A method for preloading of soft soil subgrade and flexible subgrade

Abstract

This invention discloses a surcharge preloading method for soft soil and flexible subgrades, comprising: compacting the embankment and determining the preloading material; determining the preloading length and surcharge height for each type of subgrade material; dividing the embankment into a first preloading zone and a second preloading zone, preloading the first preloading zone first, and then performing the second batch of preloading; after preloading, replenishing the soil added due to subgrade settlement and compacting it; laying the subgrade material sequentially on the preloaded embankment according to the design thickness and paving position; repeating the preloading construction to perform surcharge preloading on the next section of the embankment. This invention utilizes subgrade material (fill, gravel cushion material, etc.) for surcharge preloading, allowing paving to proceed immediately after each preloading section is completed. The two batches of surcharge preloading length of the preloading material meet the paving requirements for that section of the embankment, reducing transportation volume and improving construction efficiency; using subgrade material instead of traditional earthwork preloading reduces earthwork usage, minimizes environmental impact, and reduces project investment.

Description

Technical Field

[0001] This invention relates to the field of soft soil subgrade reinforcement, and in particular to a surcharge preloading method for soft soil subgrades and flexible subgrades. Background Technology

[0002] In highway engineering, due to the long length of roads and the complex and varied underlying surfaces, soft soil or flexible foundations are inevitably encountered during construction. The treatment of soft soil foundations must not only meet the requirements of improving the bearing capacity of the roadbed, reducing uneven settlement, and ensuring the safety and reliability of the road, but also place higher demands on accelerating construction progress, shortening project construction periods, and reducing project costs.

[0003] Currently, there are two main methods for treating soft soil foundations: replacement and reinforcement. Surcharge preloading is one of the most commonly used reinforcement methods. Surcharge preloading involves applying a load to the soft soil foundation. Under the pressure of the load, the pore water in the soft soil is discharged through the drainage system beside the roadbed, gradually consolidating the soil and increasing its bearing capacity, thus eliminating some of the foundation's settlement. Once the foundation meets the post-construction settlement requirements, the preload is gradually removed. However, most existing surcharge methods use earthwork for preloading. During the preloading process, it is necessary to replenish the preloaded earthwork according to the settlement. After the preloading period, construction machinery is needed to clean and transport the preloaded earthwork. The entire process not only requires a large amount of earthwork resources, has a significant impact on the surrounding environment, and involves a large transportation volume, increasing project investment, but also, to some extent, restricts the application of earthwork surcharge preloading schemes. Summary of the Invention

[0004] In view of this, the present invention provides a surcharge preloading method for soft soil subgrade and flexible subgrade, which uses the subgrade material as the preloading material and adopts batch preloading during preloading. The material used can be used to pave the road surface immediately in the preloading area, which can speed up the construction progress, save earthwork resources, and reduce project investment.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The surcharge preloading method for soft soil and flexible subgrades described in this invention employs segmented surcharge preloading using pavement layer materials, and specifically includes the following:

[0007] S1, compact the embankment until the compaction degree of the embankment meets the technical requirements;

[0008] S2, determine the preloading material of the embankment. The preloading material is the road base material, which includes compacted roadbed soil, gravel cushion material, granular subbase material, granular lower base material and granular upper base material;

[0009] S3, determine the preloading length and surcharge height for each type of roadbed material;

[0010] S4, each section of the embankment is divided into a first preloading zone and a second preloading zone. The first preloading zone includes multiple first preloading sections arranged at intervals along the longitudinal direction of the embankment. Each type of road base material is classified and stacked on the first preloading section for the first batch of preloading. Each first preloading section is stacked with one type of road base material.

[0011] S5, the second preloading zone has multiple second preloading sections arranged longitudinally along the embankment, and the first and second preloading sections are arranged alternately; after the soft soil subgrade of the first preloading zone reaches the settlement stability standard, each type of preloading material is moved forward to the adjacent second preloading section for the second batch of preloading.

[0012] S6. After the soft soil subgrade of the second preloading zone reaches the settlement stability standard, the compacted soil volume increased due to the subgrade settlement is added to the first and second preloading zones, and compacted to reach the subgrade design elevation.

[0013] S7, the road base material is laid sequentially on the pre-compacted embankment according to the design thickness and paving position;

[0014] S8. Repeat steps S4-S7 to perform surcharge preloading on the next section of the embankment.

[0015] In the above technical solution, the present invention uses roadbed material as preloading material to preload soft soil roadbed (or flexible roadbed) in sections, and preloads each section of embankment in batches. The roadbed material used can be used to pave the road surface immediately in the preloading area, which can not only speed up the construction progress, but also save earthwork resources and reduce the amount of transportation of preloading materials, thereby greatly reducing the project investment.

