Prefabricated 3D printed box-type concrete retaining wall and retaining wall system

Abstract

This invention relates to a prefabricated 3D-printed box-type concrete retaining wall and retaining wall system. The prefabricated 3D-printed box-type concrete retaining wall is assembled from 3D-printed concrete retaining wall units. Each 3D-printed concrete retaining wall unit is an integrated 3D-printed concrete structure, consisting of an arched outer wall panel, a concave inner wall panel, and concave side wall panels, which enclose a cavity. A transverse keyway is formed between the concave side wall panels of adjacent 3D-printed concrete box-type retaining wall units. Shear keys are formed by casting cement-based material within the transverse keyway, enabling the combined load-bearing capacity of the 3D-printed concrete retaining wall units. Under the same loading conditions, the peak bearing capacity of the structure of this invention is significantly improved compared to traditional vertical box-type retaining walls, and the bearing performance is further enhanced under simulated backfill conditions, demonstrating good engineering applicability and green construction value.

Description

Technical Field

[0001] This invention relates to the fields of 3D printed concrete engineering applications and solid waste resource utilization, specifically to prefabricated 3D printed box-type concrete retaining walls and retaining wall systems. Background Technology

[0002] 3D printed concrete technology is an emerging construction method in the field of civil engineering in recent years. Through digital modeling and automated printing equipment, it enables moldless molding of irregularly shaped concrete structures, rapid construction, and precise construction of complex structures. It offers advantages such as saving on formwork, reducing labor, shortening construction time, and providing a high degree of customization. Currently, 3D printed concrete has been initially applied in engineering projects such as building walls, small components, and landscape facilities.

[0003] Prefabricated construction technology has seen rapid development in industrialized construction in recent years. Through factory prefabrication and on-site assembly, it significantly improves construction efficiency and quality stability, while effectively reducing environmental pollution and resource waste at construction sites. Prefabricated retaining wall components, as an extension of prefabricated technology in civil infrastructure, offer advantages such as being detachable, easy to transport, and convenient for later maintenance.

[0004] Recycled concrete is a new type of green building material made by partially or completely replacing natural aggregates with recycled aggregates obtained from the crushing and processing of demolition waste (such as waste concrete blocks, bricks, stones, and slag). It has significant resource-saving and environmental benefits. Driven by the "dual carbon" target and the policy of resource utilization of construction waste, recycled concrete has been gradually applied in engineering projects such as roads, municipal engineering, and building construction.

[0005] Box-type retaining walls are a type of gravity retaining structure, consisting of several hollow "box units" assembled or cast-in-place. The interior of the box is typically filled with materials such as crushed stone, rubble, concrete, or soil to resist earth pressure using its own weight. Their structure relies heavily on concrete and steel reinforcement, requiring extensive formwork erection and rebar tying during construction, resulting in low efficiency and significant environmental impact. Furthermore, for sites with complex slope geology and limited construction space, traditional box-type retaining wall construction presents challenges such as difficult layout, long construction periods, and high safety risks. Therefore, there is an urgent need for a new type of retaining wall system that is structurally reliable, easy to construct, and environmentally friendly to meet the multiple demands of modern infrastructure construction for safety, economy, and sustainability. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a prefabricated 3D printed box-type concrete retaining wall and retaining wall system with a more reasonable stress path, higher load-bearing capacity, easy assembly and construction, and the ability to realize the resource utilization of solid waste.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: This invention first provides an assembled 3D-printed box-type concrete retaining wall, assembled from 3D-printed concrete retaining wall units. Each 3D-printed concrete retaining wall unit is an integrated 3D-printed concrete structure, consisting of an arched outer wall panel, a concave inner wall panel, and concave side wall panels. These panels enclose a cavity. At least one partition plate is provided within this cavity to divide it into at least two empty box cavities. The two ends of the partition plate are connected to the arched outer wall panel and the concave inner wall panel, respectively. A transverse keyway is formed between the concave side wall panels of two adjacent 3D-printed concrete box-type retaining wall units. A shear key is formed by casting cement-based material within the transverse keyway, enabling the 3D-printed concrete retaining wall units to jointly bear loads.

