| Blasting method in the deep foundation pit excavation has already been widely applied in transportation, water conservancy, hydropower and defense engineering and other fields. By this way, blasting seismic effect is inevitable. The influence of seismic effect on the slope stability has drawn great attention in geotechnical engineering and blasting engineering. It is especially important in blasting excavation engineering of soft rock deep foundation pit. Therefore, on the one hand, we need to study the control technology of blasting vibration, on the other hand, we must correctly analyze the stability of the slope under the blasting effect to guarantee the project safety and improve the progress and benefits of engineering. Therefore, it has important theoretical value and social significance to carry out the slope stability analysis of the soft rock blasting excavation of the deep foundation pit.Taking the gravity type anchor ingot pit excavation of Nanxi Yangtze River Bridge as a specific example, the in-situ test, mathematical statistics, and numerical simulation methods are used in the slope stability analysis of blasting excavation of the deep foundation pit, and the dynamic and static stability analyses of deep foundation pit high slope under various conditions are carried out. The research work and achievement are mainly embodied in the following aspects.Based on the engineering geology, combined with the structure characteristics and the design requirements of the soft rock deep pit, the blasting excavation scheme of the deep pit is proposed. In the process of bedrock excavation, blasting vibration test is conducted, while on-site blasting data is monitored. Test results show that the vertical peak vibration velocity is higher than the horizontal peak vibration velocity in the foundation pit excavation. The blasting charge in the same period is the key parameter to control blasting vibration. Through the statistical analysis, the seismic wave attenuation formulas of the excavation blasting are deduced.The typical section of northern pit slope is selected to set up 3-D numerical model. Through the limit equilibrium method and FLAC3D, stability of foundation pit slope in natural state and rainfall condition is analyzed. The results show that high slope after excavation keeps the basic stability. But the second soil slope toe has larger horizontal displacement, and two potential sliding zones turn up. In the rainfall condition, the numerical calculation fails to converge, and the safety factor declines 17%.Taking the in-situ measured vibration data as input loads, the dynamic response characteristics of displacement and speed in the slope under blasting loads are explored. Repeated blasting loads result in cumulate permanent displacement in the second soil slope toe. Through the comparative analysis in the calculated and the measured values, the result shows that FLAC3D is feasible for numerical simulation of dynamic response in the slope under the blasting. The results can provide the basis for improving blasting scheme and taking-support measures.Based on the supporting structures which are actually used in the foundation pit, the reinforced pit slope is simulated by FLAC3D. The effect of the bolt supporting in the slope is evaluated. The stability of the reinforced slope and the bearing forces of retaining structure under different conditions are studied. Calculation results are consistent with actual partial collapse in the process of foundation pit slope excavation due to heavy rains and repeated excavation blasting. Several suggestions are offered to prevent these kinds of collapse accidence. |
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