CN115573213A

CN115573213A - High liquid limit clay roadbed structure and construction method

Info

Publication number: CN115573213A
Application number: CN202211217003.1A
Authority: CN
Inventors: 马昊; 宋硕; 李敏; 刘智旭; 刘志红; 侯小娜; 马福莲; 吴秀娟; 张航; 楚向克; 王艳鹤; 王�义; 李红雨
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-09-30
Filing date: 2022-09-30
Publication date: 2023-01-06

Abstract

The invention relates to the technical field of roadbed filling, in particular to a high liquid limit clay roadbed structure and a construction method, wherein the high liquid limit clay roadbed structure comprises a lower roadbed and an upper roadbed which are arranged on a foundation, wherein a geotextile waterproof layer and a broken stone cushion layer are sequentially paved on the top of the upper roadbed; the lower roadbed comprises a geotextile waterproof layer, geogrids and a modified high-liquid-limit soil layer, wherein the geotextile waterproof layer, the geogrids and the modified high-liquid-limit soil layer are sequentially laid from bottom to top, and the upper roadbed comprises a geotextile waterproof layer, a stone layer, the geogrids and the modified high-liquid-limit soil layer. Compared with the prior art, the method has the advantages that the high liquid limit clay is modified and utilized, a large amount of precious land resources are saved, the construction progress is effectively accelerated, and the construction cost is reduced; the embankment slope stability is used as a basis, the slope height and the slope of the embankment, data such as the corresponding geogrid interval and the thickness of the sheet stone layer are determined based on theoretical calculation, the overall stability of the embankment is improved by adopting a layered filling mode, the specification and the design requirement are met, and the long-term operation of the embankment is guaranteed.

Description

High liquid limit clay roadbed structure and construction method

Technical Field

The invention relates to the technical field of roadbed filling, in particular to a high liquid limit clay roadbed structure and a construction method.

Background

The stability of the roadbed of the highway is a key problem in the construction process of the highway, and the roadbed with different fillers has great influence on the service life of the roadbed of the highway due to uncertainty of the physical properties (particle grading, weathering degree, water content and the like), the construction process and the control indexes of the construction quality of the roadbed fillers of the highway. However, due to the limitation of natural geological conditions in partial areas, partial lines need to pass through a poor engineering geological area mainly containing high liquid limit clay. The high liquid limit clay refers to clay with the particle size of less than 0.075mm, the content of fine particles of which exceeds 50%, the liquid limit of which is more than 50% and the plasticity index of which is more than 26. China is one of the countries with the widest distribution of high liquid limit clay, and particularly in the middle and lower reaches of Yangtze river and yellow river, and the coastal areas and the southwest areas in the south, the high liquid limit clay develops most and is distributed most widely. The high liquid limit clay has larger plasticity, viscosity and weak expansibility; the water-retaining agent has high natural water content, is not easy to air, has developed capillary pores, has poor water permeability, is easy to absorb water, can retain water for a long time, has small bearing capacity and poor stability after absorbing water, and is difficult to be directly used for roadbed filling of road engineering. If other roadbed fillers are remotely transported, the engineering construction cost is greatly increased; if the high liquid limit clay is abandoned, huge economic loss and environmental problems are caused.

At present, many researches on modification of high liquid limit clay at home and abroad are carried out, and certain progress is made, and the researches show that the modified high liquid limit clay can meet the requirements of roadbed filling construction, but hidden danger still exists in long-term stability of a roadbed filled by the modified high liquid limit clay.

Disclosure of Invention

In order to solve the problems mentioned in the background art, the invention aims to provide a high liquid limit clay roadbed structure and a construction method.

