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Research Prerequisites:
Based on the existing billing standard for construction increase fees in alpine and high-altitude areas of highway projects, this paper combines the complex geological conditions and special geographical climate in Xinjiang's alpine and high-altitude areas.
By measuring the constant cost of vibrating roller and tire roller machinery during the construction of the project under construction, the influence of the cold and high altitude environment on the depreciation, maintenance and maintenance costs of the construction machinery is systematically analyzed.
Study the magnitude of the increase in the constant cost of highway construction machinery in the cold and high altitude areas of Xinjiang.
introduction
The construction of high-cold and high-altitude highways above 3000m above sea level faces challenges such as low pressure, lack of oxygen, cold, dryness, and changeable climate.
In the complex and harsh engineering construction, due to the reduction of atmospheric oxygen content, insufficient fuel combustion, and reduced heat dissipation performance, the efficiency of mechanical operation is reduced and fuel consumption is increased.
Analysis of the influence of high cold and high altitude environment on construction machinery
2.1 Impact on diesel engines
2.1.1 Effect on dynamic performance
Increasing altitude leads to a decrease in atmospheric pressure, a decrease in air density, and a decrease in the amount of oxygen in the air. A large number of measured data show that for naturally aspirated internal combustion engines, the dynamic performance changes for every 1000m increase in altitude are shown in Table 1.
2.1.2 Impact on startup performance
Temperature has a great influence on engine starting characteristics.
The plateau low pressure and lack of oxygen, cold climate, and large daytime temperature difference cause the air pressure and temperature in the cylinder to decrease with the increase of altitude.
The starting capacity of the engine changes with sea level rise, and for every 1000m increase in altitude, the effect of this change on the gas distribution system is shown in Table 2.
High altitude areas usually have large wind and sand, and the dust content in the air can reach more than ten times that of low altitude areas, resulting in reduced air filter filtration effect, reduced service life, and increased air intake resistance in the gas distribution system.
The low oxygen content in the air at high altitudes reduces the amount of air entering the cylinder, resulting in a reduced combustion effect in the engine, which affects the engine power.
And due to the high dust content in the air, a large number of dust particles entering the cylinder will accelerate the piston wear.
Impact on the cooling system
Due to the thin air in cold and high altitude, low pressure and lack of oxygen, the amount of air entering the engine cylinder is reduced, the combustion performance deteriorates, and the serious combustion lag leads to an increase in the heat load of the engine;
At the same time, the mass flow rate of the cooling fan is reduced, and the boiling point of the cooling water is reduced.
These factors can lead to a deterioration in the heat dissipation performance of the engine and a further increase in the heat load.
3.1 Effects on the lubrication system
The engine lubrication system not only lubricates the friction surfaces, but also cools and cleanses.
Due to the cold climate, large temperature difference between day and night in high-altitude areas, and the annual average temperature is below 0 °C, higher requirements are put forward for the use of lubricating oil.
The viscosity and temperature performance of ordinary lubricants are greatly affected by climate.
If the temperature is too low, the viscosity of the lubricating oil increases, the fluidity becomes poor, and the movement resistance of the mechanical friction surface will increase. This not only affects the starting performance, but also increases the engine power consumption.
3.2 Impact on the drivetrain
The power transmission of construction machinery includes mechanical and hydraulic two ways.
Under cold and high altitude conditions, the cooperation between the transmission system and the power equipment becomes poor, so that it cannot maximize the maximum power and the transmission efficiency is reduced;
Due to internal losses, converting part of the electricity into heat energy will cause the operating temperature of the unit to exceed the specified range, which will adversely affect the mechanical work.
3.3 Effects on hydraulic systems
Oil pressure control cannot be separated from the hose and seal.
In cold and high altitude areas, the sunshine time is long, the ultraviolet radiation is strong, the temperature is low throughout the year, and the daytime temperature varies greatly.
Rubber pipe fittings, rubber seals, etc. are damaged by various environmental factors, cracking, damage and aging are accelerated, compressibility and sealing are reduced, and equipment work efficiency is reduced.
