Dam frost heaving prevention protection structure and construction method

Abstract

The invention belongs to the technical field of geotechnical engineering, and particularly relates to a dam frost heaving prevention protection structure and a construction method. Comprising a capillary barrier and an inclined drainage pipe, the capillary barrier comprises a top layer, a middle layer and a bottom layer, and the top layer comprises a plurality of soil-PCM microcapsule soilbags and a soil layer; the middle layer is composed of a plurality of fine particle-wicking geotextile geotextile bags, and the fine particle-wicking geotextile geotextile bags are located on the inner sides of the soil-PCM microcapsule geotextile bags and are adjacent to one another; the bottom layer comprises a coarse particle layer and a coarse particle recycled concrete aggregate layer, is adjacent to the middle layer and is positioned on the inner side of the middle layer; and the inclined drainage pipe is jacked into side slope soil. The capillary barrier system, the wicking geotextile, the PCM and the inclined drainage pipe are adopted, the freezing temperature of the cold region winter reservoir slope soil can be effectively reduced, the stability of the cold region winter reservoir slope can be effectively improved, the vegetation coverage rate can be increased, and the effects of preserving heat, beautifying the environment and keeping water and soil are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering, and specifically relates to a dam anti-frost heave protection structure and a construction method. Background Art

[0002] People have put forward higher requirements for a better life, including higher demands for living conditions and natural environment. The construction of reservoirs can not only improve the quality of residents' domestic water, but also improve the ecological environment.

[0003] The impact of winter frost heave on reservoir slopes cannot be ignored. During cold winters, especially in areas with minimum temperatures below -10°C, reservoir slopes are often damaged. Frost heave can cause cracks in reservoir slopes, as ice rises from the water's edge to the slopes, subjecting them to ice thrust and pressure, potentially leading to damage. More seriously, the combined effects of ice pressure, ice thrust, and freeze-thaw cycles can cause the slopes to slide and overturn. Especially during warming freeze-thaw cycles, slope soil can experience excessive and uneven subsidence, leading to the overturning of embankments and slopes. Excessive water content in the soil can even cause liquefaction and rheology of the foundation soil, resulting in extensive damage to embankments and slope protection.

[0004] Therefore, for managers and maintainers of reservoir slopes, it is necessary to fully consider the impact of ice formation and freeze-thaw cycles on reservoir slopes in winter and take corresponding measures to prevent and mitigate these impacts to ensure the safety and stability of reservoir slopes. Summary of the Invention

[0005] The present invention aims to provide a dam frost heave protection structure and construction method to improve the stability of reservoir slopes during freezing and freeze-thaw cycles. Utilizing the Gibbs-Thompson principle, the suction of a capillary barrier is leveraged to prevent freezing. Wicking geotextiles are incorporated into the capillary barrier to enhance its suction. PCM materials effectively control and delay temperature within the dam frost heave protection structure. Furthermore, a double-layered, upward-sloping drainage pipe ensures effective drainage of the slope during both the reservoir's wet and dry seasons.

[0006] In order to achieve the above objectives, the technical solutions adopted by the present invention include: A dam anti-frost heave protection structure includes a capillary barrier and an upward inclined drainage pipe. The capillary barrier includes a top layer, a middle layer and a bottom layer, wherein the top layer includes a plurality of soil-PCM microcapsule geobags and a soil layer; the middle layer is composed of a plurality of fine particle-wicking geotextile geobags, which are located inside the soil-PCM microcapsule geobags and are closely adjacent to each other; the bottom layer includes a coarse particle layer and a coarse particle recycled concrete aggregate layer, and the bottom layer is adjacent to the middle layer and located inside the middle layer; the upward inclined drainage pipe is pushed into the slope soil.

[0007] In a preferred embodiment, the ratio of PCM microcapsules mixed in the soil is 5% to 15%; the PCM microcapsules include a first PCM with a phase transition temperature of -3°C and a second PCM with a phase transition temperature of -8°C. If A2C2+A1C1 is lower than the phase transition temperature of the second PCM -8°C, then the volume ratio of the first PCM to the second PCM is: (-3°C - (-8°C)): (-8°C - (A2C2+A1C1)), where C1 is the average winter temperature of a certain location for several consecutive years, C2 is the minimum winter temperature of a certain location for several consecutive years, A1 is the weight of the average winter temperature of a certain location, A2 is the weight of the minimum winter temperature of a certain location, A1+A2=1, A2>A1, and A1 and A2 are respectively>0.

