Construction method for subgrade layering treatment

Abstract

A construction method for subgrade layering treatment comprises shallow layer treatment and deep layer treatment. The shallow layer treatment comprises construction preparation which is performed in sequence; clearing the surface; laying a working cushion layer; inserting and hitting a drainage plate; laying a vacuum pipe network and a lower non-woven fabric layer; laying a sealing film, and treating a sealing ditch; a vacuumizing system is installed, vacuumizing is conducted, and in-situ observation is conducted; the soft foundation treatment effect is detected, unloading is conducted, and the site is leveled; arranging a film pressing groove; the deep treatment comprises the step of leveling a site in sequence; laying a working cushion layer; laying a lower sand cushion layer; inserting and hitting a drainage plate; laying a vacuum pipe network and a lower non-woven fabric layer; laying a sealing film, and treating a sealing ditch; vacuumizing equipment is installed; vacuumizing is conducted; laying an upper non-woven fabric layer; laying an upper sand cushion layer; installing a monitoring instrument; geogrids are laid; and carrying out stacking construction. According to the construction method for subgrade layering treatment, the construction quality and efficiency are guaranteed.

Description

Technical Field

[0001] The invention relates to a roadbed construction method on a shoal, in particular to a roadbed layered processing construction method. Background Art

[0002] The existing shallow land soft foundation roadbed construction generally adopts the following methods: 1) Replacement method: The replacement method is to dig out the soft soil layer within a certain range below the bottom of the building foundation and replace it with non-erosive and low-compressible granular materials to accelerate the consolidation of soft soil. Disadvantages: This method requires a large amount of filler and is costly; and the effect on deep soft foundation treatment is limited, and it may need to be used in combination with other methods.

[0003] 2) Roadbed reinforcement method: The roadbed reinforcement method strengthens the roadbed's own strength by embedding high-strength and high-toughness geopolymers, tie bars, load-bearing rods or firewood (wood) branches in the roadbed, thereby increasing the ability to resist foundation deformation and settlement. Disadvantages: This method has high material costs and is more complex to construct; for some special geological conditions, the reinforcement effect may be limited.

[0004] 3) Surface drainage method: Surface drainage method is to dig trenches on the ground before filling the roadbed to drain surface water and reduce the surface moisture content of the foundation, so that construction work can be carried out under relatively dry conditions. Disadvantages: This method is only applicable to shallow soft foundations with abundant surface water, and has limited effect on deep soft foundation treatment.

[0005] 4) Compacting method: Compacting method is to press certain fillers such as sand, gravel or quicklime into the soil by impact, vibration or both to form columns, compact the original soil layer, and thus increase the strength of the foundation. Disadvantages: This method has the disadvantages of complex construction process, high cost investment, limited treatment effect, certain impact on the environment and limited scope of application.

[0006] 5) Dynamic tamping method: Dynamic tamping method is to use the strong impact force generated by the free fall of a heavy hammer from a high place to tamp the foundation. It is more effective for sandy soil foundations. The plane layout of the tamping points is generally square or triangular. Disadvantages: This method has the disadvantages of large vibration and noise, high requirements for soil quality, difficult to determine construction parameters, limited construction sites, and high construction safety risks. It is necessary to select appropriate construction methods and parameters according to specific conditions in actual projects, and strengthen construction management and supervision.

[0007] 6) Pile foundation construction method: The pile foundation construction method can transfer the building load to the deep foundation, increase the bearing capacity, reduce or adjust the settlement, etc. Pile foundations include driven piles, cast-in-place piles, jet-jet piles and deep mixing piles. Disadvantages: This method has the disadvantages of high cost, complex construction process, limited treatment depth, high soil quality requirements and environmental impact.

[0008] The patent "A river channel excavation construction process after mud blowing into land" with application number "201810985601.0" includes a foundation treatment stage, which includes shallow foundation treatment and deep foundation treatment.

[0009] The above device has some problems with the foundation treatment part: Question 1) The above-mentioned device adopts preloading construction in deep treatment. A significant disadvantage of the preloading method is the long construction period. Since the consolidation and settlement of the foundation soil is a slow process, it takes a long time to achieve the expected reinforcement effect. Especially on deep soft soil foundations, the preloading period may be as long as 1 year or even several years, which not only increases the construction cost, but also prolongs the overall construction period of the project, posing a severe challenge to the progress control of the project.

[0010] Question 2) The cost of the preloading method is relatively high, and the cost of the preloading materials is high, especially when a large amount of high-quality materials is required. This is mainly reflected in the following two aspects: one is the purchase and transportation cost of the preloading materials; the other is the capital occupation and management cost caused by the long construction period. In addition, if the preloading effect is not ideal, additional reinforcement treatment is required, which further increases the project cost.

[0011] Question 3) The preloading method is mainly applicable to soft clay foundations with good water permeability. Its effect will be greatly reduced for soil layers with extremely poor water permeability or containing a large number of impermeable layers. This is because the excess pore water pressure generated by the preloading load is difficult to dissipate effectively, resulting in slow foundation consolidation and unsatisfactory reinforcement effect. In addition, for foundations containing hard interlayers or boulders, the preloading method is also difficult to effectively penetrate these obstacles and achieve comprehensive reinforcement. Summary of the invention

[0012] The technical problem to be solved by the present invention is to provide a construction method for layered treatment of roadbed, which effectively solves the technical problems existing in traditional foundation treatment methods by means of vacuum + preloading construction to improve the bearing capacity and stability of the foundation, shorten the construction period, reduce the construction cost, enhance adaptability and other aspects.

[0013] In order to solve the above technical problems, the technical solution adopted by the present invention is: A construction method for layered treatment of roadbed, including shallow layer treatment and deep layer treatment; The shallow layer treatment includes construction preparation, surface clearing, laying of working cushion, installation of drainage board, laying of vacuum pipe network and lower non-woven fabric layer, laying of sealing film, treatment of sealing ditch, installation of vacuum system, vacuuming, in-situ observation, soft foundation treatment effect detection, unloading, site leveling, and film pressing ditch layout. The deep treatment includes leveling the site in sequence; laying the working cushion layer; laying the lower sand cushion layer; inserting drainage boards; laying the vacuum pipe network and the lower non-woven fabric layer; laying the sealing film and treating the sealing ditch; installing vacuum equipment; vacuuming; laying the upper non-woven fabric layer; laying the upper sand cushion layer; installing monitoring instruments; laying geogrids; and loading construction.

[0014] The construction process of leveling the site, laying woven cloth, inserting drainage boards, laying vacuum pipe networks and non-woven geotextiles, laying sealing membranes, treating sealing ditches, installing vacuum systems, vacuuming, and laying non-woven fabric layers in the deep treatment is consistent with the construction process of shallow treatment.

