Sand and gravel processing system of Xiaolangdi earth-rock dam?

What is the specific content of the sand and gravel processing system of Xiaolangdi earth-rock dam? The following Zhong Da Consultation will answer your questions.

1 introduction

Xiaolangdi Dam is an earth-rock dam with clayey inclined core wall, with a height of154m and a crest length of1666.3m. The total filling volume is 565,438+847,000 m3, including 26 1 10,000 m3 of filter material and 3.2 million m3 of transition material. The gravel processing system of Xiaolangdi earth-rock dam is mainly used to produce dam filter material and transition material. The filter material plays an important role in protecting the impervious soil material from being taken away by seepage water, and the transition material plays a role in protecting the filter material of earth-rock dam and transitioning to the rockfill area. Moreover, the dam filling construction requires the horizontal filling of filter materials and transition materials, so the production quality and output of filter materials and transition materials directly affect the quality and progress of earth-rock dam filling construction.

Xiaolangdi Dam was built by the Yellow River contractor with the internationally renowned Italian company Inbojillo as the responsible party, and the sand and gravel processing system of the dam was also designed and built by them. The system not only mainly produces filter materials and transition materials, but also undertakes the production of various materials needed by the dam, such as concrete aggregate, mixed aggregate in Area 5, subgrade materials and so on. The process and layout of the whole system are much more complicated than that of a simple concrete aggregate processing system, which requires that the design and layout of the system are highly compatible and open, and that the system has a high level of operation and management to ensure its normal and stable operation. The treatment system was put into operation in June 1995. After five years of high-intensity construction, the dam was successfully filled with water at the end of June 2000, 13 months ahead of schedule. The filter materials and transition materials produced by the dam sand processing system played an important role in this victory. Moreover, it is the first time in China to use alluvial sand and pebbles in the same system to produce filter materials and transition materials for earth-rock dams, and a sand and gravel processing system with a capacity of up to 1600t/h has been designed, which has accumulated valuable experience.

2, material source and finished product material gradation

2. 1 material source

Coarse filter material and transition material are taken from Maduntan yard 6 ~ 7.5 km downstream of the dam site, with an exploration reserve of about 7.66 million m3. The natural gradation is shown in table 1. As can be seen from the table, about half of coarse sand (1.2 ~ 5mm) and pebbles (5 ~ 20mm) are used, while fine sand (1.2mm) is used.

2.2 Grading requirements of filter media The three kinds of filter media 2A, 2B and 2C required to be produced in the contract documents are composed of sand and gravel with proper grading, and three grading curves are put forward. In order to accurately match the filter materials and promote the production of concrete aggregates needed for dam foundation by using this system, the contractor calculates the theoretical weight percentage of various aggregates according to the grading curve shown in Table 2:

As can be seen from the above table, the particle sizes of filter materials are all below 80 mm, among which 20~5 mm and 5~ 1.2 mm are used in large quantities. The processing system produces finished sand and gravel aggregates with different particle sizes according to the particle size range in the above table, and uses an accurate weighing system to fully mix them according to the percentage in Table 2 to meet the requirements of filter material grading in the contract documents. 2.3 The gradation requirements of the transition materials shall comply with the requirements of the contract documents and the approval of the engineer. See curve 1 for the gradation curve of the transition materials.

It can be seen that the maximum particle size of the transition material is 250mm, the particle size above 80 mm exceeds 50%, and the particle size below 5 mm only accounts for about 65,438+00%, with coarse particles and less requirements for fine materials. 3. Analysis of process flow and system layout The system is divided into two parts according to the difference of main finished products: transition material production part and filter material production part. According to the natural gradation of material source and the different gradation requirements of filter material and transition material, the production process design of transition material and filter material of the system has its own characteristics. The actual production shows that the initial process design and layout of the system are basically reasonable and successful, but there are also some problems. The contractor made some improvements according to the actual production conditions and needs. The final flow and layout of the production system are as follows. 3. 1 process flow

The process flow of the system is shown in figure 1.

