Stability Analysis Of The Fengshou Landslide And Its Control Research

The Fengshou landslide in Baoxing County is featured by huge volume,wide area,and long length.In transverse,it can be divided into two parts: the west and east parts.And in longitudinal,it is divided into a slip deformation zone and a retrogressive zone.Currently,this landslide has deformed seriously,which is an unstable geological body with great potential hazard.Therefore,with the help of theoretical analysis and numerical simulation,the Fengshou landslide is studied here.Based on the limit equilibrium theory and strength reduction theory,the stability of the landslide was analyzed with the help of numerical simulation firstly.Then,the support effects of different composite modes of anti-slide piles were simulated and compared with the optimal composite mode of anti-slide piles being reached.Finally,the optimal composite mode of anti-slide piles was used to the prevention of the landslide with prefect result being achieved.The main conclusions of this study are as follows.(1)With the help of field investigation,drill,and in-door/out-door material experiments,the geological characteristics of the landslide are analyzed qualitatively.It is reached that this landslide is large-sized retrogressive landslide with great deformation and potential hazard.(2)Based on the limit equilibrium theory and strength reduction theory,a 3D model was established in the GID software to evaluate the stability of the landslide quantitatively.Furthermore,the deformation and failure rules of the main landslide body were studied.It is reached that:(1)In natural conditions,the west and east part of the landslide are both stable.In the heavy rain and seismic conditions,the both parts of the landslide will be unstable and the safety factor of the east main sliding body is obviously lower.The stability of the landslide is sensitive to its internal friction angle.And several slips have gone through by this landslide.Under a heavy rain and seismic condition,the possibility of a further sliding of the landslide is extremely high.And its following failure mode will be characterized by a creep to pull-splitting mode with great potential hazard.(2)Take the eastern main landslide body for example,it is simulated that the eastern landslide body is stable under natural conditions.Only local compression cracking occurs in the surface with minor deformation.Under a heavy rain condition,the landslide will become unstable with deep compression cracking appeared.Great slip distance of the whole body and significant falling distance will be observed.In such situation,the failure mode of the landslide is featured by a “leading edge shearing-trailing edge tension”,which is classified as a large retrogressive landslide.(3)With the help of FLAC3 D,the effect of pile section,pile spacing,pile length,and pile built-in depth on the support effects of anti-slide pile was analyzed with the optimal composite mode of anti-slide piles being reached.Then,the optimal composite mode of anti-slide piles was used to prevent the deformation of the landslide.Meanwhile,its functionary mechanism and the mechanism of its soil arching effect were studied in detail.Finally,this mode of anti-slide piles was used to the prevention of the landslide.And it is reached that:(1)Under same conditions,the support effect of rectangular section pile is better than that of round pile.Soil arching effect is a kind of extruded and "wedged" effect,which is mainly induced by non-homogeneous deformation of soil material and local stress migration around the pile.(2)With the increase of pile spacing,the pile internal stress presents an increase firstly and then falls into decrease;the displacements of the monitoring points and pile head and maximum displacement of slope increase continuously;the safety factor of the landslide decreases continuously with the plastic zone tending to run-through.It is noticed that the root cause for the generation of above phenomenon is controlled by the strength of the soil arching effect of the pile.And it is reached that the optimal pile spacing is 6m in this study.(3)With the increase of pile length,the scope of the frontal plastic zone of the landslide,displacements of the monitoring points and maximum displacement of the slope constantly decrease;the displacement of pile head,safety factor of the landslide and the internal force of the anti-slide pile increase continuously and finally tend to be stable.It is reached that the optimal pile length is 30 m in this study.(4)With the increase of pile built-in depth,the scope of the frontal plastic zone of the landslide,displacements of the monitoring points,maximum displacement of the slope and the safety factor of the landslide present a decrease firstly and then increase gradually;the displacement of pile head and pile internal stress decrease constantly.It is reached that the optimal pile built-in depth is 13 m in this study.(5)After strengthening with the optimal anti-slide pile mode,the rear part of the landslide presents a good stability.And the internal stress of the landslide is relatively low with the whole body being controlled by a compressive stress status.The safety factor of the landslide increases from 1.02 to 1.13 and the landslide displacement is reduced by about 10 times.Compared to the status without strengthen,the scope of the plastic zone decreases significantly and the soil arching effects is obvious.(6)Under the optimal anti-slide pile mode,the deformation of the anti-slide pile presents a relatively high value in the upper part and low value in the lower part.Its internal stress displays a high value in the middle and low values at both ends.Compared with the design results,the actual internal stress of the anti-slide pile is far below its ultimate bearing capacity,which meets the requirements of the codes.The support effect of the anti-slide pile mode is well which is advantageous for the stability of the landslide.