Soft soil roadbed reconstruction and extension construction process based on existing expressway

Abstract

The invention discloses a soft soil roadbed reconstruction and extension construction process based on an existing expressway, which comprises the following steps: step 1, construction preparation: before formally entering soft foundation extension and soft foundation widening treatment, repeatedly checking corresponding geological data and a construction drawing for construction preparation; 2, site cleaning is conducted, specifically, a soft soil roadbed construction site needing to be conducted is cleaned; according to the bagged sand well construction method, after bagged sand well construction is completed, bagged sand is found and drainage of gap water in a soft soil foundation is accelerated by observing sedimentation and stability of a soft soil embankment, so that the engineering property of soft soil is improved, and the construction efficiency is improved. And the bearing capacity of the soft soil foundation is provided, the stability of the roadbed is ensured, the prepressing period of the soft soil roadbed engineering is also shortened, and a better consolidation effect is achieved in a shorter period.

Description

Technical Field

[0001] The invention relates to the technical field of construction technology, and in particular to a soft soil roadbed reconstruction and expansion construction technology based on an existing expressway. Background Art

[0002] During the construction of expressway projects, affected by the characteristics of the project, various difficult-to-handle geological environments are often encountered. Soft soil is one of them. The soft soil is relatively loose. If no effective treatment measures are taken, it is easy to cause quality problems such as settlement and decline, affecting the progress of the project construction and service life. Therefore, in actual construction, effective process treatment measures should be taken in combination with the characteristics of the soft soil layer and the construction requirements to improve the bearing capacity of roads and bridges. Usually, the permeability of soft soil roadbed is insufficient, and the common problem is uneven settlement. Professional treatment methods are required, which can be started from multiple angles such as soil quality and road conditions to ensure the treatment effect.

[0003] Along the expressway, soft soil and weak soil are distributed continuously in the shape of a lens. The depth of soft soil fluctuates according to the terrain height. It is generally distributed continuously. In some areas, there is a lens-shaped distribution. The maximum burial depth reaches 7.6m. Most of the burial depths are between 3.0m and 7.0n. The thickness does not exceed 3.0m at most. The thickness in some areas can reach 4.5m. There are also some sections with multi-layer distribution [11. The physical properties are natural water content between 30.1% and 42.9%, porosity between 0.91 and 1.23, and compression modulus of 2.74MPa at the minimum and 6.83MPa at the maximum.

[0004] Soft soil has the characteristics of loose soil layers, and contains a large amount of peat and loose sand and gravel in the pores, so it has poor permeability and insufficient compressive resistance. In actual construction, the roadbed may be compressed. If the compaction is not sufficient, settlement problems will occur. The road surface is likely to be uneven, causing problems such as bridge jumping. If the construction season is the rainy season, rainwater will seep into the roadbed, causing erosion of the foundation structure, seriously affecting the service life of the highway project. Due to insufficient permeability, a large deformation pressure will occur, so uneven settlement is likely to occur, which will directly affect the service life of the project.

[0005] Traditional construction technology has the following disadvantages:

[0006] In most cases, traditional construction technology, if you want to expand or widen a highway, usually involves connecting the new roadbed with the old roadbed. The stability of the connection between the two is poor, and if it is not handled carefully, it is very likely to threaten the safety of the entire roadbed and even interfere with normal traffic. Summary of the invention

[0007] The purpose of the present invention is to provide a soft soil roadbed reconstruction and expansion construction process based on an existing highway, so as to solve the problem that in many cases, if the traditional construction process proposed in the above background technology is to expand or widen the highway, it usually involves connecting the new roadbed with the old roadbed. The stability of the connection between the two is poor. If it is not handled carefully, it is very likely to threaten the safety of the entire roadbed and even interfere with normal traffic.

[0008] To achieve the above object, the present invention provides the following technical solution: a construction process for the reconstruction and expansion of soft soil roadbed of an existing expressway, comprising the following steps:

[0009] Step 1: Construction preparation: Before officially entering the soft foundation expansion and widening process, the relevant geological data and construction drawings must be repeatedly checked for construction preparation and site research;

[0010] Step 2: Site cleaning: Clean the soft soil roadbed construction site to be carried out;

[0011] Step 3: Construction of sand cushion: Lay the sand cushion on the cleaned soft soil roadbed site;

[0012] Step 4: Protection construction: Complete the protection construction of "bagged sand well + sand cushion + geogrid" on the laid sand cushion;

[0013] Step 5: Anti-collapse construction: Anti-collapse construction is carried out on the basis of protective construction. The anti-collapse construction specifically includes cement mixing piles, high-pressure rotary jet piles, CFG piles and prestressed concrete pipe piles;

[0014] Step 6. Monitor verticality: Monitor verticality in real time during the construction process and make timely construction adjustments.

[0015] As a preferred technical solution of the present invention, the construction preparation in step one should specifically use static penetration to detect the bearing capacity of the foundation to ensure that it meets the specific soil layer depth. The settlement information related to the soft foundation should be fully considered. When necessary, the construction party should also pay close attention to various design data to comprehensively reduce the potential settlement between the old roadbed and the new roadbed.

[0016] As a preferred technical solution of the present invention, the site cleaning in the step 2 is specifically to measure and lay out the soft foundation treatment range before construction, and use trenchers and bulldozers to clean up the topsoil and tree roots that do not meet the requirements, dig trenches for drainage and drying on the surface of perennial waterlogging, and do a good job of compaction before filling. For areas with thick silt layers in ponds and fish ponds, since the foundation is often soaked in water and soft, and has a high water content, pumping and silting should be done before construction, and silting should be done to the hard soil layer at the bottom of the ponds and fish ponds to prevent the possible fork-shaped settlement, instability and settlement difference of the roadbed due to silt, and backfilling and leveling should be done according to design requirements.