As can be seen from the figure, the processing technology of this system is totally enclosed except that the oversize material over 500mm is discarded during wool pre-screening, with less discarded materials, high wool utilization rate and reduced repeated transportation. According to the different grading requirements of filter materials and transition materials and the non-overlapping characteristics of peak demand on the dam, the system design has strong adjustment ability. Materials below 80 mm are mainly used as raw materials for filter materials, and materials above 80 mm are mainly used as raw materials for transition materials. The two production systems of transition material and filter material are independent of each other and can be adjusted with each other. The transition pile of filter material and wool pile are close together, and when the raw material of filter material is insufficient, the transition material can be automatically replenished. 1May, 1998 Before the transformation of transition materials, C28 belt conveyor was used to transport artificial crushed stones from the filter material system to the transition materials, so as to increase the crushed stone content of the transition materials, improve the gradation of the transition materials and increase the production capacity of the transition materials. This design can give full play to the production potential of the two parts, balance production and save production resources. According to the characteristics of filter material undertaking multiple production tasks, the parallel design of its screening, crushing and sand making systems can improve the system utilization rate. If one road breaks down, the other road can still run normally, reducing the impact of production stoppage on the project schedule. In the production of filter media, due to the imbalance between the gradation of natural materials and the gradation of finished products, as many as seven medium and fine crushers (two of which are used to prepare coarse sand) are designed to adjust the balanced production of the system. Because the natural materials contain less coarse sand and more fine sand, but the finished materials need more coarse sand and pebbles, and the demand for fine sand is not great, so the sand is prepared in two stages, so as to facilitate the manual production of coarse sand and discard excess fine sand. All these make it more difficult to design and prepare the sand making system. At first, the system was designed to make sand with pebbles through a rod mill. With the increase of demand, two cone crushers were added. At the same time, it is found that pebbles are not enough, and the efficiency of making sand from pebbles in cone crusher is not high, which is easy to block. Therefore, the rod mill and cone crusher are used to prepare Zhongshi at the same time. The contradiction of insufficient pebbles was solved, but at the same time, it was found that when the rod mill was used to make sand, the material contained a small amount of pebbles, and the screen with a diameter of 5 mm was not designed behind the rod mill, which made a small amount of over-diameter pebbles appear in the coarse sand, and the content was unstable, which brought trouble to the precise preparation of filter materials and affected the quality of coarse sand and the progress of the project. 3.2 System Layout The plane layout of the system is shown in Figure 2, which is arranged along the process from transition material to filter material, from screening to crushing to sand making. The feed inlet is at one side of the material yard, and the finished material is discharged at the dam side. Dump trucks receive materials under the dump hopper and transport them directly to the dam without transshipment.

