1.Overview of concrete seepage control wall
Concrete seepage control wall construction technology was born in Italy in the 1950s and is a longitudinal tangent of a vertical wall, with the wall extending along the dam body. Holes need to be created uninterruptedly in the loose permeable foundation and concrete is poured into the holes thereby forming a wall-shaped impermeable building. Concrete impermeable walls are an important way to provide vertical impermeable treatment for hydraulic projects in loose permeable foundations. According to the principle of segmental construction, a round hole or slot hole of a seepage control wall can form a wall section after pouring concrete, and several wall sections can form a wall. The top of the wall is connected to the gate and dam impermeable body. The two ends are connected to the bank impermeable facilities, and the bottom is embedded into the bedrock or to the corresponding depth in the impermeable stratum, so as to effectively cut off or reduce the infiltration of water in the foundation, so as to enhance the stability of foundation infiltration and give full play to the benefits of water conservancy projects.
2.Project case
A water conservancy project main dam plastic concrete seepage control wall construction platform elevation is 186.70m, cast-in-place C20 concrete form mainly exists in the upper part of the construction platform, plastic concrete seepage control wall is in the lower part of the construction platform, which through SG35A hydraulic grab machine into the slot, from the right side of the dam 0 + 246 pile gradually construction to the left side of the dam 0 + 000 pile number. According to the specific situation of the construction site, the construction can be divided into I and II sequence slot section, and the punching method is selected as the concrete seepage control wall joint construction method.
3.Water conservancy project concrete seepage control wall construction process
3.1 Joint construction
Integrity and seepage resistance are the characteristics of seepage control wall joint construction. Because of the project has a high seepage wall wall depth, selected joint pipe construction method, it is very easy to jam the pipe, can not pull out the joint pipe and other problems, for this reason, can be selected to punch the joint construction method, the advantages of good integrity, seepage resistance and low cost. First of all, the percussion drill is selected to drill the concrete from the end hole position after the concrete is poured in the first sequence slot to the bottom elevation of the second sequence slot. The operation can be carried out only after the first concrete set in the first sequence slot and the joint hole in the second sequence slot. In order to ensure that the thickness of the above 2 sequential slots is in line with the construction regulations, the verticality of the end hole and the joint hole construction should be effectively controlled, and the hole slope should be tested once in 2m of drilling construction, requiring the joint hole and the end hole to be in the same position, and the joint should be cleaned by wire brush joint hammer before the concrete is poured in the second sequential slot to ensure that the concrete at the joint position has good compactness.
3.2 Measuring and placing lines
In the construction of concrete impermeable wall of water conservancy project, measurement and release is extremely critical. According to the project construction needs, the measurement and release construction can choose electronic latitude and longitude meter, S3 level meter and other equipment. It is required to review the measurement datum points and datum lines first, and carry out the establishment of construction control network. And in accordance with this control network for the centerline of the impermeable wall for measurement and release.
3.3 Guide wall fabrication and slot section division
(1) Making guide wall. As the main component of construction, the guide wall is a temporary reinforced concrete structure set along the center line of the seepage control wall. Its function is to control the elevation, construction machinery support, and avoid the collapse of the top of the channel wall. According to the specific conditions of the construction site, cast-in-place C15 concrete can be selected for construction, and its production process includes: measurement and positioning, excavation, reinforcement placement, mold erection, concrete pouring, mold demolition and internal support. Generally, mechanical and manual methods are chosen for excavation and construction. After removing the formwork of guide wall, in order to avoid deformation situation, transverse wooden support needs to be set into the guide wall, 1 to 2 meters is the distance between supports.
(2) Division of slot sections. I and II sequence slots are the types of slot section division, and the excavation length of the above 2 sequence slot sections can be determined according to the specific geological conditions, which is 5 meters, and each slot section covers 2 main holes and 1 secondary hole. It is required that the I-sequence slot section is constructed first and the II-sequence slot section is constructed afterwards.
4.Mud preparation
The function of mud is to improve the stability of slot wall and lubrication of drilling tools, etc. The quality of mud selection plays a decisive role in the construction quality of underground impermeable wall. For this reason, mud selection must ensure its physical properties, rheological properties and other good. In accordance with the actual geological situation and the characteristics of the hole grasper, the project mud manufacturing can be selected bentonite finished materials, its performance indicators need to be in line with the construction standards, specific performance indicators are shown in Table 1.
