AU2021102288A4

AU2021102288A4 - Composite Replacement Structure and Treatment for Soft Base of Coastal Mudflat

Info

Publication number: AU2021102288A4
Application number: AU2021102288A
Authority: AU
Inventors: Zhenchao Chang; Chuan Chen; Haifeng Huang; Zebin HUANG; Dunren Li; Shiming Li; Xianlin Liu; Junhui Luo; Xilin Lv; Decai Mi; Peng Mo; Chun QI; Zhenghui Tang; Qinzhen Wen; Chunwei Wu; Longwang Xu; Qiongyao Ye; Fuquan Zeng
Original assignee: Guangxi Beitou Transportation Maintenance Technology Group Co Ltd; Guangxi Communications Design Group Co Ltd
Current assignee: Guangxi Beitou Transportation Maintenance Technology Group Co Ltd; Guangxi Communications Design Group Co Ltd
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2021-06-24
Anticipated expiration: 2029-04-30

Abstract

The present invention discloses a composite replacement structure and treatment for soft base of coastal mudflat, which relates to the field of soft base treatment. The present invention provides a composite replacement structure for soft base of coastal mudflat, including sea sand bedding layer, gravel bedding layer, geogrid layer, embankment filling layer and road structure layer, and is set in order from bottom to top, with sea sand bedding layer and gravel bedding layer located below the ground, and geogrid, embankment filling layer and road structure layer located above the ground. The present invention also provides a soft base replacement treatment, which is applied to the above-mentioned composite replacement structure. The composite replacement structure and treatment for soft base provided by the present invention can make full use of abundant sea sand resources, reduce the cost of soft base replacement, shorten the construction period, and effectively ensure the quality of soft base replacement, which has good economic benefits and far-reaching social benefits.

Description

Composite Replacement Structure and Treatment for Soft Base of Coastal Mudflat

TECHNICAL FIELD The present invention relates to the field of soft ground treatment, specifically, to the composite replacement structure and treatment for soft base of coastal mudflat. BACKGROUND With the rapid development of China's economy, there emerges the rapid expansion of demand for road construction and great challenges to the quality of road construction. Since China has vast territory, many highways construction, in the coastal mudflat phase on soft ground and along the coastal areas, often encounter saturated silty clay and underground fine sand layer, if improperly treated, and are very easy to cause the construction period and operation of the roadbed longitudinal delayed and cracked, roadbed slippage and bridge and bridge-culvert joints bump and other issues. Guangxi province, as an important channel connecting the coastal area of the North Gulf, has coastal highway of 314. 2km long. The route along the coastline of Beibu Gulf and its soft ground section is more than 200km long, accounting for about 70% of the total length of the route. Coastal highway is generally located in the coastal terrace plain area, which is flat and low in altitude. Therefore, there are following technical features: long-term remaining of the high water level, poor engineering properties of soft soil, few surrounding stones and abundant sea sand resources. According to the current relevant specifications, soft base replacement materials are generally sheet stone, gravel, pebbles, gravel and other. However, because the coastal areas usually lack of such materials, if all replacement fillers are outsourced, the replacement filler mobilization distance, high expense and other problems remain. If all the soft base replacement use the above outsourcing materials, the soft base treatment will solely generate huge costs. For the features of soft base in coastal mudflat, the treatment should focus on soft soil composition, structure, groundwater, replacement material type and source, and embankment stability and other aspects. The existing soft base treatment is a good solution to the problems of long-term and high water level, poor engineering properties of soft soil, and less stones around in the construction of roads on soft soil in the coastal mudflat area. The coastal area is very rich in sea sand resources while the price of sea sand is relatively cheap. If we can make full use of sea sand for soft base replacement, we will greatly reduce the cost of soft base treatment in the coastal mudflat area. SUMMARY The purpose of the present invention is to provide a composite replacement structure for soft base of coastal mudflat, which improves the problem of long-term remaining of the water level and high water level, poor engineering properties of soft soil and less stones around occurred in the construction of roads on soft base of coastal mudflat. At the same time, it fully utilizes the abundant sea sand resources by the sea, reduces the cost of soft base replacement, accelerates the speed of soft base replacement, shortens the construction period, and effectively ensures the quality of soft foundation replacement, carrying good economic and far-reaching social benefits. Another purpose of the present invention is to provide a composite replacement and treatment for soft base of coastal mudflat, which improves the problem of long-term remaining of the water level and high water level, poor engineering properties of soft soil and less stones around occurred in the construction of roads on soft base of coastal mudflat. At the same time, it fully utilizes the abundant sea sand resources by the sea, reduces the cost of soft base replacement, accelerates the speed of soft base replacement, shortens the construction period, and effectively ensures the quality of soft foundation replacement, carrying good economic and far-reaching social benefits. The present invention provides a technical solution: There is a composite replacement structure for soft base of coastal mudflat suitable to replacement treatment of soft base in coastal mudflat areas. The composite replacement structure for soft base of coastal mudflat consist of sea sand layer, gravel layer, geogrid layer, embankment fill layer and pavement structure layer; the cross sectional shape of sea sand layer, gravel layer, geogrid layer, embankment fill layer and pavement structure layer are trapezoidal, and are set in sequence from bottom to top. The sea sand layer and gravel layer are located below the ground, meanwhile the geogrid layer, embankment fill layer and pavement structure layer are above the ground.

