A method for embankment construction in permafrost regions

Abstract

The application provides a method for building a roadbed in a permafrost region, and comprises the following steps: determining a required foam light soil with a specific gravity grade and a compressive strength grade; determining a standard thickness of a heat insulation layer in the roadbed; laying a soil work cloth for preventing seepage at a road construction site, pouring the foam light soil on the laid soil work cloth for preventing seepage, and pouring the foam light soil again after the foam light soil is preliminarily solidified, so as to pour the foam light soil in cycles until the thickness of the heat insulation layer formed by the foam light soil reaches the standard thickness; wherein the thickness of the foam light soil layer poured each time is less than or equal to 30 cm; building a fill on the upper part of the heat insulation layer, and building a sun-facing heat preservation guard road and a shade-facing heat preservation guard road on the two sides of the fill, respectively. The application can control the thawing speed of the frozen soil in the range of the roadbed, protect the upper limit of the frozen soil, and further reduce the disease degree of the roadbed thawing settlement, frost heaving and slurry turning, and road surface cracking.

Description

Technical Field

[0001] This invention relates to the field of roadbed structure technology, and in particular to a roadbed construction method for permafrost regions. Background Technology

[0002] Permafrost (also known as frozen soil) refers to soil layers that remain frozen for two years or more, sometimes even tens of thousands of years. Permafrost is mainly distributed in Russia and Canada. In my country, permafrost is primarily located in the northeast, northern mountainous areas, northwestern high mountains, and the Qinghai-Tibet Plateau.

[0003] Permafrost can be divided into two layers: the upper layer is the active layer that thaws in summer and freezes in winter, and the lower layer is the perennially frozen layer. When roads are built in permafrost areas, the permafrost may thaw locally due to the influence of climate warming or human activities. The overlying soil layer will sink under its own weight and external forces, leading to severe road surface deformation. When the temperature drops, the water accumulated in the permafrost under the road surface will turn into ice, causing the volume of that area to increase, which will lead to road hazards such as frost heave, frost heave, and road surface cracking. Summary of the Invention

[0004] The main objective of this invention is to provide a roadbed construction method for permafrost regions, aiming to solve the technical problems of thaw settlement, frost heave, frost heave, and pavement cracking caused by the influence of permafrost on roadbeds in permafrost regions in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for roadbed construction in permafrost regions, comprising the following steps:

[0006] Based on the highway grade to be constructed, determine the required bulk density and compressive strength grade of the foamed lightweight soil.

[0007] Based on the frost heave grade of the permafrost seasonal thaw layer in the area where the highway to be built is located and the bulk density grade of the foamed lightweight soil, the standard thickness of the insulation layer in the roadbed is determined.

[0008] A geotextile is laid at the road construction site. Foamed lightweight soil is poured on the laid geotextile. After the foamed lightweight soil has initially solidified, it is poured again. This process is repeated until the thickness of the insulation layer formed by the foamed lightweight soil reaches the standard thickness. The thickness of the foamed lightweight soil layer poured each time is ≤30cm.

[0009] A backfill was constructed on top of the insulation layer, and a sun-facing insulation corridor and a shade-facing insulation corridor were constructed on both sides of the backfill.

[0010] Optionally, the step of determining the required bulk density and compressive strength grades of the foamed lightweight soil based on the highway grade to be constructed includes:

[0011] If the highway is classified as an expressway or a Class I highway, and the roadbed is used for light, medium, and heavy traffic, then the bulk density grade of the foamed lightweight soil used in the roadbed is greater than or equal to W6 and less than W8; and the compressive strength grade is greater than or equal to CF1.2.

[0012] If the highway is classified as an expressway or a Class I highway, and the roadbed is used for extra-heavy or extremely heavy traffic, then the bulk density grade of the foamed lightweight soil used in the roadbed is greater than or equal to W6 and less than W8; and the compressive strength grade is greater than or equal to CF1.4.

[0013] If the highway is classified as an expressway or a Class I highway, the bulk density grade of the foamed lightweight soil used in the upper and lower embankments of the roadbed is greater than or equal to W5 and less than W7; the compressive strength grade is greater than or equal to CF1.0.

[0014] If the highway is classified as a Class II highway or below, the bulk density grade of the foamed lightweight soil used in the subgrade is greater than or equal to W6 and less than W8; the compressive strength grade is greater than or equal to CF1.0.

[0015] If the highway is classified as a Class II highway or below, the bulk density grade of the foamed lightweight soil used in the upper and lower embankments of the roadbed shall be greater than or equal to W5 and less than W7; and the compressive strength grade shall be greater than or equal to CF0.8.

[0016] Optionally, before laying the impermeable geotextile at the road construction site, the method further includes:

[0017] A foundation soil was formed at the road construction site by replacing the foundation soil with foamed lightweight soil of a density grade greater than or equal to W4 and less than W6 and a compressive strength greater than or equal to CF0.6.

[0018] The laying of impermeable geotextile at the road construction site includes: laying impermeable geotextile on the foundation.

[0019] Optionally, the standard thickness of the insulation layer in the roadbed is determined based on the frost heave grade of the permafrost seasonal thaw layer in the area where the highway to be constructed is located and the bulk density grade of the foamed lightweight soil, including:

[0020] If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 120cm.

[0021] If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 140cm.

[0022] If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 160cm.

[0023] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 150cm.

[0024] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 170cm.

[0025] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 190cm.

[0026] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 180cm.

[0027] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 200cm.

[0028] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 220cm.

[0029] Optionally, the heat insulation layer includes at least a first heat insulation layer and a second heat insulation layer, with the second heat insulation layer located above the first heat insulation layer, and the casting steps of the first heat insulation layer are as follows:

[0030] First, pour a 7-13cm thick layer of foamed lightweight soil onto the impermeable geotextile. After the first layer of foamed lightweight soil has initially set, pour a 17-23cm thick layer of foamed lightweight soil. After the second layer of foamed lightweight soil has initially set, pour a 27-33cm thick layer of foamed lightweight soil. Then, place galvanized steel wire mesh into the third layer of foamed lightweight soil.

[0031] When pouring the uppermost layer of foamed lightweight soil in the second insulation layer, galvanized steel wire mesh is placed inside the uppermost layer of foamed lightweight soil in the second insulation layer, and a layer of sand is laid on top of the second insulation layer.

[0032] The heat of hydration of the foamed lightweight soil used in the first insulation layer is lower than that of the foamed lightweight soil used in the second insulation layer.

[0033] Optionally, if the frost heave level of the seasonal thaw layer in the permafrost region is Level III, a groove with a depth of 50-70cm should be dug at the road construction site first, and then impermeable geotextile should be laid on the bottom and slope of the groove, and then foamed lightweight soil should be poured.

[0034] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, then first dig trenches with a depth of 100~120cm and a width of not less than 60cm on both sides of the road construction location, then lay impermeable geotextile between the two trenches, and then pour foamed lightweight soil.

[0035] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, then first dig trenches with a depth of 150~200cm and a width of not less than 60cm on both sides of the road construction location, then lay impermeable geotextile between the two trenches, and then pour foamed lightweight soil.

