Complete Construction Technology for Soft Foundation Treatment and Subgrade Filling of Coastal Highway

Abstract

The present invention discloses a complete set of construction techniques for soft foundation treatment and subgrade filling of coastal highways, including the following steps: Excavate a shallow foundation pit on the coastal soft foundation, and then excavate a subgrade foundation pit in the middle of the shallow foundation pit, and fill a composite plain soil layer in the subgrade foundation pit; Drive hollow piles at the top of the composite plain soil layer. Multiple water-permeable holes are opened on the lower pile wall of the hollow pile. Place a drainage belt and a coil into the hollow pile. The coil includes a magnetic induction coil around the lower end of the drainage belt and an electric heating coil around the upper end of the drainage belt, and then fill the hollow pile with gravel; Pour a concrete layer on the top of the composite plain soil layer. Ventilation pipes arranged along the width direction of the subgrade are embedded in the concrete layer, and part of the ventilation pipes are communicated with the upper ends of the hollow piles; Lay a water-conducting layer, a sand cushion layer, a graded crushed stone layer and an asphalt concrete surface layer in sequence on the concrete layer. The present invention can effectively improve the foundation strength, and at the same time improve the integrity of the subgrade, and avoid uneven settlement of the subgrade caused by soft foundation liquefaction.

Description

Technical Field

[0001] The present invention relates to the technical field of construction engineering. More specifically, the present invention relates to a complete set of construction techniques for soft foundation treatment and subgrade filling of coastal highways. Background Art

[0002] With the rapid development of China's economic construction, the mileage of highway construction is getting longer and longer. China has a vast coastline, and currently, the construction of coastal highways is accelerating. Many embankments are built on marine soft soil foundations. When carrying out road engineering construction on soft soil foundations, geotechnical problems such as overall sliding instability of the subgrade and uneven settlement of the embankment are likely to occur. Since the subgrade passes through a coastal section, which is a depression and is long-term affected by rain erosion and seawater tide immersion, a long coastal soft foundation section is formed. There are significant differences between coastal soft foundation sections and inland soft foundations. Marine sedimentary soft soil is often mixed with coarser particles (coarse, medium and fine sand) formed by the hydrodynamic action of sea waves, shore currents and tides. The formed soft foundation contains a large amount of sand, making it uneven and extremely loose, enhancing the water permeability of the soft foundation and being easy to compress and consolidate. According to sampling tests, its permeability coefficient is 6×10 -2 ~8×10 -4 cm / s, the deformation modulus is 1.8~10.5MPa, the internal friction angle is 8~20°, and the measured bearing capacity is 45~90kPa. It can be seen that this soft foundation has a large permeability coefficient, a relatively high internal friction angle, and a bearing capacity that is relatively higher than that of general inland silt soft foundations, but still does not meet the requirement of the minimum bearing capacity of the subgrade of 130~150kPa. Therefore, treatment must be carried out. Summary of the Invention

[0003] An object of the present invention is to solve at least the above problems and provide at least the advantages described hereinafter.

[0004] Another object of the present invention is to provide a complete set of construction techniques for soft foundation treatment and subgrade filling of coastal highways, which can effectively improve the foundation strength, at the same time improve the integrity of the subgrade, and can stably control the moisture content in the subgrade to avoid uneven settlement of the subgrade caused by soft foundation liquefaction.

[0005] To achieve these objects and other advantages of the present invention, there is provided a complete set of construction techniques for soft foundation treatment and subgrade filling of coastal highways, including the following steps:

[0006] Step 1: Excavate a shallow foundation pit on the coastal soft foundation, and then excavate a subgrade foundation pit in the middle of the shallow foundation pit. Fill the subgrade foundation pit with composite plain soil in layers to form a composite plain soil layer, and the filling height of the composite plain soil is not less than the ground height;

[0007] Step 2: Drive a hollow pile array on the top of the composite soil layer. The hollow piles penetrate 5 - 8 m into the soft foundation below the composite soil layer. A plurality of water permeable holes are formed in the lower pile wall of the hollow piles. Place the drainage belt and the coil into the hollow piles. The coil includes a magnetic induction coil surrounding the lower end of the drainage belt and an electric heating coil surrounding the upper end of the drainage belt. Then fill the hollow piles with gravel.