Further, the long side of the above-mentioned sea sand layer's cross-section is in contact with the short side of the gravel layer's corss-section, and the long side of the gravel layer's cross-section is in contact with that of the embankment fill layer. In addition, the long side of the gravel layer's cross-section is longer than that of the embankment fill layer. Further, the above gravel layer is located between the sea sand layer and the embankment fill, and the sea sand layer is thicker than the gravel layer. Further, the above geogrid is provided between the embankment fill layer and the gravel layer, and geogrids are multiple and laminated to each other. Further, the geogrid is laid in a direction perpendicular to the forward direction of the route, and the cross-sectional direction should be laid in the outer edge of the roadbed backpacking 150cm to 200cm. The connection of two adjacent geogrids is lap joint, and their stacking length is no less than or equal to 15cm. There is a composite replacement treatment for soft base of coastal mudflat applied to composite replacement structure for soft base of coastal mudflat. The composite replacement structure and highway roadbed of coastal mudflat consist of a sand layer, gravel layer, embankment fill layer and pavement structure layer. The cross-sectional shape of sea sand layer, gravel layer, embankment fill layer and pavement structure layer are all trapezoidal, and are set in order from bottom to top, with sea sand layer and gravel layer located below the ground and embankment fill layer and pavement structure layer located above the ground. The composite replacement treatments for soft base of coastal mudflat consist of construction preparation, measurement and sampling, soft soil thickness test, soft soil layer removal, substrate bearing capacity test, backfill sea sand, backfill gravel, roadbed filling and pavement structure paving. The soft soil layer removal comprises excavating and removing of the soft soil layer of the selected coastal section by sloping. The backfilling sea sand comprises filling the replacement pit with sea sand and rolling it with a roller to secure a sea sand layer. The gravel backfilling comprises laying the gravel layer on top of the sea sand layer and rolling it with a roller to secure the gravel layer. Geogrid laying involves laying and impacting on top of the gravel layer to secure a geogrid layer. The roadbed filling involves filling on top of the gravel layer to secure the embankment filling layer. The paving of pavement structure requires carrying out the pavement structure construction on top of the embankment fill layer to secure the pavement structure layer. Further, the above-mentioned of removing the soft soil layer from the selected coastal section includes excavating the soft soil layer by using an excavator and releasing the slope in the excavation to ensure the stability of the slope of the soft soil pit. Clearing the soft soil layer from the bottom of the replacement pit requires small machinery and manual labour. Further, the above -mentioned of filling the soft soil pit with sea sand is one of steps of pushing and paving sea sand in layers. Pushing and paving sea sand in layers involves backfilling with medium coarse sand by bulldozers starting from one end of the soft soil pit to another; backfilling with gravel further involves that after each step of pushing and paving sea sand in layers being implemented, the sea sand paving layer formed after the pushing and paving should be filled with water and be compacted after water level is higher than the layer and the layer is saturated. Further, the above -mentioned of filling the soft soil pit with a sea sand layer with gravel is one of the steps of layering gravel; the gravel backfilling also involves compacting the gravel paving layer formed after layering gravel. And it is implemented by using a roller for multiple times, and the wheel tracks of each times overlap by 1/3. Further, the above-mentioned composite replacement treatments for soft base of coastal mudflat also require a geogrid laying to secure a geogrid layer; the geogrid laying is executed between the gravel backfilling and the roadbed filling; geogrid laying step involves laying the geogrid vertically on the top surface of the gravel layer along the laying direction, and two adjacent geogrids are lapped with each other. Compared with the prior technology, the beneficial effects of the composite replacement structure and treatment for soft base of coastal mudflat provided by the present invention are. The materials required by the sea sand layer come directly from the abundant local sea sand resources, which can save a lot of personnel, material and financial resources. The organic combination of sea sand and gravel for soft ground replacement treatment solves the problem of water return encountered during the process of construction and ground rolling, enhances the strength of the composite replacement structure for soft base of coastal mudflat, and reached smaller the settlement of the treated soft soil composite replacement roadbed. At the same time, the water treatment structure is stable and low in price, which greatly reduces the engineering cost. The composite replacement structure and treatment for soft base of the coastal mudflat provided by the present invention solves the problem of long-term and high water level, poor engineering properties of soft soil and less surrounding stones in the construction of highway on the soft soil of coastal mudflat phase, which can fully utilize the rich sea sand resources, reduce the cost of soft base replacement, accelerate the speed of soft base replacement and shorten the construction period; adding gravel layer on the sea sand layer solves the problems of water return of fine sea sand under the condition of high water level; and because the pressure diffusion effect of fine stone has better performance than that of sea sand, it enhances the structural strength of soft base replacement and can effectively ensure the quality of soft foundation replacement, which has good economic benefits and far reaching social benefits. BRIEF DESCRIPTION OF THE FIGURES In order to illustrate the technical solutions of embodiments of the present invention in a clearer manner, the following is a brief description of the drawings required to use in the embodiments. It should be understood that the following drawings illustrate only certain embodiments of the present invention and should not be regarded as limits of the scope. To a staff of common skill in the art, other relevant drawings may be drawn from these drawings without creative effort. FIG. 1 is a structural schematic diagram of the composite replacement structure for soft base of the coastal mudflat provided by the first embodiment of the present invention; and FIG. 2 is a schematic diagram of an enlarged structure at II in FIG. 1. FIG. 3 is a schematic diagram of the structure of the geogrid provided by the first embodiment of the present invention; and FIG. 4 is a schematic diagram of the process of the composite replacement treatment for soft base of the coastal mudflat provided by the second embodiment of the present invention.

