Dangers that often occur in dam engineering in flood season include: wind and waves impact the dam, causing the dam body to collapse in large areas in front of the water surface, bank collapse of the water crest, use of pipelines, soil flow, landslide caused by loose eluviated soil on the back slope of the high dam, and water gushing from springs at the foot. The basic method of emergency rescue is to revetment and block with soft sinking drainage in front of the water surface, drain seepage with soft drainage on the back of the water surface, and ballast the drainage body with non-slip woven bag or pillow bag.
1, high water level, large area, heavy wind and waves, dangerous operation and emergency protection. The section and standard height of dikes in some rivers meet the standard, but the soil quality of dikes is poor, which is easy to be washed away under the action of wind and waves, and the safety of dikes is often endangered when the water level is high. When this happens, the front line is often very long, the protection is difficult, and it takes manpower and material resources. In an emergency, a large number of trees nearby have to be cut down as temporary protective materials.
The method of grasping and protecting with geotextile is to hang soft rows of anti-aging geotextile on the slope, with one cloth and one membrane geotextile, with the cloth facing up and the membrane facing down. The upper part is fixed on the top of the dike, and the lower part is protected to 60cm below the slope valley. It is generally considered that it is very convenient to use wide geotextile for row when the lower part is protected below danger1m. The advantage of this emergency rescue method is that it can be quickly arranged and removed immediately after the flood, and can be used again next time.
Laying: firstly, ditch is dug to fill the embankment or pile, and the upper part of the row body is fixed, then the row body is rolled on the slope by the bottom pillow of the row body, and an assembled soil anti-slip woven bag is pressed on the row body every 3-5m according to the situation. There is an overlap of 50cm between each row, and the overlap must be ballasted.
Dangerous workers are scrambling to protect the beach at the top of the current. During flood discharge, the river bank bends to meet the current.
At the same time, due to the rise and fall of slip potential, the lower part of the dam collapsed and dangerous work occurred. The bank slope has just escaped from danger and has not collapsed into a cliff. In order to prevent the early rescue work in danger, it is only necessary to hang and sink into the weaving raft at the dangerous position until it reaches the bottom of the river, which can not only prevent the earth embankment from collapsing. If the danger develops to a certain extent and the bank slope collapses seriously, the suspension range must be expanded.
3. Vulnerability rescue. Due to the poor quality of embankment fill, or hidden dangers such as cracks and caves, under the action of high water level, water gushing holes will appear on the back slope of embankment or near the toe of embankment, and the water flow will be from small to large, from clear to miscellaneous, and the embankment will be stung and collapsed, which is serious. If it is not blocked in time, it is easy to form a burst bank. The emergency protection method is to block the water inlet, cut off the water flow, and set up a filter well at the outlet to raise the water level at the outlet, reduce the velocity of the surge tank and intercept the sediment flow.
The imported cushion adopts geotextile, one cloth and one film. Generally, the mattress is 5m wide and sinks into the upstream slope, and both sides are filled with anti-slip woven bags to prevent the mattress from moving. The method of adjusting the drainage and sand blocking at the outlet is to ballast the drainage body (5m×5m) around the backwater groove with woven bags, and then install a drainage well around the drainage body with anti-slip woven bags, and put gravel into the well for ballast, with a thickness of 20-50? If the filter soil is not lifted, there is no need to fill gravel. The requirement for woven cloth is to retain sand and filter water, not too dense or too thin.
4. Piping and soil flow. For sandy gravel foundation with strong permeability, piping or soil flow is easy to occur when it meets high water level. Once piping or soil flow occurs, the fine soil in the dike foundation will be taken away, and the dike body will collapse and collapse, which will lead to dam failure in serious cases.
When geotextile measures are adopted to grab the protection, the piping and soil flowing areas shall be cleaned and leveled first, and sharp sundries shall be removed, and then the spring shall be filled with permeable materials such as coarse sand and gravel, paving 300 ~ 400 g/? Non-woven fabrics, with overlapping sheets, are manually stepped on the periphery to embed the geotextile in the soil, and then the geotextile is spread from the periphery to the center with permeable materials for 20-50? Its thickness depends on the water pressure. The scope of geotextile laying should be more than 0.5m beyond the spring water, forming high, medium and low sides, and the piping area should be repaired with soil.
According to the data, this method has been applied to the Fanshan Lake dike in Duchang, Jiujiang. The whole dike was soaked in springs at 65,438+880 m, and piping occurred locally in the dike body, causing stabbing pain under the dike. When serious danger occurs, use it, and the danger will be eliminated soon. A similar situation has occurred in the emergency rescue of Nenjiang levee. Therefore, the author believes that geotextile should be actively promoted and applied in water conservancy projects, especially in various small and medium-sized projects, as long as the design and construction are correct.