Study On The Service Life Of X-type Flexible Mattress Under Unsteady Flow Conditions

The X-type flexible mattress is a kind of soft drainage protection beach building in waterway regulating structure.This kind of structure in waterway regulating application mainly uses its isolation and the filtration function to prevent the channel condition from changing to the disadvantageous direction,and to avoid the local deformation of the riverbed caused by the water flow directly scouring and the water seepage,so as to protect the bottom and the beach.According to the irreplaceable function,X-type flexible mattress is widely used in waterway regulating engineering.In the course of construction and maintenance of waterway regulating project,the waterway department has accumulated a lot of observational data and research results,but there are still some technical problems to be overcame,and the prediction of service life of waterway regulating building is one of the problems.Based on this,this paper has carried out the research work on the service life of X-type flexible mattress in waterway regulating buildings.Through data collection,extensive investigation,theoretical analysis and generalized model test,this research is based on the time-dependent reliability model of X-type flexible mattress.The main results are as follow:(1)Based on stochastic hydrology theory and mathematical statistic method,a new method of unsteady flow simulation is proposed.Through this method,we find an index that reflects the magnitude of discharge and variable rate feature to describe the unsteady flow process.(2)The time-dependent reliability model of X-type flexible mattress is established based on the analysis of the antiskiding stability and the reliability theory.(3)The strained condition of tie in X-type flexible mattress is complicated.The interaction between block and block,the change of the shape of the beach body and the unsteady flow process all make the strain of the tie to be time-dependent.According to the trend of change,tension-time curve can be divided into three type,respectively are continuous tense type,continuous relaxation type and repeated change type.The occurrence regions of larger value in the maximum variable tension of the tie are straight segment of slot of the beach body and beachhead near the top of the slope.(4)The structure characteristics of the beach body have significant influence on the flow velocity and the tensile distribution of the tie.The effect on the flow rate is reflected in hammed water effection around transition section of slot and beach body,the greater the steep slope gradient,the more obvious the effect of hammed water effection,and the phenomenon of hydraulic drop after hammed water is more obvious.This phenomenon shows that the larger the slope gradient,the higher the flow velocity,also the wider the distribution area of the maximum value.The effect on the force of tie tension is reflected as that the larger the slope gradient of the beach under the same position,the larger the maximum value of tension.(5)The method of calculating the critical failure-tension of tie in X-type flexible mattress is established,and the predicting method of service life based on the prescribed failure index of different beach bodies under different flow rate is put forward,combined with the time-dependent reliability model.