Backfill reinforcement construction method for dry silty-fine sand slopes

Abstract

The present invention relates to a backfill reinforcement construction method for dry silty-fine sand slopes. The method comprises the following steps: S1, on the basis of a geological investigation report, comparing a particle size distribution curve of soil samples in an excavation area with a vibro-compactibility differentiation chart to determine construction parameters; S2, on the basis of design specifications and a slope stability safety coefficient, verifying whether a checking calculation result meets requirements; and S3, performing slope reinforcement in a layered manner, each layer of slope reinforcement comprising a layered rolling compaction construction area and a filler-free vibro-compaction construction area, wherein the layered rolling compaction construction area is located on an outer side of a slope, the filler-free vibro-compaction construction area is located on an inner side thereof, and the layered rolling compaction construction of the next layer is located above a filler-free vibro-compaction construction area of the previous layer; and performing construction layer by layer to reinforce the slope, wherein each layer of slope reinforcement involves firstly performing construction on the layered rolling compaction construction area, then performing construction on the filler-free vibro-compaction construction area, and finally, when a design height is reached, performing filler-free vibro-compaction construction on the position close to the inner side of the slope, thereby completing the reinforcement of the entire slope. The solution of the present invention can improve the construction efficiency and ensure a reinforcement effect.

Description

A construction method for backfilling and reinforcing a slope using dry fine sand

[0001] This application claims priority to the Chinese invention patent application (application number: 202311838344.5) filed on December 28, 2023. Technical Field

[0002] The invention relates to the technical field of civil engineering, in particular to a dry powder fine sand slope backfill reinforcement construction method, a dry powder fine sand slope backfill reinforcement construction technology, and belongs to the slope treatment technology in the field of civil engineering. Background Art

[0003] The port area (hereinafter referred to as CI area) is located in a desert area, adjacent to several communities. There is no groundwater and no risk of soil liquefaction. In addition, there is no rain or strong wind in the area all year round, and there is no construction during the rainy season. The maximum backfill depth is 14m, and the maximum height of the slope formed by the backfill is 20m, with a slope ratio of about 1:1.6. The on-site geological conditions are dry fine sand geology, with an average high fine particle content of about 15% to 20%, a natural moisture content of less than 2%, and a maximum / minimum dry density distribution of 1.732 / 1.420g / cm 3 The project is designed to withstand a seismic intensity of 9 degrees, with a PGA value of 0.542g.

[0004] Referring to the Technical Specification for Appraisal and Reinforcement of Slope Engineering (GB 50843-2013), relevant technical papers, and construction experience from similar projects, methods for treating high-fill backfill slopes include changing the slope soil quality (soil replacement, grouting, crushed stone piles, reinforced soil, etc.), changing the slope geometry (cutting and reducing loads, stacking and counter-pressure methods), and installing anti-slide measures (anti-slide piles, anti-slide retaining walls, etc.). However, based on the current construction conditions and on-site situation in the CI area, the following analysis is made:

[0005] (1) By changing the soil quality of the slope, the naturally formed sandy slope needs to be excavated and then replaced with soil or backfilled in layers with reinforced soil to increase the cohesion and internal friction angle of the soil. However, this slope reinforcement process currently requires a large amount of rework and high material costs.

[0006] (2) Adopt the method of changing the geometric shape of the slope. The cutting and unloading method is an engineering measure to reduce the weight of the sliding body and the thrust of the landslide by slowing down the slope and excavating part of the sliding body rock and soil at the top of the slope. Since the slope of the backfill area of ​​the CI district is close to the 60kV high-voltage line and the external community, if this reinforcement process is adopted, the original design slope ratio will be changed, which is inconsistent with the design purpose. There are also great safety hazards during construction. It will be strongly opposed by community residents and is not advisable. In addition, the backloading and backpressure method is to pile up soil and load it at the anti-sliding section of the slope foot of the landslide body to increase the anti-sliding force. If this reinforcement process is adopted, large cranes and earthmoving equipment will be used to work near the high-voltage line for transportation, lifting, loading and other operations. There are great safety hazards and it is also not advisable.