[0008] Step 3: Pour a concrete layer on the top of the composite soil layer. Ventilation pipes arranged along the width direction of the roadbed are embedded in the concrete layer. A plurality of the ventilation pipes are provided and are evenly spaced along the length direction of the roadbed. Downward branch pipes are provided on the pipe walls of some of the ventilation pipes, and the branch pipes communicate with the upper ends of the hollow piles. The power connection ends of the coils extend out of the roadbed from the ventilation pipes. Through holes extending upward are formed in the pipe walls of another part of the ventilation pipes, and the through holes extend to the top of the concrete layer.

[0009] Step 4: Lay geotextiles, water-absorbing fiber cloth, and geotextiles in sequence from bottom to top on the top of the concrete layer to form a water guiding layer.

[0010] Step 5: Lay a sand cushion layer, a graded crushed stone layer, and an asphalt concrete surface layer in sequence from bottom to top on the water guiding layer.

[0011] Step 6: Build a masonry stone revetment on the roadbed slope. Reserved holes for building the masonry stone revetment communicate with the ventilation pipes.

[0012] Step 7: Bury a moisture meter in the soft foundation beside the roadbed, and install a controller beside the roadbed slope. Connect the controller to the coil, the moisture meter, and the power supply respectively to control the moisture content in the soft foundation under the roadbed.

[0013] Preferably, in Step 2, the driving method of the hollow piles includes: drilling or hammering a pile hole on the top of the soil layer, pouring concrete into the pile hole, then extruding a steel core into the pile hole concrete after applying a release agent on the outer wall of the steel core. The steel core includes: a casing with a diameter smaller than the diameter of the pile hole, and the bottom end of the casing is sealed; a piston tube coaxially arranged inside the casing, the bottom end of the piston tube is sealed, and a plurality of punch tubes are connected between the lower pipe wall of the piston tube and the casing, and the punch tubes communicate with the piston tube. Punch holes for communicating the punch tubes with the outside are formed in the pipe wall of the casing; wherein, a piston matching the main piston tube is arranged inside the piston tube, a punch matching the punch tube is arranged inside the punch tube, a working medium is filled in the pipeline between the piston and the punch, a pressure rod is further arranged inside the piston tube, the lower end of the pressure rod is connected to the top of the piston, and the upper end of the pressure rod extends out of the casing and is connected with a handle; press down the pressure rod to make the punch extend out of the casing and penetrate through the concrete wall in the pile hole to form a water permeable hole. After the concrete in the pile hole starts to set, lift the pressure rod to retract the punch from the water permeable hole into the casing, and then lift the steel core out of the pile hole to form a hollow pile with a plurality of water permeable holes in the lower pile wall.

[0014] Preferably, a spring is connected between the rear end of the punch and the inner wall of the piston tube. In the initial state, the front end of the punch is aligned with the outer wall of the sleeve.

[0015] Preferably, it further includes: Step Eight, pouring concrete on the side wall of the shallow foundation pit and at the bottom of the shallow foundation pit between the side wall of the shallow foundation pit and the masonry revetment, so as to form a drainage ditch between the masonry revetment and the side wall of the shallow foundation pit.

[0016] Preferably, before Step One, analyze the type of soft foundation and remove the organic impurities on the surface layer of the soft foundation within the range of the shallow foundation pit.

[0017] Preferably, the composite plain soil includes plain soil, slag, quicklime and glass fiber, and their mixing ratio is 70:20:8:2.