[0008] Furthermore, when C1 < 0 °C, the volume ratio of wicking geotextile to fine particles-wicking geotextile is: (1) p————the proportion of wicking geotextile in the mixed soil, C1————The average winter temperature of a certain place for several consecutive years, θ————Average volumetric moisture content in the reservoir slope soil, A———— Reservoir slope gradient, Xt————microcapsule volume ratio, d————Proportional coefficient of wicking geotextile.

[0009] Among them, the coarse particle layer in the bottom layer is adjacent to the soil layer and is located below the soil layer; the coarse particle layer in the bottom layer and the coarse particle layer are against each other and the coarse particle layer is located above the coarse particle layer; the coarse particle layer is against the slope and top surface of the reservoir slope soil and presents an approximately L-shaped shape.

[0010] Several soil-PCM microcapsule geobags are vertically staggered and basically parallel to the slope of the reservoir slope soil; the soil layer is adjacent to the upper geobags of the several soil-PCM microcapsule geobags and basically parallel to the top surface of the reservoir slope soil.

[0011] Preferably, the upward-sloping drainage pipe is set at an angle of 7 to 13 degrees to the water surface; the upward-sloping drainage pipe is pushed into the slope soil at a distance of 1.2 to 1.8 meters.

[0012] The upward inclined drainage pipe is wrapped with geotextile; the upward inclined drainage pipe is set in two layers, the first layer of upward inclined drainage pipe is set 0.4~0.6m above the water surface during the winter dry season, and the second layer of upward inclined drainage pipe is set 0.4~0.6m above the water level during the summer flood season.

[0013] Another object of the present invention is to disclose a construction method of the aforementioned dam anti-frost heave protection structure, comprising the following steps: Site survey; mixing PCM microcapsules with soil, mixing fine particles with wicking geotextiles, filling geobags; particle compaction; laying geobags, geogrids, and geotextiles; laying geogrids; turf construction; and jacking up inclined drainage pipes into the slope.

[0014] The mixing ratio of PCM microcapsules in the soil is 5%~15%; the PCM microcapsules include a first PCM with a phase transition temperature of -3°C and a second PCM with a phase transition temperature of -8°C. If A2C2+A1C1 is lower than the phase transition temperature of the second PCM -8°C, then the volume ratio of the first PCM to the second PCM is: (-3°C-(-8°C)):(-8°C-(A2C2+A1C1)), where C1 is the average winter temperature of a certain place for several consecutive years, C2 is the minimum winter temperature of a certain place for several consecutive years, A1 is the weight of the average winter temperature of a certain place, A2 is the weight of the minimum winter temperature of a certain place, A1+A2=1, A2>A1, and A1 and A2 are respectively>0.

[0015] When C1<0℃, the volume ratio of wicking geotextile to fine particles-wicking geotextile is: (1) p————Volume ratio of wicking geotextile to fine particles-wicking geotextile, C1————The average winter temperature of a certain place for several consecutive years, θ————Average volumetric moisture content in the reservoir slope soil, A———— Reservoir slope gradient, Xt————microcapsule volume ratio, d————Proportional coefficient of wicking geotextile.

[0016] The benefits of the present invention lie in that, through its implementation, the stability of reservoir slopes in cold regions during winter can be enhanced. The present invention employs a capillary barrier system, wicking geotextiles, PCM, and upward-sloping drainage pipes, which can effectively reduce the freezing temperature of soil on reservoir slopes in cold regions during winter. This not only effectively improves the stability of reservoir slopes in cold regions during winter, but also increases vegetation coverage, playing a role in heat preservation, beautifying the environment, and conserving water and soil. At the same time, the construction of this system can also achieve the secondary utilization of construction solid waste, and has a certain degree of environmental friendliness. The application of the present invention is conducive to promoting environmental improvement and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic cross-sectional view of a dam anti-frost heave protection structure; Figure 2A schematic plan view of a dam anti-frost heave protection structure; Figure 3 Schematic diagram of the cross section of an inclined drainage pipe; The meaning of the reference numerals in the figures: 1-Soil-PCM microcapsule geobag, 2-Ryegrass, 3-Water level during the high-water season in summer, 4-Water level during the low-water season in winter, 5-Geogrid, 6-Fine particles-Wicking geotextile geobag, 7-Soil layer, 8-Coarse particle layer, 9-Coarse particle recycled concrete aggregate layer, 10-Reservoir slope soil, 11-Upward inclined drainage pipe, 12-Reservoir, 13-Jack drill bit, 14-Drainage hole, 15-Drainage outlet, 16-Geotextile. DETAILED DESCRIPTION

