CN219992075U - Soft soil roadbed reinforcing structure suitable for highway - Google Patents
Soft soil roadbed reinforcing structure suitable for highway Download PDFInfo
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- CN219992075U CN219992075U CN202321373246.4U CN202321373246U CN219992075U CN 219992075 U CN219992075 U CN 219992075U CN 202321373246 U CN202321373246 U CN 202321373246U CN 219992075 U CN219992075 U CN 219992075U
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Abstract
The utility model discloses a reinforcing structure suitable for a highway soft soil roadbed, wherein a mini pile consists of a steel flower pipe, sand or broken stone in the steel flower pipe and a pile cap, and the reinforcing structure is used for forming a vertical drainage channel by sand or broken stone in the steel flower pipe so as to accelerate the drainage consolidation of a soft soil layer; all the micro piles are connected into a whole through reinforced concrete beams; the upper part of the miniature pile is sequentially provided with a drainage sand cushion layer and a mattress cushion layer. The reinforcing structure is characterized in that the miniature pile adopts the conventional steel pipe, so that the standardized customization of a factory is facilitated, the requirements on construction sites and construction machinery are low, and the construction process is more convenient, safe and reliable; compared with the tubular pile, the miniature pile has small diameter, the disturbance to the soft soil layer is reduced in the pile pressing process, the upper filling load is converted into the effective soft soil stress due to the vertical drainage channel, the shear strength of the soft soil is increased, the integral stability of the soft foundation in the upper embankment filling process is greatly enhanced, the filling rate of the early embankment is accelerated, the construction period is shortened, and the construction cost of a single pile is low.
Description
Technical Field
The utility model relates to the field of highway engineering, in particular to a soft soil roadbed reinforcing structure suitable for a highway.
Background
In the road construction composition, the roadbed is the most basic, and is also the part with larger influence on the whole quality, and the quality problem in the aspect directly leads to the reduction of the whole quality of the road. Soft soil in highway engineering is fine-grained soil with high natural water content, large natural pore ratio, low shear strength and high compressibility, and comprises silt, mucky soil, peat soil and the like, and a foundation consisting of soft soil layers is called soft soil foundation. The soft soil foundation is mostly saturated in physical properties and contains organic matters, and has the following characteristics: higher water content, larger pore, low shear strength, higher compressibility, small permeability, obvious structural property and obvious rheological property.
Considering the characteristics of soft soil layers, it is very disadvantageous to use it as a foundation for building (construction) structures. Because the strength of soft soil is very low, the empirical value of the characteristic value of bearing capacity is generally 50-80 kPa, and the soft soil cannot bear larger building load, otherwise, local damage or whole sliding of the foundation can occur. And soft soil has higher sensitivity, if the effects of vibration, extrusion, stirring and the like are generated in foundation construction, the damage of the soft soil structure can be caused, and the strength of soft soil is reduced. Therefore, it is necessary to treat the soft soil foundation by constructing a building (structure) on the soft soil foundation. The soft soil foundation treatment aims to improve the physical and mechanical properties of soft soil, improve the shear strength of foundation soil, reduce the compressibility of soft soil and reduce post-construction sedimentation and uneven sedimentation.
The highway is used as a linear strip engineering, and the soft foundation treatment method comprises a shallow layer treatment method (such as dredging, filling, shallow layer improvement and stone throwing and dredging), a drainage consolidation method (such as preloading and vacuum preloading), a dynamic compaction and dynamic compaction replacement method, a granular pile (crushed stone pile), a reinforced soil pile (such as cement stirring pile and jet grouting pile), a rigid pile (such as precast pile, square pile and cast-in-situ concrete pile) and the like.
The shallow layer treatment method is suitable for the condition that the soft soil layer is small in thickness, part or all of the soft soil layer in the treatment range can be excavated, and then the soil with high strength or other materials with good stability and no corrosiveness (usually medium coarse sand, broken stone and the like with good water permeability) are backfilled. The height of the treatment by the method is generally 2-3 m, and if the thickness of the weak soil layer is too large, the engineering cost is increased. The aim of enhancing the bearing capacity of the foundation is achieved by replacing and filling materials with higher shear strength, and the requirements of the building (construction) on the foundation are met. Representative methods include a plurality of methods of changing and filling, polishing and squeezing silts and a cushion layer.