[0018] The present invention has at least the following beneficial effects: By replacing the soft foundation of the surface layer with composite plain soil, the strength of the soft foundation of the surface layer is improved. At the same time, the replaced composite plain soil layer can also be used as the lower base course of the roadbed. By driving hollow piles into the composite plain soil layer below the composite plain soil layer to compact the soft foundation, the strength of the deep soft foundation is improved. At the same time, the combination of the hollow piles and the concrete layer in the roadbed improves the integrity of the roadbed, avoiding uneven settlement of the roadbed. Drainage plates and coils are also arranged in the hollow piles. The electromagnetic field generated by the lower magnetic induction coil can induce free water in the soft foundation to generate an induced magnetic moment, thereby changing the dynamic viscosity of the water and increasing the infiltration rate. It can also make the bound water in the soft foundation easier to break free and be absorbed by the drainage plates. The heat generated by the upper electric heating coil evaporates the moisture at the upper end of the drainage plates. Then, taking advantage of the rich coastal wind resources, part of the evaporated moisture is discharged from the roadbed through the ventilation pipes. Combining with the moisture meter and the controller to accurately control the moisture content of the soft foundation can avoid the liquefaction of coastal sandy soil under high moisture content, resulting in weakening of the foundation, and further avoid uneven settlement of the roadbed. The moisture infiltrated into the upper layer of the roadbed can be discharged into another part of the ventilation pipes through the water conduction layer and the through holes on the concrete layer, and then evaporated by means of the coastal wind resources or discharged into the drainage ditch beside the roadbed along the ventilation pipes, so that the ventilation pipes can simultaneously take into account the drainage of the upper and lower parts of the roadbed foundation.

[0019] Other advantages, objectives and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic cross-sectional structure diagram of the coastal highway subgrade according to the embodiment of the present invention;

[0021] Figure 2 It is a schematic structure diagram of the concrete layer according to the embodiment of the present invention;

[0022] Figure 3 It is a schematic structural view of the inside of the hollow pile described in the embodiment of the present invention;

[0023] Figure 4 It is a schematic structural view of the steel core described in the embodiment of the present invention. Specific embodiments

[0024] The following further describes the present invention in detail with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0025] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials, unless otherwise specified, can all be obtained from commercial channels; in the description of the present invention, the terms "horizontal", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present invention.

[0026] As Figures 1 to 3 shown, the present invention provides a complete set of construction techniques for soft foundation treatment and subgrade filling of coastal highways, including the following steps:

[0027] Step 1: Excavate a shallow foundation pit on the coastal soft foundation, and then excavate a subgrade foundation pit in the middle of the shallow foundation pit. Fill the subgrade foundation pit with composite plain soil in layers to form a composite plain soil layer 1, and the filling height of the composite plain soil is not lower than the ground height;

[0028] Step 2: Drive an array of hollow piles 2 on the top of the composite plain soil layer 1. The hollow piles 2 penetrate 5-8 m into the soft foundation below the composite plain soil layer 1. A plurality of water permeable holes 3 are opened on the lower pile wall of the hollow piles 2. Place a drainage belt and a coil into the hollow piles 2. The coil includes a magnetic induction coil 5 around the lower end of the drainage belt and an electric heating coil 6 around the upper end of the drainage belt. Then fill the hollow piles 2 with gravel;

[0029] Step 3: Pour a concrete layer 7 on the top of the composite plain soil layer 1. Ventilation pipes 8 arranged along the width direction of the subgrade are embedded in the concrete layer 7. A plurality of ventilation pipes 8 are provided and are evenly spaced along the length direction of the subgrade. Some of the ventilation pipes 8 are provided with downward branch pipes, and the branch pipes communicate with the upper ends of the hollow piles 2. The power connection ends of the coils extend out of the subgrade from the ventilation pipes 8. The other part of the ventilation pipes 8 is provided with upward through holes 9, and the through holes 9 extend to the top of the concrete layer 7;

[0030] Step 4: Lay geotextile, water-absorbing fiber cloth, and geotextile from bottom to top on the top of the concrete layer 7 to form a water-conducting layer 10;

[0031] Step 5: Lay a sand cushion layer 11, a graded crushed stone layer 12, and an asphalt concrete surface layer 13 from bottom to top on the water-conducting layer 10;

[0032] Step 6: Build a mortar rubble slope protection 14 on the roadbed slope. Reserve holes in the built mortar rubble slope protection 14 to communicate with the ventilation pipe 8;

[0033] Step 7: Bury a moisture meter in the soft foundation beside the roadbed, install a controller beside the roadbed slope, and connect the controller to the coil, moisture meter, and power supply respectively to control the moisture content in the soft foundation under the roadbed.