[0018] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] The materials used in the present invention without indicating the manufacturer are all conventional products that can be purchased from the market.

[0020] A dam anti-frost heave protection structure is composed of a capillary barrier, an upward inclined drainage pipe 11 and other structures.

[0021] The capillary barrier includes a top layer, a middle layer, and a bottom layer. The top layer includes several soil-PCM microcapsule geotextile bags 1 and a soil layer 7. The soil-PCM microcapsule geotextile bags 1 are vertically staggered and substantially parallel to the slope of the reservoir slope soil 10. The soil layer 7 is adjacent to the upper geotextile bags of the soil-PCM microcapsule geotextile bags 1 and is substantially parallel to the top surface of the reservoir slope soil. The soil layer 7 is also adjacent to the upper fine particle-wicking geotextile bags 6. The middle layer is composed of several fine particle-wicking geotextile bags 6, which are vertically staggered and located inside the soil-PCM microcapsule geotextile bags and are closely adjacent to each other. The bottom layer includes a coarse-grained layer 8 and a coarse-grained recycled concrete aggregate layer 9. The bottom layer is adjacent to the middle layer and is located on the inner side of the middle layer. The coarse-grained layer 8 in the bottom layer is adjacent to the soil layer and is located below the soil layer. The coarse-grained layer 8 and the coarse-grained recycled concrete aggregate layer 9 in the bottom layer are in contact with each other, and the coarse-grained layer 8 is located above the coarse-grained recycled concrete aggregate layer 9. The coarse-grained recycled concrete aggregate layer 9 is in contact with the slope and top surface of the reservoir slope soil 10 and presents an approximately L-shaped shape.

[0022] Soil - The soil in the PCM microcapsule geobag 1 and the soil layer 7 are composed of loose loam with good drainage, suitable for cultivation and no lumps, and do not contain any grass or weed growth, other impurities or stones with a diameter of more than 25 mm; do not contain calcium carbonate, subsoil, garbage, roots, mud, plant toxic substances and other harmful substances; it should be fertile, loose soil, non-toxic and able to support the growth of healthy plants.

[0023] PCM was added to the top layer to improve the thermal insulation effect, and wicking geotextile was added to the middle layer to remove moisture from the soil. PCM was not added to soil layer 7 because the waterside slope of the reservoir is the main area affected by frost heave, and the moisture content at the top is low, so adding PCM was not considered.

[0024] Soil, fine particles, and coarse particles are collectively referred to as soil. According to the Gibbs-Thomson effect, when the pore water in the soil begins to freeze, a curved interface is formed between the capillary water and the ice. The surface tension generated by the ice-water interface makes the water pressure less than the ice pressure. The capillary water pressure decreases relative to the pure water pressure, so the chemical potential decreases, and the freezing temperature of the soil corresponding to the intersection with the chemical potential of ice decreases. The freezing temperature of the soil is also reflected in the water content in the soil. Water first fills small pores in the soil and then fills large pores. If the water content in the soil is small, the water is only filled in the smaller pores while the large pores have no water. The capillary action of the small pores is more significant, and the freezing temperature required for freezing is lower. Therefore, the less water in the soil, the lower the freezing temperature. The present invention increases the suction of the unsaturated soil of the slope through the capillary action of the capillary barrier, increases the seepage rate, and reduces the moisture content of the reservoir slope, so that the freezing temperature of the slope soil is reduced. At the same time, the vegetation on the capillary barrier system not only enhances the stability of the slope, but also has the functions of heat preservation, beautification of the environment, and water and soil maintenance.