Impact on the braking system
The power unit of the construction machinery brake system includes hydraulic type, pneumatic type and pneumatic hydraulic type, etc., and its power transmission medium is compressed gas or brake fluid.
The cold and high altitude climate is cold, the temperature difference between day and night is large, and the brake fluid will freeze and reduce fluidity in some cases, which seriously affects the braking characteristics of the brake fluid and threatens the safety of vehicle operation and operation.
4.1 Effects on electrical machinery
The low concentration of low-pressure air will lead to the weakening of air dielectric strength, air cooling effect and arc gap air dielectric strength, as well as a decrease in the air isolation voltage of electrical appliances;
The temperature of the parts of electronic devices cooled by air conditioning and arcing in the atmosphere are currently more difficult problems.
The temperature fluctuates greatly during the day, making it difficult to maintain the sealing of the product, resulting in deformation or fracture of mechanical components. Low temperature will cause the electrical appliance to produce gas dry arc due to too low air pressure, and the discharge voltage will drop.
When the atmosphere contains oxygen and water, strong solar irradiation will cause outdoor electrical appliances to heat up, accelerate the aging of organic insulation and paint, and reduce the service life of electrical appliances.
Effects on fluid machinery
5.1 Impact on air compressors
At high altitudes, thin air causes the air compressor to be subjected to constant pressure each time it reciprocates.
When the air pressure decreases, the pressure-to-strength ratio of the compressor increases, resulting in insufficient air supply and a decrease in the volume factor; High temperature will reduce the working performance of the air compressor.
5.2 Effects on ventilators
At high altitudes, the air pressure is low, and under the same flow conditions, the static pressure of the fan decreases year by year, resulting in a decrease in the efficiency of the fan.
5.3 Cost Estimation
Based on the collection, collation and analysis of the cost standards related to the efficiency reduction of high-cold and high-altitude construction machinery in other provinces and cities, this paper selects the research and analysis of highway construction projects under construction in Xinjiang with reference value.
And investigate relevant construction units, combined with on-site construction technology observation, in-depth investigation of the use of cold and high-altitude highway machinery under construction in Xinjiang.
The typical alpine and high-altitude highway in Xinjiang is a project located in the hinterland of the Kunlun Mountains.
The project starts at the intersection of National Highway 315 and National Highway 219 in Yecheng County and ends at the New Tibet border, crossing five mountains of more than 5,000 meters, 16 icebergs reaching bans, and 44 glaciers along the way.
Among them, the first project under construction has an altitude of 2665m~3426m, the second project has an altitude of 4500m~5000m, and the third project has an altitude of 4500m~5000m.
Vibratory rollers and tire rollers are the most commonly used construction machines in subgrade engineering and pavement engineering, so these two types of machinery are studied as typical construction machinery.
Combined with the data collected from the construction site such as the service life of machinery in the plateau area, maintenance costs, maintenance times, maintenance costs, etc., depreciation costs, maintenance costs, and maintenance costs are obtained, as shown in Table 3.
Through the comparison of the above table, it can be seen that the ratio of the constant cost of typical construction machinery to the fixed cost of fixed construction machinery in alpine and high-altitude areas is 1.096, so the comprehensive adjustment coefficient of unchanged cost of construction machinery in alpine and high-altitude areas is recommended to be 1.1.
The maintenance machinery used in pavement, overhaul and maintenance machinery, and overhaul maintenance operations is almost the same, so the two are classified as one category for discussion.
5.4 Asphalt pavement recycling equipment
Asphalt pavement recycling equipment is a mechanical equipment that reprocesses old asphalt pavement materials and restores them to their original form.
It is suitable for the repair of asphalt pavement that produces cracks, ruts, various deformations, aging and wear, and is a special mechanical equipment for highway maintenance.
classify
(1) According to the different regeneration sites, it can be divided into factory mix recycling and in-situ regeneration;
(2) According to different heating methods, it is divided into hot mix regeneration and cold mix regeneration.
