Soft soil foundation embankment heightening and widening structure and construction method

Abstract

The invention discloses a soft soil foundation embankment heightening and widening structure and a construction method, and belongs to the field of water conservancy projects. In order to solve the problems of uneven settlement, landslide instability and overlarge occupied area easily occurring when the soft soil foundation embankment is heightened and widened, the structure comprises precast concrete piles (top beams and ripraps are arranged on the tops of the piles) densely arranged at the slope toe outside the embankment, an inner side cantilever retaining wall (with drainage holes and a gravel inverted filter), geogrids laid in backfill soil in a layered mode, and CFG piles arranged on the lower portion in a plum blossom shape. The guardrail base and the flower bed are integrally poured with the retaining wall. The construction method comprises the steps of slide-resistant pile construction, earthwork excavation, CFG pile construction, retaining wall pouring, embankment body backfilling and embankment top road construction. Bidirectional control over settlement and horizontal displacement is achieved through cooperation of multiple structures, variable-stiffness leveling can be achieved by adjusting parameters of the CFG piles, and the variable-stiffness leveling structure has the advantages of skid resistance, stability, landscape optimization and land occupation saving and is suitable for soft soil foundation embankment upgrading and reinforcing projects.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering, specifically to a structure and construction method for raising and widening embankments on soft soil foundations. Background Technology

[0002] Due to limitations imposed by factors such as terrain conditions, land acquisition and environmental protection, and project investment, some dikes are often built on soft soil foundations with low deformation modulus and shear strength. In addition, due to factors such as construction standards and construction quality, dikes are prone to problems such as excessive settlement and insufficient slope stability.

[0003] Soft soil foundations are primarily composed of highly compressible fine-grained soil. When subjected to external loads such as the weight of the superstructure and water pressure, they are highly susceptible to compressive deformation, leading to foundation settlement. Due to the uneven nature of this settlement, excessive differential settlement can occur in the embankment structure, affecting overall stability. Uneven settlement can also cause embankment tilting and cracking, seriously threatening the safe operation of the embankment and its flood control function. Furthermore, the weak soil layers in soft soil foundations have low shear strength, making them highly susceptible to shear failure and landslides when subjected to increased external loads, water erosion, or adverse factors such as earthquakes.

[0004] Choosing the right reinforcement method is crucial, considering the different characteristics and engineering requirements of soft soil foundations. Common reinforcement methods each have their advantages and disadvantages, and are applicable to different conditions. For example, replacement is suitable for shallow soft soil treatment or important engineering sections, effectively improving foundation bearing capacity, but it is costly. Drainage consolidation is suitable for large-area soft soil foundation treatment, accelerating the drainage and consolidation of soft soil and improving foundation strength through drainage systems and preloading. Chemical consolidation involves injecting chemical grout to react with the soft soil, forming a composite foundation with higher strength suitable for deep soft soil treatment. When selecting a reinforcement method, factors such as foundation conditions, construction conditions, economic costs, construction period requirements, and environmental impact should be fully considered, and a multi-scheme comparison approach should be adopted to determine the optimal solution.

[0005] Because soft soil has high natural water content, high compressibility, low bearing capacity, and low shear strength, raising and widening embankments on soft soil foundations can simultaneously cause uneven settlement of the embankment body and landslide instability of the embankment slope. Traditional treatment methods, such as composite foundations, can only control the vertical displacement of the soil and cannot simultaneously address the need for differential settlement control in both vertical and horizontal directions. Retaining walls can reduce the amount of fill and land area required, and can control the horizontal displacement of the soil, but they have minimum requirements for the bearing capacity of the foundation. Furthermore, when the embankment's grade is increased, the anti-sliding stability of the embankment body must also be considered. Summary of the Invention

[0006] This invention provides a structure and construction method for raising and widening embankments on soft soil foundations, which comprehensively considers the uneven settlement and landslide problems that may be caused by raising and widening the embankment, thus ensuring the safety of the embankment.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] A structure for raising and widening an embankment on soft soil foundation includes:

[0009] Precast concrete piles: Closely arranged at the toe of the outer slope of the embankment, with the bottom of the precast concrete piles entering the bearing layer, and a capping beam installed on the top of the precast concrete piles, covered with riprap.

[0010] Backfill material: It is filled in layers in the widened area inside the dike, with geogrid laid on top of each layer;

[0011] Cantilever retaining wall: Located on the inner side of the embankment, the cantilever retaining wall is equipped with drainage holes, and a drainage ditch is provided at the toe of the cantilever retaining wall. A crushed stone filter layer is provided between the cantilever retaining wall and the backfill material.

