A brief discussion on dam crack and leakage rescue techniques?

A brief discussion on the specific contents of dam crack and leakage rescue technology, Zhongda Consulting will answer it for you below.

1 Danger of cracks

1.1 Types of cracks

Turtle-shaped cracks. Turtle-shaped cracks mostly appear on the surface of earth dams, and are evenly distributed. The cracks are thin and short, and they are less harmful to the dam. The main reason is that the water in the clay soil evaporates and the surface soil shrinks, so it is also called dry shrinkage crack. The greater the viscosity and the higher the moisture content of the filling soil material, the greater the possibility of dry cracking; transverse cracks. The direction of transverse cracks is perpendicular or oblique to the axis of the dike. They often appear at the top of the dike and extend into the dike to a certain depth. In severe cases, they can develop to the dike slope, or even penetrate upstream and downstream, causing concentrated leakage, directly endangering the safety of the dike. Mainly caused by the large uneven subsidence of the dam foundation in adjacent dam sections, which often occurs in the closing section of the dam, the construction joint section between the dam body and the junction, and the dam section with large compression deformation of the dam foundation; longitudinal cracks. The trend of longitudinal cracks is parallel or nearly parallel to the axis of the dam. They often appear on the top of the dam or on the upper part of the dam slope. The cracks gradually extend vertically into the dam body. It is generally longer than the transverse crack. If not treated in time, the intrusion of rainwater will cause the dam to fall off; internal cracks. The causes and possible locations of internal cracks include: For example, when an earth dam is built on a foundation with high compressibility in a narrow valley, during the settlement process of the dam body, the weight of the upper dam body is transferred to both ends through the action of shear force and arch. into the mountain and bedrock, and the lower part of the dam body sinks, which may cause the dam body to be pulled apart on a certain plane, forming horizontal cracks; in addition, uneven subsidence occurs at the dam foundation or at the contact point between the dam and the building. Internal cracks, etc.

1.2 Protection of cracks

Excavation and backfilling. The excavation and backfilling construction is simple, the crack treatment is more thorough, and the effect is better. It is suitable for cracks that are within 5m in depth and have stopped developing. Before excavation, a small amount of lime water should be poured along the crack to control the scope of the excavation. The depth and width of the trench should exceed the crack by 0.3m to 0.5m, and the length should exceed the crack end by 1m. Ladder steps. When the trench is excavated, the trench should be dug along the seam to maintain a trapezoidal cross-section to facilitate the integration of the original embankment. When the crack is deep, a stepped trench can be dug with a step height of 1.5m. It is not advisable to pile soil materials near the notch to facilitate excavation and construction safety. Before backfilling the trench, the steps should be cut off, the trench walls should be moistened with water and shaved, then backfilled with the same soil material as the original dam body, and compacted in layers. Cross-shaped binding groove. Suitable for transverse cracks across embankments. During excavation, set up a binding groove perpendicular to the crack every 5m to 6m along the direction of the crack. When backfilling, attention should be paid to the combination of new and old soil. During the flood season, the slotting method is suitable for protecting cracks above the flood level. Generally, crack treatment should be carried out during the dry season or after the water level is lowered. If necessary, temporary cofferdams should be built on the upstream dam slope for safety. Turtle-shaped cracks are generally not treated. If treated, they can be sealed with mud, or the cracked soil layer can be loosened, moistened and compacted, and the surface layer can be covered with sandy soil for protection.

Fill with grout. For deeper cracks, the grouting method can be used, or the upper part can be excavated and backfilled and the lower part can be grouted to reduce the amount of trenching work. The top of the grouting part must be maintained with an excavation backfill layer of more than 2m as a grout blocking cover to prevent slurry from spraying out. Pre-embed grouting pipes (iron pipes or bamboo pipes) during backfilling. If conditions permit, the grouting method of segmentation and grouting can be used, which will achieve better results. The grout concentration should be thin first and then thick, and the grouting pressure should be from small to large.

