RU2449089C1 - Method to prepare permafrost soil for development - Google Patents

Abstract

FIELD: construction, road engineering.

SUBSTANCE: invention relates to the field of earth works production in stripping works, digging pits and trenches under permafrost soil condition. The method to prepare permafrost soil for development is realised by water distribution along the surface of the unfrozen section. At the same time after natural thawing of soil to the depth of 0.15-0.20 m the thawed soil is removed, to form a "trough", and running water is sent into it along the surface of the frozen section with a flow rate of 5-10 l/m² of the surface per hour. At the same time preparation of permafrost soil is carried out in summer period at the air temperature of more than 0°C and water temperature of at least +1°C.

EFFECT: higher efficiency of permafrost soils unfreezing.

2 cl

Description

The invention relates to the field of excavation during stripping, digging pits and trenches in the conditions of permafrost soil.

A known method of hydraulic thawing of frozen rocks, including the removal of the soil and plant layer in the thawed area, which then build the feed and drainage ditches, drill holes between them, fill them with an aqueous solution of NaCl, lay explosive charges in them, produce an explosion and get oblique filtration channels through which water heated by solar energy is passed from the supply to the drainage ditch, and the frozen rock is thawed in this way (RU No. 2380488, E02F 5/30, F42D 99/00, 2010).

The disadvantage of this method is the complexity of the technology of preparing the soil for thawing, the high complexity and cost of work (the installation of a deep drainage ditch in frozen soil, drilling wells, preparing saline, laying charges, the cost of explosives, NaCl, the operation of drilling equipment, etc.).

The prototype of the claimed invention is a method of preparing frozen soil for development by distributing water on the soil surface under a snow cover, after dividing the area to be thawed into parallel horizontal strips 10-15 m wide, and on the lower side each strip is limited by a compacted snow roll of 0.2- 0.4 m. Each strip is divided in the transverse direction into grips corresponding to the daily productivity of the earth-moving machine. Cold water is poured from the top side (with a temperature of + 10-0 ° C). After 1-4 days, snow from the surface of the prepared area is cleaned with a bulldozer and soil is excavated by an earth moving machine. Thawing of frozen soil and its transition from hard-frozen to frozen-plastic state occurs due to the phenomenon of latent heat of ice formation occurring at 0 ° С during the phase transition of water to ice with the release of 1 kg of water during freezing of about 335 kJ of heat, which is transferred to the soil in large quantities. the thicker the snow cover in the defrosted area (SU No. 503004, IPC E02D 3/10, 1976).

The disadvantage of this method is its low efficiency due to the insufficient heat of ice formation, which is in a static state, a small layer of water thickness (up to 0.1 m on a horizontal surface), flooded and withstand until freezing, and increasing the water layer is technically complicated due to its difficulties retention from spreading. In addition, permafrost soils contain a lot of ice and have several times lower temperature than seasonal freezing soils, therefore technically possible sequential thawing of permafrost soil in thin layers with the removal of thawed soil is long and not technologically advanced.

The objective of the invention is to simplify the technology and organization of work on the thawing of permafrost soil and reduce their cost.

The technical result of the invention is to increase the efficiency of defrosting permafrost soils.

The task and the technical result are achieved in that the method of preparing permafrost soil for development by distributing water on the surface of the defrosted area, according to the invention, after naturally thawing the soil to a depth of 0.15-0.20 m, the thawed soil is removed, with the formation of a “trough” and running water is let into it on the surface of the thawed area, taking into account the flow rate of 5 ÷ 10 l / m ^{2 of} surface per hour. In this case, the preparation of permafrost soil is carried out at an air temperature above 0 ° C and a water temperature of at least + 1 ° C. Defrosting permafrost soil can be realized only in the summer period at a stable air temperature above 0 ° C and at a water temperature of at least + 1 ° C.

These conditions are related to the fact that at an air temperature of 0 ° C and lower, water can cool to 0 ° C and lose part of the latent heat of ice formation, and the minimum allowable water temperature + 1 ° C ensures that the water has the full potential of the latent heat of ice formation.

The requirement of natural thawing of the soil by 0.15-0.20 m is due to the need to obtain a “trough” after removing this soil layer with bulldozers to obtain a sufficient recess above the defrosted area to allow flowing water through it. Distribution of the running water over the site ensures first its cooling to 0 ° C, followed by the constant return to the frozen ground of the latent water of the latent heat of ice formation. At the same time, if the volume of flowing water is less than 5 l / h on one m ^{2 of the} surface, then due to the heterogeneity of the water flow over individual parts of the site and a significant slowdown in the flow of water up to its stagnation, the depth of thawing of the soil is insignificant, which indicates the exhaustion potential of latent heat of ice formation by slowly flowing water, and therefore, a decrease in the rate of soil thawing. When water flows in a larger volume than 10 l / h on each 1 m ^{2 of} the plot surface, the fraction of latent heat of ice formation given to frozen soil significantly decreases, therefore, an increase in water flow over the indicated volume in small sections does not accelerate the rate of soil defrosting and is impractical.

The method of preparing permafrost soil for development was carried out as follows.

The experimental preparation of permafrost soil for development by thawing it began in the first half of June 2010, approximately 1100 km northeast of Yakutsk in the area of the Ust-Nera settlement. The natural thawing of permafrost soil (a water-saturated mixture of sand, gravel and coarse rocks) at that time was about 0.2 m. Thawed soil was removed with bulldozers from three successive sections of grips each 300 × 300 m in size, and “troughs” into the resulting recesses along a dug ditch from the Nera River, running water with a temperature of about +1 - + 3 ° С with a varying average daily air temperature in the range +5 - + 10 ° С was launched by gravity along the existing small slope. Along the length of the plots and at the end of the last plot after overflowing the trough, the water flowing along them poured out and flowed along the natural slope mainly into the Nera River. The rate of water flow in different parts of the plots was different, but was mainly in the range of 5-10 l / h per 1 m ^{2 of} surface. As a result of applying this technology, after 14 days, permafrost soil was thawed to a depth of 1.5 m at a rate of about 0.1 m / day in the amount of 410 thousand cubic meters. The thawing of permafrost soil to such a depth during this time occurred mainly due to the latent heat of ice formation of water after its cooling to 0 ° C and further flow over the defrosted area with the release of a significant part of this heat to the soil.

If it is necessary to further defrost the soil to develop deeper excavations, the water supply is stopped, the thawed soil layer is developed, water is let into the pit formed and its flow rate is provided, and after the thawing of the next soil layer, the water supply is stopped, water is removed from the pit, the thawed soil is developed, and then the procedure is repeated. Currently, the proposed method of preparing permafrost soil for development is at the stage of pilot testing.

The relevance of reducing energy and other material costs in the development of such soils is due to the growing need to carry out large volumes of overburden excavation works at the construction of opencast mines for the extraction of non-ferrous metals and other minerals, during the construction of a complex of facilities for the extraction, transportation, processing of gas, oil, and the laying of main pipelines, etc. in the conditions of the Far North and in other territories where permafrost soils can occur to a depth of many meters.

Claims (2)

1. A method of preparing permafrost soil for development by distributing water over the surface of the defrosted area, characterized in that after naturally thawing the soil to a depth of 0.15-0.20 m, the thawed soil is removed with the formation of a “trough”, and into it along the surface of the defrosted area let running water at the rate of 5-10 liters per 1 m ² surface per hour. 2. The method according to claim 1, characterized in that the preparation of permafrost soil is carried out at an air temperature above 0 ° C, and the water temperature should not be lower than + 1 ° C.