Exploration of new green construction technology for pit support?

(1) good water-stopping, permeability coefficient up to 10-6 level; (2) less impact on the surrounding strata; (3) high construction efficiency, can shorten the cycle; (4) can use H-beam and other materials as core material, so that it has a greater bending and compression resistance, and to play the role of both seepage control and stopping water and retaining the role of soil support of the continuous wall to realize the multi-purpose of a wall; (5) only the The same equipment construction, small vibration, low noise; (6) H-beam can be recycled, saving resources, reduce costs, in line with the national energy conservation and emission reduction, reduce pollution, resource reuse, sustainable development of industrial development policy.

2 key technologies

The creative key technologies of the new series of large-diameter composite drilling rigs mainly include the following. (1)A drilling tool for dry and wet spraying and mixing process is developed, which adopts independent powder spraying, water spraying or slurry spraying channels and powder supplying, water supplying or slurry supplying systems to adapt to different geological environments and to improve the effect of piling; at the same time, a higher-pressure (4?6MPa) BW250 mud pump is adopted to convey cement slurry during construction, which strengthens the ability of spraying cement slurry, expands the effective radius of slurry spraying, and reduces the mixing and drilling resistance. The traditional cement soil mixing pile construction adopts powder spraying or slurry spraying single dry spraying or wet spraying mixing process. The single wet spraying process drilling tools are not suitable for use in the coastal area where the wetness of the existence of undercurrents is relatively large, and the slurry is easy to flow away with the undercurrents, and the effect of pile formation is poor; the single dry spraying process drilling tools have high drilling resistance during the construction, poor mixing uniformity, high energy consumption, and low efficiency.

When the wet and dry spraying process is implemented, the timing of water spraying is determined according to the construction conditions, and when it is difficult to mix in the powder spraying construction, a certain amount of water is sprayed into the bottom of the drilling bit at the right time, which reduces the resistance to mixing, lowers the energy consumption and improves the construction efficiency, and solves the technical problems of the complex environment construction that cannot be met by the single spraying process of the soil mixing piles with a single spraying process of powder or a single spraying process of the slurry construction (Fig. 1).

(2) The slewing, drilling and lifting are driven by independent power, and the speed can be controlled independently, which realizes the optimal matching of the slewing, drilling and lifting speeds, and improves the uniformity of mixing and construction efficiency. The traditional ordinary soil mixer pile driver has no additional pressure, and the drilling pressure comes from the self-weight of the drill pipe and the power head, so the drilling speed can not be matched with the rotational speed of the drill pipe. Driven by independent speed-regulating motor, the control part is independent and can be directly controlled without stepping on the clutch. The pressurizing and lifting force is greatly improved, and the drilling and lifting effect is better.

(3) Independent clamping and pressing device is developed. Hydraulically-driven holding and pressing type is adopted when the core of composite piles is profile steel, square precast piles and precast pipe piles, and top pressing type is adopted when the core of piles is shaped precast piles. The traditional ordinary mixing pile rig can only carry out the construction of soil mixing piles. If other pile cores are to be inserted in the center of the mixing piles, it must be equipped with another expensive special equipment for pressing piles, and the purchase cost of the equipment will be greatly increased, and the labor cost will be increased at the same time. The new large-diameter composite drilling rig has a maximum diameter of Φ1150mm, and it can insert different pile cores into the already constructed mixing piles according to different construction requirements, so as to form composite piles with better performance. According to the different types of composite pile core, various types of pile pressing mechanism are developed. When the composite pile core is profile steel, square precast pile and precast pipe pile, hydraulic driven holding pressure type is adopted, and when the pile core is heterogeneous precast pile, top pressure type is adopted (Figure 2 and Figure 3).

