Foundation structure and construction method for shallow treatment of mountainous highway service area

Abstract

The application relates to the technical field of expressway foundation treatment, and particularly discloses a foundation structure for shallow treatment of a mountainous expressway service area and a construction method, the foundation structure comprises, from bottom to top, a rammed stone layer, a stone residue cushion layer and a geocell, the rammed stone layer is formed by embedding stone into soft soil through ramming, and the thickness of the inner side of the rammed stone layer is smaller than the thickness of the outer side of the rammed stone layer; the construction method comprises the following steps: material preparation, construction lofting, trial ramming, measuring elevation, laying stone, point ramming, leveling the site, general ramming, calculating total ramming settlement, checking construction data, load testing, laying the stone residue cushion layer and laying the geocell. The technical scheme provided by the application can solve the technical problems of high cost, long construction period and poor environmental protection of the prior art for shallow treatment of the soft soil foundation of a valley.

Description

Technical Field

[0001] This invention relates to the field of highway foundation treatment technology, specifically to foundation structures and construction methods for shallow treatment of highway service areas in mountainous areas. Background Technology

[0002] Site selection for highway service areas in mountainous areas is challenging. Currently, the most common method is to excavate hillsides and fill mountain gullies to level the site and create a flat area. Each service area typically covers 60-80 acres, a large area. After filling according to design requirements, the flat area resembles a small to medium-sized spoil heap. Settlement is primarily due to uneven settlement of the foundation soil, while the overall stability of the fill within the gully is relatively good. Since the fill is part of the main civil engineering structure of the highway service area in mountainous regions, and buildings and other structures will need to be placed on it later, when constructing highway service areas in low-mountain and hilly areas, methods such as replacing with crushed stone, crushed stone piles, and plain concrete piles are often used to treat the weak foundation of the gully. Then, soil and rock are filled onto the treated foundation to form the fill, ensuring its stability and settlement meeting design requirements.

[0003] However, when using the above methods to perform deep treatment of the weak foundation of the gully, the treatment scale is large and the treatment cost is high. Even when using the above methods to perform shallow treatment of the weak foundation of the gully, it is necessary to excavate a large amount of unsuitable soil and transport it to the spoil disposal site, and then backfill it with crushed stone, crushed stone piles and plain concrete piles. Not only is the transportation volume large and the cost high, but the construction time is also long and the environmental damage is significant. Summary of the Invention

[0004] The present invention aims to provide a foundation structure and construction method for shallow treatment of service areas of mountain highways, so as to solve the technical problems of high cost, long construction period and poor environmental performance of shallow treatment of soft soil foundations in gullies.

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

[0006] The foundation structure used for shallow treatment of highway service areas in mountainous areas includes, from bottom to top, a rammed rubble layer, a stone slag cushion layer, and geocells. The rammed rubble layer is formed by ramming rubble into the soft soil, and the thickness of the inner side of the rammed rubble layer is less than the thickness of the outer side of the rammed rubble layer.

[0007] Note: The inner side of the rammed stone layer refers to the side of the rammed stone layer with a lower ground elevation; correspondingly, the outer side of the rammed stone layer refers to the side of the rammed stone layer with a higher ground elevation.

[0008] The principles and beneficial effects of this solution are as follows:

[0009] Compacted riprap is a combination of riprap displacement and low-energy dynamic compaction. Its application conditions are as follows: 1) The foundation soil is generally low-liquid-limit silty clay or high-liquid-limit clay, and must not be silt or silty soil; 2) The physical and mechanical properties of the soil are: natural water content 25%≤w≤35%, void ratio 0.7≤e≤1.0, compression modulus 3≤Es≤8MPa, and static penetration index 0.4≤Ps≤1.3MPa; 3) The underlying structure is a cover layer (thickness is generally 3-8m, and the maximum does not exceed 10m) + bedrock; 4) The terrain is a gully in a mountainous area, that is, a wide and shallow gully formed by erosion, with good lateral constraint conditions for the fill; 5) The fill height in the service area is generally 10-15m, and the maximum does not exceed 20m. When the height is greater than 15m, a counterweight platform should be set up, and the height of the counterweight platform should not exceed 10m.

[0010] 1. This scheme involves filling soft soil with rubble and embedding the rubble into the soft soil through compaction to form a compacted rubble layer. Then, a stone crushing layer and geocells are sequentially installed on the compacted rubble layer to form the foundation structure. This scheme enables large-area shallow treatment of mountain highway service areas. Compared with the existing technology that uses the method of excavating soft soil and replacing it with crushed stone, crushed stone piles and plain concrete piles for shallow treatment, this scheme can greatly reduce the amount of excavation, thereby reducing transportation volume and costs, and is conducive to shortening the construction period and reducing environmental damage.

[0011] 2. This scheme embeds rubble into the soft soil using a rammed stone method. The rubble stones are interlocked and the soft soil is filled between them, forming a rammed stone layer with a hard shell. This significantly improves the strength and deformation resistance of the foundation soil, while also compacting the soft soil. Therefore, using the rammed stone layer as the bottom layer of the foundation structure can form an ideal foundation structure, ensuring that the entire foundation structure has sufficient bearing capacity to support the embankment filling in the service area, thereby ensuring the stability of the embankment filling in the service area.

[0012] 3. This scheme involves filling the top of the rammed stone layer with stone chips to form a stone chip cushion layer. Since the stone chips in the cushion layer are smaller than the rammed stone chips in the rammed stone layer, the setting of the stone chip cushion layer can improve the flatness of the top of the rammed stone layer, which facilitates the horizontal laying of geocells, thereby enabling the smooth filling of the embankment in the site area and forming a stable embankment filling body in the site area. In addition, compared with the compacted soil, the stone chip cushion layer has a looser structure, which can serve as a drainage channel for the entire foundation structure, ensuring smooth drainage of the entire foundation structure and thus ensuring the service life of the foundation structure.