[0034] After the construction of the above embodiments is completed, the structural diagram of the coastal highway subgrade in the cross-section is as Figure 1 shown, including from bottom to top: hollow piles 2, composite plain soil layer 1, concrete layer 7, water-conducting layer 10, sand cushion layer 11, graded crushed stone layer 12, and asphalt concrete surface layer 13.

[0035] In the above embodiments, the strength of the shallow soft foundation of the ground surface is improved by replacing with composite plain soil. At the same time, the replaced composite plain soil layer 1 can also be used as the lower base course of the roadbed. By driving hollow piles 2 into the composite plain soil layer 1 below the composite plain soil layer to compact the soft foundation, the strength of the deep soft foundation is improved. At the same time, the combination of the hollow piles 2 and the concrete layer 7 in the roadbed improves the integrity of the roadbed, avoids uneven settlement of the roadbed, and drainage plates 4 and coils are arranged in the hollow piles 2. The electromagnetic field generated by the lower magnetic induction coil 5 can induce free water in the soft foundation to generate an induced magnetic moment, thereby changing the dynamic viscosity of water, increasing the penetration rate, and making the bound water in the soft foundation easier to break free from bondage. Therefore, it is easier to be absorbed by the drainage plates 4 through the water-permeable holes 3 at the lower part of the hollow piles 2. The heat generated by the upper electric heating coil 6 evaporates the water at the upper end of the drainage plates 4. Then, taking advantage of the rich coastal wind resources, the evaporated water is discharged from the roadbed through part of the ventilation pipes 8. Combining with the moisture meter and the controller to accurately control the moisture content of the soft foundation can avoid the liquefaction of coastal sandy soil under high moisture content, resulting in weakening of the foundation, and further avoid uneven settlement of the roadbed. The water infiltrated into the upper layer of the roadbed can be discharged into another part of the ventilation pipes 8 through the water-conducting layer 10 and the through holes 9 on the concrete layer 7, and then evaporated by means of the coastal wind resources or discharged into the drainage ditch 16 beside the roadbed along the ventilation pipes 8, so that the ventilation pipes 8 can simultaneously take into account the drainage of the upper and lower foundations of the roadbed.

[0036] As Figure 4As shown, in another embodiment, in step two, the driving method of the hollow pile 2 includes: drilling or hammering a pile hole at the top of the plain soil layer, pouring concrete into the pile hole, and then extruding the steel core 15 into the pile hole concrete after applying a release agent to the outer wall of the steel core 15. The steel core 15 includes: a casing 151 with a diameter smaller than the diameter of the pile hole, and the bottom end of the casing 151 is sealed; a piston tube 152 coaxially arranged inside the casing 151, with the bottom end of the piston tube 152 sealed. A plurality of punch tubes 153 are connected between the lower pipe wall of the piston tube 152 and the casing 151, and the punch tubes 153 communicate with the piston tube 152. Punch holes 155 for communicating the punch tubes 153 with the outside are formed on the pipe wall of the casing 151. Among them, a piston 154 matching the main piston tube 152 is arranged inside the piston tube 152, a punch 155 matching the punch tube 153 is arranged inside the punch tube 153, and a working medium is filled in the pipeline between the piston 154 and the punch 155. The working medium can be hydraulic oil or gas. A pressure rod 156 is also arranged inside the piston tube 152. The lower end of the pressure rod 156 is connected to the top of the piston 154, and the upper end of the pressure rod 156 extends outside the casing 151 and is connected with a handle 157. Press down the pressure rod 156 to make the punch 155 extend outside the casing 151 and penetrate the concrete wall in the pile hole to form a water-permeable hole 3. After the concrete in the pile hole starts to set initially, lift the pressure rod 156 to retract the punch 155 from the water-permeable hole 3 into the casing 151, and then lift the steel core 15 out of the pile hole to form a hollow pile 2 with a plurality of water-permeable holes 3 opened on the lower pile wall.

