Research On Lateral Seisimic Behavior Of 2×2 Straight Oblique Pile-group Based On Shaking Table Test

The pile foundation is applied to various fields of civil engineering with its advantages of stability and durability.The dynamic response of pile foundation in liquefied soil has always been a hot spot in the field of geotechnical engineering.Previous studies have shown that different ground motion strengths have great differences in the damage of pile-group.In this paper,the vibrational test of the lateral dynamic response characteristics of non-liquefied sand and two groups of saturated sand with different thicknesses is carried out.The main contents include: under the input of sine wave and seismic wave,shake table test of straight slant pile group in non-liquefied sand,300 mm and 380 mm thickness saturated sand,Through the processing of the test data,the lateral acceleration and displacement response characteristics of the pile cap are analyzed,and the bending moment envelope diagram of the pile body under different working conditions and the real-time variation of the bending moment at a certain point of the pile during the vibration process are plotted.Firstly,Straight inclined pile-group model test by electromagnetic vibration table,according to similarity theory,design 2×2 straight pile-group and 2×2 inclined pile-group superstructure model,The mesa input has a sine wave with a peak value of 0.15 g and a seismic wave with a peak value of 0.2g.In the test,sensors such as acceleration,displacement and pore pressure were arranged.The model soil consisted of non-liquefied sand,300 mm and 380 mm saturated sand with different thicknesses.Straight oblique pile strain was obtained by FBG sensing system.Secondly,the comparative analysis of the experimental vibration data is carried out to compare the acceleration and displacement of the straight pile-group and the inclined pile-group cap in each type of sand with respect to the table top acceleration and displacement magnification,and at the same time,give the saturated sand.The pore water pressure develops and changes,and then studies the lateral dynamic response characteristics of pile groups under liquefaction.The comparison results show that in all types of sand,the acceleration and displacement amplitude of the pile cap of the straight inclined pile-group have a certain degree of amplification effect,and the amplification effect in the saturated liquefied sand is better than that in the non-liquefied dry sand.More significant,and the amplification effect of the thicker(380mm)saturated sand is the most obvious,indicating that the horizontal dynamic response of the pile is sensitive to the liquefaction of the sand layer,and with the increase of the thickness of the liquefied soil layer,the pile The lateral dynamic response is also more pronounced.At the same time,the magnification of the straight pile-group in all types of sand is larger than that of the inclined pile-group,and it can be concluded that the inclined pile-group can better resist horizontal seismic loads.Finally,the enveloping diagram of the bending moment of the pile body can be seen: the bending moment distribution of the straight inclined pile-group is basically symmetrical,and the maximum point of the bending moment of the pile body is the joint between the pile top and the cap and the bottom of the pile.After the liquefaction of the soil,the bending moment of the pile body of the straight inclined pile-group is obviously increased compared with the non-liquefied sand soil,which indicates that the bending moment at each section of the pile body of the pile-group is related to the liquefaction of the sand.For the straight pile-group,the bending moment of the pile body is proportional to the thickness of the saturated sand soil;while the bending pile-group has no obvious difference in the bending moment of the two kinds of saturated sand pile body,indicating the bending moment of the pile-group of the inclined pile-group the size is not proportional to the thickness of the saturated sand.This law is also observed from the real-time variation of the bending moment at the top section of the pile.In all types of sand,the difference between the straight pile-group and the inclined pile-group is the most obvious position displacement pile bottom.The maximum bending moment of the straight pile-group at the pile bottom section is significantly larger than that of the inclined pile-group,indicating that when subjected to the same lateral dynamic load,The inclined pile-group has a better bending resistance.