CN107201708A - A kind of compound cold-storage roadbed suitable for permafrost region road engineering - Google Patents

Abstract

The present invention relates to a kind of compound cold-storage roadbed suitable for permafrost region road engineering, including top embankment filled soil, bottom embankment filled soil and it is laid between the top embankment filled soil and the bottom embankment filled soil and perpendicular to the ventilation duct of trend of road, it is characterised in that：The one or both ends of the ventilation duct are installed by air door；Hollow block layer is laid between the adjacent ventilation duct, and pipe-massive stone layer is equipped with the ventilation duct and the hollow block；The pipe-massive stone layer is provided with geotextiles, the geotextiles and lays the top embankment filled soil.The present invention can effectively reach High-Grade Highway Subgrade entirety, the key technical index of uniform decrease in temperature, so as to be obviously improved the cooling efficiency of roadbed, improve subgrade stability, have significant advantage for reducing the possible heaving of the sea in road surface and fracture development.

Description

A Composite Cold Storage Subgrade Suitable for Road Engineering in Permafrost Regions

technical field

The invention relates to the technical field of frozen soil engineering, in particular to a composite cold storage subgrade suitable for road engineering in frozen soil regions.

Background technique

Permafrost is rock and soil containing ice with a temperature not higher than 0°C. According to the length of the freezing period, it can be divided into instantaneous frozen soil, seasonal frozen soil and permafrost. With the development of economy and society, engineering construction in permafrost areas has gradually increased, especially road engineering. The construction of road engineering will significantly change the thermal state of the underlying permafrost, resulting in an increase in the temperature of the permafrost and a decrease in bearing capacity, which in turn may cause subsidence of the subgrade. Therefore, the problem of permafrost has become a key issue for the success of road construction in permafrost regions.

In the research of the Qinghai-Tibet Railway, in order to ensure the long-term stability of the roadbed, the researchers proposed the idea of actively cooling the roadbed, and carried out a large number of active cooling roadbed structures based on this idea, and found that some roadbed structures are important for improving roadbed stability. It has good application effect. However, in high-temperature and high-ice-content permafrost regions, existing subgrade structures have insufficient cooling performance. At the same time, the heat absorption intensity of highway asphalt pavement is significantly higher than that of railway pavement. Related studies have shown that in permafrost regions, the strong heat absorption of asphalt pavement will cause the continuous degradation of the lower permafrost, and the upper limit of permafrost will decrease. The amount of permafrost melting, etc., and then cause a series of engineering problems such as subsidence and subsidence of road subgrade, which will become more prominent under the condition of continuous warming of the climate in the future.

At present, the construction of the Qinghai-Tibet Expressway has been put on the agenda. Since the pavement width of the expressway has increased significantly compared with the Qinghai-Tibet Highway, the heat absorption intensity of the roadbed will also increase exponentially. In order to ensure the stability of the Qinghai-Tibet Expressway after construction, reasonable active cooling control measures must be adopted for the high temperature and high ice content permafrost section. However, due to the substantial increase in the width of the embankment, the application effect of the current control measures will be further reduced. For this reason, researchers try to combine the existing control measures in order to improve the control efficiency of engineering measures, but due to the lack of design structure, it is difficult to meet the actual needs of the project. For example: "Application of a through-wall ventilation pipe-block crushed stone cooling and heat-insulating composite subgrade in wide roads" (Lai Yuanming, Dong Yuanhong, Zhang Mingyi: China, 201010133544.7[P]. 2010.09.01) proposed a through-wall Ventilation pipe-block crushed stone composite roadbed, the through-wall ventilation pipe is placed on the block of crushed stone layer, and its cooling efficiency is insufficient in the cold season; while in the warm season, the through-wall holes of this structure transmit a large amount of heat into the block Stone layers, reducing the cool storage effect of block stone layers. "Composite temperature-controlled ventilation subgrade" (Yu Qihao, Cheng Guodong, Niu Fujun, etc.: China, 200410002135.8 [P]. 2004.12.22) proposed an automatic temperature-controlled ventilation pipe-insulation board composite subgrade structure, but the cooling process of the ventilation pipe in this structure It has significant unevenness, which is unfavorable for controlling the uneven settlement of the roadbed. "Enhanced Ventilation and Heat Insulation Subgrade" (Li Guoyu, Li Ning, Niu Fujun, etc.: China, 200710017288[P]. 2007.08.08) proposed a self-controlled through-wall ventilation pipe-block gravel-insulation material enhanced ventilation and heat insulation subgrade, However, the cushion under the ventilation pipe in this structure is relatively thin, and the opening of the ventilation pipe is easily blocked by snow and sandstorms in the cold season, resulting in a significant drop in cooling in the cold season; thermal effect, the insulation material placed on the upper part has little significance in enhancing the heat insulation effect of the roadbed, but it significantly reduces the cooling effect of the roadbed in cold seasons; in addition, although the through-wall ventilation pipe has been tested in some projects, it does not There is no literature showing that this measure has significant advantages compared with ordinary ventilation pipes, but this measure will cause a substantial increase in project cost.

