An active dewatering subgrade structure and construction method for reconstructed and expanded highways by region

Abstract

The present invention discloses a sub-region active dehydration roadbed structure for reconstructed and expanded highways and a construction method. The old roadbed and the new roadbed are spliced through a stepped excavation section. A capillary blocking layer is laid at the bottom of the new roadbed. Multiple layers of conductive core-suction basalt fiber geotextiles are laid at intervals in the new roadbed. One end of the conductive core-suction basalt fiber geotextiles is embedded in the old roadbed, and the conductive core-suction basalt fiber geotextiles connected to the positive and negative poles of the DC power supply are arranged alternately in the vertical direction. Time domain reflectometry sensors are buried between every two layers of conductive core-suction basalt fiber geotextiles at the lower part of the joint between the new and old roads. The time domain reflectometry sensors are communicatively connected to the controller of the DC power supply and are used to control the connection or disconnection of the DC power supply and the corresponding conductive core-suction basalt fiber geotextiles. The present invention has both the functions of active dehydration and roadbed reinforcement and can effectively prevent and control diseases such as frost heave, differential settlement, and pumping and muddying caused by freeze-thaw cycles in the reconstruction and expansion projects in seasonal frozen areas.

Description

Technical Field

[0001] The invention belongs to the technical field of road engineering, and relates to a subgrade structure with active dehydration in different regions for reconstructed and expanded highways and a construction method thereof. Background Art

[0002] With the development of China's economy, the traffic volume of highways has been increasing year by year. Most of the two-way four-lane expressways cannot meet the current increasing traffic volume, and it is inevitable to widen the existing highways. Traditional highway reconstruction and expansion projects adopt various methods such as stepped excavation at the joint, geogrid reinforcement, subgrade dynamic compaction, surcharge preloading, replacement with lightweight subgrade fillers, and pile-supported foundations in soft soil areas. The reconstruction and expansion projects of expressways in seasonal frozen regions face more complex conditions. On the one hand, the highway itself is under the action of freeze-thaw cycles, large temperature differences, and long-term continuous low temperatures, which directly restricts the stability and durability of the subgrade and pavement. On the other hand, there are differences in the particle composition, water content, and soil strength of the old and new subgrade fills, as well as the properties and consolidation degrees of the natural foundations under the old and new subgrades. Under the action of subgrade self-weight, traffic load, and natural environment, diseases such as differential settlement, pumping mud, and cavities between the old and new subgrades are likely to occur, affecting driving safety and highway durability, and also increasing the maintenance cost during the highway operation period.

[0003] Traditional methods for controlling differential settlement of reconstructed and expanded subgrades are mainly based on subgrade and pavement mechanics, and do not consider the effects of subgrade frost heave, water migration between the old and new subgrades, etc. on the differential settlement of reconstructed and expanded highways in cold regions. Both indoor tests and actual projects have proved that the method of replacing with coarse-grained soil can only reduce frost heave and cannot eliminate water migration. The strength and deformation characteristics of subgrade soil decrease significantly with the increase of water content. The migration and accumulation of water are also the main inducements for subgrade frost heave in cold regions. The difference in water content between the old and new subgrades is one of the factors causing differential settlement. Therefore, how to effectively control the water content of the old and new subgrades in seasonal frozen regions is one of the key problems that need to be solved urgently to prevent diseases such as differential settlement, frost heave, and pumping mud of reconstructed and expanded highways.

[0004] The differential frost heave between the old and new subgrades is a thorny problem faced by reconstruction and expansion projects in seasonal frozen regions. Negative temperature, frost-sensitive soil, and water supply are the necessary conditions for subgrade frost heave. Traditional frost heave prevention methods (such as replacement, insulation method, etc.) have problems such as high transportation and construction costs, poor stability and durability, and cannot effectively drain the capillary water in the subgrade soil, so they cannot effectively prevent subgrade frost heave. The differential settlement between the old and new subgrades in reconstruction and expansion projects is mainly caused by the differences in water content, soil strength, and consolidation degree of the old and new subgrade fills. In most cases, the water content of the old subgrade soil is higher than that of the new subgrade soil. Summary of the Invention

[0005] To solve the above problems, the present invention provides a sub-region active dewatering roadbed structure for reconstructed and expanded highways, which has both the functions of active dewatering and roadbed reinforcement, and can effectively prevent and control diseases such as frost heaving, differential settlement, and pumping and mud gushing caused by freeze-thaw cycles in the reconstructed and expanded projects in seasonal frozen regions.

[0006] Another object of the present invention is to provide a construction method for a sub-region active dewatering roadbed structure of a reconstructed and expanded highway.