Icons: 100-composite replacement structure for soft base of coastal mudflat; 110-sea sand layer; 120-gravel layer; 130-geogrid; 131-first grid; 132-second grid; 133-bundle; 140-embankment fill layer; 150-pavement structure layer; S-construction preparation; S2-measurement and sampling; S3-soft soil bearing capacity testing; S4- soft soil layer removal; S5-base bearing capacity test; S6-backfill sea sand; S7-backfill grave; S8 geogrid laying; S9-roadbed filling; S10-pavement structure paving. DESCRIPTION OF THE INVENTION In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be vividly and wholly described below with the drawings in the embodiments of the present invention. Obviously, the described embodiments are a part of the embodiments of the present invention, and not all of them. The components of the embodiments of the present invention generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations. Accordingly, the following detailed description of embodiments of the invention provided in the drawings is not intended to limit the scope of the invention for which protection is claimed, but merely indicates selected embodiments of the invention. Based on the embodiments in the present invention, all other embodiments obtained without creative labour by a personnel of common skill in the art fall within the scope of protection of the present invention. It should be noted that similar symbols and letters indicate similar items in the drawings below, so that once an item is defined in one of the drawings, it would not be required to further define and explain in subsequent drawings. In the description of the present invention, it should be understood that the terms "upper", "inner", "outer", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or position of the product of the invention as it is customarily placed when being used, or as it is customarily understood by those skilled in the art. They are intended only to facilitate and simplify the description of the invention, not to indicate or imply that the equipment or components referred to must be of a particular orientation, constructed and operated in a particular orientation, and therefore are not to be construed as limits of the invention.