[0015] Insert the drainage board, including: S1: According to the control points of the local area, use a ruler to place the specific position of each drainage board in the vertical and horizontal directions according to the spacing required by the design, and then mark each position. These marks serve as the position of the board inserting machine; S2: The conduit is a round conduit, and the conduit boot is made of iron and is tied to the conduit with a small chain; the pile tip for fixing the drainage board adopts the form of inverted trapezoidal wedge extrusion connection; S3: Before and during construction, use a theodolite to check and adjust the verticality of the guide tube of the plate inserter. When sinking the casing, the verticality of the casing should not exceed 1.5%; the casing used in the construction of the drainage board should ensure that the belt inserted into the foundation is not twisted; S4: Connection between the drain board and the pile tip: insert the drain board into the conduit through the pull rope and fold the head of the drain board back. The connection between the drain board and the pile tip relies on a conical or round wedge (pin) to clamp the drain board; S5: The depth of the conduit buried in the ground is determined according to the depth of the drainage board. After the drainage board is installed to the designed elevation by measuring and testing, the conduit is lifted. During the lifting of the conduit, the back-up of the drainage board is observed. During the installation process, the back-up length of the drainage board shall not exceed 500mm, and the number of back-up roots shall not exceed 5% of the total number of roots installed, otherwise additional holes shall be drilled at adjacent board positions. When encountering boulders and boulders, it is difficult to drill holes in situ, and the drilling can be relocated. The displacement distance should not be greater than 30% of the spacing between drainage boards. During winter construction, anti-freezing and anti-breakage measures shall be taken for the drainage board. S6: Due to the large number of drainage boards in the project, the drainage boards are in disc shape before construction, and some drainage boards are extended during the construction process; when the plastic drainage belt needs to be extended, the connection method of flat overlap of the inner core of the filter membrane is adopted, and the overlap length should be greater than 200mm. Each "extended board" is only allowed to have one joint. The "extended boards" are used in a scattered manner, and there is no joint between adjacent boards. The use of "extended boards" does not exceed 10% of the total number of roots installed; when extending, first peel off the filter membranes of the two drainage boards, connect the board cores directly, and then put them together, and then tie them securely with thin wire or plastic rope. Each drainage board pile is only allowed to be extended once at most; if it is found during the construction process that the construction cannot reach the designed elevation, geological exploration should be carried out in the nearby local area in time, and the designer should be contacted to discuss solutions; S7: After each drain board is installed, the exposed part must not be contaminated; after passing the inspection, the soil around the drain board should be cleaned up in time.

[0016] When laying the vacuum pipe network, the drain board and filter tube are cut and the two ends of the drain board are sealed; the drain board is wrapped around the filter tube and tied to ensure direct contact between the drain board and the filter tube. After tying, the drain board shall not slide on the filter tube, and the passage between the drain board and the filter tube shall be unobstructed; the tie tape joints between the drain board and the filter tube and the pipeline shall face downward; the filter tube shall be soft and permeable; the head of a single drain board and the corresponding corrugated filter tube shall be connected by winding, and the filter tube shall be arranged to form a loop; the filter tube shall be connected with two-way, three-way and four-way connections, and the connection shall be wrapped with non-woven fabric.

[0017] In deep treatment, the thickness of the lower sand cushion layer and the upper sand cushion layer are both 50cm. The laying of the lower sand cushion layer and the upper sand cushion layer is assisted by surveyors to conduct measurement and observation for elevation control. The thickness must be laid evenly to prevent affecting the subsequent construction process. During foundation treatment, the horizontal drainage cushion layer uses a sand cushion layer with a thickness of not less than 50cm, a mud content of ≤5%, a particle content of more than 50% with a particle size of ≥0.075mm, a dry density of more than 1.5t / m3, and a permeability coefficient of more than 5x10-3cm / s.

[0018] The present invention provides a construction method for layered treatment of roadbed, which has the following technical effects: 1) Laying vacuum pipe network The drain board and filter tube are cut manually in the material processing area. The length of each drain board and filter tube is determined according to the design requirements. The two ends of the drain board are sealed to prevent the board head from entering the mud and blocking the drainage channel. The drain board is wrapped around the filter tube and tied with a cable tie to ensure direct contact between the drain board and the filter tube. When the drain board is tied on the filter tube, the specification of the non-woven fabric with a head is required to be 200g / m2 and the outer size is 30*40cm. The cable tie is 30-35cm long to ensure that the drain board does not slide on the filter tube after tying, and to ensure that the channel between the drain board and the filter tube is unobstructed. The tie joint between the drain board and the filter tube and pipeline should face downward to avoid damage to the sealing film. The filter tube adopts soft permeable, with a diameter of 40mm, the main pipe spacing is about 30m, and the branch pipe spacing is 0.8m. The head of a single drain board and the corresponding corrugated filter tube are connected by winding to ensure that the board head is clean, so that each drain board is effectively connected to the filter tube, and the filter tube layout should form a loop. The filter tube can be connected with two-way, three-way or four-way connections. The length of the filter tube is about 15cm and it is tied tightly with lead wire. The lead wire joint is strictly prohibited from facing upwards and the connection needs to be wrapped with non-woven fabric.

[0019] Pipe introduction: Since the subsequent construction of vacuum combined loading preloading requires loading within the block, the vacuum pump needs to be arranged at the block boundary close to the sealing ditch during the vacuum combined loading preloading construction. When laying the vacuum pipeline, it is necessary to arrange the membrane outlet at the position of the vacuum pump in the pipe and pump layout diagram in advance, pull the main pipe to the block boundary, and install the vacuum pump after laying the vacuum membrane to connect the main pipe.

[0020] 2) Lay down the non-woven fabric layer After the monitoring instrument is buried and the filter pipe is laid, first, lay a layer of 150g / m2 woven cloth, and locally lay a layer of 250g / m2 woven cloth (if there are large-scale shrubs below, it is forbidden to cut them directly to avoid affecting the sealing membrane. You can consider taking measures to flatten the existing shrubs and lay 250g / m2 flat woven cloth for protection. The coverage of the shrubs is subject to actual occurrence) to avoid damage during vacuuming. The requirements for laying woven cloth are the same as above. Then, manually lay a layer of 200g / m2 non-woven geotextile. The non-woven geotextile and the filter pipe form a horizontal drainage channel, while ensuring that the sealing membrane will not be damaged by the three-way joint of the filter pipe. When laying the non-woven geotextile, keep a certain amount of wrinkles to reserve vacuum preload settlement. The non-woven geotextiles are overlapped, and the overlap width is not less than 200mm (the overlap between each piece of non-woven fabric is overlapped or caulked, and the factory stitching width is not less than 50mm; the on-site stitching overlap width is not less than 200mm). After the non-woven geotextile is laid, there is no damage, and the damaged parts need to be repaired with the same material.

[0021] 3) Lay the sealing film and treat the sealing groove Two layers of sealing membrane with a thickness of 0.14mm are laid on the non-woven fabric. The sealing membrane is heat-formed once in the factory according to the design; when laying the membrane, it is necessary to ensure that there is no hard object under the membrane, and it cannot be pulled hard to avoid excessive local force to damage the sealing membrane. After laying, the membrane needs to be slightly loose to avoid large differential settlement causing the sealing membrane to tear. The sealing membrane is buried in the deep silt layer by manual stepping on the membrane and excavating the sealing ditch around the partition to ensure the sealing around the partition. When stepping on the membrane, the inner membrane is first followed by the outer membrane, and one person is responsible for one person stepping on it. Strengthen management during vacuuming, cover the sealing ditch with water as needed, and step on the membrane repeatedly to ensure the sealing effect. The depth of the vacuum membrane buried in the impermeable layer shall not be less than 1.0m, and the reserved spacing between adjacent sealing ditches (i.e. the range of the sealing ditch) should be 50-100cm to ensure the airtightness of the sealing ditch. If necessary, the sealing ditch should be backfilled with clay. The vacuum pump joint, the settlement rod joint, the vacuum gauge, the pore water pressure, etc. are sealed to prevent air leakage on the membrane surface during vacuuming. Strengthen the protection of the sealing membrane. During vacuuming, check the membrane surface frequently and repair any leaks in time.