[0016] In a preferred embodiment of the present invention, S3 includes the following specific contents:

[0017] S31, Calculate the load P borne by the embankment;

[0018] S311, Calculate the required compacted soil thickness of the subgrade to achieve post-construction settlement. h 1 The load provided by the compacted soil is calculated based on the thickness of the compacted soil in the subgrade and the unit weight of the soil. P 土 ;

[0019] S312, Calculate the load P provided by the subgrade and pavement structural layers of the main road based on the unit weight and paving thickness of the subgrade and pavement structural layers. 主 ;

[0020] Based on the unit weight and paving thickness of the auxiliary roadbed and pavement structural layer materials, calculate the load P provided by the auxiliary roadbed and pavement structural layers. 辅 ;

[0021] S313, based on the load obtained in step S311 P 土 and the load P in step S313 主 P 辅 Determine the total load P1 of the main road and the total load P2 of the auxiliary road, where P1 = P 主 + P 土 P2=P 辅 + P 土 ;

[0022] S314, according to P 1 and P 2 Determine the load that the embankment will bear after it is paved. P , P = max (P1, P2) And the load P is a preload;

[0023] S32, Calculate the surcharge thickness and preloading length for each type of roadbed material.

[0024] S321, determine the volume of roadbed material per meter of main road based on the paving width and thickness of the roadbed material. V 1 and the volume of road base material per meter of auxiliary road V 2 ;

[0025] S322, according to V 1 and V 2 Determine the total volume of each material on the main road and auxiliary roads. V Then, normalization is performed to obtain the normalized volume ratio, where V = V 1 + V 2 ;

[0026] S323, Based on the preload and unit weight of each material calculated in step S314, calculate and determine the surcharge height of each material, normalize it, and obtain the normalized height ratio.

[0027] S324, the preloading length of the compacted soil in the subgrade. L 0 As a benchmark, calculate the preload length for each material. L ;in, L = L0 × Normalized volume ratio ÷ Normalized height ratio

[0028] In the above scheme, the present invention makes reasonable calculations based on the load borne by the embankment (i.e. the additional load after paving), the load provided by the roadbed material, and the paving length, and determines the surcharge length, surcharge width and surcharge thickness of each material to ensure that the preloading load of the first preloading section and the second preloading section are consistent, thereby ensuring the reinforcement effect of the soft soil embankment (or flexible roadbed).

[0029] In a preferred embodiment of the present invention, in step S4, before classifying and stacking the roadbed material in the first preloading section, the method further includes: laying geotextile on the embankment corresponding to the first preloading section, wherein the width of the geotextile is greater than the stacking width of the roadbed material and the length of the geotextile is greater than the preloading length of the roadbed material.

[0030] In S5, before moving each preloading material forward to the adjacent second preloading section for the second batch of preloading, the method further includes: laying geotextile on the embankment corresponding to the second preloading section, wherein the width of the geotextile is greater than the surcharge width of the roadbed material and the length of the geotextile is greater than the preloading length of the roadbed material.

[0031] In this additional scheme, geotextile is used to isolate the compacted embankment and preloading material, effectively avoiding cross-contamination of the roadbed materials. In addition, the length and width of the geotextile are greater than the surcharge width and length of the preloading material, so as to facilitate the overall transfer of the roadbed materials and further avoid cross-contamination.

[0032] In a preferred embodiment of the present invention, both the first preloading zone and the second preloading zone are preloaded in the following order: compacted subgrade soil, gravel cushion material, granular subbase material, granular lower base material, and granular upper base material. This loading sequence of the subbase materials is consistent with the bottom-up paving sequence, facilitating differentiation and subsequent paving construction.

[0033] In a preferred embodiment of the present invention, during the first batch of preloading in S4 and the second batch of preloading in S5, settlement monitoring, horizontal displacement monitoring, deep layered settlement monitoring and pore water pressure monitoring are carried out on the preloaded roadbed to monitor whether the various indicators of surcharge preloading meet the design requirements.

[0034] In a preferred embodiment of the present invention, the settlement monitoring employs a settlement plate and settlement nails. The settlement plate is positioned at the center of the preloaded subgrade, and the settlement nails are installed at the center of the preloaded subgrade and on the earthen shoulders on both sides. In this additional embodiment, the present invention utilizes a combination of settlement plates and settlement nails to observe the settlement of the subgrade top surface, thereby facilitating control of the loading rate, prediction of settlement trends, determination of preload unloading time, and providing a calculation basis for the increase in earthwork volume due to foundation settlement.

[0035] In a preferred embodiment of the present invention, the horizontal displacement monitoring employs inclinometers and side piles, which are embedded at the toe of the fill slope of the settlement section to monitor whether lateral slippage occurs in the slope area; the deep layered settlement monitoring employs a layered settlement gauge to monitor the consolidation settlement of the underground soft soil during the preloading period; and the pore water pressure monitoring employs a pore water pressure gauge, which is installed on the centerline of the roadbed to monitor the drainage and increase of effective stress in the soft soil foundation during preloading.