On one hand, the invention provides a high liquid limit clay roadbed structure, which is characterized by comprising a lower roadbed and an upper roadbed which are arranged on a foundation, wherein a geotextile waterproof layer and a broken stone cushion layer are sequentially paved on the top of the upper roadbed; the lower roadbed comprises a geotextile waterproof layer, geogrids and modified high-liquid-limit soil layers, wherein the geotextile waterproof layer, the geogrids and the modified high-liquid-limit soil layers are sequentially laid from bottom to top;

the modified high liquid limit soil layer is formed by mixing modified soil, lime and a modifier, wherein the modified soil is high liquid limit clay, the addition amount of the lime is 5-8% of the mass of the high liquid limit clay, and the addition amount of the modifier is 7-12% of the mass of the high liquid limit clay. By adding lime and the low-viscosity high-solid-content high-polymer emulsion into the high-liquid-limit clay, soil components are directly crosslinked into a firm whole, so that the shrinkage cracking property of lime modified high-liquid-limit soil can be eliminated, and the early strength and the later stability of soil are met.

Preferably, the modifier is prepared by the following method: adding 20-25 parts of BA and 15-20 parts of MMA into an aqueous phase solution formed by mixing 1.3-1.6 parts of emulsifier, 0.01-0.03 part of sodium bicarbonate and 350-380 parts of water, stirring and heating to 60-80 ℃, adding 0.5-0.8 part of initiator, and carrying out polymerization reaction for 30-60 min to obtain a seed emulsion; continuously dropwise adding the pre-emulsified BA/MMA/AA mixed monomer into the seed emulsion, simultaneously dropwise adding 0.25-1.0 part of initiator, and finishing the addition within 4-5h, wherein the reaction temperature is 60-70 ℃; after the dropwise addition is finished, heating to 80 ℃, and continuing the reaction for 30min to obtain a large-particle-size seed emulsion with the particle size of 200-210 nm; and then taking the large-particle-size seed emulsion as a medium, adding a BA/MMA/AA mixed monomer by adopting a semi-continuous feeding process, heating to 85 ℃ after feeding is finished, and continuing to react for 40min to obtain the product. Firstly, a high-solid content monodisperse seeded emulsion is prepared by a seeded semi-continuous emulsion polymerization method, then the size and distribution of latex particles are controlled by adopting a monomer semi-continuous feeding mode by taking the seeded emulsion as a medium, and a low-viscosity high-solid content (the solid content can reach 75%) emulsion system is prepared, as shown in figure 2, the overall latex particle size in the emulsion is in binary distribution, the size of a large latex particle is about 500nm, the size of a small latex particle is about 80nm, and the particle diameter ratio of the large latex particle to the small latex particle is 6-8.

Preferably, when the height a of the roadbed is less than or equal to 8m, the gradient of the roadbed is 1.75-1; when the height of the roadbed is 8m < a < 18m, the gradient of the roadbed is 1.25-1.

Preferably, the thickness of the stone slab layer is 0.8-1.2m, and the distance between the geogrids is 0.8-1.5m.

Preferably, the waterproof layer of the geotextile is formed by laying impermeable geotextile along the cross section direction, four corners of the impermeable geotextile are fixed, adjacent impermeable geotextiles are lapped by 30cm, the longitudinal and transverse tensile strength of the geotextile is not less than 12kN/m, the longitudinal and transverse tensile elongation at break is not more than 310%, the longitudinal and transverse right-angle tear strength is not less than 35N/mm, the CBR bursting strength is not less than 4000N, and the permeability coefficient is not more than 5x10 ^-11 cm/s。

Preferably, a clay binding layer is arranged on the periphery of the modified high liquid limit soil layer, and is formed by mixing binding soil, lime with the addition amount being 3-5% of the mass of the binding soil, a modifier with the addition amount being 5-8% of the mass of the binding soil and PVA chopped fibers with the addition amount being 2-4% of the mass of the binding soil; the edge-covering soil has a liquid limit less than 50%, a plasticity index less than 26 and a permeability coefficient less than 10 ^-4 Is stickySoil; the density of the PVA chopped fibers was 1.25g/cm ³ Diameter of 0.05mm, length of 12mm, fineness of 15dtex, elongation of 7%, tensile strength of 1680MPa, and elastic modulus of 42.8GPa. The clay is doped with lime, low-viscosity high-solid emulsion and chopped fibers, so that shrinkage deformation caused by water evaporation of the exposed surface of the edge part is effectively avoided, the shaping and strength of the edge covering soil can be further improved, and the damage form of the edge covering soil is changed from brittle damage to plastic damage.