[0013] 4. In this scheme, geocells are laid on top of the stone ballast cushion layer to form a complete foundation structure. Then, soil is filled on the foundation structure to form the embankment filling body in the site area. The geocells, together with the soil filling them, can form a structure with strong lateral restraint and stiffness, which can effectively enhance the bearing capacity of the entire foundation structure, play a role in distributing the load, reduce the uneven settlement of the foundation structure, and thus reduce the deformation of the embankment filling body in the site area.

[0014] 5. This scheme sequentially sets up a rammed stone layer, a stone slag cushion layer, and geocells from bottom to top to form an integrated foundation structure. The lower rammed stone layer uses rammed stone as a framework to treat the weak soil of the foundation and ensure structural strength. The middle stone slag cushion layer is a leveling layer that can improve the flatness of the top of the rammed stone layer, facilitating subsequent construction. The upper geocells can control uneven settlement of the entire foundation structure and ensure service life. Therefore, this scheme, through the synergistic effect of the rammed stone layer, stone slag cushion layer, and geocells, not only effectively treats the weak foundation but also ensures its own structural strength, thereby guaranteeing the stability of the embankment fill in the site area.

[0015] 6. In this scheme, the thickness of the inner side of the rammed stone layer is set to be less than the thickness of the outer side. Since the side with higher ground elevation generally has a greater thickness of weak soil than the side with lower ground elevation, increasing the thickness of the rammed stone layer on the side with higher ground elevation can improve the treatment effect on the weak soil on that side, thereby improving the overall structural strength of the foundation structure. On the other hand, reducing the thickness of the rammed stone layer on the side with lower ground elevation can save on the amount of rammed stone used while ensuring the treatment effect on the weak soil on that side, thereby reducing the treatment cost.

[0016] Preferably, as an improvement, the rubble in the rammed rubble layer is rolled from sandstone, limestone, marl, conglomerate, etc., from excavated and tunnel muck, with a natural compressive strength greater than 20MPa, a length of 30-50cm, and a thickness of 15-30cm.

[0017] Beneficial effects: This scheme utilizes rolled rubble from excavated and tunnel slag, such as sandstone, limestone, marl, and conglomerate, as materials for constructing the rammed rubble layer. This not only enables the utilization of waste materials and reduces the cost of foundation filling in the service area, but also ensures the structural strength of the rammed rubble layer by using sandstone, limestone, marl, and conglomerate with natural compressive strength greater than 20MPa as raw materials for the rolled rubble. This helps to ensure the stability of the embankment filling in the site area and allows the embankment filling in the site area to meet settlement requirements. Furthermore, controlling the length of the rolled stones to be 30-50cm and the thickness to be 15-30cm ensures that the stones are successfully compacted into the soft soil while reducing or even avoiding stone breakage during the compaction process. This also ensures that the stones effectively form a framework after being compacted into the soft soil, guaranteeing the support strength of the foundation structure. If the length and thickness of the stones are too small, less than 30cm and 15cm respectively, compaction into the soft soil may cause breakage, making it difficult to form a framework for effectively treating the soft soil. This is detrimental to improving the support strength of the foundation structure and thus the stability of the embankment fill in the site area. Conversely, if the length and thickness of the stones are too large, greater than 50cm and 30cm respectively, it will be difficult to compact them into the soft soil, increasing construction difficulty.

[0018] Preferably, as an improvement, the stone chips in the stone chip cushion layer are slag produced during the rolling of rubble, with a particle size of 2-10 cm and a mud content of 5-10%.

[0019] Beneficial Effects: This scheme utilizes the slag generated during the rolling of rubble as the material for the slag cushion layer. This not only further utilizes waste materials, thereby reducing the cost of foundation filling in the service area, but also ensures the structural strength of the slag cushion layer due to its natural compressive strength exceeding 20 MPa. This enhances the overall support strength of the foundation structure and further guarantees the stability of the embankment filling in the site area, ensuring it meets settlement requirements. Furthermore, controlling the slag particle size to 2-10 cm and the mud content to 5-10% ensures effective leveling of the top of the compacted rubble layer while maintaining good drainage throughout the foundation structure. If the stone chips are too large (greater than 10cm), the amount of slag produced during the rolling of rubble will be insufficient, potentially requiring additional purchases and increasing treatment costs. Furthermore, large-sized stone chips reduce the leveling effect on the top of the rammed stone layer, hindering subsequent construction. If the stone chips are too small (less than 2cm), the structural strength of the stone chip cushion layer will be compromised, reducing the overall foundation structure's support strength for the embankment in the site area. If the mud content of the stone chips is too high (greater than 10%), the quality will be poor, resulting in poor drainage and a limited lifespan for the foundation structure formed after filling the top of the rammed stone layer. If the mud content is too low (less than 5%), the material requirements will be too high, resulting in insufficient slag produced during the rolling of rubble and necessitating additional purchases of suitable stone chips, further increasing treatment costs.

[0020] Preferably, as an improvement, the geocell has a tensile strength per unit width of 150-220 KN / m.

[0021] Beneficial Effects: This scheme limits the strength of geocells, specifically the tensile strength per unit width at 150-220 KN / m. This ensures effective control of uneven settlement of the foundation structure while keeping the cost of geocells within a reasonable range, thus controlling treatment costs. If the strength of the geocells is too low (tensile strength per unit width less than 150 KN / m), it will be difficult to effectively control uneven settlement of the foundation structure after being laid on top of the gravel cushion layer, thus compromising the service life of the foundation structure. If the strength of the geocells is too high (tensile strength per unit width greater than 220 KN / m), although it can better control uneven settlement of the foundation structure, the corresponding cost will be significantly higher, which is not conducive to controlling the overall cost.

[0022] Preferably, as an improvement, the geocell is provided in two layers, and the distance between the bottom geocell and the stone slag cushion layer is 30-60cm, and the interlayer spacing between the two layers of geocell is 50-60cm.