The basic principle of the drainage consolidation method is that the soft soil foundation gradually drains pore water under the action of additional load, so that the pore ratio is reduced, and consolidation deformation is generated. In the process, as the hyperstatic pore water pressure of the soil body is gradually dissipated, the effective stress of the soil is increased, and the foundation shear strength is correspondingly increased. The preloading method can use embankment filling soil as load, has low cost and is an ideal method for treating the soft soil roadbed of the highway. However, in the field of actual highway construction, the application is less, and the main reason is that the construction period of a highway project is high, in particular to a high-grade highway; on the other hand, when the soft foundation treatment is carried out by independently adopting the preloading method, the settlement after construction is larger, the settlement is uneven, the pavement is easy to crack or the pavement wave fluctuation is easy to cause, the normal operation of the road is seriously influenced, and the maintenance cost in the later period is greatly increased; finally, in the construction process, the roadbed is often unstable and collapses due to nonstandard control of the filling rate. In order to prevent the soft foundation from shearing and slipping and improve the overall stability of the embankment, back pressure protection channels can be arranged on two sides of the embankment, but the scheme can increase the occupied area of the highway, especially the plain area can occupy basic farmland, and is contrary to the principle of saving land for the design of the highway, so that the scheme is rarely adopted.
The dynamic compaction displacement method has certain economical efficiency and reliability for treating the soft soil layer of 3-7 m, and has the advantages that: the soil is relatively excavated, replaced and filled, so that the cultivated land area occupied by waste soil can be reduced, and the sand and stone material consumption is reduced; compared with other soft soil roadbed processing modes, the method has relatively low cost and simple operation; the method has the defects of high noise and vibration, inconvenience in use in densely populated cities and residential areas, difficulty in control of construction quality and possibility of causing large disturbance to the lower soft soil layer. The dynamic compaction machinery has high field entering and exiting cost, and when the engineering quantity is small, the use is not recommended from the view of the rationality of construction arrangement.
The granular pile (broken stone pile) is formed by firstly adopting a vibroflotation method or a pile pipe vibration method to form a hole, adding a sufficient amount of broken stone, and vibrating and compacting. The purpose of setting up the gravel stake is through the piling process of vibration, crowded close, with the foundation soil vibration compaction. On one hand, a vertical drainage channel is formed through the gravel pile, and the increase of excessive void water pressure caused by additional load is prevented or dissipated, so that the aims of accelerating foundation drainage consolidation and enhancing foundation strength are fulfilled; on the other hand, a composite foundation can be formed, and the bearing capacity and the deformation resistance of the soft soil foundation are improved. Compared with the dynamic compaction displacement method, the pile forming depth is large and the quality is controllable; when pile is formed by adopting the vibroflotation displacement method, high-pressure water flows down to form holes in soft and weak clay foundation while vibrating, a large amount of water resources are needed, the punched slurry is easy to pollute the environment, meanwhile, if the strength of soft clay is too low (such as flowing plastic-shaped silt), the constraint force of the soil can not balance the force for enabling the filler to squeeze into the hole wall all the time, and the pile body can not be formed, so that the method is not applicable any more. When the vibration immersed tube is adopted for pile forming, the structure of a soft soil layer can be damaged by high-frequency vibration, and the soft soil strength is greatly reduced.
The reinforced soil pile (cement stirring pile, jet grouting pile) uses cement as curing agent, and the soft soil and curing agent are forcedly mixed in the foundation by deep stirring machine, so that the soft foundation is hardened, and the foundation strength is improved. The method is suitable for soft foundation treatment, has obvious effect, and can be used for piling, walls and the like after treatment. The advantages are that: the construction process is simpler, the disturbance is small, and the construction period is short. Disadvantages: the effect is poor when the organic matter content of soft soil is high or the water content is large, the treatment depth is limited, and the treatment depth is generally not more than 15m; the slurry is easy to cause environmental pollution in the construction process, and when the cement content is high, the engineering cost is high; the pile forming quality is difficult to guarantee due to the limitation of the management level of a construction unit; the improvement of the foundation bearing capacity is limited, and the foundation bearing capacity after the conventional cement mixing pile is processed is generally 120-150 kPa according to the related literature data and the calculation formula in the current specification.