5.Excavation of slot holes
SG35A hydraulic grab and percussion drill is selected for effective construction. The construction method can be selected as “two drills and one grab”, that is, the impact drilling rig is selected for the construction of I sequence slot end hole, main hole and II sequence slot main hole, which requires effective control of verticality during the construction process, followed by the excavation of secondary holes, which can be constructed by the hydraulic grab. The hole position of the slot section should be marked in the guide wall, and the grab and the hole position should be aligned and then the vertical hole grab operation should be implemented. The main hole at the 2 ends is required to be constructed first, and after the completion of the main hole construction, the secondary hole operation is required, and the slot section can be slotted after the main and secondary hole operation, as shown in Figure 1.
6.Slot cleaning
In slotting construction, in order to thoroughly clean up the sediment deposited at the bottom of the slot, the slag removal work should be done, so as to effectively improve the bearing capacity and seepage resistance of the impermeable wall. Good quality mud should be sent to the pump in the tank without interruption to ensure a stable liquid level and avoid collapse of the hole. Because the project has deeper slot holes, the air lift slag removal method can be chosen for slot cleaning construction. After construction, the specific gravity of the mud located at 02-1 meters above the bottom of the tank should be in line with the relevant regulations, and three measurement points need to be set to the tank section when the thickness of the slag at the bottom of the tank is detected, and 50mm is the maximum thickness of its slag.
7.Plastic concrete production and transportation
First, because the project has a large volume of work, it is necessary to carry out self-mixing concrete mixing station setting. The mixer selection is required according to the project characteristics. The table scale is selected for material measurement and weighing, and the material is delivered manually in conjunction with the loader. In the mixing cylinder device material through the mixer uniform mixing, and plastic concrete mixing trial construction, at this time can be fed into the mixing cylinder bentonite, and add the appropriate amount of water, mixing time of 1.5 minutes, followed by cement, sand materials added in, mixing time needs to be controlled between 2 to 3 minutes.
Secondly, in order to ensure the quality of concrete construction and avoid the problem of segregation, it is necessary to choose the pumping concrete method with a working capacity of 30 cubic meters per hour. Concrete along the delivery pipe can be sent to the pouring section of the conduit aggregate hopper to, concrete can be dropped into the bin to ensure that the concrete surface in the tank always exceeds the conduit outlet position, so as to ensure that the concrete, mud does not touch.
8.Underwater concrete filling
Underwater concrete filling construction needs to be carried out in a timely manner after the quality of slot-clearing construction meets the construction regulations. As an important stage of the construction process, underwater concrete filling should avoid the problem of insufficient amount of material and equipment failure. According to the project construction needs, the conduit method can be selected for the construction of concrete filling, underwater concrete using the site self-mixing concrete construction.
The helicopter conduit method is selected for underwater plastic concrete placement. According to the specific situation of the slot section, two sets of conduits were installed into the slot section, 200mm was its pipe diameter, flange connection was selected, 3m was the distance between the conduits, and the distance between the conduits and the 2 ends of the slot section was set to 150cm. In order to ensure the quality of concrete pouring and avoid the problem of wall mud leakage, it is necessary to ensure that the concrete surface shows a rising trend during the pouring construction process, requiring effective control of its rising speed within 200cm per hour, and effective control of the buried depth of the pipe between 100cm and 600cm, and assign a person to measure the rising surface of the concrete in real time and make Accurate records, at the same time, each channel section needs to be a set of concrete test blocks reserved on site.
9.Construction process inspection and control
The main content of construction process inspection and control are hole making, slurry quality inspection and so on. Specific details are as follows: hole making and slotting inspection: slotting verticality and depth inspection are the main contents. In the case of hydraulic grab, verticality can be detected by its deflection monitoring instrument, which is required to effectively control its verticality deviation within 1/300h.
Mud quality inspection: Newly made mud, slot hole mud, etc. are the main indicators of mud quality inspection, which requires effective control of specific gravity and sand content of mud to ensure that it is in line with construction regulations. Underwater concrete pouring detection: when pouring plastic concrete need to be effective control of concrete pouring speed, height, quality, etc., to ensure that it is in line with the construction regulations.
To sum up, in order to achieve further expansion of the scale of water conservancy projects, to promote the progress of the entire water conservancy construction. Must pay attention to the construction method, construction technology, the reasonable choice. This requires the relevant departments, enterprises must fully understand the specific circumstances of the construction case, the premise of standardizing the construction process, only in this way can provide a reliable guarantee for the quality of engineering construction improvement.