The implementation of the supervision system of warping dam project in China has just begun, and there are still many theories, methods, systems and working procedures to be further improved. According to the practice of warping dam construction supervision, the author puts forward some superficial understanding of the main points of warping dam construction supervision for discussion only.
First, the preliminary work stage of supervision
1, design report and construction drawing review
The design of warping dams is generally completed by the local water conservancy and soil and water conservation design department. Due to the limitation of professional level and other factors, some of them are rough. Mainly manifested in:
① The topographic map of the dam site has not been measured on the spot? Inconsistent with the actual terrain;
(2) The main buildings can't be arranged according to the actual conditions. Some small warping dams arranged on the gullies adopt a "two-piece" structure regardless of the upstream inflow and the control area, and the main structures have the same size, which is easy to cause waste;
③ When designing, the distribution, transportation distance, nature and reserves of building materials such as soil, sandstone and water near the dam site are not investigated enough, and a one-size-fits-all approach is often adopted to save trouble. Therefore, it is very important to review the design report and drawings before construction. The supervision engineer shall conduct item-by-item examination and on-site inspection according to relevant specifications. When problems are found, the design department should be urged to revise and improve as soon as possible.
2. Engineering quantity accounting
When designing the warping dam, the design unit is required to send people to the site for measurement. Some survey work is not done seriously enough, some take 1: 10000 topographic map as the working base map, and some artificially increase the engineering quantity, resulting in a large discrepancy between the design engineering quantity and the actual engineering quantity. In the process of supervision, the author measured the quantities of some warping dams by section method. As a result, the actual quantities of many dams are inconsistent with the design, and a dam has a difference of more than 30,000 m3.
The engineering quantity of warping dam is an important index in the stages of design, project contracting, bidding and fund control, and it must be accounted before construction.
Second, the supervision of the construction stage
1, sign the commencement order
Before the project starts, the construction unit is required to submit a written application to the supervision engineer. The supervision engineer shall arrange the progress according to the planning documents and supervision plans of relevant departments in that year, and shall clearly understand the following information:
① Whether the inundation loss, land requisition, tree felling and other matters have been properly handled;
(2) Whether the responsibilities for safe construction and flood control are implemented;
③ Whether the work of "three links and one leveling" is implemented;
(4) Whether to sign a construction contract with the construction unit and whether the construction machinery is present;
(5) Whether the building materials are qualified. On this basis, the supervision engineer decides whether to issue the commencement order.
2, construction pay-off inspection
The supervision engineer shall check the line shapes of major buildings such as dams, culverts (holes), stilling basins, horizontal pipes (shafts), spillways and open channels, including horizontal position, vertical position, elevation, excavation section, slope and slope direction.
3. Quality control of foundation treatment project
The foundation of warping dam includes dam foundation cleaning, slope cutting on both sides of dam abutment, joint groove excavation, foundation treatment of drainage structure, etc. Every link of basic engineering is very important. If it is not handled well, there will be accidents such as uneven settlement, leakage, dam landslide and even dam break. Supervision engineers must attach great importance to it, and should often go deep into the site, check against the design, analyze and study the geological situation, and conduct further exploration when necessary. After the foundation project is accepted by the supervision engineer, the construction unit can proceed to the next working procedure.
4. Quality control of drainage engineering
(1) quality control of engineering raw materials
Cement: Check whether there is the manufacturer's factory quality specification, including the factory name, variety, label, factory date, compressive strength, stability and other main indicators. If the supervision engineer has any doubts or questions about the above, he should carry out necessary inspection on its quality.
Sand and gravel: test particle gradation, flatness, specific gravity, silt content and other items. Do not meet the design standards can not be used.
Steel bars and their products: Steel bars shall have ex-factory quality certificates, including factory name, steel grade, brand, ex-factory batch number, specification, quantity, mechanical indexes, etc. Reinforced concrete products should also have factory quality certificates including factory name, specification, model, quantity, compressive index and tensile index. Where the factory certificate is unknown or inconsistent with the real thing, quality inspection should be carried out when necessary.
(2) Quality control of masonry engineering
Masonry can be divided into dry masonry and mortar masonry. Dry masonry is generally used for slope protection or filtration, and mortar masonry is used for building main body. Firstly, check whether the shape and size of masonry meet the design requirements; Secondly, check whether the gradation, thickness and compaction quality of the cushion meet the design; Check the masonry method and quality again, timely correct loose joints, empty bottom, bulging, heavy joints, hanging stones, honeycomb, distorted outline and other phenomena, and require rework when necessary. During mortar masonry construction, the mixture ratio and slump of cement mortar should be checked once per shift. After the culvert is completed, irrigation inspection should be carried out. You can temporarily block the culvert outlet, irrigate it at the entrance with a repaired horizontal pipe or shaft, so that the culvert can bear the water pressure, or put smoke in the culvert. In case of water leakage or smoke leakage, cement mortar or asphalt hemp knife should be used for serious plugging. Concealed works such as culverts can only be buried after the acceptance of the supervision engineer. For the quality control of stone excavation, we should check the center line position, height, slope, section size and slope stability. When excavating spillway, we should also pay attention to the surface flatness, especially whether the flatness at the bottom of the section meets the design requirements. If necessary, we should dig and repair it.
