The Experiment Study On Dynamic Evolution Process And Critical Hydraulic Conditions Of Barrier Dams Failure

The geological disasters such as landslides,collapses,and debris flows are widely distributed and occur frequently in the strong earthquake areas.The loose materials entrained by various geological hazards are very easy to block narrow channels and river channels,forming a barrier dam.The barrier dams not only cause backwaters to flood the upstream areas,but once they break down,they often induce flood and debris flow.It will form disaster-chain,which are extremely harmful.Because the failure process of barrier dams is very fast,it is difficult to collect real-time information on the dam contour and internal dynamics at the time of the failure process.And the failure is complex and has many influencing factors.It is extremely difficult to carry out related research.There are still few studies on the dynamic evolution process and critical conditions,which has become the focus and difficulty of the current geological disaster-chain research,and urgent research is needed.Therefore,this study takes the typical debris flow gully in the strong earthquake area-Goulinping barrier dam as a prototype.Based on the collection of basic data,field investigation,real-time monitoring,and indoor and outdoor soil hydraulic parameter testing,and using the indoor model test as the main research method.Design 8 sets of dam simulation test combined with different control factors such as dam body size,particle gradation,low groove slope and upstream flow,and carry out the simulation test of the failure process of barrier dams.The dynamic evolution process established the vertical evolution mode of the failure process,explored the influence and role of the key control factors on the failure process to reveal the failure mechanism of this type of barrier dams.And based on this,the critical hydrological conditions for the failure are calculated.This will provide scientific basis and technical support for monitoring,early warning and prevention of the disaster chain.Main results and conclusions are as follows:(1)The change trend of water content in dam body:Before outbreak,wetting front moves from the water slope to the backwater slope,and from the bottom to the top.The infiltration process and wetting front of the notched face are faster than the non-notched face.(2)The failure process of barrier dams can be divided into three stages: erosion start,erosion acceleration and erosion weakening.For longitudinal surface profile changes of the barrier dam,at the beginning,due to small water flow,the erosion first began at the gap,and eroded particulate matter was deposited on the downstream slope surface,resulting in the contour of barrier dam is irregular during this period.As the gap increases,the amount of water increases,and the irregular longitudinal profile quickly flattens due to rapid flow of water and sediment.Water level in front of the dam is gradually reduced,hydrodynamic force is weakened,the amount of change in barrier dam is reduced,and there is sediment accumulation near the barrier dam foot.For horizontal surface profile changes of the barrier dam,at the phase of erosion start,the backwater slope is mainly undercut erosion.At the phase of erosion acceleration,the lateral and vertical erosion are strengthened,and the soils collapse on both sides.And at the phase of erosion weakening,the erosion is mainly on both sides.There are three important erosion phenomena in the failure process of barrier dam: slope instability,"steep ridge" and collapse.(3)During the phase of erosion accelerated and erosion weakened,erosion rate and shear stress of the midpoint of barrier dam cross section,the vertex of the backwater slope and the midpoint of the backwater slope have a linear relationship.And erosion resistance is strong in the middle of the barrier dam,weak in the backwater slope.(4)Based on the statistical analysis of the longitudinal slope profile change and erosion rate of the failure process of barrier dams,a new longitudinal evolution model of the failure is proposed: the erosion rate increases first and then decreases along the direction of the water flow,and the maximum erosion point shows a traceable movement.And it reaches the maximum in the middle of the barrier dams.(5)When the median diameter is less than 5mm,the larger the median diameter,the greater the permeability coefficient,and the larger the saturation range of the soil before the failure,which increases the erosion rate and shortens the duration of the main failure process.The greater the amount of incoming water and the slope of the bottom channel,the stronger the hydrodynamic force,which increases the erosion of the barrier dam and shortens the duration of the main failure process.The smaller the size of the dam,the less the soil material,and the weaker its erosion resistance,the shorter the duration of the main failure process.(6)Taking the starting speed of non-uniform sand and the flow rate of rupture as cut-in points,the formula for the critical failure head is introduced,and good simulation results are obtained in the verification of actual critical failure head:(?)The above research results reveal the dynamic evolution process of barrier dam,the influence of various control elements on the process and the critical hydrological conditions of the rupture,making up for the deficiencies of this type of dam break research.The research conclusions provides scientific basis and technical support for scientific monitoring,accurate early warning and emergency treatment of the failure in strong earthquake areas.And it also provides disaster prevention and mitigation of geological disaster chains in strong earthquake areas.