[0022] 4) Install the vacuum system, vacuumize, and observe in situ Arrange the vacuum pump (7.5kw) according to the design requirements, connect the main filter pipe to the vacuum pump through the film outlet and the water suction hose, install the vacuum pump system (connect the water pump, water tank, gate valve, stop valve, and film outlet), connect the circuit from the distribution box in the electrical room → the leakage switch box at the vacuum pump → the vacuum pump, and debug the vacuum jet pump without load. When the vacuum degree on the vacuum jet pump reaches 85kPa or above, try to evacuate for about 10 days. Carefully check for air leakage on the membrane surface and the film pressing groove, and make up for it in time after it is found. Maintain a certain pump opening rate, and the vacuuming time should not be less than 70 days according to the design requirements. After reaching the design unloading standard, the effect test can be arranged. In the later stage of vacuuming, after the in-situ observation of the average daily settlement of the surface layer reaches the design requirements, relevant geotechnical tests can be arranged for effect testing, and common ones include drilling and taking soil samples for indoor geotechnical tests. Divide the area according to different vacuum processes, and excavate the film pressing groove along the edge of the vacuum partition. In order to ensure the overall effect of vacuuming, the number of excavations of the middle film pressing groove should be reduced as much as possible. The excavation depth of the film-pressing trench shall be no less than 1m. If there is a sandy soil area on the surface, the depth of the bottom of the film-pressing trench into the silt layer shall be no less than 0.5m. If there is a highly permeable interlayer, it shall be excavated and backfilled with 30~50cm thick soft clay. The width of the trench bottom is 0.5-1.0m, and the width of the top surface of the film-pressing trench is 1.7m. The surface of the trench should be smooth. After the sealing film is spread on the surface of the trench, the clay soil is backfilled (the excavated soil can be used for backfilling). There shall be no sharp objects such as gravel, boulders, and debris in the soil.

[0023] 5) Lay the non-woven fabric layer The upper non-woven fabric layer is laid one month after the deep treatment is formally vacuumed, and the laying technology is the same as that of the lower non-woven fabric layer.

[0024] 6) Laying geogrid The laying surface of geogrid should be relatively flat to prevent longitudinal skew. First, draw a white line or hanging line on the paving layer according to the width, and then start paving, and then fix the end of the grid (fixed at a uniform distance). When laying the geogrid, it should be straightened and smooth, close to the base surface, and the upper grid should be fixed on the foundation every 2~2.5m. The geogrid is tied with plastic tape along the transverse joints. Joint paving: The length of the roll is used as the section length of the laying. After the section length of the grid to be laid is fully laid, the paving quality is checked again as a whole, and then the next section is laid. The connection of the geogrid adopts overlap construction. To ensure its integrity, the overlap width is not less than 500mm and not less than 3 grids, and the overlap range should be tied tightly. After a section of geogrid is laid, use 25~50Kg sandbags to press the geogrid at the overlap and edge. To prevent the geogrid from being damaged, the surface of the lower foundation should be flat, and hard protrusions such as gravel and boulders are strictly prohibited.

[0025] 7) Solidified soil filling ①Construction layout Lay out the center line of the solidified soil filling according to the construction drawings, set a pile every 30m on the straight section, and set indicator piles at the edge of the solidified soil treatment layer on both sides. Mark the filling height of the edge of the solidified treatment layer clearly on the indicator piles on both sides.

[0026] ②Material preparation, mixing and transportation The solidified soil is mixed in a centralized manner and transported to the construction site by transport vehicles. Measures are taken to cover the solidified soil during transportation to prevent evaporation, spillage, water seepage or rain. The base soil should be crushed during mixing, and the maximum size should not be greater than 15mm to prevent lumps; mixing should be carried out in accordance with the material specifications and proportions determined by the solidified soil mix design; the moisture content of the solidified soil should be 1%~2% higher than the optimal moisture content when leaving the factory.

[0027] According to the size of the project and the length of the transportation distance, a sufficient number of transport vehicles should be equipped; the transportation distance and time should be able to enable the solidified soil to be compacted within the setting time; after loading, the box should be tightly covered with tarpaulin to prevent premature evaporation of moisture; the evenly mixed solidified soil should be immediately transported to the paving site for construction, and should be mixed, transported, spread and compacted at the same time.

[0028] ③. Spread and level the solidified soil Before paving the solidified soil, ensure that there is no water on the site. Filling can only begin after the previous process of solidified soil construction is completed and accepted. If the water content of the solidified soil after mixing is high, it can be piled up to reduce the water content so that the water content meets the control index requirements, and ensure that the solidified soil is paved and rolled before initial setting.

[0029] The mixed mixture is transported to the road for paving, and is immediately shaped by a bulldozer and an excavator. The paving length is controlled at 60 meters each time, and the paving is immediately rolled and formed after completion. In straight sections, the bulldozer is used to level the road from both sides to the center; in flat curves, the bulldozer is used to level the road from the inside to the outside. Quickly discharge the pressure on the initially leveled road section to expose potential unevenness. For local low-lying areas, the surface layer of more than 5 cm should be loosened and leveled with newly mixed mixture. Use the bulldozer to shape it again, and the protruding material should be directly scraped out of the road, and no thin layer filling should be formed. Each shaping should reach the specified slope and road crown, and it should be noted that the joints must be smooth and flat. The thickness of each layer of solidified soil filling and rolling shall not exceed 40 cm, and the loose paving coefficient is tentatively set to 1.5, which is determined according to the compaction thickness experiment of the test section. Due to the foundation bearing capacity of the first layer of paving, when the crawler bulldozer is inconvenient to operate, the crawler excavator is used to shape the crawler excavator with a steel plate.

[0030] ④. Rolling Solidified soil construction is rolled from both sides to the center. The rolling speed of the roller for the first two times should be 1.5km / h~1.7km / h, and 2.0km / h~2.5km / h thereafter. It is strictly forbidden for the roller to turn around or emergency brake on the completed or rolling section of the road. If "spring", "looseness" or "peeling" occurs during the rolling process, timely measures should be taken to deal with it. The rolling should achieve the required compaction degree and there should be no obvious wheel marks.