Preferably, the flaky stone layer is a flaky stone with the particle size of 10-30 cm and the content of particles not less than 80%.

On the other hand, the invention provides a construction method of a high liquid limit clay roadbed, which is characterized by comprising the following steps: s1, determining construction parameters such as the height, the gradient, the geogrid spacing and the thickness of a stone slab layer of a suitable embankment according to an embankment slope stability calculation formula in the formula 1;

s2, sequentially paving a geotextile waterproof layer on the treated foundation from bottom to top, then alternately paving a geogrid and a modified high-liquid-limit soil layer, rolling to the middle position of the embankment, paving the geotextile waterproof layer, filling a sheet rock layer, alternately paving a filled geogrid and the modified high-liquid-limit soil layer to the top of the embankment, and rolling and leveling;

and S3, paving a waterproof layer and a gravel cushion layer of the industrial fabric on the top of the embankment in sequence, and rolling and leveling. Adopt the mode of layering filling, not only can increase embankment overall stability, can also the upright high liquid limit soil horizon of layering, reduce to subside on the one hand, on the other hand layering filling rubble, the lamella layer is more economical than layering laying geogrid layer, and the lamella layer is favorable to restricting the whole vertical deformation of embankment, geogrid is favorable to restricting the whole lateral deformation of embankment, the fine diffusion embankment internal stress of homoenergetic, reduce the uneven settlement of embankment, and use embankment side slope stability as the foundation, based on theoretical calculation, confirm the slope height of embankment, slope and corresponding geotechnique's geogrid interval of paving, data such as lamella layer thickness, guarantee the long-term operation of embankment.

Preferably, in the step S2, the geogrid should be laid within 3.5m of the side slope surface, the geogrid is fixed by bamboo nails or iron nails every 2-2.5m, then the high liquid limit soil and the edge-covered cohesive soil are uniformly laid on the geogrid, after the working surface is stabilized, the high liquid limit soil and the edge-covered soil are spread with modifiers in parts by mass, and then the geogrid is uniformly mixed by an ash soil mixer, compacted and leveled.

Preferably, the rolling is uniformly divided into primary pressure, secondary pressure and final pressure, wherein the primary pressure adopts a vibratory roller, the static pressure is twice, the secondary pressure adopts the vibratory roller, the strong vibration is twice after the weak vibration is twice, the final pressure adopts a tamping plate for tamping, and the water content in the rolling process is equal to or more than the optimal water content of + 5%. The water content of the soil material during compaction plays a significant role in the degree of compaction that can be achieved. Practice proves that the high liquid limit soil is finely crushed to the diameter of 5-6 cm, the strength and the compaction degree of the high liquid limit clay are effectively improved, the airing time is shortened, the soil body after the fine crushing treatment is aired to the water content of + 5-6% of the optimal water content, a modifier is added into the soil body, the modification efficiency is high, the roadbed strength is improved, and the roadbed strength can meet the requirements of highway roadbed design specifications.

Compared with the prior art, the invention has the following beneficial effects:

(1) The clay with high liquid limit is modified and utilized, so that roadbed filling in remote transportation is avoided, a large amount of valuable land resources are saved, the construction progress is effectively accelerated, and the construction cost can be reduced; (2) The embankment slope stability is used as a basis, data such as the slope height and the gradient of the embankment, the corresponding geogrid spacing and the sheet stone layer thickness are determined based on theoretical calculation, and a layered filling mode is adopted, so that the overall stability of the embankment can be increased, the vertical high-liquid-limit soil layers can be layered, long-term operation of the embankment is guaranteed, the embankment can be used as a construction method and a control standard of roadbed filling, and the performance of a roadbed can meet the requirements of specifications and design.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is an electron micrograph of the modifier.

Detailed Description

The present invention is described in detail below with reference to specific examples, which are given for the purpose of further illustrating the invention and are not to be construed as limiting the scope of the invention, and the invention may be modified and adapted by those skilled in the art in light of the above disclosure. In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper surface", "lower surface", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "forward", "reverse", "axial", "radial", "circumferential", and the like indicate the orientation or positional relationship indicated based on the orientation or positional relationship shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore are not to be construed as limiting the present invention, and unless otherwise specified, the parts are parts by weight, the percentages are percentages by mass, and the concentrations are percentages by mass.

