Influencing factors and determination method of the initial instability length of bedding slope along mountainous highways
Bedding slope is often encountered in highway construction in western mountainous areas.The initial instability length Lc is the key parameter of instability mechanism and reinforcement design.At present,there are some limitations in the determination method of the first instability length.Based on 31 cases of highway bedding slope instability in mountainous areas around Sichuan Basin,the influencing factors of slope structure characteristics(rock dip angle α,angle θ between slope strike and rock strike and slope length L)and external disaster inducement(cutting thickness D and rainfall Q)on Lc was systematically investigated.Combined with finite element analysis,the main influencing factors and determination method of Lc were emphatically discussed.The results show that Lc/D ranges from 3～24,with a value of 3 to 10 excluding argillaceous interlayer.For α ranging between 12° and 35°,bedding slope stability is the weakest,and Lc/D decreases with α increments.Failure in bedding slopes primarily occurs within θ≤30°,extending to unstable conditions for θ>30° with double or even three free faces in the slope.Lc increases with the increase of L,and Lc/L is in the range of 0.3～1.0.Bedding slopes within an H range of 5 m to 30 m tend to lose stability easily.The instability of bedding slope induced by rainfall is due to the saturation softening of muddy interlayer,and the excavation in flood season is the catastrophic cause of bedding slope instability with argillaceous interlayer.The sensitivity in descending order of the influencing factors of initial instability length is as follows:①Slope with weak interlayer:rock dip angle,slope length,cutting thickness,internal friction angle,cohesion,elastic modulus,excavation height;②Slope without weak interlayer:rock dip angle,internal friction angle,cutting layer thickness,cohesion,slope length.The proposed calculation formula of strike angle reduction coefficient and multi-factor Lc has guiding significance for the determination of slope failure range.
bedding slopehighway along Sichuan Basininitial instability lengthinfluencing factorfitting relationship
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