[0031] In principle, the rolling of solidified soil construction should follow the principle of light first and heavy later, slow first and fast later; generally speaking, static pressure first, weak vibration later, static pressure is usually used in the end, the rolling speed should not exceed 4km / h, and the rolling machinery generally chooses a 16~24t light roller. Due to the low bearing capacity of the foundation, when the roller cannot roll at the initial rolling, the crawler type rolling of the excavator is adopted. When the roller is capable of rolling, the roller must be used for construction. The following rolling measures are the roller rolling process: After shaping, the full width of the road should be rolled immediately with a 16~24t roller. After two static rollings, the roller should start weak vibration rolling. When rolling, both sides should roll toward the center of the road, overlapping 1 / 2 wheel width, and the rear wheel must exceed the joint of the two sections. Generally, rolling is required 4-6 times. The rolling speed of the roller should be 1.5km / h~1.7km / h for the first two times, and 2.0km / h~2.5km / h thereafter. When final rolling, turn off the vibration, statically press both sides, and eliminate the rolling wheel marks. During the rolling process, the number of times each part is rolled should be as equal as possible. After the rolling is completed, no vehicles are allowed to pass, and there should be no obvious color difference.

[0032] ⑤. Health preservation After the construction of the solidified soil is completed, it should be covered with film, geotextile and other materials for moisture maintenance. During the maintenance period, there should be no water accumulation on the surface of the solidified soil roadbed. The roadbed maintenance age should not be less than 7 days. During the entire maintenance period, the strength of the solidified soil is in a state of continuous growth. Before its maintenance reaches the required maintenance age, all types of vehicles should be prohibited from passing, especially heavy-loaded vehicles.

[0033] 8) The patent application number “201810985601.0”, “A river channel excavation construction process after mud blowing into land”, includes a foundation treatment stage, which includes shallow foundation treatment and deep foundation treatment.

[0034] The deep treatment of foundation treatment in this application adopts vacuum combined with preloading. Compared with the patent "A river channel excavation construction process after mud blowing into land" with application number "201810985601.0", it adds the steps of laying vacuum pipe network, laying non-woven fabric layer; laying sealing film, treating sealing ditch; installing vacuum equipment; vacuuming; laying upper non-woven fabric layer; laying upper sand cushion layer; installing monitoring instruments; laying geogrid, solidifying soil filling, etc.

[0035] Advantage 1: Accelerate the consolidation process Vacuum combined surcharge preloading increases the positive and negative pore water pressure difference and accelerates the rising and draining of pore water, thereby significantly accelerating the settlement process of soft soil foundation. Under the action of vacuum suction, the closed bubbles in the soil are easy to be discharged, which improves the permeability of the soil and further accelerates the consolidation process. This technology combines the advantages of vacuum preloading and surcharge preloading, making the soil consolidation faster. Compared with simple surcharge preloading, vacuum combined surcharge preloading can achieve the same consolidation effect in a shorter time.

[0036] Advantage 2: Shorten construction period Compared with traditional preloading, which requires preloading for up to one year or even several years after full loading to meet the bearing capacity and density requirements, vacuum combined preloading only requires vacuuming + loading for 4 months after full loading to meet the bearing capacity and density requirements, which greatly shortens the construction period and effectively reduces construction management costs.

[0037] Advantage 3: Cost saving Compared with traditional preloading, vacuum combined preloading can greatly shorten the construction period and effectively reduce the construction management cost. Secondly, the deep treatment of this application adopts vacuum combined preloading, which reduces the thickness of the load and the amount of load, and effectively saves the construction cost compared with the traditional pure preloading. In addition, this application adopts the loading method of solidified soil + slag construction in the subsequent loading process, and adjusts the amount of slag used for part of the loading to solidified soil. The unit price of solidified soil is much lower than the unit price of slag, which effectively saves the construction cost.

[0038] Advantage 4: Improve soil density and bearing capacity Under the condition of obtaining the same ground settlement, vacuum combined with preloading can obtain higher soil density than simple preloading method, because vacuum suction helps to discharge excess water and bubbles in the soil, making the soil more compact. With the increase of soil density, the bearing capacity of the foundation is also enhanced accordingly, which can better meet the engineering requirements for foundation bearing capacity.

[0039] Advantage 5: Wide range of applications Vacuum combined preloading is mainly suitable for soft soil foundations that can form stable negative pressure boundary conditions in the reinforcement area, such as silty soil, silt, plain fill, blown fill and flush fill, etc. For soils such as sand and fly ash, good reinforcement effects can also be achieved after taking appropriate measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 This is a construction profile diagram of shallow layer treatment in the present invention (A represents the center line of the road).

[0041] Figure 2 for Figure 1 A local enlarged schematic diagram of point B in the middle.

[0042] Figure 3 It is a construction flow chart of shallow layer treatment in the present invention.

[0043] Figure 4 This is a construction profile diagram of the deep layer treatment of the present invention (A represents the center line of the road).

[0044] Figure 5 for Figure 4 A partial enlarged schematic diagram of point C in the middle.

[0045] Figure 6 It is a construction flow chart of deep treatment in the present invention.

[0046] In the figure: drainage board 1, working cushion layer 2, vacuum pipe network 3, lower non-woven fabric layer 4, sealing membrane 5, longitudinal branch pipe 3.1, horizontal trunk pipe 3.2, sealing ditch 6, lower sand cushion layer 7, upper non-woven fabric layer 8, upper sand cushion layer 9, geogrid 10, road slag layer 11, natural soil-rock mixture layer 12. DETAILED DESCRIPTION

[0047] Example 1 This method is applied to the second phase of the shallow embankment treatment project in a certain city. The project area is a soft land foundation formed by silt blowing, which has the characteristics of high water content, high compressibility and poor permeability. And because the main construction content of this project is the roadbed treatment construction, the foundation treatment scheme of vacuum preloading without sand cushion layer + one-time vacuum combined loading preloading is adopted. Specifically including: The shallow treatment, with a total length of about 3km, was constructed using vacuum preloading of a sandless cushion layer, and the shallow reinforcement area was about 346,000 square meters.

[0048] The deep treatment is about 2.9km long (excluding the bridge area) and is carried out using a vacuum combined loading preloading method. The total treatment area is about 240,900 square meters.

[0049] like Figure 1-3 As shown, shallow processing includes the following steps: S1. Construction preparation.

[0050] Before the shallow layer treatment officially starts, the surface clearing work shall be completed, and relevant preparatory work such as material delivery, block boundary marking, and drawing of block pump layout map shall be completed.

[0051] S2. Clear the table.

[0052] Site clearing mainly includes surface clearing, demolition and removal of topsoil.

[0053] The surface clearing work includes the removal of weeds, shrubs, steel bars, hard solids, and surface fill soil. The average surface clearing thickness is tentatively set at 15cm. If there are large-scale shrubs, it is forbidden to cut them directly to avoid affecting the sealing membrane; measures may be considered to flatten the existing shrubs and lay 250g / m2 flat woven fabric for paving protection. The coverage of shrubs shall be based on actual occurrence.

[0054] Benefits of site clearing: Benefit 1: Enhanced stability. Soft soil foundations often have the problem of insufficient stability due to their high compressibility and low strength. During the surface clearing process, by removing weeds, plant roots, garbage and debris on the surface, the unstable factors in the foundation are reduced, providing a more solid foundation for subsequent reinforcement treatment. At the same time, the leveling of the site after surface clearing helps to reduce uneven settlement of the foundation, thereby significantly enhancing the overall stability of the foundation.