[0025] For details on the frost heave protection structure of the embankment, see Figure 1 、 Figure 2 , see the upward inclined drainage pipe Figure 3 . The dam anti-frost heave protection structure and construction method of the present invention have the advantages of effectively preventing frost heave from damaging the dam slope, simple construction process, and enhanced environmental ecological resilience. The structure can show excellent performance under the conditions of ice and freeze-thaw cycles on the slopes of the reservoir in winter, and effectively resist the damage to the slopes caused by ice thrust and ice expansion. The capillary barrier is set on the surface of the slope. The structure itself can enhance the stability of the slope, and the capillary barrier uses the principle of unsaturated soil and the Gibbs-Thompson effect to enhance the seepage of the slope and increase the suction of the soil by capillary action; the upward-inclined drainage pipe can effectively discharge the water that infiltrates the slope from the reservoir, reduce the moisture content of the slope, and effectively reduce the freezing temperature of the soil in winter, so that the soil on the slope of the reservoir is not easy to freeze and cause damage. By planting greenery on the upper part of the capillary barrier, it can not only beautify the environment, but also reduce runoff erosion in summer, reduce soil erosion on the slope, and enhance environmental resilience.

[0026] A capillary barrier is installed on the reservoir slope surface. The top layer, a soil-PCM microcapsule geobag, consists of soil and microcapsules containing a low-temperature phase change material (PCM). The PCM microcapsules (referred to as PCM microcapsules) are uniformly mixed with the soil. PCM is liquid at room temperature and solid at low temperatures. Mixing the PCM microcapsules with the soil effectively improves the material's durability, prevents leakage caused by microcracks, and extends the PCM's lifespan, making it suitable for slope environments with severe freeze-thaw cycles. To effectively control and delay temperature in dam frost heave structures, the PCM material undergoes a phase change at approximately -3°C to -8°C, a temperature range typically suitable for frost protection in engineering structures such as reservoirs. PCM has a high latent heat (typically 100–200 J / g or even higher), providing a sufficient buffering effect, absorbing or releasing sufficient heat during the phase change process to smooth temperature fluctuations. The soil and PCM microcapsules are thoroughly mixed and placed in the geobag. The system incorporates two types of PCM microcapsules to achieve phased temperature control. The first PCM has a phase transition temperature of -3°C, designed for rapid initial freezing, while the second PCM has a phase transition temperature of -8°C, designed for extreme cold weather. This allows for phased freezing delays, enhancing the multi-stage buffering effect during the freezing process. The middle layer of fine-grained wicking geotextile geobags consists of fine particles and wicking geotextile. Compared to conventional capillary barrier systems, the addition of wicking geotextile to the fine-grained layer enhances soil suction, draining rainwater and freeze-thaw water infiltrating from the slope surface, thereby reducing freezing temperatures. The bottom layer, composed of recycled concrete aggregate (RCA) and equivalent coarse particles, acts as a barrier. The particle sizes of the coarse and fine particles are primarily determined by the regional climate and the unsaturated hydraulic properties of different particle size combinations. The top layer of soil-PCM microcapsules and the middle layer of fine-grained wicking geotextile are both filled into the geobags. Appropriate geogrids are used, securely fastened to each geobag. Compact the geobags to ensure they are strong enough to provide the required stability during and after construction.

[0027] The upward inclined drainage pipe 11 is inserted into the slope to discharge water that has seeped into the slope from the reservoir. Optionally, intelligent control is used to control the drainage of the upward inclined drainage pipe. The controller is electrically connected to the temperature sensor, soil moisture sensor and inclined drainage pipe regulating valve respectively. A temperature sensor and a soil moisture sensor are set in the slope soil next to each inclined drainage pipe, and an inclined drainage pipe regulating valve is set on each inclined drainage pipe. The controller can be set inside or outside the slope. If the temperature sensor detects that the temperature in a certain area is lower than -3°C, or the soil moisture sensor detects that the soil moisture is higher than the preset threshold, the controller will increase the drainage speed of the area after receiving the temperature and humidity information (that is, the corresponding inclined drainage pipe regulating valve increases the drainage volume, and the drainage volume value after the increase can be preset) to accelerate the drainage of water; if the temperature sensor detects that the temperature in a certain area is not lower than -3°C, and the soil moisture sensor detects that the soil moisture is not higher than the preset threshold, the controller adjusts the corresponding inclined drainage pipe regulating valve (that is, reduces the regulating valve to reduce the drainage volume and protect capillary suction, and the drainage volume value after the adjustment can be preset), thus forming an intelligent drainage-intelligent temperature control collaborative system, which is more dynamic and precise.

