Study On Swelling Characteristics And Aging Model Of Cretaceous Mudstone In Jingmen-Yichang Region

Expansive rock is a kind of soft rock that expands with the increase of water content and shrinks with the decrease of water content.It is easy to be denudated under exposed conditions.Expansive rock is one of the important factors that produce adverse geological hazards.Geological hazards and engineering accidents caused by expansive rocks are frequent.However,engineering diseases caused by moderate-strong expansive rocks are often paid more attention to.In the construction process of high-speed railway,the settlement should be controlled within a minimum range,while The allowable expansion of the track fastener is not more than 4mm.Nowadays,when the high-speed ballastless railway passes through the weak expansion(or non-expansibility)area,The expansive rock at the bottom of the roadbed or tunnel will lead to the rise of the top of the roadbed,which will endanger the safety of the high-speed train.Therefore,The control of subgrade deformation has become one of the major problems in the construction of high-speed railway.However,the current understanding of weakly expansive rock is insufficient,and the study of its expansive characteristics can provide a scientific basis for the construction and operation safety of high-speed railway.This expansive mudstone is located between Jingmen and Yichang city of Hubei Province.By comparing and analyzing the relationship between the content of clay minerals and the physical and mechanical indexes of expansion,and the relationship between the microscopic characteristics and physical and mechanical indexes.In this paper,the correlation analysis of the influencing factors of mudstone dilatability is obtained,and the expansion model based on time factors is explored,and the following main understandings are obtained:(1)The content of clay minerals in the Cretaceous mudstones in the study area is between 6.2% and 18.1%.The basic units are mainly granular and lamellar,and the connection modes are mainly contact connection and cementation connection.And the content of micropores is high.(2)The mudstone is weakly expansive rock.The change rule of the expansion rate with time is mainly a "ladder" type,which can be divided into three stages.The first stage is the rapid expansion stage.The rock sample expands rapidly after being immersed in water,showing a large slope on the expansion rate curve,and almost a straight line in the initial expansion stage.The second stage is the slow expansion stage,in which the expansion rate slows down and the slope of the expansion curve becomes smaller,which is the transition section of the final stable expansion.The third stage is the expansion stable stage.In this stage,the expansion of rock samples gradually tends to be stable and the slope of the curve approaches 0.(3)The correlation coefficient between the dilatability parameters of mudstone and the content of clay minerals is low.Among the basic units,the dilatability of curvilinear laminated laminated unit and flat laminated laminated unit is the strongest,while the dilatability of outer grain unit and detrital grain unit is the weakest.Among the different connection characteristics,the expansibility of surface-side connection and surface-side connection is greater than that of edge-side connection and point-point connection.The lower the pore fractal dimension is,the higher the rock expansion rate(force)is.When p H is the same,the fractal dimension is positively correlated with the number of cycles.However,it is worth noting that the fractal dimension is negatively correlated with p H value for the same number of cycles.The higher the fractal dimension of mudstone mass is,the more severe and thorough the disintegration will be,and the lower the particle size of disintegration will be.(4)According to the stress-strain characteristics of weakly expansive rocks,the modelε=a-b*ln(σ-c)has a higher degree of fit than the Huder-Amberg classical model.Compared with the hyperbolic function model,logarithmic function model and power function model,the Logistic function model is more suitable for the simulation of the expansion history curve of weakly expansive rock.The parameters in the Logistic function model show a polynomial function relationship with the number of dry-wet cycles.