[0037] In the above embodiment, after pouring concrete into the pile hole, immediately insert the steel core 15 into the pile hole concrete, fully extrude the concrete poured into the pile hole, and at the same time, part of the concrete can be extruded into the soil voids around the pile hole. If the precast hollow pile 2 is used and then the construction method of driving the hollow pile 2 into the foundation is adopted, since the boundary between the hollow pile 2 and the soil around the pile hole is distinct, the method of the above embodiment can better improve the pile side friction resistance and the bearing capacity of the hollow pile 2. The above steel core 15 can not only construct a central hole in the concrete in the pile hole, but also the piston tube 152, punch tube 153, piston 154, punch 155 and other structures inside the steel core 15 are convenient for constructing water-permeable holes 3 on the pile wall, and it is simple and convenient to use.

[0038] In another embodiment, a spring 158 is connected between the rear end of the punch 155 and the inner wall of the piston tube 152. In the initial state, the front end of the punch 155 is aligned with the outer wall of the casing 151. In this way, when the front end of the punch 155 is pressed out of the casing 151, the spring 158 can play a certain limiting role to prevent the punch 155 from completely detaching from the punch tube 153. When the punch 155 needs to be retracted, the spring 158 provides a certain restoring force to better help the punch 155 reset.

[0039] In another embodiment, it further includes: Step Eight, pouring concrete on the side wall of the shallow foundation pit and at the bottom of the shallow foundation pit between the side wall of the shallow foundation pit and the rubble masonry slope protection 14, so as to form a drainage ditch 16 between the rubble masonry slope protection 14 and the side wall of the shallow foundation pit. In this embodiment, by building the drainage ditch 16 in the shallow foundation pit beside the roadbed, it is convenient for the water accumulated in the ventilation pipe 8 to be discharged, and there is no need to construct a trench for the roadside drainage ditch 16 anymore, making full use of the shallow foundation pit and saving the construction cost.

[0040] In another embodiment, before Step One, analyze the type of the soft foundation and remove the organic impurities on the surface layer of the soft foundation within the range of the shallow foundation pit. Since the content of organic impurities formed by the corruption of surface animals and plants is extremely large, it is difficult to compact, and the long-term decomposition further weakens the bearing capacity of the foundation. Therefore, it must be removed. The removal depth is determined according to the actual situation, generally with a thickness of 0.3 - 0.5 m.

[0041] In another embodiment, the composite plain soil includes plain soil, slag, quicklime and glass fiber, and its mixing ratio is 70:20:8:2. Since it contains some quicklime, when it encounters moisture, it can turn into slaked lime and then generate calcium carbonate, increasing in volume to fill the voids of soil settlement. On the other hand, when slaking, it forms a composite block with plain soil and slag and can also be interspersed with glass fiber to form a cross-linked three-dimensional structure to enhance the integrity of the composite plain soil layer 1 and avoid uneven settlement of the roadbed.

[0042] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated and described examples here.

