in mountainous areas, characterized by: The method involves first placing a large-diameter steel casing (5) at the corresponding position at the bottom of the riverbed, and then using a drilling rig to construct the pile hole (4) of the underwater pile foundation under the guidance of the large-diameter steel casing (5). After the construction is completed, a standard-diameter steel casing (6) is inserted into the upper end of the large-diameter steel casing (5), and adjacent standard-diameter steel casings (6) are fixedly connected, so that the last standard-diameter steel casing (6) extends out of the water surface. Then, the steel reinforcement construction and concrete pouring construction of the underwater pile foundation are carried out in sequence. The placement method of the large-diameter steel casing (5) is as follows: If the bottom of the riverbed is a rock accumulation layer (2) on the upper layer and a large rock band layer (3) on the lower layer, the large-diameter steel casing (5) is first inserted into the rock accumulation layer (2) through pre-compression to form the initial guide groove of the drilling rig. Then the drilling rig constructs the pile hole (4) of the underwater pile foundation. After the reinforcement construction and concrete pouring are completed, the corresponding underwater pile foundation (7) is formed. The underwater pile foundation (7) structure includes a deep section (7.1) located in the pile hole (4) of the underwater pile foundation. The deep section (7.1) completely fills the pile hole of the corresponding underwater pile foundation. The hole (4) is in full contact with the high-roughness rock material inside the pile hole (4). The upper part of the deep section (7.1) is a transition section (7.2) wrapped by a large-diameter steel casing (5). The transition section (7.2) is partially embedded in the bottom of the riverbed. The upper part of the transition section (7.2) is a main body section (7.3) wrapped by a standard-diameter steel casing (6). The upper end of the main body section (7.3) extends out of the water surface. The size of the transition section (7.2) is larger than that of the deep section (7.1) and the main body section (7.3). The lower part of the transition section (7.2) is a convex column structure of an annular embedded body (7.4). The second method for placing the large-diameter steel casing (5) is as follows: If the bottom of the riverbed is composed of large rock layers (3), firstly, a large-size impact drill bit is installed at the end of the drilling rig. The rock at the bottom of the riverbed is broken to form a shallow trench borehole of a certain depth. Then, the large-diameter steel casing (5) is installed in this borehole by pre-pressing. Replace the normal-size impact drill bit, and then the drilling rig constructs the pile hole (4) of the underwater pile foundation, so that the shallow trench borehole and the pile hole (4) of the underwater pile foundation constitute a pile hole structure with an annular mounting platform. After the reinforcement construction and concrete pouring are completed, the corresponding underwater pile foundation (7) is formed. The underwater pile foundation (7) structure includes the pile hole (4) located in the underwater pile foundation. The deep section (7.1) completely fills the pile hole (4) of the corresponding underwater pile foundation and is in full contact with the high roughness rock material inside the pile hole (4). The upper part of the deep section (7.1) is a transition section (7.2) wrapped by a large-diameter steel casing (5). The transition section (7.2) is partially embedded in the bottom of the riverbed. The upper part of the transition section (7.2) is a main body section (7.3) wrapped by a standard-diameter steel casing (6). The upper end of the main body section (7.3) extends out of the water surface. The size of the transition section (7.2) is larger than that of the deep section (7.1) and the main body section (7.3). The transition section (7.2) is a convex column structure.

2. The method for constructing deep-water bare rock geological pile foundations for mountain expressways according to claim 1, characterized in that: The surface area of ​​the large-aperture steel casing (5) covered by the bottom of the riverbed is not less than 1 / 4 of the total surface area of ​​the large-aperture steel casing (5).

3. The method for constructing deep-water bare rock geological pile foundations for mountain expressways according to claim 1, characterized in that: An annular card (5.1) is provided inside the upper connecting end of the large-diameter steel casing (5). The net size enclosed by the annular card (5.1) is smaller than the outer size of the standard-diameter steel casing (6). The net size of the large-diameter steel casing (5) is larger than the outer size of the standard-diameter steel casing (6), so that the standard-diameter steel casing (6) can be fitted with the large-diameter steel casing (5) with a clearance and be stuck on the annular card (5.1).

4. The method for constructing deep-water bare rock geological pile foundations for mountain expressways according to claim 1, characterized in that: A sealing strip (5.2) is provided above the large-diameter steel casing (5). The sealing strip (5.2) and the standard-diameter steel casing (6) are connected by a transition fit, so as to achieve a seal between the standard-diameter steel casing (6) and the large-diameter steel casing (5).

5. The method for constructing deep-water bare rock geological pile foundations for mountain expressways according to claim 1, characterized in that: The inner surface of the pile hole (4) of the underwater pile foundation is made of rock material with high roughness. The large-diameter steel casing (5), the standard-diameter steel casing (6) in the water and the standard-diameter steel casing (6) extending out of the water surface constitute the steel cofferdam structure of the pile hole (4) of the underwater pile foundation.

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