When the soft soil foundation is treated, the rigid piles (precast tubular piles, square piles and cast-in-situ concrete piles) are combined into a composite foundation by the pile itself, inter-pile soil and mattress layer engineering effects, and jointly bear the embankment filling and driving load effects. Under the external load, the pile body bears most of the load, the load borne by the pile can account for 40% -90% of the total load, the single pile bearing capacity mainly comprises pile side friction resistance and pile end resistance, and along with the increase of the acting time of the load, the pile peripheral friction resistance is fully exerted, and the pile end resistance is gradually enhanced. Under the action of external load, the pile top mattress layer plays a role in adjusting, and partial load is transferred to soil between piles to bear the external load, so that the soil between piles and the piles jointly bear the external load. In recent years, the main soft foundation treatment used in highway engineering is prestressed pipe piles. Compared with other pile foundations, the prestressed pipe pile has the following characteristics: (1) the bearing capacity of the single pile is high, the single pile is much higher than that of a common plain concrete pile and a pellet pile, and the settlement after construction is small; (2) the factory standardized production has large yield and stable quality, and is particularly suitable for projects with a relatively tight construction period and high sedimentation deformation requirement; (3) the transportation is convenient, the construction is convenient, and the construction quality can also be better controlled. The construction method of the prestressed pipe pile is many, mainly adopts a hammering method and a static pressure method in terms of road projects at present, and the hammering method is adopted between the prestressed pipe pile and the static pressure method, and the static pressure method is mainly applicable to urban areas or areas with limited construction conditions. Although the advantages of the prestressed pipe pile are more, the disadvantages are obvious, (1) the shearing resistance is weak because the content of the steel bars is less; (2) the manufacturing cost is high, and mushroom-shaped height fluctuation easily occurs when the embankment height is small; (3) because the diameter of the pipe pile is larger, no matter the static pressure method or the hammering method is adopted during construction, the soft soil layer can be disturbed, the super pore water pressure is formed in the soft soil layer, and the strength of the soft soil layer is greatly reduced before the super pore water pressure is dissipated. Related engineering practice also shows that the highway soft soil roadbed constructed by adopting the tubular pile composite foundation treatment in the early period of traffic has the case of collapse and instability.
In theory, the method can be used for soft foundation treatment, but because the highway is a linear strip-shaped project, the soft foundation distribution is scattered, and the soft foundation treatment engineering quantity in a single pile number section is not large, in the practical engineering application of the highway, the common soft foundation treatment method comprises the following steps:
(1) the soft foundation with small thickness (H is less than or equal to 3 m) is removed, materials with good water stability such as qualified soil, rubble and medium coarse sand of roadbed are adopted after all the soft foundation is removed, and the earth and stone sides are excavated by utilizing the waste slag of a tunnel and the cutting slope as much as possible.
(2) The cement stirring pile is mainly used for filling soft foundation with medium thickness (H is more than 3m and less than or equal to 15 m) and small height on the upper embankment. The length, diameter and spacing of the cement mixing piles are determined according to stability and sedimentation calculation. The length of the cement mixing pile is determined according to the requirements of the upper structure on the bearing capacity and the deformation, and the cement mixing pile can penetrate through soft soil layers to reach soil layers with relatively high bearing capacity. The pile body is arranged for improving the anti-slip stability, the pile length of the pile body is 2m below a dangerous slip arc, the pile diameter of the cement mixing pile is not less than 0.5m, and the distance between adjacent piles is not more than 4 times of the pile diameter.
(3) The rigid pile method is mainly aimed at soft foundation with large thickness (H is more than or equal to 15 m) or large filling height of upper embankment and strict deformation requirement. In particular, the method is mainly used for treating the road embankment sections, bridge heads or road-embankment joint sections with high load and strict deformation requirements on the deep soft soil foundation. The highway soft soil foundation treatment can adopt rigid piles such as prestressed concrete thin-wall pipe Piles (PTC), prestressed high-strength concrete Pipes (PHC), precast concrete square piles, bored cast-in-situ piles, cast-in-situ concrete large-diameter pipe piles (PCC piles) and the like. The prestressed concrete thin-wall pipe pile is prefabricated in a factory, welded and lengthened on site, the outer diameter is 300-500 mm, and the wall thickness is 60-100 mm; the external diameter of the cast-in-situ concrete large-diameter pipe pile is preferably 1.0-1.5 m, and the wall thickness is preferably 120-200 mm. The rigid piles may be arranged in a square or equilateral triangle. The pile diameter is preferably determined according to pile forming equipment, and is not preferably less than 5 times the pile diameter. Pile length can be determined by calculation according to engineering requirements on foundation stabilization and deformation and by combining geological conditions. The pile top of the rigid pile is provided with a pile cap, and the shape of the rigid pile can be a cylinder, a table body or a reverse taper table body. The pile cap is preferably 1.0-1.5 m in diameter or side length, 0.3-0.4 m in thickness and is preferably formed by casting cement concrete on site. The pile cap top is paved with a flexible geosynthetic material reinforced cushion layer with certain thickness, strength, rigidity and integrity. The form of the cushion layer is determined according to the design load size and the requirement and the condition of a concrete foundation layer, and the geogrid reinforced cushion layer, the high-strength geotechnical cloth reinforced cushion layer, the geocell reinforced cushion layer and the like are preferably selected.
