Retaining wall drainage system and construction method

Abstract

The invention provides a retaining wall drainage system and a construction method, and belongs to the technical field of building construction. The lower water interception system comprises a concrete cushion layer for providing stable support, and a high-quality clay layer and a rigid waterproof layer are laid on the concrete cushion layer; the middle drainage system comprises an inverted filter arranged on the back face of the retaining wall body, the inverted filter adopts welded reinforcement cages as an outer frame, the reinforcement cages are connected through spiral bars, sand and pebbles are filled in the reinforcement cages, the inverted filter is fixedly connected with the back face of the retaining wall body through embedded bars, and a set of evenly-distributed drainage holes penetrating through the wall body are formed in the inverted filter. A drainage ditch is arranged at the front bottom of the retaining wall body; the upper water retaining system comprises a concrete coping and a water stop ridge which are arranged at the top of the retaining wall body; the functions of intercepting water, rapidly draining water and intercepting ground water flow can be achieved, the filtering effect is improved, the construction difficulty is reduced, the stability is enhanced, and rapid drainage is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of building construction, and in particular to a retaining wall drainage system and a construction method. Background Art

[0002] Concrete retaining walls, as an important civil engineering structure, are widely used in the construction of roads, railways, embankments, and other projects. They are available in various structures, including gravity, cantilever, buttress, and column-slab types. The drainage system is crucial for the stability and durability of retaining walls and typically consists of two components: surface drainage and wall drainage. Surface drainage primarily involves drainage ditches to intercept surface water; wall drainage involves weep holes installed at appropriate heights within the wall to quickly drain water accumulated behind the wall. However, due to the interaction of water and soil, weep holes can easily become clogged, posing a safety risk. Therefore, a filter layer is required behind the wall to filter out soil particles and impurities.

[0003] The back-of-wall sand and pebble filter layer is a filter layer formed by a specific gradation combination of sand and pebbles. It is set between the back of the retaining wall and the fill. By intercepting soil particles step by step, it ensures that water can drain away when passing through and prevents fine soil particles from being carried away. Existing retaining wall filter layers often use graded crushed stone, medium-coarse sand, geotextile and other materials. They are suitable for situations with low wall heights. They are difficult to construct for high wall heights and the filtering effect cannot be guaranteed.

[0004] Therefore, there is an urgent need for a retaining wall drainage system and construction method that not only has excellent filtration performance but also simplifies the construction process and reduces the construction difficulty. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a retaining wall drainage system and construction method to address the shortcomings of the existing technology. The present invention can respectively realize the functions of water interception, rapid water discharge and interception of ground water flow, improve the filtering effect, reduce the construction difficulty, enhance the stability and realize rapid drainage.

[0006] Technical solution: The retaining wall drainage system described in the present invention includes a lower water interception system, a middle water discharge system and an upper water interception system; the lower water interception system includes a concrete cushion layer located at the bottom to provide stable support, a high-quality clay layer is laid on the concrete cushion layer, and a rigid waterproof layer is laid on the high-quality clay layer; the middle water discharge system includes a filter layer arranged on the back of the retaining wall, the filter layer is fixedly connected to the back of the retaining wall by embedded steel bars, and a group of evenly distributed drainage holes penetrating the wall are provided on the filter layer, and the water outlets of the drainage holes are inclined downward toward the front of the retaining wall, and a drainage ditch is provided at the bottom of the front of the retaining wall; the upper water interception system includes a concrete capping arranged on the top of the retaining wall, and a water stop is vertically provided above the concrete capping.