In addition, the terms "first", "second", etc. are used only to distinguish the description and should not be understood as indications or implications of relative importance. Specific embodiments of the present invention are described in detail below with drawings. First Embodiment As Referred in FIG.1 and FIG.2, this embodiment provide a composite replacement structure for soft base of coastal mudflat 100, which improves the problem of long remained and high water level, poor engineering properties of soft soil, and less surrounding stones that exist in the construction of roads on the coastal mudflat of soft base, and offering good economic and far-reaching social benefits. This embodiment provides the composite replacement for soft base of coastal mudflat, including the ground (figure not marked). For the characteristics of the soft soil in the coastal mudflat, the soft soil treatment should focus on the soft soil composition, structure, groundwater, replacement material and embankment stability. The composite replacement structure for soft base of coastal mudflat 100 provided by this embodiment consists of sea sand layer 110, gravel layer 120, geogrid 130, embankment fill layer 140 and pavement structure layer 150, the cross-sectional shape of sea sand layer 110, gravel layer 120. The embankment fill layer 140 and pavement structure layer 150 are trapezoidal, and are set in order from bottom to top, on which sea sand layer 110 and gravel layer 120 are located below the ground, and embankment fill layer 140 and pavement structure layer 150 are located above the ground; geogrid 130 is located between gravel bedding layer 120 and embankment fill layer 140. It will be understood that the sea sand layer 110 is formed by pushing and paving the sea sand and that the gravel layer 120 is also formed by pushing and paving the gravel. In this embodiment, the cross-sectional shape of the sea sand layer 110, the gravel layer 120, the embankment fill layer 140 and the pavement structure layer 150 are all trapezoidal. It is understandable that the trapezoidal cross-section of the sea sand layer 110, the gravel layer 120, the embankment fill layer 140 and the pavement structure layer 150 may be isosceles trapezoidal or any other trapezoidal shape.

In this embodiment, the long side of the sea sand layer 110's cross-section is in contact with the short edge of the gravel layer 120 cross-section; the long edge of the gravel layer 120's cross-section is in contact with the long edge of the embankment fill layer 140; the long edge of the gravel layer 120's cross-section has an edge length longer than that of the embankment fill layer 140. In this embodiment, both the sea sand layer 110 and the grave layer 120 are located below the ground surface, and both the embankment fill layer 140 and the pavement structure layer 150 are located above the ground surface. The long side of the cross section of the gravel layer 120 is longer than that of the embankment fill layer 140, which can make the embankment fill layer 140 and the pavement structure layer 150 located on the ground more stable in structure under the support of the sea sand layer 110 and the gravel layer 120, thus improving the stability of composite replacement structure for soft base of coastal mudflat 100. The range of the long side of the cross-section of the sea sand layer 110 can be selected between one of the excavation lengths from 60m and 200m (including the end point value) depending on the geological conditions. In this embodiment, the long side of the cross-section of the sea sand layer 110 is 100 m. Of course, it is not limited to this, but in other embodiments of the present invention, this side length may also be of other variables, such as 90 m, etc. In this embodiment, the thickness of the sea sand layer 110 is greater than that of the gravel layer 120. The pressure spreading ability of the gravel layer 120 is stronger than that of the sea sand layer 110, so the gravel layer 120's can make the composite replacement structure for soft base of coastal mudflat 100's more stable. In this embodiment, the thickness of sea sand layer 110 is 1. 5 m, and the thickness of gravel bedding layer 120 is 0. 5 m. Of course, it is not limited to this. In other embodiments of the present invention, sea sand layer 110 and gravel layer 120 can also vary in thickness. For instance, the thickness of sea sand layer 110 is 2. 0 m and the thickness of gravel layer 120 is 0. 8 m, etc. The specific thickness of sea sand layer 110 and gravel layer 120 can be determined according to the embankment filling height, groundwater level and stress diffusion calculation.

In order to make the composite replacement structure for soft base of coastal mudflat 100 resistant in terms of compression. The compaction degree of the sea sand layer 110 is from 85% to 95%, and that of the gravel layer 120 is greater than the 90%. In this embodiment, the compaction degree of the sea sand layer 110 is 90% and the compaction degree of the gravel layer 120 is 90%. Of course, it is not limited to this. In other embodiments of the present invention, the compaction degree of the sea sand layer 110 and the gravel layer 120 may also be of other variables. For instance the compaction degree of the sea sand layer 110 is 89% and the compaction degree of the gravel layer 120 is 91%, etc. As referred to FIG. 3, the geogrids 130 provided in this embodiment is one-layered, and the geogrids 130 are buried in between the embankment fill layer 140 and the gravel layer 120. It is understood that the geogrid 130 can also be set in multiple layers depending on the stability requirements of the specific roadbed. Preferably, the number of layer of geogrid 130 is from I to 3. The role of geogrid 130 is to enhance the stability of the composite replacement structure for soft base of coastal mudflat 100. The geogrid 130 is set between the embankment fill layer 140 and gravel layer 120, making the composite replacement structure for soft base of coastal mudflat 100 more stable It can be understood that the geogrid 130 is laid in a direction perpendicular to the forward direction of the route, and the cross-sectional direction should be laid in the outer edge of the roadbed backpacking 150cm to 200cm. The connection of two adjacent geogrids 130 is lap joint, and their stacked length is no less than 15cm. In this embodiment, the geogrid 130 consist of the first grid 131, the second grid 132 and the bundle 133. The first grid 131 and the second grid 132 are set perpendicular to each other; two adjacent geogrids 130 are connected to each other by lap joints; the bundle 133 serves as binding tool to lap the first grid 131 and the second grid 132 to each other. In this embodiment, the bundle 133 is a wire. Of course, it is not limited to this. In other embodiments of the present invention, the bundle 133 can also bear other structures. For instance,bundle 133 can be a rope made of nano-polymer material, etc.