[0007] The technical solution adopted by the present invention is a sub-region active dewatering roadbed structure for reconstructed and expanded highways. The old roadbed and the new roadbed are spliced through a stepped excavation section. A capillary barrier layer is laid at the bottom of the new roadbed. Multiple layers of conductive wicking basalt fiber geotextiles are laid at intervals in the new roadbed. One end of the conductive wicking basalt fiber geotextile is embedded in the old roadbed, and the conductive wicking basalt fiber geotextiles respectively connected to the positive and negative poles of the DC power supply are arranged alternately in the vertical direction; Time domain reflectometry sensors are buried between every two layers of conductive wicking basalt fiber geotextiles at the lower part of the joint between the old and new roads. The time domain reflectometry sensors are communicatively connected to the controller of the DC power supply and are used to control the connection or disconnection of the DC power supply and the corresponding conductive wicking basalt fiber geotextile.

[0008] Further, the conductive wicking basalt fiber geotextile is obtained by longitudinally and transversely weaving conductive wicking basalt fibers. The conductive wicking basalt fiber is obtained by coating a carbon black coating with a thickness of 0.1 - 5μm on the surface of the wicking fiber, and the wicking fiber is a continuous basalt fiber.

[0009] Further, the cross-section of the conductive wicking basalt fiber is circular, cross-shaped, three-leaf-shaped, H-shaped or T-shaped.

[0010] Further, the diameter of the conductive wicking basalt fiber is 5 - 20μm, and the tensile strength of the conductive wicking basalt fiber is 2.5 - 3GPa.

[0011] Further, the width of the conductive wicking basalt fiber geotextile extending into the old roadbed is at least 1.0m to ensure that the conductive wicking basalt fiber absorbs moisture from the old roadbed.

[0012] Further, the resistivity of the conductive wicking basalt fiber does not exceed 10 -3 Ω·m.

[0013] Further, the distance between adjacent two layers of the conductive wicking basalt fiber geotextiles is not less than 0.3m.

[0014] Further, the capillary barrier layer is sandy soil or gravel, and an anti-filter layer is laid between the capillary barrier layer and the underlying foundation.

[0015] Furthermore, the top of the old roadbed is the old surface layer, and a lap section with a width of 50 - 100 cm is reserved on the old surface layer.

[0016] A construction method for a regional active dewatering roadbed structure of a reconstructed and expanded highway includes the following steps:

[0017] S1, Clear the surface of the original ground and compact it before filling.

[0018] S2, Lay a capillary barrier layer on the foundation.

[0019] S3, Lay a new roadbed on the capillary barrier layer and compact it. The filler of the new roadbed is the same as that of the old roadbed.

[0020] S4, Lay a conductive core-suction basalt fiber geotextile in the new roadbed, ensuring that at least 1 m of one end of the conductive core-suction basalt fiber geotextile is embedded in the old roadbed, and the fiber axis of the conductive core-suction basalt fiber geotextile is perpendicular to the road driving direction.

[0021] S5, Connect the old roadbed and the new roadbed through a stepped excavation section.

[0022] S6, Repeat steps S3 - S5, lay multiple layers of conductive core-suction basalt fiber geotextiles at intervals in the new roadbed. The conductive core-suction basalt fiber geotextiles connected to the positive and negative poles of the DC power supply are arranged alternately in the vertical direction. Time domain reflectometry sensors are buried between every two layers of conductive core-suction basalt fiber geotextiles at the lower part of the joint between the new and old roads. The time domain reflectometry sensors are communicatively connected to the controller of the DC power supply, and are used to control the connection or disconnection of the DC power supply and the corresponding conductive core-suction basalt fiber geotextile. As the water content of the subgrade soil decreases, the electroosmotic drainage efficiency of the conductive core-suction basalt fiber geotextile gradually decreases. When the water content of the subgrade soil is lower than the threshold, disconnect the connection between the DC power supply and the corresponding conductive core-suction basalt fiber geotextile.

[0023] The beneficial effects of the present invention are:

[0024] 1. The subgrade structure proposed in the embodiments of the present invention has three functions: electroosmotic drainage, wicking active dehydration, and subgrade reinforcement, and can effectively prevent and control diseases such as frost heave, differential settlement, and pumping and mud boiling in the reconstruction and expansion projects in seasonal frozen regions. By using conductive wicking basalt fiber geotextiles, the problems of surface corrosion and potential loss existing in traditional electroosmotic methods using metal electrodes are overcome; at the same time, the micron-scale fiber filaments have strong surface tension and can play a wicking role, absorb moisture from the surrounding soil, and timely export the moisture electroosmotically migrated to the cathode vicinity, balance the moisture difference between the new and old subgrade soils, and effectively block the moisture supply for subgrade frost heave, effectively alleviating the uneven frost heave caused by the moisture content difference between the new and old roads. The conductive wicking basalt fiber geotextiles can enhance the shear strength at the connection of the new and old subgrades, effectively disperse the traffic load in the working area, avoid plastic deformation of the subgrade soil, and reduce the settlement difference between the new and old subgrades.