(3) Quality control of concrete engineering
The supervision engineer shall check whether the cement, aggregate and mixing maintenance meet the specified requirements. When pouring, the mixture ratio of concrete must be determined by the batching box and scale, not less than twice per shift, and pay attention to vibrating compaction, and at the same time make necessary tests and records on the concrete label. In addition to the above requirements, the straightness, corrosion degree, protective layer thickness and reinforcement requirements of reinforced concrete should also be checked. In addition, the construction unit must pay attention to the protection and maintenance of concrete engineering.
5. Quality control of earth dam filling.
The control indexes of earth dam filling are mainly filling thickness and dry bulk density. For roller compacted earth dams, the thickness of each layer of soil shall not be higher than 30cm, and it shall be rolled to about 2 1cm, and the dry bulk density shall not be lower than 1.55t/m3. For submerged dams, the filling thickness should be reasonably determined according to the clay content in the soil, and the dry bulk density should not be lower than 1.50 t/m3. Supervision engineers need to inspect the construction site regularly and irregularly, and those who do not meet the requirements shall be ordered to make rectification.
6, engineering change and treatment
Supervision engineers often encounter problems of engineering changes in the process of on-site supervision, so they must treat them correctly and handle them carefully. Here, we might as well divide engineering changes into two categories, namely "goodwill change" and "malicious change". The so-called "goodwill change" refers to the situation that it is really necessary to change the dam site due to improper design or geological problems before or during construction. After consultation with the construction unit, design unit and construction unit, the supervision engineer shall examine and approve the project, issue the approval of engineering design change, and submit it to the superior for approval. After approval, the construction unit can carry out the construction according to the changed drawings. "Malicious change" refers to the unreasonable change requirements put forward by the construction unit in order to save the engineering quantity or due to previous work mistakes, such as moving the dam site and partially lowering the standard, which should be resolutely rejected by the supervision engineer.
Third, the supervision of the completion acceptance stage
1, preparation and self-inspection before acceptance
Before acceptance, the construction unit must prepare acceptance materials, including the basic situation, construction situation, project settlement and final accounts, memorabilia, completion drawings and other contents of the acceptance project, and organize technical forces to conduct self-inspection. If it is found to be inconsistent with the design, it should be corrected in time. After the completion of the project, the construction unit should also clean up the construction site and tidy up the borrow yard in time, do a good job in the layout and protective measures of the internal and external slopes of the project, and clean up the drainage ditches on both sides of the project to ensure smooth drainage.
2. Initial inspection
The initial inspection of the warping dam project is carried out on the basis of self-inspection, organized by the supervision engineer, and attended by the construction unit and relevant technical personnel of the construction unit. During the initial inspection, the supervision engineer must control and measure the dam height, the slope ratio inside and outside the dam, and the structural size of the drainage project (except the hidden part), check the appearance quality of the whole building, and rectify or rework those that do not meet the design and specification requirements within a time limit, and form the initial inspection data to prepare for the final inspection.
3. Final inspection
The final inspection shall be conducted by relevant experts and engineers organized by the competent engineering department. According to the preliminary inspection data of the supervision engineer, the inspection team decides whether to pass the inspection through on-site inspection and sampling of relevant data. If the acceptance is unqualified, it shall be ordered to make rectification within a time limit, and the reinspection shall be conducted on another day; If it passes the acceptance, the project can be handed over and put into use in accordance with relevant procedures.
Fourth, the capital control of warping dam project
The warping dam project implements the central fund reimbursement system. According to the plan document of that year, the fund management department will prepay 30% of the central funds as the project start-up fee, and the supervision engineer will reimburse it according to the image progress of the project (deducting the start-up fee), which is generally reported 2 ~ 4 times a year. 5% ~ 10% of the quality deposit of the construction unit shall be withheld after the project is qualified in the initial inspection and paid in one lump sum after the final inspection. Local facilities and self-raised funds by the masses are raised and managed by the construction unit, and the reimbursement system is not implemented for the time being.
Five, several problems in the process of warping dam supervision
1, the preliminary work is not solid.
Some places blindly promise to win projects. As soon as the project started, land disputes and inundation compensation followed, which affected the progress of the project. Some designs are rough, and warping dams are arranged in places with poor construction conditions, which brings a lot of inconvenience to the supervision engineer to control the construction progress and quality.
2. The release period of planning documents is long.
At present, the plan management mode of soil and water conservation projects such as warping dams is issued by the superior-provincial (municipality directly under the central government, autonomous region) water resources department (water conservancy bureau)-local (city, league) water conservancy bureau (water conservancy bureau)-county (flag, district) water conservancy bureau (water conservancy bureau) step by step. Due to many intermediate links, long cycle and short construction period (except in flood season and winter)
3. The supervision work is more difficult.
Due to the large and scattered area of the warping dam project, the start time of soil and water conservation supervision is short, and the construction unit and the construction unit have insufficient understanding of the position and role of supervision in the warping dam project, which brings certain difficulties to the supervision personnel in controlling the project.
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