[0036] Optionally, the sun-facing insulation shield and the shade-facing insulation shield respectively cover both sides of the first insulation layer, and the sun-facing insulation shield covers one side of the bottom layer of the second insulation layer, which is made of lightweight foam.

[0037] Optional:

[0038] If the frost heave level of the seasonal thaw layer in permafrost regions is Class III, then the width of the insulation protection channel on the sunny side should be ≥300cm and the thickness should be ≥100cm; the width of the insulation protection channel on the shady side should be ≥200cm and the thickness should be ≥60cm.

[0039] If the frost heave level of the seasonal thaw layer in permafrost regions is Class IV, then the width of the insulation protection road on the sunny side should be ≥250cm and the thickness should be ≥150cm; the width of the insulation protection road on the shady side should be ≥150cm and the thickness should be ≥120cm.

[0040] If the frost heave level of the seasonal thawing layer in permafrost regions is Class V, then the width of the insulation protection channel on the sunny side should be ≥250cm and the thickness should be ≥150cm; the width of the insulation protection channel on the shady side should be ≥150cm and the thickness should be ≥120cm.

[0041] Furthermore, the present invention also includes a roadbed for permafrost regions, comprising a roadbed body, the roadbed body including a heat insulation layer, the heat insulation layer including a first heat insulation layer and a second heat insulation layer, the first heat insulation layer being disposed below the second heat insulation layer, the heat of hydration of the first heat insulation layer being lower than that of the second heat insulation layer, a sand cushion layer being provided on the second heat insulation layer, a layer of impermeable geotextile being attached below the first heat insulation layer, the roadbed body being covered with fill soil, and a sun-facing heat-insulating protective road and a shade-facing heat-insulating protective road being respectively provided on both sides of the roadbed body;

[0042] The first insulation layer comprises several layers of lightweight foam soil, and the uppermost layer of the first insulation layer is provided with galvanized wire mesh; the second insulation layer comprises several layers of lightweight foam soil, and the uppermost layer of the second insulation layer is provided with galvanized wire mesh.

[0043] The first insulation layer is located on both sides within the sun-facing insulation corridor and the shaded insulation corridor, respectively, and one side of the bottommost layer of the second insulation layer, the lightweight foam soil layer, is located within the sun-facing insulation corridor.

[0044] Optional:

[0045] The width of the sun-facing insulation channel is ≥250cm and the height is ≥100cm, while the width of the shaded-facing insulation channel is ≥150cm and the height is ≥60cm.

[0046] The technical solution described above has the following beneficial effects:

[0047] This invention provides a method for roadbed construction in permafrost regions, which uses foamed lightweight soil as the insulation layer in the roadbed. The thermal conductivity of foamed lightweight soil is only about 20% of that of traditional insulation roadbed fillers. Compared with traditional roadbed insulation fillers, foamed lightweight soil has the characteristics of low thermal conductivity and good freeze-thaw resistance. Using foamed lightweight soil to make the insulation layer in the roadbed can effectively isolate the frozen soil from the influence of external temperature changes, thereby controlling the freezing rate of the frozen soil within the roadbed area, protecting the upper limit of the frozen soil, and preventing the frozen soil from melting and softening or freezing and expanding. This minimizes the degree of roadbed settlement, frost heave and frost heave, and road surface cracking. Attached Figure Description

[0048] Figure 1 This is a schematic cross-sectional view of a roadbed constructed using the roadbed construction method for permafrost regions according to the present invention under the condition of seasonal thawing layer frost heave level III.

[0049] Figure 2 This is a schematic cross-sectional view of a roadbed constructed using the roadbed construction method for permafrost regions according to the present invention under the condition of seasonal thawing layer frost heave level IV.

[0050] Figure 3 This is a schematic cross-sectional view of a roadbed constructed using the roadbed construction method for permafrost regions according to the present invention under the condition of seasonal thawing layer frost heave level V.

[0051] Figure 4 This is a schematic diagram of the roadbed model.

[0052] Figure 5 This is a schematic diagram showing the distribution of reference points;

[0053] Figure 6 The graph shows the variation curves of three climatic conditions in the experiment on the influence of different climatic conditions on the temperature field of thermal insulation roadbed.

[0054] Figure 7 (1) Temperature curves of 5 reference points as a function of ambient temperature during the test on the influence of thermal insulation layers of different thicknesses on the temperature field of the roadbed;

[0055] Figure 8 The lowest temperature curves over one year at five reference points in the experiment on the influence of thermal insulation layers of different thicknesses on the temperature field of the roadbed.

[0056] Figure 9 The annual temperature difference curves at 5 reference points in the experiment on the influence of thermal insulation layers of different thicknesses on the temperature field of the roadbed;

[0057] Figure 10 Temperature curves of five reference points as a function of ambient temperature during the experiment on the influence of different climatic conditions on the roadbed temperature field;

[0058] Figure 11 The lowest temperature curves over one year at five reference points in the experiment on the impact of different climatic conditions on the roadbed temperature field are shown.

[0059] Figure 12 The annual temperature range curves of five reference points in the experiment on the influence of different climatic conditions on the temperature field of the roadbed are shown.

[0060] Figure 13 Temperature monitoring chart at the bottom of thermal insulation layers with density grades W6 to W10 in the Greater Khingan Mountains region;

[0061] Figure 14 This is a temperature monitoring chart of the bottom of thermal insulation layers with density grades W6 to W10 in the Urumqi area.

[0062] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0063] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0064] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0065] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0066] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0067] Common road damage phenomena in permafrost regions include: thaw settlement, frost heave, frost heave, and road surface damage.

[0068] 1) Melting

[0069] Thaw settlement is one of the major roadbed defects in permafrost regions, generally occurring in sections of cohesive soil with high ice content (6584). When a thick layer of underground ice is distributed on the permafrost above the roadbed base or on the slope of the cut, due to the shallow burial of the underground ice layer, various human factors during construction and operation cause localized thawing of the permafrost. The overlying soil layer then subsides under its own weight and external forces, resulting in severe deformation of the roadbed. This deformation manifests as roadbed settlement, cracking and sliding of the sunny shoulder and slope of the embankment, and landslides on the cut slope. Thaw settlement is mainly related to the following factors:

[0070] ① Height of the roadbed

[0071] The construction of embankments and the paving of roads alter the original surface's water and heat exchange conditions, causing a series of changes such as compression of the base soil layer. Under certain conditions, these changes lower the upper limit of the embankment's potential height, while road construction increases thermal resistance, which is a factor that favors an increase in the upper limit. When the embankment is very low, the thermal resistance is small, so the factors that cause an increase are weaker than those that cause a decrease, and therefore the upper limit generally decreases. As the embankment height increases, the effect of factors that cause an increase in the upper limit also strengthens. When this effect increases to be equal to or greater than the effect that causes a decrease in the upper limit, the upper limit below the embankment will remain unchanged or increase. Thus, there exists an embankment height where, when the upper limit is greater than this roadbed height, the upper limit will increase; and when it is less than this height, the upper limit will decrease. This height is called the critical height. When constructing roads in permafrost regions using the principle of permafrost protection, it is essential to ensure that the actual embankment height is greater than the critical height. However, a higher embankment is not necessarily more beneficial for permafrost protection. In high-temperature permafrost regions, when the height of an embankment constructed in summer exceeds a certain value, thawing cores will form within the embankment, causing the underground ice to melt and the embankment to subside.