[0012] CFG piles: arranged in a quincunx pattern under the cantilever retaining wall and the inner backfill material, with the pile bottom entering the bearing layer;

[0013] The top structure of the dike includes a newly built dike top road, a wave wall, guardrails and flower beds, among which the base of the guardrail and the cantilever retaining wall of the flower bed are cast in one piece.

[0014] Furthermore, the precast concrete piles are C80 hollow square concrete piles, with the pile body extended by sulfur mortar anchoring, and the thickness of the riprap covering the pile top is 30cm.

[0015] Furthermore, the geogrid is a bidirectional geogrid, and during installation, the slope end is folded back 1.5m and fixed to the excavated steps of the embankment with hook nails.

[0016] Furthermore, a gravel filter layer is provided within 20cm behind the cantilever retaining wall, and the drainage holes are arranged in a quincunx pattern with a spacing of 2m and a diameter of 10cm.

[0017] Furthermore, the newly constructed embankment road is located on the top of the heightened and widened embankment. The water-facing slope is protected by ecological slope protection, the water-facing shoulder is equipped with a wave-breaking wall, and the back-water shoulder is equipped with guardrails and flower beds.

[0018] A method for raising and widening an embankment on soft soil foundation includes the following steps:

[0019] Step 1: Construction of anti-slide piles

[0020] Precast concrete piles were constructed and arranged closely at the toe of the outer slope of the embankment, with the pile bottoms penetrating the bearing layer; after the pile tops were roughened, a capping beam was poured, and riprap was placed on top of the capping beam;

[0021] Step 2: Earthwork Excavation

[0022] The existing embankment top road was demolished, and the inner slope was excavated in a stepped manner. At the same time, the foundation trench for the cantilever retaining wall was excavated. After excavation, the foundation trench and the embankment body were compacted.

[0023] Step 3: CFG pile construction

[0024] In the retaining wall foundation and inner backfill area after excavation in step 2, CFG piles are constructed using the vibratory driven pipe grouting method. The pile bottom enters the bearing layer and the pile body is arranged in a quincunx pattern.

[0025] Step 4: Retaining Wall Construction

[0026] Tie the reinforcing steel of the cantilever retaining wall and install the formwork. Cast the base of the guardrail and flower bed into the cantilever retaining wall as a whole, and reserve drainage holes. After the casting is completed, construct a drainage ditch at the toe of the wall.

[0027] Step 5: Backfilling the embankment

[0028] Cohesive soil was backfilled in layers to the design elevation, compacted, and then geogrid was laid; a permeable gravel filter layer was installed within 20cm behind the retaining wall.

[0029] Step 6: Construction of the embankment road

[0030] Complete the construction of the ecological slope protection and wave-breaking wall outside the dike, lay the new dike top road, and install guardrails.

[0031] Furthermore, before the CFG pile construction described in step 3, pile forming process and pile strength test are carried out. The mixture uses 32.5 grade ordinary Portland cement, and the maximum particle size of crushed stone is not greater than 50mm.

[0032] Furthermore, during the laying of the geogrid in step 5, the folded-back end covers the excavation steps and is fixed with hook nails, and the overlap width of adjacent geogrids is not less than 20cm.

[0033] Furthermore, in step 1, the precast concrete piles are formed using static pressure or hammer driving methods, and the pile tip penetrates into the bearing stratum to a depth of not less than 1.5m.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) This invention combines cantilever retaining walls, CFG piles and geogrids to achieve bidirectional control of vertical settlement and horizontal displacement after the dike is heightened and widened, and can reduce the land occupied inside the dike.

[0036] (2) The present invention can combine the prediction results of uneven settlement of the embankment body and adjust the cement parameters, crushed stone gradation and pile length of CFG piles to achieve the leveling of the embankment body with variable stiffness.

[0037] (3) The present invention integrates cantilever retaining walls, guardrail bases and flower beds, which are simple and stable as a whole and have a good landscape effect.

[0038] (4) The present invention enhances the anti-sliding stability of the dike by arranging precast concrete anti-sliding piles closely outside the dike, and fills the pile top with crushed stone to reduce the scouring of the pile top and the dike toe by the water flow. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall structure for raising and widening the embankment road according to the present invention;

[0040] Figure 2 This is a schematic diagram of the cantilever retaining wall of the present invention;

[0041] Figure 3 This is a schematic diagram of the geogrid structure used in this invention;

[0042] Figure 4 This is a schematic diagram of the CFG pile plan layout of the present invention;

[0043] Figure 5 This is a schematic diagram of the reinforcement of the outer slope toe of the dike according to the present invention.