[0023] Beneficial effects: This scheme involves setting two layers of geocells on the gravel cushion layer, which can further prevent uneven settlement of the foundation structure, thereby further ensuring the service life of the foundation structure and the embankment filling in the site area. If multiple layers of geocells are set, although the control effect on uneven settlement of the foundation structure can be further improved, the cost will also increase accordingly. Two layers of geocells can keep the cost within a reasonable range while ensuring a good control effect on uneven settlement of the foundation structure, thus reducing treatment costs. This scheme sets the distance between the bottom geocell and the stone crushing layer to 30-60cm, and the interlayer spacing between the two geocell layers to 50-60cm. That is, after filling the top of the stone crushing layer with 30-60cm of fill, the bottom geocell is laid, and then the top geocell is laid after filling the top of the bottom geocell with 50-60cm of fill. In this way, the geocells and the fill can be fully integrated to form a structure with strong lateral restraint and stiffness, which can effectively enhance the bearing capacity of the entire foundation structure, play a role in distributing the load, reduce the uneven settlement of the foundation structure, and thus reduce the deformation of the embankment fill in the site area.

[0024] The above-mentioned construction method for the foundation structure used in shallow treatment of service areas along mountain highways includes the following steps:

[0025] S1. Material preparation: Prepare construction materials such as rubble, stone chips, and geocells, and prepare construction machinery such as dynamic compaction machines, excavators, and loaders.

[0026] S2. Construction layout: Using surveying instruments, the plan position and elevation of the engineering structure on the design drawings are set out on the actual site;

[0027] S3. Test compaction: Determine the impact energy, number of blows, and time interval between two rounds of compaction for point compaction; determine the number of rounds and impact energy for general compaction; and obtain the total settlement of the test compaction.

[0028] S4. Laying a rammed stone layer: Fill the soft soil with rammed stones in layers. Each layer of rammed stones is rammed once. After all the rammed stones are rammed, a general ramming is carried out to form a rammed stone layer.

[0029] S4-1: Elevation Measurement: Clear and level the site, and measure the site elevation;

[0030] S4-2: Laying rubble: Lay 0.5-0.8m rubble, measure the site, and mark the tamping points;

[0031] S4-3, Spot compaction: Complete the spot compaction of one point according to the compaction energy and number of blows determined by the test compaction, and repeat the operation to the next point until one round of spot compaction is completed;

[0032] S4-4. Leveling the site: Use a bulldozer to fill the rammed pits;

[0033] S4-5, General compaction: Repeat steps S3-1 to S3-4 above until all points are compacted. Then, complete the general compaction according to the number of compaction passes and compaction energy determined by the trial compaction.

[0034] S5. Calculate the total settlement: Calculate the actual total settlement. Actual total settlement = site leveling elevation + rubble filling thickness - site elevation after ordinary compaction. The positive and negative error between the actual total settlement and the test compaction total settlement shall not exceed 10%.

[0035] S6. Check the construction data and conduct load tests: Check the hammer weight, hammer bottom area, drop distance, tamping point layout, number of tamping passes, and interval between two passes, etc. Conduct load tests on the tamped stone layer to determine the bearing capacity of the tamped stone layer. Bearing capacity = fill height × soil unit weight / 1.2-1.5;

[0036] S7. Laying stone ballast subbase: Laying stone ballast on the rammed stone layer and compacting it with a vibratory roller to form a stone ballast subbase.

[0037] S8. Laying geocells: After backfilling the stone crushing layer with soil, the geocells are laid and compacted by a vibratory compactor.

[0038] The principles and beneficial effects of this solution are as follows:

[0039] 1. This solution employs shallow treatment for the weak soil foundation of service area platforms in gullies, avoiding the use of composite foundations such as crushed stone piles and plain concrete piles. This results in high construction efficiency and reliable project quality. It also avoids extensive excavation of weak soil, directly using excavated stones crushed into rubble and compacted into the foundation soil, saving transportation distance and reducing earthwork volume, which aligns with the concept of green highways. Compared to existing technologies that use composite foundations and extensive excavation and replacement, this solution significantly reduces the cost of foundation treatment for service area platforms on mountainous highways.

[0040] 2. This scheme utilizes layered rubble to embed into the soft soil, forming a hard shell layer to meet the bearing capacity and stability requirements of the embankment filling body in the site area. It also utilizes the effective reinforcement depth of the dynamic compaction method to reinforce the deeper soft layers, forming a certain settlement before the embankment is filled, thereby meeting the post-construction settlement requirements after the higher embankment is filled.

[0041] 3. Before laying the rammed stone layer, this plan involves test compaction to determine the impact energy, number of blows, and interval between two rounds of compaction for spot compaction, as well as the number of rounds and impact energy for general compaction. This can effectively improve the compaction efficiency of spot compaction and general compaction, and ensure the compaction effect. It is beneficial to ensure that the bearing capacity of the resulting foundation structure meets the design requirements, thereby ensuring the support stability of the embankment filling in the site area.

[0042] 4. After the general compaction is completed, the actual total compaction settlement is calculated. The actual total compaction settlement can be compared with the total compaction settlement of the test compaction. If the actual total compaction settlement is less than the total compaction settlement of the test compaction, and the negative error between the actual total compaction settlement and the total compaction settlement of the test compaction exceeds 10%, supplementary compaction can be carried out in time to ensure that the compacted rubble structure meets the construction requirements.

[0043] 5. Before laying the stone slag cushion layer, this plan first conducts a load test on the rammed stone layer to determine its bearing capacity. The determined bearing capacity of the rammed stone layer can then be compared with the design specifications. If the determined bearing capacity of the rammed stone layer does not meet the requirements of the design specifications, it can be reinforced in time to ensure the support strength of the rammed stone layer, thereby ensuring the support strength of the entire foundation structure.

[0044] Preferably, as an improvement, the impact energy of the spot tamping is 400-2000KN, with each pass of spot tamping gradually increasing from 400-600KN; the number of impacts per pass of spot tamping is 2-5, and the number of impacts per pass of spot tamping increases with the number of passes of spot tamping; the number of passes of spot tamping is 3.

[0045] Beneficial effects: This scheme sets the above-mentioned tamping energy, number of tamping blows per pass, and number of tamping passes to ensure that the rubble is effectively compacted into the soft soil without excessive fragmentation, while also avoiding excessive disturbance to the foundation soil. If the tamping energy, number of tamping blows per pass, and number of tamping passes are too small, it will be difficult to guarantee the compaction depth of the rubble; if these parameters are too large, excessive fragmentation will occur, both of which will reduce the structural strength of the compacted rubble layer and make it difficult to provide stable support for the embankment fill in the site area.

