| With the increase of the depth and difficulty of underground excavation,the requirement of the construction technology level and safety of artificial freezing method will be higher and higher.However,the current underground engineering research basically ignores the effect of closed cavity on temperature field of soil,which is not rare in freezing engineering.The existence of cavities will lead to the loss of cold volume in the transfer process.If the amount is small and the distribution is concentrated,it may lead to the time delay of freezing wall circle.If its number is large and its distribution is not uniform,it may lead to the formation of frozen wall thickness is not up to standard,and serious or even do not cross the circle,which will cause landslides in the process of manual excavation,causing immeasurable losses to the project.Therefore,the existence of these cavities is bound to affect the development of the frozen wall,which is worth our further study.In this thesis,numerical simulation and physical model experiment are used to study the development law of freezing temperature field of soil with closed cavity.Typical parameters,single factor and orthogonal test were analyzed,and physical model tests were designed and carried out by using similarity criteria.The results of numerical simulation and physical model tests were mutually verified.Finally,the development law of freezing temperature field was summarized and analyzed.The main conclusions of this thesis are as follows:(1)When the freezing tube is located outside the cavity: due to the heat insulation effect of the cavity,the cold volume released by the freezing tube accumulates at the bottom of the cavity in large quantity,resulting in the accelerated development of frozen soil at the bottom of the cavity.When the thickness of the freezing wall at the bottom of the cavity reaches 0.55 m,the frozen wall is 8 days faster than the surrounding soil,and the final freezing temperature is about 4℃ lower than the surrounding soil.At the bottom 1/3 position of the cavity,the frozen wall develops faster than the surrounding soil in the first 14 days,and then develops slower than the surrounding soil in the middle position of the cavity.The top of the cavity could not receive the cooling capacity basically,and the measurement point 8 located on the S1 path through the center of the cavity on the main surface of the freezing tube had the most obvious effect,and only decreased by 21℃ during the whole process of 120 days of freezing.The frozen wall thickness of the vertical path S3 outside the cavity basically increases linearly after the 10 th day and finally reaches2.26 m,which is 0.15 m more than that of the final frozen wall thickness of S1 path 2.1m.(2)When the freezing tube is located inside the cavity,the thickness of S1 path freezing wall passing through the center of the cavity has a maximum difference of more than0.8m in the freezing process compared with that without cavity under typical parameter conditions,and the difference is 0.1m for 120 days after the final freezing.The temperature development of the upper part of the frozen tube in the cavity is faster than that of the lower part.The freezing wall thickness of the upper part of the freezing tube is greater than 0.1m than that of the lower part of the freezing tube.(3)The detection index proposed in this thesis can detect the existence of cavity.Within 0-10 D,the measuring point with the detection index greater than 0 is already located in the cavity;within 0-30 D or 0-60 d,the cavity index of the later measuring point changes from negative sign to positive,so the measuring point is already located at the top of the cavity,that is,there is a cavity between the two measuring points.(4)During the first60 days of freezing,the change of cavity length has the greatest effect on the freezing wall.When the cavity length increases from 1.6m to 2.8m,the thickness of the freezing wall decreases by nearly 5cm.The change of cavity width has the least effect on the freezing wall.When the cavity width increases from 1.2m to 2.4,the freezing wall thickness decreases less than 2cm.(5)As the height of the cavity increases from 0.1m to 1.3m,measuring point 2 on the vertical research path S1,which is located on the main surface of the freezing tube and passes through the center of the cavity,enters the cavity from the bottom of the cavity,the freezing development is slowed down and the final freezing temperature rises to 24.83,which is nearly 3℃ higher than before.Measuring point 4 enters the cavity from the top of the cavity,and the freezing speed is accelerated.Finally,the freezing temperature is reduced to-12.1℃,which is 11.7℃lower than before.There are 53 figures,10 tables and 95 references in this thesis. |
