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黄土塬地区桩基问题研究匮乏,依托陇东首栋超高层建筑,在试验桩身上布置混凝土应变计、钢筋应力计,承台底板下和桩端布置土压力盒,对原地基土、单桩基础和单桩承台基础分别进行现场原位载荷试验;利用ANSYS有限元软件对全短桩基、全长桩基及长短桩组合桩基在竖向荷载作用下的筏板沉降变形、地基土应力场与沉降变化进行分析。结果发现:(1)黄土塬场地地基土夹层交互分布、湿陷性不连续,存在由非湿陷性黄土变成湿陷性黄土的可能,桩周土层对桩基内力传递与分布影响显著,桩身出现多个中性点,湿陷性土层下限深度确定更加复杂;(2)各级荷载作用下,桩基Q-S曲线呈缓变型发展,表现为典型的摩擦型桩,桩身内力发挥具有异步性;试验加载至8 000 k N时,桩顶最大沉降为8.15 mm,单桩和单桩承台端阻力分别仅占桩顶荷载的4.8%和2.1%;(3)单桩承台基础中承台底部实测反力呈倒“盆”形分布、边缘应力较大,桩–土–承台体系的承载性能优于单桩基础;桩基础设计时,可结合经验以承载力和最大允许变形量进行控制,提高桩身线刚度抵抗自身压缩变形,减小桩基上部沉降;(4)长短桩组合桩基础充分利用与发挥了长桩控制沉降的作用与地基土浅层承载的能力,减少了长桩数量,节省了桩基造价,值得进一步深入研究。
In the loess plateau, there is a lack of research on the pile foundation. Based on the first super high-rise building in Longdong, concrete strain gauges, steel bar stress gauges, soil pressure boxes under the bottom plate and pile ends are arranged on the test pile, The foundation and single-pile cap foundation are respectively subjected to on-site load test in situ. The deformation and deformation of raft under full-pile foundation, full-length foundation and long and short pile foundation are simulated by ANSYS finite element software. Stress field and settlement changes are analyzed. The results show that: (1) the interbed and subsoil of loess plateau are interactively distributed and the collapsible collapses are not continuous, and the possibility of the formation of collapsible loess from non-collapsible loess is obvious. The effect of soil around the pile on the internal force transmission and distribution of pile foundation is significant , Multiple neutral points appear in pile body, and the lower limit depth of collapsible soil layer is more complicated. (2) The QS curve of pile foundation shows a gradual change development under all load levels, which is typical of friction pile and pile body internal force The maximum settlement of pile top is 8.15 mm, the end resistance of single pile and single pile cap only accounts for 4.8% and 2.1% of the pile top load respectively; (3) Single pile cap In the foundation, the measured reaction force at the bottom of the cap was inverted “basin ” shape distribution, the edge stress is larger, and the bearing capacity of pile-soil-cap platform system is better than that of single pile foundation. And the maximum allowable deformation control, improve the stiffness of the pile body to resist its own compression deformation, reducing the settlement of the upper pile; (4) long and short pile combined pile foundation make full use of and play the role of long pile control settlement and shallow foundation soil bearing The ability to reduce the number of long piles, saving pile cost, it is worth further Study.