Example 1 construction method of high liquid limit clay roadbed

S1, determining the condition of an initial balance state by monitoring the maximum unbalanced force, node speed or displacement under the action of given boundary conditions and initial conditions according to a calculation formula of the slope stability of the embankment; in the solving process, the model conditions including the excavation of materials, the change of node loads, the change of unit material characteristics and the like can be changed as required; when the model function drops to a negligible value, a static or quasi-static solution K may be determined;

the specific process is as follows: designing a filling scheme, wherein the filling scheme comprises construction parameters such as the height of an embankment, the gradient, the space of geogrids, the thickness of a stone slab and the like, and the vertical load is determined primarily and slightly;

calculation formula for solving bank slope stability

Assuming a safety factor K (K =1 in the first iteration), c on the moving surface is set,

Reducing K times according to formula 1, solving the stress and deformation of the slope under given load and boundary conditions, and respectively solving the slip resistance F on the unit slip surface for all units on the slip surface by adopting

formulas

2 and 3 _r And a sliding force F _t ，

Wherein, N _i Is the total number of units; n is a radical of _g Counting the number of Gaussian integrals for each unit; sigma _nig The positive stress of the g-th Gaussian point of the ith unit; tau is _nig The shear stress of the g Gaussian point of the ith unit; v _ig The control volume of the g-th Gaussian point of the ith unit; t is the calculated thickness of the sliding surface unit;

is the reduction friction angle of the unit i; c _ei To reduce the cohesion; solving new anti-skid stability safety factor K according to formula 4 ^* ，

When (K) ^* -K)/K ^* If the error is less than or equal to the given error, the calculation is completed, K ^* Namely the real slope safety coefficient.

S2, performing foundation dredging and bearing capacity tests, performing embankment layered filling according to construction parameters determined by S1, specifically, paving a geotextile waterproof layer 1 on a treated foundation, then alternately paving geogrids 3 and modified high-liquid-limit soil layers 4, paving the geogrids within 3.5m of a side slope surface, fixing the geogrids by bamboo nails or iron nails every 2-2.5m, then uniformly paving high-liquid-limit soil and edge-covered cohesive soil on the geogrids, finely crushing the high-liquid-limit soil to 5-6 cm in diameter, airing until the water content reaches the optimal water content of + 5-6%, spreading modifiers with mass parts on the high-liquid-limit soil and the cohesive soil, uniformly mixing by using an ash soil mixer, compacting and leveling, wherein the water content is equal to or more than the optimal water content of +5% during rolling, layering and rolling to the middle position of the embankment, paving the geotextile waterproof layer 1, paving a bedding stone layer 5, alternately filling the geogrids 3 and the modified high-liquid-limit soil layers 4 to the top of the embankment, and rolling;

and the control of the optimal water content of the high liquid limit soil is strictly executed according to the control range of the water content difference of the compaction of the high liquid limit soil. The method for reducing the water content of the filler high liquid limit soil comprises the following steps: 1. high liquid limit soil with the absolute value difference between the natural water content and the optimal water content less than 10. Directly airing in a soil sampling field; spreading on embankment according to loose paving thickness, and airing. According to local climatic conditions, the airing time can be shortened by adopting the measures of airing in the daytime, spreading a plastic film at night for sealing and the like; and the forms of rotary tillage and the like can also be adopted, so that the speed of reducing the natural water content is accelerated. 2. The absolute value difference between the natural water content and the optimal water content is more than 10; or in the case of high liquid limit soil with local weather conditions which lead to extremely long airing time (more than 7 days), more than 2 percent of quicklime is doped in the soil sampling field for braising, and if the filling requirement can not be met, the water content is continuously reduced by adopting the two methods.

And S3, paving a geotextile waterproof layer 1 and a broken stone cushion layer 2 on the top of the embankment in sequence, and rolling and leveling. In the construction process of the embankment, settlement and stable monitoring are strictly carried out to control the filling speed, the ground settlement speed of the center line of the embankment is less than 1.0cm every day and night, and the horizontal displacement rate of the slope toe is less than 0.5cm every day and night.