[0072] ② Subgrade fill material

[0073] Different soil types have different thermal properties, water content, and water conductivity, which obviously affect the thermal condition of roads. When fine-grained soil is used as fill material, it is generally packed tightly with small porosity and low air content. Heat conduction is mainly carried out by the soil particles themselves, which is relatively slow. In contrast, when filled with rock fragments, gravel, or coarse-grained soil, the porosity is generally larger, and air convection is easily generated in the gaps, thus enhancing the heat conduction performance. It is easier to absorb heat in summer and release heat in winter, allowing the heat source energy to be transferred deeper.

[0074] ③ Drainage conditions

[0075] The construction of embankments alters the runoff conditions of surface and groundwater. Inadequate drainage measures can lead to water overflowing into the embankment and water accumulation on its sides. The consequences often include melting of underground ice, roadbed subsidence, and even sudden collapse.

[0076] ④ Road surface

[0077] The paving of roads, especially asphalt roads, disrupts the original water and heat exchange balance of frozen soil due to the heat absorption and water sealing effect of the road surface, thereby increasing the possibility of road thaw settlement.

[0078] 2) Frost heave and frost heave

[0079] Frost heave is another important road construction problem that needs to be considered in permafrost regions. Improperly designed frost protection layers can create channels for water circulation, leading to water accumulation. As water freezes and its volume increases, frost heave becomes inevitable. During spring thaw, the upper layer begins to thaw, while the lower layer continues to freeze or stops freezing, forming an impermeable layer. Excess water in the upper soil layer cannot drain in time, causing the soil subgrade to weaken and its strength to drop sharply. Under vehicle loads, this results in road surface defects such as springing, cracking, and bulging.

[0080] 3) Road surface cracks

[0081] Road surface cracking is one of the most common defects in asphalt pavements in permafrost regions. Road surface cracks can be classified into longitudinal cracks, transverse cracks, and network cracks based on their appearance. Road surface cracking is a very common phenomenon in cold regions of my country.

[0082] The causes of longitudinal and transverse cracks in the road surface include:

[0083] ① Shrinkage cracking caused by severe cold weather, which often manifests as transverse cracks;

[0084] ② Thawing settlement of frozen soil subgrade: The construction of subgrade in frozen soil areas changes the original thermal balance. Under the heat absorption effect of the road surface, heat is continuously transferred downward, causing the frozen soil subgrade to settle.

[0085] ③ Frost heave deformation of the roadbed;

[0086] ④ The bearing capacity of the roadbed is reduced, including due to frost heave, inadequate drainage facilities, and insufficient compaction;

[0087] ⑤ Reflective cracks in semi-rigid substrates, etc.

[0088] With the increasing number of highway construction projects in cold regions, the protection of permafrost foundations and the prevention of road frost heave and mud pumping have become new technical challenges. In my country, there are three main methods for treating permafrost: protecting it from thawing, controlling the thawing rate, and accelerating the thawing process. Foamed lightweight soil is a newly developed material with characteristics such as low thermal conductivity, good freeze-thaw resistance, high strength, simple processing, and fast construction speed. It can be applied to roadbed construction to control the thawing rate of permafrost.

[0089] This invention provides a method for roadbed construction in permafrost regions, comprising the following steps:

[0090] Based on the highway grade to be constructed, determine the required bulk density and compressive strength grade of the foamed lightweight soil.

[0091] Based on the frost heave grade of the permafrost seasonal thaw layer in the area where the highway to be built is located and the bulk density grade of the foamed lightweight soil, the standard thickness of the insulation layer in the roadbed is determined.

[0092] A geotextile is laid at the road construction site. Foamed lightweight soil is poured on the laid geotextile. After the foamed lightweight soil has initially solidified, it is poured again. This process is repeated until the thickness of the insulation layer formed by the foamed lightweight soil reaches the standard thickness. The thickness of the foamed lightweight soil layer poured each time is ≤30cm.

[0093] A backfill was constructed on top of the insulation layer, and a sun-facing insulation corridor and a shade-facing insulation corridor were constructed on both sides of the backfill.

[0094] Foamed lightweight soil is characterized by high porosity and good thermal insulation performance. Conventional single-layer pouring thickness is 0.3m to 1.0m. After pouring, the accumulated heat of hydration cannot be effectively dissipated for a long time, lowering the natural upper limit of permafrost. Therefore, this invention uses multiple pours of 30cm or less each time to allow the heat of hydration to dissipate promptly. Using low-heat-of-hydration foamed lightweight soil in the layer directly in contact with permafrost can reduce the impact of heat of hydration on the natural upper limit of permafrost and improve the stability of the roadbed after pouring. In permafrost areas, embankment design should not remove surface vegetation. When encountering weak surface layers such as silt, sand, peat, or swamp, effective surface treatment measures should be taken, including but not limited to replacement, rockfill, and silt removal.

[0095] The frost heave classification of the seasonal thaw layer of permafrost should comply with the relevant provisions of the current "Technical Specification for Highway Design and Construction in Permafrost Areas" (JTG / T 3331-04). The selection of suitable performance parameters for foamed lightweight soil and the standard thickness of the insulation layer can be determined by those skilled in the art based on industry standards or their own experience; methods for determining these parameters are also presented below.

[0096] The steps for determining the required bulk density and compressive strength grades of foamed lightweight soil based on the highway grade to be constructed include:

[0097] If the highway is classified as an expressway or a Class I highway, and the roadbed is used for light, medium, and heavy traffic, then the bulk density grade of the foamed lightweight soil used in the roadbed is greater than or equal to W6 and less than W8; and the compressive strength grade is greater than or equal to CF1.2.

[0098] If the highway is classified as an expressway or a Class I highway, and the roadbed is used for extra-heavy or extremely heavy traffic, then the bulk density grade of the foamed lightweight soil used in the roadbed is greater than or equal to W6 and less than W8; and the compressive strength grade is greater than or equal to CF1.4.

[0099] If the highway is classified as an expressway or a Class I highway, the bulk density grade of the foamed lightweight soil used in the upper and lower embankments of the roadbed is greater than or equal to W5 and less than W7; the compressive strength grade is greater than or equal to CF1.0.

[0100] If the highway is classified as a Class II highway or below, the bulk density grade of the foamed lightweight soil used in the subgrade is greater than or equal to W6 and less than W8; the compressive strength grade is greater than or equal to CF1.0.

[0101] If the highway is classified as a Class II highway or below, the bulk density grade of the foamed lightweight soil used in the upper and lower embankments of the roadbed shall be greater than or equal to W5 and less than W7; and the compressive strength grade shall be greater than or equal to CF0.8.

