Discussion on engineering characteristics of debris flow deposits and its initiating mechanism in typical earthquake disturbance area
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Abstract:
In earthquake disturbance and alpine-gorge area, instability slope with crushing rock is caused by active faults and frequent earthquakes. Particle migration in the deposits is caused by water infiltration, resulting in the change of saturation， density， thus weakening its strength， which subsequently induces occurrence of debris flow initiation. Debris flow gullies in two areas including Gansu Zhouqu county in the west Qinling mountains fault zone and Duwen highway in Longmen mountain fault zone were taken as an example， physical and mechanical properties tests of the loose accumulation body were carried out. Experimental results showed that the two groups of debris flow deposits were silty gravel soil with wide and non-uniform grading. Fine grain content in Zhouqu debris deposits was relatively high， its specific gravity， liquid limit, plastic limit, liquid index，and plasticity index were greater than those of soil sample of Duwen highway. When the moisture content of Zhouqu debris flow soil and Duwen highway slope soil increased to 15%-18% and 12%-15% respectively， the soil cohesion c reduced sharply. It hinted the existence of critical moisture content in soil strength decline process. The specific moisture content could be used as the critical water content of debris flow initiation. Further statistical analysis showed one-hour critical rainfall before occurrence of debris flow and the critical moisture content was closely related. By fitting the linear relativity between them, the critical rainfall of debris flow could be deduced, which can provide technical support for the prevention and early warning of debris flow in earthquake disturbed area.
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