Narrow site shallow soft soil roadbed treatment combined structure

Abstract

The utility model belongs to municipal engineering technical field, concretely relates to a kind of shallow soft soil subgrade treatment combination structure in narrow site, comprising: replacement boundary line, roadbed replacement base layer, replacement demarcation line, ground line, excavation replacement slope line, cement soil mixing pile solid pile, cement soil mixing pile empty pile, cement solidification area and replacement granular material.Excavation replacement slope line starts from replacement demarcation line, and ends in replacement boundary line;Cement soil mixing pile solid pile is located below the area inside replacement boundary line road, its pile bottom is below replacement demarcation line, and pile top is cut off in excavation replacement slope line;Cement soil mixing pile empty pile is only as the "virtual section" that cement soil mixing pile solid pile body extends upwards;Cement solidification area is the area that replacement boundary line, cement soil mixing pile solid pile bottom and excavation replacement slope line, ground line are enclosed to form.The utility model can reduce the range of slope excavation, reduce the influence of excavation replacement subgrade treatment to surrounding environment and building structures.

Description

Technical Field

[0001] This utility model belongs to the field of municipal engineering technology, specifically relating to a combined structure for treating shallow soft soil subgrade in narrow sites. Background Technology

[0002] If there is soft soil or other unfavorable geological soil beneath newly constructed urban roads, special subgrade treatment design is required. According to Section 7.2 of the "Code for Design of Subgrade of Urban Roads" (CJJ194-2013), for soft soil foundations with a thickness of less than 3m and a shallow burial depth, shallow subgrade treatment measures such as inorganic binder shallow mixing, excavation and replacement, and rockfill and silt removal should be adopted; for soft soil subgrades with a larger thickness, methods such as granular piles, reinforced soil piles (cement-soil mixing piles, high-pressure jet grouting piles), dynamic compaction and dynamic compaction replacement treatment, and rigid pile composite foundations should be adopted.

[0003] Shallow soft soil subgrade excavation and replacement treatment refers to the removal of the underlying weak soil layer and the replacement with good quality granular materials such as sand, gravel, and crushed stone in layers, which are then compacted to improve the bearing capacity of the foundation and reduce settlement. This subgrade treatment method is relatively inexpensive. When using the excavation and replacement method for subgrade treatment, a full-section slope excavation scheme is generally adopted, with a temporary slope ratio of 1:1 to 1:2. When land around the road is scarce and slope conditions are not available, or when slope excavation would affect the safety of buildings and structures on both sides, the subgrade replacement design and construction method need to be reconsidered.

[0004] Method one involves reducing the excavation area by adjusting to vertical slope excavation. The roadbed replacement excavation is treated as a foundation pit project. Patent application CN202510258609 proposes a support mechanism for foundation pit excavation, which involves driving sheet piles to a certain depth at the replacement boundary to prevent lateral soil displacement, thus providing temporary excavation support. This method has been widely implemented in engineering, but it is relatively expensive. Alternatively, other support structures such as rigid piles can be constructed on both sides to provide vertical support to the outer soil.

[0005] Method two involves direct foundation treatment, avoiding slope excavation and eliminating the need for replacement construction. For example, cement-soil mixing piles are a commonly used method for soft soil foundation treatment. By forcibly mixing cement slurry or dry cement powder with the original foundation soil, cement-soil piles are formed, thereby improving the bearing capacity of the roadbed and reducing settlement. The working principle of cement-soil mixing piles has three aspects: first, solidification, where cement and soil undergo a hydration reaction to form high-strength cement-soil; second, replacement, where some soft soil is replaced by cement piles, improving the overall soil properties; and third, composite foundation, where the soil between the piles shares the load, forming a composite foundation. This method is suitable for narrow sites, eliminates the need for roadbed excavation and slope protection, and has minimal impact on the surrounding environment, but it is more expensive.

[0006] Both of the above methods can significantly reduce the impact on the surrounding environment, but their overall cost is relatively high and not economical. In the case of narrow sites, researching shallow soft soil subgrade treatment methods, considering site conditions, construction methods, and project costs, is of great significance for the feasibility of subgrade treatment schemes, cost savings, and reduction of impact on the surrounding environment.

[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this utility model and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Utility Model Content

[0008] The purpose of this utility model is to provide a combined structure for treating shallow soft soil subgrade in narrow sites, so as to reduce the excavation range of slope protection and reduce the impact of excavation and replacement subgrade treatment on the surrounding environment and buildings.

[0009] To achieve the above objectives, this utility model provides the following technical solution:

[0010] A combined structure for treating shallow soft soil subgrade in narrow sites includes:

[0011] The boundary line was replaced and used as the outer edge line of the designed sidewalk.

