One of the main factors for the destruction of slope protection in cold regions is frost damage. In the coldest Heilongjiang Province, the freezing period in winter is as long as six months. The average temperature in many years is generally between -54°C and the minimum temperature is up to -52.3°C. The freezing thickness of the reservoir is 1.0~1.5m, and the maximum frozen thickness Up to 3.05m. The depth of frozen soil is generally 1.53.0m, and the maximum frozen soil depth is 4.0m. After the water freezes into ice, it will cause the soil body to produce frost heave, which will arch the slope, causing the slope to be uneven, and the temperature will warm up easily. Damaged under waves and scouring. Second, the ice layer freezes with the slope protection. When the temperature rises, ice bending moments will be generated, and the slope protection will be displaced to make the slope damaged. According to statistics, of the 630 reservoirs built in Heilongjiang Province, more than half are plain reservoirs, and these reservoirs have serious frost heave damage. Over the years, a lot of research has been conducted on the anti-freezing technology of slope protection engineering in cold regions and some experience has been gained. For example, non-frosting material is used in the dam shell in the deep-freezing range to increase the thickness and insulation of slope protection. However, the vast majority of plain reservoirs are located in the absence of non-frost bulge dams such as pebbles, gravel, sand, and blocks. Therefore, it is difficult for the plain reservoir slopes to be completely constructed with non-frost-swelling materials in the deep-freezing range. In particular, the plain reservoir has complex terrain, high and low dam heights, long axis of the dam, large quantities of works, and a large amount of construction materials required. The method of increasing the thickness of the slope protection will insulate the heat, and will inevitably increase capital investment. Using polystyrene insulation technology can block the negative temperature of the soil on the base of the invasion, increase the temperature of the soil base, thereby reducing the frost depth or eliminate frost heave, so as to achieve the purpose of anti-frost heave and reduce the project cost. Based on the analysis of experimental data, this paper analyzes the anti-frost heave characteristics of polystyrene insulation board, and has significance for further research on related issues and anti-freezing design for slope protection.
2 Characteristics of Polystyrene Thermal Insulation Boards 2.1 Physical Characteristics Polystyrene (EPS) insulation boards are plate-shaped materials that are formed by the compression of Styrofoam particles. The dimensions are usually 2000 mm. It is a kind of light and compressible. Strong, water-repellent and heat-insulating plastic materials. Its physical properties include heavyness, water absorption (weight water absorption, volumetric water absorption), thermal conductivity, and specific heat.
The dry weight of EPS is determined by the multiple of the expansion of the EPS particles in the forming stage. The dry weight commonly used in the project is between 200500N/m3. The physical properties of the EPS insulation board are shown in Table 1. Table 1 shows that the EPS is A material with a lighter weight, lower water absorption, and lower thermal conductivity, but the water absorption rate affects the thermal conductivity of the EPS. The thermal conductivity of two dry specimens with a density of 300 N/m3 was measured to be 0.140, 0.144 kJ/(mh°C), and the thermal conductivity was 0.1480.194 kJ/(mh'C) for different water absorption rates. 0.1510.202 kJ/(mh'C). The thermal conductivity increases by 1.051.4 times. It is the relationship between the thermal conductivity and the water absorption rate that the EPS is placed in water for 96 hours. The increase in water absorption causes a corresponding decrease in the insulation effect, so the effect of water absorption on the insulation performance should be considered.
2.2 Mechanical properties EPS insulation board mechanical properties include deformation characteristics and strength characteristics. A 75 mm cylindrical specimen with a different diameter was used for the unconfined uniaxial compression test in the room. The mechanical properties of EPS were obtained at a strain rate of 5 mm/min, see Table 1, Table 2 . According to the test results, EPS is a kind of plastic material with high compressive strength. When the strain is less than 2%, the EPS of different severity shows good elastic properties, and then the yield phenomenon occurs. EPS's yield does not occur at a certain point but within a certain range. The post-yield EPS shows yield hardening and is initially linear. When the strain continues to grow, EPS is non-linear plastic project name dry weight /Nm'3 saturated weight /Nm'3 weight water absorption /% volume water absorption /% deformation modulus five / kPa compressive strength /kPa immersion 7 days Vacuum saturated average table 2 EPS insulation board compression strength Table Table deformation / deformation, the cavity structure of the EPS has been destroyed.
If the concrete cover is used on the EPS and the thickness is calculated as 24kN/m3, the thickness that can be covered on the EPS insulation board can reach 12m. Considering that the deformation is controlled within the elastic range, the cover layer 2.3 freeze-thaw cycle characteristics through the freezing of the EPS The melt test found no significant change in the linear thermal expansion coefficient, but the water content increased with the number of freeze-thaw cycles, see. It shows that the number of freeze-thaw cycles has an effect on the thermal conductivity of EPS. It can be seen that the design parameters of EPS meet the anti-frost-resistance requirements of slope protection.
3 Antifreeze design When the temperature drops below 0C, the water freezes to ice. Different ice thicknesses have different forces on slope protection. Usually, the ice thickness is 1.2m for analysis. Slope protection structure For example, a layer of 0.3mm thick polyethylene membrane is placed on the EPS insulation board to prevent water seepage. A 2cm thick cushion is used on the slope, and a concrete cover is used on the slope surface.