[0008] The arched outer wall panel is an arc-shaped arch; the concave inner wall panel is an arc-shaped concave surface; and the concave side wall panel is an arc-shaped concave surface.

[0009] The arc shape of the arched outer wall panel is consistent with the arc shape of the concave inner wall panel.

[0010] Solid waste filler is used to fill the two empty boxes to stabilize the retaining wall and increase its load-bearing capacity.

[0011] This invention also provides a prefabricated 3D-printed box-type concrete retaining wall system, comprising: The above-mentioned prefabricated 3D printed box-type concrete retaining wall; The cast-in-place foundation slab has an embedded groove and a drainage hole on its upper surface, and a water trough connected to the drainage hole is also provided inside the slab; the lowest 3D printed concrete retaining wall unit of the assembled 3D printed box-type concrete retaining wall is set in the embedded groove, and a drainage filter layer is provided in the lowest 3D printed box-type concrete retaining wall unit. as well as A concrete wall cap is installed at the top of the prefabricated 3D printed box-type concrete retaining wall.

[0012] The present invention also provides an assembled 3D printed box-type concrete retaining wall system, which further includes a water collection tank, and the outlet of the water channel is connected to the water collection tank.

[0013] The present invention also provides an assembled 3D printed box-type concrete retaining wall system, which further includes corner fixing keys, wherein the corner fixing keys are detachably fixed to the cast-in-place foundation plate.

[0014] The water-cement ratio of the printable concrete used to print the assembled 3D printed box-type concrete retaining wall unit is 0.28 to 0.36; recycled fine aggregate accounts for 30% to 100% of the total fine aggregate, and the remainder is natural aggregate.

[0015] The transverse keyway is formed by splicing together the arched grooves reserved during the printing and molding process of each retaining wall unit. After the adjacent units are in place, the cement-based material is cast in place in the keyway to form a shear key, so that the retaining wall units are combined to form a box-type retaining wall system with joint load-bearing capacity.

[0016] The upper part of the foundation plate is provided with a groove that matches the bottom of the 3D printed retaining wall unit, and it is poured on the construction site.

[0017] The solid waste filler mainly consists of slag, fly ash, steel slag, blast furnace slag, recycled construction waste powder, red mud, gypsum, and other solid waste. The solid waste filler is filled into the shell of the 3D printed concrete retaining wall at the construction site and compacted to form a box-type retaining wall system with good mechanical properties.

[0018] The solid waste filler is permeable, effectively filtering moisture and achieving drainage. Water flows through drainage channels arranged on the foundation slab into a collection tank, thus achieving soil drainage.

[0019] The assembled 3D printed box-type concrete retaining wall unit can be printed using mix proportions with different recycled concrete replacement rates. Common recycled concrete replacement rates are 0%, 30%, 50%, 70%, and 100%. Through testing, it was found that the average 28-day strength of recycled concrete is reduced by approximately 6.7%, 14.5%, 22.1%, and 34.5% compared to natural aggregate concrete at the above replacement rates. In engineering projects, a mix proportion with an appropriate replacement rate should be selected based on the stress conditions and bearing requirements of the project.

[0020] As the replacement rate increases, the fluidity and thixotropic stability of the mortar will decrease, specifically resulting in a significantly shorter printable time. Therefore, when designing large retaining walls that require long printing times, mix proportions with a replacement rate greater than 50% should not be used.

[0021] Drainage holes are arranged in two horizontal rows and two vertical columns at equal intervals on the foundation slab. The diameter of the reserved drainage holes is 20-50mm, preferably 30mm.

[0022] The arch curvature of the prefabricated 3D printed box-type concrete retaining wall shell can be customized according to the actual requirements of on-site construction.

[0023] The concrete wall cap can be customized using 3D printing concrete technology to match the specifications of the wall unit, and high-strength bolts can be used to connect it to the retaining wall system as a whole.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. Resource utilization and low-carbon construction: The wall unit is made of printable concrete with recycled fine aggregate. The empty box cavity can be filled with a high proportion of screened construction solid waste or soil, reducing the consumption of natural aggregate and the amount of concrete used in the structural entity, and improving the resource utilization level of solid waste.

