The topsoil construction method can be divided into two categories: ordinary construction method and special construction method. For the stable topsoil, the common construction method is generally adopted, and for the unstable topsoil, a special construction method or a combination of ordinary and special construction methods can be adopted. 1. Common construction of the topsoil of the wellbore (1) General construction method of well back plate The common construction method of the backing plate of the well circle is to use the artificial or rock-carrying machine (the small cannon can be placed when the soil is hard). After a small section is drilled (the empty distance is determined according to the stability of the soil layer, generally no more than 1.2m). That is to use the well ring and the back plate for temporary support. After a long period of excavation (generally no more than 30m), the well ring and the back plate are removed from the bottom and then the permanent wall is built. This method is suitable for a more stable soil layer. (2) Hanging wall construction method The hanging wall construction method is a short-section excavation construction method suitable for the soil layer with poor stability. (3) Sheet pile construction method Second, the special method construction of the topsoil The construction of the wellbore and the roadway in the unstable topsoil and the soft and broken rock formation usually adopts special construction methods, including freezing method, drilling method, sinking method, grouting method and curtain method. (1) Freezing Act In unstable aquifers or aquifers, prior to the construction of underground works, artificially cooled methods are used to freeze the water-bearing rocks and soil layers around the underground works to form a closed frozen soil structure-freezing wall to resist Geotechnical pressure, isolation of the connection between groundwater inside and outside the frozen wall, and then special construction techniques for the construction of underground works under the protection of the frozen wall. It is suitable for various water-bearing strata with small salt content and low groundwater flow rate. (2) Drilling method Drilling method is a mechanized well-drilling method that uses a bit cutter to break rock, use mud or other medium to wash well, protect the wall and drain the slag, and generally carry out permanent support after the wellbore is drilled to the design diameter and depth. The drilling method is applicable to a variety of different geological and engineering conditions. China's current vertical drilling rigs have a maximum drilling diameter of no more than 9.5m and a maximum drilling depth of less than 700m. (3) The sinking method A special construction method for drilling a wellbore in an unstable aquifer, which is a kind of advanced support, which is essentially in the wellbore design position, under the prefabricated wellbore cover, with the excavation, until it sinks to the design elevation . This well sinking method is called the sinking method. It is generally considered that in the unstable topsoil layer with no pebbles, boulders, and a layer of water-repellent clay at the bottom and a total thickness of about 100 m, the sinking method is suitable. If the water inflow is less than 30m 3 /h, the flowing sand layer is thin (about 1m), the soil layer is stable, and the depth is shallow (<30m). It can be considered to use the method of drainage and sinking well. If the amount of water inflow is large, the topsoil layer and the flowing sand layer are thicker, and the submerged sinking method should be used for construction. (4) Grouting method The grouting method is to inject the slurry into the pores, cracks or cavities of the rock. The slurry is diffused, solidified and hardened in the rock and soil, which can reduce the permeability of the rock and soil, increase its strength and stability, and achieve the reinforcement of the rock and soil. The purpose of water shutoff. Divided into pre-grouting and post-grouting. Pre-grouting can be divided into two kinds of construction schemes: ground pre-grouting and pre-grouting on the working face. Post-grouting is the grouting work carried out after the excavation of the well. The grouting method is widely used, and pre-grouting of all aquifers in the whole well can achieve “dry well†construction. (5) Curtain method The curtain method is a special construction method for the roadway with advanced support. The essence is to construct a closed circular or other shape concrete curtain in advance around the design position of the wellbore or other underground structure. The depth should pass through. Stabilize the topsoil and embed it in a 3-6m impervious stable rock formation. Under the protection of the curtain, it can safely carry out the excavation work, smoothly pass the unstable water-bearing stratum, build the wellbore, or build the underground structure. It is currently only applicable to vertical shafts and inclined shafts in water-constant unstable topsoils up to 100 m deep.
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Types and application of topsoil construction method for vertical shaft