[0017] As a preferred technical solution of the present invention, the construction of the sand cushion layer in step 3 is specifically to discharge the water vertically from the bagged sand out of the roadbed to achieve the effect of continuous drainage. Usually, a sand cushion layer of a certain thickness is laid between the embankment and the top of the sand well to form a good drainage channel between the sand well and the sand cushion layer to enhance drainage and strengthen the foundation. Therefore, the sand cushion material must be made of medium and coarse sand with good permeability, cleanliness and good gradation, and the mud content should not be greater than 5%, and the permeability coefficient should not be less than 10-3 cm / s, fineness modulus greater than 2.5. To ensure the quality of roadbed construction, the quality of medium-coarse sand must be controlled to meet the design requirements. The sand cushion layer should be constructed in upper and lower layers. The thickness of the lower sand cushion layer is generally 30cm. After the site is rolled and leveled, the sand cushion layer can be layered and rolled and spread. The width should be 1.5 meters wider than the corner of the roadbed slope protection road to prevent insufficient sand cushion layer due to settlement, affecting the drainage, settlement and consolidation of the sand cushion layer. The two sides should be protected by sand bags or other methods to prevent sand loss. The upper cushion layer can be constructed after the sand well construction is completed.

[0018] As a preferred technical solution of the present invention, the "bagged sand well + sand cushion + geogrid" in step 4 specifically refers to bagged sand well construction and geogrid construction, and the bagged sand well construction is specifically as follows: S1, machine selection: the main machine is a duct-type vibrating pile driver, which is self-propelled with wide crawlers; S2, material preparation: the sandbag should be made of polypropylene woven fabric with good water permeability, water resistance and toughness; S3, sand selection: dry medium and coarse sand with high water permeability should be selected, and the particle size greater than 0.5mm should account for more than 50% of the total, the mud content should not exceed 3%, and the fineness number should be greater than 3.0; S4, sandbag production: the length of the sandbag should be 10-15c longer than the designed well depth, and the sand filling should ensure a sand filling rate of more than 95%. After sand filling, long-term exposure should be avoided to prevent sandbag aging. At the same time, in order to ensure the density of sand filling, a sand filling machine is introduced, and mechanical sand filling is adopted with manual assistance; S5, machine positioning: according to the measurement Measure the position and spacing of the layout, and drive into the sand well. When driving into the sand well, ensure the verticality of the casing, and its inclination rate shall not exceed 1.5%; S6, driving the casing: the casing and the machine can be driven in after positioning, and the initial vibration frequency is slightly slow to prevent the casing from shifting. The depth of the sand well should be marked on the casing to prevent it from being too deep; S7, placing the sand bag: the filled sand bag is placed near the pile driver, and the sand bag is placed manually. When placing the sand bag, a roller or a slide is set at the casing mouth to slowly place the sand bag into the casing ; S8. Pull out the casing: When the sandbag is basically in place and 1m away from the bottom, the casing can be pulled out. Use the 1m high impact force to open the pile tip. The pulling should be done continuously and slowly. The lifting rope must not be loosened in the middle to prevent the sandbag from falling and damaging the sandbag; S9. Bag head treatment: The bag head is generally exposed 15-20c above the ground. After the inspection by the supervisor, the part that is higher than the sand cushion layer should be cut off and the bag mouth should be re-tied. The bagged sand must be buried 30cm into the sand cushion layer and must not lie down.

[0019] As an optimal technical solution of the present invention, the geogrid construction is specifically the geogrid construction. After the sand well is constructed, the sand cushion layer is leveled and the geogrid is laid. When the geogrid is laid, tension is adopted at both ends to ensure its flatness, and then the two ends are anchored with bamboo strips. The role of the geogrid is mainly manifested in: increasing the stability of the soft foundation. Since the geogrid itself has the characteristics of high tensile strength, low deformation and low stretching as well as considerable surface roughness, it can achieve the effect of strengthening the foundation. In the section without geotextile, the daily settlement rate of the roadbed filling is generally controlled at about 15mm / d, while in the section with geotextile, the measured settlement rate mostly reaches 20mm / d, and the roadbed is still in a stable state, indicating that the geotextile can greatly improve the stability of the roadbed and accelerate the filling speed of the roadbed; reducing the uneven settlement of the roadbed base. Since the geotextile is a reinforcing layer, it plays a role in increasing the base strength and dispersing the concentrated stress of the soil. It can be seen from the measured data that its settlement curve is flat, indicating the reduction of uneven settlement.