[0025] 2. No formwork required and labor-saving cost reduction: The wall unit is formed in one piece by 3D printing. The empty box cavity and the arched shell are formed simultaneously, eliminating the need for the complex internal and external formwork system and the vibration operation in a confined space in the construction of traditional vertical box retaining walls. On-site construction mainly involves hoisting and positioning, keyway grouting, layered filling and capping, which can significantly reduce the investment in formwork, labor and construction period, and is especially suitable for sites with limited working area or complex terrain.

[0026] 3. Reliable prefabricated connection: Adjacent wall units are connected on-site by prefabricated keyways to form shear key connections, enabling rapid assembly and overall collaborative work; combined with the texture of the printed layer on the surface of the wall units, the mechanical interlocking of the shear key interface can be enhanced, improving shear resistance and anti-slip capability.

[0027] 4. Stable Structural System and Verifiable Load-Bearing Capacity: This invention adopts an "outer arch + central partition" hollow box configuration, optimizing the traditional vertical box-type component's bending-dominated stress mode into a force transmission path dominated by membrane forces. Comparative loading tests show that, under the same loading and constraint conditions, the peak load-bearing capacity of the prefabricated 3D-printed box-type concrete retaining wall specimen of this invention is increased by approximately "50% to 95%" compared to the traditional commercial concrete box-type retaining wall specimen, demonstrating a significant load-bearing advantage. Compared to traditional vertical box-type retaining walls, this invention also exhibits the advantages of more stable pre-peak load growth and the ability to withstand greater displacement before reaching peak load capacity.

[0028] 5. Synergistic Stabilization of Inner Filler: The soil and solid waste filling in the empty box cavity can form counterpressure and constraint, optimize force flow and share the effects of external forces; in the test, under the simulated inner filling condition, the peak bearing capacity of the arched box retaining wall specimen of the present invention is further improved (about 16%) compared with the condition without inner filling, indicating that the inner filler can enhance the overall bearing capacity and stability to a certain extent, and the displacement control capability is further enhanced under the action of inner filling.

[0029] 6. Standardization and easy maintenance: The wall unit adopts a modular design, which facilitates factory prefabrication and quality control; the prefabricated structure allows for partial replacement and maintenance, reducing the maintenance cost throughout the entire life cycle. Attached Figure Description

[0030] Figure 1 Vertical cross-sectional view of a prefabricated 3D-printed box-type concrete retaining wall system; Figure 2 Exploded view of components of a prefabricated 3D printed box-type concrete retaining wall system; Figure 3 A top view of the prefabricated 3D-printed box-type concrete retaining wall system; Figure 4 Top view of a 3D-printed box-type concrete retaining wall unit; Figure 5 This is a bottom view of the concrete wall cover; Figure 6 This is a top view of the cast-in-place foundation slab. Figure 7 A comparison chart of the load-bearing performance of 3D-printed box-type concrete retaining wall units and traditional box-type retaining walls. In the diagram: 1 is the arched exterior wall panel, 2 is the concave interior wall panel, 3 is the concave side wall panel, 4 is the central partition, 5 is the cast-in-place foundation slab, 6 is the concrete wall cover, 7 is the corner fixing key, 8 is the horizontal keyway, 9 is the embedded groove, 10 is the drainage hole, 11 is the water channel, 12 is the water collection tank, 13 is the high-strength bolt, 14 is the solid waste filler, and 15 is the drainage filter layer. Detailed Implementation

[0031] To further illustrate the present invention, the following detailed description is provided in conjunction with the accompanying drawings and embodiments, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0032] like Figure 1-3 As shown, the present invention relates to an assembled 3D-printed box-type concrete retaining wall and retaining wall system, comprising a 3D-printed box-type concrete retaining wall unit, a cast-in-place foundation slab 5, a concrete wall cover 6, corner fixing keys 7, a transverse keyway 8, an embedded groove 9, a drainage hole 10, a water channel 11, a water collection tank 12, high-strength bolts 13, solid waste filler 14, and a drainage filter layer 15. The 3D-printed box-type concrete retaining wall unit is an integrated structure composed of an arched outer wall panel 1, a concave inner wall panel 2, a concave side wall panel 3, and a central partition baffle 4, formed by 3D printing.