3.1 Force Analysis The force on the insulation board comes from two aspects: one is static ice pressure corpse, the other is lining layer of gravity ash. As shown. The static ice pressure can be decomposed into the upward force component Ph along the slope and the component force V of the vertical slope; the corpse H is the thrust that causes the upward movement of the concrete slab, and the corpse V IJ is the pressure exerted on the polystyrene insulation board. . The gravity W of the lining concrete slab is also divided into the component force Pf down the slope and the component force Pw of the vertical slope surface. 3.1.1 The static ice pressure The static ice pressure formula The horizontal direction ice pressure is the vertical slope ice pressure ( The pressure applied by the insulation board is PV 3; mt is the time coefficient, and the general weather is taken as 1.0, and the temperature in the 2d temperature is taken as 1.82. The static ice pressure is checked according to the method for determining the static ice pressure of the hydraulic building anti-freezing design code.
For a large plain reservoir at =1.2m, the total pressure of static ice 3.1.3 EPS can be calculated. According to the calculation results, we can see that EPS with a weight of 300N/m3 or more can withstand the damage from ice pressure and lining layer pressure.
3.2 The thickness of the insulation board EPS insulation board has good heat insulation, but the water absorption rate has a significant effect on its thermal conductivity. With the increase of water absorption, the thermal conductivity also increases. Tests show that when the volumetric water absorption rate of EPS insulation board is equal to 2%, the thermal conductivity can be increased by 12.5%; when the volumetric water absorption rate reaches the maximum 4%, the thermal conductivity can be increased by 40%. Therefore, if EPS insulation board is pressed It is not safe to determine the thickness of the insulation board in the dry state thermal conductivity.
3.2.1 Design thickness of insulation board in dry state The thickness of EPS insulation board is usually determined by relative comparison method.
Through the observation data of typical test engineering, the critical thermal resistance value (typical thermal resistance) of the thermal insulation base under the board just below the board is obtained, which is used as the design thermal resistance of the thermal insulation board of the same type engineering, and then based on the thermal resistance value and the freezing index. Relationships, calculation of thermal insulation resistance of the proposed project. Typical site thermal insulation base design thermal resistance is determined by factors such as quality, generally take 1.11.2; KW is the thermal resistance correction factor, when /. = 1002 is the typical thermal resistance (m2k/W); / is the frozen site of the proposed project Index (°Cd);/. is the freezing index (°Cd) of the typical engineering site (information of the Wanjiazhai Permafrost Experimental Station of the Heilongjiang Institute of Hydraulic Research); basic foundation of the fully-insulated foundation (just below the foundation plate without freezing layer) The thermal resistance is R=2.6m2k/W, and the corresponding measured freezing index/.=1870°Cd. The thermal resistance value of the proposed thermal insulation foundation is substituted into (3). The design thickness of the thermal insulation plate in the dry state can be calculated by the following formula. : D Frost Resistance Design Code (SL23-91) selects 0.651.5; D0 is the product of the thermal conductivity coefficient of the insulation board in the dry state and the thermal resistance value of the thermal insulation foundation of the proposed project (see Table 3); Table 4 The revised thickness of the insulation board Calculation table (unit: cm) Table4 Heat conductivity after water absorption j Freezing exponent/0/(Cd if the known dry state EPS thermal conductivity j; Sunshine shading correction coefficient is sufficient (1=1; D0=10.8cm; cover for Concrete, lining thickness 5 = 12cm; concrete sheath thermal conductivity j = °C); then dry state protection The design thickness of the warm plate can be obtained from Formula (7): D=10.5cm. When the EPS has a certain water absorption rate, the thermal conductivity increases from j to 0.14kJ/(mC) to j'=0.162kJ/(mhC). When looking at Table 4, we can see that the thickness of the insulation board Df has to be selected in the design of the EPS insulation board under wet conditions D 4 Conclusion EPS insulation board light weight, high strength, low water absorption, good insulation, can effectively protect the dam The soil temperature field is stable and it is a good material for freezing and heat insulation slope protection.
The EPS insulation board has sufficient carrying capacity. Different insulation boards of different severity are to be selected according to different design loads. For the protection surface that does not allow deformation, the strength index of the EPS elastic phase should be selected.
EPS insulation board can not only insulate, but also can be cold, while at the same time have a certain water-proof seepage prevention ability. Its anti-seepage performance will affect the thermal insulation board insulation and anti-freezing ability. Therefore, the effect of water absorption on the insulation performance must be considered in the design choice.
Design thermal conductivity to consider the hydrogeology situation according to the most unfavorable situation design.
It is calculated that the thickness of antifreeze used in gravel cushions is 45105cm, while the use of EPS insulation board can reduce the investment by 12%. This paper is valuable for the design of EPS insulation board in slope protection works in cold regions. Due to the limited experimental conditions, a large number of relevant tests have not been conducted. To further study the antifreeze effect of EPS, the experimental data must be supplemented, analyzed, and improved.
Under the reliability of page 406, it is recommended that you try it out in this kind of landslide prediction. Of course, it is limited to the constraints of level, understanding, research area, and research sample size. The mathematical model given is inevitably flawed and inadequate. The considerations of landslide elements may not be comprehensive, and regional features must exist. Hopefully, they can be obtained through trials by everyone. Constantly revised and improved, but also hope to get the criticism and advice of industry peers and experts.
Thermolaminated Door,Thermolaminated Panels,Thermolaminated Doors Panels,Thermolaminated Accessories
PRO CABINET SOLUTION PTY LTD , https://www.pcscabinet.com.au