[0036] In a preferred embodiment of the present invention, the monitoring frequencies for settlement monitoring, horizontal displacement monitoring, deep stratified settlement monitoring, and pore water pressure monitoring are as follows: during the surcharge construction process, the number of monitoring sessions per day shall not be less than twice; within two weeks after the completion of the surcharge, the monitoring sessions shall be conducted once every other day; and between two and six months after the completion of the surcharge construction, the monitoring sessions shall be conducted twice a week to ensure that the settlement height and pore water pressure and other indicators meet the design requirements.

[0037] In a preferred embodiment of the present invention, in step S5, the paving length of the roadbed material used in the first preloading zone and the second preloading zone is equal, and the sum of the preloading lengths of the first preloading zone and the second preloading zone is equal to the paving length of the roadbed material. This means that the roadbed material used for paving the embankment can just meet the preloading requirements of two batches of the embankment section. After preloading is completed, the preloaded embankment can be paved directly, reducing the amount of transportation work, improving the construction progress, and reducing the project cost.

[0038] Compared with existing technologies, the present invention has the following advantages: The present invention utilizes road base materials (fill, gravel cushion material, granular subbase material, granular lower base material, and granular upper base material) for surcharge preloading. Paving can be carried out after each section of preloading is completed. The surcharge preloading length of the two batches of preloading material is slightly less than the paving length of the material. After preloading is completed, it can be used to pave the embankment section, reducing the amount of transportation and improving construction efficiency. In addition, using road base materials instead of traditional earthwork preloading reduces the amount of earthwork used, reduces the impact on the surrounding environment, and reduces project investment. Attached Figure Description

[0039] Figure 1 This is a construction flowchart of the present invention.

[0040] Figure 2 This is a cross-sectional view of a highway expansion project in Example 1 (the total width of the embankment in the figure is 41.2m, and the old roadbed is on the left, with a width of 11.1m).

[0041] Figure 3This is the first batch of preloading distribution map in Example 1 (from left to right in the map, it shows roadbed compacted soil, gravel cushion material, granular subbase material, granular upper base material and granular lower base material).

[0042] Figure 4 This is the second batch of preloading distribution map in Example 1 (from left to right in the map, the subgrade compacted soil, gravel cushion material, granular subbase material, granular upper base material and granular lower base material are respectively). Detailed Implementation

[0043] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0044] This invention provides a surcharge preloading method for soft soil subgrade and flexible subgrade. This surcharge preloading method uses pavement layer material for segmented surcharge preloading, realizing batch preloading of each embankment section. The pavement base material used can be laid immediately in the preloading area, which can not only speed up the construction progress, but also save earthwork resources and reduce the amount of transportation of preloading materials, thereby greatly reducing project investment.

[0045] Combination Figure 1 It is understood that the surcharge preloading method for soft soil subgrade and flexible subgrade described in this invention includes the following steps: S1, compacting the embankment and testing the compaction degree (which can be tested using a compaction density meter); if the compaction degree does not meet the technical requirements, increasing the number of compaction passes until the compaction degree of the embankment meets the design requirements.

[0046] S2, determine the preloading material of the embankment. The preloading material is the road base material, which includes compacted roadbed soil, gravel cushion material, granular subbase material, granular lower base material and granular upper base material;

[0047] S3, determine the preloading length and surcharge height for each type of pavement structure layer material;

[0048] S4, divide each section of the embankment into a first preloading zone and a second preloading zone. Divide the first preloading zone into multiple first preloading sections arranged longitudinally along the embankment (due to the different thicknesses and densities of the base materials, the preloading height and length of each material are also different)); each type of base material is classified and stacked on the first preloading section for the first batch of preloading, with each first preloading section stacking one type of base material.

[0049] During the first batch of preloading, settlement monitoring, horizontal displacement monitoring, deep layered settlement monitoring, and pore water pressure monitoring were carried out on the preloaded roadbed until the settlement stability standard was reached (i.e., the estimated post-construction settlement should be less than the design allowable value, and the observed settlement for two consecutive months should not exceed 5 mm / month); if the settlement parameters of the first preloading zone do not meet the design requirements, the preloading time of the first batch of preloading will be extended.

[0050] S5, the second preloading zone has multiple second preloading sections arranged longitudinally along the embankment, and the first and second preloading sections are arranged alternately; after the soft soil subgrade of the first preloading zone reaches the settlement stability standard, each type of preloading material is moved forward to the adjacent second preloading section for the second batch of preloading.

[0051] During the second batch of preloading, settlement monitoring, horizontal displacement monitoring, deep layered settlement monitoring, and pore water pressure monitoring were carried out on the preloaded roadbed until the settlement stability standard was met (i.e., the estimated post-construction settlement should be less than the design allowable value, and the observed settlement for two consecutive months should not exceed 5 mm / month). If the settlement parameters of the second preloading zone do not meet the design requirements, the preloading time of the second batch of preloading will be extended.