[0033] The number of partition baffles 4 is 1 to 3, arranged along the length or width of the wall, and connected to the wall panel in a T-shape or cross shape.

[0034] The arched exterior wall panel 1, concave interior wall panel 2, concave side wall panel 3, and central partition 4 are made of printable concrete with recycled fine aggregate as the main fine aggregate, realizing the recycling of building resources.

[0035] The transverse keyway 8 is a closed cavity formed by the concave side wall plate 3 between adjacent 3D printed box-type concrete retaining wall units. After the adjacent 3D printed box-type concrete retaining wall units are in place, the cement-based material is cast in place in the transverse keyway 8 to form a shear key, so that the retaining wall units are combined to form a box-type retaining wall system that bears the load.

[0036] An embedded groove 9 is provided on the cast-in-place foundation slab 5. A drainage hole 10 is provided in the closed area enclosed by the groove. A water trough 11 is provided below the drainage hole 10. The water trough 11 is connected to the water collection tank 12. A drainage filter layer 15 is provided between the cast-in-place foundation slab 5 and the solid waste filling material 14 to realize soil drainage.

[0037] The concrete wall cover 6 and the corner fixing key 7 are connected and installed to the retaining wall system using high-strength bolts 13 to achieve the limiting and capping of the retaining wall system.

[0038] The box-type retaining wall units are printed using mortar mixed with recycled fine aggregate. Due to the high moisture content and high water absorption of recycled fine aggregate, additional water needs to be added to adjust the mix proportions of the original 3D printed concrete mortar during the mortar mixing process. The adjusted material mix proportions are shown in the table below: Table 2. Mix proportions of recycled concrete (unit: kg·m³) -3 )

[0039] In the mix designation number, NC represents ordinary concrete, RC represents recycled concrete, and the following number represents the replacement rate of recycled fine aggregate (%). In addition to the above materials, admixtures need to be added according to the actual printing requirements. The above are typical results measured in this embodiment. They may vary depending on the source of raw materials and curing regime. The actual test results shall prevail.

[0040] By adjusting the material mix ratio of the 3D printing mortar, the retaining wall unit can be printed and constructed smoothly, and its structural strength and mechanical properties meet the engineering requirements.

[0041] The 3D printed box-type concrete retaining wall units are customized according to the on-site construction requirements. The number of prefabricated units is determined by the width and height of the retaining wall in the engineering design. All units are identical in size and specifications. They are prefabricated in the factory and then transported to the construction site for assembly.

[0042] An embedded groove 9 with the same size as the retaining wall unit is reserved on the foundation slab 5. The box-type retaining wall unit is inserted into the embedded groove 9. Adjacent retaining wall units are connected by cast-in-place cement-based material in the transverse keyway 8 to form a shear key connection, thus completing the assembly of the first-layer wall unit.

[0043] Clean the laitance and debris from the top surface of the first-floor wall unit, moisten it with water, and then evenly apply a non-shrink mortar layer with a thickness of 5-20 mm to correct the elevation and minor unevenness of the upper layer. A local thickening strip can be set at the intersection of the intermediate partition 4 to improve the stress transfer.

[0044] The upper unit is positioned by hoisting or sliding, and the joint width, straightness and outer arch shape are controlled by installing positioning components. The joint is sealed with grouting mortar or fine stone concrete to form a continuous load-bearing surface.

[0045] After each unit is assembled, solid waste filler material 14 is immediately filled into the corresponding empty cavity layer by layer and compacted to the designed density. Backfilling is carried out simultaneously from bottom to top to form temporary counterweight and stability during the construction phase. The construction steps are repeated layer by layer until the designed top wall elevation is reached.

