1. Introduction
In today's construction of cast-in-place piles, there are mud retaining pile bored piles, rotary bored cast-in-place piles, punched cast-in-place piles, long spiral bored piles, dry work piles and sinking piles. In the drilling process of bored piles, mud wall protection technology is usually adopted, but the treatment of waste mud has always been a problem that plagues engineering construction. The waste mud contains a large amount of cohesive soil, sand, gravel soil, weathered rock, minerals and cuttings, etc. It has a large consistency and cannot be directly discharged, and it is difficult to settle naturally. The use area of the construction site itself is limited. If it is not treated in time, it will not only affect the construction, but also cause environmental pollution or water pollution. The existing treatment method is to transport the tank to the suburban garbage dump for natural drying or shipping to the sea. The former treatment method was originally backward, which caused many problems: First, the cost was high and the efficiency was low. When the construction was tight, the day and night transportation of the tank truck could not meet the construction progress requirements; the second was that the construction site was in a bad environment and the muddy water overflowed, which made it difficult. Insertion; the latter is constrained by geographical conditions, etc., which greatly increases transportation costs. The engineering team often suffers huge fines due to the blockage of mud water leaking into the sewer. In addition, tank trucks often pollute the city's environment due to muddy water spilling over the urban trunk roads.
In this test, a horizontal spiral discharge sedimentation centrifuge (hereinafter referred to as a horizontal spiral centrifuge) was used to conduct laboratory theoretical research and on-site dehydration experiments on the drilling mud. The mud after dewatering separation increased the dryness of the sediment and reduced the volume. It can be used as a green backfill for loading or transporting bricks. Therefore, the transportation and discharge cost of the mud will be greatly saved; and the solid content of the liquid separated by the horizontal spiral centrifuge can be reduced, and can be returned to the mud tank to adjust the mud concentration at any time, which is beneficial to improve the drilling speed and the quality of the hole.
1. Working principle and structure of sludge centrifugal dewatering machine
The sludge centrifugal dewatering machine is a new and energy-efficient solid-liquid separation mechanical device.
The machine consists of a rotating drum, a screw ejector, a differential and power, and a main part of the frame.
The drum and the screw ejector rotate in the same direction, and the speed difference between the drum and the screw ejector is 10-35 rpm under the action of the differential. The drilling mud enters the rotating drum of high speed through the feeding port. Under the action of centrifugal force, the suspended particles such as particles and dense sediment (lithic cuttings) in the mud rapidly accumulate to the wall of the cylinder, and the density in the mud is relatively small. The liquid (water) is discharged from the outlet hole of the inner ring of the water layer through the liquid outlet. The sediment is pushed by the auger to the conical end of the drum and discharged through the slag outlet.
The sludge centrifugal dewatering machine is compared with other forms of solid-liquid separation mechanical equipment: a. It has compact structure, small volume, light weight and relatively convenient movement under the same processing capacity; b, large processing capacity and good separation performance Wide application range; c, high solid recovery rate, low operating cost, no filter cloth; d, automatic continuous operation, simple operation, easy to use, convenient installation and maintenance. It has been widely used in many industrial and mining fields such as geology, minerals, petroleum, chemical, metallurgy, pharmaceutical and environmental protection.
2 , test mud
The test mud was taken from a mud pool at a foundation construction site. The characteristics of the test mud are: water content of 85%, solid phase true density of 2226 kg / L, solid content of about 28.7%, and wet mud cake density of 1084 kg / L.
3 , test system
The test system is mainly composed of vibrating screen, cyclone, concentration tank, mud pump, electromagnetic flowmeter and LWnj -6500-B horizontal screw centrifuge.
During the test, the bored mud of the cast-in-place pile to be dewatered is placed in the first-stage transitional sedimentation tank, and transported to the vibrating screen and cyclone through the mud pump to screen the coarse granular particles such as coarse hard rock particles and sandstone. The medium with a specific gravity less than 50 and a light specific gravity flows into the concentration tank, and is pumped by the self-priming mud to the electromagnetic flowmeter for measurement, and then enters the centrifuge for centrifugal sedimentation and dehydration test.
4 , the main technical parameters of the test centrifuge
Model LWJ- 550× 2200 , drum diameter 550mm, drum length 2200 mm, working speed 2700 r/min (stepless adjustable), separation factor 2228 (max), differential speed 0～35 r/ min adjustable The main motor power is 45kW, the auxiliary machine motor power is 15KW, and the external dimensions are 3600 mm × 1650 mm × 1050 mm.