[0046] This scheme gradually increases the energy level of each tamping pass to ensure that the rubble is pressed into the soft soil as expected. Compared with using high energy level for each tamping pass, this scheme can avoid breaking the rubble and ensure that the rubble skeleton formed by the rubble pressed into the soft soil has a high degree of integrity, which is conducive to improving the bearing capacity of the foundation structure and thus ensuring the stability of the embankment filling in the site area.

[0047] This scheme increases the number of tamping blows per pass as the number of passes increases, which can save energy while ensuring the compaction effect of the rubble. Since the rubble in the first pass is unobstructed, a smaller number of tamping blows is sufficient to compact it into the soft soil as expected. However, the rubble in subsequent passes requires a larger number of tamping blows due to the obstruction of the rubble in the previous passes, in order to ensure that all rubble is compacted into the soft soil as expected, thereby improving the structural strength of the compacted rubble layer.

[0048] Preferably, as an improvement, the number of tamping passes is 1-3, the tamping energy is 800-1000KN, and the number of single-point tamping blows is 2-3.

[0049] Beneficial effects: This scheme, by setting the above-mentioned number of compaction passes, compaction energy, and number of single-point compaction blows for general compaction, can effectively achieve the purpose of initially adjusting the rubble skeleton structure after point compaction and initially leveling the site. The purpose of general compaction is only to level the site. If the compaction energy and the number of single-point compaction blows are too small, the expected leveling effect cannot be achieved. Furthermore, general compaction cannot further press rubble into the soft soil. If the number of compaction passes, compaction energy, and the number of single-point compaction blows are too large, it will result in energy waste.

[0050] Preferably, as an improvement, the tamping points of the spot tamping are arranged in an equilateral triangle and the hammer marks do not overlap each other; the hammer marks of the ordinary tamping overlap each other by no less than 1 / 4 of the hammer diameter.

[0051] Beneficial Effects: This scheme arranges the tamping points in an equilateral triangle pattern, which, compared to a matrix arrangement, achieves a higher replacement rate and better compaction effect. For point compaction, which aims to drive rubble into soft soil, a certain spacing is required between the tamping points. This scheme sets the hammer marks for point compaction to not overlap, preventing overly dense tamping and effectively driving the rubble into the soft soil. The purpose of general compaction is to adjust the rubble skeleton structure at the top of the compacted rubble layer, achieving site leveling. Therefore, this scheme sets the hammer marks for general compaction to overlap by at least 1 / 4, ensuring the effectiveness of general compaction and improving the flatness of the top of the compacted rubble layer, facilitating subsequent construction steps.

[0052] Preferably, as an improvement, when the moisture content of the soft soil is high, the number of compaction passes should be 5-6, and the interval between two compaction passes should be 4-6 days.

[0053] Beneficial effects: When the moisture content of soft soil is high, the pore water pressure during compaction is also high, resulting in significant energy loss during compaction. Each pass of tamping has an insignificant pre-consolidation effect on the soil beneath the rubble. Therefore, the number of tamping passes needs to be increased (from 3 passes to 5-6 passes) to ensure adequate settlement of the soil beneath the rubble, thereby minimizing post-construction settlement and extending service life. Furthermore, setting the interval between two tamping passes to 4-6 days allows sufficient time for pore water pressure to dissipate, ensuring the effective consolidation and compression of the soil beneath the rubble through tamping.

[0054] In summary, the above-mentioned construction method for shallow treatment of foundation structures in mountainous highway service areas adopts the principle of "low energy level, fewer blows, more passes, and light to heavy" in its design and construction. Its hammer bottom area is much larger than that of the dynamic compaction replacement method, and it has significant differences in reinforcement mechanism and design concept from dynamic compaction replacement and dynamic compaction semi-replacement. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the foundation structure in this invention.

[0056] Figure 2 This is a flowchart of the construction method in this invention.

[0057] Figure 3 This is a schematic diagram of the distribution of tamping points in the tamping process of this invention.

[0058] Figure 4 This is a schematic diagram of the distribution of tamping points in the general tamping process of the present invention.

[0059] Figure 5 This is a schematic diagram of the overall structure of Embodiment 1 of the present invention. Detailed Implementation

[0060] The following detailed description illustrates the specific implementation method:

[0061] The reference numerals in the accompanying drawings include: 1. Soft soil; 2. Bedrock; 3. Soil-rock boundary; 4. Rock weathering boundary; 5. Ground line; 6. Drainage ditch; 7. Embankment fill in the site area; 8. Service area site; 9. Service area through lane; 10. Expressway main line; 11. Compacted rubble layer; 12. Geocell; 13. Stone cushion layer; 14. Rubble; 15. Roadbed width B1; Through lane width B2; Service area width B3; Fill platform width B4; First-level fill height H1; Second-level fill height H2; Foundation soil layer thickness h1; Outer compacted rubble layer thickness h2; Inner compacted rubble layer thickness h3; Distance between the bottom geocell and stone cushion layer h4; Spacing between two geocell layers h5; Stone cushion layer thickness h6; Height of the compacted rubble layer above the original ground line h7.

[0062] Foundation structures used for shallow treatment of highway service areas in mountainous areas, such as Figure 1 As shown, it includes a rammed stone layer 11, a stone slag cushion layer 13 and a geocell 12 arranged sequentially from bottom to top. The rammed stone layer 11 is formed by rammed stones 14 embedded in the soft soil 1, and the thickness of the inner side of the rammed stone layer 11 is less than the thickness of the outer side of the rammed stone layer 11.

[0063] The rubble 14 in the rammed rubble layer 11 is rolled from sandstone, limestone, marl, conglomerate and other materials from excavation and tunnel spoil. It has a natural compressive strength greater than 20MPa, a length of 30-50cm and a thickness of 15-30cm.

