In order to obtain a sufficient return speed and a high drilling efficiency, in general, the pressure of the air compressor is preferably larger. Because of the high pressure and the depth of the mixer, high drilling efficiency can be obtained. Generally, the depth of the mixer can be calculated according to the pressure of 8 to 9 m per 0.1 MPa. (The consumption is large and the cost is increased. Therefore, the pressure of the hole is generally selected within a depth of 300 m and the pressure air compressor is 1.5 MPa, and the depth of the hole is selected to be 1.05 MPa. Press, the inner hole depth of 150m can choose 0.7MPa pressure air compressor to basically work normally.
Choice of drill type: It is necessary to select a special drill according to the lithology of the formation, the pressurization capacity of the drill. At present, a three-four-blade scraper bit or a combined roller cone bit with a baffle is generally used in the Quaternary stratum; the bedrock is an external rib stepped alloy drill bit or a modified roller bit. For drilling into the Quaternary viscous ground layer, in order to prevent sticking, a cylindrical converging blade bit should be used.
Selection of rinsing fluid: Although the circulation speed outside the tube is low during drilling, and there is no direct scouring effect of the rinsing liquid on the hole wall, it is drilled in the Quaternary loose formation due to the steel pressure suction effect during drilling. At the time of the collapse, there may be a phenomenon of collapse, and it is easy to stick to the drill when drilling into the sticky ground layer. Generally, high-quality mud with small static shear force, good rheology and high recovery rate should be used as the flushing fluid for drilling into the loose formation. However, when the groundwater level is >3m, the formation is relatively stable and the bedrock is drilled, clean water can be used as the flushing liquid.
In production and operation, it is necessary to do the work of sealing the bottom of the sinking well. Corresponding to the sinking and undrained sinking, the sinking bottom also has two ways: drainage back cover and undrained back cover.
Drainage back cover (dry seal bottom) Drainage back cover usually consists of two stages. The first stage is to seal the part outside the short pipe collecting sump, and the groundwater is discharged from the sump without interruption to ensure the quality of the concrete pouring. The second stage is that after the cushion concrete reaches the design strength, the sump is sealed with a cover, the waterproof layer of the linoleum is laid, and the reinforced concrete floor is poured.
When the undrained back cover (wet seal bottom) is used for undrained back cover, the water level in the well should not be lower than the water table outside the well. The process is roughly to first lay the gravel cushion and carry out the concrete cushion underwater casting. After the cushion concrete reaches the design strength, Drain the water and make a reinforced concrete floor. Underwater pouring is generally carried out by means of a pipe method. The thickness of the underwater concrete cushion should be such that after the design strength is reached, if the well water is drained, the maximum pressure of the groundwater can still be assumed, and the anti-floating requirements should also be met.
In addition to the shore type pumping house, in the water supply and drainage project, the construction of other structures often uses the caisson construction method. Such as Dakou Well, Suction Well, Jiangxin Water Head, etc.
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