Study On Water And Salt Transport Of Weathering Materials Of Mirabilite Salt Rocks In Lufeng,Yunnan

Jiaozi Mountain Tunnel of Chengkun Railway is located in Lufeng County,Yunnan Province.The excavated slag in this area is mainly granite salt,containing a large amount of Na⁺、SO₄^2-、Ca²⁺and Cl^-,mainly in the form of granite and calcium granite,and containing gypsum and chlorine salt.After rock excavation exposed to the surface,a kind of weathered material with high salt content will be formed in a short time.Under the double action of rainfall and evaporation,the slag dump formed by the accumulation of the weathered material generates a large amount of salt out through water and salt migration,which pollutes the surface soil and the surrounding environment,leading to the instability of slope and the difficulty of vegetation recovery.In order to deeply study the law of water and salt migration of mirabilite salt rock weathering,this paper takes the mirabilite salt rock slag dump site in Jiaozi Mountain tunnel project of Heiwell as the research object,combined with the actual site of the slag dump body,first through field investigation and sampling and a series of indoor soil tests to obtain the basic physical,chemical and mechanical properties of mirabilite salt rock weathering in the dump site.After that,the physical and mechanical properties of weathering materials of salt salt were analyzed by salt-washing test and related laboratory mechanical tests,so as to predict the extreme properties of the compounds in the process of water and salt migration,which can be used as the boundary conditions in related simulation research.Finally,an indoor soil column simulation test was carried out to explore the law of water and salt migration in the process of rainfall infiltration,evaporation after rainfall and phreatic evaporation in the weathering deposits of glauburite salt rock.Based on this,relevant engineering improvement schemes were proposed.Specific conclusions are as follows:1.After salt washing treatment,the salt content in the samples decreased,and the salt-out phenomenon was no longer produced after the same treatment,and the engineering properties were more stable than before salt washing.At the same time,the particle composition changes greatly,the content of sand（0.075mm<d≤2mm）increases obviously,the content of clay（d≤0.005mm）and powder（0.005mm<d≤0.075mm）decreases to a certain extent.After salt washing,the liquid limit,plastic limit and plastic index increased,the optimal water content and maximum dry density decreased to a certain extent,and the compaction curve moved to the lower left.The cohesive force decreased greatly,while the internal friction Angle increased,but the increase was not large.The microstructure also changed to some extent,the aggregate became smaller,the number decreased and the surface became rounded,and there were gaps between the particles.2.During rainfall infiltration,with the increase of infiltration duration,the depth of deep moisture peak and the cumulative infiltration of water increased gradually,and the increasing rate was first fast and then slow.The change curve of infiltration rate with time changes from steep to gentle in a short time and gradually becomes stable.The change value is suitable for the description of Philip model,and the imbibition rate of weathering weathering rock is 0.0648cm/min0.5,and the stable infiltration rate is 0.0002 cm/min.From the beginning to the end of infiltration,the salt content of 0-5cm soil layer decreased from the initial value of 34.73k/kg to 24.85g/kg,and the salt content decreased by 0.988%,accounting for 28.44%of the initial salt content.The change range of the middle layer is relatively small,and the salt content of the bottom layer is increased greatly.On the whole,salt migration shows the trend of"salt goes with water"and accumulates downward.3.During the surface evaporation test,the evaporation rate of water in salt weathering is lower than that in normal water,and its evaporation capacity is 52.06%of that in normal water.The reduction of water content in different soil layers in the soil column and the average reduction rate are different.The closer the soil layer is to the evaporation surface,the greater the evaporation intensity is,the faster the water loss is.The average moisture content of soil column profile decreases with the increase of evaporation time,and the distribution of soil moisture content profile increases gradually from top to bottom.With the increase of evaporation duration,the salinity in the soil column accumulates to the surface,but the variation of salinity in different soil layers is different.In the early stage of evaporation（before 432h）,the conductivity distribution of soil profile gradually decreased from surface layer to deep layer,but after 432h,the conductivity distribution of soil profile gradually decreased from surface layer to deep layer.After the experiment,the electrical conductivity of the 1-5cm layer increased by 71.4%compared with that before the experiment,while the lowest electrical conductivity of the 30-40cm layer decreased by17.8%compared with that before the experiment.The migration of salt follows the general rule of"salt goes with water,and water removes salt and stores salt".However,the migration of salt with water has certain restrictions,which may be related to the solubility of soluble salt,soil moisture content and soil voids.4.In the process of submersible evaporation test,with the increase of capillary seepage duration,the height of capillary water rise and the cumulative seepage amount in the sample increased gradually,and the increasing rate was first fast and then slow.The ratio of daily evaporation to water surface evaporation is about 51%.During the test period,the cumulative evaporation of the test soil column was 17.92cm,accounting for 63.91%of the surface evaporation（23.04）.In the process of water infiltration,the salt at the bottom of the pure capillary tube changed the most,from the initial salt content of 34.73g/kg to28.58g/kg,and the salt content decreased by 0.615%,accounting for 17.71%of the initial salt content.The change range of the middle layer is small,and the salt content of the surface layer increases greatly and salt-out occurs in the later stage.On the whole,there is a trend of"salt goes with water"and upward accumulation.And in the weathering of glauber salt,due to its higher internal salt content,the salt migration in the process of fresh water infiltration has a certain lag compared with water migration.As the phreatic evaporation continues,the water evaporation on the surface of the soil column transfers to the atmosphere,and the salt in the soil column accumulates with the water to the upper layer,and the salt crystal precipitation on the surface of the soil column can be observed,which conforms to the basic law of water and salt migration in the weathering of the mirite salt rock:"salt goes with water,water removes salt and stores salt".