[0007] The lower water interception system intercepts and drains groundwater or deep seepage behind the wall, preventing rising groundwater levels from generating hydrostatic pressure on the retaining wall and preventing soil particles from being lost with the water. The concrete cushion layer, located at the base of the foundation, provides stable support and prevents scouring of the foundation soil. A high-quality clay layer and a rigid waterproof layer act as an anti-seepage layer, reducing groundwater infiltration and preventing water erosion of the wall. The central drainage system rapidly drains water behind the wall, reducing water pressure and preventing clogging of the filter layer and soil instability. Specifically, welded steel cage units serve as the outer framework of the filter layer, connected by spiral reinforcement to form a monolithic structure welded to the pre-embedded steel bars of the retaining wall for enhanced stability. Graded sand and pebbles are filled into the steel cage, providing both permeability and filtration, preventing the loss of fine soil particles. Drain holes penetrate the retaining wall and cooperate with the filter layer to quickly drain water behind the wall. The upper water retention system prevents surface runoff from seeping into the soil behind the wall, thereby avoiding additional water pressure and the risk of scour. The concrete capping layer, located at the top of the retaining wall, acts as a sealing layer to prevent rainwater from seeping in and enhance the integrity of the wall top. The water stop is set on the top surface of the wall to intercept and drain surface water into the drainage ditch.

[0008] Furthermore, the filter layer is formed by welding a group of steel cage units in the transverse or longitudinal direction. The length and height of the steel cage units are not more than 1m. Each adjacent two steel cage units are connected by spiral bars to form an overall skeleton. The steel cage units are filled with sand and pebbles.

[0009] The miniaturized design of the steel cage units (≤1m) facilitates prefabrication, transportation, and on-site assembly, making them particularly suitable for high-altitude or confined working environments, significantly reducing construction complexity. Adjacent units are connected by spiral reinforcement to form a continuous, stable framework, eliminating the looseness of traditional bulk filter layers and improving construction precision and speed. Furthermore, the steel cage framework provides rigid restraint for the sand-pebble filter layer, preventing deformation, settlement, or gradation separation caused by fill pressure or water erosion. The horizontally or vertically welded steel cage units form a grid structure that evenly distributes soil pressure, reduces local stress concentration, and enhances overall anti-overturning capacity. Sand-pebble-filled steel cages are filled with the stone particles, and the cage spacing (≤100mm) constrains the pebble particle size (typically ≤50mm) to ensure a stable gradation and prevent fine particles from escaping or coarse particles from clogging the weep holes. The steel cage framework forms a regular permeable path, which, combined with the tilted weep holes, accelerates the drainage of accumulated water behind the wall and reduces the threat of hydrostatic pressure to the retaining wall. The steel cage units are tied or welded with spiral reinforcement to form an overall frame, which enhances the shear and tensile resistance and avoids structural failure caused by local unit detachment.

[0010] Furthermore, the steel cage unit is composed of a set of evenly distributed main bars and stirrups. The main bars are arranged along the longitudinal direction of the steel cage unit, and the stirrups are arranged along the transverse direction. The spacing between each adjacent main bar or stirrup is no more than 100mm. The rigid skeleton formed by the main bars and stirrups can withstand the load of the fill and the scouring force of the water flow, preventing the collapse or deformation of the filter layer. At the same time, the spacing of no more than 100mm can limit the displacement of pebbles and maintain the gradation stability of the sand and gravel mixture. The sand layer (fine particles) intercepts the silt and clay in the soil, and the pebble layer (coarse particles) prevents sand loss, forming a "fine-coarse" gradient filtration. The large pores between the pebbles form highly permeable channels, quickly draining accumulated water to the drainage holes, reducing the water pressure behind the wall.