5 , test results
In the test, the dewatering effect of the centrifuge on the drilling mud was investigated by adjusting the separation factor of the centrifuge while maintaining the treatment volume of 50 m3 / h (the feed solid content control was controlled at 11.7%). 8T / h out of the mud (water content 37%), the effluent solid content rate of 5% or less.
6 , economic evaluation
The economic benefit of using the sludge centrifugal dewatering machine for dewatering of drilling mud is very significant. According to a site survey in a construction site in Jiangsu, the mud produced by drilling a cast-in-place pile is about 120 m3, and the current mud-laying fee is as high as 85 yuan. / m3 , that is, the mud transportation fee required for a cast-in-place pile is 10,200 yuan; and if the centrifuge dewatering process is adopted, the electricity cost, machine depreciation expense, labor management fee, sediment loading and transportation cost, and centrifuge installation are comprehensively considered. The fee for a pile of mud treatment is only about 4,300 yuan, which is 58% less than the original process.
7 , conclusion
Through the site site conditions of the bored pile drilling mud dewatering treatment test, the following conclusions can be drawn:
(1) Sludge centrifugal dewatering machine can be used for dewatering of bored piles to obtain better dewatering effect. After dewatering, the solid content of sediment can reach 75%~81%, and the moisture content of sediment after dewatering reaches below 40%. The volume is greatly reduced, and can be stacked and formed, and can be stacked separately for further natural drying or direct loading and transportation.
(2) The clear liquid separated by the centrifuge can be used to adjust the mud concentration, which is beneficial to improve the drilling progress and the quality of the hole formation, and also save water, which is especially important for the drilling of water-deficient areas.
(3) The economic benefit of using the sludge centrifugal dewatering machine for the dewatering treatment of the bored pile drilling mud is very significant, and has a good engineering application prospect.
(4) The centrifuge dewatering process can effectively improve the working environment of the drilling site, reduce transportation vehicles and environmental pollution, and has obvious social benefits.
(5) Limited to the test conditions, no more in-depth comparison tests were conducted. If the test results are to be applied to engineering practice, further changes in the structure and technical parameters of the machine are required.
1. Introduction
In today's construction of cast-in-place piles, there are mud retaining pile bored piles, rotary bored cast-in-place piles, punched cast-in-place piles, long spiral bored piles, dry work piles and sinking piles. In the drilling process of bored piles, mud wall protection technology is usually adopted, but the treatment of waste mud has always been a problem that plagues engineering construction. The waste mud contains a large amount of cohesive soil, sand, gravel soil, weathered rock, minerals and cuttings, etc. It has a large consistency and cannot be directly discharged, and it is difficult to settle naturally. The use area of the construction site itself is limited. If it is not treated in time, it will not only affect the construction, but also cause environmental pollution or water pollution. The existing treatment method is to transport the tank to the suburban garbage dump for natural drying or shipping to the sea. The former treatment method was originally backward, which caused many problems: First, the cost was high and the efficiency was low. When the construction was tight, the day and night transportation of the tank truck could not meet the construction progress requirements; the second was that the construction site was in a bad environment and the muddy water overflowed, which made it difficult. Insertion; the latter is constrained by geographical conditions, etc., which greatly increases transportation costs. The engineering team often suffers huge fines due to the blockage of mud water leaking into the sewer. In addition, tank trucks often pollute the city's environment due to muddy water spilling over the urban trunk roads.
In this test, a horizontal spiral discharge sedimentation centrifuge (hereinafter referred to as a horizontal spiral centrifuge) was used to conduct laboratory theoretical research and on-site dehydration experiments on the drilling mud. The mud after dewatering separation increased the dryness of the sediment and reduced the volume. It can be used as a green backfill for loading or transporting bricks. Therefore, the transportation and discharge cost of the mud will be greatly saved; and the solid content of the liquid separated by the horizontal spiral centrifuge can be reduced, and can be returned to the mud tank to adjust the mud concentration at any time, which is beneficial to improve the drilling speed and the quality of the hole.
1. Working principle and structure of sludge centrifugal dewatering machine
The sludge centrifugal dewatering machine is a new and energy-efficient solid-liquid separation mechanical device.
The machine consists of a rotating drum, a screw ejector, a differential and power, and a main part of the frame.
