The main contents of the freezing method sinking construction include: drilling of frozen holes, freezing of wellbore and excavation of wellbore.

(1) Drilling of frozen holes

The freezing holes are generally equidistantly disposed on a circumference concentric with the wellbore. The freezing hole spacing is generally 1.2m-1.5m, the hole diameter is 200-250mm, and the hole depth should be 5-10m larger than the freezing depth. The number of laps of the freezing hole is generally determined according to the required thickness of the frozen wall. When the topsoil is shallow, it is generally frozen in a single circle. For deep topsoil, double or three rings can be used for freezing.

(2) Wellbore freezing

The brine is a refrigerant and the ammonia is a refrigerant; the entire refrigeration equipment includes an ammonia circulation system, a brine circulation system, and a cooling water circulation system.

The wellbore freezing scheme has several types of frozen deep, partial freezing, differential freezing and staged freezing. It is suitable for a full freeze and is widely used. Local freezing is only frozen in the water inrush. The structure of the freezer is complicated, but the freezing cost is low. The differential freezing is called the long and short pipe freezing. The length of the two freezing pipes is arranged at intervals. The upper part of the freezing tube is arranged densely, which can speed up the freezing speed, make the wellbore excavate as soon as possible, and avoid the freezing of the lower part of the well, and waste the cold amount; the freezing of the stage is the freezing depth, in order to avoid using too much refrigeration equipment, Divide the whole depth into several segments and freeze them from top to bottom.

(3) Digging of the wellbore

Wellbore excavation must have the following conditions:

1. The water level in the hydrological observation hole should rise regularly and overflow the orifice. When the groundwater level is shallow and there is water in the working face of the wellbore, the water level of the wellbore should rise regularly.

The frozen shaft wall is generally made of reinforced concrete or concrete double-layer wall. The thickness of the outer well wall is about 400-600mm, and it is poured along with the excavation. The inner wall thickness of the inner layer is generally about 500-1000 mm, which is from the bottom to the top of the well after passing through the freezing section.

The construction of the frozen shaft wall shall be carried out in accordance with the requirements of low temperature concrete construction.

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