[0012] The subgrade replacement base layer is the original soil layer of the subgrade, and its top surface line serves as the boundary line for replacement.

[0013] The ground line represents the original surface of the site.

[0014] The excavation and replacement slope line starts from the replacement boundary line and ends at the replacement boundary line;

[0015] The cement-soil mixing pile is located in the area below the road inside the replacement boundary line, with its bottom extending below the replacement boundary line and its top ending at the excavation and replacement slope line.

[0016] The empty cement-soil mixing pile is located in the area above the inner side of the road within the replacement boundary line. Its bottom is at the excavation and replacement slope line, and its top ends at the bottom of the designed sidewalk.

[0017] The cement-soil solidification zone is the area enclosed by the replacement boundary line, the bottom of the cement-soil mixing pile, the excavation and replacement slope line, and the ground line.

[0018] The granular material used for replacement is placed in the area enclosed by the upper surface of the roadbed replacement base layer, the lower surface of the ground line, and the inner side of the excavation and replacement slope line.

[0019] Preferably, the ratio of the excavation and backfill slope line is designed to be 1:0.5-1:0.75.

[0020] Preferably, the cement-soil mixing piles have a diameter of 600mm, a spacing of 1m, and are arranged in a triangular or rectangular pattern. The pile length reaches at least 3.5m below the replacement boundary line.

[0021] Preferably, the empty pile of the cement-soil mixing pile is the part above the excavation and replacement slope line, which, after being excavated, serves only as a "virtual segment" extending upward from the solid pile of the cement-soil mixing pile.

[0022] Preferably, the soil cohesion in the cement-solidified zone is ≥40kPa and the friction angle is ≥15°.

[0023] Preferably, the granular material used for replacement is crushed stone or medium-coarse sand.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The combined structure for treating shallow soft soil subgrade in narrow spaces of this utility model is well applicable to narrow spaces where land around the road is scarce and there is no slope condition.

[0026] (2) The combined structure for treating shallow soft soil subgrade in narrow sites of this utility model utilizes the characteristics of high strength and good self-stabilization ability of cement-soil solidification zone. The ratio of replacement excavation slope is adjusted from 1:1-1:2 to 1:0.5-1:0.75. The slope toe of the excavation and replacement slope line is moved from inside the replacement boundary line to the side of the cement-soil mixing pile near the road, which greatly reduces the slope excavation range and reduces the impact of excavation and replacement subgrade treatment on the surrounding environment and buildings.

[0027] (3) The combined structure for treating shallow soft soil subgrade in narrow sites of this utility model replaces some soft soil in the cement-soil solidification zone with cement piles, which can improve the overall soil properties, replace some subgrade replacement filler, avoid using expensive support measures such as steel sheet piles, reduce project cost, and achieve good economic benefits in practice. Attached Figure Description

[0028] Figure 1 This is a cross-sectional view of the structure of this utility model;

[0029] Explanation of key figure labels:

[0030] 1. Replacement boundary line; 2. Subgrade replacement base layer; 3. Replacement dividing line; 4. Ground line; 5. Excavation and replacement slope line; 6. Cement-soil mixing pile solid pile; 7. Cement-soil mixing pile empty pile; 8. Cement-soil solidification zone; 9. Replacement granular material. Detailed Implementation

[0031] The technical solution of this utility model patent will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0032] In the description of this utility model, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the utility model.

[0033] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0034] See attached document Figure 1 This utility model discloses a combined structure for treating shallow soft soil subgrade in narrow sites, comprising: a replacement boundary line 1, a subgrade replacement base layer 2, a replacement dividing line 3, a ground line 4, an excavation and replacement slope line 5, solid cement-soil mixing piles 6, hollow cement-soil mixing piles 7, a cement-soil solidification zone 8, and granular replacement material 9.

[0035] The replacement boundary line 1 is the outer edge of the designed sidewalk. The unfavorable geological soil inside this boundary line needs to be replaced. The roadbed replacement base layer 2 is the original soil layer of the roadbed, which does not require treatment. The replacement dividing line 3 is the top surface line of the roadbed replacement base layer 2. The ground line 4 is the original pavement of the site. The excavation and replacement slope line 5 is designed at a certain scale, starting from the replacement dividing line 3 and ending at the replacement boundary line 1. The cement-soil mixing piles 6 are located in the area below the road inside the replacement boundary line 1, with the pile bottom penetrating to a certain depth below the replacement dividing line 3. The top of the pile ends at the excavation and replacement slope line 5; the empty pile 7 of the cement-soil mixing pile is located in the area above the inner side of the road of the replacement boundary line 1, the bottom of the pile is at the excavation and replacement slope line 5, and the top of the pile ends below the designed sidewalk; the cement-soil solidification zone 8 is the area enclosed by the replacement boundary line 1, the bottom of the cement-soil mixing pile 6, the excavation and replacement slope line 5, and the ground line 4; the replacement granular material 9 is set in the area enclosed by the upper surface of the roadbed replacement base layer 2, the lower surface of the ground line 4, and the inner side of the excavation and replacement slope line 5.

