Experimental Study On The Deterioration Mechanism Of The Open Channel Lining Of Water Conveyance In The Dry And Cold Areas Of Northwest China

In order to solve the problem of uneven distribution of water resources in the dry and cold areas of Northwest China,my country has built many long-distance water transmission and transfer projects.Among them,the concrete open channel is one of the most important structures in the series project.The open channels have been exposed to sunlight,freezing,water power and harmful ions for a long time,causing frost heave and cracking of the lining board,leakage of the slope,and exposure of pebbles on the floor.The structural safety of the open channel affects the irrigation,people’s livelihood and ecological issues of the entire region.This article takes the open channel linings of Bring the university into the qin project as the research object,combined with the National Natural Fund’s"Research on the Deterioration Mechanism of Long-distance Open Channels under the Coupling Effect of Multi-factors in the Salty and Dry Cold Regions of Northwest China",to carry out the deterioration mechanism of the open channel lining in this area.the study.This paper analyzes the characteristics of the open channel linings disease through the prototype channels observation and on-site sample collection of Bring the university into the qin project,and determines the solution erosion medium for the indoor accelerated test.Based on the existing mature theory,a simple numerical simulation of the open channel lining head was done through finite element software.In the experiment,two mass fractions of double salt solutions were used as the erosion medium,and clear water was used as a blank comparison;three damage methods were set up:dry-wet cycle,freeze-thaw cycle,and dry-wet-freeze-thaw cycle;Based on the water-cement ratio used in the lining,the test adds two water-cement ratios for comparison;a total of 27 working conditions are analyzed for the test law.The 27 working conditions are classified by the destruction method,and the response surface fitting analysis is carried out.The mass loss rate R₁,the compressive strength loss rate R₂,and the relative dynamic elastic modulus R₃ under the three failure modes are used to establish response surface analysis indicators,and for these three indicators,establish the water-cement ratio A,the mass fraction B,and the number of cycles.C is the fitting analysis equation of the three factors.The main conclusions obtained are as follows:（1）Clarified the related mature theories of concrete freeze-thaw failure such as the hydrostatic pressure hypothesis,summarized the deterioration mechanism of open channel linings in detail,and determined the failure mode of open channel lining in this area.Combining the existing meteorological data and hydrological data,on the basis of the existing mature theory,a simple numerical simulation analysis of the open channel linings at the head of the canal is carried out,and it is found that the stress and strain of the open channel linings slab is the largest during the lowest temperature period.（2）The analysis of the test results shows that at the beginning of the test,the appearance of the concrete was slightly damaged and the overall structure was good;in the middle of the test,the corners of the surface of the test pieces were cracked and the aggregates were exposed,but it had not reached the level of complete destruction;In the later stage,large cracks appeared in the specimens,which caused the concrete blocks to fall off,and even a large amount of coarse aggregate fell off,and the integrity of the specimens were lost.According to the test designed in this paper,the durability rule is based on the test failure mode,and the order of the damage degree is:dry-wet-freeze-thaw cycle>dry-wet cycle>freeze-thaw cycle;in the case of different water-cement ratios,as the water-cement ratio increases,The more severe the damage of the specimen.The order of damage degree according to the water-cement ratio is:0.35>0.45>0.55;under the erosion of different mass fractions of the double salt solution,the damage degree of the concrete specimen is proportional to the mass fraction of the double salt solution,and the order of damage according to the mass fraction of the erosion solution is:5%>3%>0%（clear water）.Under different test ages,the damage of concrete specimens is positively correlated with the number of cycles.（3）From the analysis of the response surface results,it can be seen that for the mass loss rate R₁,the compressive strength loss rate R₂,and the dynamic elastic modulus R₃,the difference between the water-cement ratio A and the mass fraction B is not obvious,and the water-cement ratio The degree of influence of A is slightly higher than that of quality fraction B,and the degree of influence of cycle number C is much greater than the other two factors.The response surface method is suitable and effective for explaining and predicting the response changes under the interaction of three influencing factors:water-cement ratio,erosion mass fraction and cycle number.This article provides some theoretical foundations for the design and construction of long-distance water delivery projects in the complex environment of this area through the indoor accelerated test research and durability index fitting analysis of open channel linings in the cold northwestern region.