黄土地区桩基水平承载性状及计算方法研究

Loads and moistening will cause damage to the micro-structure of loess around pile, which influences the behavior of laterally loaded piles. However, the mechanism of the pile-soil interaction under lateral loads in loess region is still not clear. In this project, field tests for the laterally loaded pile in loess region will be firstly carried out. The change rules of the lateral deflection and inner force of the pile and the soil reaction around pile with the lateral and axial loads at pile head and the water content of loess will be determined. Then the numerical models for piles subjected to lateral loads and to combined axial and lateral loads will be built respectively. The distribution characteristics of soil stresses around pile and the damage evolution law of the micro-structure of loess under loads and moistening will be analyzed and obtained. Influences of pile diameter, pile length, pile stiffness, boundary conditions at pile head, and properties of loess around pile on the lateral deflection and inner force of the pile and soil reaction around pile, especially on the maximum pile displacement, the maximum pile bending moment and its position, will be determined. Based on the field test and the numerical computing results, the simple and convenient calculation methods of the lateral deflection and inner force for laterally loaded piles and piles under combined axial and lateral loads, in which influences of the increase of the water content of loess are considered, will be put forward. The achievements of the project help to more deeply understand the bearing features of laterally loaded piles in loess region, and provide some basis and calculation methods for design.

加载和增湿会引起桩周黄土结构损伤，从而对桩基水平承载性状产生影响，然而目前对黄土地区水平荷载作用下桩土相互作用机理的认识尚不清楚。本项目首先开展黄土地区桩基水平承载现场试验研究，确定桩身侧向变形和内力及桩侧土反力随桩顶水平荷载、轴向荷载及黄土含水量的变化规律。然后分别建立水平荷载作用下及轴、横向荷载共同作用下桩基承载数值计算模型，分析并得到加载及增湿作用下桩周土应力分布特点及桩周黄土结构损伤演化规律，确定桩径、桩长、桩身抗弯刚度、桩顶约束条件、桩周黄土的性质等因素对桩身侧向变形和内力及桩侧土反力的影响，重点分析对桩身最大位移、最大弯矩及桩身最大弯矩所在位置的影响。基于现场试验及数值分析结果，提出可以考虑黄土增湿影响的水平荷载作用下及轴、横向荷载共同作用下桩身侧向变形和内力的简便计算方法。研究成果有助于深入认识黄土地区桩基水平承载特性，为该地区水平承载桩的设计提供依据和计算方法。

加载和增湿会引起桩周黄土结构损伤，从而对桩基水平承载性状产生影响，然而目前对黄土地区水平荷载作用下桩土相互作用机理的认识尚不清楚。本项目开展了水平荷载作用下和竖向荷载作用下湿陷性黄土场地桩基现场浸水试验，分析了桩土荷载传递规律；开展了竖向与水平向组合荷载作用下及上拔与水平向组合荷载作用下桩基室内模型试验，分析了竖向荷载对黄土地层中桩基水平承载性状的影响，以及水平荷载对桩基竖向承载性状的影响；开展了常法向应力和变法向应力下原状黄土与混凝土接触面大型直剪试验；开展了重塑黄土与混凝土接触面大型直剪试验，分析了法向压力、剪切速率、接触面粗糙程度、黄土含水量、土样固结、泥皮厚度等对接触面剪切性状的影响。针对工程中桩基础存在初始微倾斜、有承台的桩基础桩头旋转等问题，基于地基反力法提出了纵向和横向组合荷载作用下桩身侧向变形和内力的计算方法。提出了竖向与水平向组合荷载作用下斜桩承载的p-y曲线法。揭示了黄土地区地形地貌对桩基工程和公路建设的影响。研究成果有助于深入认识黄土地区桩基水平承载特性，为该地区水平承载桩的设计提供依据和计算方法。