[0102] Before laying the impermeable geotextile at the road construction site, the method further includes:

[0103] A foundation soil was formed at the road construction site by replacing the foundation soil with foamed lightweight soil of a density grade greater than or equal to W4 and less than W6 and a compressive strength greater than or equal to CF0.6.

[0104] The laying of impermeable geotextile at the road construction site includes:

[0105] An impermeable geotextile was laid on the foundation. The above data is compiled into a table, as shown in Table 1.

[0106] Table 1 Performance Indicators of Foamed Lightweight Soil in Permafrost Regions

[0107]

[0108] The unit weight of foamed lightweight soil is controlled by its internal porosity. The higher the porosity, the lower the unit weight, and the better the thermal insulation performance of the lightweight soil. Generally, the higher the unit weight, the higher the compressive strength of the foamed lightweight soil. In permafrost regions, the temperature changes drastically, which places higher demands on the durability of lightweight soil. Considering the decrease in compressive strength and the thermal insulation performance of lightweight soil, the unit weight grades proposed in the table above should not be too low or too high.

[0109] Based on the frost heave grade of the permafrost seasonal thaw layer in the area where the highway to be constructed is located and the bulk density grade of the foamed lightweight soil, the standard thickness of the insulation layer in the roadbed is determined, including:

[0110] If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 120cm.

[0111] If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 140cm.

[0112] If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 160cm.

[0113] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 150cm.

[0114] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 170cm.

[0115] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 190cm.

[0116] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 180cm.

[0117] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 200cm.

[0118] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 220cm.

[0119] The above data is organized into a table, as shown in Table 2.

[0120] Table 2 Thickness of Foamed Lightweight Soil Insulation Layer in Permafrost Regions

[0121]

[0122] If different density grades of foamed lightweight soil are used in the insulation layer, the standard thickness value of the insulation layer is determined by the weighted average method.

[0123] The heat insulation layer includes a first heat insulation layer and a second heat insulation layer, with the second heat insulation layer located above the first heat insulation layer. The casting steps for the first heat insulation layer are as follows:

[0124] First, pour a 7-13cm thick layer of foamed lightweight soil onto the impermeable geotextile. After initial setting, pour a 17-23cm thick layer of foamed lightweight soil. After initial setting, pour a 27-33cm thick layer of foamed lightweight soil. Then, place galvanized steel wire mesh into the third layer of foamed lightweight soil.

[0125] When pouring the uppermost layer of foamed lightweight soil in the second insulation layer, galvanized steel wire mesh is placed inside the uppermost layer of foamed lightweight soil in the second insulation layer, and a layer of sand is laid on top of the second insulation layer.

[0126] The heat of hydration of the foamed lightweight soil used in the first insulation layer is lower than that of the foamed lightweight soil used in the second insulation layer. The first insulation layer is in direct contact with the frozen soil, uses low-heat-of-hydration foamed lightweight soil, and is first poured in a thin layer to minimize the impact of heat of hydration on the frozen soil.

[0127] If the frost heave level of the seasonal thaw layer in the permafrost region is Class III, then first dig a groove with a depth of 50-70cm at the road construction location, then lay impermeable geotextile on the bottom and slope of the groove, and then pour foamed lightweight soil.

[0128] If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, then first dig trenches with a depth of 100~120cm and a width of not less than 60cm on both sides of the road construction location, then lay impermeable geotextile between the two trenches, and then pour foamed lightweight soil.

[0129] If the frost heave level of the seasonal thawing layer in the permafrost region is level V, then first dig trenches with a depth of 150~200cm and a width of not less than 60cm on both sides of the road construction location, then lay impermeable geotextile between the two trenches, and then pour foamed lightweight soil.

[0130] The aforementioned trenches serve as insulation walls to prevent the frozen soil beneath the roadbed from being affected by temperature changes in the nearby frozen soil, thus further protecting the roadbed.

[0131] The sun-facing insulation shield and the shade-facing insulation shield respectively cover both sides of the first insulation layer, and the sun-facing insulation shield covers one side of the bottom layer of the second insulation layer, which is made of foamed lightweight soil.

[0132] The different heat exchange conditions between the surface and the atmosphere on both sides of the high roadbed slope, such as solar radiation and surface turbulence, result in significant differences in ground temperature distribution on the two sides of the roadbed. This phenomenon exists in both high-temperature and low-temperature permafrost regions. These thermal differences between the two sides of the slope lead to an unbalanced freeze-thaw cycle, potentially causing road defects such as longitudinal cracks and uneven settlement. In the high-altitude, long-day, intensely solar-radiated, and highly transparent natural environment of the Qinghai-Tibet Plateau, the asymmetry in heat absorption on both sides of the roadbed due to different slope aspects causes significant differences in the upper limit of permafrost beneath the roadbed, severely affecting the stability of the roadbed.

[0133] The present invention provides a method for constructing insulated slope protection walkways on both sides of the roadbed:

[0134] If the frost heave level of the seasonal thaw layer in permafrost regions is Class III, then the width of the insulation protection channel on the sunny side should be ≥300cm and the thickness should be ≥100cm; the width of the insulation protection channel on the shady side should be ≥200cm and the thickness should be ≥60cm.

[0135] If the frost heave level of the seasonal thaw layer in permafrost regions is Class IV, then the width of the insulation protection road on the sunny side should be ≥250cm and the thickness should be ≥150cm; the width of the insulation protection road on the shady side should be ≥150cm and the thickness should be ≥120cm.

[0136] If the frost heave level of the seasonal thawing layer in permafrost regions is Class V, then the width of the insulation protection channel on the sunny side should be ≥250cm and the thickness should be ≥150cm; the width of the insulation protection channel on the shady side should be ≥150cm and the thickness should be ≥120cm.

[0137] Furthermore, the present invention also provides a roadbed for permafrost regions, comprising a roadbed body, the roadbed body including a heat insulation layer, the heat insulation layer including a first heat insulation layer and a second heat insulation layer, the first heat insulation layer being disposed below the second heat insulation layer, the heat of hydration of the first heat insulation layer being lower than that of the second heat insulation layer, a sand cushion layer being provided on the second heat insulation layer, a layer of impermeable geotextile being attached below the first heat insulation layer, the roadbed body being covered with fill soil, and a sun-facing heat-insulating protective road and a shade-facing heat-insulating protective road being respectively provided on both sides of the roadbed body;

[0138] The first insulation layer comprises several layers of lightweight foam soil, and the uppermost layer of the first insulation layer is provided with galvanized wire mesh; the second insulation layer comprises several layers of lightweight foam soil, and the uppermost layer of the second insulation layer is provided with galvanized wire mesh.

[0139] The first insulation layer is located on both sides of the sun-side insulation corridor and the shady side insulation corridor, respectively, and the bottommost layer of the second insulation layer, the foam lightweight soil layer, is located on one side of the sun-side insulation corridor.

[0140] The width of the sun-facing insulation channel is ≥250cm and the height is ≥100cm, while the width of the shaded-facing insulation channel is ≥150cm and the height is ≥60cm.

