Water Filling Load Test And Bearing Capacity Safety Evaluation Of Kezi River Aqueduct

The climate change in Xinjiang is obvious,the temperature difference between day and night is big,and the weather such as gale lasts for a long time.For a long time,under the influence of cold,hot and dry climate conditions,the concrete structures of various buildings generally appear cracking phenomenon,such as a aqueduct in Xinjiang has a web through crack and a bottom plate inclined crack,which affects the safe operation of aqueduct.Water filling load test is an effective way to test the bearing capacity of aqueduct in the south to North Water Transfer Project,but it is not perfect in the safety evaluation of the bearing capacity of aqueduct and needs further study.The research results provide a theoretical basis for testing the bearing capacity and safe operation of aqueduct,and also provide a reference for the bearing capacity evaluation of similar projects.Based on the investigation of the current situation of Kezi river aqueduct in Xinjiang,the quality inspection of cracks,concrete strength,roof prestress and steel stress state is carried out,and the structural bearing capacity and safety stability of the aqueduct are analyzed;The research is carried out through the water load test,and the wireless static monitoring system is used to monitor the deflection,stress and strain of aqueduct and the change law of pier settlement under various levels of water load;According to the hydraulic industry standard and the evaluation method of highway bridge static load test,the bearing capacity of aqueduct is evaluated systematically.The main conclusions are as follows:（1）There are 1019 cracks in 22 span aqueduct,294 cracks with width greater than 0.2mm,most of which are temperature shrinkage cracks.Inclined cracks appear in the bottom plate of the seventh span,and the number of through cracks in the web is large;The concrete strength of the other spans is more than50MPa,except that the estimated strength of the 6th and 12th spans is lower than the design value;The stress state of aqueduct roof is tested by selecting the middle section of the 19th,20th and 21st spans.The measured stress values are 1.82 MPa,2.12 MPa and 1.91 MPa respectively,which are slightly higher than the design theoretical calculation value of 1.55～1.68 MPa;The prestressed reinforcement of aqueduct concrete is in the state of compressive stress.Although the aqueduct has some defects,the bearing capacity of the aqueduct under no-load condition basically meets the design requirements.（2）When the water load is loaded to the check water depth,the measured deflection extremum of the displacement meter and the dial indicator are 3.12mm and 2.93mm respectively,and the relative deflection is 1.04×10^-4、9.8×10^-5,Compared with the theoretical deflection value of 3.75mm calculated by the southern Academy of Sciences,it has a larger margin;When the tank is full of water,the maximum deflection measured by dial indicator is 3.40mm;After unloading,the residual deflection is 0.39mm,which is normal;The average value of settlement deflection measured by dial indicator is 0.50 mm;The measured results of this aqueduct are similar to those of other similar aqueducts.（3）When the water load is loaded to the check water depth,the deflection check coefficient is 0.78calculated from the deflection extreme value and residual deflection monitored by the dial indicator,which meets the requirement that the limit value of the regulation is less than 1;when the water load is loaded to the full water depth,the relative residual deflection is 11.5%,which meets the requirement that the limit value of the regulation is less than 20%.The measured deflection extreme value and residual deflection of aqueduct can comprehensively reflect the bearing capacity of the structure,which improves the deflection evaluation method of aqueduct static load test.（4）Under the full channel water depth,the strain extreme values of the 7th and 8th span middle beams are 60.89μεand 52.35μεrespectively.After the first level load is applied,the strain increment of the7th and 8th span middle beams is 29.10μεand 23.21μεrespectively,and the change amount reaches40%-50%of the total strain,which indicates that it is unreasonable for the strain result to change too much under small stress.Therefore,the correction method of strain zero point when the strain drift is too large is proposed After correction,the strain increment under check flow is 42.29μεand 30.40με.（5）The theoretical stress increment of the 8th span is 1.37 MPa and the strain increment is 34.25με,Combined with the corrected measured strain increment,the strain calibration coefficient of the aqueduct is 0.89 under the check discharge,which meets the requirement that the limit value of the regulation is less than 1;The residual strain in the middle of the middle beam is 4.58με,The relative residual strain is 8.7%,which meets the requirement that the limit value is less than 20%,which further verifies that the aqueduct has abundant bearing capacity reserve.