[0007] (3) Anti-slip measures, similar to the back-loading method, require the use of large cranes and earthmoving equipment to work near the high-voltage lines, including laying out the lines and excavating, hoisting the formwork, hoisting the steel cage, and pouring concrete. According to local regulations, the vertical safety distance between the 60kV high-voltage line and the construction area is 4.43m and the horizontal distance is 2.93m, so this reinforcement method is not advisable.

[0008] (4) Layered compaction is the most reliable and safe reinforcement process, with a total volume of approximately 1.24 million m 2 However, this reinforcement process requires a large amount of construction equipment and testing equipment. In addition, field tests have shown that the equipment is stuck while traveling, making it impossible to directly compact the fine sand. If the compaction process is continued, the surface layer must be replaced with gravel or clay, which will greatly increase construction costs, reduce excavation and backfill efficiency, and be extremely detrimental to the project schedule.

[0009] (5) With reference to the Technical Specification for Building Foundation Treatment 01-JGJ79-2012, after comprehensive consideration, the project team intends to use a non-filler vibro-compaction method combined with layered compaction to reinforce the slope. However, based on previous engineering practice and literature references, the non-filler vibro-compaction method is suitable for coarse-grained fillers with a fine particle content of less than 12-15%. While the feasibility of this process for foundation reinforcement in the CI area remains to be determined through further testing.

[0010] Summary of the Invention

[0011] The present invention aims to overcome the shortcomings of existing dry fine sand slope construction methods, which cannot meet engineering requirements, by providing a novel dry fine sand slope backfill reinforcement construction method. This method overcomes the existing problems of increased construction costs, low construction efficiency, strong opposition from community residents, and forced project delays, thereby resolving the difficulties of slope reinforcement construction in dry fine sand slopes.

[0012] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0013] A dry fine sand slope backfill reinforcement construction method comprises the following steps:

[0014] S1. According to the geological survey report, the particle gradation curve of the soil sample in the excavation area is compared with the vibrocompaction differentiation diagram. After field tests, the technical parameters of the filler-free vibrocompaction construction of the dry fine sand layer are determined.

[0015] S2. Verify the calculation results based on the design specifications and slope stability safety factor to see if they meet the safety requirements. If the calculation results do not meet the requirements, adjust the slope factor based on the unmet safety requirements.

[0016] S3. Carry out slope reinforcement in layers, and each layer of slope reinforcement includes: a layered rolling construction area and a non-filling vibro-flotation construction area; the layered rolling construction area is located on the outer side of the slope, and the non-filling vibro-flotation construction area is located on the inner side adjacent to the layered rolling construction area; the layered rolling construction of the latter layer of slope reinforcement construction is located above the non-filling vibro-flotation construction area of ​​the previous layer.

[0017] The slope is reinforced layer by layer. For each layer of slope reinforcement, the layered compaction construction area is constructed first, and then the non-filling vibro-compaction construction area is constructed. The slope height formed by the layered compaction construction reaches the designed height, and the non-filling vibro-compaction construction is carried out near the inner side of the slope in the last completed layered compaction construction area to complete the entire slope reinforcement.

[0018] The slope backfill reinforcement construction method disclosed in this paper was developed through geological research and testing to determine the technical parameters for vibrocompaction with dry fine sand. The method utilizes a "vibrocompaction + layered compaction" process, adjusting the parameters based on empirical calculations to ensure slope stability. This process combines filler-free vibrocompaction with layered compaction to effectively reinforce high sandy slopes and ensure their stability.

[0019] Compared with the traditional high fill slope reinforcement technology, the dry fine sand slope construction technology formed by innovative backfilling can effectively improve construction efficiency, ensure the foundation reinforcement effect, save project time and construction costs, and minimize the adverse impact on the community.

[0020] Specifically, it has the following two advantages:

[0021] (1) The slope construction technology of the present invention was pre-tested with vibro-compaction tests. After the tests were successful, relevant technical parameters were obtained, and the filler-free vibro-compaction method was successfully applied to extremely thick, dry, fine sand layers in desert areas. At the same time, process optimization measures such as "localized filling, timely backfilling, reducing water pressure, and layered backfilling" were proposed, ultimately effectively consolidating the loose backfill fine sand.