[0055] Benefit 2: Improved construction conditions. The site after clearing is flatter, providing convenient conditions for subsequent construction and the entry and exit of machinery and materials.

[0056] Benefit 3: Increase the safety of subsequent construction. By clearing the surface to eliminate the height difference of the ground, the site surface is flat, reducing the safety hazards of overturning and tipping during the subsequent plug-in construction process, and improving construction efficiency.

[0057] S3. Lay the working cushion layer.

[0058] After the surface is cleared, lay a layer of 150g / m2 woven cloth as a working cushion, which serves as a bearing layer and isolates silt.

[0059] In S3, the woven fabric is sewn with a portable industrial sewing machine, and is sewn into a whole by overlock or tack stitching. It is advisable to relax 3-4m according to the short side length of the block, and sew 2 straight sewing lines at the edge of the fabric for overlap. The overlap width of the stitching is not less than 200mm, without missing threads, skipped stitches, and wrinkles. Lead wire is not allowed to be used for interval binding.

[0060] In S3, the working cushion is laid, which specifically includes: S3.1: Rationally utilize the site to process materials and sew the woven fabric into large geotextiles that meet size requirements.

[0061] S3.2: In areas with deep silt and water levels, use the floating bridge channel to first lift the sewn woven cloth into the site, then use foam rowing and life jackets to spread the woven cloth out and lay it.

[0062] S3.3: Woven fabric must be laid straight (sewn edge facing down) with some drape.

[0063] S4. Insert the drain board.

[0064] The plastic drainage board used this time is a shallow plug-in board. The shallow soft foundation treatment adopts the "vacuum preloading method without sand cushion layer". The treatment depth is about 4m. The spacing between the drainage boards is 0.8m. They are arranged in a square. The preloading time must not be less than 70 days. The actual vacuuming time shall be based on the needs of the pile load preloading construction.

[0065] S4 inserts the drainage board, specifically including: S4.1: Before construction, stake out according to the design drawings and determine the boundary line of the construction scope.

[0066] S4.2: The core grooves of the plastic drain board should be evenly distributed and without lodging. The core must be free of holes, bubbles and smooth. The filter membrane should be processed with the core by an integrated hot melt process, flat, without wrinkles and loose sleeve detachment. The filter membrane fibers must be evenly distributed and free of lint. Other quality and inspection requirements of plastic drain boards should be implemented in accordance with JTS206-1-2009 "Technical Specifications for the Application of Plastic Drain Boards in Water Transport Engineering".

[0067] S4.3: Plastic drain panels must be randomly sampled on site and sent to the laboratory for performance testing, including longitudinal water flow, composite tensile strength, membrane tensile strength, membrane permeability and equivalent pore diameter. Drain panels should be properly protected on site to prevent sunlight, damage or contamination. Damaged or contaminated plastic drain panels shall not be used in the project. When constructing plastic drain panels, equipment that can detect their depth should be configured, and the depth should not be less than the design requirements.

[0068] S4.4: When constructing plastic drain boards, it is advisable to configure equipment that can detect their depth, and the depth shall not be less than the design requirements. The length of the inserted drain board should be higher than the ground surface (the partition using high-strength PVC spiral elastic steel wire hose should not be less than 50cm, and the partition using soft filter pipe should not be less than 30cm), the allowable deviation of the plane position of the plug board should not be greater than 70mm, and the verticality deviation should not be greater than 1.5%. When encountering boulders, boulders, etc., it is difficult to drill holes in situ, they can be moved and supplemented, and the displacement distance should not be greater than 30% of the spacing between drain boards; during winter construction, anti-freeze and anti-breakage measures should be taken for the drain board.

[0069] S4.5: The casing used in the construction of plastic drainage boards should ensure that the belt inserted into the foundation is not twisted. When the plastic drainage board needs to be extended, the connection method of flat overlap of the filter core belt should be adopted, and the overlap length should be greater than 200mm. Each "extended board" is only allowed to have one joint. The "extended boards" are used in a dispersed manner, and there is no joint between adjacent boards. The number of extended boards used shall not exceed 10% of the total number of installed boards.

[0070] S4.6: During the construction process, it is strictly forbidden for the plastic drainage board to be kinked, broken, or the filter membrane to be damaged; the length of the return belt during installation shall not exceed 500mm, and the number of return belts should not exceed 5% of the total number of roots.

[0071] S5. Lay the vacuum pipe network and the lower non-woven fabric layer.

[0072] S5.1: Lay vacuum pipe network.

[0073] S5.2: Bury monitoring instruments.

[0074] S5.3: Lay nonwoven fabric.

[0075] S5.1 Laying of vacuum pipe network includes: S5.1.1: Drain boards and filter tubes are cut manually in the material processing area. The length of each drain board and filter tube is determined according to the design requirements. The two ends of the drain board are sealed to prevent mud from entering the board head and blocking the drainage channel.

[0076] S5.1.2: Wrap the drain board around the filter tube and tie it with a cable tie to ensure direct contact between the drain board and the filter tube. When tying the drain board on the filter tube, the non-woven fabric with a specification of 200g / m2 and an external size of 30*40cm is required. The cable tie is 30-35cm long to ensure that the drain board does not slide on the filter tube after tying, and to ensure that the passage between the drain board and the filter tube is unobstructed.

[0077] S5.1.3: The tie-wrap joints between the drain plate and the filter pipe and pipeline should face downward to avoid damage to the sealing membrane.

[0078] S5.1.4: The filter pipes are soft and permeable, with a diameter of 40 mm. The spacing between main pipes is about 30 m, and the spacing between branch pipes is 0.8 m.

[0079] S5.1.5: The head of a single drain board is connected to the corresponding corrugated filter tube by winding to ensure that the head of the board is clean and that each drain board is effectively connected to the filter tube. The filter tube should be arranged to form a loop.

[0080] S5.1.6: The filter tube can be connected with two-way, three-way or four-way connections. The length of the filter tube is about 15 cm and it is tied tightly with wire. The wire joint is strictly prohibited from facing upwards and the connection needs to be wrapped with non-woven fabric.

[0081] Monitoring instruments buried in S5.2 include: After the drainage board is installed and before the non-woven fabric is laid, considering the monitoring needs during the vacuum pre-pressure and vacuuming stage, the monitoring instruments should be buried in time according to the designed position to ensure that the monitoring instruments are buried and protected after the drainage board construction is completed.

[0082] S5.3 provides for laying nonwoven fabrics, including: S5.3.1: After the monitoring instrument is buried and the filter pipe is laid, first, lay a layer of 150g / m2 woven cloth, and locally lay a layer of 250g / m2 woven cloth (if there is a large area of ​​shrubs below, it is forbidden to cut them directly to avoid affecting the sealing film. You can consider taking measures to flatten the existing shrubs and lay 250g / m2 flat woven cloth for paving protection. The coverage of the shrubs shall be based on the actual situation) to avoid damage during vacuuming. The requirements for laying woven cloth are the same as above.

[0083] S5.3.2: Then, manually lay a layer of 200g / m2 non-woven geotextile. The non-woven geotextile and the filter tube form a horizontal drainage channel, while ensuring that the sealing membrane will not be damaged by the three-way joints of the filter tube. When laying the non-woven geotextile, maintain a certain wrinkle to reserve vacuum preload settlement.