Example 2

The modified soil adopted by the modified high liquid limit soil layer is formed by mixing high liquid limit clay, lime with the addition amount of 5% of the mass of the high liquid limit clay and a modifier with the addition amount of 7% of the mass of the high liquid limit clay; the liquid limit of the high liquid limit clay is 54.9%, the plastic limit is 29.6%, the porosity ratio is about 1.089, and the expansion rate is 34%.

The modifier is prepared by adopting the following method: adding 20-25 parts of BA and 15-20 parts of MMA into an aqueous phase solution formed by mixing 1.3-1.6 parts of emulsifier (the mass ratio of SDS/OP-15 is 1; sequentially adding 250-270 parts of BA, 170-190 parts of MMA and 10-15 parts of AA into an aqueous phase solution formed by mixing 11-13 parts of emulsifier (the mass ratio of SDS/OP-15 is 1; after the dropwise addition is finished, heating to 80 ℃, and continuing the reaction for 30min to obtain a large-particle-size seed emulsion with the particle size of 200-210 nm; and then taking 500-700 parts of large-particle-size seed emulsion as a medium, adding 1-2 parts of an initiator (APS) and 1-2 parts of sodium bicarbonate, dropwise adding 75-90 parts of a BA/MMA/AA mixed monomer (the mass ratio of BA/MMA/AA is 23.

And (3) detection results: the liquid limit of the modified soil is 45.5%, the plastic limit is 16.4%, the porosity ratio is about 0.817, and the expansion rate is 18.5%.

Example 3

The modified soil adopted by the modified high liquid limit soil layer is formed by mixing high liquid limit clay, lime with the addition amount of 8% of the mass of the high liquid limit clay and a modifier with the addition amount of 12% of the mass of the high liquid limit clay; the liquid limit of the high liquid limit clay is 54.9%, the plastic limit is 29.6%, the porosity ratio is about 1.089, and the expansion rate is 34%.

The modifier is prepared by adopting the following method: adding 25 parts of BA and 20 parts of MMA into an aqueous phase solution formed by mixing 1.6 parts of emulsifier (the mass ratio of SDS/OP-15 is 1; sequentially adding 270 parts of BA, 190 parts of MMA and 15 parts of AA into an aqueous phase solution formed by mixing 13 parts of emulsifier (SDS/OP-15 mass ratio is 1; after the dropwise addition is finished, heating to 80 ℃, and continuing the reaction for 30min to obtain a large-particle-size seed emulsion with the particle size of 200-210 nm; and then taking 700 parts of large-particle-size seed emulsion as a medium, adding 2 parts of an initiator (APS) and 2 parts of sodium bicarbonate, dropwise adding 90 parts of a BA/MMA/AA mixed monomer (the mass ratio of BA/MMA/AA is 23.

And (3) detection results: the liquid limit of the modified soil is 43.7 percent, the plastic limit is 21.4 percent, the porosity ratio is about 0.697, and the expansion rate is 16.4 percent.

Example 4

The modified soil adopted by the modified high liquid limit soil layer is formed by mixing high liquid limit clay, lime with the addition amount of 6% of the mass of the high liquid limit clay and a modifier with the addition amount of 10% of the mass of the high liquid limit clay;

the modifier is prepared by adopting the following method: adding 22 parts of BA and 18 parts of MMA into an aqueous phase solution formed by mixing 1.5 parts of emulsifier (the mass ratio of SDS/OP-15 is 1; sequentially adding 270 parts of BA, 180 parts of MMA and 14 parts of AA into an aqueous phase solution formed by mixing 12 parts of emulsifier (SDS/OP-15 mass ratio is 1; after the dropwise addition is finished, heating to 80 ℃, and continuing the reaction for 30min to obtain a large-particle-size seed emulsion with the particle size of 200-210 nm; and then taking 600 parts of large-particle-size seed emulsion as a medium, adding 1.8 parts of an initiator (APS) and 1-2 parts of sodium bicarbonate, dropwise adding 85 parts of a BA/MMA/AA mixed monomer (the mass ratio of BA/MMA/AA is 23/15).