[0022] (2) During the slope reinforcement process using the technology of the present invention, a combination of layered rolling and vibro-compaction is used to reinforce the slope, based on the natural slope conditions formed by the backfill. The compaction degree of the layered rolling area is tested by the sand injection method, and the slope vibro-compaction area is tested by the standard penetration test. After testing, both meet the design requirements. Compared with similar engineering data, the most significant feature of the present invention is that the vibro-compaction method without fillers is used throughout the entire process. This method is suitable for silty sand geology with a high fine particle content. It combines the layered rolling and vibro-compaction process requirements in an economical, reasonable, and efficient manner to complete the slope backfill and reinforcement construction.

[0023] Furthermore, in step S1, the vibro-compactability differentiation diagram is the Brown 1977 vibro-compactability differentiation diagram. The particle gradation curve of the soil sample in the excavation area is compared with the Brown 1977 vibro-compactability differentiation diagram, and the scientific vibro-compactability differentiation diagram is used to perform pre-construction prediction and assessment.

[0024] Furthermore, in step S1, in the Brown 1977 vibrocompactability categorization diagram, zone 1 is the sand material most suitable for vibrocompacting; zone 2 corresponds to sandy soils with compacted sand, crushed stone soil, and cemented sand, and vibrocompacting is less efficient; zone 3 corresponds to sandy soils with a high fine particle content and poor vibrocompactability, requiring testing to determine the vibrocompacting construction technical parameters.

[0025] Furthermore, in step S2, the slope stability safety factor includes the slope stability safety factor under general working conditions and the slope stability safety factor under earthquake working conditions.

[0026] Furthermore, in step S2, the slope grade is determined according to GB 50330-2013 "Technical Specification for Slope Engineering in Construction Projects", and then the slope stability safety factor under general working conditions and the slope stability safety factor under seismic working conditions are determined, and whether the slope after vibro-impacting meets the safety factor requirements is verified.

[0027] Furthermore, in step S3, the thickness of each layer in the layered rolling construction area is 40 to 80 cm, that is, the layered rolling is performed every 40-80 cm thickness.

[0028] Preferably, when layered rolling is carried out in the layered rolling construction area, each layer includes a sand layer and a crushed material layer, which are filled and rolled in sequence, and the thickness ratio of sand and crushed material in each layer is 4:5-7. Sand and crushed material are used to fill and roll in sequence, and the thickness ratio of sand and crushed material is 4:5-7, so as to give full play to the role of sand and crushed material in compacting and consolidating each other through rolling. For example, in the layered rolling construction area, that is, the outer area of ​​the slope reinforcement construction, layered rolling is carried out every 60 cm (40 cm on-site sand + 20 cm crushed material), and the crushed material is fully spread in the layered rolling range, and the source of the crushed material is generated by blasting and excavation.

[0029] Furthermore, in step S3, when layered rolling is performed in the construction area, after each layer is rolled, a geogrid is laid near the edge of the slope. Preferably, a 3m wide, bidirectional, 55kN / m geogrid is laid. For example, after the aforementioned layered paving and rolling of 40cm of on-site sand and 20cm of crushed slag, a 3m wide, bidirectional, 55kN / m geogrid is laid after a single layer of rolling is completed. This enhances the bearing capacity of the soil slope foundation, prevents slope deformation and collapse, and prevents soil erosion or rainwater erosion.

[0030] Furthermore, in step S3, the transverse width along the slope in the filler vibro-floating construction area is not less than the crane width + a safety margin, for example, not less than 7.5 meters. Preferably, the transverse width along the slope is not less than 8 meters.

[0031] Furthermore, in step S3, non-filler vibro-compaction construction is carried out in the filler vibro-compaction construction area, and a standard penetration test is carried out after the vibro-compaction is completed.

[0032] Preferably, after the vibro-impacting is completed, a standard penetration test is performed, and the number of standard penetration tests is not less than 0.5% of the number of vibrated holes.

[0033] Preferably, the parameters for vibro-impact construction without filler are as follows: spacing 2 to 3 m, hole-making speed 1 to 2 m / min, lifting speed 0.5 to 1 m / min, lifting spacing 0.5 to 1 m, vibration at the bottom of the hole 20-30 s, vibration in the hole 8 to 10 s, water pressure range 0.3 to 1.0 MPa, and current range 100 to 120 A.