[0046] After backfilling the top empty box, clean the top surface, pour the sealing and leveling layer, and install the concrete wall cover 6. Its bottom surface fits into the cavity set at the corresponding position of the wall. It is reliably connected to the embedded parts / connection holes by high-strength bolts 13 to form an integral sealing structure.

[0047] A drainage filter layer 15 is arranged between the foundation slab 5 and the solid waste filling material 14. Drainage holes 10 are arranged on the foundation slab 5. A water trough 11 is set under the drainage holes and connected to the water collection tank 12. The longitudinal slope is 0.5% to 1.0%. The collected water is directed into the water collection tank for unified external discharge or recycling, so as to achieve the function of soil drainage.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0049] Load-bearing performance comparison test To verify the load-bearing advantages of the prefabricated 3D-printed box-type concrete retaining wall of this invention, a comparative test was conducted using a concentrated loading method equivalent to engineering earth pressure. The specimens included: the arched box-type retaining wall specimen of this invention (3D-printed group) and a comparative specimen of a traditional vertical box-type retaining wall (traditional cast-in-place group). Both groups of specimens were designed with two working conditions: no internal filling and simulated internal filling.

[0050] In the loading device, the specimen is approximately confined to the ground / reaction frame via a rigid pressure beam and high-strength bolts. The load output by the MTS actuator is transmitted through the distribution beam and applied to the mid-span positions of the two spans of the specimen via two rigid round bars. The loading height is located at approximately 1 / 3 of the wall height to simulate the equivalent effect of the lateral pressure of the backfill. The load-displacement response is recorded simultaneously until failure.

[0051] The experimental results show that, under the same loading and constraint conditions, the peak bearing capacity of the arched box retaining wall specimen of this invention is significantly higher than that of the traditional vertical box retaining wall. Under the condition of no backfill, the peak bearing capacity of the specimen of this invention is approximately 76 kN, while that of the traditional cast-in-place specimen is approximately 39 kN; under the simulated backfill condition, the peak bearing capacity of the specimen of this invention is approximately 88 kN, while that of the traditional cast-in-place specimen is approximately 57 kN. Before the peak load, the specimen of this invention exhibits a stable upward trend with increasing displacement, followed by a sudden drop in load and failure after the peak load. The overall response conforms to the bearing failure characteristics of retaining walls.

[0052] Traditional vertical box-type retaining wall specimens showed a displacement of approximately 6–7 mm near the peak value, with the load rapidly decreasing after reaching the peak, indicating that they entered instability and failure during the intermediate deformation stage. In contrast, the arched box-type retaining wall of this invention significantly improved the peak bearing capacity while maintaining the peak displacement within a controllable range (approximately 9–10 mm in the case of no backfill and approximately 7–8 mm in the case of simulated backfill), demonstrating that the structure of this invention possesses better deformation adaptability while improving load-bearing capacity.

[0053] Furthermore, under simulated infill conditions, the specimen of the present invention exhibits a steeper rising section before the peak value and a relatively smaller peak displacement, demonstrating that the infill provides counter-pressure and constraint to the wall, resulting in a more rational force transmission path and thus achieving higher bearing capacity at the same displacement level.

[0054] The above results verify that the synergistic effect of the 3D printed box-type concrete retaining wall's load-bearing system and internal filling can effectively improve the bearing capacity and structural efficiency of the retaining wall unit, and has better deformation control capabilities.

[0055] Figure 7 This is a comparison of the load-displacement curves of the 3D-printed box-type concrete retaining wall (3D-E, 3D-F) and the traditional vertical box-type retaining wall (CB-E, CB-F) under the same loading conditions. E represents the condition without internal backfill, and F represents the condition with simulated internal backfill. In this embodiment, the outer arch curvature is 0.7 rad (central angle 40°), and the side arch curvature is 1 rad (central angle 57.7°). These parameters are a typical example of determining the combined effect of improved bearing capacity and printability. Due to experimental limitations, load-displacement data measurements were not conducted for other curvatures. In practical applications, the curvature selection can be determined through parametric design based on wall height, earth pressure, and construction conditions. For example, "under the premise of meeting the forming curvature limitations of construction equipment and out-of-plane deflection requirements, the combination of the outer arch curvature radius and the spacing between the diaphragms is determined by minimizing the peak out-of-plane bending moment."