Disclosure of Invention
Aiming at the treatment of a deep soft foundation, the utility model aims to overcome the defects of the prior art, and aims to provide a reinforcing structure suitable for a soft soil roadbed of a highway, which combines the advantages of a drainage consolidation method and a rigid pile method.
Arranging micro piles in the soft soil layer through the reinforcing structure, forming vertical drainage channels by sand or broken stone in the piles, and enabling the soft soil layer to be subjected to drainage consolidation in the roadbed filling process, so that partial main consolidation settlement is completed, and the strength of the soft soil layer is improved; the rigid pile can also play a role of the rigid pile, improve the bearing capacity and shearing resistance of the soft soil roadbed and the overall stability of the roadbed, reduce post-construction settlement and uneven settlement of the soft soil roadbed, accelerate the filling rate of the embankment and shorten the construction period.
The micro pile structure for solving the technical problems is as follows:
a soft soil roadbed reinforcing structure suitable for a highway comprises a plurality of micro piles, reinforced concrete beams, a drainage sand cushion layer and a mattress cushion layer; the method is characterized in that: the miniature pile consists of a steel flower pipe, sand or broken stone in the steel flower pipe and pile caps, wherein the diameter, the length and the distance of the steel flower pipe are comprehensively determined according to factors such as the thickness of a soft soil layer, the filling height of an upper embankment, the grade of a highway, sedimentation deformation and the like; sand or broken stone is filled in the steel flower pipe to form a vertical drainage channel, so that the drainage consolidation of the soft soil layer is accelerated; all the micro piles are connected into a whole through reinforced concrete beams, so that a support is formed for the soft soil layer, and the soft soil layer can be effectively prevented from lateral sliding and overall instability in the upper embankment filling process; a water-draining sand cushion layer and a mattress cushion layer are sequentially arranged on the upper part of the pile cap of the miniature pile; under the action of the filling load of the embankment at the upper part, the soft soil layer is subjected to drainage consolidation, pore water forms a vertical drainage channel through sand or broken stone of the mini-type piles to be discharged into a sand cushion layer, and then the soft soil layer is discharged out of the range of the roadbed, and consolidation settlement occurs in the soft soil layer; the pile top elevation is adjusted to the miniature stake according to the subsidence deformation characteristic of weak soil embankment, and after weak soil subsides and warp, through mattress bed course and pile cap, the sharing of the perpendicular load of adjustment stake reduces the stress concentration of miniature stake top surface, coordinates the deformation of embankment, can effectively reduce the post-construction subsidence and the differential settlement of weak soil roadbed.
And a PVC sleeve is arranged between the miniature pile and the reinforced concrete beam, so that the miniature pile can move vertically and freely under the action of filling load.
The bagged sand or broken stone in the steel flower pipe can be used as a vertical drainage channel to accelerate the drainage consolidation of the soft soil layer, and meanwhile, the steel flower pipe has high shear strength, so that the integral instability of the soft soil embankment can be effectively prevented in the process of filling the soil in the upper embankment; the steel pipe penetrates through the soft soil layer, so that the bearing capacity is high, the filling height of the embankment and the filling rate in the construction process can be improved, the construction period is shortened, and the post-construction settlement of the soft soil foundation is reduced. The miniature piles refer to the characteristics of basin-shaped deformation curves (large settlement in the middle and small settlement at two sides) of the soft soil embankment, refer to the concept of pre-camber in bridge engineering construction, adjust pile top elevation and solve the problem of uneven settlement of roadbed. Meanwhile, in order to prevent stress concentration caused by contact between the mattress pad layer and the pile top of the micro pile and the situation that the micro pile pierces the mattress pad layer, the pile top is provided with a pile cap.