[0052] The present invention achieves preloading of the entire embankment by first preloading half of the road section (i.e., the first batch of preloading), and then preloading the other half of the road section (i.e., the second batch of preloading), with the first batch of preloading and the second batch of preloading arranged at intervals.

[0053] S6. After the soft soil subgrade of the second preloading zone reaches the settlement stability standard, add the compacted soil to the first and second preloading zones due to the subgrade settlement, and compact it to reach the subgrade design elevation; if the compaction degree of the added soil does not meet the design requirements, increase the number of compaction passes.

[0054] S7, the road base material is laid sequentially on the pre-loaded embankment according to the designed thickness; preferably, the paving length of the road base material used in the first pre-loaded zone and the second pre-loaded zone is equal, and the sum of the pre-loaded lengths of the first pre-loaded zone and the second pre-loaded zone is equal to the paving length of the road base material.

[0055] S8. Repeat steps S4-S7 to perform surcharge preloading on the next section of the embankment.

[0056] In this invention, the amount of base course material used and the preloading length are the key design challenges. The length of the base course material should not be too long, otherwise it will increase transportation costs. Therefore, within a certain road section, ensuring that the base course material used for preloading is precisely used for the base course construction of that section is crucial for reducing transportation volume and lowering project costs. The calculation process for the preloading length of each base course in this invention is as follows:

[0057] S31, Calculate the load P borne by the embankment;

[0058] S311, Calculate the required compacted soil thickness of the subgrade to achieve post-construction settlement. h The load provided by the compacted soil is calculated based on the thickness of the compacted soil in the subgrade and the unit weight of the soil. P 土 ;

[0059] S312, Calculate the load P provided by the subgrade and pavement structural layers of the main road based on the unit weight and paving thickness of the subgrade and pavement structural layers. 主 ;

[0060] Based on the unit weight and paving thickness of the auxiliary roadbed and pavement structural layer materials, calculate the load P provided by the auxiliary roadbed and pavement structural layers. 辅 ;

[0061] S313, based on the load obtained in step S311 P 土 and the load P in step S313 主 P 辅 Determine the total load P1 of the main road and the total load P2 of the auxiliary road, where P1 = P 主 + P 土 P2=P 辅 + P 土 ;

[0062] S314, according to P 1 and P 2 Determine the load that the embankment will bear after it is paved. P , P = max (P1, P2) And the load P is a preload;

[0063] S32, Calculate the surcharge thickness and preloading length for each type of roadbed material.

[0064] S321, determine the volume of roadbed material per meter of main road based on the paving width and thickness of the roadbed material. V 1 and the volume of road base material per meter of auxiliary road V 2 ;

[0065] S322, according to V 1 and V 2 Determine the total volume of each material on the main road and auxiliary roads. V The normalized volume ratio is obtained by normalization, where V = V 1 + V2 ;

[0066] S323, Based on the preload and unit weight of each material calculated in step S314, calculate and determine the surcharge height of each material and normalize it to obtain the normalized height ratio;

[0067] S324, the preloading length of the compacted soil in the subgrade. L 0 As a benchmark, calculate the preload length for each material. L ;in, L = L 0 × Normalized volume ratio ÷ Normalized height ratio

[0068] In subsequent segmentation, because the thickness and density of the materials used in the embankment construction vary for each segment, the surcharge height and preloading length of each type of subgrade material also differ. To facilitate construction, preloading is carried out in the following order: compacted subgrade soil, gravel cushion material, granular subbase material, granular lower base material, and granular upper base material, with each batch of material having an equal preloading length. Furthermore, to reduce transportation volume, the surcharge sequence for the second batch of preloading materials is the same as the first batch. This way, during actual construction, each material only needs to be moved forward to the empty second preloading section.

[0069] In actual construction, to avoid cross-contamination between the roadbed material and the compacted embankment, before the roadbed material is sorted and stacked in the first preloading section, the following steps are taken: laying geotextile on the embankment corresponding to the first preloading section. The width of the geotextile is greater than the stacking width of the roadbed material, and the length of the geotextile is greater than the preloading length of the roadbed material. The length and width of the geotextile are both greater than the stacking width and length of the preloading material, which facilitates the overall transfer of the roadbed material and further avoids cross-contamination.

[0070] In S5, before moving each preloading material forward to the adjacent second preloading section for the second batch of preloading, the following is also included: laying geotextile on the embankment corresponding to the second preloading section, wherein the width of the geotextile is greater than the surcharge width of the subgrade material and the length of the geotextile is greater than the preloading length of the subgrade material.

[0071] If the geotextile is not damaged after the first preloading is completed, it can be laid in the second preloading section; if the geotextile is damaged after the first preloading is completed and its use is affected, a new geotextile should be replaced.