[0020] As a preferred technical solution of the present invention, the cement mixing pile in step 5 is specifically used to reinforce soft clay, select cement as a curing agent, use a mixing machine, and mix the soft soil and the curing agent together by stirring in the depth of the roadbed. After a series of physical and chemical reactions, the soft soil will condense into a high-quality foundation with good stability and high strength. The reinforcement depth of this technology is more than 5m. If dry reinforcement is adopted, the depth is controlled within 15m, and the wet reinforcement depth is controlled within 20m. The general silicate cement composition includes silicon dioxide, ferric oxide, and calcium oxide, which can constitute cement minerals. After cement is mixed into saturated soft soil, the minerals on the surface of cement particles will quickly hydrolyze and hydrate with the soft soil moisture to generate calcium hydroxide and water content acid calcium compounds. These compounds will further form a suspended solution with a cementing effect, and improve the strength of cement soil after solidification. In the actual application process, the pile diameter is set to 50cm, and a gravel cushion layer with a thickness of 30cm is set on the top of the pile. After the cushion layer construction is completed, a single-layer geogrid is also required to ensure the construction effect. In the step five, the high-pressure rotary jet pile is specifically prepared first. The grouting materials, including two main materials, cement and water, are selected according to needs. Whether to add admixtures, the cement type and grade are selected in combination with the specific construction environment. Usually, ordinary Portland cement with a strength grade of 42.5 is selected, and admixtures and admixtures are added according to needs.This process has high requirements on cement quality. It should ensure that the cement meets the standard requirements, and do a good job of storage management to avoid cement moisture. Reasonable planning should be used to shorten the storage time to ensure quality. Sampling inspection should be carried out during construction. If cement with quality defects is found due to moisture and agglomeration, it needs to be replaced in time. The pile diameter of the high-pressure rotary jet pile is set to 50cm, and a square layout is adopted. A 20cm transition length is set for the bridge head roadbed, and a spacing of 1.5m is maintained between them. A 30cm encryption length is set at the bridge head, and the distance between the piles is 1.3m. A gravel cushion layer with a thickness of 20cm is set on the top, and the cushion layer is covered with geogrids. In step five, the CFG piles are passed through By setting up a cushion layer and connecting the engineering foundation, a stable reinforcement effect can be achieved. The body strength and modulus are greater than those of the soil between piles. Therefore, under the influence of the load, the top stress can bear the load transferred to the deep soil, increasing the load bearing capacity of the soil between piles. Under the action of, the bearing capacity of the foundation will be improved and the deformation will be reduced. In addition, CFG piles are not reinforced, and industrial waste will be used as admixtures to make piles, which not only reduces construction costs but also meets environmental protection requirements. In the actual construction process, appropriate process technology should be selected according to design requirements. The treatment depth of the bridgehead section does not exceed 10m, so this treatment method is selected, the pile diameter is set to 50cm, and a triangular distribution method is adopted. The long spiral drilling process is selected for construction. The bridgehead roadbed needs to be processed for 50m, the transition section is set to 20m, the pile spacing is controlled to 1.8m, the dense section is set to 30m, and a sand cushion layer is laid on the pile top with a thickness of 30cm. The prestressed concrete pipe piles in the step 5 are specifically prefabricated in the factory or on-site. The pile body is first prefabricated and then transported to the designated pile location. Mechanical equipment such as free fall hammers are used to perform static pressure impact on the piles to make them enter the soil layer. Cast-in-place piles are further divided into various types such as manually dug cast-in-place piles and sunken pipe cast-in-place piles; cement-soil mixing piles are flexible piles used in composite foundations that use mixing machinery to mix concrete and cement; gravel piles are used in actual construction. During the process, preparation work needs to be done first, including lifting, transportation and stacking of pipe piles, cleaning the construction area, ensuring the flatness of the site, checking the quality of the pipe piles, and starting construction after preparation is ready to ensure construction quality and safety. Prestressed concrete piles not only have the advantages of ordinary pipe piles, but also have unique advantages due to their own characteristics. During construction, the treatment depth of the bridgehead section exceeds 10m. This treatment method is adopted. Pipe piles with an outer diameter of 40cm and a wall thickness of 6.5cm are selected. The distribution method is a square layout. The bridgehead roadbed treatment length is 50m, the transition section is 20m, the pile spacing is 2.2m, a gravel cushion layer is laid with a thickness of 50cm, and a double-layer geogrid is set.

[0021] As a preferred technical solution of the present invention, the key to monitoring the verticality in step six should be implemented on the verticality of the pile foundation itself, which should not be ignored. It is best to arrange a 50cm gravel cushion layer for the construction site to smoothly connect the new embankment with the old embankment, and build a smooth drainage system under this premise. If conditions permit, the embankment slope should be provided with corresponding protection with the help of plastic sheeting to ensure that the roadbed is filled at the fastest speed.

[0022] As a preferred technical solution of the present invention, the site study in step 1 is specifically to briefly describe the distribution of the soft soil of the project, and to explain the selection of reinforcement schemes in combination with common roadbed treatment methods, and then to establish a roadbed numerical model using ABAQUS software, to study the replacement treatment, in-situ solidification treatment, bidirectional cement mixing piles, bored piles, and geogrid reinforcement methods, and to analyze the settlement, lateral displacement, and vertical stress distribution of the roadbed; finally, on the basis of finite element numerical simulation, by changing the specific parameters of foundation treatment, the soil layer below the pile end, and the influencing factors of embankment construction, the changing law of the roadbed settlement is studied.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. After the construction of the bagged sand well was completed, through the observation of the settlement and stability of the soft soil embankment, it was found that the bagged sand accelerated the discharge of the pore water in the soft soil foundation, thereby improving the engineering properties of the soft soil, increasing the bearing capacity of the soft soil foundation, ensuring the stability of the roadbed, and shortening the preloading period of the soft soil roadbed project, achieving a better consolidation effect in a shorter period of time;

[0025] 2. During the construction of expressways, in order to effectively treat the soft soil roadbed, reasonable treatment processes need to be adopted, including cement mixing piles, high-pressure rotary grouting, CFG piles and prestressed concrete piles. They should be selected according to needs and the process parameters should be reasonably set to ensure the effectiveness of the treatment and avoid uneven settlement problems on the highway. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of the present invention;

[0027] Figure 2 The figure is a flow chart of the bagged sand well construction of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] See also Figure 1-2 The present invention provides a soft soil roadbed reconstruction and expansion construction process based on an existing expressway, comprising the following steps:

[0030] Step 1: Construction preparation: Before officially entering the soft foundation expansion and widening process, the relevant geological data and construction drawings must be repeatedly checked for construction preparation and site research;

[0031] Step 2: Site cleaning: Clean the soft soil roadbed construction site to be carried out;

[0032] Step 3: Construction of sand cushion: Lay the sand cushion on the cleaned soft soil roadbed site;

[0033] Step 4: Protection construction: Complete the protection construction of "bagged sand well + sand cushion + geogrid" on the laid sand cushion;

[0034] Step 5: Anti-collapse construction: Anti-collapse construction is carried out on the basis of protective construction. The anti-collapse construction specifically includes cement mixing piles, high-pressure rotary jet piles, CFG piles and prestressed concrete pipe piles;

[0035] Step 6. Monitor verticality: Monitor verticality in real time during the construction process and make timely construction adjustments.

[0036] Specifically speaking, in step one, construction preparation should use static penetration to detect the bearing capacity of the foundation to ensure that it meets the specific soil depth. The settlement information related to the soft foundation should be fully considered. When necessary, the construction party should also pay close attention to various design data and comprehensively reduce the potential settlement between the old roadbed and the new roadbed.

