Preparing the ice fence

At site No. 17, where the second vestibule of the Okruzhnaya metro station will be located, preparations are underway for digging an escalator tunnel. Drilling of wells for soil freezing is being completed. A Metrostroevets correspondent found out how a high-quality ice fencing will help in the fight against quicksand and water-saturated rock.

Scheme for constructing a freezing well at site No. 17

The development of wells on the “Okruzhnaya” Lyublinsko-Dmitrovskaya line began in August 2018. They are drilled parallel to the future inclined course, at an angle of 30 degrees. According to the project, it will stretch for 109 meters. The wells are made shorter than the tunnel so as not to disrupt the operation of the existing metro. Their length is 91.4 meters.

“The ice fence will ensure the safety of the slope,” explains Nikolai Kuzmin, deputy head of the first section of SMU-12. – After the first layer of soil there is quicksand – fine-grained water-logged sand. Then, alternating with layers of clay, the Izmailovsky and Meshchersky aquifers are made of water-saturated limestone. They need to be frozen.

By the end of June, 63 of the 69 wells were ready. They are drilled sequentially around the clock: only after one is completely completed do they begin the next one. Each one takes an average of two to five days.

The process begins with unfastening the SM-20 drilling rig. After passing 10 meters, the well is lined with the first pipe. This is the so-called conductor, which is used as a guide. Then, as the depth increases, the diameter of the excavation and pipes gradually decreases.

In the area of ​​the future inclined movement, almost all the wells for freezing soils are ready

The drilling rig operator is working with two assistants. In addition to them, a pumping station operator is involved in the case. From it, a bentonite solution is fed into the working tool of the machine, which is necessary to wash the rock out. You can't do without a welder. He is engaged in unfastening the installation and joining the pipes during immersion. Each stage of drilling is carefully monitored by surveyors.

The freezing system at Okruzhnaya includes 40 main and 16 additional wells. Another nine are thermometric. They are needed for temperature monitoring. The four remaining are hydro-observational. They are used to control changes in water level.

After drilling, SMU-9 specialists will come to site No. 17. They will carry out inclinometer measurements to check the wells and then begin freezing the soil.

Subsequently, they plan to integrate the second Okruzhnaya lobby into the transport hub of the same name. The large transport hub should connect the Savelovskoe direction of the Moscow Railway, the Moscow Central Circle, the metro and Aeroexpress.

REFERENCE

The finished wells are awaiting piping - they will be connected into a single circuit. Then a special solution will be introduced into them and the temperature will begin to be reduced using refrigeration units. The soil will be frozen for two months - this is exactly how long the active phase of the process lasts. This is followed by passive, when the finished ice fence is simply maintained in proper condition. It will last until the excavation of unstable soils is completed.

BY THE WAY

Okruzhnaya is located in the north of the Timiryazevsky district, at the intersection of Lokomotivny and 3rd Nizhnelikhoborsky passages. While its northern vestibule is being built, the station operates with one exit - the southern one, which leads to Gostinichny Proezd.