[0072] In a preferred embodiment of the present invention, settlement monitoring employs settlement plates and settlement nails. The settlement plates are placed at the center of the preloaded roadbed, and the settlement nails are installed at the center and on both sides of the earthen shoulders of the preloaded roadbed. During the preloading process, the settlement of the roadbed top surface is observed using a combination of settlement plates and settlement nails to facilitate control of the loading rate, prediction of settlement trends, determination of preloading unloading time, and calculation of the amount of earthwork required to compensate for foundation settlement.

[0073] Horizontal displacement monitoring uses inclinometers and edge piles, which are buried at the toe of the fill slope of the settlement section to monitor whether lateral slippage occurs in the slope area; deep layered settlement monitoring uses a layered settlement meter to monitor the consolidation settlement of underground soft soil during the preloading period.

[0074] Pore ​​water pressure monitoring uses pore water pressure gauges, which are installed on the centerline of the roadbed to monitor the drainage and increase of effective stress in the preloaded soft soil foundation.

[0075] In actual monitoring, the monitoring frequencies for settlement monitoring, horizontal displacement monitoring, deep stratified settlement monitoring, and pore water pressure monitoring are consistent. During the surcharge construction process, monitoring is conducted at least twice a day to accurately grasp the changes in embankment parameters. Within two weeks after the completion of surcharge, monitoring is conducted once every other day. Between two and six months after the completion of surcharge construction, monitoring is conducted twice a week.

[0076] Example 1: Taking a highway expansion project as an example, a more detailed explanation of its surcharge preloading scheme is provided.

[0077] The highway expansion project has a total length of approximately 53 kilometers, a roadbed width of 41.2 meters, an existing road width of 12.3 meters, a main road roadbed width of 25.2 meters, and auxiliary roads on both sides of 6.8 meters. Its standard cross-section is as follows: Figure 1 As shown.

[0078] The project is located in the plains of the Bay of Bengal, a region with a dense network of waterways and numerous ponds, resulting in a large amount of soft soil subgrade. Geological surveys indicate that most sections of the road have a 6-8m thick soft soil subgrade.

[0079] exist Figure 2 In the middle, the old road is located on the left. Because the old road has been in operation for many years, its subgrade settlement has reached a stable state. Therefore, no settlement reinforcement treatment is needed for the old road foundation; only surcharge preloading of the widened section is required. Figure 2 The width of the roadbed of the China-Laos Highway is 1.0m + 5.5m + 0.3m + 4.3m = 11.1m; therefore, the surcharge preloading width W = 41.2m - 1.0m - 5.5m - 0.3m - 4.3m = 30.1m.

[0080] Taking the surcharge preloading of a section of soft soil subgrade in this project as an example, the surcharge preloading of its widened section will be explained in more detail. Specifically, the following steps are included:

[0081] S1. Compact the embankment and use a compaction tester to test the compaction degree of the embankment. If the compaction degree of the embankment after compaction does not meet the technical requirements, the embankment will be compacted a second time until the compaction degree of the embankment meets the technical requirements.

[0082] S2, determine the preloading material. The preloading material is the roadbed material used for road construction, including roadbed compacted soil, gravel cushion material, granular subbase material, granular lower base material and granular upper base material;

[0083] S3, determine the preloading length and surcharge height for each type of pavement structure layer material, specifically including:

[0084] S31, Calculate the load P borne by the embankment;

[0085] The calculation determined the amount of surcharge preloading required to meet post-construction settlement requirements for soft soil sections. It was calculated that a certain section of the project required surcharge preloading of 1m high earthwork. This was based on the compacted soil thickness (1m) and the earthwork unit weight (17 KN / m³). 3 ) Calculate the load P provided by the compacted soil 土 P 土 = 17 kPa ;

[0086] S312, based on the paving thickness and material of the main road subgrade structure layer, as well as the material and paving thickness of the pavement structure layer, calculate the load P provided by the main road subgrade structure layer and pavement structure layer. 主 The results are shown in Table 1;

[0087] Table 1 Loads provided by various materials on the main road

[0088]

[0089] Note: The load provided by each material in Table 1 = the material's density × the material's paving thickness.

[0090] Table 1 shows that the total load P provided by the subgrade structure layer and pavement structure layer of the main road is... 主 P equals the sum of the loads provided by each material. 主 = 29.665 kPa;

[0091] Based on the unit weight and paving thickness of the subgrade and pavement structural layer materials of the auxiliary road, calculate the load P provided by the subgrade and pavement structural layers of the auxiliary road. 辅 Since granular materials are not required for the subbase during the construction of the auxiliary road, they are not considered in the calculation. The specific results are shown in Table 2.

[0092] Table 2 Loads provided by various materials on the auxiliary road

[0093]

[0094] Note: The load provided by each material in Table 2 = the material's density × the material's paving thickness.