[0034] Furthermore, in step S3, when the vibrator is raised to within 6m of the surface layer, the reverse insertion method of vibratory construction is used to reinforce the upper area. Typically, the SPV in the top area after vibratory construction is close to the design requirement. Therefore, when the vibrator is raised to within 6m of the surface layer, the reverse insertion method of vibratory construction is used to enhance the reinforcement effect of the upper area.

[0035] Furthermore, in step S3, during the vibro-impact construction process using the back-insertion method, the local filling in the vibro-impact area is raised by 2 m to increase the overlying stress of the vibro-impact point and the foundation soil.

[0036] Furthermore, in step S3, during the back-insertion vibro-construction process, timely backfilling is performed to ensure that the vibro-construction hole is sufficiently filled. Preferably, a loader can be used to timely backfill during the vibro-construction lifting process.

[0037] Furthermore, in step S3, during the vibro-compaction construction process using the reverse insertion method, a reverse insertion process is added in the top 6 m, and vibration is retained for 20 seconds to enhance the reinforcement effect within the top 6 m depth range and ensure the uniformity and density of the vibro-compaction pile body.

[0038] Furthermore, in step S3, during the vibroflotation process, the water pressure is reduced during the lifting phase to reduce local voids caused by the loss of fine sand particles with water. For example, the water pressure during the lifting phase can be reduced to 0.3-0.5 MPa. This process is used in all vibroflotation processes.

[0039] Furthermore, in step S3, the layered slope reinforcement also includes an area within 3 to 5 m near the top of the slope, and vibro-floating construction without filler is performed in this area.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. The present invention can ensure that the slopes formed by backfill are effectively reinforced, and the slope reinforcement is fully covered. The slope reinforcement effect is better than the original design scheme. The average compaction test value after vibration can reach 98%, which is 11.4% higher than that before reinforcement. The standard penetration number of blows is 15 to 60, with an average of about 30 blows, which is 625% higher than that before reinforcement, far exceeding the average standard penetration number of 15 blows required by the specification, and the slope is more stable.

[0042] 2. The present invention involves low labor costs, low material costs, low testing costs, and high utilization rate of mechanical equipment. The construction period is expected to be shortened by 3 months compared with the original design. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the vibroimpactability classification diagram of Brown (1977).

[0044] FIG2 is a cross-sectional view of the high fill slope of the project in Example 1 of the present invention.

[0045] FIG3 is a schematic diagram of the first layer of layered compaction area during construction of Example 1.

[0046] FIG4 is a schematic diagram of the first layer of the vibro-impact area without filler during construction in Example 1.

[0047] FIG5 is a schematic diagram of the second layer of layered compaction area during construction of Example 1. FIG.

[0048] FIG6 is a schematic diagram of the preparation work for sand backfilling and sand excavation before constructing the second layer of the unfilled vibro-impact area in Example 1.

[0049] FIG7 is a schematic diagram of the construction of the second layer of the vibro-impact area without filler in Example 1.

[0050] FIG8 is a schematic diagram of the third layer of layered compaction area during construction of Example 1. FIG.

[0051] FIG9 is a schematic diagram of the vibro-impact area without filler during construction of the third layer in Example 1.

[0052] Figures 10a and 10b are on-site construction photos of the layered compaction construction area backfilled with 40 cm thick sand and 20 cm thick crushed material.

[0053] Figures 11a and 11b show photos of the layered compaction construction area being watered at a ratio of 2:1 to the backfill volume.

[0054] Figures 12a and 12b are photos of the rolling and compaction test after water was injected into the layered rolling construction area.

[0055] Figures 13a and 13b are construction photos of laying geogrids and continuing layered backfilling in the layered compaction construction area.

[0056] Figures 14a and 14b are construction photos of vibro-compaction without filler in the vibro-compaction area without filler.

[0057] Figure 15 is a photo of the standard penetration test after vibratory impact without filler.

[0058] Figure 16 is a photo of the high slope reaching the designed height after the last layer of layered compaction construction area was backfilled.

[0059] Figure 17 is a photo of the reinforced high slope.