[0084] The non-woven geotextiles are overlapped with each other, and the overlap width is not less than 200mm (the overlap between each piece of non-woven fabric is overlapped or slit, and the factory stitching width is not less than 50mm; the on-site stitching overlap width is not less than 200mm).

[0085] S5.3.3: After the non-woven geotextile is laid, there should be no damage. If there is any damage, it should be repaired with the same material.

[0086] S6. Lay the sealing membrane and treat the sealing groove.

[0087] S6.1: Lay two layers of sealing film on the non-woven fabric with a thickness of 0.14mm. The sealing film is heat-formed once in the factory according to the design; when laying the film, ensure that there is no hard object under the film, and do not pull it hard to avoid excessive local force to damage the sealing film. After laying, the film needs to be slightly relaxed to avoid large differential settlement causing the sealing film to tear.

[0088] S6.2: Manual membrane stepping and excavation of sealing trenches are used around the partitions to bury the sealing membrane deep in the silt to ensure the sealing around the partitions. When stepping on the membrane, first the inner membrane and then the outer membrane, one person for maintenance and one person for stepping. Strengthen management during vacuuming, cover the sealing trench with water as needed, and step on the membrane repeatedly to ensure the sealing effect.

[0089] S6.3: The depth of the vacuum membrane buried in the impermeable layer shall not be less than 1.0m. The reserved spacing between adjacent sealing trenches (i.e. the sealing trench range) should be 50 to 100cm to ensure the airtightness of the sealing trench. If necessary, the sealing trench should be backfilled with clay.

[0090] S6.4: The vacuum pump joints, sedimentation rod joints, vacuum gauges, pore water pressure, etc. are sealed to prevent air leakage from the membrane surface during vacuuming.

[0091] S6.5: Strengthen the protection of the sealing membrane. During vacuuming, check the membrane surface frequently and repair any leaks in time.

[0092] S7. Install the vacuum system, evacuate the air, and conduct on-site observation.

[0093] S7.1: Arrange the vacuum pump (7.5kw) according to the design requirements, connect the main filter pipe to the vacuum pump through the film outlet and the water suction hose, install the vacuum pump system (connect the water pump, water tank, gate valve, stop valve, and film outlet), connect the circuit from the distribution box in the electrical room → the leakage switch box at the vacuum pump → the vacuum pump, and debug the vacuum jet pump without load. When the vacuum degree on the vacuum jet pump reaches 85kPa or above, try to evacuate the vacuum for about 10 days. Carefully check for air leakage on the membrane surface and the film pressing groove, and repair it in time if found.

[0094] S7.2: Maintain a certain pump-on rate, and the vacuuming time shall not be less than 70 days according to the design requirements. After reaching the design unloading standard, the effect test can be arranged.

[0095] S8. Check the soft foundation treatment effect, unload and level the site.

[0096] S8.1: At the later stage of vacuuming, after the in-situ observation of the average daily settlement of the surface reaches the design requirements, relevant geotechnical tests can be arranged to test the effect. Common tests include drilling holes to take soil samples and indoor geotechnical tests.

[0097] S9. Layout of film pressing grooves.

[0098] S9.1: Divide the area according to different vacuum processes and excavate the film pressing trench along the edge of the vacuum partition. To ensure the overall vacuum effect, reduce the number of excavated intermediate film pressing trenches as much as possible.

[0099] S9.2: The excavation depth of the film-forming trench shall be not less than 1m. If there is a sandy surface soil area, the bottom of the film-forming trench must also be at least 0.5m into the silt layer. If there is a highly permeable interlayer, it should be excavated and backfilled with 30~50cm thick soft clay.

[0100] S9.3: The width of the trench bottom is 0.5-1.0m, and the width of the top of the film-pressing trench is 1.7m.

[0101] S9.4: The surface of the trench shall be smooth. After the sealing membrane is spread on the surface of the trench, it shall be backfilled with clay soil (excavated soil may be used for backfill). The soil shall not contain sharp objects such as gravel, boulders, and debris.

[0102] Deep processing includes the following steps: S1. Level the site.

[0103] S2. Lay the working cushion (woven cloth).

[0104] S3. Lay the lower sand cushion layer.

[0105] The thickness of the lower sand cushion is 50cm. The laying of the sand cushion is assisted by surveyors to conduct measurement and observation for elevation control. The thickness must be laid evenly to prevent affecting the subsequent construction process. When treating the foundation, the horizontal drainage cushion layer uses a sand cushion with a thickness of not less than 50cm, a mud content of ≤5%, a particle size of ≥0.075mm and a particle content of more than 50%. The dry density of the sand cushion should be greater than 1.5t / m3, and the permeability coefficient should be greater than 5x10-3cm / s.

[0106] During the construction of the sand cushion layer, poles are densely laid out in the block, and elevation markings are made according to the calculated control elevation (the influence of settlement and consolidation factors must be considered). A 30m×30m grid is used to ensure that there are accurate reference marks for the sand elevation nearby.

[0107] S4. Install drainage board.

[0108] In S4, the plastic drain board of this project adopts C-type drain board, which is arranged in a square with a spacing of 0.8m. The length of the plastic drain board is 21m and 18m. The plastic drain board is to be installed by casing installation method and use casing boots; the cross-sectional shape, size and material and type of casing boots should meet the requirements of casing strength and rigidity such as verticality and depth, and reduce disturbance to the foundation. The material of the casing boot can be steel plate, steel bar, concrete or hard plastic, and the type can be determined according to the test.

[0109] In S4, drainage boards are installed, including: S4.1: Plate position layout and positioning Onshore, according to the control points of the local area, use a steel ruler to lay out the specific position of each drainage board in the vertical and horizontal directions according to the design requirements, and then mark each position (the plate core can be used as the position of the plate inserter). When actually setting the position, the deviation between the pipe shoe and the plate position mark should be controlled within ±70mm.

[0110] S4.2: Selection of conduit The drainage board of this project adopts circular conduit. Since the drainage board is C-shaped, the lower part of the conduit is pressed into a slightly flat shape, and a conduit boot of similar shape and slightly larger is put on its outer cover. The conduit boot is made of iron and tied to the conduit with a small chain, so that the conduit can be reused. The pile tip for fixing the drainage board adopts the form of inverted trapezoidal wedge extrusion connection.

[0111] S4.3: Control of the verticality of the conduit Before and during construction, the verticality of the conduit of the plugging machine should be checked and adjusted regularly with two theodolites. When sinking the casing, the verticality of the casing should not exceed 1.5%. The casing used in the construction of plastic drainage boards should ensure that the belt inserted into the foundation is not twisted.

[0112] S4.4: The connection between the drain board and the pile tip is to insert the plastic drain board into the conduit through the pull rope and fold the head of the drain board back. The connection between the drain board and the pile tip relies on a conical or round wedge (pin) to clamp the drain board, which acts as an anchor for the bottom end of the drain board, so that the sinking of the conduit drives the sinking straightness of the drain board to be checked and adjusted.