[0011] Furthermore, the concrete cushion layer is made of 150mm thick C20 plain concrete, the high-quality clay layer is made of cement with a clay mixture accounting for 5% by weight, and the rigid waterproof layer is made of C20 plain concrete. The concrete cushion layer primarily carries and transfers loads. In the present invention, it is located below the bottom surface of the foundation and evenly distributes the load of the retaining wall's upper structure to the foundation. C20 plain concrete has a certain compressive strength and its thickness of 150mm can withstand vertical pressure from the upper structure. When the retaining wall is subjected to external loads, the concrete cushion layer, through its own strength and rigidity, transfers the load more evenly to the underlying foundation soil layer, preventing localized excessive stress on the foundation soil layer and uneven settlement, thereby ensuring the stability of the retaining wall. High-quality clay inherently possesses certain waterproof properties. This is due to its fine particles, which can fill soil pores and reduce water penetration. When 5% cement by weight is mixed into the clay, the hydration products (such as calcium hydroxide and hydrated calcium silicate) produced by the cement hydration reaction further fill the pores between the clay particles, increasing the density and strength of the entire clay layer. Furthermore, the addition of cement improves the clay's physical and mechanical properties, enhancing its impermeability and compressive strength, thereby further enhancing its waterproofing and load-bearing properties.

[0012] Furthermore, a PVC plastic drain pipe is embedded within the drain hole. Its body is perforated in a plum blossom pattern. The outer wall of the PVC drain pipe is wrapped with a double-layered needle-punched geotextile, with the spaces between the layers filled with coarse sand. The drain hole is angled downward, leveraging gravity to accelerate drainage while preventing backflow. The PVC drain pipe is the core of the drainage system. The plum blossom-shaped perforations within its body play a crucial role in water inflow. When groundwater or water within the structure accumulates near the drain pipe, the water, driven by a pressure differential (groundwater pressure or gravity), flows through these small holes into the pipe. The double-layered needle-punched geotextile acts as a filter, effectively blocking impurities such as dirt and fine particles from entering the drain pipe, preventing blockage and ensuring smooth water flow. Furthermore, the coarse sand filling layer between the double-layered needle-punched geotextile further enhances filtration and water permeability. The particle size of coarse sand is relatively large, allowing water to flow through, but it can intercept smaller particles. Together with the needle-punched geotextile, it forms an efficient filtration system, making the water entering the drain pipe relatively pure.

[0013] A construction method comprising the above retaining wall drainage system comprises the following steps: Step 1: Prefabricate the filter layer: 1.1. Connect thin steel bars with a diameter of 5 mm to form a steel cage unit, and the steel cage units are connected by spiral reinforcement welding; 2.2. According to the design, several steel cage units are connected axially or transversely to form an inverted filter frame, and pebbles and sand are filled in the inverted filter frame to form an inverted filter layer; Step 2: Excavation of foundation trench: Excavate the foundation trench according to the designed elevation and width, ensuring that the bottom of the trench is flat and free of loose soil; Step 3: Construction of cushion layer: pouring 150mm thick C20 plain concrete cushion layer as the foundation of the lower water interception system; Step 4: Retaining wall pouring: 4.1. Concrete the retaining wall body, reserve drainage holes on the retaining wall body, and embed PVC plastic drainage pipes in the drainage holes. The pipes of the PVC plastic drainage pipes 801 have small thorn-shaped holes; the horizontal spacing between each two adjacent drainage holes is 2m; 4.2. Wrap the outer wall of the PVC plastic drain pipe with a double-layer needle-punched geotextile, and fill the middle of the double-layer needle-punched geotextile 802 with coarse sand; 4.3. Pre-embed steel bars at equal intervals along the back of the wall for subsequent welding and fixing of the filter layer; Step 5: Backfill the bottom soil: Lay a high-quality clay layer along the entire length of the retaining wall and tamp it; Step 6: Construction of rigid waterproof layer and drainage ditch: Pour C20 plain concrete along the length of the backfill soil side to form a rigid waterproof layer. The rigid waterproof layer and the concrete cushion form a continuous waterproof barrier. Pour C20 plain concrete drainage ditch at the bottom of the retaining wall to ensure smooth drainage. Step 7, filter layer construction: Weld the filter layer prepared in step 1 to the embedded steel bars to prevent deformation; Step 8: Concrete capping and waterstop construction: Pour capping concrete on the top of the retaining wall, and then vertically pour waterstop on the capping to prevent surface water from seeping into the back of the wall; Step 9: Backfill the soil behind the wall in layers, and ensure that the compaction degree meets the design requirements to avoid local settlement.