The reinforced concrete beam connects all the micro piles into a whole, and the anti-skid capability of the micro piles is greatly improved. Meanwhile, as the reinforced concrete beam has high integral rigidity, which is equivalent to forming a hard shell layer on the ground surface, the bearing capacity of the soft soil foundation is improved, and the problem of slow soil filling in the early stage of a soft soil drainage and fixation method can be solved (the soil filling is prevented from being too fast, and the foundation is prevented from being unstable and damaged). When the reinforced concrete beam is poured, the PVC sleeve is pre-buried in advance, so that the micro pile can freely move in the vertical direction.
The drainage sand cushion layer mainly comprises medium coarse sand with a certain thickness, the drainage sand cushion layer is connected with the peripheral drainage ditch, and pore water discharged after consolidation of the soft soil layer is led out. Meanwhile, according to the size of the estimated settlement, the thickness of the drainage sand cushion layer is controlled, the distance between the mattress cushion layer and the miniature piles is adjusted, so that the soft soil embankment actively generates drainage consolidation before the construction of the pavement structure layer, the ideal thickness of the drainage sand cushion layer is that the mattress cushion layer contacts with all the miniature piles before the construction of the pavement structure layer when the embankment is filled to the top standard height, and the miniature piles exert the vertical bearing function to be fully exerted.
The mattress layer consists of broken stone, gravel or stone scraps with good grading of medium coarse sand with a certain thickness, and a flexible geogrid with certain strength, rigidity and integrity and continuity. The geogrid has the engineering properties of high tensile strength, high tangential modulus, non-brittleness, good durability, aging resistance, corrosion resistance and the like. The function of the method is to coordinate the deformation of the micro pile.
The miniature pile construction method suitable for reinforcing the highway soft foundation reinforcing structure is characterized by comprising the following steps of: (A), preparing construction; (B), pile pressing; (C), cast-in-situ reinforced concrete beams; (D) presetting pile top elevation and installing pile caps; (E) paving a sand cushion; (F) And paving a mattress layer, and directly starting to fill the embankment after forming the micro pile structure for reinforcing the soft foundation through the steps.
The miniature pile construction method suitable for reinforcement treatment of highway soft foundation reinforcement structure is characterized by comprising the following steps:
(A) And (3) preparation of construction: finishing site cleaning and leveling, pile position measurement and lofting, steel flower pipe customization and construction material purchase preparation, wherein the important points are that the diameter and the length of the steel flower pipe are determined through calculation by combining the thickness of a soft foundation and the filling height of an upper embankment; determining a standard section of the steel floral tube according to the capability of construction mechanical equipment and the site clearance requirement; after the basic parameters of the steel floral tube are determined, standardized and customized by manufacturers;
(B) Pile pressing: pressing the steel floral tube of the first section of micro pile into the soil layer by adopting a static pile press according to the pile position placed in the step (A), lengthening the steel floral tube of the micro pile after filling bagged sand in the steel floral tube, and circularly constructing by adopting threaded connection among the steel floral tubes of each micro pile until the micro pile tip reaches the designed elevation for facilitating site construction; in order to reduce disturbance of the pile pressing on the soft soil layer, pile jumping construction is carried out;
(C) Cast-in-situ reinforced concrete beam: after the mini pile is pressed, before concrete is poured, a PVC sleeve is arranged between the reinforced concrete beam (3) and the mini pile (1); the reinforced concrete beam (3) is cast in situ, all the micro piles are connected into a whole, the anti-instability capability of a soft foundation is greatly improved, and the filling rate of the upper embankment is accelerated;
(D) Presetting pile top elevation and installing pile caps, namely estimating total settlement of the soft soil layer under the action of upper filling load according to the thickness of the soft soil layer, the strength of the pile tip soil layer and the upper filling load, drawing an estimated settlement curve of the embankment, combining the estimated drainage consolidation settlement value, adjusting the miniature pile top elevation, and installing the pile caps with high middle and low two sides;
(E) Paving a sand cushion layer: paving a sand cushion layer on the reinforced concrete beam, wherein the top elevation of the sand cushion layer is higher than the top elevation of the pile cap of the miniature pile, and the concrete numerical value is determined according to the estimated main consolidation settlement value before the pavement structure layer begins to be constructed;
(F) Laying a mattress layer: and paving graded broken stone with a certain thickness on the sand cushion, and rolling and backfilling the sand cushion in two layers, wherein two layers of high-strength geogrids are paved, so as to coordinate the deformation of the whole roadbed.