[0028] The construction process of the dam's anti-frost heave protection structure: During the construction of the dam's frost heave protection structure, rainwater should be prevented from intruding into the site. During the construction process, if it rains, temporary protective coverings should be prepared to reduce rainwater from penetrating into the slope.

[0029] Step 1: Site Measurement Before starting work, the density of the original slope soil should be measured on site, and the slope surface should be trimmed and re-leveled, including size, depth or slope, to facilitate the construction of the capillary barrier (GBS).

[0030] Specifically, before construction begins, the density of the original slope soil should be measured at three locations and compacted to ensure that the effective internal friction angle of the compacted slope soil reaches at least 34 degrees and the minimum dry density is 1.8Mg / m³. The soil at the foot of the slope should be compacted to a minimum dry density of 18.5KN / m³. 3 , with a depth of at least 1 meter. Compaction should be carried out in units of 500mm depth, or in other appropriate depth units. Figure 1 As shown, the slope surface is trimmed and re-leveled, including size, depth or slope, to facilitate the construction of the capillary barrier (GBS). The lowermost layer of the capillary barrier is set at the water surface during the winter dry season.

[0031] Step 2: Mixing PCM microcapsules with soil, mixing fine particles with wicking geotextiles, and filling geotextile bags Use qualified geotextile bags, Polyfelt TS nonwoven geotextile TS80, or materials with equivalent field performance, and fill the geotextile bags with soil, PCM microcapsules, fine-grained materials, or wicking geotextiles for slope construction. After the filling process is completed, all geotextile bags should be closed and sewn (or other equivalent methods should be used) to prevent the material inside the geotextile bags from being washed away by rainwater.

[0032] Using a geotextile bag (i.e., a bag that meets the requirements), PCM microcapsules are uniformly mixed with soil in a specific ratio. The PCM microcapsule volume ratio is controlled between 5% and 15% (the ratio of the PCM microcapsules to the total volume of the PCM microcapsules and soil within the bag, preferably 10%) to ensure sufficient latent heat reserve during the phase change process. If the PCM microcapsule ratio is less than 5%, the release temperature is limited, and the PCM's anti-freezing function cannot be effectively exerted when the temperature drops. If the PCM microcapsule ratio exceeds 15%, the soil strength is reduced and it is uneconomical. Fine-grained materials and wicking geotextiles are used to fill the geotextile bag for slope construction.

[0033] The PCM includes a first PCM and a second PCM. In some embodiments, the first PCM and the second PCM can be set to a fixed ratio, such as a volume ratio of 1:1.

[0034] In other embodiments, the ratio of the two PCMs can be set as follows: if A2C2 + A1C1 is lower than the phase transition temperature of the second PCM -8°C, then the volume ratio of the first PCM to the second PCM is: (-3°C - (-8°C)): (-8°C - (A2C2 + A1C1)), where C1 is the average winter temperature of a certain place for several consecutive years, C2 is the lowest winter temperature of a certain place for several consecutive years, A1 is the weight of the average winter temperature of a certain place, A2 is the weight of the lowest winter temperature of a certain place, A1 + A2 = 1, A1 and A2 are respectively greater than 0. When setting the ratio of the two PCMs, the lowest winter temperature and the average winter temperature are comprehensively considered, and the lowest winter temperature is more important, so Setting A2>A1, since the number of days with the lowest winter temperature is limited and the present invention also adopts other anti-frost heave measures such as capillary barriers, wicking geotextiles, and inclined drains, there is no need to use the method of determining the ratio of the two PCMs based solely on the lowest temperature (when determining the ratio based solely on the lowest temperature, the relative amount of the second PCM added is high and the relative amount of the first PCM added is small, but in most cases the temperature is not low enough for the second PCM to be effective). The method of the present invention can better exert the staged delay freezing effect and increase the multi-stage buffering effect of the freezing process. If the winter A2C2+A1C1 in a certain location is higher than the phase transition temperature of the first PCM -3°C, there is no need to add PCM microcapsules. If the winter A2C2+A1C1 in a certain location is lower than -3°C and higher than -8°C, only the first PCM is added.

