Research On Shrinkage Of Concrete Shield Tunnel Segment

Shrinkage of concrete will cause different problems in different structures.For prefabricated shield tunnel segments,shrinkage and deformation during the period from prefabrication to on-site assembly at the construction site may cause them to fail to meet the requirements of shield machine assembly accuracy,and at the same time cause the size of steel prefabricated molds.For shrinkage characteristics,there are differences in the research methods of ordinary concrete and high performance concrete.Therefore,the dissertation will study the shrinkage law of high-performance concrete with different contents of fly ash,slag powder,admixture and polyoxymethylene fiber under natural conditions,based on a river crossing tunnel project in Nanjing.The mix ratio with the best shrinkage reduction effect is applied to the shrinkage test of the shield tunnel segment to explore the shrinkage law of the shield tunnel segment;finally,based on the test data,the shield tunnel segment is numerically simulated to explore the engineering practice shrinkage characteristics of shield tunnel segments in.According to the contact shrinkage test of the prismatic test block under normal conditions,when the content of fly ash increases from 15% to 25%,the shrinkage strain decreases with the increase of fly ash;when the slag powder increases from 15% to 25%,the shrinkage strain of concrete mixed with polyoxymethylene fiber is significantly reduced;the shrinkage reduction effect of mixing shrinkage reducer and polyoxymethylene fiber is better than that of polyoxymethylene fiber alone.The existing shrinkage prediction model is used to predict the shrinkage strain of concrete in different test groups.The results show that the existing shrinkage prediction model cannot predict the shrinkage of the mineral admixture,shrinkage reducer and polyoxymethylene fiber well;this paper randomly based on the results of three groups of experiments,and the time course development of shrinkage is considered by the hyperbolic square root function,and the influence of relative humidity is considered in the form of multiple functions,and the final value of shrinkage in the B3 model is corrected.The proposed model for shrinkage prediction of slag powder,shrinkage-reducing agent and fiber content was used to predict the development trend of shrinkage strain in the other three groups of tests,and the predicted values were in good agreement with the measured values.According to the prism shrinkage test results,the shield tunnel segment shrinkage test is set up.The results show that the chordwise shrinkage of the segment is slightly larger than the longitudinal shrinkage,and the shrinkage prediction model established based on plain concrete has low prediction accuracy for the shield tunnel segment shrinkage.In order to predict the precision of the prism shrinkage test block,the shrinkage deformation of the 28 d and 100 d prism and the shield tunnel segment were compared,and it was concluded that the nonprestressed tendons had a significant inhibitory effect on the shrinkage of the concrete structure.The finite element model of the shield tunnel segment is established,and the humidity field is analyzed by the thermal analysis module in the finite element.The results show that the humidity field of the segment gradually decreases with time,and the surface humidity diffusion rate is greater than the interior,and the humidity field and humidity gradient.Change of the temperature has a consistent distribution along the radial and circumferential directions of the segment;the humidity condition is set as the humidity environment where the shield tunnel segment is located in the actual engineering,and the shrinkage deformation is predicted through the wet-structure coupling,and the conclusion is drawn: the shrinkage deformation level of the group that mixes shrinkage reducing agent and polyoxymethylene fiber,increases the content of fly ash,and reduces the content of slag powder is significantly reduced,which can meet the requirements of assembly accuracy and reduce the risk of shrinkage cracking of segments.