The beneficial effect of the composite replacement structure for soft base of coastal mudflat 100 provided by this embodiment is that the material required for the sea sand layer 110 comes directly from the rich local sea sand resources, and the organic integration of sea sand and gravel is used for the composite replacement treatment of the soft base, which solves the problem of resurgence of water when compressed countered during construction, improves the strength of the composite replacement structure for soft base of coastal mudflat 100, and crack down huge settlement of the composite soft soil roadbed. The composite replacement structure for soft base of coastal mudflat 100 provided by this example solves the problems of long-term remaining of high water level, poor engineering properties of soft soil, less surrounding stone, water resurgence when compressed, etc. that exist in the coastal mudflat soft soil construction road. It, by fully utilizing the rich sea sand resources by the sea, reduces the cost of soft base replacement, accelerates the speed of soft base replacement, shortens the construction period. The treatment structure has good stability in water and low price, greatly reducing the project cost and bringing significant economic and far-reaching social benefits. Second embodiment As referred to Figure 4, this embodiment provides a composite replacement treatment for soft base of coastal mudflat, which solves the problem of long-term existence of the water level and high water level, poor engineering properties of soft soil, less surrounding stone on the construction of roads on the coastal mudflat phase. The treatment is easy to operate on-site construction, to have soft base replacement quality control. And construction costs are small, construction period is short, with good economic benefits and Far-reaching social benefits. This example provides the composite replacement treatment for soft mudflat of coastal mudflat includes construction preparation Sl, measurement and sampling S2, soft soil bearing capacity test S3, removal of soft soil layer S4, substrate bearing capacity test S5, backfill sea sand S6, backfill gravel S7, geogrid laying S8, roadbed filling S9 and pavement structure paving S10, which are described below are described below. Construction preparation step SI In this embodiment, the construction preparation S1 includes: preparing to lay sea sand layer 110 with the particle size above medium coarse sand, mud content < 5%, permeability coefficient > 6x10-2 to 6x10-3cm/s; preparing to lay gravel bedding layer 120 in which the gravel is hard - harder rock material and the mud content< 5%; preparing to lay geogrid 130 with tensile strength, elongation, junction-limit releasing force should meet the design requirements; the liquid limit of the filler in the ready-to-lay embankment fill layer 140 is less than 50%; the plasticity index is less than 26%, and the roadbed bearing ratio is >3; the material of the ready-to-lay pavement structure layer 150 should meet the relevant design requirements. In this embodiment, the proportion of particle composition of sea sand layer 110 is 46. 3% for particle size 0. 5-2. 0mm, 38. 9% for 0. 25-0. 5mm, 7. 2% for 0. 75-0. 25mm, 85. 2% for medium and coarse sand content, 0. 7% for mud content, and 5x10-2cm/s for permeability coefficient. Gravel layer 120 material is medium weathered granite rock, It is hard, with compressive strength more than 30Mpa and mud content of 0. 2%. The gravel rock cannot be made of swelling rock, easily softened rock, soluble rock or salinized rock. The geogrid 130 is GDZ150 two-way rigid plastic tack-welded geogrid 130 with a longitudinal ultimate tensile strength of 15OkN/m per linear meter, an elongation of 2. 5% under the longitudinal nominal tensile strength, a width of 6m, and a junctional ultimate releasing force of 60N. The physical and mechanical indexes of the filler of embankment fill layer 140 are the range of liquid limit from 19. 5% to 40. 3%, the range of plasticity index from 8. 6% to 22. 4%, and the range of roadbed bearing ratio from 3. 8 to 19. 6. Measurement and sampling S2 In this example, the measurement and sampling S2 includes: finishing the remeasurement of the level points according to the requirements of the fourth class level measurement, finishing the remeasurement of the attached conductor and the adding additional level points according to the requirements of the first class conductor measurement, and the encryption of the conductor points. Checking the longitudinal and cross-sectional map, putting out the highway land area line, and putting out the middle and side piles according to 20m a pile, carrying out the original ground elevation, longitudinal section elevation, cross-sectional resurvey are required. Soft soil bearing capacity test step S3