[0025] 2. According to the information fed back by the water content sensors in different regions, control the local opening and closing of the electroosmotic drainage system in that region to achieve targeted regulation of the moisture distribution in each region of the subgrade. When the water content in a certain region is low, the electroosmotic efficiency will also decrease accordingly, and the system will automatically stop working without manual operation, which can effectively solve the problem of high energy consumption in traditional electroosmotic methods and improve the energy utilization efficiency. In addition, the conductive wicking basalt fiber geotextiles can serve as both the cathode and the anode, and the two-way migration of moisture can be achieved through the conversion of the electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings without creative efforts based on these drawings.

[0027] Figure 1a It is a schematic diagram of the subgrade diseases before reconstruction and expansion in the seasonal frozen region.

[0028] Figure 1b It is a schematic diagram of the subgrade diseases after formation in the reconstruction and expansion in the seasonal frozen region.

[0029] Figure 2 It is a structural diagram of the active dehydration subgrade of the reconstructed and expanded highway in the seasonal frozen region in the embodiments of the present invention.

[0030] Figure 3 It is a schematic diagram of the conductive wicking basalt fiber structure.

[0031] Figure 4 It is a schematic diagram of the drainage of the active dehydration subgrade in the saturated state in the embodiments of the present invention.

[0032] Figure 5Schematic diagram of active dewatering subgrade drainage in the unsaturated state of the embodiment of the present invention.

[0033] In the figure, 1. Old surface layer, 2. New surface layer, 3. Joint of old and new roads, 4. Old subgrade, 5. New subgrade, 6. Road surface crack, 7. Saturated base layer, 8. Vehicle dynamic load, 9. Mud pumping, 10. Cavity, 11. Foundation, 12. Capillary retardation layer, 13. Conductive wicking basalt fiber geotextile, 14. Time domain reflectometry sensor, 15. Step excavation section, 16. DC power supply, 17. Carbon black coating, 18. Wicking fiber, 19. Fiber shaft, 20. Moisture migration in the old subgrade, 21. Moisture migration in the new subgrade, 22. Moisture migration in the capillary geotextile, 23. Infiltration moisture migration. Specific embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0035] Basic concept of the embodiment of the present invention:

[0036] As Figure 1a-1b shown, an old surface layer 1 is provided at the top of the old subgrade 4, a new surface layer 2 is provided at the top of the new subgrade 5, and the joint 3 of the old and new roads is between the old surface layer 1 and the new surface layer 2. During the service period of the cold region road, it is subjected to freeze-thaw cycles, large temperature differences and long-term continuous low temperature effects, and the stability and durability of the road face severe challenges.

[0037] The non-uniformity of the soil quality, moisture and freezing conditions of the old subgrade 4 and the new subgrade 5 results in uneven frost heave during the freezing process. Generally speaking, during the service period of the old subgrade 4, affected by rainfall infiltration and capillary water rise, its water content is higher than that of the soil of the new subgrade 5. The joint 3 of the old and new roads is a weak surface of the seasonal frozen region road structure. The uneven settlement of the old and new subgrades causes the road surface to crack. During spring thawing, snowmelt and rainfall infiltrate into the base layer through the road surface crack 6. Due to the unthawed lower subgrade soil causing poor drainage, a saturated base layer 7 is gradually formed below the road surface crack 6 and above the thawing front. The saturated base layer 7 generates instantaneous excess pore water pressure under the action of the vehicle dynamic load 8, and the fine particles in the subgrade soil are separated from the subgrade soil as the pore pressure dissipates, causing the disease of mud pumping 9 ( Figure 1b). The fine particles in the subgrade soil detach, causing rainwater to backflow along the pavement crack 6, resulting in a larger area of the subgrade soil being in a saturated state. As the service life of the road increases, under the repeated actions of freeze-thaw cycles and vehicle loads, the structure of the subgrade soil becomes loose, leading to the occurrence of cavity 10 diseases. However, traditional reconstructed and expanded highways often adopt methods such as geogrid reinforcement, subgrade dynamic compaction, surcharge preloading, and replacement of lightweight subgrade fillers at the joint 3 between the new and old roads, which cannot effectively control the water accumulation problem at the joint. Therefore, the most fundamental and effective method to prevent diseases such as differential settlement and pumping mud 9 in reconstructed and expanded projects in seasonal frozen areas is to improve the water migration conditions.

[0038] Example 1,

[0039] A subgrade structure for actively dewatering different regions of a reconstructed and expanded highway, as Figure 2 shown, the old subgrade 4 and the new subgrade 5 are spliced through a stepped excavation section 15. The stepped excavation section 15 adopts a multi-step form with wide and gentle platforms and low heights. The old surface layer 1 reserves a lap section with a width of 50 - 100 cm, and the lap is located at the new subgrade 5.