[0064] The stone chips in the stone chip cushion layer 13 are slag produced during the rolling of stone chips 14, with a particle size of 2-10 cm and a mud content of 5-10%; preferably, the particle size is 2-5 cm and the mud content is 5%; more preferably, the mud content is less than 5%.

[0065] Geocell 12 has a height of 5cm, a mesh size of 400mm×400mm, and a tensile strength per unit width of 150-220KN / m, preferably 180KN / m. The connection nodes of the geocell 12 mesh are formed by one-time injection molding. Two layers of geocell 12 are provided, with the distance h4 between the bottom geocell and the stone cushion layer being 30-60cm, and the interlayer spacing between the two layers of geocell 12 being 50-60cm. For ease of construction, the distance h4 between the bottom geocell and the stone cushion layer and the interlayer spacing between the two layers of geocell 12 can both be set to 50cm. Geocell 12 is generally available in 5cm, 8cm, and 10cm heights. For foundation treatment, a 5cm height is sufficient to meet strength requirements and reasonably control costs.

[0066] The above-mentioned construction method for the foundation structure used in shallow treatment of service areas of mountain highways, such as Figure 2 As shown, it includes the following steps:

[0067] S1. Material preparation: Prepare construction materials such as 14 rubble stones, stone chips, and 12 geocells, as well as construction machinery such as dynamic compaction machines, excavators, and loaders.

[0068] The rammer is a cylindrical steel rammer with a high modulus of elasticity, or a cylindrical rammer made of reinforced concrete with a thick steel shell. The weight of the rammer is determined according to the design impact energy. Four to six symmetrical vent holes, penetrating the top surface of the rammer, must be installed at the bottom to quickly expel air from the pit when the rammer hits the ground, reducing suction at the bottom of the pit during hammer lifting. The design impact energy is determined based on the designer's experience and needs to be slightly adjusted during subsequent trial rammering. The diameter of the vent holes is generally 15-20 cm, and the diameter of the rammer is 2.52 m.

[0069] S2. Construction layout: Using surveying instruments, the plan position and elevation of the engineering structure on the design drawings are set out on the actual site.

[0070] S3. Test compaction: Determine the impact energy, number of blows, and time interval between two rounds of compaction for point compaction; determine the number of rounds and impact energy for general compaction; and obtain the total settlement of the test compaction.

[0071] S3-1, Point tamping test: Select a typical section of 20m×20m, and each point tamping test must be performed to determine the tamping energy and number of tamping blows. The determination principle is: it is difficult to start the hammer, the soft soil at the edge of the pit rises more than 15cm; the upper stone is crushed; the settlement difference between the first and second blows is less than 2-3cm, and the settlement difference between the second and third blows is less than 3-4cm.

[0072] For example: the first tamping energy is 400-800KN, and the number of tamping blows is 2-3; the second tamping energy is 800-1100KN, and the number of tamping blows is 3-4; the third tamping energy is 1100-2000KN, and the number of tamping blows is 4-6.

[0073] If the moisture content of the soft soil 1 is high, it is also necessary to determine the interval between the two compaction passes, which is generally 4-6 days.

[0074] S3-2, General compaction test compaction: The number of compaction passes before the settlement of the two previous general compaction passes is less than 1.5-3.0cm is taken as the number of compaction passes, which is used to determine the number of compaction passes for test compaction; for example, if the settlement of the second and third general compaction passes is less than 1.5-3.0cm, and the settlement of the fourth general compaction pass is greater than 3.0cm, then the number of compaction passes is determined to be 3.

[0075] The tamping energy for conventional compaction should initially be 800-1000 KN·m based on engineering experience. Specifically, 800 KN·m, 900 KN·m, and 1000 KN·m can be used. During trial compaction, 2, 3, and 4 tamping passes should be used respectively. When the required settlement amount is met, any combination can be selected based on the convenience of construction.

[0076] In a certain civil engineering construction contract section, the first construction site was selected as the first project. The design unit went to the site to conduct trial compaction together with the construction unit in order to adjust the compaction settlement, compaction energy and other indicators in a timely manner and reasonably determine the final values.

[0077] S4. Laying the compacted stone layer 11: Fill the soft soil 1 with stone 14 in layers. Each layer of stone 14 is compacted once. After all the compaction is completed, general compaction is carried out to form the compacted stone layer 11.

[0078] The compaction energy of spot tamping is 400-2000 kN, gradually increasing from 400-600 kN per pass. Each pass consists of 2-5 blows, with the number of blows increasing with the number of passes. A total of 3 passes are required. When the soft soil has a high moisture content, 5-6 passes are needed, with an interval of 4-6 days between passes. Figure 3 As shown, the tamping points are arranged in an equilateral triangle with a spacing of 3.5m, and the hammer marks do not overlap.

[0079] (1) First tamping:

[0080] S4-1: Elevation Measurement: Clear and level the site, and measure the elevation of the site.

[0081] S4-2: Laying 14 rubble stones: Lay 14 rubble stones of 0.5-0.8m and level them, measure the site, and mark the tamping points for the first pass; position the machinery and measure the elevation of the hammer top before tamping.

[0082] S4-3, Spot compaction: Complete the spot compaction of one point according to the compaction energy and number of blows determined by the first round of spot compaction. Repeat the operation for the next point until the first round of spot compaction is completed; measure the elevation of the hammer top after compaction.

[0083] S4-4. Leveling the site: Use a bulldozer to fill the rammed pits.

[0084] (2) Second round of compaction:

[0085] S4-1: Elevation Measurement: Clear and level the site, and measure the elevation of the site.

[0086] S4-2: Laying 14 rubble stones: Lay 14 rubble stones of 0.5-0.8m and level them, measure the site, and mark the tamping points for the second round of tamping; position the machinery and measure the elevation of the hammer top before tamping.

[0087] S4-3, Point compaction: Increase the compaction energy and number of blows, and complete the point compaction of one point according to the compaction energy and number of blows determined by the second round of point compaction. Repeat the operation for the next point until the second round of point compaction is completed; measure the elevation of the hammer top after compaction.