Construction method of in-situ thermal recycling of asphalt pavement
There are two main construction methods of in-situ thermal regeneration: remix recycling and resurfacing recycling.
The remix and recycling method is mainly used in the road section where the quality of the old mixture needs to be improved, including heating, loosening, mixing and paving the new and old mixture, rolling and other processes;
The resurfacing recycling method is mainly used on road sections that do not require improvement of the quality of the old mixture, including heating, loosening, paving, and re-laying a new layer of asphalt mixture on its pavement, and finally rolling and forming.
In-situ cold recycling construction method for asphalt pavement
Due to the different recycled materials used, the cold recycling construction methods will also be different, and here we mainly introduce several construction methods commonly used in asphalt pavement maintenance operations.
Construction method using cement for cold in-situ recycling
a. Spreading cement, in order to spread evenly, the cement should be spread by a special spreader. The amount of cement spread should be determined according to the material test.
Experience shows that the spreading amount is about 3.5%~4.5% of the weight of the aggregate.
b. Milling and mixing, through the in-place cold recycler milling and mixing, the waste asphalt pavement material will be evenly mixed with cement and water, and then flow out through the gap of the crushing shovel on the recycler.
c. Paving of milling materials, whether to use a grader or a recycler for the whole plate paving mixture should be based on the slope of the road surface
Decide. If the slope is large, use a motor grader.
In other cases, the entire slab of the recycler can pave the required pavement. Finally, the crushing should be appropriate
Heavyweight tyre or drum rollers.
In-situ cold recycling using bitumen emulsion
Using emulsified bitumen for cold in-place recycling, be sure to check the stability of the materials on site. The following material properties should be tested in the laboratory:
a. Grading;
b. Properties of the binder;
c. Matching of emulsified bitumen;
d. Maximum compactness (modified Duriez test;
e. Mechanical properties of the mixture.
Because the emulsified asphalt is more convenient to mix, the temperature of the donor is not high, and it can be mixed at room temperature, so in the area where the asphalt mixing plant is lacking or too far from the mixing plant, the construction method of using emulsified asphalt recycling pavement has great advantages.
In-situ cold recycling using cement and bitumen emulsion
This method is based on the second method above, using cement instead of part of the emulsified bitumen as a recycler.
On the one hand, the use of cement plus emulsified asphalt can reduce the amount of emulsified asphalt, and when the current price of emulsified asphalt is higher than that of cement, it can save engineering investment;
On the other hand, the addition of emulsified bitumen can reduce the rigidity of the cement stabilizer layer and thus reduce reflective cracks.
Thin propeller sealing machinery
Emulsified asphalt slurry sealing layer is made of four materials such as appropriate graded aggregate, filler, asphalt emulsion and water, mixed and mixed in a certain proportion, mixed into a uniform slurry mixture, and spread on the road surface according to the required thickness to form a dense, strong and wear-resistant surface treatment thin layer.
Emulsified asphalt slurry sealing machine is a special equipment to complete the construction of slurry sealing.
Asphalt slurry sealing machine can be divided into trailer slurry sealing machine, semi-hanging slurry sealing machine and self-propelled slurry sealing machine according to mobility;
According to the operation mode, it can be divided into two types of slurry sealing machine with front hopper and without front hopper; According to the mixing method of the slurry sealing machine, it can be divided into single-shaft spiral agitator and twin-shaft paddle agitator slurry sealing machine.
epilogue
This paper systematically analyzes the influence of alpine and high altitude environment on construction machinery.
Through the actual measurement of the constant cost of vibrating roller and tire roller machinery during the construction of the project under construction, the added value of the constant cost of construction machinery in the cold and high altitude areas of Xinjiang Highway is obtained.
In order to comprehensively study the increase cost of highway construction in Xinjiang's alpine and high-altitude areas, it provides research methods and ideas, which can provide reference for Xinjiang to formulate construction cost standards in high-cold and high-altitude areas in the future.
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