The beneficial effects of the utility model are as follows:
the utility model is based on the design concept that the deep soft soil layer actively subsides before the construction of the road surface structure in the embankment filling process, and does not adopt engineering measures (such as cement stirring piles and prestressed concrete pipe piles) to limit the settlement deformation of the soft soil roadbed. The advantage of soft foundation treatment by a drainage consolidation method and a rigid pile method is combined, the upper embankment filling is regarded as a favorable load, the upper embankment filling is converted into the effective stress of a soft soil layer through drainage consolidation in the early stage, the physical and mechanical properties of the soft soil layer are improved, and meanwhile, the problem that the overall progress of a project is influenced due to the slow filling rate in the early stage of drainage consolidation is solved; all the micro piles are coordinated through the mattress layer to bear the partial load together, so that the problem that the soft soil embankment is easy to be unstable integrally and sedimentated unevenly (which is easy to cause later-stage pavement pits to be uneven) can be effectively solved. Meanwhile, all the micro piles can be manufactured in a factory standardized manner, assembled on site, and the construction machinery can adopt small static pressure equipment, so that the construction is convenient and quick, and the cost is low.
The reinforced structure has the advantages that the miniature pile adopts the conventional steel pipe, so that the standardized customization of a factory is facilitated, the requirements on construction sites and construction machinery are low, and the construction process is more convenient, safe and reliable; compared with the tubular pile, the miniature pile has small diameter, the disturbance to the soft soil layer can be reduced as much as possible in the pile pressing process, meanwhile, the sand or broken stone in the steel flower pipe forms a vertical drainage channel, the soft soil layer is solidified under the action of upper filling load, the upper filling load is converted into the effective stress of soft soil, the shearing strength of the soft soil is increased, the integral stability of a soft foundation in the upper embankment filling process is greatly enhanced, the filling rate of the early embankment is accelerated, and the construction period is shortened. Compared with cement mixing piles and concrete piles by other deep soft foundation treatment methods, the construction cost of a single pile is low.
Drawings
FIG. 1 is a schematic diagram of the structure of the present utility model;
FIG. 2a is a schematic diagram of a micropile coupling system of the present utility model;
FIG. 2b is an enlarged schematic view of the node A of FIG. 2a
Fig. 2c is a schematic view of a reinforced concrete beam according to the present utility model;
FIG. 3 is an enlarged view of the steel tube of FIG. 1 according to the present utility model;
FIG. 4 is an enlarged view of the sand or crushed stone bag of FIG. 1 according to the utility model;
FIG. 5a is a front view of the pile cap of FIG. 1 according to the present utility model;
FIG. 5b is a top view of the pile cap of FIG. 1 according to the present utility model;
fig. 6 is a graph showing the calculation result of the stability of the roadbed by the drainage fixation method.
Fig. 7 is a graph showing the calculation result of the stability of the roadbed of the micro pile reinforcing structure according to the present utility model.
In the figure: 1. a mini pile; 2. sand or crushed stone; 3. a reinforced concrete beam; 4. a drainage sand cushion layer; 5. a mattress pad layer; 6. a pile cap; 7. a PVC sleeve; 8. grading crushed stone; 9. geogrid.
Detailed Description
The following description of the embodiments of the present utility model will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present utility model, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.