[0141] I. Test to verify the thermal insulation effect of the insulation layer in the roadbed

[0142] 1. Thermal insulation roadbed structure design

[0143] In seasonally frozen areas, embankment subgrades are recommended. The design of subgrades should follow the guidelines of "Subgrade and Pavement Engineering" (5th Edition), "Highway Subgrade Design Specifications" (JTG D30-2015), and "Technical Specifications for Highway Design and Construction in Seasonally Frozen Areas" (JTGT D31-06-2017), and be based on urban arterial road design.

[0144] (1) The top surface of the roadbed is 22m wide and the half-width of the roadbed is 11m wide.

[0145] (2) The height of the embankment roadbed is 1.5m and the slope ratio of the roadbed side slope is 1:1.5.

[0146] (3) Designed according to the heavy traffic load level, the pavement structure layer is 60cm thick, consisting of a 10cm thick asphalt concrete surface layer and a 50cm thick composite base layer from top to bottom.

[0147] (4) A certain thickness of foamed lightweight soil (FCB) thermal insulation layer is installed under the pavement structure layer.

[0148] (5) For large-area fill, the depth of influence during heat transfer is 7.2 times the thickness of the fill.

[0149] Therefore, the foundation soil here is taken to a depth of 10.8m, and ordinary roadbed fill is used.

[0150] (6) The roadbed has little impact on the natural soil beyond 10m of the slope, so the width of the foundation is 10m on each side.

[0151] A defined roadbed model, such as Figure 4 As shown in the figure, the unit of length is cm.

[0152] 2. Experimental Design

[0153] Considering that seasonally frozen soil subgrades are not suitable for construction during the freezing period, it is assumed that the thermal insulation subgrade is completed at 10℃. Using finite element method (ABAQUS CAE6.14) simulation analysis, the temperature field distribution at different depths under the pavement is simulated during a 360-day freeze-thaw cycle after the project is completed. The analysis explores: ① the influence of thermal insulation layers of different thicknesses on the subgrade temperature field; ② the influence of different climatic conditions on the temperature field of the thermal insulation subgrade.

[0154] (1) Setting up reference points

[0155] To accurately study the influence of various factors on the temperature field of the thermally insulated roadbed, five reference points (A, B, C, D, and E) were set at different depths below the road surface, at distances of 0m, 0.5m, 1.0m, 2.0m, and 3.0m from the top surface of the thermal insulation layer, respectively. The reference points were set as follows: Figure 5 As shown.

[0156] (2) Test plan

[0157] 1) Experimental Scheme 1: The Influence of Thermal Insulation Layers of Different Thicknesses on the Temperature Field of the Subgrade

[0158] The thermal insulation layer was analyzed using foamed lightweight soil (FCB) with a density grade of W6. The thickness of the thermal insulation layer was set to 0m, 0.3m, and 0.5m to analyze the temperature change over time at five reference points under the road surface. The test plan is shown in Table 3.

[0159] Table 3 Experimental Scheme for the Influence of Thermal Insulation Layer Thickness on the Subgrade Temperature Field

[0160]

[0161] 2) Experimental Scheme Two: The Influence of Different Climatic Conditions on the Temperature Field of Thermal Insulation Subgrade

[0162] The thermal insulation layer thickness is set at 0.5m, and lightweight foamed soil with a density rating of W6 is selected. Three different climatic conditions are set up, as follows: Figure 6 As shown in Table 4, the temperature changes over time at five reference points under the road surface are analyzed.

[0163] Table 4. Test Plan for the Influence of Climatic Conditions on the Temperature Field of Thermal Insulation Subgrade

[0164]

[0165] 3. Test Results

[0166] (1) The influence of thermal insulation layers of different thicknesses on the temperature field of the roadbed

[0167] This experiment, following test plan one, investigates the impact of different thermal insulation layer thicknesses on the subgrade temperature field. It uses W6 density grade foamed lightweight soil (FCB) thermal insulation layers, with thicknesses of 0m, 0.3m, and 0.5m, to simulate the temperature field changes in the subgrade over 360 days after project completion. Five reference points (A, B, C, D, and E) located 0, 0.5, 1, 2, and 3m from the top surface of the thermal insulation layer, respectively, are used as temperature monitoring points. Temperature curves for these five reference points versus ambient temperature are plotted. Figure 7 As shown.

[0168] from Figure 7 It can be seen that the thicker the thermal insulation layer, the smaller the temperature change at different depths beneath the road surface, and the flatter the temperature curve. A 50cm thick thermal insulation layer basically meets the requirement of a positive annual temperature under the roadbed. The effectiveness of the thermal insulation layer is mainly evaluated from two aspects: ① The lowest winter temperature of the roadbed fill under the thermal insulation layer should be close to 0℃; ② The temperature field of the roadbed fill under the thermal insulation layer should tend to be stable under freeze-thaw cycles, and the annual temperature range should be small. Regarding the two indicators of the lowest annual temperature and the annual temperature range, from... Figure 7Extract the lowest and highest annual temperature values ​​at different depths, calculate the annual temperature range, and plot the lowest temperature curve for the year. Figure 8 ) and annual temperature range curve ( Figure 9 ).

[0169] from Figure 8 as well as Figure 9 It can be seen that: ① After the thermal insulation layer is installed, the temperature difference between the upper and lower parts of the thermal insulation layer is very large. When the thermal insulation layer is 0m thick, the temperature difference between 0m and 0.5m depth from the top surface of the functional layer is only 3℃. When the thermal insulation layer is 0.3m thick, the temperature difference between the upper and lower surfaces of the thermal insulation layer reaches 16℃. When the thermal insulation layer is 0.5m thick, the temperature difference between the upper and lower surfaces exceeds 20℃, indicating that the foamed lightweight soil (FCB) thermal insulation layer has a very good thermal insulation effect; ② The thermal insulation layer has a very significant effect on improving negative temperatures. When the thermal insulation layer is 0m thick, the lowest temperature at the reference point under the road surface is between -17.3℃ and -5.2℃. When the thermal insulation layer is 0.3m thick... When the insulation layer is 0m thick, the lowest temperature at the reference point under the insulation layer is between -4.3 and -0.1℃. When the insulation layer is 0.5m thick, the lowest temperature at the reference point under the insulation layer is between -1.9 and 1.1℃. ③ The thicker the insulation layer, the smaller and more stable the temperature change within the roadbed. When the insulation layer is 0m thick, the annual temperature difference at the reference point under the road surface is between 21.4 and 46.1℃. When the insulation layer is 0.3m thick, the annual temperature difference at the reference point under the insulation layer is between 13 and 23.5℃. When the insulation layer is 0.5m thick, the annual temperature difference at the reference point under the insulation layer is between 10.8 and 19.1℃.