And (3) detection results: the modified soil had a liquid limit of 41.1%, a plastic limit of 23.4%, a porosity ratio of about 0.615, and an expansion rate of 12.4%.

Example 5

The clay binding layer is prepared by mixing binding soil, lime with the addition amount of 3% of the mass of the binding soil, a modifier with the addition amount of 5% of the mass of the binding soil and PVA chopped fibers with the addition amount of 2% of the mass of the binding soil;

the edge-covering soil has a liquid limit less than 50%, a plasticity index less than 26 and a permeability coefficient less than 10 ^-4 The powdery clay; the density of the PVA chopped fibers was 1.25g/cm ³ Diameter of 0.05mm, length of 12mm, fineness of 15dtex, elongation of 7%, tensile strength of 1680MPa, and elastic modulus of 42.8GPa.

And (3) detection results: the compression strength is 1.58Mpa (soaked), the compression strength is 2.16Mpa (not soaked), and the expansion rate is 0.53%.

Example 6

The clay binding layer is made of materials formed by mixing binding soil, lime with the addition amount of 5% of the mass of the binding soil, a modifier with the addition amount of 8% of the mass of the binding soil and PVA chopped fibers with the addition amount of 4% of the mass of the binding soil;

And (3) detection results: the compression strength is 1.36Mpa (soaked), the compression strength is 2.03Mpa (not soaked), and the expansion rate is 0.48 percent.

Example 7

The clay binding layer is made of materials formed by mixing binding soil, lime with the addition of 4% of the mass of the binding soil, a modifier with the addition of 7% of the mass of the binding soil and PVA chopped fibers with the addition of 3% of the mass of the binding soil;

the edge-covering soil adopts a liquid limit less than 50%, a plasticity index less than 26 and a permeability coefficient less than 10 ^-4 The powdery clay; the density of the PVA chopped fibers was 1.25g/cm ³ Diameter of 0.05mm, length of 12mm, fineness of 15dtex, elongation of 7%, tensile strength of 1680MPa, and elastic modulus of 42.8GPa.

And (3) detection results: the compression strength is 1.74Mpa (soaked), the compression strength is 2.57Mpa (not soaked), and the expansion rate is 0.41%.

Comparative example 1

The same as in example 1, except that the modifier was removed.

And (3) detection results: the liquid limit of the modified soil is 48.5%, the plastic limit is 24.4%, the porosity ratio is about 0.921, and the expansion rate is 24.5%.

Comparative example 2

Same as example 2, except that the modifier was replaced with a constantan soil stabilizer.

And (3) detection results: the liquid limit of the modified soil is 47.5%, the plastic limit is 23.4%, the porosity ratio is about 0.867, and the expansion rate is 22..4%.

Comparative example 3

The same as in example 5, except that the PVA chopped fibers were removed.

And (3) detection results: the compressive strength is 0.98Mpa (soaked), the compressive strength is 1.24Mpa (not soaked), and the expansion rate is 13.53 percent.

Comparative example 4

The same as in example 6, except that the chopped fibers were replaced with glass fibers.

And (3) detection results: the compression strength is 1.12Mpa (soaked), the compression strength is 1.57Mpa (not soaked), and the expansion rate is 2.58%.

Application examples of the present invention:

the embankment filling thickness of a certain high liquid limit highway section is about 4-19m, the highway section is unevenly distributed, the excavation material of the highway section generally belongs to the category of red clay, the liquid limit is 54.9 percent, the plastic limit is 29.6 percent, and the maximum dry density is about 1.91kg/m ³ Porosity ratio of about 1.089, saturation of about 94.12, low shear strength, minimum cohesive force of 26.3kPa, minimum internal friction angle of 13.2 DEG, and compression coefficient of about 0.29MPa ^-1 ；