[0044] In the diagram: 1-Soft soil layer; 2-Precast concrete pile; 3-Rockfill; 4-Existing embankment; 5-Existing embankment top road; 6-Ecological slope protection; 7-Wave wall; 8-Newly built embankment top road; 9-Backfill material; 10-Geogrid; 11-Existing inner slope of the embankment; 12-Guardrail; 13-Flower bed; 14-Cantilever retaining wall; 15-Drainage ditch; 16-Existing ground line behind the embankment; 17-Bearing layer; 18-CFG pile; 19-Gravel filter layer; 20-Drainage hole; 21-Heel side retaining wall foundation excavation line; 22-Toe side retaining wall foundation excavation line; 23-Cap beam. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] For conventional dikes, since the outer slope is higher than the inner slope, to reduce the amount of fill, it is preferable to increase the height and width of the dike inwards. Please refer to [link / reference]. Figure 1-5 This invention provides a structure for raising and widening a soft soil foundation embankment, including precast concrete piles 2, riprap 3, ecological slope protection 6, wave wall 7, newly built embankment top road 8, backfill material 9, geogrid 10, guardrail 12, flower bed 13, cantilever retaining wall 14, drainage ditch 15, CFG piles 18, crushed stone filter layer 19, drainage hole 20, and capping beam 23, etc.

[0047] The precast concrete piles 2 are installed at the outer slope toe of the embankment. The pile body penetrates the soft soil layer 1, and the pile bottom enters the bearing layer 17. They are arranged closely together to improve the anti-sliding stability of the embankment. A cap beam 23 is installed on the pile top. To reduce the scouring of the pile top and the embankment toe by the water flow, a riprap 3 (such as...) is placed on top. Figure 5 (As shown).

[0048] The newly built embankment road 8 is located on the top of the embankment after it has been raised and widened. The water-facing slope is protected by an ecological slope protection 6. A wave wall 7 is installed on the water-facing shoulder, and a guardrail 12 and flower bed 13 are installed on the back shoulder.

[0049] The cantilever retaining wall 14 (such as Figure 2 (As shown) is arranged on the inner side of the dike to reduce the land occupation area and control the horizontal displacement of the backfill material 9. A crushed stone filter layer 19 is provided between the wall and the backfill material 9. Drainage holes 20 are provided in the wall body. A drainage ditch 15 is provided at the toe of the wall. The top of the ditch is flush with the existing ground line 16 behind the dike.

[0050] The CFG piles 18 are installed inside the existing embankment 4, on the backfill soil 9, and below the cantilever retaining wall 14. The pile body penetrates the soft soil layer 1, and the pile bottom enters the bearing layer 17, arranged in a staggered pattern (e.g., Figure 4 As shown in the figure, the stiffness of the pile body is controlled by adjusting the cement content and the aggregate gradation.

[0051] The base of the guardrail 12 and flower bed 13 is integrally cast with the cantilever retaining wall 14.

[0052] Geogrid 10 is installed inside the backfill material 9 to improve the shear strength of the backfill soil.

[0053] As a preferred option, the precast concrete pile 2 can be a precast concrete hollow square pile C80 500(300) PHS-AB.

[0054] As a preferred option, in order to improve the bonding between the backfill material 9 and the embankment, the existing inner slope 11 of the embankment is excavated, and the excavation line 21 of the retaining wall foundation on the heel side adopts a stepped form.

[0055] As a preferred option, the backfill material 9 can be cohesive soil to improve the impermeability of the embankment.

[0056] Preferably, the geogrid 10 can be a bidirectional geogrid (such as...). Figure 3As shown in the figure, this is to control the cracking of the backfill soil in both the horizontal and vertical directions of the embankment.

[0057] As a preferred option, the existing embankment top road 5 can be demolished and used as riprap 3 for backfilling at the toe of the embankment slope.

[0058] Preferably, streetlights can be placed at intervals at positions 12 of the guardrail.

[0059] As a preferred option, the excavated material is used for backfilling after excavation at the toe of the retaining wall foundation at line 22 on the toe side.