In addition, there are also problems in the application of heat pipe measures commonly used in permafrost engineering to road engineering. Due to the significant inhomogeneity of the cooling process of this measure, the existing application experience shows that the application of this measure in road engineering has caused the development of cracks in the subgrade. Developed cracks (Yu Qihao, Fan Kai, Qian Jin, Guo Lei, You Yanhui, Research on Key Issues of Expressway Construction in Permafrost Areas in my country, Science in China: Technical Science, 2014, 44(4): 425 ~ 432)). Based on the strict requirements of the expressway for the settlement and cracks of the subgrade, this type of highway has special requirements for the overall and uniform cooling of the subgrade. Therefore, the existing methods are still unable to meet the construction requirements of expressways in permafrost regions, and it is necessary to seek more efficient and reasonable protection measures for subgrades in permafrost.

Contents of the invention

The technical problem to be solved by the present invention is to provide a composite cold storage subgrade suitable for road engineering in frozen soil regions, which can effectively reduce the temperature of the frozen soil and improve the stability of the frozen soil.

In order to solve the above problems, a composite cold storage subgrade suitable for road engineering in permafrost regions according to the present invention includes an upper embankment fill, a lower embankment fill, and an embankment layer arranged between the upper embankment fill and the lower embankment fill The ventilation pipe between and perpendicular to the direction of the road is characterized in that: dampers are installed at one or both ends of the ventilation pipe; a hollow block layer is laid between the adjacent ventilation pipes, and the ventilation pipe and the hollow block are A crushed stone layer is laid; a geotextile is arranged on the crushed stone layer, and the upper embankment fill is laid on the geotextile.

The diameter of the ventilation pipe is 30-60 cm, the thickness of the pipe wall is 3-6 cm, and the distance between the center of the pipe and the natural ground surface is 0.5-2.0 m.

The distance between adjacent ventilation pipes is 1 to 3 times the diameter of the ventilation pipes.

The thickness of the hollow block layer is consistent with the diameter of the ventilation pipe, and the hollow block is composed of a concrete prefabricated hollow cube or cuboid with a side length of 6-30 cm and a wall thickness of 2-6 cm.

The particle size of the crushed stone layer is 10-40cm, and the laying thickness is 1-2m.