In the embodiment, as shown in fig. 1, a reinforcing structure suitable for a highway soft foundation comprises a plurality of micro piles 1, reinforced concrete beams 3, a drainage sand cushion layer 4 and a mattress layer 5; the method is characterized in that: the miniature pile 1 consists of a steel flower pipe, sand or broken stone 2 and a pile cap 6, wherein the steel flower pipe is filled with sand or broken stone 2, the sand or broken stone 2 can be filled into the steel flower pipe after being bagged, the bagged sand or broken stone is shown in fig. 4, the steel flower pipe structure is shown in fig. 3, the pile cap 6 structure is shown in fig. 5a and 5b, the steel flower pipe is connected with the pile cap 6 through threads, the sand or broken stone 2 is filled in the steel flower pipe to form a vertical drainage channel, and the drainage consolidation of a soft soil layer is accelerated; all the micro piles 1 are connected into a whole through reinforced concrete beams 3, as shown in fig. 2a, 2b and 2c, the soft soil layer is supported, and the soft soil layer can be effectively prevented from lateral sliding and overall instability in the upper embankment filling process; a PVC sleeve 7 is arranged between the micro pile 1 and the reinforced concrete beam 3, so that the micro pile 1 can move vertically and freely under the action of filling load; a pile cap 6 of the miniature pile 1 is sequentially provided with a drainage sand cushion layer 4, a mattress layer 5, graded broken stones 8 and a geogrid 9; under the action of the filling load of the embankment at the upper part, the soft soil layer is subjected to drainage consolidation, pore water is discharged into a sand cushion layer 4 through a vertical drainage channel formed by sand or broken stone 2 of a micro pile 1, and then is discharged out of the range of the roadbed, and consolidation settlement is generated on the soft soil layer; the miniature pile 1 adjusts pile top elevation according to the settlement deformation characteristics of the soft soil embankment, after the soft soil is subjected to settlement deformation, the vertical load sharing of the pile is adjusted through the mattress cushion layer 5 and the pile cap 6, the stress concentration of the top surface of the miniature pile is reduced, the deformation of the embankment is coordinated, and post-construction settlement and uneven settlement of the soft soil roadbed can be effectively reduced.
The sand or broken stone in the miniature pile forms a vertical drainage channel, so that the consolidation of soft soil is accelerated under the loading effect of the filled soil of the upper embankment, the physical and mechanical properties of the soft soil are improved, and the stability of the soft soil embankment can be enhanced. The micro piles are connected into a whole through the reinforced concrete beam, so that the stability of the embankment is greatly enhanced, and the soil filling rate can be accelerated. The micro piles are large in settlement at the center of the embankment according to the settlement deformation characteristics of the soft soil embankment, small in settlement at the edge of the embankment, pile top elevation of each micro pile is adjusted in advance, and post-construction settlement and uneven settlement of the soft soil embankment can be effectively reduced. The construction is convenient and fast, and the defects of limited filling rate, large settlement after construction, easy instability of roadbed and long construction period of the drainage consolidation method are overcome. The construction cost is low, compared with the conventional rigid pile, the construction machinery requirement is low, the miniature pile is simple in manufacturing process, and the construction cost of a single pile is low.
The miniature pile construction method suitable for reinforcement treatment of highway soft foundation reinforcement structure is characterized by comprising the following steps:
(A) And (3) preparation of construction: finishing site cleaning and leveling, pile position measurement and lofting, steel flower pipe customization and construction material purchase preparation, wherein the important points are that the diameter and the length of the steel flower pipe are determined through calculation by combining the thickness of a soft foundation and the filling height of an upper embankment; determining a standard section of the steel floral tube according to the capability of construction mechanical equipment and the site clearance requirement; after the basic parameters of the steel floral tube are determined, standardized and customized by manufacturers;
(B) Pile pressing: pressing the steel floral tube of the first section of micro pile into the soil layer by adopting a static pile press according to the pile position placed in the step (A), lengthening the steel floral tube of the micro pile after filling bagged sand in the steel floral tube, and circularly constructing by adopting threaded connection among the steel floral tubes of each micro pile until the micro pile tip reaches the designed elevation for facilitating site construction; in order to reduce disturbance of the pile pressing on the soft soil layer, pile jumping construction is carried out;
(C) Cast-in-situ reinforced concrete beam: after the mini pile is pressed, before concrete is poured, a PVC sleeve is arranged between the reinforced concrete beam (3) and the mini pile (1); the reinforced concrete beam (3) is cast in situ, all the micro piles are connected into a whole, the anti-instability capability of a soft foundation is greatly improved, and the filling rate of the upper embankment is accelerated;
(D) Presetting pile top elevation and installing pile caps: estimating total settlement of the soft soil layer under the action of upper filling load according to the thickness of the soft soil layer, the strength of the pile tip soil layer and the upper filling load, drawing an estimated settlement curve of the embankment, adjusting the elevation of the miniature pile top by combining the estimated drainage consolidation settlement value, and installing pile caps at the middle part and the two sides of the miniature pile top;
(E) Paving a sand cushion layer: paving a sand cushion layer on the reinforced concrete beam, wherein the top elevation of the sand cushion layer is higher than the top elevation of the pile cap of the miniature pile, and the concrete numerical value is determined according to the estimated main consolidation settlement value before the pavement structure layer begins to be constructed;
(F) Laying a mattress layer: and paving graded broken stone with a certain thickness on the sand cushion, and rolling and backfilling the sand cushion in two layers, wherein two layers of high-strength geogrids are paved, so as to coordinate the deformation of the whole roadbed.