[0088] S4-4. Leveling the site: Use a bulldozer to fill the rammed pits.

[0089] (3) Third tamping:

[0090] S4-1: Elevation Measurement: Clear and level the site, and measure the elevation of the site.

[0091] S4-2: Laying 14 rubble stones: Lay 14 rubble stones of 0.5-0.8m and level them, measure the site, and mark the tamping points for the third round of tamping; position the machinery and measure the elevation of the hammer top before tamping.

[0092] S4-3, Point compaction: Continue to increase the compaction energy and number of blows. Complete the point compaction of one compaction point according to the compaction energy and number of blows determined by the test compaction for the third round of point compaction. Repeat the operation for the next compaction point until the third round of point compaction is completed; measure the elevation of the hammer top after compaction.

[0093] S4-4. Leveling the site: Use a bulldozer to fill the rammed pits.

[0094] If the tamping pit overturns during the tamping process, the flatness of the pit bottom should be adjusted in time.

[0095] The number of tamping passes for ordinary compaction is 1-3, the tamping energy is 800-1000KN, and the number of blows for single-point tamping is 2-3. For example... Figure 4 As shown, the tampers are arranged at 1.92m intervals, and the hammer marks of the tampers overlap each other by 1 / 4 of the hammer diameter, which is 0.6m.

[0096] S4-5, General compaction: After the spot compaction is completed, the general compaction is completed according to the number of compaction passes and compaction energy determined by the test compaction.

[0097] S5. Calculate the total compaction settlement: Calculate the actual total compaction settlement. Actual total compaction settlement = site leveling elevation + thickness of rubble 14 filling - site level after ordinary compaction. The positive and negative error between the actual total compaction settlement and the test compaction total compaction settlement should not exceed 10%. If the actual total compaction settlement is less than the test compaction total compaction settlement and the error exceeds 10%, the rubble 11 layer needs to be compacted. If the site is uneven, the average compaction settlement at multiple points can be used as the actual total compaction settlement.

[0098] S6. Review construction data and conduct load tests: Check hammer weight, hammer base area, drop height, tamping point layout, number of tamping passes, and interval between passes; conduct load tests on the tamped stone layer 11 to determine its bearing capacity. Bearing capacity (KPa) = fill height (m) × soil unit weight (KN / m³) 3 ) / 1.2-1.5, compare the determined bearing capacity with the design specifications. If it is less than the design specifications, the rammed stone layer 11 needs to be reinforced.

[0099] In the formula for calculating bearing capacity, the specific value of the denominator (1.2-1.5) can generally be taken as 1.35; however, it can also be determined based on the height of the rammed stone layer: when the fill height is high, a smaller value within the range of 1.2-1.5 should be taken; correspondingly, when the fill height is low, a larger value within the range of 1.2-1.5 should be taken. If the fill height is high and a counter-pressure platform is installed, the value can be further reduced.

[0100] S7. Laying stone ballast subbase 13: Lay 0.1m of stone ballast on the rammed stone layer 11, and compact it by a 40t vibratory roller to form stone ballast subbase 13.

[0101] S8. Laying geocells 12: After filling 0.5m of soil on the stone ballast cushion layer 13, lay the first layer of geocells 12. After compacting with a 40t vibratory press, fill 0.5m of soil on the first layer of geocells 12 and lay the second layer of geocells 12. Compact with a 40t vibratory press.

[0102] After the above construction methods are used, the bearing capacity of the foundation is generally 220-300 kPa. Random checks will be conducted after construction is completed, and no fewer than 3 checks will be conducted in each section.

[0103] Example 1

[0104] like Figure 5As shown, a certain expressway in Wanzhou District, Chongqing, is 23.4 km long, a two-way four-lane expressway with a design speed of 80 km / h. The roadbed width B1 is 24.5 m, the through lane width B2 is 10.0 m, the service area width B3 is 60 m, and the embankment platform width B4 is 4.0 m. This service area is located in the low mountainous area of ​​northeastern Chongqing, covering an area of ​​60 mu (approximately 4 hectares). The terrain features a relative elevation difference of 80-100 m, forming a gully. The ground line 5 is relatively flat. The embankment 7 in the service area crosses the gully, with the first embankment height H1 being 8.0 m and the second embankment height H2 being 7.0 m. The current surface is a fishpond. According to geological survey: the thickness h1 of the foundation soil layer 1 (overlying soft soil) in the valley is 3.5-6.5m, the thickness of the surface soft soil layer is 0.6-1.1m, and there is no weak underlying layer. The underlying bedrock 2 is an alternating layer of purplish-red sandy mudstone and grayish-yellow sandstone from the Jurassic Shaximiao Formation (J2s). The rock weathering boundary 4 is 1.1m below the rock-soil boundary 3. The static cone penetration test (Ps) values ​​of the surface soil (0.6-1.1m) are 0.51-0.88MPa, and the static cone penetration test (Ps) values ​​of the lower soil (1.1-6.5m) are 0.93-1.24MPa. The natural water content of the soil is w = 28.9%, the void ratio is e = 0.984, and the liquid limit is W. L =36.6%, Plastic limit Wp=23.5%, Plasticity index Ip=13.1, Compression modulus Es 100-200 =5.3MPa.

[0105] The embankment adopts a shallow foundation treatment scheme, using the aforementioned foundation structure for shallow treatment of service areas on mountainous highways, such as... Figure 1 As shown, it includes a layer of rammed stone 11, a layer of stone slag cushion 13 and two layers of geocells 12 arranged from bottom to top, with a total thickness of 2.3m. The soil is filled on top to form the embankment 7 of the site area.

[0106] The rubble stones 14 in the rammed rubble layer 11 are made from sandstone excavated from the excavation. Their saturated compressive strength is 23.4 MPa. The length of the rubble stones is 30 cm and the thickness is not less than 15 cm. The thickness of the rammed rubble layer 11 on the side with the lower ground elevation is 30 m, which is the thickness of the outer rammed rubble layer h2, which is 2.0 m. The thickness of the rammed rubble layer 11 on the side with the higher ground elevation is 30 m, which is the thickness of the inner rammed rubble layer h3, which is 1.0 m. The height of the rammed rubble layer exposed above the original ground line h7 is 0.3 m.