[0060] The existing seawall reinforcement project in a coastal city uses a flood control standard of once every 50 years. With urban economic development, according to flood control planning, the standard needs to be upgraded to once every 100 years. The existing seawall is laid out along the coastline and is relatively straight, with a 5-meter-wide road on the top. The seawall foundation mainly consists of fill, silt, and silty clay, with a silt layer 6-8 meters thick. The foundation bearing capacity and strength indicators are low, leading to uneven settlement of the existing seawall.

[0061] Due to the need for upgrading standards, the overall embankment will be raised by 0.8~1.5m, and the road on the top of the embankment will be widened to 8m. This embodiment of the invention provides a construction method for raising and widening an embankment on a soft soil foundation. The specific steps are as follows:

[0062] Step 1: Construction of anti-slide piles

[0063] (1) Use a total station to mark out the pile positions according to the design coordinates, and verify the pile positions before construction;

[0064] (2) Precast hollow square concrete piles (C80 500(300) PHS-AB) were used as precast concrete piles 2. Pile construction was carried out using static pressure or hammer driving methods. When the pile length was insufficient, sulfur mortar was used for anchoring.

[0065] (3) When the pile tip enters the bearing layer 17 and the pile top reaches the design elevation, roughen the pile top and pour the capping beam 23;

[0066] (4) A 30cm thick layer of crushed stone is placed at the top of the precast concrete pile 2 and at the toe of the outer slope of the embankment as riprap 3.

[0067] Step 2: Earthwork Excavation

[0068] (1) Demolish the existing embankment road 5 and screen slag with a particle size of 10~20cm for crushed stone filling;

[0069] (2) Clear the surface within the project area and excavate the inner slope according to the steps, while completing the excavation of the retaining wall foundation;

[0070] (3) Compact the excavated embankment and retaining wall foundation trench.

[0071] Step 3: CFG Pile Construction

[0072] (1) Conduct pile forming process and pile strength tests before construction;

[0073] (2) The mixture is prepared by a forced mixer with a maximum particle size of no more than 50 mm. Sand and stone chips can be added to improve the gradation. 32.5 grade ordinary Portland cement is used.

[0074] (3) Before sinking the pipe, fill the pile position with 50cm thick gravel to reduce blockage at the bottom of the pipe, start the vibratory hammer, and sink the pipe at a uniform speed to the design depth.

[0075] (4) After the pipe is in place, feed the material immediately (mix crushed stone with cement fly ash slurry) to avoid water entering the pipe and causing the mixture to segregate;

[0076] (5) After the grouting is completed, start the vibratory hammer to pull the pipe at a uniform speed and carry out the construction of the next pile.

[0077] Step 4: Retaining Wall Construction

[0078] (1) Reinforcing steel binding and formwork installation;

[0079] (2) The base of the guardrail 12, the flower bed 13 and the cantilever retaining wall 14 are cast in one piece, and the drainage hole 20 is reserved.

[0080] (3) Construction drainage ditch 15, and backfilling the wall toe with excavated material.

[0081] Step 5: Backfilling the embankment

[0082] (1) Use cohesive soil material, compact and backfill in layers, with each layer being 50cm thick. Set up a well-permeable crushed stone filter layer 19 within 20cm behind the retaining wall.

[0083] (2) A bidirectional geogrid of 10mm is laid on the top of each layer of fill, and the slope end is folded back 1.5m and fixed to the excavation step with hook nails;

[0084] (3) Backfill in layers to the design elevation.

[0085] Step Six: Construction of the Embankment Road

[0086] (1) Complete the construction of the ecological slope protection 6 and the wave wall 7 outside the dike;

[0087] (2) Complete the construction of the embankment top road surface;

[0088] (3) Install guardrail 12 and street lights.

[0089] This invention has the following features and effects:

[0090] 1. Two-way displacement control and land occupation optimization: By combining cantilever retaining walls, CFG piles and geogrids, two-way control of vertical settlement and horizontal displacement after the dike is heightened and widened can be achieved, while reducing the land occupation area inside the dike.

[0091] 2. Variable stiffness leveling design: Based on the quincunx arrangement of CFG piles, the embankment can be leveled by adjusting the cement content, crushed stone gradation and pile length of the piles, combined with the settlement prediction results, to adapt to the uneven settlement characteristics of soft soil foundation.

[0092] 3. Structural integration and landscape enhancement: The guardrail base, flower beds and cantilever retaining walls of the embankment top structure are cast in one piece, resulting in a simple and stable overall structure that enhances the landscape effect of the embankment.