[0037] The site cleaning in step 2 specifically involves measuring and marking out the soft foundation treatment range before construction, and using trenchers and bulldozers to clean up the topsoil and tree roots that do not meet the requirements. Dig trenches to drain and dry the surface of water that accumulates all year round, and compact it before filling. For areas with thick silt layers in ponds and fish ponds, since the foundation is often soaked in water and soft, and has a high water content, pumping and silting should be done before construction, and silt should be cleared to the hard soil layer at the bottom of the ponds and fish ponds to prevent possible fork-shaped settlement, instability and settlement differences in the roadbed due to silt, and backfilling and leveling should be done according to design requirements.

[0038] Step 3: The construction of the medium sand cushion layer is specifically to allow the water discharged vertically from the bagged sand to flow out of the roadbed to achieve the effect of continuous drainage. Usually, a sand cushion layer of a certain thickness is laid between the embankment and the top of the sand well to form a good drainage channel between the sand well and the sand cushion layer to enhance drainage and strengthen the foundation. Therefore, the sand cushion layer material must be made of medium and coarse sand with good permeability, cleanliness and good gradation. The mud content should not be greater than 5%, the permeability coefficient should not be less than 10-3cm / s, and the fineness modulus should be greater than 2.5. In order to ensure the quality of roadbed construction, the quality of medium and coarse sand must be controlled to meet the design requirements. The sand cushion layer should be constructed in upper and lower layers. The thickness of the lower sand cushion layer is generally 30cm. After the site is rolled and leveled, the layered rolling and paving construction of the sand cushion layer can be carried out. The width should be 1.5 meters wider than the corners of the roadbed slope protection to prevent insufficient sand cushion layer due to settlement, which will affect the drainage, settlement and consolidation of the sand cushion layer. The two sides should be protected by sand bags or other means to prevent sand loss. After the sand well construction is completed, the upper pad is constructed.

[0039] In step 4, "bagged sand well + sand cushion + geogrid" specifically refers to bagged sand well construction and geogrid construction. The bagged sand well construction is specifically as follows: S1. Machine selection: The main machine is a duct-type vibrating pile driver, which is self-propelled with wide crawlers; S2. Material preparation: The sandbag should be made of polypropylene woven fabric with good permeability, water resistance and toughness; S3. Selection of sand material: Dry medium and coarse sand with high water permeability should be used, and the particle size greater than 0.5mm should account for more than 50% of the total, the mud content should not exceed 3%, and the fineness number should be greater than 3.0; S4. Sandbag production: The length of the sandbag should be 10-15c longer than the designed well depth, and the sand filling should ensure a sand filling rate of more than 95%. After sand filling, long-term exposure should be avoided to prevent sandbag aging. At the same time, in order to ensure the density of the sand filling, a sand filling machine is introduced, and mechanical sand filling is adopted with manual assistance; S5. Machine positioning: According to the measured position and spacing of the layout , driving into the sand well, when driving into the sand well, the verticality of the casing must be ensured, and its inclination rate shall not exceed 1.5%; S6, driving the casing: the casing and the machine can be driven in after positioning, the initial vibration frequency is slightly slow to prevent the casing from shifting, and the depth of the sand well should be marked on the casing to prevent it from being too deep; S7, placing sand bags: the filled sand bags are placed near the pile driver, and the sand bags are placed manually. When placing the sand bags, rollers or slides are set at the casing mouth to slowly place the sand bags into the casing; S8, Pull out the casing: When the sandbag is basically in place and 1m away from the bottom, the casing can be pulled out. Use the 1m high impact force to open the pile tip. It should be pulled out continuously and slowly. The lifting rope must not be loosened in the middle to prevent the sandbag from being damaged due to the falling of the casing; S9. Bag head treatment: The bag head is generally exposed 15-20c above the ground. After the inspection by the supervisor, the part that is higher than the sand cushion layer should be cut off and the bag mouth should be re-tied. The bagged sand must be buried 30cm into the sand cushion layer and must not lie down.

[0040] Geogrid construction is specifically geogrid construction. After the sand well is constructed, the sand cushion layer is leveled and the geogrid is laid. When laying the geogrid, tension is adopted at both ends to ensure its flatness, and then the two ends are anchored with bamboo strips. The role of geogrid is mainly manifested in: increasing the stability of soft foundation. Since the geogrid itself has the characteristics of high tensile strength, low deformation and low stretching as well as considerable surface roughness, it can achieve the role of strengthening the foundation. In the section without geotextile, the daily settlement rate of roadbed filling is generally controlled at about 15mm / d, while in the section with geotextile, the measured settlement rate mostly reaches 20mm / d, and the roadbed is still in a stable state, indicating that geotextile can greatly improve the stability of the roadbed and speed up the filling speed of the roadbed; reducing the uneven settlement of the roadbed base. Since geotextile is a reinforcing layer, it plays the role of increasing the base strength and dispersing the concentrated stress of the soil. It can be seen from the measured data that its settlement curve is flat, indicating the reduction of uneven settlement.