[0040] Multiple layers of conductive core-suction basalt fiber geotextiles 13 are laid at intervals in the new subgrade 5. One end of the conductive core-suction basalt fiber geotextile 13 is embedded in the old subgrade 4, sucking out the excess water in the old subgrade 4 soil with high water content and laterally migrating it, making the water content of the new and old subgrades approximately the same, ensuring the balance of the water content of the new and old subgrades, and thus alleviating the differential settlement between the new and old subgrades.

[0041] The conductive core-suction basalt fiber geotextiles 13 connected to the positive and negative poles of the DC power supply 16 are arranged alternately vertically; a time domain reflectometry sensor 14 is buried between every two layers of conductive core-suction basalt fiber geotextiles 13 at the lower part of the joint 3 between the new and old roads. The time domain reflectometry sensor 14 is communicatively connected to the controller of the DC power supply 16, and is used to control the connection or disconnection of the DC power supply 16 and the corresponding conductive core-suction basalt fiber geotextile 13. Through the time domain reflectometry sensor 14, the water content of the subgrade soil at the joint is monitored in different regions for a long time, and at the same time, as the controller determines the working states of the positive and negative electrodes in each region, the zonal regulation of the water content of the subgrade soil is realized, effectively avoiding the problems of low electroosmosis efficiency and poor drainage under the unsaturated state.

[0042] A capillary barrier layer 12 is laid at the bottom of the new subgrade 5. Below the capillary barrier layer 12 is the foundation 11. The capillary barrier layer 12 is sand or gravel, preventing groundwater from migrating to the subgrade soil under capillary action. The particle sizes of the foundation 11 and the capillary barrier layer 12 are quite different. It is advisable to lay a non-woven geotextile between the capillary barrier layer 12 and the foundation 11 as an anti-filter layer to prevent the loss of skeleton particles from causing seepage deformation.

[0043] As Figure 3As shown in the figure, the conductive wicking basalt fiber geotextile 13 is obtained by knitting conductive wicking basalt fibers in warp and weft directions. The fiber axis 19 of the conductive wicking basalt fiber geotextile 13 is perpendicular to the road alignment. The conductive wicking basalt fiber is obtained by coating a carbon black coating 17 on the surface of the wicking fiber 18. The thickness of the carbon black coating 17 is 0.1 - 5 μm, which is much smaller than the diameter of the fiber itself, so it will not affect the water conduction function of the wicking fiber 18. The wicking fiber 18 is a continuous basalt fiber, and the diameter of the conductive wicking basalt fiber is 5 - 20 μm to ensure that the material has good wicking and moisture conduction properties. The tensile strength of the conductive wicking basalt fiber is 2.5 - 3 GPa. The conductive wicking basalt fiber has the characteristics of low cost, high strength, and environmental friendliness, which can reinforce the roadbed, effectively distribute the overlying traffic load, reduce the settlement difference between the new and old roadbeds, improve the overall stability of the newly built embankment, and prevent plastic deformation of the subgrade soil.

[0044] Micron-scale fibers have strong surface tension and can play a wicking role. If profiled-section fibers are used, the specific surface area of the fibers can be increased, making them have better water-holding characteristics. By changing the shape of the micropores on the spinneret plate, profiled fibers with surface grooves are spun. After weaving, the wicking effect of the capillary channels between the fibers plays a role in water conduction. The water conduction performance is related to the profile degree of the fibers and the depth and shape of the grooves. Utilize the microvoids between the filaments inside the fiber bundle and the surface grooves to allow water to enter between the fibers. At the same time, tubular grooves (capillary channels) are formed along the fiber axis to provide a channel for the migration of water. The cross-section of the conductive wicking basalt fiber is circular, cruciform, trilobal, H-shaped or T-shaped to improve the wicking and water conduction performance of the fiber. The equivalent radius of the inter-filament pores of the conductive wicking basalt fiber is 0.01 - 6 μm. The groove depths of different-shaped cross-sections are different, and the groove depth ranges from 0 to 4 μm. When the cross-section of the conductive wicking basalt fiber is circular, the groove depth is 0. The pore size affects the unsaturated water conduction rate; the groove size affects the specific surface area of the material, and thus affects the wettability of the material.

[0045] The length of the conductive wicking basalt fiber geotextile 13 extending into the old roadbed 4 is at least 1 m, and the spacing between adjacent layers of the conductive wicking basalt fiber geotextile 13 is not less than 0.3 m. The conductive wicking basalt fiber geotextile 13 has three functions: electroosmotic drainage, capillary water absorption, and roadbed reinforcement.