[0056] Regarding peak load, 3D-E (76kN) shows a 94% improvement compared to CB-E (39kN); 3D-F (88kN) shows a 54% improvement compared to CB-F (57kN). To avoid inconsistencies, it is proposed to revise "approximately 50% improvement" to "50%–95% improvement" in typical tests. The load capacity without backfill is approximately 76 kN, while the load capacity with backfill is approximately 88 kN, representing an increase of approximately 15.8%.

[0057] Meanwhile, since the wall unit of this invention is formed by 3D printing without templates, the process of setting up internal and external templates, vibrating and demolding in narrow spaces required for traditional vertical box-type hollow thin-walled retaining wall components can be significantly reduced. On-site construction mainly involves hoisting and positioning, keyway grouting and keying, and filling and sealing. This can save labor, reduce costs and shorten the construction period while ensuring load-bearing performance.

Claims

1. A prefabricated 3D-printed box-type concrete retaining wall, assembled from 3D-printed concrete retaining wall units, characterized in that, The 3D printed concrete retaining wall unit is a 3D printed concrete integrated structure, which consists of an arched outer wall panel, a concave inner wall panel, and a concave side wall panel. The arched outer wall panel, the concave inner wall panel, and the concave side wall panel form a cavity. At least one partition plate is provided in the cavity formed by the arched outer wall panel, the concave inner wall panel, and the concave side wall panel to divide the cavity into at least two empty box cavities. The two ends of the partition plate are connected to the arched outer wall panel and the concave inner wall panel, respectively. A transverse keyway (8) is formed between the concave side wall panels of two adjacent 3D printed concrete box-type retaining wall units. A shear key is formed by casting cement-based material in the transverse keyway (8), so that the 3D printed concrete retaining wall units can be combined to bear load.

2. The prefabricated 3D printed box-type concrete retaining wall according to claim 1, characterized in that, The arched outer wall panel is an arc-shaped arch; the concave inner wall panel is an arc-shaped concave surface; and the concave side wall panel is an arc-shaped concave surface.

3. The prefabricated 3D-printed box-type concrete retaining wall according to claim 1, characterized in that, The arc shape of the arched outer wall panel is consistent with the arc shape of the concave inner wall panel.

4. The prefabricated 3D-printed box-type concrete retaining wall according to any one of claims 1-3, characterized in that, Solid waste filler (14) is filled into the two empty box cavities to achieve the stabilization and joint bearing of the retaining wall.

5. A prefabricated 3D-printed box-type concrete retaining wall system, characterized in that, include: The assembled 3D printed box-type concrete retaining wall according to any one of claims 1-4; The cast-in-place foundation slab (5) has an embedded groove (9) and a drainage hole (10) on its upper surface, and a water trough (11) connected to the drainage hole (10) is also provided inside the slab. The 3D printed concrete retaining wall unit at the bottom of the assembled 3D printed concrete box retaining wall is set in the embedded groove, and a drainage filter layer (15) is provided in the 3D printed concrete retaining wall unit at the bottom. as well as A concrete wall cover (6) is installed at the top of the assembled 3D printed box-type concrete retaining wall.

6. The prefabricated 3D printed box-type concrete retaining wall system according to claim 5, characterized in that, It also includes a water collection tank (12), the outlet of which is connected to the water collection tank (12).

7. The prefabricated 3D printed concrete box retaining wall system according to claim 5, characterized in that, It also includes a corner fixing key (7), which is detachably fixed to the cast-in-place foundation slab (5).

8. The prefabricated 3D printed concrete box retaining wall system according to claim 5, characterized in that, The water-cement ratio of the printable concrete used to print the 3D printed concrete retaining wall unit is 0.28 to 0.36; recycled fine aggregate accounts for 30% to 100% of the total fine aggregate, and the remainder is natural aggregate.

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