Study On The Feature Of Argillitization And The Evolution Law Of Formation About Weak Interlayer In Red Strata Area

The red strata area in northeastern of Sichuan province has been a geological disaster-prone area.In recent years,with the extreme rainfall events frequently occurred,a large number of low dip angle rocky landslides have been formed in the red strata of the northeastern part of Sichuan province,Which resulting in heavy casualties and serious economic losses: Such as Tiantai landslide occurred in Tiantai Township of Xuanhan County in September 5,2004,2500 person are affected.June 18,2007 many landslides occurred in the Sichuan Basin,resulting in 1933 houses collapsed;on September 2011 16,a great number of landslides occurred in Nanjiang County,caused two people killed seven people were missing,166 houses collapsed,the direct economic losses reached up to 1.511 billion;June 28,2015,heavy rain triggered geological disasters to the 48 townships in Nanjiang county,affected 48.9 million people in different degrees,resulted in two deaths,one missing,damaged 18104 houses,direct economic losses reached 1.92 billion.At present,it is concluded that the extreme rainfall has caused the hydrostatic pressure and Uplift pressure at the potential sliding surface leading to rock slope instability.However,it is found that the partial landslide does not have the condition of forming a high water head at the trailing edge through detailed field investigation.This type of landslides have a close relationship with weak layer.Weak interlayer,especially the clay interlayer,plays an important role in landslides' occurrence.In this paper,researching the formation of clay interaction is the key to study the genetic mechanism of the low dip angle rocky landslide.Researching the strength characteristics of the weak interlayer under the long term action of the groundwater are the core to prevention and mitigation of the rocky landslides.Based on field investigation,a large number of experiments are made to study the macroscopic and microscopic evolution characteristics of the formation of the clay interlayer.Researching the spatial distribution law of weak layers through catalog large numbers of geological profiles through the data collection and summary reveals the formation of the weak sandwich performance environment and tectonic environment.The relationship between the clay interlayer and the geological environment are analyzed in this paper.The Characteristics of argillitization are analyzed by XRD,Electron microscopy observation test,Particle grading analysis,ICP cation analysis test,Ion chromatography anion analysis and other test,revealing the microscopic changes and water-rock interaction in the mud simulation process.The influence of the internal and external geological effects on the formation process of the clay interlayer is discussed.The initial understanding of the process of mud as follows:?1?The weak interlayer in the red strata area of Nanjiang County is mainly composed of shear fracture zone,clay layers are formed in the range of surface unloading zone where fissure is too many and groundwater is active.The formation of mud interlayer is divided into three stages,Soft rock sedimentary stage?Soft rock?? tectonic shear stage?interlayer shear fracture zone?? groundwater water physical and chemistry action stage?including mud shear fracture zone?? clay interlayer formation stage?mud interlayer?;The simulation results show that the argilization process is very slow in static ambient.?2?The results show that the higher the clay mineral content is,the faster the muddy rate is.The dry and wet circulation mainly causes the mudstone to break down and increase the specific surface area of the sample to accelerated dissolution of soluble salts,but not significantly accelerate the water chemical reaction.Shear crushing zone to the evolution of the mud zone,the structure becomes loose,clay minerals,especially chlorite,illite and other clay minerals increaseing,feldspar and other skeletal minerals reduceing.The clay mineral will be converted into a more stable silicon oxide after immersion in water.After the immersion of the interlayer,the content of the alpine,the petal petaloid and the montmorillonite are significantly increased.?3?A comparative study of the three different weak interlayer minerals found that the higher the content of clay minerals and feldspars,the more prone to mulching of the original rocks and the higher clay content after argilization.Stone kaolinite and other mineral content is significantly reduced,and illite,chlorite,montmorillonite significantly increased,indicating that the process of argilizaition is the process of conversion of siliceous minerals to clay minerals.The main dissolved ions are Ca²⁺,Mg²⁺,Al³⁺,K⁺,HCO₃^-,Cl^-,SO₄^2-,the relative concentration of cationic c?Na⁺?> c(Ca²⁺),the relative concentration of anions c?HCO₃^-?>c(SO₄^2-)>c?Cl^-?,according to the ion,it is speculated that the main soluble salt are calcium bicarbonate,Sodium sulphate,calcium sulfate and so on.In the simulation test,the pH value and the conductivity of the immersion solution were different.The ion concentration in the process of immersion and immersion increases with the immersion time,The hydrolysis of feldspar and other minerals makes the aqueous solution weakly alkaline.?5?The shear stress-shear displacement curves of the mudstones after different immersion times were obtained by the direct shear test of the rocks.It was found that the shear stress-shear displacement curves of the mudstones without the water loss process can show the brittle characteristics,c and ? values of the mudstone are 3.25 MPa and 39.27 degrees.The shear strength parameters c and ? of mudstone have different degrees of attenuation with immersion time.Through the direct shear test,the shear strength characteristic curve and strength parameter of the original sample of the weak interlayer were obtained after different water saturation time,the shear strength parameters c and phi were reduced from 0.85 MPa to 0.22 MPa,32.64 degrees to 10.59 degrees,the decay curves showed two order exponential relationship.Through the immersion shear test of mudstone and weak interlayer showed that,a soaking time water later cohesion of rock and soil is weakened more than the interior angle of friction.The attenuation amplitude of shear strength of weak interlayer is greater than that of mudstone,which indicates that the structure is loose and the softening effect becomes more obvious?especially the cohesion?.When the water saturation of the clay interlayer is large,the water content is not changed any more,and the mechanical strength is still decay,which shows that long term effect of groundwater will weaken the structure and mechanical properties of soil.