[0113] S4.5: Lifting of the conduit The depth of the conduit for the drainage board of this project is determined according to the depth of the drainage board. After the drainage board is installed to the design elevation by measuring and testing, the conduit is lifted. During the lifting of the conduit, pay attention to the back-up of the drainage board. During the installation process, the back-up length of the drainage board shall not exceed 500mm, and the number of back-ups shall not exceed 5% of the total number of installed roots, otherwise additional holes shall be drilled at adjacent board positions. When encountering boulders, boulders, etc., it is difficult to drill holes in situ, and the displacement distance shall not be greater than 30% of the spacing between the drainage boards; during winter construction, anti-freezing and anti-breaking measures shall be taken for the drainage board.

[0114] S4.6: Extension of drainage board Due to the large number of drainage boards in general projects, the drainage boards are in disc shape before construction, and the length of each drainage board is generally 200m. It is not guaranteed that all drainage boards driven into the foundation are whole boards, so some drainage boards need to be extended during the construction process. When the plastic drainage belt needs to be extended, the connection method of flat overlap of the inner core of the filter membrane should be adopted. The overlap length should be greater than 200mm. Each "extension board" is allowed to have only one joint. The "extension boards" are used in a scattered manner, and there is no joint between adjacent boards. The use of "extension boards" does not exceed 10% of the total number of roots. When extending, first peel off the filter membrane of the two drainage boards, connect the board core directly, and then put them together, and then tie them firmly with thin wire or plastic rope. Each drainage board pile is allowed to be extended only once. The number of extensions meets the design requirements. It is strictly forbidden to have kinks, breaks and tearing of the filter membrane during the application of plastic drainage boards. If this happens, it should be re-inserted near the insertion point. The bottom elevation of the plastic drainage board must meet the design requirements. If it is found during the construction process that the design elevation cannot be reached, geological surveys should be conducted in the nearby local area in a timely manner, and the designers should be contacted to discuss solutions.

[0115] S4.7: Inspection and protection work: After each drain board is installed, the exposed part must not be contaminated. After passing the inspection, the soil around the drain board should be removed in time.

[0116] S5. Lay the vacuum pipe network and the lower non-woven fabric layer.

[0117] In the process of laying vacuum pipe network, the laying of vacuum pipe network, buried monitoring instruments and non-woven fabrics are the same as the shallow treatment construction process. The difference is the treatment measures of vacuum pumps when loading in deep treatment. The specific measures are as follows: Pipe introduction: Since the subsequent construction of vacuum combined loading preloading requires loading within the block, the vacuum pump needs to be arranged at the block boundary close to the sealing ditch during the vacuum combined loading preloading construction. When laying the vacuum pipeline, it is necessary to arrange the membrane outlet at the position of the vacuum pump in the pipe and pump layout diagram in advance, pull the main pipe to the block boundary, and install the vacuum pump after laying the vacuum membrane to connect the main pipe.

[0118] S6. Lay the sealing film and treat the sealing groove.

[0119] S7. Install vacuum equipment.

[0120] S8. Vacuum.

[0121] S9. Lay the non-woven fabric layer.

[0122] S10. Lay the upper sand cushion layer.

[0123] The thickness of the upper sand cushion layer is 50cm, which is consistent with the construction requirements and processes of the sand cushion layer (lower layer).

[0124] S11. Install monitoring equipment.

[0125] S12. Lay geogrid.

[0126] S12.1: The laying surface of the geogrid should be relatively flat to prevent longitudinal skew. First, draw a white line or hanging line on the paving layer according to the width, then start paving, and then fix the ends of the grid (fix at a uniform distance).

[0127] S12.2: When laying geogrids, they should be straightened and smooth, close to the base surface, and the upper geogrid should be fixed to the foundation every 2 to 2.5 m. The geogrid should be tied with plastic tape along the transverse joints.

[0128] S12.3: Joint laying: The length of the roll is used as the section length for laying. After the section length of the geogrid is fully laid, the laying quality is checked again as a whole, and then the next section is laid. The connection of the geogrid is constructed by overlapping. To ensure its integrity, the overlapping width is not less than 500mm and not less than 3 grids, and the overlapping range should be tied tightly.

[0129] S12.4: After a section of geogrid is laid, use 25-50 kg sand bags to press and secure the geogrid at the overlap and edges.

[0130] S12.5: To prevent damage to the geogrid, the surface of the underlying foundation should be flat and free of hard protrusions such as gravel and boulders.

[0131] S13, loading construction.

[0132] In S13, the loading is layered and graded, and the loading is controlled according to the design elevation of the loading section. During construction, the loading rate will be controlled based on the on-site monitoring data and the following control standards.

[0133] In S13, the material requirements are as follows: the particle size of backfill materials should be <15cm, the liquid limit of solidified soil should be <50%, the plasticity index should be <26, and the minimum strength CBR should be >3%. The particle size of slag within 80cm of the roadbed of permanent roads should be ≤10cm, and the mud content should not exceed 15%. The minimum strength CBR within 0~0.3m below the roadbed is 8%, and the minimum strength CBR within 0.3~0.8m below the roadbed is 5%.

[0134] The roadbed filling material is used as the permanent roadbed. The road slag has a bulk density of y=1.8~2.1t / m3, the stone strength contained in the natural soil-stone mixture is>20Mpa, the particle size is not more than 15cm, and the mud content is <10%. During the construction period, attention should be paid to roadbed drainage, and appropriate road cross slopes should be reserved to facilitate roadbed drainage.

[0135] In S13, the loading construction includes: Before the preloading is completed to a depth of 50 cm, the compaction requirements can be appropriately reduced depending on the actual situation. The loading materials for this project are mountain materials, which are transported to the temporary dock by water and then transported to the site by dump trucks. During the preloading construction, dump trucks will transport the loading materials to the construction area for stacking. At the same time, excavators and forklifts are arranged to spread the loading materials. The paving operation is carried out in layers, and the loading stabilization time must meet the requirements of the bidding documents and design. During the loading process, the loading area is tested and inspected in strict accordance with the requirements of the bidding documents and design specifications to ensure the quality of the project. The preloading is a layered and graded loading, and the loading height is controlled according to the design section drawing. During construction, the loading rate must be controlled according to the on-site monitoring data and the following control standards.

[0136] 1) Loading should be graded and layered, and the roadbed must be filled and compacted in layers. The maximum paving thickness of each layer should generally not exceed 40cm, and the loading should be uniform.

[0137] 2) The compaction of the roadbed shall be based on the heavy compaction standard and shall meet the relevant requirements of the "Urban Road Engineering Design Code (2016 Edition)" (CJJ37-2012). Heavy vibrating rollers shall be used for layered compaction of the roadbed in general sections; for areas with narrow sites, small compactors shall be used to cooperate with the construction to meet the compaction requirements.

[0138] 3) The preloading should be carried out in stages, and the loading rate is controlled by three indicators: settlement rate, horizontal displacement, and pore water pressure coefficient. The roadbed loading rate should meet the following requirements: ① The settlement of the center of the embankment shall not exceed 15mm per day and night; ② Horizontal displacement observation: horizontal displacement rate <4mm / d; ③ Pore water pressure coefficient (ratio of pore water pressure increment to load increment): B≤0.6; 4) During roadbed filling, if the settlement rate or horizontal displacement index does not meet the requirements, loading should be stopped immediately, and loading can only be resumed after the roadbed is stable according to the monitoring data analysis. If the roadbed stability still cannot meet the design requirements after slowing down the loading rate, measures such as counter-pressure protection should be added.