[0046] As Figure 4As shown in the figure, under conditions such as short-term heavy rainfall during the spring thaw period or the rainy season, snowmelt and rainfall enter the subgrade soil through the joint 3 between the new and old roads. The subgrade soil is in a saturated or near-saturated state. At this time, the time domain reflectometry sensor 14 buried in the new subgrade 5 senses an increase in the water content of the subgrade soil and activates the electroosmotic drainage system (including the DC power supply 16, the time domain reflectometry sensor 14, and the electroconductive wicking basalt fiber geotextile 13). Under the action of the DC electric field, the water in the soil of the new subgrade 5 moves from the anode to the cathode, accelerating the water migration 21 in the new subgrade; soil particles carry negative charges on their surfaces due to isomorphic substitution within the crystal layer, lattice defects, or dissociation of minerals on the crystal layer surface. Under the action of the surface negative charge, surrounding cations and polar water molecules are oriented on the surface of the soil particles to form an electric double layer. Among them, the part close to the surface of the soil particle is called the fixed layer, which is not easily discharged due to strong adsorption, but its properties are close to those of a solid and have little impact on the performance of the subgrade soil; the part close to the fixed layer is affected by less electrostatic attraction, and the free diffusion movement between molecules is obvious, which is called the diffusion layer, and it is not easily discharged by traditional drainage methods. The part outside the diffusion layer that is not affected by the surface negative charge of the soil particle is called free water. The saturated or near-saturated subgrade soil contains a large amount of free water. By arranging anode and cathode electrodes in the subgrade and applying direct current to form an electric field, the exchangeable cations in the diffusion layer and free water will drag the polar water molecules to migrate from the anode to the cathode, thereby accelerating the water migration in the subgrade soil (including the water migration 21 in the new subgrade and the water migration 20 in the old subgrade). The electroconductive wicking basalt fiber geotextile 13 actively conducts the water electroosmotically migrated to the vicinity of the cathode in a timely manner, quickly reducing the water content of the subgrade soil under the joint 3 between the new and old roads.

[0047] For electroosmosis, the positive pole of the power supply is connected to the anode and the negative pole is connected to the cathode. Under the saturated state, electroosmosis and wicking drainage work simultaneously. Since the electroosmotic drainage efficiency is relatively high under the saturated state, and the wicking effect can laterally conduct the excess water electroosmotically migrated to the vicinity of the cathode to the shoulder slope in a timely manner, the combined action of the two can effectively reduce the time when the subgrade soil is in a saturated or near-saturated state. The strength of the subgrade soil decreases significantly with the increase in water content, and the combined action of the two can enable the strength of the subgrade soil to recover to the design value as soon as possible.

[0048] It is better to connect the electroconductive wicking basalt fiber geotextile 13 close to the road surface to the cathode. The water molecules in the soil move from the anode to the cathode under the action of cations. If connected to the anode, the upper part near the road surface is the anode and the lower part is the cathode, and the water migrates downward, reducing the water content of the upper soil layer and accelerating the rainfall infiltration rate; if connected to the cathode, the upper part near the road surface is the cathode and the lower part is the anode, and the water migrates upward, increasing the water content of the upper soil layer and reducing the rainfall infiltration rate.

[0049] The moisture in the subgrade soil is laterally discharged under the action of the suction difference at both ends of the conductive wicking basalt fiber geotextile 13, and finally dissipates into the air through evaporation on the shoulder slope. After the water content of the subgrade soil decreases, diseases such as pumping, mud gushing, and cavities 10 are not likely to occur under the action of traffic dynamic loads. In the initial stage, the water content of the subgrade soil is relatively high, and the electroosmotic drainage efficiency is high. As the water content of the subgrade soil decreases, the electroosmotic drainage efficiency gradually decreases. When the water content sensor (time domain reflectometry sensor 14) monitors that the water content of the subgrade soil is lower than 80% of the saturated water content, the electroosmotic drainage system is turned off, and the wicking fibers 18 are relied on for drainage, which has little impact on the dehydration efficiency of the subgrade, but greatly reduces the energy consumption and improves the energy utilization efficiency.

[0050] The electrical energy efficiency of the electroosmotic material is calculated by formula (1), and the resistivity of the conductive wicking basalt fiber should not exceed to ensure that the electrical energy efficiency is not less than 80%.

[0051] (1)

[0052] In the formula: is the electrical energy efficiency, %; is the resistivity of the electrode, ; is the resistivity of the soil mass, ; l is the length of the electrode, m; is the thickness of the electrode, m; D is the spacing between the anode and the cathode, m.

[0053] As Figure 5 shown, in the unsaturated state, the conductive wicking basalt fibers in the conductive wicking basalt fiber geotextile 13 mainly play the roles of reinforcement, active dehydration, and moisture distribution. Under unsaturated conditions, the conductive wicking basalt fibers in the conductive wicking basalt fiber geotextile 13 actively absorb the excess moisture from the surrounding subgrade soil, carry out infiltration moisture migration 23, effectively block the moisture supply for frost heaving, and reduce the differential frost heaving between the new and old subgrades. On the one hand, the continuous conductive wicking basalt fibers in the conductive wicking basalt fiber geotextile 13 form continuous capillary channels, absorb the excess moisture from the old subgrade 4 with a relatively high water content and migrate along the fiber axis, carrying out capillary geotextile moisture migration 22. On the other hand, in the soil of the new subgrade 5, due to the lateral water conductivity of the conductive wicking basalt fiber geotextile 13, it can effectively prevent the problem of excessive water content in local areas of the soil of the new subgrade 5.

