Study On Properties Of Inclined Pile And Distribution Characteristics Of Soil Pressure In Foundation Pit Supporting

With the development of engineering construction in China,the underground space has been developed on a large scale,and new types of foundation pit support have emerged continuously.In recent years,inclined piles as one of the new types of support structures has been applied in some regions.Engineering practice shows that compared with traditional vertical piles,under the same conditions,the inclined supporting piles has a better ability to control deformation and smaller bending moments in the pile body,it has a good application prospect.At present,the calculation model and design method of inclined pile support structure are not perfect,the mechanism of stress and deformation of inclined pile support structure needs further research.In this paper,the indoor model test and numerical simulation analysis methods are used to study the behavior and earth pressure variation of inclined piles during foundation pit excavation.The main research contents and results are as follows:(1)The research status of inclined pile model tests,numerical simulation and earth pressure variation is summarized by reviewing relevant domestic and foreign literature.(2)An indoor model test method was used to study the behavior and earth pressure changes of two types of support structures(single row piles and inclined straight piles)during the excavation of the foundation pit.The results show that compared with straight piles,when the inclination angle increases from 10 ° to 20 °,the bending moment of the pure inclined pile decreases by 26.91% ～55.35%,the displacement of the crown beam of the pure inclined pile decreases by 21.54% ～57.23%,the ground settlement after the pure inclined pile decreases by 36.32% ～49.45%,the displacement of the crown beam of the oblique straight pile decreases by 75.40%～92.67%,and the ground settlement after the oblique straight pile decreases by 84.57%～93.43%.Compared with the inclined straight pile at 10 °,as the inclination angle increases from 15 ° to 20 °,the bending moment of the straight pile on the non-excavation side decreased by 20.54%～31.50%,and the bending moment of the inclined pile on the excavation side decreased by 17.39%～24.64%.The two types of support structures are superior to traditional straight pile support structures in limiting the settlement of ground soil in the foundation pit and improving the stability of the pile structure.Among them,there is an internal support effect for the integral rigid frame structure formed by the crown beam of the inclined straight pile,with smaller stress and deformation of the support structure,and the support effectiveness ability is significantly improved;The earth pressure behind the piles of the two support structures gradually decreases with the excavation of the foundation pit while the earth pressure before the piles gradually increases.Under the same excavation depth,the relationship between the magnitude of active lateral earth pressure meets the following requirements: straight pile>inclined straight pile>pure inclined pile.The relationship between the magnitude of passive lateral earth pressure meets the following requirements:straight pile>pure inclined pile.(3)FLAC3D numerical simulation method was used to study the mechanical deformation,soil displacement and earth pressure changes of inclined pile support structures.The results show that the deformation of pure inclined piles in single row piles is similar to that of straight piles.With the increase of the inclination angle,the ability of the support structure to resist horizontal loads increases and the displacement of the pile body gradually decreases.Compared with straight piles,the displacement of pure inclined piles decreases by 33.37% ～ 61.43% with the increase of the inclination angle.Compared with 10 ° inclined straight piles,the displacement of the straight piles on the nonexcavation side decreases by 69.72%,and the displacement of the inclined piles on the excavation side decreases by 59.24% with the increase of the inclination angle.The deformation and stress of the inclined straight pile are smaller,and the displacement distribution pattern of the pile body is similar to that of the straight pile with internal support.The variation of earth pressure behind piles and the law of ground settlement behind piles for single row piles and inclined straight piles are the same as the results of indoor tests.The maximum lateral displacement of soil behind piles gradually decreases with the increase of inclination angle.The relationship between the magnitude of passive earth pressure before piles meets the following requirements: straight pile >pure inclined pile >inclined straight pile.(4)The coupling numerical simulation method PFC3D-FLAC3 D was used to study the micromechanism of soil deformation behind piles during foundation pit excavation.The results show that with the excavation of the foundation pit,the porosity between the particles behind the pile gradually increases,the size and position of the contact force chain change,the horizontal stress between the particles gradually decreases,and the horizontal and vertical displacement of the particles behind the pile gradually increases.