[0139] In S13, uninstallation criteria (satisfied simultaneously): 1) The average degree of consolidation is greater than 85%.

[0140] 2) When the pump opening rate is not less than 80%, the vacuum degree is not less than 85Kpa and the pile is fully loaded, the measured ground settlement rate is less than or equal to 2mm / d for 10 consecutive days.

[0141] 3) The calculated post-construction settlement of the road meets the design requirements.

[0142] 4) Do a good job of drainage.

[0143] The water pumped out by vacuum preloading should be discharged outside the project area. The drainage path can be a temporary drainage ditch excavated 5m outside the foot of the roadbed slope. The temporary earth ditch is in the form of a trapezoidal ditch. The bottom width of the drainage ditch is 50cm, the depth is 60cm, and the surface width is 2.9m. It is excavated at a slope of 1:2 and connected to the temporary river channel in the existing area. The water discharged by the foundation consolidation will seep into the drainage ditch through the cushion layer and flow along the drainage ditch to the river channel. The excavation of the temporary drainage ditch should ensure that there is no water accumulation in the roadbed and the drainage is unobstructed. When the drainage is not smooth, combined with the actual needs of the project construction, water collection wells are arranged along the temporary drainage ditch, and the spacing should be 200m to meet the needs of forced drainage. The size of the water collection well is excavated according to the actual needs of the current situation.

[0144] The construction techniques of leveling the site, laying woven cloth, installing drainage boards (mechanically), laying vacuum pipe networks and non-woven geotextiles, laying sealing membranes, treating sealing ditches, installing vacuum systems, vacuuming, laying non-woven fabrics (secondary) and other deep treatments are similar to those of shallow treatments, and the similarities will not be repeated here.

Claims

1. A construction method for layered treatment of roadbed, characterized in that: Includes superficial treatment and deep treatment; The shallow layer treatment includes construction preparation, surface clearing, laying of working cushion, installation of drainage board, laying of vacuum pipe network and lower non-woven fabric layer, laying of sealing film, treatment of sealing ditch, installation of vacuum system, vacuuming, in-situ observation, soft foundation treatment effect detection, unloading, site leveling, and film pressing ditch layout. The deep treatment includes leveling the site in sequence; laying the working cushion layer; laying the lower sand cushion layer; inserting drainage boards; laying the vacuum pipe network and the lower non-woven fabric layer; laying the sealing film and treating the sealing ditch; installing vacuum equipment; vacuuming; laying the upper non-woven fabric layer; laying the upper sand cushion layer; installing monitoring instruments; laying geogrids; and loading construction.

2. A construction method for layered treatment of roadbed according to claim 1, characterized in that: The construction process of leveling the site, laying woven cloth, inserting drainage boards, laying vacuum pipe networks and non-woven geotextiles, laying sealing membranes, treating sealing ditches, installing vacuum systems, vacuuming, and laying non-woven fabric layers in the deep treatment is consistent with the construction process of shallow treatment.

3. A construction method for layered treatment of roadbed according to claim 2, characterized in that: Insert the drainage board, including: S1: According to the control points of the local area, use a ruler to place the specific position of each drainage board in the vertical and horizontal directions according to the spacing required by the design, and then mark each position. These marks serve as the position of the board inserting machine; S2: The conduit is a round conduit, and the conduit boot is made of iron and is tied to the conduit with a small chain; the pile tip for fixing the drainage board adopts the form of inverted trapezoidal wedge extrusion connection; S3: Before and during construction, use a theodolite to check and adjust the verticality of the guide tube of the plate inserter. When sinking the casing, the verticality of the casing should not exceed 1.5%; the casing used in the construction of the drainage board should ensure that the belt inserted into the foundation is not twisted; S4: Connection between the drain board and the pile tip: insert the drain board into the conduit through the pull rope and fold the head of the drain board back. The connection between the drain board and the pile tip relies on a conical or circular wedge to clamp the drain board; S5: The depth of the conduit buried in the ground is determined according to the depth of the drainage board. After the drainage board is installed to the designed elevation by measuring and testing, the conduit is lifted. During the lifting of the conduit, the back-up of the drainage board is observed. During the installation process, the back-up length of the drainage board shall not exceed 500mm, and the number of back-up roots shall not exceed 5% of the total number of roots installed, otherwise additional holes shall be drilled at adjacent board positions. When encountering boulders and boulders, it is difficult to drill holes in situ, and the displacement distance shall not be greater than 30% of the spacing between drainage boards. During winter construction, anti-freezing and anti-breakage measures shall be taken for the drainage board. S6: Due to the large number of drainage boards in the project, the drainage boards are in disc shape before construction. Some drainage boards are extended during the construction process. When the plastic drainage belt needs to be extended, the connection method of flat overlap of the inner core of the filter membrane is adopted. The overlap length should be greater than 200mm. Each "extended board" is only allowed to have one joint. The "extended boards" are used in a scattered manner, and there is no joint between adjacent boards. The use of "extended boards" does not exceed 10% of the total number of roots. When extending, first peel off the filter membranes of the two drainage boards, connect the board cores directly, then put them together, and then tie them securely. Each drainage board pile is only allowed to be extended once at most. If it is found during the construction process that the design elevation cannot be constructed, geological exploration of the nearby local area should be carried out in time, and the designer should be contacted to discuss solutions; S7: After each drain board is installed, the exposed part must not be contaminated; after passing the inspection, the soil around the drain board should be cleaned up in time.

4. A construction method for layered treatment of roadbed according to claim 2, characterized in that: When laying the vacuum pipe network, the drain board and filter tube are cut and the two ends of the drain board are sealed; the drain board is wrapped around the filter tube and tied to ensure direct contact between the drain board and the filter tube. After tying, the drain board shall not slide on the filter tube, and the passage between the drain board and the filter tube shall be unobstructed; the tie tape joints between the drain board and the filter tube and the pipeline shall face downward; the filter tube shall be soft and permeable; the head of a single drain board and the corresponding corrugated filter tube shall be connected by winding, and the filter tube shall be arranged to form a loop; the filter tube shall be connected with two-way, three-way and four-way connections, and the connection shall be wrapped with non-woven fabric.

5. A construction method for layered treatment of roadbed according to claim 2, characterized in that: In deep treatment, the thickness of the lower sand cushion layer and the upper sand cushion layer are both 50cm. The laying of the lower sand cushion layer and the upper sand cushion layer is assisted by surveying personnel to conduct measurement and observation for elevation control. The thickness must be laid evenly to prevent affecting the subsequent construction processes. During foundation treatment, the horizontal drainage cushion layer uses a sand cushion layer with a thickness of not less than 50cm, a mud content of ≤5%, a particle content of more than 50% with a particle size of ≥0.075mm, a dry density of more than 1.5t / m3, and a permeability coefficient greater than 5x10-3cm / s.

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