Study On The Influence Of Weathering Effect On The Evolution Characteristics Of Hard Rock Slope With Soft Layer

Collapse is a common geological disaster in road construction in mountainous areas.Due to the particularity of slope rock mass structure formed by the characteristics of soft layers,hard rock slopes with soft layers are the main slope types prone to collapse.Since the occurrence of large collapse often causes huge casualties and property losses,the mechanism of collapse has become a long-term concern of geotechnical engineers and scientific researchers.In this paper,the hard rock slope with soft layer is taken as the research object.Through field investigation,simulation test of differential weathering of rocks,numerical simulation of discrete element and finite element.This paper systematically and deeply analyzes the characteristics of differential weathering of hard rock slope with soft layer,the development mode of slope collapse when differential weathering occurs,and the law of time limit of slope collapse.It is found that the effect of heat and cold alternation on rock weathering in dry environment is small,and the rate of rock weathering and destruction greatly increases under the influence of water.The differential weathering rate of the lime-marl combination is the largest under the wet-dry cycle,and the minimum under the cold-heat cycle.The differential weathering rate of sand-silt-rock assemblage is the largest under natural conditions,and the minimum under thermal and cold cycles.The collapse mechanism of the slope with soft layer under differential weathering is as follows:Differential weathering leads to cavity formation in soft rock,resulting in stress concentration in soft rock.This stress concentration leads to the fracture and disintegration of the soft rock.Hard rock on top of soft rock can be tensile failure,hard rock rotates around the foot,topples,and eventually collapses.Other conditions of the slope being equal,the greater the thickness of the soft layer,the more unstable the slope.When the vertical joint inclination is opposite to the slope surface,the slope is more likely to collapse when it encounters differential weathering.The concept of differential weathering collapse coefficient P_bis put forward in this paper,which is the ratio between the differential weathering depths of hard and soft rocks and the spacing between vertical joints when the collapse occurs naturally.And the time limit of the collapse is studied.The result is applied to the high and steep slope of hard rock with soft layer,Finally,the time of slope collapse is deduced.