Modifying the excavated earth by adopting the method of embodiment 4, modifying the edge-covered earth by adopting the method of embodiment 7, designing the structure of the embankment by taking the height of the embankment of 8m as a boundary, respectively establishing embankment models with the heights of 10m, 12m, 14m, 16m, 18m and 20m, and setting the gradient as 1:1.25-2, wherein the slope height is 8m, the thickness of a stone slab is 80-120cm, the soil layer is filled with equal thickness of 1.5m, the broken stone cushion layer is 30-50cm, the pavement thickness is 0.7m, and the top surface of the embankment can be converted into uniform vertical load of 56.4kpa under the action of a trailer-80; building embankment models with the height of 4m, 4m and 8m, wherein the gradient is 1:0.75-1:1.25, the thickness of the rubble layer is 80-120cm, the soil layer is 1.5m and the like for filling, the thickness of the rubble cushion layer is 30-50cm, the thickness of the road surface is 0.7m in the first consideration, and the top surface of the embankment can be converted into 56.4kpa of uniformly distributed vertical load under the action of a trailer-80. The embankment slope stability calculation method in embodiment 1 is adopted for analysis, the safety coefficient obtained through calculation needs to be larger than 1.35, the requirements of 'design specifications for highway subgrades' are met, construction schemes of all road sections are formulated according to simulation results, actual settlement observation data parameters and a prediction analysis structure are compared and verified in the construction process, the fact that the overall effect of model analysis and the correlation of actual engineering effects are consistent is shown, high-liquid limit soil is used for modification, adjustment and optimization of embankment structure parameters of different heights are achieved, the high-liquid limit soil subgrade slope stability is improved, the drainage capacity of the middle of an embankment is improved, uneven settlement of the embankment is reduced, a set of relatively mature high-liquid limit soil subgrade filling method is formed, and high-liquid limit soil subgrade filling construction is completed quickly on the basis that the construction safety and quality of the subgrades are guaranteed. The high liquid limit soil abandon amount and the improvement engineering amount are reduced, the comprehensive utilization rate of the high liquid limit soil is greatly improved, and great economic benefits are brought to projects, the construction cost is totally estimated and saved by the 156-square high liquid limit soil roadbed of the standard section by about 380 ten thousand yuan, meanwhile, the roadbed filling construction progress is accelerated by the construction method, and the construction period is saved by about 3.5 months.

Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.

Claims

1. High liquid limit clay roadbed structure, its characterized in that: the soil engineering cloth waterproof layer comprises a lower roadbed and an upper roadbed which are arranged on a foundation, wherein a soil engineering cloth waterproof layer (1) and a broken stone cushion layer (2) are sequentially paved on the top of the upper roadbed; the lower roadbed comprises a geotextile waterproof layer (1), geogrids (3) and a modified high-liquid-limit soil layer (4), wherein the geotextile waterproof layer (1), the geogrids (3) and the modified high-liquid-limit soil layer are sequentially laid from bottom to top, and the upper roadbed comprises the geotextile waterproof layer (1), the stone layer (5), the geogrids (3) and the modified high-liquid-limit soil layer (4);

the modified high liquid limit soil layer (4) is formed by mixing modified soil with high liquid limit clay, lime with the addition amount of 5-8% of the mass of the high liquid limit clay and a modifier with the addition amount of 7-12% of the mass of the high liquid limit clay.

2. The high liquid limit clay subgrade structure according to claim 1, wherein the modifier is prepared by the following method: adding 20-25 parts of BA and 15-20 parts of MMA into an aqueous phase solution formed by mixing 1.3-1.6 parts of emulsifier, 0.01-0.03 part of sodium bicarbonate and 350-380 parts of water, stirring and heating to 60-80 ℃, adding 0.5-0.8 part of initiator, and carrying out polymerization reaction for 30-60 min to obtain a seed emulsion; continuously dropwise adding the pre-emulsified BA/MMA/AA mixed monomer into the seed emulsion, simultaneously dropwise adding 0.25-1.0 part of initiator, and finishing the addition within 4-5h, wherein the reaction temperature is 60-70 ℃; after the dropwise addition is finished, heating to 80 ℃, and continuously reacting for 30min to obtain a large-particle-size seed emulsion with the solid content of 10-12% and the particle size of 200-210 nm; and then taking the large-particle-size seed emulsion as a medium, adding a BA/MMA/AA mixed monomer by adopting a semi-continuous feeding process, heating to 85 ℃ after feeding is finished, and continuing to react for 40min to obtain the product.