[0107] The stone chips in the stone chip cushion layer 13 are slag produced during the rolling of sandstone rubble. The particle size is required to be no more than 10cm and the mud content is less than 5%. The thickness of the stone chip cushion layer h6 is 0.3m.

[0108] The embankment fill 7 in the site area is formed by filling mudstone, argillaceous sandstone, and sandstone from the excavation, and has no requirements for natural strength. First, soil is filled on top of the stone crushing layer 13, with a thickness equal to the distance h4 between the bottom geocells and the stone crushing layer being 0.5m. Then, the bottom geocells 12 are laid, followed by soil filling on top of the bottom geocells 12, with a thickness equal to the distance h5 between the two layers of geocells being 0.5m. Then, the top geocells 12 are laid, and finally, the embankment fill 7 in the site area is constructed. Its technical parameters are: geocell height 5cm, mesh size 400mm x 400mm, unit width breaking tensile strength 180KN / m, and the geocell mesh connection nodes are formed by one-time injection molding. The geocells mainly function to control uneven settlement.

[0109] The dynamic compaction parameters for the rammed stone layer 11 are as follows: the first compaction energy is 600KN, with 3 blows; the second compaction energy is 1000KN, with 3 blows; and the third compaction energy is 1500KN, with 4 blows. The interval between the two compaction passes is 2 days. The settlement after the two passes of ordinary compaction is less than 2.0cm, and the number of ordinary compaction passes is 3. The thicknesses of the rammed stone filling for the three passes are 0.6m, 0.6m, and 0.8m, respectively.

[0110] The above-mentioned construction method for the subgrade structure used for shallow treatment of service areas on mountain expressways is as follows: Figure 2 The procedure shown was implemented. The final calculated settlement was 1.25m, and the bearing capacity test result was 250KPa.

[0111] Engineering economic analysis:

[0112] The treatment area in this embodiment is 38,500 m². 2 When using crushed stone piles for treatment, with a pile spacing of 1.8m and a pile diameter of 0.5m, 13,730 crushed stone piles are needed. Assuming an average pile length of 5m, a total of 68,650m of crushed stone piles is required, at a unit price of 160 yuan / m. The total cost of this deep treatment scheme is 10.984 million yuan.

[0113] When this scheme is adopted, 77,000 cubic meters of sandstone slabs need to be rolled, with a unit price of 80 yuan / m³ based on self-mining and utilization. 3 The cost was 6.16 million yuan, with a dynamic compaction cost of 20 yuan / m. 2 The cost was 770,000 yuan. The cost of the shallow treatment plan was 6.93 million yuan.

[0114] A total of 4.054 million yuan was saved, reducing the project cost by 36.9%, resulting in significant economic benefits.

[0115] Example 2

[0116] A 48.8km long expressway in Tongliang District, Chongqing, is a six-lane, two-way expressway with a design speed of 120km / h. The roadbed width (B1) is 34.5m, the through lane width (B2) is 10.0m, the service area width (B3) is 65m, and the embankment platform width (B4) is 2.0m. Located in western Chongqing, the service area features terrain with relative elevation differences of 30-50m. The ground level (5) is relatively flat. The embankment (7) in the service area crosses a gully. The first-stage embankment height (H1) is 8.0m, and the second-stage embankment height (H2) is 4.0m. The current surface is paddy fields. Geological surveys indicate that the thickness of the foundation soil layer (h1) within the gully (1) is 1.5-5.5m, the thickness of the surface soft soil layer (0.8-1.5m), and there is no underlying soft soil layer. The lower bedrock 2 is Jurassic Shaximiao (J2s) purplish-red mudstone interbedded with sandstone. The rock weathering boundary 4 is 1.1m below the soil-rock boundary 3. The static cone penetration test (Ps) values ​​of the surface soil (0.5-1.1m) are 0.68-0.91MPa, and the static cone penetration test (Ps) values ​​of the lower soil (2.7-4.0m) are 0.95-1.25MPa. The natural water content of the soil is w = 30.1%, the void ratio is e = 0.973, and the liquid limit is W. L =36.2%, Plastic limit Wp=23.1%, Plasticity index Ip=13.1, Compression modulus Es 100-200 =4.7MPa.

[0117] The embankment adopts a shallow foundation treatment scheme, using the aforementioned foundation structure for shallow treatment of service areas on mountainous highways, such as... Figure 1 As shown, it includes a layer of rammed stone 11, a layer of stone slag cushion 13 and two layers of geocells 12 arranged from bottom to top, with a total thickness of 2.3m. The soil is filled on top to form the embankment 7 of the site area.

[0118] The rubble 14 in the rammed rubble layer 11 is made of limestone rolled from tunnel slag, with a saturated compressive strength of 36 MPa. The length of the rubble is 30 cm and the thickness is not less than 15 cm. The thickness of the rammed rubble layer 11 on the side with lower ground elevation, 30 m deep into the soft soil, i.e., the thickness h2 of the outer rammed rubble layer is 1.5 m. The thickness of the rammed rubble layer 11 on the side with higher ground elevation, 30 m deep into the soft soil, i.e., the thickness h3 of the inner rammed rubble layer is 0.8 m. The height h7 of the rammed rubble layer exposed above the original ground line is 0.3 m.

[0119] The stone slag in the stone slag cushion layer 13 is made from the slag produced during the rolling of limestone rubble. The particle size is required to be no more than 10cm and the mud content is less than 5%. The thickness of the stone slag cushion layer h6 is 0.3m.

[0120] The embankment fill 7 in the site area is formed by filling mudstone, argillaceous sandstone, and sandstone from the excavation, and has no requirements for natural strength. First, soil is filled on top of the stone crushing layer 13, with a thickness equal to the distance h4 between the bottom geocells and the stone crushing layer being 0.5m. Then, the bottom geocells 12 are laid, followed by soil filling on top of the bottom geocells 12, with a thickness equal to the distance h5 between the two layers of geocells being 0.5m. Then, the top geocells 12 are laid, and finally, the embankment fill 7 in the site area is constructed. Its technical parameters are: geocell height 5cm, mesh size 400mm x 400mm, unit width breaking tensile strength 180KN / m, and the geocell mesh connection nodes are formed by one-time injection molding. The geocells mainly function to control uneven settlement.