The transition material part includes raw material pre-screening building, screening and coarse crushing building, finished product pile and its unloading bin. The filter material part includes wool pile, screening building, middle and fine crushing building, sand making system, finished aggregate pile, batching system and unloading bin. The system layout is quite compact, which is convenient for centralized operation and management. The operation of the whole system is completely controlled by computers in three central control rooms, among which H 1 room controls the production of transition materials, H2 room controls the production of filter materials, and H3 room controls the configuration of filter materials. The operation of these three parts is independent of each other and does not interfere with each other, and any part of them can run independently as needed, which makes the system more flexible in production and enables the system to be overhauled and maintained according to components. When a part of the system fails, other parts can run as usual, so that the whole system will not be paralyzed and the influence of some failures on the whole project schedule can be reduced. 4. The production capacity of the production capacity analysis system directly affects the progress of the project. If the production capacity is designed too little, it will delay the dam filling progress, but if it is designed too much, it will cause unnecessary waste. According to the overall construction schedule, the peak filling strength of transition materials is198,000m3/month, and that of filter materials is 7100,000m3/month (including other 500,000m3). Considering the peak coefficient, the transition material is 1.05 and the filter material is 1.25, and the production efficiency is 85%. The designed production capacity of transition materials is1100t/h, that of filter materials is 750t/h, and that of total production capacity is1600t/h (the peak periods of transition materials and filter materials do not overlap, so the total production capacity can be adjusted, so the total production capacity is less than the sum of them), which can meet the requirements. However, in actual operation, the problems of rough transition materials and serious separation once appeared. In order to ensure the quality of transition materials, the system was reformed twice. The first time was 1 month, 1997, which mainly solved the problem of coarse transition material. C28 belt conveyor is used to provide fine materials for transition materials, and the opening size of coarse bucket crusher is reduced. In the second transformation, in the first half of 1998, a cone crusher was added to replace the fine materials supplied by C28 belt conveyor, and all the transitional materials were input into the finished product pile through the same belt conveyor to reduce separation. After two transformations, the problems of rough and separated transition materials were successfully solved. However, due to the reduction of the opening size of the share crusher, which controls the overall production capacity, the C28 belt conveyor that transports transition materials from the filter material production part stops running, which makes the total production capacity and transition material production capacity of the processing system decline. In actual operation, the total maximum production capacity in peak period is only 1335t/h, the maximum production capacity of transition material is only about 900t/h, and the maximum production capacity of filter material is 732 t/h. It can be seen that the transformation has great influence on the production capacity of transition material, but has little influence on the production capacity of filter material. In addition, from the second half of 1998 to before the flood season of 1999, the dam filling was accelerated at the request of the contractor and the flood control situation of the Yellow River, which further aggravated the contradiction between the filling quality and progress of transitional materials and filter materials. Xiaolangdi project is a Millennium project, quality comes first, and quality cannot be sacrificed to ensure the progress. Finally, through the drilling and blasting excavation of other material fields, the existing slope protection material processing factory is used to screen the transition materials; In view of the characteristics that the filling peak of filter material is relatively lagging behind, by opening an intermediate storage yard, the production peak of filter material is advanced and the surplus is used for the filling peak, which successfully meets the requirements of speeding up the construction without affecting the filling quality. 5. The best design of equipment selection and operation management will eventually realize the production of finished materials through equipment and its operation. Better selection of equipment and scientific management and operation can ensure product quality and project progress. 5. 1 Equipment Selection Except for steel structure and non-standard equipment, the processing system is imported from abroad (mainly Italy and France). According to the requirements of process design, the treatment system is huge and there are many equipments, including 1 17 sets. Main equipment, such as crushers, including 9 crushers, cone crushers and gyratory crushers. There are 16 different types of vibrating screens and static screens in dewatering screen. There are 37 belt conveyors with a total length of about1700m, and there are four models:1200mm,1000mm, 800mm and 650mm. The production situation in recent five years shows that the system equipment runs stably and reliably, the equipment utilization rate reaches about 85%, and the intact rate of main equipment is 100%. Compared with similar treatment systems in China, sand washing and dewatering equipment, computer automatic control operation and computer weighing and batching system for filter materials are particularly advanced. The sand washing and dewatering equipment has changed the situation of single use of spiral sand washer in China in the past, and adopted a variety of equipment including sand washing tank, static screen, vibrating screen, cyclone and vibrating dewatering screen. The sand washing and dewatering equipment has achieved good results. The silt content of sand is about 2.5%, the water content of coarse sand is 7%, and the water content of fine sand is about 18%. After storage and drainage, it completely meets the quality requirements of filter materials and concrete aggregates. The computer automatic control operation and computer weighing and batching system of filter material adopts Siemens automatic control system in Germany, which realizes the automatic control of all equipment operation and computer weighing and batching of filter material, makes the system operation and batching of filter material fast and accurate, and plays an important role in ensuring the progress and quality of the project. 5.2 The management of the operation management processing system is under the overall responsibility of a foreign supervisor, including 4 electromechanical and quality inspection engineers, 40 production workers and 30 maintenance workers. The main contents of management include producing qualified transitional filter materials according to the dam filling progress, maintaining the system to ensure its continuous normal operation, and purchasing spare parts in advance according to production experience. The system produces 20 hours a day and the equipment is maintained for 3 hours. No matter what happens, the maintenance time is guaranteed. The maintenance contents mainly include: checking whether the waterway, circuit, oil circuit and automatic control system are normal every day, checking whether the opening size of the crusher is reasonable, checking whether the screen is damaged or blocked, supplementing and adjusting the steel bars of the rod mill, replacing worn parts, etc. Equipment maintenance is an important aspect of system management, which is very important to ensure the lasting and normal operation of the system. Some maintenance measures are insignificant, but they have a great impact on product quality and production efficiency. For example, static screen, vibrating screen and dewatering screen used for screening and washing dehydrated sand are easy to be blocked due to their small pore sizes, so it is necessary to knock and wash the screen to clear the blockage during maintenance, otherwise the screening efficiency will be reduced, and the screening will be incomplete, and the coarse sand contains fine sand, which will affect the quality of coarse sand, thus affecting the quality of filter materials. It is also very important to check the opening size of each crusher every day and adjust it to a reasonable opening according to the crushing characteristics, raw material characteristics and aggregate balance requirements of the system. Fig. 3 is the grading curve before and after the typical quality improvement of filter media in area 2 B. The filter material in area 2B is composed of three kinds of aggregates in a certain proportion: small stones (5 mm ~ 20 mm), medium stones (20 mm ~ 40 mm) and large stones (40 mm ~ 80 mm). The first curve is that the quality of the mixed filter material is unqualified and exceeds the lower envelope of the envelope, because the fine material content is not enough; The second curve is the mixed result after increasing the pebble content. The curve rises upward, but does not exceed the lower envelope, but exceeds the upper envelope. The reason is that the pebble content below 10mm is too little, but the aggregate below 10mm is really lacking, and the pebble content (5mm~20mm) is simply increased, among which the aggregate with the particle size of 10mm~20mm is also increased. Therefore, simply increasing the pebble content cannot solve the problem of thin material, and we should try our best to increase the pebble content below10 mm. Finally, according to the properties of aggregate, the crushing characteristic curve of crusher is checked at the same time. Through many tests, the opening of the medium-fine crusher is adjusted to a reasonable size, so that the maximum content is below 10 mm. Then, the pebbles produced by adjusting the opening of the crusher are still mixed with the three kinds of aggregates when bending, and the qualified filter material in zone 2B is made, as shown in Figure 3.

6. Conclusion Sand-gravel processing system can produce filter material and transition material for earth-rock dam. Its production directly affects the quality and progress of earth-rock dams, and its influencing factors are complex and multifaceted, which need to be further studied in actual production and analyzed in detail. As far as filling quality and progress are concerned, quality is the first, and we can't simply pursue progress and ignore quality at any time. The filling quality of filter material and transition material of earth-rock dam should be tested from the production of finished material processing system, and the processing system should be adjusted reasonably according to the actual testing situation finally fed back from the filling site until it meets the requirements of technical specifications. After five years of high-intensity construction by Chinese and foreign builders, the filling operation of Xiaolangdi dam shows that the construction quality is good, and the quality and progress have been improved, and its sand and gravel processing system has contributed greatly. In addition, the design, installation, operation and management of sand and gravel processing system is an applied and experienced complex work, involving geology, water conservancy and hydropower, electromechanical, automatic control and management. This requires the cooperation and efforts of various professionals. The professionalism and rich management experience of foreign contractors are also worth learning.

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