73 / 2019-07-29 00:21:12

Typical failure mode of soil arch behind cantilever anti-slide pile in strong earthquake zone

cantilever anti-slide pile,earthquake,soil arch,numerical simulation,deflection

水库地质灾害防治与生态环境保护 > 表生地质作用与地质灾害演化过程

The study on the stability of overburden rock and soil accumulation slope is a hot and difficult point in the field of engineering geology. For the reinforcement of this kind of slope, the cantilever pile with extremely long and large cross-sectional area must be used. Due to the large content of coarse particles in the accumulation body, the value of internal friction Angle is larger, and the soil before and between anti-slide piles is excavated after the construction of anti-slide piles, which gives full play to its shear strength. So cantilever anti - slide pile soil arch effect is obvious. For anti-slide pile, soil arch is the structure to transfer the landslide thrust, and for the sliding (slope) body behind the soil arch, soil arch is the supporting structure to prevent it from moving forward, so the stable existence of soil arch behind the pile is the premise for cantilever anti-slide pile to play the supporting function. So this paper studies the mechanism of sudden failure of soil arch behind cantilever anti-slide pile.
Through literature research and field investigation, this study concludes that there are three typical modes of soil arch effect failure of cantilever anti-slide pile in strong earthquake zone. One is the increase of the load on the soil arch body caused by the seismic dynamic force. Another one is that the combined effects of vibration and rainfall during the earthquake cause the soil strength of the arch to decrease, which leads to the sudden failure of the arch. The last one is the anti-slide pile deflects during the earthquake, which causes the soil arch to lose its stable support and become invalid. The first two failure modes have been involved in existing researches, while the third mode has not been studied or described in existing literatures due to the regional particularity of seismic zones. Therefore, the failure mode of soil arch caused by deflection of anti-slide pile is studied.
Through FLAC3D finite difference numerical simulation software, this study established a cantilever anti-slide pile simulation, as shown in Fig. 1. In this model, there are 3 rectangular cantilever anti-slide piles. By simulating sliding surface and accumulation body, this model can simulate different landslide thrust forces. The geometric characteristics of the model and the strength parameters of related rock and soil mass and pile are set according to the existing literature. Fig. 2 shows the layout and naming of anti-slide piles. After the model successfully simulated the arch effect, the numerical study was carried out in two situations: one was to simulate the failure process of soil arch when pile B deflected, and the other was to simulate the failure of soil arch when all anti-slide piles deflected at the same time. The deflection of anti-slide pile is realized by applying traction force on the top of anti-slide pile and the cloud maps of the maximum principal stress at the section 5 meters below the pile top are taken as research objects.
In Fig. 3, a, b and c are respectively the maximum principal stress nephograms of the single pile deflection test before the deflection of the pile, when the pile has a small amount of deflection and when the pile has a large amount of deflection. It can be seen from the figure that the soil arch existed before the deflection of the pile, but the original soil arch began to break after the deflection of the pile, and a new arch formed between the two adjacent piles. As the deflection of the pile increased, the new arch broke. By checking the displacement of each pile, it can be found that when the displacement of a single pile occurs, there is no deflection of adjacent piles at the beginning, but later all piles are deflected, which indicates that the deflection of a single pile will not only cause the failure of soil arch, but also cause the overall failure of adjacent piles.
When all the anti-slide piles deflect together, the original arch does disappear. Fig. 4 and Fig. 5 are the cloud maps of the maximum principal stress before and after the overall migration of anti-slide pile. Meanwhile, in this model, when the offset of anti-slide pile reaches 3 cm, the original soil arch will disappear.