[0054] Under the saturated state or near-saturated state, electroosmotic drainage and capillary core absorption drainage coexist. On the one hand, under the saturated or near-saturated state, the moisture distribution in the subgrade is also uneven. Capillary core absorption drainage can balance the moisture difference between the new and old subgrades and laterally drain water by using the suction difference at both ends of the geotextile inside the subgrade soil and on the shoulder slope. On the other hand, the electroosmotic effect will cause the water content near the cathode to increase, and the conductive core absorption basalt fabric can timely drain the water collected at the cathode through capillary core absorption drainage.

[0055] Under the unsaturated state, capillary core absorption drainage is adopted and electroosmotic drainage does not exist. Because the water content of the soil under the unsaturated state is relatively low, the electroosmotic drainage efficiency will also decrease accordingly. Continuing to use electroosmotic drainage will consume a large amount of energy, but the improvement effect on the soil water content is very limited. Closing the electroosmotic system can effectively improve the energy utilization efficiency.

[0056] The connection between the new and old subgrades is the weak point of the entire subgrade pavement structure. Only using mechanical strengthening means such as stepped excavation, geogrid reinforcement, and surcharge preloading cannot effectively prevent diseases such as mud pumping and boiling of the subgrade pavement. In the embodiment of the present invention, by laying a conductive core absorption basalt fiber geotextile 13 in the structural layer, the problems brought by using metal electrodes in the traditional electroosmotic method are overcome. At the same time, the micron-level fiber filaments can play a core absorption role, absorb water from the surrounding soil, and timely and actively drain the water migrated to the cathode by electroosmosis, making the subgrade soil in an unsaturated state, reducing the water content difference between the new and old subgrades, and effectively alleviating the uneven frost heaving and thaw settlement caused by the water content difference between the new and old subgrades; in addition, the conductive core absorption basalt fiber geotextile 13 can enhance the shear strength at the connection between the new and old subgrades, effectively disperse the traffic load in the working area, avoid plastic deformation of the subgrade soil, and reduce the settlement difference between the new and old subgrades. The subgrade structure of the embodiment of the present invention has both the functions of active dehydration and subgrade reinforcement and compounding, and can effectively eliminate diseases such as frost heaving, differential settlement, and mud pumping and boiling generated under the action of freeze-thaw cycles in the reconstruction and expansion projects in seasonal frozen areas.

[0057] Using conductive core absorption basalt fiber, on the one hand, through the electroosmotic effect, the weak bound water and free water in the subgrade soil during the spring thawing period and rainy season can be quickly drained, preventing the subgrade soil from being in a saturated state for a long time and stabilizing the water content of the subgrade soil near the target water content; on the other hand, using the core absorption effect to actively dehydrate, absorb water from the old subgrade 4 with a relatively high water content, and balance the water content difference between the new and old subgrade soils; the conductive core absorption basalt fiber geotextile 13 plays a role of capillary blockage. There is a difference in the hydraulic conductivity between the subgrade soil and the geotextile. When the water migrates upward to reach the soil-geotextile interface, due to the permeability coefficient of the geotextile being less than that of the subgrade soil, the water is blocked at this interface, effectively cutting off the water supply source for frost heaving, and can effectively inhibit the frost heaving of the subgrade, thereby reducing the water content of the new and old subgrade soils and alleviating the uneven frost heaving and uneven settlement of the new and old subgrades.

[0058] Example 2

[0059] A construction method for the active dewatering subgrade structure of a reconstructed and expanded highway, comprising the following steps:

[0060] S1. Surface cleaning operation. Garbage, organic residues within the widened subgrade red line, and roots and topsoil within a thickness range of 30 cm below the original ground surface should be cleaned up. After the original ground surface is cleared, soil samples should be taken from the pre-filling compaction section for standard compaction tests to determine indicators such as the maximum dry density and the optimum moisture content of the soil. When the moisture content of the foundation soil is close to the optimum moisture content, pre-filling compaction can be carried out.

[0061] S2. Laying of the capillary barrier layer 12. The capillary barrier layer 12 can be selected from sand and gravel or crushed materials. The crushed materials are obtained by crushing the old road protection, drainage, concrete masonry and stone masonry of bridges and culverts, and the road surface base course. The vibration method (including surface vibration, insertion vibration, ramming), the water ramming method, and the rolling method are used for layered compaction. The thickness of each layer depends on the magnitude of the vibration force, generally being 15 - 20 cm. There is no obvious separation of coarse and fine materials in the capillary barrier layer 12, and the maximum particle size should not be greater than 5 cm. The width should be 0.5 - 1.0 m wider than the outer edge of the new subgrade 5, and it should be protected by stone masonry or other methods to prevent the loss of sand materials.