[0014] Beneficial effects: Compared with the prior art, the advantages of the present invention are: (1) The drainage system in the present invention has a three-layer structure, namely the lower water interception system, the middle water discharge system and the upper water interception system. The lower part (concrete cushion layer + drainage ditch) and the middle part (filter layer + drainage hole) form a "drainage-filtration-drainage" path; the upper part (pressure top + water stop) and the middle drainage ditch form an anti-seepage-drainage closed loop to reduce the interaction between surface water and groundwater; the present invention realizes water pressure control throughout the whole process by targeted water interception, water discharge and anti-seepage in the lower, middle and upper parts; (2) The filter layer of the present invention adopts a steel cage frame + sand and pebble filter layer to solve the problem of high wall construction. The steel cage unit is prefabricated and assembled on site, which reduces the difficulty of high-altitude operation and is particularly suitable for high retaining walls. The length and width of the steel cage unit are both ≤1m, which is convenient for transportation and lifting and adaptable to complex terrain. At the same time, the steel cage frame constrains the sand and gravel grading, avoiding the grading disorder problem of the traditional scattered filter layer, and achieving both filtering effect and stability. (3) The multi-layer filtration of PVC drainage pipe + geotextile + coarse sand, combined with the sand and pebble filter layer in the present invention, can significantly reduce the risk of clogging. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural diagram of the drainage system of the present invention; Figure 2 It is a schematic diagram of the welding of the steel cage unit in the present invention; Figure 3 It is a schematic diagram of the drain hole in the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the embodiments.

[0017] Example 1 like Figure 1The retaining wall drainage system shown in the figure includes a lower water interception system, a middle water discharge system, and an upper water retention system. The lower water interception system includes a concrete base 10 at the bottom, providing stable support. A high-quality clay layer 5 is laid on top of the concrete base 10, and a rigid waterproof layer 4 is laid on top of the high-quality clay layer 5. The concrete base 10 is made of 150mm thick C20 plain concrete, the high-quality clay layer 5 is made of cement with a clay content of 5% by weight, and the rigid waterproof layer 4 is made of C20 plain concrete. The middle water discharge system includes a filter layer 2 installed on the back of the retaining wall 1. The filter layer 2 is fixed to the back of the retaining wall 1 via embedded steel bars 3. The filter layer 2 is provided with a set of evenly distributed drainage holes 8 extending through the wall. A drainage ditch 9 is provided at the bottom of the front of the retaining wall 1. The upper water retention system includes a concrete capping 7 installed on the top of the retaining wall 1, with a water stop 6 vertically installed above the concrete capping 7.

[0018] like Figure 2 As shown, the filter layer 2 is constructed from a set of steel cage units 202 welded together along the transverse direction. The length and height of each cage unit are no greater than 1 meter. Spiral bars 201 connect each adjacent cage unit to form a monolithic framework. The cage units 202 are filled with sand and pebbles. The cage units 202 are composed of a set of evenly distributed main bars and stirrups. The main bars are arranged longitudinally, while the stirrups are arranged transversely. The spacing between adjacent main bars or stirrups is no greater than 100 mm.

[0019] like Figure 3 As shown, the water outlet of the drainage hole 8 is tilted downward toward the front of the retaining wall 1, and a PVC plastic drainage pipe 801 is pre-buried in the drainage hole 8. The pipe body of the PVC plastic drainage pipe 801 is provided with puncture holes distributed in a plum blossom shape. The outer wall of the PVC plastic drainage pipe 801 is wrapped with a double-layer needle-punched geotextile 802, and the gaps between the double-layer needle-punched geotextile 802 are filled with coarse sand 803.