In this embodiment, the soft soil bearing capacity test S3 includes: surface drainage and soft soil bearing capacity test by standard light power tapping, so as to verify whether the excavation depth of soft base provided by design is accurate and reasonable. The longitudinal test spacing of the roadbed is controlled by 20m, and the cross section of the roadbed is controlled by 3 points on the left, middle and right, and the test depth is controlled by the designed foundation bearing capacity required for different fill heights, and the design foundation bearing capacity ranges from 120kPa to 150kPa. Removal of soft soil layer S4 In the section to be replaced, suitable construction sections are delineated and the length of each replacement area is determined. The soft soil layer is removed from the selected coastal section to obtain a soft soil pit. Preferably, the soft soil pit is sloped so that the cross-sectional shape of the soft soil pit is trapezoidal. In this embodiment, an excavator is used to excavate and remove the soft soil layer within the depth of the replacement fill. Usually the replacement pit obtained by the excavator will have a certain thickness of soft soil layer remaining at the bottom of the pit, which is cleared by small machines or manually. According to the weather, construction capacity, soft soil geological conditions, etc., a suitable construction section is defined, with each section being 60 to 200m long. In this example, the excavator is used to excavate the soft soil layer within the depth of the replacement. When excavating, attention is paid to the stability of the slope of the pit wall and the bottom of the replacement pit to avoid serious disturbance of the submerged layer. When the bottom of the replacement pit is not level, it should be made into a step form, and the backfill should be filled according to the principle of deep first and then shallow. Soft base pits should not be exposed for a long time, and sea sand layer 110 and gravel layer 120 should be prepared in in advance. Subgrade bearing capacity test S5 In this embodiment, the subgrade bearing capacity test S5 includes: after the excavation of soft soil foundation pit, the soft soil bearing capacity test is carried out again by standard light power tapping to verify whether the soft soil excavation is complete, otherwise the second excavation should be carried out to remove the soft soil.

Subgrade bearing capacity test's spacing is still controlled according to the longitudinal direction of the roadbed 20m, the roadbed cross-section is controlled according to the left, middle and right 3 points, the test depth is controlled according to the design foundation bearing capacity range of 12OkPa ~ 150kPa. Sea sand Backfilling S6 Filling the soft soil pit with sea sand to obtain a sea sand layer 110. In this embodiment, the step of filling the soft soil pit with sea sand is a plurality of steps of pushing and paving the sea sand in layers, and the step of pushing and paving the sea sand in layers includes backfilling with medium coarse sand by bulldozers starting from one end of the soft soil pit and assisted by small machinery and manual paving. At the end of each step of pushing and paving the sea sand in layers, the sea sand pavement formed after the step of pushing and paving the sea sand in layers is filled with water and the water surface is raised above the level of the sea sand pavement, and after the sea sand pavement reaches saturation, the sea sand pavement is compacted. When starting to backfill with medium coarse sand, the water in the pit should be drained. Backfill with coarse sand by bulldozer starting from one end, pushing and paving in layers of 30-40cm thick, with individual dead ends paved by manual assistance. After paving a layer of water injection, the water surface requirements just diffuse over the top surface of the sand layer, in a water-filled state, using a bulldozer with a weight of more than 15t to walk back and forth, using the self-weight of the bulldozer through the crawler will be compacted sand layer, compaction route along the route longitudinal, from the road side to the road or from the lower side to the higher side of the order of compaction, between the two walking routes must overlap 1/3 machine, to ensure that no leakage of pressure. The construction is based on the number of passes and compactness testing as quality control points. If the pit is particularly rich in groundwater, thick layer of sea sand paving can also be used, the thickness of the sea sand is controlled by slightly higher than the groundwater surface, using a small self-weight crawler bulldozer from one end of the pit to the other end of the paving, through the crawler bulldozer to move back and forth for initial rolling, and then use the vibratory roller for compaction, the vibration strength of the rolling from small to large. Backfilling gravel S7