[0170] (2) The influence of different climatic conditions on the temperature field of the roadbed

[0171] This experiment, according to Experimental Scheme 2, investigates the impact of different climatic conditions on the temperature field of the thermally insulated roadbed. Three different climatic conditions are used: Condition 1 (temperature range -25 to 35℃), Condition 2 (temperature range -15 to 25℃), and Condition 3 (temperature range -5 to 15℃). The experiment simulates the temperature field changes in the roadbed over 360 days after project completion. Five reference points (A, B, C, D, and E) located at distances of 0, 0.5, 1, 2, and 3 m from the top surface of the thermal insulation layer, as previously mentioned, are used as temperature monitoring points. Temperature curves for these five reference points versus ambient temperature are plotted, as shown below. Figure 10 As shown.

[0172] from Figure 10 It can be seen that climatic conditions have a significant impact on the temperature field of thermally insulated roadbeds. The lower the minimum air temperature, the greater the temperature variation at different depths beneath the pavement, and the steeper the temperature variation curve. Regarding the two indicators of the minimum annual temperature and the annual temperature range, from... Figure 10Extract the lowest and highest annual temperature values ​​at different depths, calculate the annual temperature range, and plot the lowest temperature curve for the year. Figure 11 ) and annual temperature range curve ( Figure 12 ).

[0173] from Figure 8 and Figure 9 As can be seen, under climate condition 1, the minimum temperature under the insulation layer is partially below zero, while under the other two climate conditions, the temperature under the insulation layer remains positive year-round. The lower the minimum temperature, the greater the annual temperature range under the insulation layer. This is because the minimum temperature under climate condition 1 is lower, and the air temperature...

[0174] The annual temperature range is the largest, and the specific temperature characteristics are shown in Table 5.

[0175] Table 5. Characteristic values ​​of roadbed temperature under different climatic conditions

[0176]

[0177] 4. Experiment Summary

[0178] This invention combines current standards and data to conduct experiments on the design of thermally insulated roadbeds. It simulates the temperature field distribution at different depths beneath the pavement during a 360-day freeze-thaw cycle after project completion. The study focuses on analyzing the impact of thermal insulation layers of different thicknesses on the roadbed temperature field and the influence of different climatic conditions on the temperature field of the thermally insulated roadbed. It simulates the thermal conditions within the roadbed during the 360-day post-construction period to explore the factors affecting the stability of the temperature field of the thermally insulated roadbed, leading to the following two important conclusions:

[0179] (1) Foamed lightweight soil (FCB) thermal insulation subgrade can be used for the prevention and control of frost damage in seasonally frozen soil subgrades. It is a high-performance subgrade insulation layer material.

[0180] (2) The thickness of the thermal insulation layer and external climate conditions will affect the temperature field in the subgrade, and the following rules apply: ① The greater the thickness of the thermal insulation layer, the more stable the temperature field in the subgrade; ② The lower the annual temperature range of the outside air, the more stable the temperature field in the thermal insulation subgrade.

[0181] II. Analysis of Thermal Insulation Layer Thickness

[0182] The previous study shows that the temperature in the roadbed gradually increases with depth. When the lowest temperature at the bottom of the insulation layer is 0℃, the temperature in all other parts of the roadbed is above 0℃. Therefore, temperature monitoring at the bottom of the insulation layer is necessary; the minimum thickness of the insulation layer is when the lowest temperature at the bottom approaches 0℃.

[0183] Thermal insulation layers with density grades of W6 to W10 were installed on the thermal insulation roadbeds in the Greater Khingan Mountains and Urumqi, Xinjiang. The temperature at the bottom of the thermal insulation layer was monitored using the finite element software ABAQUS CAE6.14 to investigate the minimum thickness of the thermal insulation layer for each density grade.

[0184] 1. Analysis of the thickness of thermal insulation layer in heavily frozen soil areas

[0185] Temperature monitoring graph at the bottom of thermal insulation layer with density ratings of W6 to W10 is shown below. Figure 13 The research results are shown in Table 6:

[0186] Table 6 Minimum Thermal Insulation Layer Thickness in the Daxinganling Region

[0187]

[0188] As can be seen from Table 6, due to the long winter duration and minimum temperature exceeding -40℃ in the Daxinganling area, a thicker thermal insulation layer is required to effectively improve the negative temperature conditions under the roadbed. The thermal insulation layer with density grades of W6 to W10 has a thickness range of 120 to 250 cm, which meets the thickness range for self-stability. The annual temperature difference at the bottom of the thermal insulation layer is between 12.0 and 14.8℃, which is relatively stable.

[0189] Therefore, the thickness range of thermal insulation layer for density grades W6 to W10 in the Greater Khingan Mountains is 120 to 250 cm.

[0190] 2. Analysis of the thickness of thermal insulation layer in the medium-frozen soil region

[0191] Temperature monitoring graph at the bottom of thermal insulation layer with density ratings of W6 to W10 is shown below. Figure 14 The research results are shown in Table 7:

[0192] Table 7 Minimum Thermal Insulation Layer Thickness in Urumqi Area

[0193]

[0194] As shown in Table 7, compared to the Greater Khingan Mountains region, the minimum thickness of thermal insulation layers in the Urumqi region is smaller. The thickness range for W6-W10 density grade thermal insulation layers is 50-110 cm, and the annual temperature difference at the bottom of the insulation layer is relatively stable, between 18.9 and 19.7℃. Therefore, the thickness of thermal insulation layers less than 50 cm should be adjusted to meet self-sufficiency and economic and technical requirements, and the thickness should be adjusted to 100-110 cm.

[0195] Therefore, the thickness range of thermal insulation layer for density grades W6 to W10 in Urumqi is 100 to 110 cm.

[0196] Based on the above-mentioned experimental method, the inventors conducted thermal insulation layer thickness tests in appropriate areas of the heavily frozen soil region, and obtained the minimum thermal insulation layer thickness under environments with seasonal thawing layer frost heave levels IV to V. Based on the above-mentioned experimental method, the inventors conducted thermal insulation layer thickness tests in the moderately frozen soil region, and obtained the minimum thermal insulation layer thickness under environments with seasonal thawing layer frost heave level III. Finally, the data in Table 2 of this invention, "Temperature Insulation Layer Thickness of Foamed Lightweight Soil in Permafrost Regions," were obtained.

[0197] The inventors conducted experiments in the Kunlun Mountains plateau platform, specifically at the K207-end section, at an altitude between 4900-5250m. The soil environment is primarily characterized by low-ice permafrost to high-ice permafrost, with some areas rich in ice permafrost. In this region, a 200m-long foamed lightweight soil test road section was constructed using the method provided in this invention. This test road section was completed in October 2021 and has since undergone two freeze-thaw cycles. No thaw settlement, frost heave, frost heave, or cracking was observed on the road surface, demonstrating the high practical value of the method involved in this invention.

[0198] Taking an environmental condition with a seasonal thawing layer frost heave level of III as an example, the implementation steps of this invention are as follows:

[0199] 1. Remove the soil within 60cm below the ground line to form a groove.

[0200] 2. Lay impermeable geotextile at the bottom of the groove and on both sides of the slope.

[0201] 3. Pour a 10cm thick layer of low-hydration-heat foam lightweight soil and wait for it to initially set.