[0121] The dynamic compaction technical parameters for the rammed stone layer 11 are as follows: the first compaction energy is 800KN, with 3 blows; the second compaction energy is 1200KN, with 3 blows; and the third compaction energy is 1800KN, with 3 blows. The interval between the two compaction passes is 3 days. The settlement after the two passes of ordinary compaction is less than 2.0cm, and the number of ordinary compaction passes is 3. The thickness of the rammed stone filling for the three passes is 0.5m, 0.5m, and 0.5m respectively.

[0122] The above-mentioned construction method for the subgrade structure used for shallow treatment of service areas on mountain expressways is as follows: Figure 2 The procedure shown was implemented. The final calculated settlement was 1.45m, and the bearing capacity test result was 260KPa.

[0123] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A foundation structure for shallow treatment of mountainous highway service areas, characterized by: The foundation structure comprises, from bottom to top, a rammed stone layer, a stone residue cushion layer and a geocell, the rammed stone layer is formed by embedding stone into soft soil through ramming, and the thickness of the inner side of the rammed stone layer is less than the thickness of the outer side of the rammed stone layer; The method for laying the rammed stone layer comprises: layer by layer filling stone on the soft soil, and performing point ramming for each layer of stone, and then performing general ramming after all the point ramming is completed to form the rammed stone layer; and then sequentially arranging the stone residue cushion layer and the geocell on the rammed stone layer to form the foundation structure, and the bearing capacity of the foundation structure is 220-300 KPa; The stone in the rammed stone layer is rolled from sandstone, limestone, mudstone and gravel in the excavation and tunnel residue, and has a natural compressive strength greater than 20 MPa, a length of 30-50 cm and a thickness of 15-30 cm; and the stone residue in the stone residue cushion layer is residue generated during rolling of the stone.

2. The foundation structure for shallow treatment of mountainous highway service area according to claim 1, characterized in that: The stone residue in the stone residue cushion layer has a particle size of 2-10 cm and a mud content of 5-10%.

3. The foundation structure for shallow treatment of mountainous highway service areas according to claim 2, characterized in that: The geocell has a unit width breaking tension of 150-220 KN / m.

4. The foundation structure for shallow treatment of mountainous highway service areas according to claim 3, characterized in that: The geocell is arranged in two layers, the distance between the bottom layer of the geocell and the stone residue cushion layer is 30-60 cm, and the layer spacing between the two layers of the geocell is 50-60 cm.

5. The construction method of foundation structure for shallow treatment of mountainous highway service area according to any one of claims 1-4, characterized in that: The method comprises the following steps: S1, material preparation: preparing construction materials of stone, stone residue and geocell, and preparing construction machinery of the rammer, excavator and scraper; S2, construction lofting: using measuring instruments to measure the plane position and elevation of the engineering building on the design drawing to the actual site; S3, trial ramming: determining the ramming energy, ramming number and interval time between the front and rear two times of point ramming, determining the ramming number and ramming energy of general ramming, and obtaining the total ramming settlement of trial ramming; S4, laying the rammed stone layer: layer by layer filling stone on the soft soil, and performing point ramming for each layer of stone, and then performing general ramming after all the point ramming is completed to form the rammed stone layer; S4-1, measuring elevation: cleaning and leveling the site, and measuring the site elevation; S4-2, laying stone: laying 0.5-0.8 m stone, measuring the site, and arranging the ramming points of point ramming; S4-3, point ramming: completing point ramming of one ramming point according to the ramming energy and ramming number of point ramming determined by trial ramming, repeating the operation of the next ramming point, and until one time of point ramming is completed; S4-4, leveling the site: filling the ramming pit with a bulldozer; S4-5, general ramming: repeating steps S4-1 to S4-4 until all the point ramming is completed, and then completing general ramming according to the ramming number and ramming energy of general ramming determined by trial ramming; S5, calculating the total ramming settlement: calculating the actual total ramming settlement, the actual total ramming settlement = site leveling elevation + stone filling thickness - site elevation after general ramming, and the positive and negative error of the actual total ramming settlement and the total ramming settlement of trial ramming is not more than 10%; S6, checking construction data and performing load test: checking the hammer weight, hammer bottom area, drop distance, ramming point arrangement, ramming number, interval time between the front and rear two times, performing load test on the rammed stone layer, determining the bearing capacity of the rammed stone layer, and the bearing capacity = filling height x soil bulk density / 1.2-1.5; S7, laying stone slag cushion: laying stone slag on the tamped stone layer, and compacting by vibrating roller to form stone slag cushion; S8, laying geocell: laying geocell after filling soil on the stone slag cushion, and compacting by vibrating roller.

6. The construction method of foundation structure for shallow treatment of mountainous highway service area according to claim 5, characterized in that: The ramming energy of the point rammer is 400-2000KN, and the energy level of each point ramming is gradually increased according to the first level of 400-600KN; the ramming number of each point ramming is 2-5, and the ramming number of each point ramming is increased with the increase of the number of point ramming; the number of point ramming is 3.

7. The construction method of foundation structure for shallow treatment of mountainous highway service area according to claim 6, characterized in that: The number of ramming of the general rammer is 1-3, the ramming energy is 800-1000KN, and the single point ramming number is 2-3.

8. The construction method of the foundation structure for the shallow treatment of the mountainous highway service area according to claim 7, characterized in that: The ramming points of the point rammer are arranged in a regular triangle, and the hammer marks do not overlap each other; the hammer marks of the general rammer overlap each other by not less than 1 / 4 of the hammer diameter.

9. The construction method of the foundation structure for the shallow treatment of the mountainous highway service area according to claim 8, characterized in that: When the water content of the soft soil is large, the number of point ramming is 5-6, and the interval time between the front and rear two ramming is 4-6 days.

Images