[0062] S3. Subgrade compaction. In principle, the filling materials for the widened subgrade should be the same as those for the old subgrade 4, and materials with high strength and good water stability such as sand and gravel should be used as much as possible for filling. It is prohibited to use materials that do not meet the specification requirements for subgrade filling. Before the embankment filling, surveyors should first set out the slope toe line of the widened subgrade according to the designed width and slope of the widened subgrade, and sprinkle the embankment filling side line with lime. To ensure that the compaction degree at the embankment edge also meets the specification requirements, the embankment filling side line should be 50 cm wider than the slope toe line of the widened subgrade. Before subgrade compaction, the appropriate compaction equipment and reasonable compaction plan should be determined through a test section. During construction, the compaction combination sequence and compaction method summarized from the test section should be strictly followed for compaction. The subgrade soil should meet the requirements for the particle size and compaction degree of the filled stones in the "Code for Design of Highway Subgrade" (JTGD30 - 2020).

[0063] S4. Lay the electro-conductive wicking basalt fiber geotextile 13. At least 1 m of one end of the electro-conductive wicking basalt fiber geotextile 13 is embedded into the old roadbed 4, which can not only reduce the construction difficulty, but also ensure that the electro-conductive wicking basalt fiber can absorb the excess moisture from the old roadbed 4. The composite drainage and reinforcement geotextile is required to have a longitudinal and transverse ultimate tensile strength ≥ 80 kN / m per linear meter, a longitudinal and transverse elongation at break ≤ 3% per linear meter, and the anti-freezing test index should meet the requirements at -35 °C (in severe cold regions), and the remaining indexes should meet the relevant requirements of "Geosynthetics for Highway Engineering" (JT / T 925.1-2014). The fiber axis 19 of the electro-conductive wicking basalt fiber geotextile 13 is perpendicular to the road alignment. The surface of the soil layer where the geotextile is laid should be flat, and hard protrusions such as broken stones and boulders are strictly prohibited on the surface.

[0064] S5. The old roadbed 4 and the new roadbed 5 are spliced through the stepped excavation section 15. To control the differential deformation between the old and new roadbeds, it is necessary to ensure that the soil quality between the old and new roadbed fillers is as close as possible. Before the stepped excavation, the slope of the old roadbed 4 should be cleared first. It is not easy to complete the cleaning all at once. The slope should be cleared while excavating the steps to ensure the stability of the old roadbed 4. Different step sizes are adopted for the stepped excavation of the old roadbed 4 according to different roadbed fillers of the old road. When the filler of the old roadbed 4 is clay, silt clay and gravelly soil, the step height at the splicing part should be 1.0 m and the width should be 1.5 m; when the filler of the old roadbed 4 is sand or silty sand, the step height at the splicing part should be 0.4 m and the width should be 0.6 m.

[0065] S6. Repeat steps S3 - S5. Lay multiple layers of electro-conductive wicking basalt fiber geotextiles 13 at intervals in the new roadbed 5. The electro-conductive wicking basalt fiber geotextiles 13 connected to the positive and negative poles of the DC power supply 16 are arranged alternately in the vertical direction; Time domain reflectometry sensors 14 are buried between every two layers of electro-conductive wicking basalt fiber geotextiles 13 at the lower part of the joint 3 between the old and new roads. The time domain reflectometry sensors 14 are communicatively connected to the controller of the DC power supply 16, and are used to control the connection or disconnection of the DC power supply 16 and the corresponding electro-conductive wicking basalt fiber geotextile 13; As the water content of the subgrade soil decreases, the electro-osmotic drainage efficiency of the electro-conductive wicking basalt fiber geotextile 13 gradually decreases. When the water content of the subgrade soil is lower than the threshold value, the connection between the DC power supply 16 and the corresponding electro-conductive wicking basalt fiber geotextile 13 is disconnected.

