Basic working principle
With the help of the thrust of the main jacking cylinder, the pipeline and the relay room, the tool pipe or roadheader is pushed through the soil layer from the working shaft to the receiving shaft and hoisted. At the same time, the pipeline immediately behind the tool pipe or the roadheader is buried between the two wells, in order to realize the construction method of trenchless laying of underground pipelines.
2. Main engineering technology
The pipe jacking scheme is generally to jack the reinforced concrete casing first, and then pass through the engineering pipe - steel pipe in the casing. In the process of pipe jacking, it is necessary to fully consider the obstacles that may be encountered, such as solitary stones. In the past, there have been cases where the entire pipeline was scrapped due to obstacles that could not be jacked, especially when the small diameter pipe could not be excavated. Therefore, before the pipe jacking construction, it is necessary to find out the geological conditions at the pipe jacking crossing path. There should be an adequate and reliable solution to the obstacles encountered. The following takes artificial pipe jacking construction as an example to introduce pipe jacking construction.
This method is suitable for soft soil strata, loess strata above groundwater level, and strong windy rock strata above groundwater level. It is characterized by low construction cost, and can be removed manually immediately if the obstacle in front of it is encountered in the jacking process; The disadvantage is that the jacking pipe diameter should be greater than 800mm, otherwise it is not convenient for personnel to enter and exit, and the jacking distance should not be too long.
The pipe jacking system for artificial pipe jacking construction mainly includes: jack, jacking iron, backrest, guide rail, and pipe jacking section. The construction diagram is as follows:
2.1. Preparation for construction
1) Pipe jacking work well construction, the well is equipped with a water collection pit to facilitate the pumping and discharge of stagnant water; (2) The back backrest is set, and after the foundation of the working well is set, the back backrest is set according to the direction of the pipeline. (3) guide rail installation, the guide rail installation firm and accurate has a greater impact on the jacking quality of the pipe, so the guide rail installation is determined according to the size of the pipe diameter, the slope of the pipe, and the jacking direction, and the jacking direction must be straight, and the elevation and axis are accurate. The guide rails can be made of light steel rails. (4) The jacking equipment adopts a jack, and the head is equipped with a cutting edge tool pipe, which plays the role of cutting soil and protects the pipeline and guidance. In order to prevent the soil from collapsing, a grille is set in the tool tube. (5) Other equipment (6) A movable working platform is set above the working pit, which is generally made of No. 30 channel steel as a beam and paved with square wood. The lower tube is lifted by a temporary crane, and the shaking head lever is used for unearthing. (7) Note: Pipe jacking work pit must be surrounded by enclosure measures, color steel tile enclosure, rain canvas protection, and eye-catching warning signs. When jacking, passing vehicles should slow down, and large-tonnage and heavy-duty vehicles are prohibited from passing. 2.2. Excavation and jackingAfter the equipment in the working pit is installed, and the parts are in good and normal condition after inspection, they can be excavated and jacked. First of all, the pipe is lowered to the guide rail, and after it is in place, the top iron is installed, and the elevation of the pipe center and the bottom of the pipe is calibrated to meet the design requirements, and the front end of the pipe can be excavated. (1) excavation and excavation before the pipe is the key to ensure the quality of jacking and the safety of the above-ground structure, the direction of excavation and the shape of excavation in front of the pipe directly affect the accuracy of the jacking pipe position, so the excavation around the front of the pipe should be strictly controlled. The soil excavated in front of the pipe should be transported in time, and the large pipe diameter can be pushed by a trolley, and when the pipe diameter is small, the double-drum winch is used to pull the trolley unearthed. The soil is transported to the outside of the pipe, and then hoisted to the platform with the moving head lever on the working platform, and then transported out of the pit. (2) jacking using jack jacking out pickaxe in the case of back does not move to push the jacking pipe forward, its operation process is as follows: 1) install the jacking iron, squeeze firmly, after the front end of the pipe has dug a certain length of soil, start the oil pump, jack into the oil, piston stretch out a working stroke, push the pipe to a certain distance; 2) Stop the oil pump, open the control valve, the jack returns the oil, and the piston retracts; 3) Add the top iron and repeat the above operation until the next section of the pipe needs to be installed; (3) Precautions for jacking: 1) Jacking should follow the principle of "digging first and then topping, and digging with the top". It should be operated continuously to avoid stopping halfway, resulting in increased resistance and increasing jacking difficulties. 2) The direction and elevation of the jacking of the first section of the pipe are related to the jacking quality of the whole section, and the deviation should be measured frequently, checked and corrected in time. 3) The installation of the top iron should be smooth, no skew and twist, each time the piston is added to the top iron, the longest top iron that may be placed should be replaced, so that the number of connected top iron is the least. 4) In the process of jacking, if it is found that the earthwork in front of the pipe collapses or the pointer of the oil pump pressure gauge increases suddenly, etc., the jacking should be stopped immediately, the cause should be identified, and the jacking should be continued after the fault is eliminated. 2.3. Measurement and error correction(1) Measure the center line of pipe jacking and the leveling point into the working pit, and control the installation position and jacking direction and elevation of the guide rail and pipe jacking machine 1-3=1-1*9 10+2*9-7=3. When jacking, measure once at a certain distance from each jack, and the measurement spacing of the first section of the tube should be shortened. During the correction, each jacking pick is measured once. (2) When the correction of the jacking deviation is found to be about 10mm in the process of jacking, the correction should be carried out, and the correction should be carried out slowly, so that the pipe is gradually reset, and the hard adjustment shall not be violently corrected. The correction method is generally adopted: 1) excavation correction method: this method is used when the deviation value is 10-20mm. That is, when the pipe is biased to the left side of the design center, it can be appropriately over-excavated on the right side of the pipe center, and not over-excavated on the biased side, so that the pipe can gradually return to the design position in the continuous jacking. 2) top timber correction method: when the deviation is large or the excavation correction method is invalid, a round log or square timber can be used, one end is pressed against the inner pipe wall of the pipe deviated to one side, and the other end is supported on the soil layer in front of the pipe with a wooden board, and the jack is started, and the component generated by the top wood is used to make the pipe corrected.
2.4. Settlement observation and control
In the process of pipe jacking, ground subsidence will be caused by the looseness of the soil on the front of the excavation, the insufficient filling of the void around the pipeline by deviation correction, and the friction between the pipeline and the soil layer.
Analysis of this project
The pipes used in this project are: reinforced concrete casing + steel pipe. Different pipes and soil are suitable for pipe jacking construction methods, and the specific construction methods are determined by the construction unit and the construction unit according to the specific local conditions. Before construction, on-site investigation and research should be carried out, and the relevant engineering geology, hydrogeology and surrounding environment conditions along the project provided by the construction unit, as well as the detailed information of underground and above-ground pipelines, surrounding buildings (structures), obstacles and other facilities along the line should be verified and confirmed; Pit exploration is carried out if necessary.