1) General construction method
The ordinary construction of shaft topsoil can mainly adopt the common construction method of the well ring backboard, the hanging wall construction method and the sheet pile method.
(1) General construction method of well back plate
The common construction method of the backing plate of the well ring is to use the artificial or rock-carrying machine (the small cannon can be placed when the soil is hard) to unearth a small section (the empty distance is less than 1.2m), that is, the temporary support is supported by the well ring and the back plate. After excavating for a long period (generally no more than 30m), the well ring and the backing plate are removed from the bottom and then the permanent wall is built. So repeating this week, until the bedrock. This method is suitable for a more stable soil layer.
(2) Hanging wall construction method
The hanging wall construction method is a short-section (slope height 0.5~1.5m) excavation construction method suitable for the soil layer with poor stability. According to the soil layer conditions, stepped or segmented small blocks are used respectively, and the advanced small wells are used to lower the water level. In order to prevent the well wall from losing its self-supporting ability before the concrete has reached the design strength, causing the wall to crack or fall off, it is necessary to set the steel bar in the well wall and hang it with the upper wall.
(3) Sheet pile method
The essence of the sheet pile method is: for the unstable topsoil layer with small thickness, before the excavation, the manual or pile driver can be used to hit the well surface along the wellbore (the diameter of the wellbore before the unsupported) on the working surface or the ground. Into a circle of sheet piles, forming a closed cylinder to support the well wall and under the protection of the topsoil.
2) Special construction method
In the construction of shaft wells in unstable soil layers, special construction methods must be adopted to facilitate the smooth excavation, such as freezing method, drilling method, sinking method, grouting method and curtain method. At present, the freezing method and the drilling method are mainly used.
(1) Freezing method
The freezing method is to drill a frozen hole around the wellbore before the wellbore is drilled, and the unstable topsoil and weathered rock layers around the wellbore are frozen into a closed freezing circle by artificial cooling to prevent water or sand from flowing into the wellbore. And resist the ground pressure, and then dig the wellbore under the protection of the freezing circle. After the concrete has been drilled to a predetermined depth, the freezing is stopped, and the extubation and filling work is performed.
(2) Drilling method
The drilling method is to use the drilling machine to form the wellbore into a well in full section, or to drill the wellbore in several times. At present, most of the rotary drills used in China are used. The main processes of the drilling method include wellbore drilling, mud washing and retaining wall, sinking prefabricated well wall and wall grouting cementing.
(3) sinking method
The sinking well method is a special construction method belonging to the advanced support type. The essence is that in the design position of the wellbore, a section of the wellbore with the blade foot attached to the bottom is prefabricated. Under the cover, the wellbore is unloaded with the excavation in the well. The self-weight overcomes the frictional resistance between the outer wall and the soil layer and the frontal resistance of the lower part of the blade, and sinks continuously, and the long well wall is correspondingly connected on the ground, so that it is repeated until it sinks to the design elevation.
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