[0041] In step 5, cement mixing piles are used to reinforce soft clay. Cement is selected as a curing agent. A mixing machine is used to mix the soft soil and curing agent together by stirring at the depth of the roadbed. After a series of physical and chemical reactions, the soft soil will solidify into a high-quality foundation with good stability and high strength. The reinforcement depth of this technology is more than 5m. If dry reinforcement is used, the depth is controlled within 15m, and the wet reinforcement depth is controlled within 20m. The general composition of silicate cement includes silicon dioxide, ferric oxide, and calcium oxide, which can constitute cement minerals. After cement is mixed into saturated soft soil, the minerals on the surface of cement particles will quickly hydrolyze and hydrate with the moisture in the soft soil to generate calcium hydroxide and water-containing acid calcium compounds. These compounds will further form a suspended solution with a cementing effect, which will increase the strength of cement soil after solidification. In actual application, the pile diameter is set to 50cm, and a gravel cushion layer with a thickness of 30cm is set on the top of the pile. After the cushion layer construction is completed, a single-layer geogrid is also required to ensure the construction effect. In step 5, the high-pressure rotary jet pile is first prepared with grouting materials, including two main materials, cement and water. Whether to add admixtures is selected according to needs. The type and grade of cement are selected in combination with the specific construction environment. Usually, ordinary Portland cement with a strength grade of 42.5 is selected, and admixtures and admixtures are added according to needs.This process has high requirements on cement quality. It should ensure that the cement meets the standard requirements and do a good job of storage management to avoid cement moisture. Reasonable planning should be used to shorten the storage time to ensure quality. Sampling inspection should be carried out during construction. If cement with quality defects is found due to moisture and agglomeration, it needs to be replaced in time. The diameter of the high-pressure rotary jet pile is set to 50cm, and a square layout is adopted. A 20cm transition length is set for the bridgehead roadbed, and a spacing of 1.5m is maintained between them. A 30cm encryption length is set at the bridgehead, and the distance between the piles is 1.3m. A gravel cushion layer with a thickness of 20cm is set on the top, and the cushion layer is covered with geogrids. In step five, the CFG piles are A cushion layer is set up to connect the engineering foundation to achieve a stable reinforcement effect. The body strength and modulus are greater than those of the soil between piles. Therefore, under the influence of load, the top stress can bear the load transferred to the deep soil, increasing the load bearing capacity of the soil between piles. Under the action of, the bearing capacity of the foundation will be improved and the deformation will be reduced. In addition, CFG piles are not reinforced, and industrial waste will be used as admixtures to make piles, which not only reduces construction costs but also meets environmental protection requirements. In the actual construction process, appropriate process technology should be selected according to design requirements. The treatment depth of the bridgehead section does not exceed 10m, so this treatment method is selected, the pile diameter is set to 50cm, and a triangular distribution method is adopted. The village section The long spiral drilling process is selected for construction. The bridgehead roadbed needs to be processed for 50m, the transition section is set to 20m, the pile spacing is controlled to 1.8m, the dense section is set to 30m, and a sand cushion layer with a thickness of 30cm is laid on the pile top. The prestressed concrete pipe piles in step five are specifically prefabricated in the factory or on-site. The pile body is prefabricated first, and then transported to the designated pile location. Mechanical equipment such as free fall hammers are used to perform static pressure impact on the piles to make them enter the soil layer. Cast-in-place piles are further divided into various types such as manually dug cast-in-place piles and sunken pipe cast-in-place piles; cement-soil mixing piles are flexible piles used in composite foundations that use mixing machinery to mix concrete and cement; gravel piles are used in the actual construction process. During the process, preparation work needs to be done first, including lifting, transportation and stacking of pipe piles, cleaning the construction area, ensuring the flatness of the site, checking the quality of the pipe piles, and starting construction after preparation to ensure construction quality and safety. Prestressed concrete piles not only have the advantages of ordinary pipe piles, but also have unique advantages due to their own characteristics. During construction, the treatment depth of the bridgehead section exceeds 10m. This treatment method is adopted. Pipe piles with an outer diameter of 40cm and a wall thickness of 6.5cm are selected. The distribution method is a square layout. The bridgehead roadbed treatment length is 50m, the transition section is 20m, the pile spacing is 2.2m, a gravel cushion layer is laid with a thickness of 50cm, and a double-layer geogrid is set.

[0042] The key to monitoring verticality in step six should be the verticality of the pile itself, which should not be ignored. It is best to arrange a 50cm gravel cushion layer for the construction site to smoothly connect the new embankment with the old embankment, and build a smooth drainage system on this premise. If conditions permit, the embankment slope should be provided with corresponding protection with the help of plastic sheeting to ensure that the roadbed is filled at the fastest speed.

[0043] The site study in step one is to briefly describe the distribution of soft soil in the project, and explain the selection of reinforcement schemes in combination with common roadbed treatment methods. Then, using ABAQUS software, a roadbed numerical model is established to study the replacement treatment, in-situ solidification treatment, bidirectional cement mixing piles, bored piles, and geogrid reinforcement methods, and analyze the settlement, lateral displacement, and vertical stress distribution of the roadbed. Finally, on the basis of finite element numerical simulation, by changing the specific parameters of foundation treatment, the soil layer below the pile end, and the influencing factors of embankment construction, the changing law of roadbed settlement is studied.

[0044] Embodiment 1:

