Based on the geological report and the company's construction experience, the pipe jacking head decided to use a gas pressure balanced grid (water flush) head for construction. During the jacking process, the head is stabilized by air pressure to balance the frontal earth pressure, reducing the impact of external soil on the surrounding ground.
Jacking equipment and jacking process
(1) Main top:
Four 200 ton / unit jacks are used as the main jack, and the jack travel is 1.4 meters. Jack power is provided by an oil pump. At the rear end of the jack, the reaction force is evenly applied to the working well with a datum and a partial pressure ring. The front end pushes into the partial pressure ring, and the top iron transmits the top force to the pipe joint. The partial pressure ring is made with sufficient rigidity, and the contact with the end face of the pipe is relatively flat without deformation.
(2) Relay room:
In the long-distance jacking process, when the jacking resistance exceeds the allowable total jacking force, and the jacking distance cannot be reached at one time, the relay relay section jacking must be set. When the jacking project exceeds 100 meters in length, consider setting up a relay room behind the machine head and using thixotropic slurry grouting technology.
The relay room consists of a front case, a jack, and a rear case. The front shell is connected to the front pipe, the rear shell is connected to the rear pipe, and the front and rear shells are socket-type connections. The two are sealed by a rubber water stop to prevent the soil and slurry outside the pipe from flowing back into the pipe.
10 jacks are installed in each relay room, each with a jacking force of 30 tons, and the jacks are evenly arranged along the circumference. The jack has a stroke of 28 cm and is fastened to the front housing with fasteners made of flat iron. The steel shell structure is finished to ensure that it does not deform during use. The outer diameter of the relay room shell is the same as the outer diameter of the pipe joint, which can reduce soil disturbance, ground settlement and jacking resistance.
After the pipeline is jacked up, 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.
The pipe joint interface is mainly composed of a rubber ring (steel collar) rubber water stop and a soft soil pad. The steel collar cannot be deformed during the process of transportation from the processing place to the site, and the joint is not damaged to ensure that the rubber band does not shift or flip during the butt joint process, ensuring the tightness of the pipe joint. At the same time, the steel ring sleeve must be treated with anticorrosion before entering the site.
The rubber waterstop should be kept clean and free of oil, and stored in a dark place to prevent aging. During construction, the rubber waterstop is glued to the groove of the concrete pipe mouth and firmly attached. Before the joints of the pipe joints are coated, non-corrosive lubricant is used to reduce friction and prevent the waterstop from flipping, shifting and breaking. .
The cork liner is made of multilayer plywood (about 1cm thick), which is sandwiched between the steel collars of the front and rear pipe joints, so that the interaction force between the pipe joints is evened and the joint damage is reduced. After the pipe is jacked up, the pipe must be treated as an inner joint. The plywood between the pipe sections should be chiseled to the same depth (2 to 3 cm in depth), and smoothed with asphalt elastic caulking paste or cement mortar.
(4) Grouting process:
In the long-distance (greater than 100 meters) pipeline jacking process, grouting must be used. The thixotropic mud jacket is used to reduce the friction between the pipe wall and the soil during the jacking process. Deformation, sedimentation and water resistance.
Thixotropic mud is made by mixing bentonite and water with a mixing ratio of 1: 8. The thixotropic mud is stored in a storage tank after being stirred, and then transported through a pipe to a grouting hole of a concrete pipe through a grouting machine, and injected into the soil to form a mud jacket.