Study On The Mechanism And Development Law Of Mudstone Expansion

As a soft rock,mudstone is very widely distributed in China,and the increasing mileage of China’s high-speed railway inevitably crosses mudstone areas.At present,there is a lack of understanding on the harmfulness caused by mudstone swelling,and a large number of damage problems of roadbed arch caused by mudstone swelling appear,which brings great challenges to high-speed railway operation.The main reasons are lack of effective test means,evaluation method and unclear factors affecting expansion.Therefore,the study on the expansion mechanism of mudstone and its development law is of great theoretical and practical significance to the design,construction and operation of existing railway lines.The expansion of mudstone which causes the deformation of the arch on the roadbed of high-speed railway is studies in this paper;The law of water absorption and expansion of mudstone under different stress is studied by means of dilatometer;The mechanism of water absorption and expansion considering the structural strength of mudstone is revealed by expansion test of mudstone block and mudstone powder and sem test;The energy conversion of mudstone in the process of water absorption and expansion is analyzed and an expansion model considering the structural strength of mudstone is proposed;Based on the calculation method of arch deformation of mudstone subgrade considering water content,the deformation characteristics of arch deformation of mudstone subgrade are analyzed.The main achievements are as follows:(1)The expansive deformation measuring instrument for mudstone was designed and developed,and the expansive deformation law of mudstone under different stress constraints was obtained.There is a linear relationship between water absorption and swelling of mudstone;There is a significant logarithmic function between the confining pressure and the peak of Volume expansion;The slight change of water content of mudstone under natural conditions will cause expansion deformation;The modified huder-amberg expansion model with free expansion rate can accurately describe the variation law of volume expansion under different stress constraints.(2)The expansion process of mudstone water absorption is a process of energy release.Part of the energy is used to destroy its internal structure,and the other part is used for external work to produce expansion and deformation;The expansion discrimination model considering the strength of mudstone structure is established: The potential expansion strain energy generated by the expansion of mudstone powder is equal to the sum of the expansion strain energy generated by the expansion of mudstone rock mass and its structural strain energy.(3)A method for testing and evaluating mudstone expansion considering both powder expansion and rock block strength is presented.To judge the expansion of mudstone blocks,uniaxial compressive strength test and water-immersed expansion test should be carried out simultaneously,and the expansibility of mudstone blocks should be judged by their structural strength and powder expansion potential energy;When the powder expansion potential energy is greater than the structural strength strain energy,the rock mass will appear as expansion.(4)Based on the migration and infiltration process of water,a calculation method for arch deformation of mudstone subgrade considering water action is proposed.The arch deformation characteristics and water distribution characteristics of mudstone subgrade are obtained: Water in the subgrade below the belt distribution and parallel to the subgrade;The swelling deformation of mudstone foundation decreases gradually along the direction of depth and has logarithmic relationship with depth;There is a linear relationship between expansion deformation and subgrade moisture content and penetration depth.