[0202] 4. Pour a 20cm thick layer of low-hydration-heat foam lightweight soil and wait for initial setting. After initial setting, lay galvanized wire mesh.

[0203] 5. Pour a 30cm thick layer of low-hydration-heat foam lightweight soil, wait for initial setting, and complete the pouring of the first insulation layer 6.

[0204] 6. Pour a 30cm thick layer of foamed lightweight soil, extending it into the sun-facing insulation embankment, and wait for it to initially set.

[0205] 7. Pour a 30cm thick layer of foamed lightweight soil, with galvanized wire mesh laid inside, and wait for final setting to complete the pouring of the second insulation layer 5, which also completes the pouring of the insulation layer.

[0206] 8. Lay a 10-15cm thick sand cushion layer on top of the top layer of foamed lightweight soil.

[0207] 9. Fill the roadbed and superstructure. Cover the soil 1 with the heat insulation layer to build the main body of the roadbed. Build the sun-facing heat insulation protection road 3 and the shade-facing heat insulation protection road 2 on both sides of the main body of the roadbed. The width of the sun-facing heat insulation protection road 3 shall not be less than 300cm and the thickness shall not be less than 100cm; the width of the shade-facing heat insulation protection road 2 shall not be less than 200cm and the thickness shall not be less than 60cm.

[0208] The performance parameters of the foamed lightweight soil and the thickness of the insulation layer were determined with reference to Tables 1 and 2. A schematic diagram of the roadbed cross-section after construction is shown below. Figure 1 As shown.

[0209] Taking an environmental condition with a seasonal thawing layer frost heave level of IV as an example, the implementation steps of this invention are as follows:

[0210] 1. Remove the topsoil at the road construction site.

[0211] 2. Excavate trenches 9 on both sides with a depth of 100-120cm and a width of not less than 60cm.

[0212] 3. Lay impermeable geotextile on the ground surface.

[0213] 4. Pour low-heat foam lightweight soil into trench 9 and up to 10cm above the ground surface. The low-heat foam lightweight soil extends into the reserved positions of the insulation and protection channels on both the yin and yang sides and waits for initial setting.

[0214] 5. Pour a 20cm thick layer of low-heat foam lightweight soil, extending it into the reserved positions of the insulation channels on both the yin and yang sides, and wait for initial setting.

[0215] 6. Pour a 30cm thick layer of low-heat foam lightweight soil, extending it into the reserved positions of the insulation channels on both the yin and yang sides. Lay galvanized wire mesh inside and wait for initial setting to complete the pouring of the first insulation layer 6.

[0216] 7. Pour a 30cm thick layer of foamed lightweight soil, extending it into the reserved position of the sun-facing insulation duct, and wait for initial setting.

[0217] 8. Pour a 30cm thick layer of foamed lightweight soil and wait for it to set.

[0218] 9. Pour a 30cm thick layer of foamed lightweight soil, with galvanized wire mesh laid inside, and wait for final setting to complete the pouring of the second insulation layer 5, which also completes the pouring of the insulation layer.

[0219] 10. Lay a 10-15cm thick sand cushion layer on top of the top layer of foamed lightweight soil.

[0220] 11. Fill the roadbed and superstructure. Cover the soil 1 with the heat insulation layer to build the main body of the roadbed. Build the sun-facing heat-insulating walkway 3 and the shade-facing heat-insulating walkway 2 on both sides of the main body of the roadbed. The width of the sun-facing heat-insulating walkway 3 shall not be less than 250cm and the thickness shall not be less than 150cm; the width of the shade-facing heat-insulating walkway 2 shall not be less than 150cm and the thickness shall not be less than 120cm.

[0221] The performance parameters of the foamed lightweight soil and the thickness of the insulation layer were determined with reference to Tables 1 and 2. A schematic diagram of the roadbed cross-section after construction is shown below. Figure 2 As shown.

[0222] Taking an environmental condition with a seasonal thaw layer frost heave level of V as an example, the implementation steps of this invention are as follows:

[0223] 1. Remove the topsoil at the road construction site.

[0224] 2. Excavate trenches 9 on both sides with a depth of 150-200cm and a width of not less than 60cm.

[0225] 3. Lay impermeable geotextile on the ground surface.

[0226] 4. Pour low-heat foam lightweight soil into trench 9 and up to 10cm above the ground surface. The low-heat foam lightweight soil extends into the reserved positions of the insulation and protection channels on both the yin and yang sides and waits for initial setting.

[0227] 5. Pour a 20cm thick layer of low-heat foam lightweight soil, extending it into the reserved positions of the insulation channels on both the yin and yang sides, and wait for initial setting.

[0228] 6. Pour a 30cm thick layer of low-heat foam lightweight soil, extending it into the reserved positions of the insulation channels on both the yin and yang sides. Lay galvanized wire mesh 7 inside the soil and wait for initial setting to complete the pouring of the first insulation layer 6.

[0229] 7. Pour a 30cm thick layer of foamed lightweight soil, extending it into the reserved position of the sun-facing insulation duct, and wait for initial setting.

[0230] 8. Pour a 30cm thick layer of foamed lightweight soil and wait for it to set.

[0231] 9. Pour a 30cm thick layer of foamed lightweight soil and wait for it to set.

[0232] 10. Pour a 30cm thick layer of foamed lightweight soil, with galvanized wire mesh 7 laid inside, and wait for final setting to complete the pouring of the second insulation layer 5, which also completes the pouring of the insulation layer.

[0233] 11. Lay a 10-15cm thick sand cushion layer on top of the top layer of foamed lightweight soil.

[0234] 12. Fill the roadbed and superstructure. Cover the soil 1 with the heat insulation layer to build the main body of the roadbed. Build the sun-facing heat-insulating walkway 3 and the shade-facing heat-insulating walkway 2 on both sides of the main body of the roadbed. The width of the sun-facing heat-insulating walkway 3 shall not be less than 250cm and the thickness shall not be less than 150cm; the width of the shade-facing heat-insulating walkway 2 shall not be less than 150cm and the thickness shall not be less than 120cm.

[0235] The performance parameters of the foamed lightweight soil and the thickness of the insulation layer were determined with reference to Tables 1 and 2. A schematic diagram of the roadbed cross-section after construction is shown below. Figure 3 As shown.

[0236] This invention provides a method for roadbed construction in permafrost regions, employing foamed lightweight soil as the insulation layer in the roadbed. The thermal conductivity of foamed lightweight soil is only about 20% of that of traditional insulation roadbed fillers. Compared to traditional roadbed insulation fillers, foamed lightweight soil has the characteristics of low thermal conductivity and good freeze-thaw resistance. Using foamed lightweight soil as the insulation layer in the roadbed can effectively isolate the permafrost from the influence of external temperature changes, control the rate of permafrost thawing within the roadbed area, protect the upper limit of permafrost, and prevent the permafrost from softening or expanding upon freezing. This minimizes the severity of roadbed subsidence, frost heave, and pavement cracking. The foamed lightweight soil insulation layer in this invention is constructed using a thin-layer, multiple-layer pouring method, allowing the heat of hydration generated by the foamed lightweight soil after each pour to dissipate promptly, avoiding the generation of excessive heat of hydration that could affect the permafrost. Because foamed lightweight soil has low thermal conductivity, good freeze-thaw resistance, and high strength, the roadbed construction method involved in this invention results in a lower filling height than typical roadbeds, reducing the roadbed's impact on the local natural environment. Based on the strong thermal insulation properties of foamed lightweight soil, combined with sun-facing and shade-facing insulating abutments of different heights and widths, the heat absorption on both sides of the roadbed can be balanced, avoiding longitudinal settlement caused by uneven heat absorption.