[0095] Table 2 shows the total load provided by the subgrade structure layer and pavement structure layer of the auxiliary road. P 辅 It equals the sum of the loads provided by each material. P 辅 = 23.83 kPa ;

[0096] S313, according to load P 土 and the load calculated in step S312 P 主 、P 辅 Determine the total load P1 borne by the main road and the total load borne by the auxiliary road. P 2 ;

[0097] in, P 1 = P 主 + P 土 = 29.665 KPa+ 17 KPa = 46.665 KPa;

[0098] P 2 =P 辅 + P 土 = 23.83 KPa+ 17 KPa= 40.83 KPa;

[0099] S314, Determine the load borne by the embankment. P , P = max (P1, P2) = 46.665 kPa; The preloading load is set at 46.665, based on the load borne by the embankment after paving. kPa ;

[0100] S32, In actual surcharge loading, given the characteristics of asphalt materials, this invention uses only roadbed materials (i.e., roadbed compacted soil, gravel cushion material, granular subbase material, granular upper base material, and granular lower base material) as preloading materials for surcharge loading and preloading.

[0101] S321. Based on the paving width and paving thickness of the base course materials for each road section, calculate the volume of the base course material per linear meter. The results are shown in Tables 3 and 4.

[0102] Table 3. Volume of subgrade material per linear meter of road section (main road)

[0103]

[0104] Table 4. Volume of subgrade material per linear meter of road section (auxiliary road)

[0105]

[0106] S322. Based on the volume of each material required for the paving of the main road and auxiliary road in Tables 3 and 4, calculate the surcharge volume of each material per linear meter of road section and normalize it. The results are shown in Table 5.

[0107] Table 5 Total volume and normalized volume ratio of each material per linear meter of road section

[0108]

[0109] Among them, Table 5 V = V 1 + V 2 ;

[0110] S323. Based on the required preload of 46.665 kPa and the unit weight of each road base material, the surcharge height of each material was calculated and normalized. The results are shown in Table 6.

[0111] Table 6. Load height per meter and normalized height ratio for each material

[0112]

[0113] Note: In Table 6, the surcharge height = preload ÷ material density;

[0114] S324, using the compacted subgrade soil as a benchmark, calculate the surcharge height and preloading length of each material. The preloading length of the compacted subgrade soil is used as the benchmark. L 0 As a calculation benchmark, the preload length of the remaining materials L = L 0 × Normalized volume ratio ÷ Normalized height ratio, the pre-compression length and required total volume of each material are shown in Table 7;

[0115] Table 7 Preloading length and total surcharge volume for each material

[0116]

[0117] Note 1) The preloading length of the compacted soil in Table 7 is as follows: L 0 500m; 2) Total surcharge volume of each material in Table 7 = preload length × preload width × surcharge height;

[0118] S4, a section of embankment is divided into a first preloading zone and a second preloading zone. The first preloading zone includes five preloading sections arranged longitudinally along the embankment. Each type of road base material is classified and stacked on the first preloading section for the first batch of preloading. Each first preloading section is stacked with one type of road base material.

[0119] In actual surcharge loading, the surcharge is categorized and loaded longitudinally along the embankment in the following order: compacted subgrade soil, gravel cushion layer, granular subbase, granular lower base course, and granular upper base course. The surcharge width is 30.1m for all layers, with preloading lengths of 500m, 490m, 512.4m, 288.3m, and 401.2m respectively, and surcharge thicknesses of 2.745m, 2.745m, 2.333m, 2.222m, and 2.222m respectively. See details... Figure 3 ;

[0120] S5, the second preloading zone has five preloading sections spaced longitudinally along the embankment, with the first and second preloading sections interleaved. After the soft soil subgrade in the first preloading zone reaches the settlement stability standard, the compacted subgrade soil, gravel cushion layer, granular subbase, granular lower base course, and granular upper base course are moved forward to the adjacent second preloading sections for a second batch of preloading. The surcharge width of the five materials is 30.1m; the preloading lengths are 500m, 490m, 512.4m, 288.3m, and 401.2m respectively, and the surcharge thicknesses are 2.745m, 2.745m, 2.333m, 2.222m, and 2.222m respectively. See details below. Figure 4 ;

[0121] S6. After the soft soil subgrade in the second preloading zone reaches the settlement stability standard, add the compacted soil to the first and second preloading zones due to the subgrade settlement, and compact it to reach the subgrade design elevation; if the compaction degree does not meet the design requirements, increase the number of compaction passes.

[0122] S7. The road base material is laid sequentially on the pre-compacted embankment according to the design thickness (the design paving thickness of the road base material for the main road is shown in Table 1 and the design paving thickness of the road base material for the auxiliary road is shown in Table 2). The length that the road base material used for pre-compacting can be paved is shown in Table 8.

[0123] Table 8 Paving length of pre-compacted road base materials

[0124]

[0125] Note: Paving length = Total surcharge volume ÷ Paving thickness ÷ Paving width;

[0126] S8. Repeat steps S4-S7 to perform surcharge preloading on the next section of the embankment.