[0035] The present invention is mainly applicable to extremely cold weather, that is, mainly applicable to the situation where the phase transition temperature of A2C2+A1C1 is lower than the phase transition temperature of the second PCM by -8°C.

[0036] For example, the average winter temperature in a certain place is -7℃ for three consecutive years, the lowest winter temperature is -17℃ for three consecutive years, A1 is 0.3, A2 is 0.7, and the volume ratio of the first PCM to the second PCM is 5:6.

[0037] The proportion of wicking geotextile mixed with the fine particles (i.e., the volume ratio of wicking geotextile to fine particles / wicking geotextile) can be 0-20% (preferably 0-15%) to achieve water absorption and prevent swelling while preventing excessive wicking geotextile from significantly affecting the properties of fine particles. When C1 < 0°C, in some embodiments, the proportion of wicking geotextile mixed with the fine particles can be directly preset to 1-15%.

[0038] Further, when C1 ≥ 0°C, no wicking geotextile is added to the fine particles.

[0039] Furthermore, in other embodiments, when C1 < 0°C, the ratio of the wicking geotextile mixed in the fine particles (i.e., the volume ratio of the wicking geotextile to the volume of the fine particles-wicking geotextile) can also be determined by formula (1): (1) p————Volume ratio of wicking geotextile to fine particles-wicking geotextile, C1————The average winter temperature of a certain place for several consecutive years, C1<0℃, θ————The average volumetric moisture content of the soil on the reservoir slope. Usually, θ is between 0.1 and 0.4. A ———— Reservoir slope gradient, usually, A is 20-45°, Xt————microcapsule volume ratio, d————wicking geotextile proportion coefficient, which reflects the coefficient relationship between the wicking geotextile proportion and the overall proportion composed of the directly proportional winter average temperature, volume moisture content, slope and the inversely proportional microcapsule volume proportion.

[0040] Affected by the different wicking capacities of different wicking geotextiles, d may be different for different wicking geotextiles.

[0041] When the amount calculated by formula (1) is higher than the threshold of 20%, the proportion of the wicking geotextile mixed in the fine particles is determined to be 20%; otherwise, the proportion of the wicking geotextile mixed in the fine particles is determined to be the calculated amount. 20% is set with reference to the threshold value of the addition amount of wicking geotextile in the prior art.

[0042] For example, the average winter temperature in a certain place for three consecutive years is -7℃ (C1 is -7 in formula (1)), the slope is 25° (θ is 25 in formula (1)), the average volume moisture content is 0.4, and the total proportion of PCM microcapsules added is 10% (in formula (1) X t Take 10), d=0.5, and through formula (1) we can get: =3.5 (unit: %).

[0043] Step 3: Particle Compaction The fine-grained material is compacted, and the coarse-grained material (the coarse-grained layer 8 and the coarse-grained recycled concrete aggregate layer 9, collectively referred to as the coarse-grained layer) is compacted.

[0044] Compact the fine-grained material (which can be fine sand) to a relative density (Dr) between 70% and 90%, or to a minimum dry density (ρd) of 1.55 Mg / m³. Compact the coarse-grained layer to a relative density (Dr) between 70% and 90%, or to a minimum dry density (ρd) of 1.8 Mg / m³. Compact the coarse-grained recycled concrete aggregate layer to a relative density (Dr) between 70% and 90%, or to a minimum dry density (ρd) of 1.8 Mg / m³.

[0045] Step 4: Geobag laying, geogrid laying, geotextile laying Lay the coarse-grained recycled concrete aggregate layer, the coarse-grained layer, the soil layer, the fine-grained wicking geotextile geobags, and the soil-PCM microcapsule geobags. The geogrid must be securely fastened to each geobag. Use an appropriate geogrid, ensuring it is strong enough to provide the required stability during and after GBS construction.