[0020] Example 2 A construction method comprising the above retaining wall drainage system comprises the following steps: Step 1: Prefabricate the filter layer: 1.1. Connect thin steel bars with a diameter of 5 mm to form a steel cage unit, with the spacing between the main bars and the stirrups ≤ 100 mm to ensure structural rigidity; adjacent steel cage units are welded together using spiral bars 201 to form an overall skeleton; 2.2. According to the design dimensions, connect several steel cage units axially or transversely to form a filter layer frame, fill the filter layer frame with pebbles and sand, and vibrate and compact it to form a filter layer; Step 2: Excavation of foundation trench: Excavate the foundation trench according to the designed elevation and width, ensuring that the bottom of the trench is flat and free of loose soil. If groundwater is encountered, set up a water collection well and a water pump to keep the foundation trench dry. Step 3: Construction of cushion layer: Pour 150mm thick C20 plain concrete cushion layer, smooth the surface and maintain it as the foundation of the lower water interception system; Step 4, retaining wall casting: 4.1, cast the retaining wall body, reserve drainage holes on the retaining wall body, and embed A50-PVC plastic drainage pipes in the drainage holes. The pipe body of A50-PVC plastic drainage pipe 801 has plum blossom-shaped holes with a diameter range of 5-8mm, a spacing of 100mm, and a horizontal spacing of 2m between the drainage holes; 4.2, wrap the outer wall of the PVC plastic drainage pipe with a double-layer needle-punched geotextile, and fill the middle of the double-layer needle-punched geotextile 802 with coarse sand to form an anti-blocking filter layer; 4.3, embed steel bars at equal intervals along the back of the wall, and remove rust on the welding surface for subsequent welding and fixation of the filter layer; Step 5, backfilling the bottom soil: Lay a high-quality clay layer along the entire length of the retaining wall, backfill with high-quality clay 5 mixed with 5% cement, and compact it layer by layer; Step 6: Construction of rigid waterproof layer and drainage ditch: Pour C20 plain concrete along the length of the backfill soil side to form a rigid waterproof layer. The thickness of the rigid waterproof layer should be ≥150mm, and an interface agent should be applied to the joints. The rigid waterproof layer and the concrete cushion form a continuous waterproof barrier. Pour a C20 plain concrete drainage ditch at the bottom of the retaining wall to ensure smooth drainage. Step 7, filter layer construction: Weld the filter layer prepared in step 1 to the embedded steel bars to prevent deformation; Step 8: Concrete capping and waterstop construction: Pour C20 plain concrete capping 7 on the top of the retaining wall with a thickness of ≥200mm; then vertically pour a waterstop on the capping with a height of ≥150mm to prevent surface water from seeping into the wall back; Step 9: Backfill the back of the wall in layers, with each layer ≤500mm loose, and use a combination of mechanical rolling and manual tamping to ensure that the compaction meets the design requirements and avoid local settlement. After backfilling to the design elevation, restore vegetation or lay a hardened layer to prevent soil erosion.

[0021] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A retaining wall drainage system, characterized by: It comprises a lower water interception system, a middle water discharge system and an upper water interception system; the lower water interception system comprises a concrete cushion layer (10) at the bottom for providing stable support, a high-quality clay layer (5) is laid on the concrete cushion layer (10), and a rigid waterproof layer (4) is laid on the high-quality clay layer (5); The central drainage system comprises a filter layer (2) provided on the back of the retaining wall (1), the filter layer (2) being fixedly connected to the back of the retaining wall (1) via pre-buried steel bars (3), the filter layer (2) being provided with a group of evenly distributed drainage holes (8) penetrating the wall, the water outlets of the drainage holes (8) being arranged downwardly and tilted toward the front of the retaining wall (1), and a drainage ditch (9) being provided at the bottom of the front of the retaining wall (1); The upper water retaining system comprises a concrete pressure top (7) arranged on the top of the retaining wall (1), and a water stop (6) is vertically arranged above the concrete pressure top (7).