[0060] Markings in the figure: 11-first layer layered compaction area, 12-first layer sand and soil backfill area, 14-first layer vibroflotation construction area, 21-second layer layered compaction area, 22-second layer sand and soil backfill area, 23-second layer sand and soil excavation area, 24-second layer vibroflotation construction area, 31-third layer layered compaction area, 32-third layer sand and soil backfill area, 33-third layer sand and soil excavation area, 34-third layer vibroflotation construction area, 5-vibroflotation crane, 100-existing slope line, 200-designed slope line, 300-original mud surface line, 800-reinforced area, 900-unreinforced area. DETAILED DESCRIPTION

[0061] In order to more clearly describe the invention objectives, technical solutions and technical effect advantages in the specific implementation cases of the present invention, the solutions in the specific embodiments will be described in detail in conjunction with the drawings of the specification of the present invention. The specific technical solutions involved in the following specific embodiments are only for the purpose of clearly and completely describing the innovative technical solutions of the present invention. They themselves are only part of the specific implementation plans that can be adopted by the present invention, not all examples, and should not be understood as limiting the innovative solutions of the present invention. Any solution that adopts the same inventive concept of the present invention should be included in the scope of protection of the present invention.

[0062] It should be noted that, unless otherwise specified, in the description of the specific embodiments of the present invention, the terms indicating the orientation or positional relationship, such as "up", "down", "left", "right", "center", "inside", and "outside", are all based on the expression of the orientation or positional relationship shown in the accompanying drawings, or are the orientation or positional relationship in which the invented product / device / apparatus is placed when it is conventionally used. These terms of orientation or positional relationship are merely for the purpose of facilitating the description of the scheme of the present invention or simplifying the description in the specific embodiments to facilitate the rapid understanding of the scheme by technicians, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship, and therefore should not be understood as limiting the present invention.

[0063] In addition, if terms such as "horizontal" and "vertical" appear, it does not mean that the corresponding device / component / element is required to be absolutely horizontal or vertical or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. Alternatively, it can be simply understood that the corresponding device / component / element is set in a specific direction such as "horizontal" and "vertical", and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, and more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its role in the solution of the present invention.

[0064] In addition, the expressions “first”, “second”, “third”, etc. in the terms are merely used to distinguish the description of the same or similar components, and should not be understood as emphasizing or implying the relative importance of specific components.

[0065] Example 1

[0066] Area C1 of a certain port is located in a desert area, adjacent to several communities. It has no groundwater and poses no risk of soil liquefaction. Furthermore, the area experiences year-round rainfall and strong winds, eliminating the need for construction during the rainy season. After extensive preliminary research, the decision was made to utilize a dry fine sand slope construction technique formed by fresh backfill. This technique improves construction efficiency, ensures effective foundation reinforcement, reduces project time and costs, and minimizes adverse impacts on the community.

[0067] Step 1: Based on the geological survey report, obtain the particle gradation curve for the soil sample in the excavation area. Compare the particle gradation curve for the soil sample in the excavation area with the vibrocompaction gradation diagram (Brown (1977)) shown in Figure 1. In Figure 1, Area ① represents the sand material most suitable for vibrocompaction. Area ② corresponds to sands and soils with larger particle sizes, such as dense sand, crushed stone, and cemented sand, which are less efficient for vibrocompaction. Area ③ corresponds to sands and soils with a high fine particle content and poor vibrocompaction, and the vibrocompaction density decreases with increasing silt and clay content. As shown in Figure 1, the fine particle content of the sand at the site is relatively high, falling within Area ③, the vibrocompaction boundary. Therefore, experimental testing is required to determine the technical parameters for vibrocompaction without filler for extremely thick, dry, fine sand layers.

[0068] Vibro-compaction tests were conducted to determine relevant technical parameters for vibro-compaction. The unfilled vibro-compaction method was successfully applied to extremely thick, dry, fine sand layers in the desert region of the CI region. The equipment and technical parameters determined through vibro-compaction tests are shown in the table below.

[0069] Table 1 Equipment parameters of vibrator BJV100E-426100kW

[0070] Table 2: Non-filled vibroflotation construction parameters applicable to dry fine sand geology in the desert areas of CI region

[0071] When the vibrator is lifted to within 6m of the surface, the reverse insertion method of vibratory construction (re-drilling 0.5m for every 1m of lifting, the construction parameters are the same as above) can effectively improve the reinforcement effect of the upper area.

[0072] Specifically, the reverse insertion vibroflotation construction process is improved as follows:

[0073] (1) The local fill in the vibro-impact area is raised by 2 m to increase the overlying stress at the vibro-impact point and the foundation soil.