[0046] The geotextile was placed between the coarse and fine particle layers (i.e., fine particles-wicking geotextile geobags), and between the soil-PCM microcapsule geobag layer and the grass planting medium, at the top of the slope.

[0047] Step 5: Sod Construction Turfgrass is planted at the top of the slope (specifically, a planting medium layer is placed above the soil-PCM microcapsule geobag layer and the soil layer, and the turfgrass is planted in this planting medium layer). The grass seed is ryegrass2. The planting medium layer should be at least 100 mm deep. The planting medium consists of three parts topsoil and one part soil amendment (e.g., straw biochar), with 1 kg of granular fertilizer added per cubic meter (with a mass ratio of N, P, and K of 15:15:6.4). The topsoil used should be free of garbage, roots, tree stumps, or other debris, and should be loose and well-aerated.

[0048] Step 6: Insert the inclined drainage pipe into the slope and install the temperature and humidity sensor and the regulating valve of the inclined drainage pipe.

[0049] The upward-sloping drainage pipe has a diameter of 10 cm, which is convenient for jacking into the slope soil and meeting drainage requirements. It is wrapped with geotextile 16 to prevent fine particles from entering the upward-sloping drainage pipe and causing blockage when jacking into the capillary barrier system and the slope. During construction, the upward-sloping drainage pipe should be set at a 10° angle to the water surface to facilitate water outflow. The upward-sloping drainage pipe should pass through the soil-PCM microcapsule geobag layer, the fine particle-wicking geotextile geobag layer, and the coarse-grained layer (here refers to the coarse-grained recycled concrete aggregate layer) and be pushed into the slope soil by a jacking drill bit 13 for a distance of 1.5m (1.5m refers to the extended length of the upward-sloping drainage pipe in the slope soil); the upward-sloping drainage pipe passes through the soil-PCM microcapsule geobag layer, the fine particle-wicking geotextile geobag layer, and the coarse-grained layer in the same way: by jacking in by a jacking drill bit 13. The upward inclined drainage pipes are set up in two layers. The first layer is set at 0.5m above the water level 4 in the winter dry season (the highest point of the drainage pipes on the first layer is 0.5m above the water level in the winter dry season), and the second layer is set at 0.5m above the water level 3 in the summer flood season (the highest point of the drainage pipes on the second layer is 0.5m above the water level in the summer flood season). The upper drainage pipes can be used in the flood season, and the lower drainage pipes are submerged in water. In this way, the system can reduce the moisture content of the slope in both winter and summer.

[0050] Drain holes 14 are evenly distributed on the surface of the upward-sloping drainage pipe 11. One end of the upward-sloping drainage pipe 11 is located in the slope soil, and the other end is located next to the turf, and a drain outlet 15 is provided at the other end.

[0051] The above steps 1 to 7 were used to construct the slope embankment anti-frost heave structure at this site, with a concentration of 3.5%. The volume ratio of PCM microcapsules was controlled at 10%, and the volume ratio of the first PCM to the second PCM was 5:6. After a winter with an average temperature of -7°C and a minimum temperature of -18°C, the slope remained stable and no cracks or collapse were observed.

[0052] In the description of the present invention, reference to terms such as "embodiment", "specific example" or "practical application" means that the specific features, structures, materials or characteristics described in combination with the embodiment are included in at least one embodiment or example of the present invention; the schematic expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation fall within the scope of protection of the present invention.

Claims

1. A dam anti-frost heave protection structure, characterized by: It includes a capillary barrier and an upward inclined drainage pipe. The capillary barrier includes a top layer, a middle layer and a bottom layer. The top layer includes several soil-PCM microcapsule geobags and a soil layer; the middle layer is composed of several fine particle-wicking geotextile geobags, which are located on the inner side of the soil-PCM microcapsule geobags and are adjacent to each other; the bottom layer includes a coarse particle layer and a coarse particle recycled concrete aggregate layer, and the bottom layer is adjacent to the middle layer and located on the inner side of the middle layer; the upward inclined drainage pipe is inserted into the slope soil.