The drum and the screw ejector rotate in the same direction, and the speed difference between the drum and the screw ejector is 10-35 rpm under the action of the differential. The drilling mud enters the rotating drum of high speed through the feeding port. Under the action of centrifugal force, the suspended particles such as particles and dense sediment (lithic cuttings) in the mud rapidly accumulate to the wall of the cylinder, and the density in the mud is relatively small. The liquid (water) is discharged from the outlet hole of the inner ring of the water layer through the liquid outlet. The sediment is pushed by the auger to the conical end of the drum and discharged through the slag outlet.
The sludge centrifugal dewatering machine is compared with other forms of solid-liquid separation mechanical equipment: a. It has compact structure, small volume, light weight and relatively convenient movement under the same processing capacity; b, large processing capacity and good separation performance Wide application range; c, high solid recovery rate, low operating cost, no filter cloth; d, automatic continuous operation, simple operation, easy to use, convenient installation and maintenance. It has been widely used in many industrial and mining fields such as geology, minerals, petroleum, chemical, metallurgy, pharmaceutical and environmental protection.
2 , test mud
The test mud was taken from a mud pool at a foundation construction site. The characteristics of the test mud are: water content of 85%, solid phase true density of 2226 kg / L, solid content of about 28.7%, and wet mud cake density of 1084 kg / L.
3 , test system
The test system is mainly composed of vibrating screen, cyclone, concentration tank, mud pump, electromagnetic flowmeter and LWnj -6500-B horizontal screw centrifuge.
During the test, the bored mud of the cast-in-place pile to be dewatered is placed in the first-stage transitional sedimentation tank, and transported to the vibrating screen and cyclone through the mud pump to screen the coarse granular particles such as coarse hard rock particles and sandstone. The medium with a specific gravity less than 50 and a light specific gravity flows into the concentration tank, and is pumped by the self-priming mud to the electromagnetic flowmeter for measurement, and then enters the centrifuge for centrifugal sedimentation and dehydration test.
4 , the main technical parameters of the test centrifuge
Model LWJ- 550× 2200 , drum diameter 550mm, drum length 2200 mm, working speed 2700 r/min (stepless adjustable), separation factor 2228 (max), differential speed 0～35 r/ min adjustable The main motor power is 45kW, the auxiliary machine motor power is 15KW, and the external dimensions are 3600 mm × 1650 mm × 1050 mm.
5 , test results
In the test, the dewatering effect of the centrifuge on the drilling mud was investigated by adjusting the separation factor of the centrifuge while maintaining the treatment volume of 50 m3 / h (the feed solid content control was controlled at 11.7%). 8T / h out of the mud (water content 37%), the effluent solid content rate of 5% or less.
6 , economic evaluation
The economic benefit of using the sludge centrifugal dewatering machine for dewatering of drilling mud is very significant. According to a site survey in a construction site in Jiangsu, the mud produced by drilling a cast-in-place pile is about 120 m3, and the current mud-laying fee is as high as 85 yuan. / m3 , that is, the mud transportation fee required for a cast-in-place pile is 10,200 yuan; and if the centrifuge dewatering process is adopted, the electricity cost, machine depreciation expense, labor management fee, sediment loading and transportation cost, and centrifuge installation are comprehensively considered. The fee for a pile of mud treatment is only about 4,300 yuan, which is 58% less than the original process.
7 , conclusion
Through the site site conditions of the bored pile drilling mud dewatering treatment test, the following conclusions can be drawn:
(1) Sludge centrifugal dewatering machine can be used for dewatering of bored piles to obtain better dewatering effect. After dewatering, the solid content of sediment can reach 75%~81%, and the moisture content of sediment after dewatering reaches below 40%. The volume is greatly reduced, and can be stacked and formed, and can be stacked separately for further natural drying or direct loading and transportation.
(2) The clear liquid separated by the centrifuge can be used to adjust the mud concentration, which is beneficial to improve the drilling progress and the quality of the hole formation, and also save water, which is especially important for the drilling of water-deficient areas.
(3) The economic benefit of using the sludge centrifugal dewatering machine for the dewatering treatment of the bored pile drilling mud is very significant, and has a good engineering application prospect.
(4) The centrifuge dewatering process can effectively improve the working environment of the drilling site, reduce transportation vehicles and environmental pollution, and has obvious social benefits.
(5) Limited to the test conditions, no more in-depth comparison tests were conducted. If the test results are to be applied to engineering practice, further changes in the structure and technical parameters of the machine are required.
: Liu (Technology, Sales) Chen : , : 741502981 , 279077258
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Jiangsu Haiheng Buiding-Materials Machinery Co.,Ltd
March 11, 2019