[0036] The excavation and replacement slope line 5 is designed with a certain ratio, generally 1:0.5-1:0.75. The cohesion and friction angle of the soil layer after cement-soil mixing pile reinforcement are determined by design calculation based on this ratio.

[0037] The cement-soil mixing piles (6) are arranged with a certain diameter and at certain intervals, in a triangular or rectangular pattern. The pile bottom must reach a certain depth below the replacement boundary line (3), which is calculated and determined according to the surface settlement requirements. The pile top is on the excavation and replacement slope line (5). Ordinary Portland cement is used for the pile body. The cement admixture, water-cement ratio, and cement-soil strength are determined by calculation and should be confirmed by experiments. The cohesion and friction angle of the soil layer after cement-soil mixing pile reinforcement are determined by calculation according to the temporary slope ratio requirements. When the test indicators do not meet the design requirements, reinforcement measures such as densification are taken. The construction and acceptance of cement-soil mixing piles should be strictly carried out in accordance with the "Technical Specification for Building Foundation Treatment". During construction, the amount of filling material and the pile length should be strictly controlled to ensure the quality of the pile body.

[0038] The empty pile 7 of the cement-soil mixing pile is the part above the excavation and replacement slope line 5, which needs to be excavated. This part of the pile body has not undergone cement solidification reaction with the surrounding soil and is only used as a "virtual section" for the upward extension of the pile body.

[0039] The cement-soil solidification zone 8 functions similarly to a retaining wall, supporting the soil outside the replacement boundary line 1 during excavation and backfilling to prevent excessive settlement of the road surface and buildings. In this solidified zone, some soft soil is replaced by cement piles, improving the overall soil properties and replacing part of the roadbed backfill material. The cement piles and the soil between them share the load, forming a composite foundation that jointly bears the road load.

[0040] For the replacement of granular materials, it is advisable to use granular materials with good permeability, such as crushed stone or medium-coarse sand, and to carry out compaction and backfilling in layers.

[0041] Example 1

[0042] A new road construction project is located near buildings and internal roads of a residential community. Surveying revealed that the road beneath the project has soft soil with a thickness of 3 meters and a shallow depth, requiring special subgrade treatment design. According to Section 7.2 of the "Urban Road Subgrade Design Code" (CJJ194-2013), a cut-and-fill subgrade treatment method is proposed. Specifically, the replacement boundary line 1 is located at the outer end of the sidewalk, and all unfavorable soil within the road section inside the replacement boundary line 1 needs to be replaced. Preliminary estimates indicate that if a full-section slope excavation scheme is used, the slope ratio will be 1:1, and the excavation boundary line will be 4 meters outside the replacement boundary line. This method of excavation will significantly impact traffic within the existing community. Furthermore, the excavation slope is adjacent to existing buildings, requiring a special protection plan and increasing related protection costs. To avoid these problems, a combined structure of cut-and-fill and cement-soil mixing piles is proposed for subgrade treatment.

[0043] The subgrade replacement base layer 2 below the soft soil is the original soil layer of the subgrade, which has good bearing capacity and can be directly used as the bearing layer of the subgrade. Only the soft soil above the replacement boundary line 3 is replaced.

[0044] According to calculations, the design ratio of the excavation and replacement slope line 5 is 1:0.75, starting from the replacement boundary line 3 and ending at the replacement boundary line 1. The replacement will be excavated according to this boundary line. The excavation and replacement slope line 5 is also the boundary line between the solid cement-soil mixing pile 6 and the empty cement-soil mixing pile 7.

[0045] Cement-soil mixing piles 6 are driven into the area below the inner side of the road near the replacement boundary line 1. The cement-soil mixing piles 6 have a diameter of 600mm, are spaced 1m apart, and are arranged in a rectangular pattern. The pile bottom reaches at least 3.5m below the replacement boundary line 3, and the pile top ends at the excavation and replacement slope line 5. The cement used for the cement-soil mixing piles 6 is 42.5 grade ordinary Portland cement, with an admixture content of 15% of the weight of the reinforced soil and a water-cement ratio of 0.5. The portion above the excavation and replacement slope line 5 consists of empty cement-soil mixing piles 7, which need to be removed. This portion of the pile body has not undergone cement solidification with the surrounding soil and serves only as a "virtual section" extending upwards from the pile body.