[0074] (2) A special loader is equipped to backfill in time during the vibratory lifting process to ensure that there is sufficient filler in the vibratory hole.

[0075] (3) Add the reverse insertion process in the top 6m and leave the vibration for 20s to enhance the reinforcement effect within the top 6m depth range and ensure the uniformity and density of the vibro-compaction pile body.

[0076] (4) Reduce the water pressure during the lifting stage to 0.3-0.5 MPa to reduce the local voids caused by the loss of fine sand particles with water. This process is used in subsequent vibro-compaction.

[0077] Step 2: Referring to the "Technical Specification for Slope Engineering in Construction Projects GB 50330-2013," the CI area slope is a Class II slope with a service load of 20 kPa. Under normal operating conditions, the slope stability safety factor must be greater than 1.30, and under seismic conditions, the slope stability safety factor must be greater than 1.10. Based on the design parameters provided by the design institute and the slope reinforcement process employed in this invention, "Li Zheng" calculations were performed, and the results met the safety factor requirements under both normal and seismic conditions. The decision was made to adopt the process optimization measures of "localized backfilling, timely backfilling, reducing water pressure, and layered backfilling," ultimately effectively reinforcing the loose backfill fine sand.

[0078] The specific operation process is as follows:

[0079] First, the site's reinforced area and natural slope profile were collected. A comparative analysis of the design section and the naturally formed backfill slope section was conducted, identifying the unreinforced area 900, as shown in Figure 2. The slope reinforcement area 800 was determined, along with a high fill slope cross-section. The design slope profile 200, the unreinforced area 900, and the existing slope profile 100 were analyzed. The design slope profile had a gradient of 1:1.5. Based on site conditions, a revised design adopted a slope ratio of 1:1.75 at the bottom and 1:1.5 at the top. The actual slope ratio can be adjusted and optimized based on the project's specific circumstances, enhancing slope stability through optimized slope ratios. The soil structure above the design slope has largely been vibro-reinforced, and the existing slope profile lies within the design slope profile. Therefore, the slope gradient needs to be increased during the reinforcement process, and a second transition step needs to be designed.

[0080] Step three: Slope reinforcement was carried out. Based on the natural slope of the backfill, a combination of layered rolling and vibro-compaction was used. Compaction was tested using sand injection in the layered rolling areas, and standard penetration tests were used in the vibro-compaction areas. Both tests met design requirements.

[0081] Specifically, as shown in Figure 3, at the foot of the natural slope line 100, the first layer of layered compaction area and unfilled vibro-compaction area are constructed. During the construction process, first, as shown in Figures 10a and 10b, along the toe of the natural slope, layered compaction is carried out every 60 cm along the toe area to form a layered compaction construction area 11, and each layer is "backfilled with 40 cm sand + 20 cm crushed material" to the designed slope line. When backfilling, the inner edge line of the layered compaction must be recorded and the vibro-compaction boundary must be controlled to achieve the purpose of reinforcing all the slope areas formed by the new backfill. The crushed (slag) materials used for backfilling are fully spread over the layered compaction range, and the source of the crushed materials is generated by blasting and excavation.

[0082] As shown in Figures 11a and 11b, after each layer of "40cm sand + 20cm crushed material backfill," water is added to the sand at a ratio of 2:1 based on the backfill volume. Then, the compaction is tested after rolling with a roller, as shown in Figures 12a and 12b. Finally, a 3m-wide, bidirectional, 55kN / m geogrid 11a is laid, as shown in Figures 13a and 13b. Note that if the geogrid width is less than 3m, construction in the layered compaction area is stopped, the current layered compaction position is recorded, and the sand backfill area 12 in Figure 3 is backfilled.

[0083] After the sand backfill area 12 is backfilled, a vibroflotation crane 5 is used to perform unfilled vibroflotation in the adjacent filler vibroflotation area 14 (at the same height as the layered compaction area) according to established technical parameters, as shown in Figures 14a and 14b. After the vibroflotation is complete, a standard penetration test is performed, as shown in Figure 15. The number of standard penetration tests is no less than 0.5% of the total number of vibrated holes.