Filling the soft soil pit having a sea sand layer 110 with fine stone to obtain a fine stone layer 120. The step of filling the soft soil pit having the sea sand layer 110 with fine stone is a plurality of steps of spreading crushed stone in layers. In this embodiment, the backfilling gravel S7 further comprises compacting the gravel pavement layer formed after the step of layered paving gravel, and the step of compacting the gravel pavement layer formed after the step of layered paving gravel is performed by using a roller for multiple rolling and overlapping the wheel tracks by 1/3 for each rolling. After the completion of backfilling sea sand layer 110 can be backfilled with gravel layer 120, before backfilling sea sand layer 110 top surface can not have open water, gravel using graded gravel, gravel paving and medium coarse sand paving method is the same, the difference is that the graded gravel using the roller compaction, compaction requirements greater than 90%. The crushed stone bedding layer 120 thick Im, backfilled in layers, the thickness of the layers and the number of times to roll through the test section to determine the thickness of layered paving < 25cm, using 30t vibratory roller rolling more than 4 times, rolling follow the principle of "first low then high, first static then dynamic, first slow then fast", while each time the wheel tracks should overlap 1/3, no leakage of pressure, where In the place where the roller cannot be pressed, use small tamping machine to tamp until the required degree of compaction is achieved. Geogrid laying S8 The coastal beach soft base composite replacement treatment method further comprises a geogrid laying step S8 to obtain a geogrid 130 bedding layer, the geogrid 130 laying step being intermediate between the backfilling gravel step S7 and the roadbed filling step S9. In this embodiment, the geogrid laying S8 includes laying the geogrid 130 vertically on the top surface of the gravel bedding layer 120 along the laying travel direction, with two adjacent geogrids 130 lapping each other. Using manual laying, the surface should be smooth, laying direction perpendicular to the direction of the route forward, paving the entire top surface of gravel bedding layer 120, cross-sectional direction laid to 30cm beyond the outer edge of the roadbed, the geogrid 130 of the outer edge of the roadbed should be backpacked 150cm ~ 200cm, geogrid 130 coupling method using lap, wire tied coupling, and its laminated length should not be less than 15cm. to protect Geosynthetic material tendon role, must be tensioned before covering soil, filling must be strictly in accordance with the side to the other side of the unidirectional lay flat to advance, it is strictly prohibited to drive directly on the geogrid 130. Roadbed filling S9 Filling is performed on the gravel bedding layer 120 to obtain the embankment fill layer 140. Pavement structure paving S10 The pavement structure is constructed on the embankment fill layer 140 to obtain the pavement structure layer 150. The beneficial effect of the coastal beach soft base composite replacement treatment method provided by this embodiment: the sea sand required for the sea sand bedding layer 110 comes directly from the local area, which can save manpower and financial resources. The organic combination of sea sand and gravel is used to treat the soft foundation, thus improving the strength of the composite replacement structure 100 of the soft foundation of the coastal mudflat, and the settlement of the treated composite soft foundation is small. The construction process of the treatment method is simple, without special construction machinery and equipment, less constrained factors, easy to construct, and the construction progress is faster. At the same time, the treatment structure has good water stability and low price, which greatly reduces the project cost. This embodiment provides the coastal mudflats soft base composite replacement structure 100 to improve the construction of highways on the coastal mudflats phase of soft soil exists in the groundwater table for a long time and the water table is high, soft soil engineering properties are poor, the surrounding stone less problems, with good economic benefits and far-reaching social benefits. The above described is only a preferred embodiment of the present invention only, and is not used to limit the present invention, for the skilled person in the field, the present invention can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A composite replacement structure for soft base of coastal mudflat, suitable for replacement of soft base of coastal mudflat areas, characterized in that it includes a sea sand layer, a gravel layer, a geogrid layer, an embankment fill layer and a pavement structure layer, the sea sand layer, the gravel layer, the geogrid layer, the embankment fill layer and the pavement structure layer all have a trapezoidal cross-sectional shape and are set in sequence from the bottom up. The sea sand layer and the gravel layer are located below the ground level, and the geogrid layer, the embankment fill layer and the pavement structure layer are located above the ground level.
2. The composite replacement structure for soft subgrade of coastal mudflat according to claim 1, characterized in that the long side of the sea sand layer cross section is in contact with the short side of the gravel layer cross-section, the long side of the gravel layer cross-section is in contact with the long side of the embankment fill layer, and the long side of the gravel layer cross-section is longer than the long side of the embankment fill layer.
3. The composite replacement structure for soft base of the coastal mudflat according to claim 1, characterized in that the gravel layer is located between the sea sand layer and the embankment fill, and the sea sand layer is greater than the thickness of the gravellayer.
4. The composite replacement structure for soft base of the coastal mudflat according to claim 1, characterized in that the geogrid is provided between the embankment fill layer and the gravel layer, and the number of the geogrid is a plurality, and the plurality of the geogrid is laminated to each other.
5. The composite replacement structure for soft base of coastal mudflat according to claim 4, characterized in that two adjacent geogrids are connected by lap joints, and their stacked length is greater than or equal to 15cm.
6. A composite replacement and treatment for soft base of the coastal mudflat as claimed in any one of claims 1-5, characterized in that the composite replacement and treatment for soft base of coastal mudflat includes construction preparation, measurement and sampling, soft soil bearing capacity test, soft soil layer removal, subgrade bearing capacity test, sand backfilling, gravel backfilling, geogrid laying, roadbed filling and pavement structure paving.

