| In recent years,along with economic development,rural residents have basically been lifted out of poverty and entered a moderately prosperous society.Every family has savings and they are willing to rebuild or renovate their houses and improve their existing living conditions.In recent years,engineering activities in the Loess Plateau Region have become increasingly frequent.In order to obtain a wider construction land,it is inevitably needed to cut slopes to build houses and excavate mountains to build roads.Therefore,many engineering construction projects inevitably have to cross the landslide zone,and the occurrence of geological disasters of loess landslides has become increasingly fierce and the scale has become larger and larger.Many experts,scholars and engineers and technicians have carried out in-depth exploration and research on loess landslides in the Loess Plateau Region.At present,a series of effective theories and experiences have been achieved in the formation mechanism,failure mode,induction factor,monitoring and alarming,prevention theory and technology and other aspects of loess landslide.However,it is still a difficult problem for engineers and technicians to accurately determine the position of sliding surface of loess landslide.Accurate determination of the position of the sliding surface of loess landslide will have a great influence on the stability evaluation of landslide body,the calculation of landslide thrust and even the treatment design.Therefore,in order to comprehensively evaluate landslide bodies and provide accurate data for landslide treatment design and subsequent construction,it is necessary to accurately determine the position of the sliding surface of loess landslide and carry out a comprehensive study on the identification index of the sliding surface of loess landslide.In this topic,the landslide of Beimen to Majiagou,Echeng Town,Jingle County,Shanxi Province is taken as the object of study.The landslide belongs to a typical loess landslide,with clear slide boundary,obvious characteristics of the landslide trailing edge,intuitional landslide steps and clear position of the shear crack at the front edge of the landslide,which is of loess landslide with complete landslide elements.In this paper,in accordance with the basic principles of soil science and soil mechanics and the applicable conditions of geophysical exploration methods,the sliding surface of the loess landslide is explored and studied by means of engineering drilling,exploration well exposure,surface wave method and high density electrical method.The position of the sliding surface of the selected object of study is investigated based on the laws of variation of water content with depth,the void ratio with depth,the propagation velocity of transverse wave in different geotechnical media and resistivity in different geotechnical medium,and the change law of sliding surface identification indexes is studied.Main achievements as follows:(1)The key point of the investigation and evaluation of loess landslides in the Loess Plateau is to accurately determine the position of the sliding surface.The methods of engineering drilling,exploratory well and geophysical exploration can be used in the investigation and evaluation of loess landslide.(2)Engineering drilling,exploratory well and geophysical exploration have their own advantages in Loess Landslide Survey.The advantage of engineering drilling and exploration well survey method is that it can directly observe the change law of landslide soil structure with depth through the rock and soil samples,so as to accurately locate the sliding surface of loess landslide.The advantages of geophysical exploration are wide coverage and continuous data of vertical and horizontal sections,which can grasp the development and change law of sliding surface as a whole.In engineering practice,two kinds of survey methods can be used for Landslide Survey at the same time.(3)Through the research and analysis of the formation mechanism and failure form of the sliding surface of the landslide in the Loess Plateau area,in the exploration stage of the loess landslide,the field engineering drilling,trench exposure,combined with the indoor geotechnical test method are used to accurately determine the position of the sliding surface of the Loess Landslide,and the water content and void ratio can be selected as the identification marks of the sliding surface of the loess landslide;the surface wave method and high-density resistivity method are used The wave velocity and resistivity can be selected as the identification marks of the sliding surface of the loess landslide.(4)Through the indoor geotechnical test analysis of undisturbed soil samples taken from exploration wells tj03,tj04 and tj05,the moisture content of the soil near the sliding surface of the loess landslide will suddenly increase;at the same time,the variation law of void ratio with depth of undisturbed soil samples taken from the above three exploration wells is analyzed,and the void ratio of the soil near the sliding surface of the loess landslide will suddenly increase.(5)When the surface wave method is used to survey the sliding surface of loess landslide,the soil near the sliding surface will creep and become loose.There will be an obvious low velocity zone on the isovelocity curve of the surface wave method,and the extension direction of the low velocity zone basically coincides with the direction of the sliding surface of the landslide.The velocity of the surface wave at the loose deposits at the foot of the landslide is also lower than that of the surrounding original strata,and the velocity of the surface wave will suddenly decrease on the isovelocity curve of the surface wave.(6)In general,the shallow resistivity is relatively high,which changes little with the depth,and is basically layered distribution.But near the sliding surface,there will be abnormal resistance and low resistance.(7)By comparing the exploration methods of engineering drilling and exploration Wells with those of geophysical exploration,it is found that it is more practical to determine the position of the sliding surface of landslide.When surface wave method is used to determine the buried depth of sliding surface,the error is generally less than 0.5m.When high density electric method is used to determine the buried depth of sliding surface,the error is generally less than 1.5m.It can be seen that surface wave method and high density electric method can not be used alone in loess landslide exploration,but should be used together with engineering drilling and trough disclosure methods to verify each other. |
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