[0237] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for roadbed construction in permafrost regions, characterized in that, It includes the following steps: Based on the highway grade to be constructed, determine the required bulk density and compressive strength grade of the foamed lightweight soil. Based on the frost heave grade of the permafrost seasonal thaw layer in the area where the highway to be built is located and the bulk density grade of the foamed lightweight soil, the standard thickness of the insulation layer in the roadbed is determined. A geotextile is laid at the road construction site. Foamed lightweight soil is poured on the laid geotextile. After the foamed lightweight soil has initially solidified, it is poured again. This process is repeated until the thickness of the insulation layer formed by the foamed lightweight soil reaches the standard thickness. The thickness of the foamed lightweight soil layer poured each time is ≤30cm. A backfill is constructed on the upper part of the insulation layer, and a sun-facing insulation corridor and a shade-facing insulation corridor are constructed on both sides of the backfill. The heat insulation layer includes at least a first heat insulation layer and a second heat insulation layer, with the second heat insulation layer located above the first heat insulation layer. The casting steps for the first heat insulation layer are as follows: First, pour a 7-13cm thick layer of foamed lightweight soil onto the impermeable geotextile. After the first layer of foamed lightweight soil has initially set, pour a 17-23cm thick layer of foamed lightweight soil. After the second layer of foamed lightweight soil has initially set, pour a 27-33cm thick layer of foamed lightweight soil. Then, place galvanized steel wire mesh into the third layer of foamed lightweight soil. When pouring the uppermost layer of foamed lightweight soil in the second insulation layer, galvanized steel wire mesh is placed inside the uppermost layer of foamed lightweight soil in the second insulation layer, and a layer of sand is laid on top of the second insulation layer. The heat of hydration of the foamed lightweight soil used in the first insulation layer is lower than that of the foamed lightweight soil used in the second insulation layer.

2. The method for roadbed construction in permafrost regions according to claim 1, characterized in that, The steps for determining the required bulk density and compressive strength grades of foamed lightweight soil based on the highway grade to be constructed include: If the highway is classified as an expressway or a Class I highway, and the roadbed is used for light, medium, and heavy traffic, then the bulk density grade of the foamed lightweight soil used in the roadbed is greater than or equal to W6 and less than W8; and the compressive strength grade is greater than or equal to CF1.

2. If the highway is classified as an expressway or a Class I highway, and the roadbed is used for extra-heavy or extremely heavy traffic, then the bulk density grade of the foamed lightweight soil used in the roadbed is greater than or equal to W6 and less than W8; and the compressive strength grade is greater than or equal to CF1.

4. If the highway is classified as an expressway or a Class I highway, the bulk density grade of the foamed lightweight soil used in the upper and lower embankments of the roadbed is greater than or equal to W5 and less than W7; the compressive strength grade is greater than or equal to CF1.

0. If the highway is classified as a Class II highway or below, the bulk density grade of the foamed lightweight soil used in the subgrade is greater than or equal to W6 and less than W8; the compressive strength grade is greater than or equal to CF1.

0. If the highway is classified as a Class II highway or below, the bulk density grade of the foamed lightweight soil used in the upper and lower embankments of the roadbed shall be greater than or equal to W5 and less than W7; and the compressive strength grade shall be greater than or equal to CF0.

8.

3. The method for roadbed construction in permafrost regions according to claim 1, characterized in that: Before laying the impermeable geotextile at the road construction site, the method further includes: A foundation soil was formed at the road construction site by replacing the foundation soil with foamed lightweight soil of a density grade greater than or equal to W4 and less than W6 and a compressive strength greater than or equal to CF0.

6. The laying of impermeable geotextile at the road construction site includes: An impermeable geotextile was laid on the foundation.

4. The method for roadbed construction in permafrost regions according to claim 1, characterized in that: Based on the frost heave grade of the permafrost seasonal thaw layer in the area where the highway to be constructed is located and the bulk density grade of the foamed lightweight soil, the standard thickness of the insulation layer in the roadbed is determined, including: If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 120cm. If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 140cm. If the frost heave level of the seasonal thawing layer in the permafrost region is Class III and the bulk density grade of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 160cm. If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 150cm. If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 170cm. If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, and the bulk density level of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 190cm. If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W5, then the standard thickness of the insulation layer is 180cm. If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W6, then the standard thickness of the insulation layer is 200cm. If the frost heave level of the seasonal thawing layer in the permafrost region is level V, and the bulk density level of the foamed lightweight soil used is W7, then the standard thickness of the insulation layer is 220cm.

5. The method for roadbed construction in permafrost regions according to claim 1, characterized in that: If the frost heave level of the seasonal thaw layer in the permafrost region is Class III, then first dig a groove with a depth of 50-70cm at the road construction location, then lay impermeable geotextile on the bottom and slope of the groove, and then pour foamed lightweight soil. If the frost heave level of the seasonal thawing layer in the permafrost region is level IV, then first dig trenches with a depth of 100~120cm and a width of not less than 60cm on both sides of the road construction location, then lay impermeable geotextile between the two trenches, and then pour foamed lightweight soil. If the frost heave level of the seasonal thawing layer in the permafrost region is level V, then first dig trenches with a depth of 150~200cm and a width of not less than 60cm on both sides of the road construction location, then lay impermeable geotextile between the two trenches, and then pour foamed lightweight soil.

6. The method for roadbed construction in permafrost regions according to claim 5, characterized in that: The sun-facing insulation shield and the shade-facing insulation shield respectively cover both sides of the first insulation layer, and the sun-facing insulation shield covers one side of the bottom layer of the second insulation layer, which is made of foamed lightweight soil.

7. The method for roadbed construction in permafrost regions according to claim 1, characterized in that: If the frost heave level of the seasonal thaw layer in permafrost regions is Class III, then the width of the insulation protection channel on the sunny side should be ≥300cm and the thickness should be ≥100cm; the width of the insulation protection channel on the shady side should be ≥200cm and the thickness should be ≥60cm. If the frost heave level of the seasonal thaw layer in permafrost regions is Class IV, then the width of the insulation protection road on the sunny side should be ≥250cm and the thickness should be ≥150cm; the width of the insulation protection road on the shady side should be ≥150cm and the thickness should be ≥120cm. If the frost heave level of the seasonal thawing layer in permafrost regions is Class V, then the width of the insulation protection channel on the sunny side should be ≥250cm and the thickness should be ≥150cm; the width of the insulation protection channel on the shady side should be ≥150cm and the thickness should be ≥120cm.

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