Engineering Properties And Softening Mechanism Study Of Triassic Mudstone In Panzhihua Airport

The study area is located in the east of the Panzhihua Airport 12# landslide,bedrock is mainly T3 bd,which dominated by carbonaceous mudstone,mixed sandstone and silty mudstone.The 12# landslide and Yijiaping old landslide underlying bedrock,and most of the distribution of mudstone.For filling material from T3 bd mudstone with a large number of fragments of mudstone.It is obvious that the instability of the 10.3 filling body and the reactivation of the old landslide are related to the softening of the mudstone in Panzhihua airport.In this paper,a series of experiments were conducted to study the characteristics of mudstone softening in water:(1)The initial composition and structure of mudstone are the basis of water softening of mudstone.Mudstone in the study area is mainly composed of clay minerals,primary minerals,simple salts and carbonaceous materials.Among them,the clay mineral content accounted for 50 to 95%,the primary minerals accounted for 4%~35%;most of the simple salts were soluble salts.Carbonaceous content of 1% ~ 10%,and clay minerals in a mutual staining,will weaken the clay mineral particles between the joint.From the microscopic structure,the clay minerals are aphianitic-microcrystalline aggregates and parallel stacked structures,and the clay minerals are cemented by solid salts with the primary mineral particles.The initial composition structure,determines the weak natural strength of mudstones(uniaxial compressive strength is 10MPa),poor water resistance and easy to soften.(2)Saturated water test with pure water showed that:(1)the water content and porosity of mudstone in the study area all increase continuously in the process of saturated water.And the anti shear strength and uniaxial compressive strength showed a sustained decay trend.Enough water for 30 days,water content and porosity increased 122.77% and 142.72% respectively;The uniaxial compressive strength decreased by 81%,and the c and f decreased by 67.86% and 53.12% respectively;(2)The change trend of the physical and mechanical properties of the mudstone structural surface is roughly the same as that of mudstone,but it is more active with water,the softening process is faster,and the shear strength index of saturated water begins to become stable after 10 days.After 30 days of saturation,the moisture content and porosity increased by 166.67% and 195.97% respectively,and the c and f decreased by 63.27% and 41.67% respectively.(3)The infiltration of mudstone has obvious different characteristics.when infiltration direction parallel to bedding plane,water content,porosity and the depth of infiltration rose faster than the vertical bedding group.At different levels of shear stress,shear along the surface direction(potential failure)water content,porosity and the depth of infiltration increases with the shear stress level.The shear plane parallel bedding when the depth of infiltration,water content,porosity growth is higher than that of vertical level shear conditions,and in the low difference of stress level both in larger,higher stress level difference is small.(4)The effect of groundwater and stress is the main external factor leading to the softening of mudstone.Using the groundwater in the study area as soaking solution,the dissolution and precipitation of the chemical components of mudstone are restrained to some extent,and the softening degree of the mechanical properties of mudstone is less than that of the pure water soaking liquid.In addition,in effect under a certain stress,not only will directly lead to the weakening of structure coupling between mudstone mineral particles,and micro cracks produced by immersion for groundwater,thereby increasing the softening process of mudstone.(5)The study area of mudstone softening mainly has four kinds: one is the physical and chemical effects of soluble salt soluble solid analytical chemical dissolution characteristics;the two is with the increase of pore of mudstone dissolution,the wedging action;three is the hydrolysis of mudstone muscovite and feldspar;four is water lubrication.Among them,chemical dissolution is the main,and decreases with increasing saturation time,wedging effect mainly occurs in the water saturated in the late(i.e.chemical erosion to a certain extent);hydrolysis of overall weak lubrication mainly exists in a situation through cracks(such as mudstone structure plane).(6)The softening process of mudstone(block)and structural plane is roughly divided into three processes.Mudstone(block): start softening stage(0~10 days)→continued softening stage(10~30 days)→softening the stable stage(30~60 days);mudstone structures: softening stage(0~5 days)→continued softening stage(5~30 days)→softening the stable stage(30~60 days).