[0066] Quality acceptance: The subgrade compaction degree shall adopt the standard of heavy compaction test and shall meet the relevant provisions in the "Code for Highway Subgrade Design" (JTG 3430-2020). The base of the embankment shall be compacted before filling, and the base compaction degree (heavy) shall not be less than 90%. To prevent the instability caused by the rapid filling of the embankment, it is required that the ground settlement rate of the center line of the newly widened embankment during construction shall not be greater than 10 mm / day, and the horizontal displacement of the toe of the slope shall not be greater than 5 mm / day. When the settlement or displacement exceeds the standard, the filling of the embankment shall be stopped immediately.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. An active dehydration subgrade structure for reconstructed and expanded highway in different regions, where the old subgrade (4) and the new subgrade (5) are spliced through a stepped excavation section (15), and it is characterized in that, A capillary blocking layer (12) is laid at the bottom of the new roadbed (5). Multiple layers of conductive wicking basalt fiber geotextiles (13) are laid at intervals within the new roadbed (5). One end of the conductive wicking basalt fiber geotextile (13) is embedded in the old roadbed (4), and the conductive wicking basalt fiber geotextiles (13) respectively connected to the positive and negative poles of the DC power supply (16) are arranged alternately in the vertical direction. Time domain reflectometry sensors (14) are buried between every two layers of conductive wicking basalt fiber geotextiles (13) at the lower part of the joint (3) between the old and new roads. The time domain reflectometry sensors (14) are communicatively connected to the controller of the DC power supply (16) and are used to control the connection or disconnection between the DC power supply (16) and the corresponding conductive wicking basalt fiber geotextile (13). The conductive wicking basalt fiber geotextile (13) is obtained by longitudinally and transversely weaving conductive wicking basalt fibers. The conductive wicking basalt fiber is obtained by coating a carbon black coating (17) with a thickness of 0.1 - 5 μm on the surface of the wicking fiber (18), and the wicking fiber (18) is a continuous basalt fiber. The diameter of the conductive wicking basalt fiber is 5 - 20 μm, and it is a profiled fiber with surface grooves. The equivalent radius of the pores between the conductive wicking basalt fiber filaments is 0.01 - 6 μm.

2. The active dewatering subgrade structure for reconstructed and expanded highway by region according to claim 1, characterized in that The cross-section of the conductive wicking basalt fiber is circular, cruciform, trilobal, H-shaped or T-shaped.

3. The active dehydration subgrade structure for reconstructed and expanded highway by sub-region according to claim 1, wherein The tensile strength of the conductive wicking basalt fiber is 2.5 - 3 GPa.

4. The active dehydration subgrade structure for reconstructed and expanded highways according to claim 1, wherein The width of the conductive wicking basalt fiber geotextile (13) extending into the old roadbed (4) is at least 1.0 m to ensure that the conductive wicking basalt fiber absorbs moisture from the old roadbed (4).

5. The actively dewatering subgrade structure for reconstructed and expanded highway by regions according to claim 1, wherein, The resistivity of the conductive wicking basalt fiber does not exceed 10 -3 Ω·m.

6. The active dewatering subgrade structure for reconstructed and expanded highway by region according to claim 1, characterized in that, The spacing between adjacent two layers of the conductive wicking basalt fiber geotextiles (13) is not less than 0.3 m.

7. The active dehydration subgrade structure for reconstructed and expanded highway by region according to claim 1, wherein The capillary blocking layer (12) is sandy soil or gravel, and an anti-filter layer is laid between the capillary blocking layer (12) and the underlying foundation (11).

8. The active dewatering subgrade structure for reconstructed and expanded highway by sub-region according to claim 1, characterized in that, The top of the old roadbed (4) is the old surface layer (1), and a lap section with a width of 50 - 100 cm is reserved on the old surface layer (1).

9. The construction method of a sub-region active dehydration roadbed structure for highway reconstruction and expansion as described in claim 1, characterized in that, It includes the following steps: S1, Clear the surface of the original ground and compact before filling. S2, Lay the capillary blocking layer (12) on the foundation (11). S3, Lay the new roadbed (5) on the capillary blocking layer (12) and compact it. The filler of the new roadbed (5) is the same as that of the old roadbed (4). S4, Lay the conductive wicking basalt fiber geotextile (13) in the new roadbed (5), ensure that at least 1 m of one end of the conductive wicking basalt fiber geotextile (13) is embedded in the old roadbed (4), and the fiber axis of the conductive wicking basalt fiber geotextile (13) is perpendicular to the road driving direction. S5, The old roadbed (4) and the new roadbed (5) are spliced through the stepped excavation section (15). S6. Repeat steps S3 - S5, and lay multiple layers of conductive wicking basalt fiber geotextiles (13) at intervals within the new subgrade (5). The conductive wicking basalt fiber geotextiles (13) connected to the positive and negative electrodes of the DC power supply (16) are arranged alternately in the vertical direction. Time domain reflectometry sensors (14) are buried between every two layers of conductive wicking basalt fiber geotextiles (13) at the lower part of the joint (3) between the new and old roads. The time domain reflectometry sensors (14) are communicatively connected to the controller of the DC power supply (16) and are used to control the connection or disconnection of the DC power supply (16) and the corresponding conductive wicking basalt fiber geotextile (13). As the water content of the subgrade soil decreases, the electroosmotic drainage efficiency of the conductive wicking basalt fiber geotextile (13) gradually decreases. When the water content of the subgrade soil is lower than the threshold, the connection between the DC power supply (16) and the corresponding conductive wicking basalt fiber geotextile (13) is disconnected.

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