Study On Stability In Rocky Layered Slope Under Blasting Vibration

With the rapid progress of the society and with the rapid development of our national economy, the infrastructure industry, such as highway, railway, water conservancy and hydropower engineering, and strip mine always meet layered slope, which is the most hazardous and the most difficult to be treated. Using the pseudo-static method, how to select the reasonable pseudo-static coefficient to evaluate and research the influence of blasting vibration on the layered slope becomes a hot problem concerned by rock mass field and blasting engineering field. Combining with the practical engineering of limestone strip mine of Emei cement plant and the characteristic of blasting, the mini-type blasting vibration test-bed was designed. The stability of layered slope with weak intercalation caused by blasting was systemically analyzed based on the theory deductions, experiments in laboratory and the in-site blasting test.1. Analyzed the main factors effected the deformation and failure of the layered rock slope. Because the static analysis methods of landslide system had been fully developed, and the stability analysis methods under blasting were still at a stage of exploration, the pseudo-static analysis method was often used to calculate the safety factor of slope stability.2. Based on the Mohr-Column criteria, the explicit expression of the safety factor of layered slope stability was deduced by method of limit analysis under the blasting load acting on the center of slice mass and the unload of surface of slope.(1) From the viewpoint of the direction of blasting load, the outwards horizontal blasting load, the downwards vertical one as well as their combined one were disadvantageous to the stability of layered slope.(2) There was a negative exponential relationship between the safety factor of layered slope stability and the pseudo-static coefficient of the outwards horizontal blasting load, when the potential landslide under the nature condition was acted on the outwards horizontal blasting load. When the pseudo-static coefficient of the horizontal load was added 0.05 from 0 to 0.3, the safety coefficient of layered slope with or without stratification cracking was reduced 7.786% to 10.665% and 7.61% to 10.546%, respectively.(3) When the potential landslide was under the nature condition, the relationship between the safety factor of layered slope stability and the downwards vertical blasting load submitted to the curve of s. When the pseudo-static coefficient of the upwards vertical load was added 0.05 from 0 to 0.3, the safety coefficient of layered slope was reduced 2% to 3.5%. So, the upwards vertical blasting load influenced little on the stability of layered slope.(4) When the potential landslide under the nature condition was acted on the outwards horizontal and downwards vertical blasting loads, with the increase of the pseudo-static coefficient of the combined blasting load of outwards horizontal one and the downwards vertical one, the safety factor of layered slope in instability condition reduced continuously. When the downwards vertical blasting load was invariable, the relationship between the safety factor of layered slope stability and the pseudo-static coefficient of the outwards horizontal blasting load and downwards vertical one submitted to the curve of negative exponential and s, respectively.(5) The stratification cracking effect had a bad influence on the stability of layered slope and reduced its stability. Under the same other terms, the stability of layered slope linearly reduced with the increase of length of stratification cracking, and especially, the reduction was the most obvious when the length was less than 20m. Under the same other terms, the stability of layered slope clearly increased with the increase of cohesive force of sliding interfaces, and especially, the influence was the most obvious when the cohesive force was less than 60KPa. Under the same other terms, the stability of layered slope clearly increased with the increase of internal friction angle of sliding interfaces, and especially, the influence was the most obvious when the internal friction angle was less than 20°.(6) When the potential landslide was under the nature condition, the influence of blasting load on the stability of layered slope not only related to the level of blasting load, but also related to the action direction. When the potential layered rock slope was acted on the outwards horizontal and downwards vertical blasting loads, the angle between the direction of load and the horizontal direction was beneficial to the stability of layered rock slope.3.The simple motion mechanics model of layered rock slope was established. Only when the acceleration was less than zero, the potential landslide system could be in a stable state. But there were various factors that could affect the stability of the potential landslide system, and the change of factors and theirs effects induced the change of equilibrium between F cos(α-β) + w sinαand T (v₀), even induced the change of stability of the potential landslide system.4. According to the similarity principle of the simulation, the mini-type blasting vibration test-bed was designed, which could simulate the blasting vibration of vertical direction, horizontal direction and arbitrary direction. The blasting vibration test-bed was independent on the simulation objects, and could simulate the vibration of layered rock slope under blasting.(1) When the potential landslide was acted on the downwards vertical blasting load, the relationship between velocity of vertical vibration and obliquity and decrement of internal friction angle of sliding interfaces of layered slope in limit equilibrium state obeyed the logarithm law and linearity law, respectively.(2) When the velocity and the frequency of vertical vibration were invariable, the relationship between the angle of static friction and its decrement obeyed linearity law, and the relationship between the frequency of vertical vibration and the decrement of static friction angle submitted to the curve of power function.(3) When the potential interface under different intensity condition was acted on the outwards horizontal blasting loads, the relationship between the velocity of vertical vibration and the of obliquity of potential interface and the decrement of the internal friction angle submitted to the curve of logarithm function and linearity, respectively.(4) When the velocity of vertical vibration acted on the outwards horizontal blasting loads were invariable, the relationship between the velocity of vertical vibration and the cohesive force of potential interface submitted to the curve of logarithm function, and the relationship between the obliquity of potential interface and the internal friction angle submitted to the curve of linearity function.(5) When the layered slope in different condition was acted on the outwards horizontal blasting load with different velocity of vertical vibration, the pseudo-static coefficient of the potential landslide system in limit equilibrium state was tens times to hundreds times. When the layered slope with the obliquity invariable was acted on the outwards horizontal blasting load, the relationship between the pseudo-static coefficient of the outwards horizontal blasting load and the internal friction angle of sliding interfaces of layered slope obeyed the linearity law, that was to say, the pseudo-static coefficient of the outwards horizontal blasting load decreased with the increase of internal friction angle.5. When the velocity of vertical vibration of the layered rock slope was 7or 8 cm/s, the pseudo-static coefficient of the blasting load was less than 0.3, that was to say, blasting dynamic reduction coefficient was 5.25‰or 3.28‰when strength reduction method was accepted, blasting dynamic reduction coefficient was 0.242‰or 0.154‰when equivalent safety coefficient method was accepted, and the slope was in stabile condition. Meantime the relation between the velocity of vertical vibration and blasting dynamic reduction coefficient was obtained, therefore the pseudo-static coefficient of the outwards horizontal blasting load was determined under different velocity of vertical vibration. Generally, using the same blasting dynamic reduction factor would lead to the safety factor of layered slope stability much difference with the difference of the velocity of vertical vibration, which indicated that the blasting dynamic reduction factor must be taken into account to modified the pseudo-static coefficient of the blasting load.