Construction scheme of cement pipe jacking
1, head selection:
According to the geological report and the construction experience of our company, the head of the pipe jacking machine decided to adopt the head of the air pressure balance grid (water flushing) for construction. In the process of jacking, the nose is stabilized by the air pressure balance of positive earth pressure, which reduces the influence of external soil on the surrounding ground.
2. Jacking equipment and jacking technology
(1) main roof:
Four 200-ton jacks are used for the main jacking, and the jack stroke is1.4m. The power of the jacks is provided by the oil pump. The back end of the jack evenly exerts a reaction force on the working well through the track wood and the pressure dividing ring, and the front end pushes into the pressure dividing ring, and the jacking force is transmitted to the pipe joint through the jacking iron. The pressure dividing ring has enough rigidity, and the contact with the end face of the pipe is relatively flat and does not deform.
(2) relay room:
In the process of long-distance jacking, when the jacking resistance exceeds the allowable total jacking force and the one-time jacking distance cannot be reached, relay jacking between relays should be set. In this pipe jacking project, when the jacking length exceeds 100 m, it is considered to set a relay room behind the nose and adopt thixotropic mud grouting technology.
The relay room consists of a front shell, a jack and a rear shell. The front shell is connected with the front nozzle, and the rear shell is connected with the rear nozzle. The front shell and the rear shell are connected by socket type and sealed with rubber water stop to prevent water, soil and mud from flowing back into the pipeline.
Each relay room is equipped with 10 jacks, and the jacking force of each jack is 30 tons, and the jacks are evenly arranged along the circumference. The stroke of the jack is 28 cm, and it is fixed on the front shell with fasteners made of flat iron. Fine steel shell structure ensures no deformation during use. The outer diameter of relay chamber shell is the same as that of pipe joint, which can reduce soil disturbance, ground settlement and jacking resistance.
When the pipeline is jacked in, the jack and various accessories are removed, and the gap between the shell and the inner wall of the pipe joint is filled with fine stone concrete.
(3) Interface:
The joint interface is mainly composed of outer ring (steel ring) rubber water stop and soft soil liner. During the transportation and hoisting from the processing site to the site, the steel collar shall not be deformed and the joint shall not be damaged, so as to ensure that the rubber belt will not shift or turn over during the butt joint of the pipe joint and ensure the tightness of the pipe joint. At the same time, the steel trap must be preserved before entering the site.
Rubber water stop should be kept clean and free of oil stains, and stored in a dark place to prevent aging. During construction, the rubber water stop is stuck in the groove of the concrete nozzle with super glue, and the paste is firm. Before butt joint of pipe joint, apply non-corrosive lubricating oil to reduce friction and prevent water stop from turning over, shifting and breaking.
The cork gasket is made of multi-layer plywood (about 1cm thick) and sandwiched between the steel collars of the front and rear pipe joints, so as to even the interaction force between the pipe joints and reduce the joint damage. After the pipe is jacked, the internal interface of the pipe shall be treated, and the plywood between the pipe sections shall be chiseled to the same depth (depth 2 ~ 3 cm), and leveled with asphalt elastic caulking paste or cement mortar.
(4) Grouting process:
In the process of long-distance (100 meters above) pipeline jacking, grouting technology must be adopted, thixotropic mud jacket should be adopted to reduce the friction between pipe wall and soil during jacking, and the lost soil should be filled to reduce the deformation, settlement and water resistance of soil.
Thixotropic mud is made of bentonite and water with a ratio of 1: 8. Thixotropic mud is stored in a slurry storage box after being stirred, transported to the grouting hole of the concrete pipe by a grouting machine through a pipeline, and injected into the soil to form a slurry sleeve.
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