[0127] During the preloading process, to avoid cross-contamination between the roadbed material and the embankment, geotextile is laid on the embankment before the preloading material is loaded. The width of the geotextile is greater than the loading width of the roadbed material, and the length of the geotextile is greater than the preloading length of the roadbed material. The geotextile is used for isolation. If the geotextile is intact after the first batch of preloading is completed, it can still be used as an isolation layer for the second batch of preloading. If the geotextile is damaged after the first batch of preloading is completed, it should be replaced with a new geotextile.

[0128] During both the first and second batches of preloading, settlement monitoring, horizontal displacement monitoring, deep stratified settlement monitoring, and pore water pressure monitoring of the embankment are required. Settlement monitoring utilizes settlement plates and settlement nails, with the settlement plates positioned at the center of the preloaded subgrade and the settlement nails installed at the center and on both sides of the earthen shoulders. Horizontal displacement monitoring employs inclinometers and side piles, which are embedded at the toe of the fill slope along the settlement section. Deep stratified settlement monitoring uses a stratified settlement gauge. Pore water pressure monitoring uses a pore water pressure gauge, which is positioned along the centerline of the subgrade.

[0129] In addition, the monitoring frequencies for settlement monitoring, horizontal displacement monitoring, deep stratified settlement monitoring, and pore water pressure monitoring are as follows: during the surcharge construction process, the number of monitoring sessions per day shall not be less than twice; within two weeks after the completion of the surcharge, the monitoring sessions shall be conducted every other day; and between two and six months after the completion of the surcharge construction, the monitoring sessions shall be conducted twice a week.

[0130] As can be seen from this invention, the paving length of the road base material used in the first and second preloading zones is equal, approximately 4561m (see Table 8); the sum of the preloading lengths of the first and second preloading zones is (500+490+512.4+288.3+401.2)×2=4384m; the preloading length of the road base material is slightly less than the paving length. This means that after the preloading period, all materials used in the preloading can be used to pave the road surface immediately in the preloading area, accelerating the construction progress, saving earthwork resources, and reducing project investment.

[0131] Compared with conventional earthwork surcharge preloading methods, the surcharge preloading method of the present invention can save 84% of the transportation volume, reduce transportation costs, and also save a large amount of preloading earthwork, thus reducing investment. Specifically:

[0132] (1) Based on the preloading load of 46.665 kPa, the surcharge material is converted into earthwork. The surcharge height of the earthwork is H = 46.665 / 17 = 2.745 m, and the preloading width is 30.1 m. The total volume of earthwork required to complete the 2192 m preloading is as follows. V=2.745 m ×2192 m×30.1 m=181112.9m 3 .

[0133] The earthwork for conventional surcharge preloading methods is taken from within a 5km radius, therefore the haul distance is taken as 5km. Multiplying the required haul volume by the haul distance gives the total haul volume.

[0134] (2) The total volume of the roadbed compacted soil, gravel cushion material, granular subbase material, granular lower base material and granular upper base material in this invention is shown in Table 5; the average transport distances are 2192m, 2192m, 855m, 1165m and 1480m respectively, and the total transport volume is shown in Table 9.

[0135] Table 9 Comparison of Total Transport Work Volume

[0136]

[0137] As shown in Table 9, the total transportation volume required for preloading a 2192m long road section using the traditional surcharge preloading method is 9.06 × 10⁻⁶ m. 8 Using the preloading method of this invention, the total transport engineering volume is 2.72 × 10⁻⁶. 8 It can save 70% of the transportation volume, save a lot of pre-stressed earthwork, speed up the construction progress, reduce project investment, and generate significant economic benefits.

[0138] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some of the technical features. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A surcharge preloading method for soft soil subgrades, characterized in that: The aforementioned surcharge preloading method employs segmented surcharge preloading using roadbed materials. Includes the following: S1, compact the embankment until the compaction degree of the embankment meets the technical requirements; S2, determine the preloading material of the embankment. The preloading material is the road base material, which includes compacted roadbed soil, gravel cushion material, granular subbase material, granular lower base material and granular upper base material; S3, determine the preloading length and surcharge height for each type of roadbed material; S4, divide each section of the embankment into a first preloading zone and a second preloading zone. The first preloading zone includes multiple first preloading sections arranged at intervals along the longitudinal direction of the embankment. Each type of road base material is classified and stacked on the first preloading section for the first batch of preloading. Each first preloading section is stacked with one type of road base material. S5, the second preloading zone has multiple second preloading sections arranged longitudinally along the embankment, and the first and second preloading sections are arranged alternately; after the soft soil subgrade of the first preloading zone reaches the settlement stability standard, each type of preloading material is moved forward to the adjacent second preloading section for the second batch of preloading. S6. After the soft soil subgrade of the second preloading zone reaches the settlement stability standard, the compacted soil volume increased due to the subgrade settlement is added to the first and second preloading zones, and compacted to reach the subgrade design elevation. S7, the road base material is laid sequentially on the pre-compacted embankment according to the design thickness and paving position; S8. Repeat steps S4-S7 to perform surcharge preloading on the next section of the embankment.