(4) The rear supporting construction recording instrument adopts master-slave dual-computer communication to realize synchronous display of the front and rear stations, and has the functions of data saving and printing, with the maximum measuring weight of 3000kg and the maximum measuring depth of 30 m. It can realize the monitoring and recording of the date of powder spraying construction, the number of piles, the depth, and the amount of powder spraying and the weight per meter. After software redesign, with LCD screen can intuitively display the current total weight and depth, successfully completed to increase the instrument weight and depth measurement range, respectively, 9000kg and 30m. weight display fluctuations (±5kg range change), up to the target value.

(5) Adopting special drill bit, according to different geological conditions, different construction techniques and different pile diameters, the cutter head of the drill blade adopts different forms of alloy cutter head, which improves the drilling capacity. The special drill bit is welded with different alloy cutterheads on the tip and blades according to different geological conditions, which can not only construct ordinary soft ground, but also work smoothly in other soil layers such as coarse sand layer. (6) One of the new series of large diameter composite drilling rigs, PDF28 model, can form piles up to a maximum depth of 28m, and adopts the holding pressure pile driver to press into the pile core. The four main bearing rectangular profiles of the tower are made of materials with good mechanical properties, which reduces the weight and the first section of the tower adopts the pagoda-shaped truss structure, which has good lateral stability, and the tower bracing rod also adopts the form of main and vice bracing rods, which greatly enhances the stability of the whole machine (Fig. 4 and Fig. 5). ).

3 Structural Features of PDF28 Type

The PDF28 type large-diameter composite drilling rig mainly consists of hydraulic walk-behind undercarriage, derrick and guided pressurizing mechanism, drilling rig transmission system, drilling tools, pile pressing system, winch system, hydraulic system, powder spraying (slurry) system, electrical system and other parts (Figure 6). The structural features are as follows: (1) The drilling rig part of the machine is mechanically driven: the drilling rod rotation and pressurizing device are driven by their own power respectively, with multi-step rotation speed, and the pressurizing device adopts stepless speed control with overload protection device, which is more functional and easy and reliable to operate. (2)The pile frame of this machine is hydraulic walking type, which can move vertically and horizontally, and it is quick to position the hole, easy to operate and has strong mobility.

(3)The drilling rig adopts chain-type pressurizing mechanism, within the range of reinforcement depth, the drilling tools can be continuously drilled or lifted, and the drilling tower (derrick) and drilling rods can be lengthened or shortened according to the reinforcement depth, which makes the working efficiency high. (4) Derrick raising and lowering is carried out by hydraulic maneuvering cylinder, which is simple and reliable. (5)The drilling footage has depth meter and digital display, which is easy to operate and control. (6) The whole machine has compact structure, flexible maneuvering, small ground pressure, good stability, and can be applied to the site with narrow space and poor ground conditions. (7)The main machine adopts block-type assembly, which is easy to assemble and disassemble and transfer to other places for transportation; the main parts are mostly standard parts, with a high degree of generalization, and it is easy to use and maintain.

(8)The drilling bit of this machine is specially designed, according to different geological conditions, different construction techniques and different piling diameters, there are ordinary standard type and special special type, whose functions are mainly to break the soil quickly when drilling, to spray ash (or slurry) smoothly when lifting, and to make the powder or slurry mix and knead with the soil debris sufficiently and evenly, so as to form piles with high quality. (9) The hydraulic system of this machine adopts open oil circuit, which is mainly used for controlling and completing the longitudinal and transverse displacement of the host machine, the expansion and contraction of the outriggers, the rise and fall of the derrick, the clamping of piles, the pressing of piles and other actions. The hydraulic system consists of oil tank, oil pump, special multi-way reversing valve, longitudinal displacement cylinder, transverse displacement cylinder, outrigger cylinder, derrick cylinder, pile clamping cylinder, pile pressing cylinder and pipeline accessories, etc. The hydraulic system is mainly used for controlling and completing longitudinal and transverse displacement of the main machine, derrick up and down, pile clamping and pile pressing.