3. The high liquid limit clay roadbed structure of claim 1, wherein: when the height a of the roadbed is less than or equal to 8m, the gradient of the roadbed is 1.75-1; when the height of the roadbed is 8m < a < 20m, the gradient of the roadbed is 1.25-1.

4. The high liquid limit clay roadbed structure of claim 1, wherein: the thickness of the lamella (5) is 0.8-1.2m, and the distance between the geogrids (3) is 0.8-1.5m.

5. The high liquid limit clay roadbed structure of claim 1, wherein: the geotextile waterproof layer (1) is formed by laying impermeable geotextiles along the cross section direction, four corners of the impermeable geotextiles are fixed, adjacent impermeable geotextiles are lapped by 30cm, the longitudinal and transverse tensile strength of the geotextiles is not less than 12kN/m, the longitudinal and transverse tensile elongation at break is not more than 310%, the longitudinal and transverse right-angle tear strength is not less than 35N/mm, the CBR bursting strength is not less than 4000N, and the permeability coefficient is not more than 5x10 ^-11 cm/s。

6. The high liquid limit clay roadbed structure of claim 1, wherein: the clay binding layer (6) is arranged on the periphery of the modified high liquid limit soil layer (4) and is formed by mixing binding soil, lime with the addition amount being 3-5% of the mass of the binding soil, a modifier with the addition amount being 5-8% of the mass of the binding soil and PVA chopped fibers with the addition amount being 2-4% of the mass of the binding soil; the edge-covering soil has a liquid limit less than 50%, a plasticity index less than 26 and a permeability coefficient less than 10 ^-4 The powdery clay; the density of the PVA chopped fibers was 1.25g/cm ³ Diameter of 0.05mm, length of 12mm, fineness of 15dtex, elongation of 7%, tensile strength of 1680MPa, and elastic modulus of 42.8GPa.

7. The high liquid limit clay roadbed structure of claim 1, wherein: the flaky stone layer (5) is made of flaky stones with the particle size of 10-30 cm and the content of particles not less than 80%.

8. A construction method of a high liquid limit clay roadbed is characterized by comprising the following steps:

s1, determining construction parameters such as the height, the gradient, the geogrid spacing and the thickness of a stone slab layer of a suitable embankment according to an embankment slope stability calculation formula in the formula 1;

k is the safety coefficient of the side slope; c is cohesive force;

is an internal angle of friction

S2, sequentially paving geotextile waterproof layers (1) on the treated foundation from bottom to top, then alternately paving geogrids (3) and modified high-liquid-limit soil layers (4), rolling to the middle position of the embankment, paving geotextile waterproof layers (1), filling stone layers (5), alternately paving filled geogrids (3) and modified high-liquid-limit soil layers (4) to the top of the embankment, and rolling and leveling;

and S3, paving a geotextile waterproof layer (1) and a broken stone cushion layer (2) on the top of the embankment in sequence, and rolling and leveling.

9. The construction method of the high liquid limit clay subgrade according to claim 7, characterized in that in step S2, the geogrid should be laid within 3.5m of the side slope surface, the geogrid is fixed by bamboo nails or iron nails every 2-2.5m, then the high liquid limit soil and the edge-covered cohesive soil are uniformly laid on the geogrid, after the working surface is stabilized, the high liquid limit soil and the edge-covered soil are spread with modifiers in parts by mass, and then an ash-soil mixer is adopted to mix uniformly and compact and level.

10. The construction method of the high liquid limit clay roadbed according to claim 7, wherein the rolling is divided into an initial pressure, a second pressure and a final pressure, the initial pressure is performed by using a vibratory roller, the static pressure is performed twice, the second pressure is performed by using a vibratory roller, the weak vibration is performed twice and then the strong vibration is performed twice, the final pressure is performed by using a tamping plate for tamping, and the water content during the rolling is equal to or more than the optimal water content of + 5%.