Experimental Study On Engineering Characteristics Of Inclined Friction Slope-foot Piles Under Repeated Loading And Unloading Of Embankment

Inclined piles are often used in the foundation of high-rise structures such as bridges,wharfs and transmission lines to resist large horizontal loads.As active piles,their working mechanism is concerned.According to the patent(patent number:ZL 201621328014.7)of the research group,the inclined piles are used at the foot of embankment slope to resist the lateral movement of soft soil.Through the model test,the displacement law of double-row inclined friction piles at the top of the embankment at the foot of repeated loading and unloading downhill is studied,which provides a basis for the design,construction and monitoring of anti-slide piles at the foot of the slope.The results show that:(1)During the loading process,relationship between the longitudinal axis and the lateral displacement curve of the friction pile body with the top constraint presents inverted trapezoid with "the top wide,and the bottom narrow",and the destroy mode is"moving and turing around the bottom of the pile".For the inclined pile with 0?9°,the lateral displacement of the pile body is decreasing as tilt angle increasing during loading.During the first loading process,the lateral displacement of pile increases with the increase of loading.During the second loading process,the lateral displacement of pile is not sensitive at the first limit pressure range,when the pressure exceeds the first limit pressure,the lateral displacement increases with the increase of load;The growth of lateral displacement decreases when loaded to a certain pressure.(2)During the first loading process,the lateral displacement of the top of each inclined pile is getting larger with the increase of load.When loading improves to a certain value,the lateral displacement of the top of vertical pile suddenly increases and takes the lead in yielding,and then tends to stability.During the second loading process,the lateral displacement of the top of pile is slow getting larger with the increase of load.The lateral displacement of the top of inclined pile increases suddenly when the load exceeds the maximum load of the first loading,the lateral load and the lateral displacement curve will return to the extension line of the first loading curve,and it is memory effect,then yield and stabilize.(3)During the unloading process,the lateral displacement of each section of the pile is not sensitive,and only the unloading to final 1-2 stage load is significantly reduced.(4)During the loading process,the change curve of axial force P and the distance z from the top of the pile is "S" shape after the load reaches a certain value,while the change curve of the 9 pile presents "3" shape with two peaks.The maximum axial force and bending moment section of 0,3 and 6 degree piles with relatively large displacement at the top of piles show cracks,and the axial force and bending moment of the pile section increase sharply at the corresponding crack location.The bending moments of cracked 0 pile,3 pile and 6 pile in 51.14 kN-70.988 kN load range are abnormally large,while the bending moments of other positions are basically unchanged.When the load is increased to 84.22 kN,the axial force and bending moment of pile body will no longer increase.(5)During the unloading process,the axial force and bending moment of each section of the pile are very sensitive at first,and they are no longer sensitive to the subsequent stages of loads.Only when the final stage of loads is unloaded,there are obvious changes.The axial force curves of cracks in 0 pile,3 pile and 6 pile after the second and third complete unloading are obviously convex,and there is no axial force in other positions.(6)Before cracks occur,that is,during the first loading process,the maximum frictional resistance of the back row piles is obviously smaller than that of the front row piles,and the inclined piles with larger angle are obviously larger than those with smaller angle.When unloading,unloading friction changes most at the beginning.(7)During the loading process,the change curve of soil pressure along the pile side and the longitudinal axis are all triangular with "small up and down and large in the middle".That is to say,with the increase of load,the soil pressure on the side of 0 and 3 piles increases gradually,and the increase rate of soil pressure on the middle side of the pile is greater than that on the top.and bottom of the pile.The earth pressure of the maximum pile side of the 3 degree pile is greater than 0 degree.When loading is added to 70.988kN,the lateral pressure of the front pile does not increase.