(10)The winch system of this machine mainly consists of winch, hanger, hinge base, pulley, wire rope hook, etc., which is used for pile core lifting. (11)The pile clamp of this machine is located in the middle of two gantries, which is box-shaped structure. There are two clamping plates inside, one is fixed and the other one is connected with the pile clamping cylinder through ball hinge, which can realize the clamping and slackening through the expansion and contraction of the hydraulic cylinder. There are positioning wheels on the top and bottom of the clamp box, which are in friction contact with the sliding plate on the gantry column. The overall structure of the clamp is simple and reliable.

4Remarkable benefits

The new series of large-diameter composite drilling rigs create remarkable social and economic benefits. In Guangdong, for example, after 2009, the annual new urban construction area of more than 120 million m2, of which about 4,000 sites need pit support, if 50% of the new series of large-diameter composite drilling rig SMW method of support, it can save more than 1 million tons of steel, equivalent to less than the burning of standard coal 1.25 million tons, to reduce carbon emissions of 3.1 million t. It can be seen that through the popularization of the new technology, the material recycling, energy saving, emission reduction, and the promotion of the new technology, it can be used for the purpose of recycling materials, energy saving and emission reduction. It can be seen that through the promotion of new technology, it can make the material recycling, energy saving and emission reduction, reduce the underground garbage, and help the sustainable development of underground space. Comparison of similar technologies (Comparison of SMW method piles constructed by new series of large-diameter composite piling machine and other drilling rig methods) (1) Two-level basement (taking a project in Houjie, Dongguan as an example).

Program comparison: A: bored pile + water stop pile + support; B: new SMW water stop wall + support. Comprehensive comparison is shown in Table 1.(2) First floor basement (take a project in Wanjiang as an example). Comparison of schemes: A: water-stopping wall + mini-pile + soil nail wall; B: new SMW wall + anchor cable. Comprehensive comparison is shown in Table 2. The comparison results show that the new series of large diameter composite drilling rigs for SMW work type steel hydraulic soil mixing wall construction program has obvious advantages over the program taken by other domestic equipment, and this program has been widely used in the Pearl River Delta and Jianghan Plain and other areas. The new series of large-diameter composite drilling rigs are set with the power below, which not only makes a breakthrough in the construction capacity of the equipment itself, but also adopts a combination of wet and dry spraying construction process in the construction of mixing piles in special strata, which reduces the energy consumption and strengthens the ability of adapting to all kinds of complex construction environments. In addition, this series of equipment also comes with a set of pressure pile construction mechanism, which is a kind of efficient multi-purpose composite pile construction equipment.

Because of the multi-purpose of one machine, it reduces the purchasing cost of the equipment users. After the construction of mixing piles, there is no need to move the main machine, by manipulating the longitudinal cylinder, the pile pressing mechanism can be quickly moved to the cement mixing pile station, and then the insertion of profiles and prefabricated piles can be carried out, which is of high construction efficiency, saves the cost of manpower and material resources, and has significant social benefits.

So far the new series of large-diameter composite drilling rigs have been sold to many customers, most of whom are located in the geographical area south of the Yangtze River, and have been successfully constructed and applied in the construction sites in the Pearl River Delta and the Jianghan Plain, etc. The new series of drilling rigs have completed the construction of cement mixing piles with high quality and high efficiency. This series of equipment has completed many influential pile foundation and pit projects, such as the foundation support project of Fuying Township Hall Phase III in Zhongtang Town, Dongguan City, Guangdong Province, and Jinqiao Plaza in Qianjiang, Hubei Province, with high quality and high efficiency. The new series of large diameter composite drilling rigs can insert prefabricated pipe piles, square piles, wedge piles, etc. in the center of the pile after construction of the mixing piles by replacing the different accessories of the pile pressing mechanism, forming a bone-core composite pile, which can be used as the pile foundation of the high-rise building, filling the blank of the application of the soil mixing piles in the pile foundation of the high-rise building, and expanding the application field of the soil mixing piles.

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