To verify the effectiveness of the present reinforcing structure, it is illustrated by computational analysis of one example of an item. In the project of constructing the expressway in a plain area, the width of the roadbed is 34m, and the filling height is 8m. According to the survey and drilling data, the foundation soil is sequentially soft plastic mucky soil, plastic powdery clay, medium-density fine sand and dense fine sand from top to bottom. The analytical calculation main parameters are shown in Table 1.1.
Table 1.1 soil layer basic information table
1. Drainage fixing method
When the drainage fixation method is adopted independently, the embankment filling soil needs to be filled in multiple times. According to the standard calculation, the limit height h=5.14×c/gamma=5.14×10/20=2.55 m of the first layer of filling soil, the height of the embankment filling soil in the case is 8m, in order to ensure the overall stability of the embankment in the embankment filling process, the preliminary design can be carried out according to 4 times, the height of each filling is 2m, and when the preloading is adopted, the preloading time is not less than 6 months according to the standard requirement.
If the increase of the consolidation strength is not considered, the soil filling height is 8m, and the calculation result of the roadbed stability is shown in fig. 6.
The swedish strip division method is adopted for calculation, the integral stability coefficient of the roadbed is 0.844 < 1.1, the requirement of the standard 'highway soft soil foundation embankment design and construction technical rules' is not met, the time for waiting for the growth of the shearing strength of the mucky soil is long, and the integral construction period of the project is seriously influenced. The overall stability of the subgrade is poorer if the dead weight of the pavement structure layer and the load of the automobile are considered.
2. Micro pile reinforcing structure
The specifications of the common steel floral tube are phi 42mm, phi 48mm, phi 50mm, phi 60mm, phi 89mm and phi 108mm, and the common steel floral tube can be processed and customized according to special requirements. As the filling height of the present case is 8m and the filling height is not large, the diameter of the steel flower pipe is 48m, the wall thickness is 4mm, and the sectional area is 5.529cm 2 According to the steel structural design standard (GB 50017-2017), the design value of the shear strength of a single micro pile is 125N/mm 2 ×5.529×10 2 mm 2 The stability analysis and calculation of this time takes 65kN, the distance between micro piles is 1.5m, the pile length is 12m, the quincuncial arrangement is adopted, and the calculation result of the roadbed stability is shown in fig. 7.
The swedish strip division method is adopted for calculation, the integral stability coefficient of the roadbed is 1.205 & gt1.1, the requirement of the standard 'highway soft soil foundation embankment design and construction technical rule' is met, the strength increase after the solidification of the later-stage mucky soil can be used as a safety reserve, the integral stability of the soft soil roadbed is greatly improved, the roadbed filling can be filled to the design elevation at one time, and the construction period is greatly shortened.
Although embodiments of the present utility model have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the utility model, the scope of which is defined in the appended claims and their equivalents.
Claims (3)
1. A soft soil roadbed reinforcing structure suitable for a highway comprises a plurality of micro piles (1), reinforced concrete beams (3), a drainage sand cushion layer (4) and a mattress layer (5); the method is characterized in that: the miniature pile (1) consists of a steel flower pipe, sand or broken stone (2) in the steel flower pipe and a pile cap (6), wherein the sand or broken stone (2) in the steel flower pipe forms a vertical drainage channel to accelerate the drainage consolidation of a soft soil layer; all the micro piles (1) are connected into a whole through reinforced concrete beams (3); the upper part of the pile cap (6) of the miniature pile (1) is sequentially provided with a drainage sand cushion layer (4) and a mattress layer (5).
2. A reinforcing structure for a soft soil subgrade of a highway according to claim 1, wherein: PVC sleeves (7) are arranged between the micro piles (1) and the reinforced concrete beams (3).
3. A reinforcing structure for a highway soft soil subgrade according to claim 1 or 2, characterized in that: the mattress layer (5) consists of laid graded broken stones (8) and geogrids (9).
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