2. The surcharge preloading method for soft soil subgrade according to claim 1, characterized in that: S3 includes the following specific contents: S31, Calculate the load P borne by the embankment; S311, Calculate the required compacted soil thickness of the subgrade to achieve post-construction settlement. h 1 The load provided by the compacted soil is calculated based on the thickness of the compacted soil in the subgrade and the unit weight of the soil. P 土 ; S312, Calculate the load P provided by the subgrade and pavement structural layers of the main road based on the unit weight and paving thickness of the subgrade and pavement structural layers. 主 ; Based on the unit weight and paving thickness of the auxiliary roadbed and pavement structural layer materials, calculate the load P provided by the auxiliary roadbed and pavement structural layers. 辅 ; S313, based on the load obtained in step S311 P 土 and the load P in step S312 主 P 辅 Determine the total load P1 of the main road and the total load P2 of the auxiliary road, where P1 = P 主 + P 土 P2=P 辅 + P 土 ; S314, according to P 1 and P 2 Determine the load that the embankment will bear after it is paved. P , P = max (P1, P2) And the load P is a preload; S32, Calculate the surcharge thickness and preloading length for each type of roadbed material. S321, determine the volume of roadbed material per meter of main road based on the paving width and thickness of the roadbed material. V 1 and the volume of road base material per meter of auxiliary road V 2 ; S322, according to V 1 and V 2 Determine the total volume of each material on the main road and auxiliary roads. V The normalized volume ratio is obtained by normalization, where V = V 1 + V 2 ; S323, Based on the preload and unit weight of each material calculated in step S314, calculate and determine the surcharge height of each material, normalize it, and obtain the normalized height ratio. S324, the preloading length of the compacted soil in the subgrade. L 0 As a benchmark, calculate the preload length for each material. L ;in, L = L 0 × Normalized volume ratio ÷ Normalized height ratio 3. The surcharge preloading method for soft soil subgrade according to claim 1, characterized in that: In S4, before classifying and stacking the roadbed material into the first preloading section, the process further includes: laying geotextile on the embankment corresponding to the first preloading section, wherein the width of the geotextile is greater than the stacking width of the roadbed material and the length of the geotextile is greater than the preloading length of the roadbed material. In S5, before moving each preloading material forward to the adjacent second preloading section for the second batch of preloading, the method further includes: laying geotextile on the embankment corresponding to the second preloading section, wherein the width of the geotextile is greater than the surcharge width of the roadbed material and the length of the geotextile is greater than the preloading length of the roadbed material.

4. The surcharge preloading method for soft soil subgrade according to claim 1, characterized in that: Both the first and second preloading zones are preloaded in the following order: compacted subgrade soil, gravel cushion material, granular subbase material, granular lower base material, and granular upper base material.

5. The surcharge preloading method for soft soil subgrade according to claim 1, characterized in that: During the first batch of preloading in S4 and the second batch of preloading in S5, settlement monitoring, horizontal displacement monitoring, deep stratified settlement monitoring, and pore water pressure monitoring are carried out on the preloaded roadbed, respectively.

6. The surcharge preloading method for soft soil subgrade according to claim 5, characterized in that: The settlement monitoring uses settlement plates and settlement nails. The settlement plates are placed in the center of the preloaded roadbed, and the settlement nails are installed in the center of the preloaded roadbed and on the soil shoulders on both sides.

7. The surcharge preloading method for soft soil subgrade according to claim 5, characterized in that: The horizontal displacement monitoring uses inclinometers and side stakes, which are embedded at the toe of the embankment slope of the settlement section; the deep layered settlement monitoring uses a layered settlement meter; the pore water pressure monitoring uses a pore water pressure gauge, which is installed on the centerline of the roadbed.

8. The surcharge preloading method for soft soil subgrade according to claim 5, characterized in that: The monitoring frequencies for settlement monitoring, horizontal displacement monitoring, deep stratified settlement monitoring, and pore water pressure monitoring are as follows: during the surcharge construction process, the number of monitoring sessions per day shall not be less than twice; within two weeks after the completion of the surcharge, the monitoring sessions shall be conducted every other day; and between two and six months after the completion of the surcharge construction, the monitoring sessions shall be conducted twice a week.

9. The surcharge preloading method for soft soil subgrade according to claim 2, characterized in that: In S5, the paving length of the road base material used in the first preloading zone and the second preloading zone is equal, and the sum of the preloading lengths of the first preloading zone and the second preloading zone is equal to the paving length of the road base material.

Images