Compared with the prior art, the present invention has the following advantages:

1. Innovate the control mechanism of engineering measures.

The first is the level linkage and cooling mechanism in the embankment. During the cooling process in the cold season, the large porosity in the hollow block layer between the ventilation pipes greatly enhances the convective heat transfer effect between the ventilation pipes, effectively forming a ventilation pipe-hollow block level linkage and cooling mechanism, which is to realize the overall and uniform subgrade. The fundamental mechanism of cooling; the second is the self-balancing mechanism. In the warm season, due to the difference in solar radiation and slope temperature between the shady and sunny slopes of the embankment, there will be a certain difference in ground temperature between the left and right sides of the embankment in the cross section of the embankment. The existence of the embankment can generate a certain convective heat transfer process between different parts on the left and right sides of the embankment in the block stone and hollow block layer of the embankment cross section, thereby balancing the ground temperature difference of the embankment and creating a ground temperature self-balancing mechanism of the embankment ; Finally, the present invention is the cold storage mechanism of the roadbed. During the heating process, due to the automatic temperature sensing, the timely closing of the control damper, the cessation of the vertical convective heat transfer process in the ventilation pipe, the hollow block and the stone layer, the thermal conductivity is greatly reduced, and the cold energy accumulated in the subgrade in winter is effectively stored. In this way, the cycle effectively achieves the purpose of continuously reducing the temperature of the frozen soil.

2. Effectively solve the key technical problems of overall and uniform regulation of ground temperature of high-grade road subgrades.

First of all, due to the formation of the above-mentioned level linkage and cooling mechanism, the overall level of the embankment in the cooling process is synchronized and uniformly cooled, and a 0°C ground temperature contour line and a flat and symmetrical favorable shape of the overall ground temperature field are formed. Secondly, under the above-mentioned self-balancing mechanism, the temperature difference of the subgrade in warm seasons can be effectively alleviated, and the uniformity of the ground temperature field can be further ensured. Therefore, through the combination of the two, the problem of overall and uniform ground temperature control on high-grade highways can be effectively solved.

3. Significantly improve the cooling performance of the subgrade.

It is precisely because of the existence and superposition of the above-mentioned triple mechanism of cooling, balancing, and cold storage in the present invention that the overall and uniform cooling of the roadbed is effectively guaranteed, and the cooling efficiency is also greatly improved.

4. Effectively increase the stability of the roadbed.

Although the existing measures have effectively reduced the ground temperature of the subgrade to a large extent, with the seasonal changes and the freezing and thawing process of the subgrade within a certain depth range, it is inevitable to cause subgrade frost heaving, thawing and settlement to a certain extent. have a certain impact on the stability of the subgrade. Since the block layer is a flexible and self-stress-balanced foundation, the block layer laid in the present invention can largely alleviate the adverse effects caused by freezing and thawing. Therefore, the block stone layer of the present invention has dual functions of temperature regulation and deformation regulation. As a result, the occurrence probability of potential secondary roadbed engineering diseases of the roadbed is greatly reduced, and the stability of the roadbed is improved.

Description of drawings

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Figure 1 shows the development of cracks under the action of a typical heat pipe a.

Figure 2 shows the development of cracks under the action of a typical heat pipe b.

Figure 3 is a cross-sectional view of the present invention.

Fig. 4 is a longitudinal sectional view of the present invention.

Fig. 5 is the comparison of the upper limit of permafrost and other two measures in the subgrade cross section of the ventilation pipe position after using the present invention.

Fig. 6 is the comparison of the upper limit of frozen soil in the longitudinal section of the central position of the subgrade after using the present invention and the other two measures.

In the figure: 1—ventilation pipe 2—damper 3—gravel layer 4—hollow block layer 5—geotextile 6—upper embankment filling 7—lower embankment filling 8—natural surface.

detailed description

As shown in Fig. 3 and Fig. 4, a composite cold storage subgrade suitable for road engineering in permafrost regions includes an upper embankment fill 6, a lower embankment fill 7, and is arranged between the upper embankment fill 6 and the lower embankment fill 7. Ventilation pipes 1 that are spaced and perpendicular to the direction of the road. Air door 2 is installed at one or both ends of the ventilation pipe 1; a hollow block layer 4 is laid between adjacent ventilation pipes 1, and a crushed stone layer 3 is laid on the ventilation pipe 1 and the hollow block layer 4; A geotextile 5 is provided, and the upper embankment fill 6 is laid on the geotextile 5 .