The construction preparation step: preparing the sea sand, gravel, geogrid, roadbed fill and pavement material etc. required for preparing the composite replacement structure for soft base of coastal mudflat, requiring each material parameter to meet the relevant specification requirements. The soft soil bearing capacity test: soft soil base bearing capacity for standard light dynamic touch test, verify whether the proposed excavation of soft soil thickness is consistent with the design documents, determine whether the excavation depth is accurate and reasonable;. The soft soil layer removal: the soft soil layer of the selected coastal section of the slope excavation to remove, in order to get soft soil foundation pit. The subgrade bearing capacity test: after excavation of the soft soil pit, testing the bearing capacity of the soft soil again to verify whether the soft soil removal is complete, otherwise the second excavation should be carried out to remove the soft soil. The backfilling of sea sand: underwater filling of sea sand to the soft soil foundation pit and rolling with a roller to obtain a sea sand layer meeting compaction requirements. The step of backfilling with gravel: laying the gravel layer on top of the sea sand layer and rolling it with a roller to obtain a gravel layer meeting the compaction requirements.

The geogrid laying: laying a geogrid on top of the gravel layer to obtain the geogrid layer. The roadbed filling: filling on top of the geogrid layer to obtain the embankment filling layer. The pavement structure paving: carrying out the construction of a pavement

structure on the embankment fill layer to obtain the pavement structure layer.
7. The treatment and replacement for soft base of coastal mudflat according to claim 6, characterized in that the step of removing the soft soil layer on a selected coastal section comprises excavating the soft soil layer using an excavator and releasing the slope in the excavation of the soft soil pit to ensure the stability of the slope of the soft soil pit; using small machinery and manual cleaning of the soft soil layer at the bottom of the replacement pit to avoid serious disturbance of the lower the bearing layer.
8. The composite replacement and treatment for soft base coastal mudflat according to claim 6, characterized in that the step of filling the soft soil pit with sea sand is a plurality of steps of pushing and spreading sea sand in layers, the step of pushing and spreading sea sand in layers comprising: backfilling with medium and coarse sand by bulldozers starting from one end of the soft soil pit. The step of backfilling with gravel further comprising: at the end of each the step of pushing and paving sea sand in layers, injecting water into the sea sand pavement formed after the step of pushing and paving sea sand in layers and making the water surface higher than the level of the sea sand pavement, and compacting the sea sand pavement after the sea sand pavement has reached saturation.
9. The composite replacement and treatment for soft base of a coastal mudflat according to claim 6, characterized in that the step of filling the soft base pit having the sea sand bedding layer with gravel is a plurality of steps of spreading gravel in layers. The backfilling gravel step further comprising compaction of the gravel pavement layer formed after the step of layered paving gravel, the step of compaction of the gravel pavement layer formed after the step of layered paving gravel being carried out using a roller for multiple times and overlapping the wheel tracks by 1/3 for each times.
10. The composite replacement and treatment for soft base of coastal mudflat according to claim 6, characterized in that the composite replacement and treatment for soft base of coastal mudflat further comprises a geogrid laying step to obtain the geogrid bedding layer, the geogrid laying step being between the backfilling gravel step and the roadbed filling step. The geogrid laying step comprising laying a geogrid vertically on the top surface of the gravel layer in the direction of laying travel, with two adjacent the geogrids lapped to each other.