[0046] After the cement-soil mixing piles (6) are driven into place, a cement-soil solidification zone (8) is formed. After the cement-soil mixing piles (6) reinforce the soft soil, the cement and soil undergo a hydration reaction, forming a cement-soil solidification zone (8) with high strength and good slope self-stability. The soil cohesion of the solidified zone is ≥40 kPa, and the friction angle is ≥15°. When the test indicators do not meet the design requirements, reinforcement measures such as densification are taken. The cement-soil solidification zone (8) functions similarly to a retaining wall, supporting the soil outside the replacement boundary line (1) during excavation and preventing excessive settlement of the road surface and buildings. Utilizing the solidification characteristics of the cement-soil mixing piles, the proportion of temporary excavation slope can be reduced, and the slope toe line is moved from inside the replacement boundary line (1) to the inner edge of the cement-soil mixing piles, greatly reducing the excavation range and minimizing the impact of excavation and replacement of the roadbed on the surrounding environment and buildings. Specifically, this method can reduce the excavation area by approximately 8 m². 2 This reduces the costs of excavation and restoration of related external works, and also reduces the costs of protecting buildings and structures.

[0047] The soft soil area on the upper surface of the roadbed replacement base layer 2 is replaced with granular material 9. The granular material used for replacement is crushed stone or medium-coarse sand with good permeability, and it is compacted and backfilled in layers.

[0048] Simultaneously, the cement-soil mixing piles 6 reinforce the soil to form a cement-soil solidification zone 8, replacing part of the roadbed replacement material. The cement-soil strength of the solidified zone 8 must be greater than or equal to 1700 kPa, and should be determined experimentally. The bearing capacity must be no less than 140 kPa. In this solidified zone, the cement piles and the soil between the piles share the load, forming a composite foundation that jointly bears the road load. The cement piles replace some of the soft soil in the solidified zone 8, improving the overall soil properties and replacing part of the roadbed replacement material. This avoids the need for expensive support measures such as sheet piles, reducing project costs. The construction and acceptance of the cement-soil mixing piles 6 should strictly follow the "Technical Specification for Building Foundation Treatment." During construction, the amount of fill material and the pile length should be strictly controlled to ensure the quality of the piles.

[0049] In summary, the combined structure for treating shallow soft soil subgrade in narrow sites in this embodiment can greatly reduce the excavation range and the impact of excavation and replacement subgrade treatment on the surrounding environment and buildings. At the same time, the cement-soil mixing piles 6 reinforce the subgrade to form a cement-soil solidification zone 8, forming a composite foundation, which replaces part of the subgrade replacement material and has good economic benefits.

[0050] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the present invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the present invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the present invention, as well as various different choices and variations. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A narrow site shallow soft soil subgrade treatment combined structure, characterized in that, include: The boundary line was replaced and used as the outer edge line of the designed sidewalk. The subgrade replacement base layer is the original soil layer of the subgrade, and its top surface line serves as the boundary line for replacement. The ground line represents the original surface of the site. The excavation and replacement slope line starts from the replacement boundary line and ends at the replacement boundary line; The cement-soil mixing pile is located in the area below the road inside the replacement boundary line, with its bottom extending below the replacement boundary line and its top ending at the excavation and replacement slope line. The empty cement-soil mixing pile is located in the area above the inner side of the road within the replacement boundary line. Its bottom is at the excavation and replacement slope line, and its top ends at the bottom of the designed sidewalk. The cement-soil solidification zone is the area enclosed by the replacement boundary line, the bottom of the cement-soil mixing pile, the excavation and replacement slope line, and the ground line. The granular material used for replacement is placed in the area enclosed by the upper surface of the roadbed replacement base layer, the lower surface of the ground line, and the inner side of the excavation and replacement slope line.

2. The narrow site shallow soft soil subgrade treatment composite structure according to claim 1, characterized in that, The ratio of the excavation and replacement slope line is designed to be 1:0.5-1:0.

75.

3. The combined structure for treating shallow soft soil subgrade in narrow sites according to claim 1, characterized in that, The cement-soil mixing piles have a diameter of 600mm, are spaced 1m apart, and are arranged in a triangular or rectangular pattern. The pile length reaches at least 3.5m below the replacement boundary line.

4. The combined structure for treating shallow soft soil subgrade in narrow sites according to claim 1, characterized in that, The empty pile of the cement-soil mixing pile is the part above the excavation and replacement slope line. After being excavated, it only serves as a "virtual segment" extending upward from the solid pile of the cement-soil mixing pile.

5. The combined structure for treating shallow soft soil subgrade in narrow sites according to claim 1, characterized in that, The soil cohesion in the cement-solidified zone is ≥40 kPa, and the friction angle is ≥15°.

6. The combined structure for treating shallow soft soil subgrade in narrow sites according to claim 1, characterized in that, The granular material used for replacement is crushed stone or medium-coarse sand.

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