[0093] 4. Anti-sliding stability and scour protection: The anti-sliding stability of the dike is enhanced by the dense arrangement of precast concrete piles at the outer slope toe, and the pile tops are covered with riprap to reduce the scour of the pile tops and dike toe by the water flow.

[0094] This invention is applicable to the upgrading and reinforcement of embankments on soft soil foundations, and has the advantages of convenient construction and stable structure. The invention provides a structure and construction method for raising and widening embankments on soft soil foundations, which can effectively reduce the risk of uneven settlement and landslides on soft soil foundation embankments, and has good potential for widespread application.

[0095] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A structure for raising and widening an embankment on soft soil foundation, characterized in that, include: Precast concrete piles: Closely arranged at the toe of the outer slope of the embankment, with the bottom of the precast concrete piles entering the bearing layer, and a capping beam installed on the top of the precast concrete piles, covered with riprap. Backfill material: It is filled in layers in the widened area inside the dike, with geogrid laid on top of each layer; Cantilever retaining wall: Located on the inner side of the embankment, the cantilever retaining wall is equipped with drainage holes, and a drainage ditch is provided at the toe of the cantilever retaining wall. A crushed stone filter layer is provided between the cantilever retaining wall and the backfill material. CFG piles: arranged in a quincunx pattern under the cantilever retaining wall and the inner backfill material, with the pile bottom entering the bearing layer; The top structure of the dike includes a newly built dike top road, a wave wall, guardrails and flower beds, among which the base of the guardrail and the cantilever retaining wall of the flower bed are cast in one piece.

2. The structure according to claim 1, characterized in that, The precast concrete piles are C80 hollow square concrete piles, with the pile body extended by sulfur mortar anchoring, and the pile top is covered with 30cm thick riprap.

3. The structure according to claim 1, characterized in that, The geogrid is a bidirectional geogrid. During installation, the slope end is folded back 1.5m and fixed to the excavated steps of the embankment with hook nails.

4. The structure according to claim 1, characterized in that, A gravel filter layer is installed within 20cm behind the cantilever retaining wall, and drainage holes are arranged in a quincunx pattern with a spacing of 2m and a diameter of 10cm.

5. The structure according to claim 1, characterized in that, The newly constructed embankment road is located on the top of the heightened and widened embankment. The water-facing slope is protected by ecological slope protection, the water-facing shoulder is equipped with a wave wall, and the back shoulder is equipped with guardrails and flower beds.

6. A method for raising and widening an embankment on soft soil foundation, characterized in that, Includes the following steps: Step 1: Construction of anti-slide piles Precast concrete piles were constructed and arranged closely at the toe of the outer slope of the embankment, with the pile bottoms penetrating the bearing layer; after the pile tops were roughened, a capping beam was poured, and riprap was placed on top of the capping beam; Step 2: Earthwork Excavation The existing embankment top road was demolished, and the inner slope was excavated in a stepped manner. At the same time, the foundation trench for the cantilever retaining wall was excavated. After excavation, the foundation trench and the embankment body were compacted. Step 3: CFG pile construction In the retaining wall foundation and inner backfill area after excavation in step 2, CFG piles are constructed using the vibratory driven pipe grouting method. The pile bottom enters the bearing layer and the pile body is arranged in a quincunx pattern. Step 4: Retaining Wall Construction Tie the reinforcing steel of the cantilever retaining wall and install the formwork. Cast the base of the guardrail and flower bed into the cantilever retaining wall as a whole, and reserve drainage holes. After the casting is completed, construct a drainage ditch at the toe of the wall. Step 5: Backfilling the embankment Cohesive soil was backfilled in layers to the design elevation, compacted, and then geogrid was laid; a permeable gravel filter layer was installed within 20cm behind the retaining wall. Step 6: Construction of the embankment road Complete the construction of the ecological slope protection and wave-breaking wall outside the dike, lay the new dike top road, and install guardrails.

7. The method according to claim 6, characterized in that, Before the construction of the CFG piles in step 3, the pile forming process and pile strength test are carried out. The mixture uses 32.5 grade ordinary Portland cement and the maximum particle size of crushed stone is no more than 50mm.

8. The method according to claim 6, characterized in that, When laying the geogrid in step 5, the folded-back end covers the excavation step and is fixed with hook nails, and the overlap width of adjacent geogrids is not less than 20cm.

9. The method according to claim 6, characterized in that, In step 1, the precast concrete piles are formed using the static pressure method or the hammer driving method, and the pile tip penetrates into the bearing stratum to a depth of not less than 1.5m.

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