Study On The Weathering Characteristics Of P₂? And The Weathering Factors Formed By The Headslide

The Emeishan basalt?P₂??is widely distributed in the junction area of the three provinces of Yunnan and Guizhou.The P₂?distribution area usually has a vertical and horizontal river valley,various structural forms,and the rock mass is developed and loosely broken.Such geological environment conditions make the Emeishan basalt a set of landslide disaster-prone rock series.Landslide gestation is a multi-factor coupling process.Previous studies have focused on disaster record and debris flow kinematics.There are not many studies on the contribution of P₂?weathering to rock mass landslides.The degree of weathering of rock mass depends on the discontinuous surface provided by its geological structure and gravity deformation.The geological structure of P2?specific lithology makes the rock mass become a discontinuous medium composed of different scale blocks.Its original columnar structural features,concentrated regional structure and geographical features of the distribution area laid the foundation for the occurrence of concentrated instability events.Therefore,the research on the weathering factor of the Emeishan basalt landslide will improve the understanding level and defense ability of the P₂?landslide disaster.In view of the typicality of the P2?landslide event,the research results have similar reference and guiding significance for other lithologic landslide events.It will promote the deepening and development of landslide theory and disaster assessment technology.Based on the full collection of existing data,this paper selects a typical research area for geological survey.Field experiments and laboratory tests were carried out on P₂?rock samples with different degrees of weathering in the study area.The weathering characteristics of P₂?slope rock mass were studied by rock flake identification,electron scanning microscopy,rock chemical analysis and X-ray diffraction..The engineering properties of P₂?slope rock mass are revealed from the aspects of rock microscopic properties,physical properties and mechanical properties.Then,the large-scale landslide of Yunnan Tuzhai,a typical P₂?landslide,was selected to study the weathering factors in the landslide breeding process,in order to reveal the relationship between the weathering of P₂?and the geological disasters of landslides.The paper mainly achieved the following results and conclusions:?1?The humus formed by the weathering of the P₂?slope rock mass,macroscopically,it retains part of the strength of the original rock,the deformation modulus is small,and the bearing strength is low.The density of the humus rock is smaller than that of the parent rock,and the water content and permeability are increased.The color difference between the structure and the parent rock is significant,but the original rock structure and structural features are retained,the secondary voids are relatively developed,the porosity is high,the structure is loose,and the water stability is poor.?2?Observing the weathered structure of P₂?by scanning electron microscopy,the weathering front has a tortuous shape,and the rock minerals on both sides are significantly different.The side of the core stone is dense,while the side of the shale shell has a honeycomb structure.More pores and cracks appear.And small clay minerals appear inside the crack.These cracks are capable of trapping and storing moisture,providing conditions for the continuous weathering of rocks in the unsaturated zone.?3?The petrochemical and mineral characteristics of P₂?humus were analyzed by chemical analysis and X-ray diffraction.The results of chemical analysis showed that the fresh basalt was not significantly changed except for Fe,and the core stone was rotted.During the weathering process of rock,Si,Ca,Na,Mg and other elements exhibit loss characteristics,and Fe and Al elements gradually accumulate,and the loss on ignition and chemical alteration index increase significantly.During the weathering of P₂?,the vitreous,pyroxene and plagioclase in the fresh basalt gradually formed secondary minerals such as montmorillonite and chlorite.?4?The relationship between the weathering of P₂?and the formation of geological hazards can be summarized as follows:1)The special structure and mineral composition of P₂?constitute the weathering foundation of Emeishan basalt,and the strong tectonic activities in this area make the rock mass break,joint fissure development,Under natural conditions such as alternating heat and cold,dry and wet cycles,the weathering speed of the rock is accelerated.2)The defects of rock mass structure under chemical weathering lead to the weakening of physical and mechanical properties.The deterioration of weathering leads to the stress relaxation of rock mass and the overall decrease of rock mass density.A large number of loose fractures are formed in the rock mass,and the mechanical behavior of hard rock mass begins to Plastic conversion.3)The three-dimensional expansion of the weathering front of the structure allows the weathering of the structure to extend to the deep part of the rock body at a long distance,so that the weathering in a certain depth range of the rock mass can occur simultaneously with the surface of the rock mass.4)The infiltration of surface water is also involved in the physical weathering of P₂?.The runoff water inside the rock mass will form hydrodynamic pressure in the rock mass,reducing the cohesive force seen by the particles.In addition,the infiltrated fissure water will cause pore water pressure in the cracks in the inner surface of the rock mass,and reduce the shear resistance and effective stress of the rock mass.