2 Leakage and rescue operations

2.1 Classification of leakage dangers

Water leakage dangers. Under the action of high water level, water seeps into the dam, dividing the dam body into two parts: upper dry and lower wet. The dividing line between dry and wet soil is called the infiltration line. The slope surface and slope foot below the infiltration line may be in danger of water seepage. The direct causes of dangerous water seepage are usually the sandy soil layer in the embankment body, the embankment body is not solid, and there are snake and mouse holes, termite holes, badger holes, rotten tree roots, waste culverts, hard soil, masonry and other debris in the embankment. . A thin dam section and too steep backwater slope will increase the seepage velocity, raise the infiltration line, and accelerate the development of dangerous water seepage situations; dangerous piping situations. When the dam is at high water level, the seepage slope of the highly permeable foundation is greater than the critical slope of the covering layer. Seepage causes fine particles in the soil to move along the pores and be brought to the ground, forming a sand ring around the seepage outlet. As the amount of lost soil particles increases, the sand ring becomes thicker, and passages throughout the dam gradually form, causing dangers of piping and drifting soil. When the seepage force exceeds the effective pressure of the topsoil, the soil at the embankment slope or at the foot of the slope will be destroyed, forming a sand boil or the soil will be washed away, resulting in dangerous soil erosion and dangerous leaks.

Dangerous situations such as water seepage, piping or flowing soil are not rescued in time, and the continued development will cause concentrated seepage, massive soil loss, and gradually form a seepage channel that runs through the dam or penetrates the foundation. This is called a leakage hazard. The most dangerous situation is the muddy water with sand and soil flowing out of the leakage. .

2.2 Emergency protection in case of dangerous leakage

Principles and methods of emergency protection: seepage interception on the waterfront slope and reverse filtration and seepage conduction on the backwater slope.

Seepage interception on waterfront slopes: The main protection methods include: geomembrane interception, plugging leaky water inlets, loose clay interception and other methods; geomembrane seepage interception: when the hole is large or near the hole For more, a large area of ??geomembrane or tarpaulin can be used to cover the hole from top to bottom along the shoulder of the water-facing slope of the dam, and then the soil bags are thrown and filled, and the clay is thrown and filled to form a front wall to intercept seepage; the loopholes can be plugged to enter. Water inlet: The most effective way to deal with dangerous leaks is to promptly and accurately block the water inlet; scattered clay interception: when there are many small holes on the water slope of the dam and the scope is large, and the water inlet is difficult to find or cannot be found completely, in Where there is sufficient clay material, clay can be scattered along the waterfront slope to form a seepage barrier.

Backwater slope reverse filtration and seepage conduction: reverse filtration and seepage conduction ditch. At the seepage point at the foot of the backwater slope, a longitudinal trench parallel to the axis of the embankment is excavated and connected to the original drainage ditch. At the same time, a vertical trench is excavated along the slope at the top where water seepage occurs.

The sand and gravel filter material should be filled in the seepage trench. It should be filled in layers and should be constructed in sections from the foot of the slope upward. It should be filled as it is excavated and no work should be stopped to wait for materials. After the reverse filter material is filled, woven bags, straw bags or mats should be laid on the top surface and compacted with stones and earth. Where conditions permit, geotextiles can be used as seepage trenches. Geotextiles with effective apertures should be spread around the trenches. The middle should be filled with permeable water material, and the upper part should be covered with straw bags, mats, earth bags, etc. In areas where sand and gravel filter materials are lacking, fine materials such as wheat straw and rice straw and coarse materials such as willow branches and reeds can be used as drainage trenches. The material is pressed fine and thick at the top, with the roots upward and the tips downward. The upper part is compacted with earth bags, rocks, etc. All seepage trenches must be connected to slope toes and drainage ditches.

The method of the reverse filter layer is: first remove the soft mud, turf, masonry and other debris on the ground, and then fill the reverse filter layer with sand, gravel, geotextile, tip materials, etc. according to the requirements of the reverse filter layer. Material. The anti-filter material and rocks should be appropriately extended beyond the foot of the slope. For places where the embankment body is thin, the water seepage range is large, and there is a lack of sand and gravel materials, fine materials such as wheat straw and straw and coarse materials such as willow branches and reeds can be used to filter the anti-filter material. After the water filter is made into layers, the tip material should be thin at the top and bottom and thick in the middle. The upper part of the tip material should be filled with soil and compacted. Spread a layer of material and fill with a layer of soil until the height of the post-cutting is planned.

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