[0084] The horizontal width of the filler vibro-compaction construction area shall not be less than 9 meters. According to the width design of the vibro-compaction crane 5, the movement safety of the vibro-compaction crane 5 must be ensured (along the slope direction, as shown horizontally in Figure 4). Due to the natural slope line, the width is narrow after the sand is backfilled, which does not meet the requirements for the movement of the vibro-compaction crane. Therefore, the natural slope is partially excavated first, and the second layer of sand excavation area 23 (above the first layer) is marked. When there is no obvious sliding on the natural slope after excavation, the excavation is stopped. At the same time, it is necessary to ensure that the width of the vibro-compaction area meets the requirements for the movement of the crane (100t or 150t). Then, the first layer of the filler-free vibro-compaction area 14 in Figure 4 is vibro-compacted, and the inner edge line of the vibro-compaction (the inner edge line of the layered compaction control) is recorded. After the vibro-compaction is completed, a standard penetration test is carried out.

[0085] After the first layer of unfilled vibro-compacted area 14 is reinforced, backfilling of the second layer of layered compacted area 21 continues on the finished vibro-compacted surface, using the same process as the first layer of layered compacted area. Backfilling stops when the geogrid width is less than 3m, and the current layered compacted position is recorded. Simultaneously, backfilling of the second layer of sand backfill area 22 (Figure 5) is also performed.

[0086] Then, as with the first layer construction method, the natural slope is partially excavated. As shown in FIG6 , the third layer of sand excavation area 33 (above the second layer) is excavated. When no obvious sliding of the natural slope occurs after excavation, the excavation is stopped. At the same time, the vibro-compaction width must be ensured to allow the crane (100t or 150t) to travel, and the inner edge of the vibro-compaction (the inner edge of the layered compaction control) is recorded.

[0087] As shown in FIG7 , according to the recorded inner and outer edges of the vibration, the second layer of the vibratory area 24 without filler in FIG7 is vibrated, and a standard penetration test is performed after the vibration is completed.

[0088] As shown in Figure 8 , the third layer of layered compaction area 31 is backfilled in layers on the completed surface of the vibroflotation area, using the same process as the first layer of layered backfill. The backfill is then continued to the top layer, where the final layer of geogrid is laid, until the newly backfilled high slope reaches the designed height, as shown in Figure 16 . If the geogrid width is less than 3m and the top of the slope has not been reached, the construction is stopped and the aforementioned layered compaction and unfilled vibroflotation processes are repeated until the layered backfill construction structure reaches the top of the slope. Then, the adjacent third layer backfill area 32, located inside the third layer of layered backfill area, is backfilled, as shown in Figure 8 .

[0089] Finally, as shown in Figure 9, based on the recorded vibroflotation inner boundary, the third vibroflotation area 34, a 3-meter radius adjacent to the final layered backfill area 31 at the top of the slope, was vibroflotated to complete the final fill vibroflotation process and ensure that the slope reinforcement process covered the previously reinforced areas. This was done to prevent disturbances in the previously reinforced areas caused by slope construction, allowing for further reinforcement of the previously reinforced areas, thus achieving full coverage of the high backfill yard area and the slope area. After vibroflotation, a standard penetration test was conducted. Finally, the reinforced high slope is shown in Figure 17.

[0090] The slopes formed by backfilling with previous technologies were tested for compaction and standard penetration. After watering, the compaction was in the range of 86% to 89%, with an average compaction of 88%; the standard penetration number after watering was 2 to 7, with an average standard penetration number of 4. The average compaction test value of the method in this embodiment after vibration can reach 98%, which is an increase of 11.4% compared to before reinforcement, meeting the design requirement of 96% compaction; the standard penetration number is 15 to 60, with an average of about 30, which is an increase of 625% compared to before reinforcement, far greater than the average standard penetration of 15 required by the specification, and the sand can reach medium density and above. The present invention obtains the technical parameters of the dry fine sand vibration process through research and testing on local geology. For the proposed "vibration + layered rolling" process, the "rectification" modeling calculation is adopted, and the slope is in a stable state after empirical calculation.

[0091] After comparing and referring to similar engineering practices and consulting literature, the greatest innovation of this invention is to apply the filler-free vibrocompaction method to fine sand geology with a high fine particle content, while economically, reasonably and efficiently combining layered compaction and vibrocompaction technology to complete slope backfill and reinforcement construction.