Claims

1. A complete set of construction techniques for soft foundation treatment and subgrade filling of coastal highways, characterized in that, The following steps are involved: Step 1: excavate a shallow foundation pit on the coastal soft foundation, then excavate a roadbed foundation pit in the middle of the shallow foundation pit, and fill the roadbed foundation pit with composite soil in layers to form a composite soil layer. The filling height of the composite soil should not be lower than the ground level. Step 2: A hollow pile array is driven on top of the composite soil layer. The hollow piles are driven 5 to 8 meters deep into the soft foundation below the composite soil layer. Multiple water-permeable holes are opened in the lower pile wall of the hollow piles. Drainage belts and coils are placed in the hollow piles. The coils include a magnetic induction coil around the lower end of the drainage belt and an electric heating coil around the upper end of the drainage belt. Gravel is then filled into the hollow piles. Step 3: pouring a concrete layer on top of the composite soil layer, pre-buried in the concrete layer ventilation pipes arranged along the width direction of the roadbed, multiple ventilation pipes are provided and evenly spaced along the length direction of the roadbed, downward branches are provided on the walls of some ventilation pipes, the branches are connected to the upper ends of the hollow piles, the power connection ends of the coils extend out of the roadbed from the ventilation pipes, and upward through holes are opened on the walls of other ventilation pipes, the through holes extending to the top of the concrete layer; Step 4: laying geotextile, absorbent fiber cloth and geotextile in order from bottom to top on top of the concrete layer to form a water conducting layer; Step 5: laying a sand and gravel cushion layer, a graded crushed stone layer and an asphalt concrete surface layer on the water-conducting layer from bottom to top; Step 6: Build mortar-laid stone slope protection on the roadbed slope, and reserve holes in the mortar-laid stone slope protection to connect with the ventilation pipe; Step 7: Bury a moisture meter in the soft foundation beside the roadbed, install a controller beside the roadbed slope, and connect the controller to the coil, moisture meter and power supply respectively to control the moisture content in the soft foundation under the roadbed.

2. The complete construction process for soft foundation treatment and subgrade filling of coastal highways according to claim 1, characterized in that, In step 2, the method for driving the hollow pile includes: drilling or hammering a pile hole on the top of the soil layer, pouring concrete into the pile hole, then applying a release agent to the outer wall of the steel core and squeezing it into the pile hole concrete, the steel core includes: a casing, the diameter of which is smaller than the diameter of the pile hole, the bottom end of the casing is sealed; a piston tube, which is coaxially arranged in the casing, the bottom end of the piston tube is sealed, a plurality of punch tubes are connected between the lower tube wall of the piston tube and the casing, the punch tube is connected to the piston tube, and a punch hole is opened on the tube wall of the casing to connect the punch tube with the outside; wherein, the movable A piston matching the piston tube is provided in the plug tube, a punch matching the punch tube is provided in the punch tube, the pipeline between the piston and the punch is filled with working fluid, and a pressure rod is also provided in the piston tube, the lower end of the pressure rod is connected to the top of the piston, and the upper end of the pressure rod extends out of the sleeve and is connected to a handle; the pressure rod is pressed down to make the punch extend out of the sleeve and pass through the concrete wall in the pile hole to form a water-permeable hole. After the concrete in the pile hole is initially solidified, the pressure rod is lifted to retract the punch from the water-permeable hole into the sleeve, and then the steel core is lifted out of the pile hole to form a hollow pile with multiple water-permeable holes opened in the lower pile wall.

3. The complete construction process for soft foundation treatment and subgrade filling of coastal highways according to claim 2, characterized in that, A spring is connected between the rear end of the punch and the inner wall of the piston tube. In an initial state, the front end of the punch is aligned with the outer wall of the sleeve.

4. The complete construction process for soft foundation treatment and subgrade filling of coastal highways according to claim 1, characterized in that, Further included are: Step Eight, pouring concrete on the side wall of the shallow foundation pit and at the bottom of the shallow foundation pit between the side wall of the shallow foundation pit and the masonry rubble slope protection, so as to form a drainage ditch between the masonry rubble slope protection and the side wall of the shallow foundation pit.

5. The complete construction process for soft foundation treatment and subgrade filling of coastal highways as described in claim 1, characterized in that, Before Step One, analyze the type of the soft foundation and remove the organic impurities on the surface layer of the soft foundation within the range of the shallow foundation pit.

6. The complete construction process for soft foundation treatment and subgrade filling of coastal highways as described in claim 1, characterized in that, The composite loess includes loess, slag, quicklime and glass fiber, and their mixing ratio is 70:20:8:2.

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