Study On Physical And Mechanical Properties Of Deep Buried Calcareous Clay Artificially Frozen In Lianghuai Mining Area

Artificial ground freezing method is the first choice for vertical shaft construction in deep alluvium rich in water.How to safely cross deep alluvium,especially deep clay layer,is the key.However,in the construction of vertical shaft in Lianghuai area,pipe breaking accidents occur frequently at the interface between calcareous clay layer and other soil layers.The field investigation found that the calcareous clay layer was frozen late and has low strength.When the shaft is driven to this point,due to radial unloadding,the calcareous clay layer has large rheological deformation and generates strong mutual dislocation force at the interface,resulting in pipe breaking.In view of the"diffic ult"freezing and"low"strength characteristics of calcareous clay layer,it is necessary to deeply study its freezing and strength characteristics.Therefore,this paper re understands the macro distribution law micro macro of calcareous clay from the combination of macro distribution,micro physical and chemical properties,indoor experimental research,model experimental research and theoretical analysis.This paper mainly completes the following research work:（1）The analysis of borehole data in Lianghuai mining area by using statistical theory showed that the calcareous clay layer was widely distributed in Lianghuai mining area.The maximum thickness of calcareous clay in Fudong mining area was 46.1m,the average value was 24.86m,and the buried depth was basically about 400m;The maximum depth of Panxie Mining Area was 55.85m,with an average of 25.7m,and the buried depth was in the range of 250～400m;The trend of top and bottom plate of calcareous clay layer was basically consistent with that of bedrock surface.（2）The basic physical properties of calcareous clay were studied experimentally,such as particle gradation,specific surface area,cation adsorption content,determination of thermophysical parameters,mineral composition analysis and internal microstruct ure characteristics.Due to the high content of Ca²⁺in calcareous clay,the ion exchange between free Ca²⁺and Na⁺,K⁺on the surface of soil colloidal particles increases the surface charge of soil particles,the adsorption force between particles increases,the adsorption force on the surface of particles also increases,and the adsorption energy for water is greater,which makes the calcareous clay"difficult"to freeze from the surface.On this basis,the variation law of unfrozen water content in frozen soil of calcareous clay under continuous cooling state is studied.The freezing characterist ic curve is roughly divided into three stages-the rapid freezing section of free water after phase change,the slow freezing section of film water and the basically stable section of unfrozen water content.（3）Based on the Gouy Chapman diffusion double layer model,a unified theoretical solution of the change of unfrozen water content in z-z symmetric electrolyte and 2z-z/z-2z asymmetric electrolyte is established.Through the cross comparison of the test results with the empirical formula of unfrozen water content and the theoretical solution of unfrozen water content in the diffusion electric double layer,it is found that the theoretical solution comprehensively considers the influence mechanism of the mineral composition,soluble salt,microstructure and other parameters in the clay on its freezing characteristics,and has good applicability;The bridge between micro physical quantity and macro physical and mechanical properties of frozen soil is constructed.（4）The uniaxial acoustic emission curve of calcareous clay under different water content or salt content shows that the acoustic emission signal quantity is more when the temperature is higher,such as-5℃and-10℃,and the signal quantity decreases gradually with the decrease of temperature.When the temperature is high,although most of the water has been frozen and the content of ice crystals is high,the binding energy is low.Under the action of loading,it is easy to break the cementation bond,and a large number of small cracks breed in the frozen soil with large signal volume;At-15℃and-20℃,the signal quantity decreases significantly,which means that there is little unfrozen water content,and a strong binding water film is formed with soil particles.The lower the temperature,the higher the strength,and the failure surface angle of the sample is 450.Continuous shear cracks are formed on this surface and through failure is developed.（5）The orthogonal true triaxial test of frozen clay under the influence of multiple factors is carried out.The results show that the primary and secondary influencing factors of strength are confining pressureσ₃.Moisture contentω,Temperature T,bishop parameter b value,salt contentψ;When the interaction is not considered,the influe nce of confining pressure and water content on strength is always significant.Only when the significance levelΩ>0.05,the influence of temperature is significant.The influence of salt content and b value on strength is not significant,and the significa nce order of each factor is consistent with the results of range method and analytic hierarchy process;When considering the interaction,the interaction factors have different degrees of influence on the strength.WhenΩ>0.01,the influence of the interaction factors temperature and moisture A×B content on the strength is significant,even exceeding the temperature.It can be seen that when studying the strength of frozen soil,it is necessary to comprehensively consider the factors and their interaction,so as to more accurately characterize the mechanical behavior of frozen soil.（6）Taking the freezing method construction of a mine shaft in Lianghuai mining area as the background,the model test of freezing temperature field of calcareous clay is designed and carried out.Compared with the engineering site,the formation parameters of temperature field are found:the cross circle time of freezing temperature field test（-1.3℃）is 2.5h,which is equivalent to 127.6 days of actual engineering;The development rate of frozen wall in calcareous clay layer is 17.9mm/h in the early stage（5～16h）and 1.96mm/h in the later stage（16～70h）.Through similarity ratio inversio n,the actual development rates are 0.0123m/d and 0.0014m/d respectively.Compared with 0.0515m/d in the early stage and 0.02m/d in the later stage of general Sandy clay layer,the development rate of frozen wall thickness is significantly slower,which further indicates its"difficult"freezing characteristics.Figure[83]Table[32]Reference[204]...