Theoretical Calculation And Crack Prevention Treatment Method For Seamless Design Of Underground Super-long Engineering

Based on the seamless design of an ultra-long underground project in a Lugang town,this thesis introduces the principle of mass concrete cracks in detail on the basis of a large number of references,and the causes of temperature cracks in mass concrete and the corresponding treatment measures were also summarized.The crack control of underground engineering is studied in detail from aspects of theoretical calculation,finite element analysis,construction preparation,construction technology measures and so on.The underground project is finally well performed through the creative design,well-controlled construction and seamless treatment measures,and there is no harmful cracks appear in this project.This project belongs to the first mass concrete underground structure forming project in Shandong,which has very important significance.The main research works are as follows:(1)This thesis summarizes that temperature stress is the root cause of cracks in underground mass concrete,and it is mainly caused by the temperature difference between the center and surface of concrete caused by the heat release of cement hydration heat and environmental temperature.Therefore,attention should be paid to the selection of materials,proportion and insulation measures before and during concrete construction to avoid temperature cracks caused by uneven temperature.The temperature stress can be divided into early,middle and late stress according to the formation time of concrete temperature caused by temperature change of concrete;the calculation formula of temperature stress and the design principle of post pouring belt are also given in this thesis.(2)The causes of cracks and corresponding measures in mass concrete were summarized and analyzed in the aspects of design,material mismatch,construction process and maintenance period.Four existing construction temperature control methods(insulation material covering method,embedded cold water pipe method,phase change material control method and circulating water storage control method)are given,and the application scenarios,advantages and disadvantages of these four methods are compared in this thesis.By identifying the causes of cracks in mass concrete structure,the appropriate solutions are selected according to these construction temperature control methods.(3)In this thesis,ANSYS finite element analysis software is used to carry out the temperature simulation analysis of mass concrete.The simulation shows that the temperature peaks after 3 to 4 days of age.During this period,the temperature rises and falls rapidly,and the temperature gradient changes greatly.During the construction period,the maintenance and temperature control measures described in Chapter 3 should be taken in this period.In the age of 3 to 6 days,the core temperature of the concrete decreases slowly,and the external surface temperature decreases rapidly.This phenomenon will cause a large temperature difference between the inside and outside of the mass concrete.Therefore,during this period,it is necessary to carry out heat preservation treatment on the outside to reduce the temperature difference between the inside and the outside.The simulation results provide technical references and scientific suggestions for actual engineering construction and concrete maintenance.(4)According to the results of the theoretical analysis and finite element analysis,the concrete floor of 311 m * 256 m mass concrete seamless design was chose as an example in this research.The author introduce the preliminary work for construction,the material selection and anti-cracking measures.This research summarizes the raw materials selection,the considerations and principles of the concrete construction and the proportioning of the concrete and the concrete temperature and stress.The PKPM software is used to build an underground mass concrete structure model.According to the calculation program set by the PKPM software,the temperature stress of the floor,beam,external wall and the vertical bar was calculated.The result shows that the existing scheme meets the design standards.On the basis of the good control and seamless treatment measures,this underground project is good without harmful crack.