2. The dam anti-frost heave protection structure according to claim 1, characterized in that: The proportion of PCM microcapsules mixed in the soil is 5%~15%; the PCM microcapsules include a first PCM with a phase transition temperature of -3°C and a second PCM with a phase transition temperature of -8°C. If A2C2+A1C1 is lower than the phase transition temperature of the second PCM -8°C, then the volume ratio of the first PCM to the second PCM is: (-3°C-(-8°C)):(-8°C-(A2C2+A1C1)), where C1 is the average winter temperature of a certain location for several consecutive years, C2 is the minimum winter temperature of a certain location for several consecutive years, A1 is the weight of the average winter temperature of a certain location, A2 is the weight of the minimum winter temperature of a certain location, A1+A2=1, A2>A1, and A1 and A2 are respectively>0.

3. The dam anti-frost heave protection structure according to claim 1, characterized in that: When C1<0℃, the volume ratio of wicking geotextile to fine particles-wicking geotextile is: (1) p————the proportion of wicking geotextile in the mixed soil, C1 ———— The average winter temperature of a certain place for several consecutive years, θ————Average volumetric moisture content in the reservoir slope soil, A———— Reservoir slope gradient, Xt————microcapsule volume ratio, d————Proportional coefficient of wicking geotextile.

4. The dam anti-frost heave protection structure according to claim 1, characterized in that: The coarse particle layer in the bottom layer is adjacent to the soil layer and is located below the soil layer; the coarse particle layer in the bottom layer abuts against the coarse particle recycled concrete aggregate layer and the coarse particle layer is located above the coarse particle recycled concrete aggregate layer; the coarse particle recycled concrete aggregate layer abuts against the slope and top surface of the reservoir slope soil and presents an approximately L-shaped shape.

5. The dam anti-frost heave protection structure according to claim 1, characterized in that: Several soil-PCM microcapsule geobags are vertically staggered and basically parallel to the slope of the reservoir slope soil; the soil layer is adjacent to the upper geobags of the several soil-PCM microcapsule geobags and basically parallel to the top surface of the reservoir slope soil.

6. The dam anti-frost heave protection structure according to claim 1, characterized in that: The inclined drainage pipe is set at an angle of 7~13° to the water surface; the inclined drainage pipe is inserted into the slope soil at a distance of 1.2~1.8m.

7. The dam anti-frost heave protection structure according to claim 1, characterized in that: The upward inclined drainage pipe is wrapped with geotextile; the upward inclined drainage pipe is set in two layers, the first layer of upward inclined drainage pipe is set 0.4~0.6m above the water surface during the winter dry season, and the second layer of upward inclined drainage pipe is set 0.4~0.6m above the water level during the summer flood season.

8. The construction method of a dam anti-frost heave protection structure according to any one of claims 1 to 7, characterized in that: The steps include: Site survey; mixing PCM microcapsules with soil, mixing fine particles with wicking geotextiles, filling geobags; particle compaction; laying geobags, geogrids, and geotextiles; laying geogrids; turf construction; and jacking up inclined drainage pipes into the slope.

9. The construction method according to claim 8, wherein: The proportion of PCM microcapsules mixed in the soil is 5%~15%; the PCM microcapsules include a first PCM with a phase transition temperature of -3°C and a second PCM with a phase transition temperature of -8°C. If A2C2+A1C1 is lower than the phase transition temperature of the second PCM -8°C, then the volume ratio of the first PCM to the second PCM is: (-3°C-(-8°C)):(-8°C-(A2C2+A1C1)), where C1 is the average winter temperature of a certain location for several consecutive years, C2 is the minimum winter temperature of a certain location for several consecutive years, A1 is the weight of the average winter temperature of a certain location, A2 is the weight of the minimum winter temperature of a certain location, A1+A2=1, A2>A1, and A1 and A2 are respectively>0.

10. The construction method according to claim 8, wherein: When C1<0℃, the volume ratio of wicking geotextile to fine particles-wicking geotextile is: (1) p————the volume ratio of wicking geotextile to fine particles-wicking geotextile, C1 ———— The average winter temperature of a certain place for several consecutive years, θ————Average volumetric moisture content in the reservoir slope soil, A———— Reservoir slope gradient, Xt————microcapsule volume ratio, d————Proportional coefficient of wicking geotextile.

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