2. A retaining wall drainage system according to claim 1, characterized in that: The filter layer (2) is formed by welding a group of steel cage units (202) in a transverse or longitudinal direction, wherein the length and height of the steel cage units are both no greater than 1 m, and each adjacent two steel cage units are connected by spiral bars (201) to form an integral skeleton, and the steel cage units (202) are filled with sand and pebbles.

3. A retaining wall drainage system according to claim 2, characterized in that: The steel cage unit (202) is composed of a group of evenly distributed main bars and stirrups, wherein the main bars are arranged along the longitudinal direction of the steel cage unit, and the stirrups are arranged along the transverse direction of the steel cage unit, and the spacing between each two adjacent main bars or each two adjacent stirrups is not greater than 100 mm.

4. The retaining wall drainage system according to claim 1, characterized in that: The concrete cushion layer (10) is made of 150 mm thick C20 plain concrete, the high-quality clay layer (5) is made of a mixture of clay and cement accounting for 5% by mass, and the rigid waterproof layer (4) is made of C20 plain concrete.

5. The retaining wall drainage system according to claim 1, characterized in that: A PVC plastic drainage pipe (801) is pre-buried in the drainage hole (8), and the pipe body of the PVC plastic drainage pipe (801) is provided with puncture holes distributed in a plum blossom shape. The outer wall of the PVC plastic drainage pipe (801) is wrapped with a double-layer needle-punched geotextile (802), and the gaps between the double-layer needle-punched geotextile (802) are filled with coarse sand (803).

6. A construction method comprising the retaining wall drainage system according to any one of claims 1 to 5, characterized in that The steps include: Step 1: Prefabricate the filter layer: 1.

1. Thin steel bars with a diameter of 5 mm are connected to form a steel cage unit, wherein the steel cage units are connected by welding spiral bars (201); 2.

2. According to the design, several steel cage units are connected axially or transversely to form an inverted filter frame, and pebbles and sand are filled in the inverted filter frame to form an inverted filter layer; Step 2: Excavation of foundation trench: Excavate the foundation trench according to the designed elevation and width, ensuring that the bottom of the trench is flat and free of loose soil; Step 3: Construction of cushion layer: pouring 150mm thick C20 plain concrete cushion layer as the foundation of the lower water interception system; Step 4: Retaining wall pouring: 4.

1. Cast the retaining wall body, reserve a drainage hole (8) on the retaining wall body, and embed a PVC plastic drainage pipe (801) in the drainage hole (8). The pipe of the PVC plastic drainage pipe (801) has a thorn plum blossom-shaped small hole; the horizontal distance between each two adjacent drainage holes (8) is 2m; 4.

2. Wrapping the outer wall of the PVC plastic drain pipe (801) with a double-layer needle-punched geotextile (802), and filling the middle of the double-layer needle-punched geotextile (802) with coarse sand (803); 4.

3. Pre-embed steel bars (3) at equal intervals along the back of the wall for subsequent welding and fixing of the filter layer (2); Step 5, backfilling the bottom soil: laying a high-quality clay layer (5) along the entire length of the retaining wall and compacting it; Step 6, construction of rigid waterproof layer and drainage ditch: pour C20 plain concrete in the longitudinal direction of the backfill soil side to form a rigid waterproof layer (4), the rigid waterproof layer (4) and the concrete cushion layer (10) form a continuous waterproof barrier; pour C20 plain concrete drainage ditch at the bottom of the front of the retaining wall (1) to ensure smooth drainage; Step 7, construction of the filter layer: welding the filter layer prepared in step 1 to the embedded fixed steel bars (3) to prevent deformation; Step 8, construction of concrete capping (7) and water stop (6): pour capping concrete on the top of the retaining wall (1), and then vertically pour water stop on the capping to prevent surface water from seeping into the back of the wall; Step 9: Backfill the soil behind the wall in layers, and ensure that the compaction degree meets the design requirements to avoid local settlement.

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