[0045] In the present invention, the soft foundation treatment range should be measured and laid out before construction, and the topsoil and tree roots that do not meet the requirements should be cleaned with trenchers and bulldozers. The surface of the perennial waterlogged land should be drained and dried, and compacted before filling. For areas with thick silt layers in ponds and fish ponds, since the foundation is often soaked in water and soft, and has a high water content, pumping and dredging should be done before construction, and the silt should be dredged to the hard soil layer at the bottom of the pond and fish pond to prevent the forked settlement, instability and settlement difference of the roadbed that may occur due to silt. Backfilling and leveling should be done according to design requirements, and the water discharged vertically from the bagged sand flows out of the roadbed to achieve the effect of continuous drainage. Usually, a sand cushion layer of a certain thickness is laid between the embankment and the top of the sand well to form a good drainage channel between the sand well and the sand cushion layer. In order to enhance drainage and strengthen the foundation, the sand cushion material must be made of medium and coarse sand with good permeability, cleanliness and good gradation. The mud content should not be greater than 5%, the permeability coefficient should not be less than 10-3cm / s, and the fineness modulus should be greater than 2.5. In order to ensure the quality of roadbed construction, the quality of medium and coarse sand must be controlled to meet the design requirements. The sand cushion should be constructed in upper and lower layers. The thickness of the lower sand cushion is generally 30cm. After the site is rolled and leveled, the layered rolling and paving construction of the sand cushion can be carried out. The width should be 1.5 meters wider than the corners of the roadbed slope protection to prevent insufficient sand cushion due to settlement, which will affect the drainage, settlement and consolidation of the sand cushion. The two sides should be protected by sand bags or other means to prevent sand loss.After the construction of the sand well is completed, the upper pad will be constructed. For the construction of bagged sand wells, the main machine is a duct-type vibrating pile driver with wide crawler and self-propelled; the sandbags should be made of polypropylene woven fabric with good water permeability, water resistance and toughness; dry medium and coarse sand with high water permeability should be used, and the particle size greater than 0.5mm should account for more than 50% of the total, the mud content should not exceed 3%, and the fineness number should be greater than 3.0; the length of the sandbag should be 10-15c longer than the designed well depth, and the sand filling rate should be guaranteed to be more than 95%. After sand filling, long-term exposure should be avoided to prevent sandbag aging. At the same time, in order to ensure the density of the filled sand, Introduce sand filling machine, use mechanical sand filling, and manual assistance; according to the measured position and spacing, drive into the sand well. When driving into the sand well, ensure the verticality of the casing, and its inclination rate does not exceed 1.5%; After the casing and the machine are positioned, they can be driven in. The initial vibration frequency is slightly slow to prevent the casing from shifting. The depth of the sand well should be marked on the casing to prevent it from being too deep; the filled sand bags are placed near the pile driver and are manually placed. When placing the sand bags, rollers or slides are set at the casing mouth to slowly put the sand bags into the casing; when the sand bags are basically in place and 1m away from the bottom, the casing can be pulled out, and the 1m high impact force is used to open the pile tip. It is advisable to pull out continuously when pulling out. Proceed slowly, and do not loosen the rope in the middle to prevent the sandbag from being damaged by the falling of the casing; the bag head is generally exposed 15-20c above the ground. After the inspection by the supervisor, the part that is higher than the sand cushion layer should be cut off and the bag mouth should be tied again. The bagged sand must be buried 30cm into the sand cushion layer and must not lie down. After the sand well is constructed, the sand cushion layer is leveled and the geogrid is laid. When laying the geogrid, tension is used at both ends to ensure its flatness, and then the two ends are anchored with bamboo strips. The main function of the geogrid is to increase the stability of the soft foundation because the geogrid itself has high tensile strength, low deformation and low stretching. And considerable surface roughness and other characteristics, so it can achieve the effect of strengthening the foundation. In the section without geotextile, the daily settlement rate of roadbed filling is generally controlled at about 15mm / d, while in the section with geotextile, the measured settlement rate mostly reaches 20mm / d, and the roadbed is still in a stable state, indicating that geotextile can greatly improve the stability of the roadbed and speed up the filling speed of the roadbed; reduce the uneven settlement of the roadbed base. Because geotextile is a reinforcing layer, it plays the role of increasing the base strength and dispersing the concentrated stress of the soil. From the measured data, it can be seen that its settlement curve is flat, indicating the reduction of uneven settlement.

[0046] Embodiment 2:

[0047] In the present invention, the soft soil foundation has the characteristics of large water content, large porosity, high compressibility, etc., so reducing the compressibility of the soil, lowering the porosity and water content and increasing the density of the soil have become the main purposes of soft foundation treatment; after constructing the sand cushion layer and bagged sand wells in the soft soil foundation, under the action of the upper soil load, the additional stress generated between the soil bodies causes the pore water between the soil particles to be discharged outside the stratum through the sand wells and sand cushion layers in the soft soil layer, thereby achieving the compaction between the soil particles, thereby accelerating the consolidation and settlement of the foundation, achieving a higher degree of consolidation in a shorter time, and improving the bearing capacity and shear resistance of the soft soil roadbed, thereby ensuring the stability of the embankment and foundation.

[0048] Embodiment 3:

[0049] In the present invention, the soft soil layer is relatively thick, and the depth of the bagged sand well treatment is also correspondingly deeper. The thickness of the soft soil silt layer of Jiangzhu Expressway reaches 25-40m. Considering the characteristics of this project and economic factors, the designed length of the sand well is 25m. Due to the large treatment depth, it is easy to produce bag back during the construction process. After the steel casing is driven into the designed depth, during the lifting process, the sand bag rises with the lifting of the steel pipe, which is called the "bag back" phenomenon. During construction, attention should be paid to the following aspects to reduce bag back: (1) After the steel pipe sinks to the designed depth, water is poured into the steel casing to balance the water pressure inside and outside the pipe. Because the pile is deep and the pressure at the bottom of the pipe is high, it is easy to press the silt into the pipe from the pipe mouth. In order to reduce the pressure inside the pipe, water is poured into the pipe to reduce the back pressure, which will reduce the silt entering the pipe; (2) The cover of the steel casing should not be too small or too large. If the sandbag is too small or too large, it is easy for silt to enter the steel casing during the pile sinking process. The steel casing cover should be controlled within a gap of 1mm. (3) When pulling out the steel pipe, hang the sandbag on the bagged sand machine. Due to the weight of the sandbag, the sandbag will remain vertical, and then slowly put it into the steel casing; the sandbag should be filled with natural and clean medium-coarse sand, and it is required to be kept in an air-dried state to avoid the sand in the sandbag from reducing in volume after drying, causing the sand well to shorten or "broken piles". Sandbags are filled with sand using a sand filling machine, and are manually laid to assist in shaking. If the sandbag head is found to be incomplete when the catheter is pulled out, it should be manually filled in time. Sandbags should be placed as they are filled, and should not be stored too much or for too long. The sandbags should be filled with sand. The sandbag filling rate (r) is calculated according to the formula in the specification. Neck shrinkage and fracture are most likely to occur during the construction of bagged sand wells. During construction, the sand bag should be tied after it is filled with sand. When entering the well, the operator should hold the bag tightly and put it vertically and slowly into the well. When pulling out the steel casing, attention should also be paid to vertical lifting to prevent the sand bag from being dragged out or damaged. After each sand pile is driven, the silt on site must be cleaned up to ensure that the sand bag has a hole extending into the sand cushion layer for at least 30 cm. The sand bag extending into the sand cushion layer must be upright and not lying down, so that the sand and sand cushion layer are fully connected to ensure smooth drainage. Sand bags should be driven as soon as they are loaded and should not be stored too much or for too long; they should not be exposed to the sun to prevent the sand bags from aging and breaking.