Among them: the diameter of the ventilation pipe 1 is 30~60cm, the thickness of the pipe wall is 3~6cm, and the distance between the center of the pipe and the surface of the natural surface 8 is 0.5~2.0m.

The distance between adjacent ventilation pipes 1 is 1 to 3 times the diameter of the ventilation pipes 1 .

The thickness of the hollow block layer 4 is consistent with the diameter of the ventilation pipe 1, and the hollow block is composed of a concrete prefabricated hollow cube or cuboid with a side length of 6-30 cm and a wall thickness of 2-6 cm.

The particle size of the gravel layer 3 is 10-40 cm, and the laying thickness is 1-2 m.

Working mechanism of the present invention:

In the cold season, the self-control damper 2 of the ventilation pipe 1 is automatically opened, and the cold air from the outside enters the ventilation pipe 1, which quickly reduces the temperature of the surrounding embankment soil and releases a large amount of heat in the roadbed; at the same time, because the temperature of the pipe wall is very low, and the surrounding hollow blocks The inner gap is relatively large, so under the effect of strong convective heat transfer in the hollow block layer 4, the cooling range of the soil between the tubes is increased, and the integrity of the subgrade cooling process is improved. In the warm season, the ventilation pipe 1 automatically controls the damper 2 to automatically close, preventing the external heat from entering the pipe, and greatly reducing the heat absorption of the roadbed; Due to convective heat transfer, its own thermal conductivity is poor, so it can prevent heat transfer to the roadbed in warm seasons. The application of geotextile 5 on the top of the crushed stone layer 3 can ensure that the gaps in the layer do not change for a long period of time. A significant reduction occurs, ensuring the long-term effectiveness of the unidirectional thermal conductivity of the roadbed.

The specific application example 1 of the present invention:

⑴Fill the lower embankment fill soil 7 on the compacted natural surface 8 and compact it, the filling soil is 0.5~2.0m higher than the original natural surface.

(2) On the rammed lower embankment fill soil 7, prefabricated ventilation pipes 1 with self-control dampers 2 are arranged perpendicular to the road direction. The diameter of the ventilation pipes 1 is 30-60 cm, the thickness of the pipe wall is 3-6 cm, and the distance between the pipes is 1~3 times.

(3) Randomly stack prefabricated concrete hollow blocks between the ventilation pipes 1. The concrete hollow blocks are cubes or cuboids with a side length of 6-30cm and a wall thickness of 2-6cm.

(4) Pile a crushed stone layer 3 on the upper part of the ventilation pipe 1 and the hollow block layer 4, the particle size of the crushed stone is 10~40cm, and the thickness of the crushed stone layer is 1~2m, and then carry out vibration compaction.

(5) Lay a layer of geotextile 5 on the gravel layer 3, and then fill the upper embankment with soil 6 and compact it.

In order to verify the application efficiency of the present invention, and compare with the application efficiency of the prior art, the numerical simulation analysis of the application efficiency of different engineering measures is carried out, and the distribution of the upper limit of frozen soil under different working conditions calculated is compared, as Figure 5~6. Wherein Fig. 5 shows the upper limit distribution of frozen soil on the cross section of the central position of the ventilation pipe, and Fig. 6 shows the upper limit distribution of frozen soil on the longitudinal section of the central position of the embankment. Existing technology 2" is the technology whose application number is 201010133544.7. It can be seen that the present invention has significant application advantages compared with the current existing technology, and can greatly reduce the natural surface temperature of permafrost, and ensure the integrity and uniformity of the cooling process. in:

① Efficiency improvement:

Compared with the two existing similar technologies at present, the cooling efficiency of the present invention is greatly improved in the cold season, and the heat insulation performance in the warm season is also enhanced. Technology has improved significantly. Figure 5 shows the distribution of the upper limit of frozen soil (that is, the 0°C isotherm) on the cross-section of the subgrade ventilation pipe position. It can be seen from the figure that there are currently two similar technologies that can only raise the upper limit of frozen soil from the middle of the road to the lower part of the shady slope, and The uplift range is limited; and near the sunny slope, the upper limit of permafrost at the lower part of the subgrade is even lower than the upper limit of natural permafrost, and the effect of shady and sunny slopes is significant. The invention can greatly improve the cooling efficiency of the subgrade, and the upper limit of permafrost on shady slopes is slightly raised compared with the other two technologies. At the same time, the invention can significantly raise the upper limit of permafrost at the lower part of the sunny slope, so that the 0°C isotherm reaches near the natural surface and remains basically horizontal along the cross-section of the roadbed, eliminating the shady and sunny slope effect of the roadbed to a large extent.

② In terms of overall cooling:

Figure 6 shows the distribution of the upper limit of frozen soil (that is, the 0°C isotherm) on the longitudinal section of the center of the subgrade. It can be seen from the figure that the application of the present invention has significantly raised the upper limit of frozen soil compared with the existing technology, and it is more The most remarkable advantage is that: the difference between the upper limit position of frozen soil under the pipe and between the pipes is very small, and the integrity of the subgrade cooling process is very remarkable, while other technologies, especially the upper limit buried depth of frozen soil in the existing technology 1, fluctuate more along the direction of the roadbed. Large, the integrity of roadbed cooling is poor.

Because the mechanical strength of frozen soil is significantly affected by temperature, temperature rise or even thawing will cause a significant decrease in the mechanical strength of frozen soil. Therefore, if the upper limit buried depth of the soil between the ventilation pipes is greater than that of the soil below the pipes, the mechanical strength of the soil between the pipes will be significantly reduced. Cause the undulation of the road surface, the development of cracks, and even the muddying of the road. Since expressways have strict requirements on road surface smoothness and cracks, the existing technologies cannot meet the needs of future expressway construction. The application of the present invention enhances the cooling range of the roadbed in the cold season, and greatly improves the integrity of the roadbed's cooling; meanwhile, the heat insulation performance of the roadbed in the warm season is enhanced. Through the use of the present invention, not only the cooling efficiency of the roadbed can be effectively improved, but also the integrity and uniformity of the temperature field of the roadbed can be greatly improved, which has significant advantages in reducing possible undulations and crack development of the road surface.

Claims (5)

1. A composite cool-storage subgrade suitable for road engineering in permafrost regions, comprising an upper embankment fill (6), a lower embankment fill (7) and A ventilation pipe (1) between the soil (7) and perpendicular to the direction of the road, characterized in that: dampers (2) are installed at one or both ends of the ventilation pipe (1); A hollow block layer (4) is laid between them, and a crushed stone layer (3) is laid on the ventilation pipe (1) and the hollow block layer (4); a geotextile is arranged on the crushed stone layer (3) (5), laying the upper embankment fill (6) on the geotextile (5). 2. A composite cold storage subgrade suitable for road engineering in permafrost regions as claimed in claim 1, characterized in that: the ventilation pipe (1) has a pipe diameter of 30-60 cm and a pipe wall thickness of 3-6 cm. The height of the tube center from the natural surface (8) is 0.5~2.0m. 3. A composite cold storage subgrade suitable for road engineering in permafrost regions according to claim 1, characterized in that the distance between adjacent ventilation pipes (1) is 1 of the diameter of the ventilation pipe (1) ~3 times. 4. A composite cold storage subgrade suitable for road engineering in permafrost regions according to claim 1, characterized in that: the thickness of the hollow block layer (4) is consistent with the diameter of the ventilation pipe (1), and the hollow The block is composed of a concrete prefabricated hollow cube or cuboid with a side length of 6-30cm and a wall thickness of 2-6cm. 5. A composite cool-storage subgrade suitable for road engineering in permafrost regions as claimed in claim 1, characterized in that: the crushed stone layer (3) has a particle size of 10-40 cm and a laying thickness of 1-2 m .