[0092] Finally, the area with the largest backfill height was selected on site for construction verification. The high slope was backfilled and treated by combining the filler-free vibration and layered rolling process. The final result was approved and recognized by the supervisor, designer and owner, proving that the scheme can effectively reinforce high-fill sandy slopes and ensure slope stability.

[0093] The above embodiments describe only the basic principles, main features and / or advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and the invention content of the specification only describe the principles or specific cases of the present invention. Without departing from the essence of the innovative ideas of the present invention, the innovative solutions of the present invention may be subject to various changes and improvements, and these changes and improvements all fall within the scope of protection claimed by the present invention.

Claims

1. A construction method for backfilling and strengthening a dry fine sand slope, characterized in that, It includes the following steps: S1. According to the geological exploration report, compare the particle size distribution curve of the soil sample in the excavation area with the vibroflotation distinguishability diagram, and after on-site tests, determine the technical parameters of vibroflotation construction without filler for the dry fine sand layer; S2. According to the design specifications and the safety factor of slope stability, check whether the calculation results meet the safety requirements; if the calculation results do not meet the requirements, adjust the slope coefficient according to the unmet safety requirements; S3. Strengthen the slope in layers. Each layer of slope strengthening includes: the layered compaction construction area and the vibroflotation construction area without filler; the layered compaction construction area is located on the outer side of the slope, and the vibroflotation construction area without filler is located on the adjacent inner side of the layered compaction construction area; the layered compaction construction of the subsequent layer of slope strengthening is located above the vibroflotation construction area without filler of the previous layer; Construct and strengthen the slope layer by layer; for each layer of slope strengthening, first construct the layered compaction construction area, and then construct the vibroflotation construction area without filler; until the slope height formed by the layered compaction construction reaches the design height, and perform vibroflotation construction without filler at the position close to the inner side of the slope for the finally completed layered compaction construction area to complete all slope strengthening.

2. The construction method for backfilling and reinforcing a dry fine sand slope according to claim 1, wherein In step S1, the vibroflotation distinguishability diagram is the Brown 1977 vibroflotation distinguishability diagram.

3. The construction method for backfilling and reinforcing a dry fine sand slope according to claim 1, characterized in that, In step S2, according to GB 50330-2013 "Technical Code for Slope Engineering of Building Engineering", determine the slope grade, and then determine the safety factor of slope stability under normal conditions and the safety factor of slope stability under seismic conditions, and check whether the slope after vibroflotation meets the safety factor requirements.

4. The construction method for backfilling and reinforcing a dry fine sand slope according to claim 1, characterized in that, In step S3, the thickness of each layer in the layered compaction construction area is 40 - 80 cm.

5. The construction method for backfilling and reinforcement of a dry fine sand slope according to claim 4, characterized in that, When performing layered compaction in the layered compaction construction area, each layer includes a sand layer and a crushed slag layer, which are filled and compacted in sequence, and the thickness ratio of sand to crushed slag in each layer is 4:5 - 7.

6. The construction method for backfilling and reinforcing a dry fine sand slope according to claim 1, wherein, In step S3, when performing layered compaction construction in the layered compaction construction area, after each layer of compaction is completed, lay geogrid at the position close to the slope edge.

7. The construction method for backfilling and reinforcing a dry fine sand slope according to claim 1, characterized in that, The technical parameters of vibroflotation construction without filler are as follows: spacing 2 - 3 m, hole forming speed 1 - 2 m / min, lifting speed 0.5 - 1 m / min, upward lifting spacing 0.5 - 1 m, vibration retention at the bottom of the hole for 20 - 30 s, vibration retention in the hole for 8 - 10 s, water pressure range 0.3 - 1.0 Mpa, current range 100 - 120 A.

8. The construction method for backfilling and reinforcement of a dry fine sand slope according to claim 1, characterized in that, In step S3, when the vibroflot is lifted to the range of 6 m from the surface layer, the reverse insertion method is used for vibroflotation construction.

9. The construction method for backfilling and reinforcing a dry fine sand slope according to claim 1 is characterized in that, In step S3, during the vibroflotation construction using the reverse insertion method, add the reverse insertion process at the top 6 m and retain vibration for 20 s.

10. The construction method for backfilling and reinforcing a dry fine sand slope according to claim 1, characterized in that, In step S3, during the vibroflotation construction process, reduce the water pressure during the upward lifting stage.

Images