[0050] Embodiment 3:

[0051] In the present invention, the distribution of soft soil in the project is briefly described, and the selection of reinforcement schemes is explained in combination with common roadbed treatment methods. Then, a roadbed numerical model is established by using ABAQUS software, and replacement treatment, in-situ solidification treatment, bidirectional cement mixing piles, bored piles, and geogrid reinforcement methods are studied to analyze the settlement, lateral displacement, and vertical stress distribution law of the roadbed. Finally, on the basis of finite element numerical simulation, by changing the specific parameters of foundation treatment, the soil layer below the pile end, and the influencing factors of embankment construction, the change law of the roadbed settlement is studied and then the construction is carried out.

[0052] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction process for the reconstruction and expansion of soft soil roadbed based on an existing expressway, characterized in that: The following steps are involved: Step 1: Construction preparation: Before officially entering the soft foundation expansion and widening process, the relevant geological data and construction drawings must be repeatedly checked for construction preparation and site research; Step 2: Site cleaning: Clean the soft soil roadbed construction site to be carried out; Step 3: Construction of sand cushion: Lay the sand cushion on the cleaned soft soil roadbed site; Step 4: Protection construction: Complete the protection construction of "bagged sand well + sand cushion + geogrid" on the laid sand cushion; Step 5: Anti-collapse construction: Anti-collapse construction is carried out on the basis of protective construction. The anti-collapse construction specifically includes cement mixing piles, high-pressure rotary jet piles, CFG piles and prestressed concrete pipe piles; Step 6. Monitor verticality: Monitor verticality in real time during the construction process and make timely construction adjustments.

2. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 1 is characterized in that: Specifically speaking, in the construction preparation of step one, static penetration should be used to detect the bearing capacity of the foundation to ensure that it meets the specific soil depth. The settlement information related to the soft foundation should be fully considered. When necessary, the construction party should also pay close attention to various design data and comprehensively reduce the potential settlement between the old roadbed and the new roadbed.

3. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 1 is characterized in that: The site cleaning in the second step specifically includes measuring and staking out the soft foundation treatment range before construction, and using trenchers and bulldozers to clean up the topsoil and tree roots that do not meet the requirements, digging trenches to drain and dry the surface of water all year round, and compacting before filling. For areas with thick silt layers in ponds and fish ponds, since the foundation is often soaked in water and soft, and has a high water content, pumping and silting should be done before construction, and silt should be cleared to the hard soil layer at the bottom of the ponds and fish ponds to prevent possible fork-shaped settlement, instability and settlement differences of the roadbed due to silt, and backfilling and leveling should be done according to design requirements.

4. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 1 is characterized in that: The construction of the sand cushion in step 3 is specifically to vertically discharge the water from the bagged sand and flow out of the roadbed to achieve the effect of continuous drainage. Usually, a sand cushion of a certain thickness is laid between the embankment and the top of the sand, so that a good drainage channel is formed between the sand well and the sand cushion to enhance drainage and strengthen the foundation. Therefore, the sand cushion material must be made of medium and coarse sand with good permeability, cleanliness and good gradation, with a mud content of no more than 5%, a permeability coefficient of no less than 10-3cm / s, and a fineness modulus greater than 2.

5. In order to ensure the quality of roadbed construction, the quality of medium and coarse sand must be controlled to meet the design requirements. The sand cushion layer should be constructed in upper and lower layers. The thickness of the lower sand cushion layer should be 30 cm. After the site is rolled and leveled, the layered rolling and paving construction of the sand cushion layer can be carried out. The width should be 1.5 meters wider than the corners of the roadbed slope protection road to prevent insufficient sand cushion layer due to settlement, which will affect the drainage, settlement and consolidation of the sand cushion layer. The two sides should be protected by sand bags or other means to prevent sand loss. The upper cushion layer should be constructed after the sand well construction is completed.

5. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 1 is characterized in that: The "bag sand well + sand cushion + geogrid" in step 4 specifically refers to the construction of bag sand well and geogrid. The bag sand well construction specifically includes: S1. Machine selection: The main machine is a duct-type vibrating pile driver with wide crawler tracks and self-propelled; S2. Material preparation: Sandbags should be made of polypropylene woven fabric with good water permeability, water resistance and toughness; S3. Sand material selection: dry medium-coarse sand with high water permeability should be selected, and the particle size greater than 0.5mm should account for more than 50% of the total amount, the mud content should not exceed 3%, and the fineness number should be greater than 3.0; S4. Sand bag production: The length of the sand bag should be 10-15c longer than the designed well depth. The sand filling rate should be more than 95%. After sand filling, long-term exposure should be avoided to prevent sand bag aging. At the same time, in order to ensure the density of sand filling, a sand filling machine is introduced, mechanical sand filling is adopted, and manual assistance is used; S5. Machine positioning: according to the measured position and spacing, drive into the sand well. When driving into the sand well, ensure the verticality of the casing, and its inclination rate shall not exceed 1.5%; S6. Casing driving: After the casing and the machine are positioned, they can be driven in. The initial vibration frequency is slightly slow to prevent the casing from shifting. The sand well depth should be marked on the casing to prevent it from being too deep. S7, sand bag placement: The filled sand bags are placed near the pile driver by hand. When placing the sand bags, rollers or slides are set at the casing opening to slowly place the sand bags into the casing; S8. Pull out the casing: When the sandbag is basically in place and 1m away from the bottom, the casing can be pulled out. The 1m high impact force is used to open the pile tip. The pulling should be done continuously and slowly. The lifting rope should not be loosened in the middle to prevent the sandbag from being damaged by the falling of the casing. S9. Bag head treatment: The bag head is exposed 15-20cm above the ground. After inspection by the supervisor, the part protruding from the sand cushion layer should be cut off and the bag mouth should be re-tied. The bagged sand must be buried 30cm into the sand cushion layer and must not lie down.

6. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 5 is characterized in that: The geogrid construction is specifically the geogrid construction. After the sand well is constructed, the sand cushion layer is leveled and the geogrid is laid. When the geogrid is laid, tension is adopted at both ends to ensure its flatness, and then the two ends are anchored with bamboo strips. The role of the geogrid is manifested in: increasing the stability of the soft foundation. Since the geogrid itself has the characteristics of high tensile strength, low deformation and low stretching as well as considerable surface roughness, it can achieve the role of strengthening the foundation. In the section without geotextile, the daily settlement rate of the roadbed filling is generally controlled at about 15mm / d, while in the section with geotextile, the measured settlement rate mostly reaches 20mm / d, and the roadbed is still in a stable state, indicating that the geotextile can greatly improve the stability of the roadbed and accelerate the filling speed of the roadbed; reducing the uneven settlement of the roadbed base. Since the geotextile is a reinforcing layer, it plays the role of increasing the base strength and dispersing the concentrated stress of the soil. It can be seen from the measured data that its settlement curve is gentle, indicating the reduction of uneven settlement.

7. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 1 is characterized in that: The cement mixing pile in step 5 is specifically used to reinforce the soft clay. Cement is selected as a curing agent. A mixing machine is used to mix the soft soil and the curing agent together by stirring at the depth of the roadbed. After a series of physical and chemical reactions, the soft soil will condense into a high-quality foundation with good stability and high strength. The reinforcement depth of this technology is more than 5m. If dry reinforcement is adopted, the depth is controlled within 15m, and the wet reinforcement depth is controlled within 20m. The general silicate cement composition includes silicon dioxide, ferric oxide, and calcium oxide. These substances can constitute cement minerals. After the cement is mixed into the saturated soft soil, the minerals on the surface of the cement particles will quickly hydrolyze and hydrate with the soft soil moisture to generate hydrogen Calcium oxide, water content of acid calcium compounds, these compounds will further form a suspended solution with a cementing effect, and improve the strength of cement soil after solidification. In the actual application process, the pile diameter is set to 50cm, and a gravel cushion layer with a thickness of 30cm is set on the top of the pile. After the cushion layer construction is completed, a single-layer geogrid must be set to ensure the construction effect. In the step 5, the high-pressure jet grouting pile is specifically prepared first. The two main materials are cement and water. Whether to add admixtures is selected according to needs. The type and grade of cement are selected in combination with the specific construction environment. Ordinary Portland cement with a strength grade of 42.5 is usually selected. Admixtures and admixtures are added according to needs. This process has high requirements on cement quality and should ensure that the cement Meet the standard requirements, do a good job of storage management, avoid cement moisture, shorten the storage time through reasonable planning to ensure quality, and conduct sampling inspection during construction. If cement with quality defects is found due to moisture and agglomeration, it needs to be replaced in time. The pile diameter of the high-pressure rotary jet pile is set to 50cm, and a square layout is adopted. A 20cm transition length is set for the bridgehead roadbed, and a spacing of 1.5m is maintained between them. A 30cm encryption length is set at the bridgehead, and the distance between the piles is 1.3m. A gravel cushion layer with a thickness of 20cm is set on the top, and geogrids are used to cover the cushion layer. In the step five, the CFG pile is connected to the engineering foundation by setting a cushion layer to achieve a stable reinforcement effect, and the body strength and modulus are greater than The soil between piles is affected by the load. The top stress can bear the load and transfer it to the deep soil, increasing the load bearing capacity of the soil between piles. Under the action of, the bearing capacity of the foundation will be improved and the deformation will be reduced. In addition, CFG piles are not reinforced, and industrial waste will be used as admixtures to make piles, which not only reduces construction costs but also meets environmental protection requirements. In the actual construction process, appropriate process technology should be selected according to design requirements. The treatment depth of the bridgehead section does not exceed 10m, so this treatment method is selected, the pile diameter is set to 50cm, and the triangular distribution method is adopted. The long spiral hole-forming process is selected for the village section. The bridgehead roadbed needs to be treated for 50m, the transition section is set to 20m, and the pile spacing is controlled to 1.8m, the densification section is set to 30m, and a sand cushion layer with a thickness of 30cm is laid on the top of the pile. The prestressed concrete pipe piles in step 5 are specifically prefabricated in the factory or on site, and then transported to the designated pile location. The piles are subjected to static pressure blows by mechanical equipment such as free fall hammers to make them enter the soil layer. Cast-in-place piles are further divided into various types such as artificially dug cast-in-place piles and sunk pipe cast-in-place piles; cement-soil mixing piles are flexible piles used in composite foundations that use mixing machinery to mix concrete and cement; gravel piles require preparation in advance during the actual construction process, including pipe pile lifting, transportation Transportation and stacking work, clean up the construction area, ensure the site is flat, check the quality of the pipe piles, and start construction after preparation to ensure construction quality and safety. Prestressed concrete piles not only have the advantages of ordinary pipe piles, but also have unique advantages due to their own characteristics. During construction, the treatment depth of the bridgehead section exceeds 10m. This treatment method is adopted. Pipe piles with an outer diameter of 40cm and a wall thickness of 6.5cm are selected. The distribution method is a square layout. The bridgehead roadbed treatment length is 50m, the transition section is 20m, the pile spacing is 2.2m, and a gravel cushion layer is laid with a thickness of 50cm. A double-layer geogrid is set. .

8. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 1 is characterized in that: The key to monitoring verticality in step six should be the verticality of the pile itself, which should not be ignored. It is best to arrange a 50cm gravel cushion layer for the construction site to smoothly connect the new embankment with the old embankment, and build a smooth drainage system on this premise. If conditions permit, the embankment slope should be provided with corresponding protection with the help of plastic sheeting to ensure that the roadbed is filled at the fastest speed.

9. The construction process for reconstruction and expansion of soft soil roadbed based on an existing expressway according to claim 1, characterized in that: The site study in step 1 is specifically to briefly describe the distribution of the soft soil of the project, and to explain the selection of reinforcement schemes in combination with common roadbed treatment methods. Then, the roadbed numerical model is established using ABAQUS software, and replacement treatment, in-situ solidification treatment, bidirectional cement mixing piles, bored piles, and geogrid reinforcement methods are studied to analyze the settlement, lateral displacement, and vertical stress distribution of the roadbed. Finally, on the basis of finite element numerical simulation, by changing the specific parameters of foundation treatment, the soil layer below the pile end, and the influencing factors of embankment construction, the changing law of roadbed settlement is studied.

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