Research on Pile Settlement Caused by Large-area Disorderly Soil Stacking
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摘要: 某大型建筑工程因出土条件发生变化，施工工序有所调整，需在已施工的基桩上大面积堆土。大面积堆土会引起群体基桩的沉降，基槽开挖后基桩沉降离散性较大，最大基桩沉降高达670 mm，单体建筑物中基桩间沉降差最大极值高达510 mm，远超过规范计算值，沉降原因存在争议。采用有限元软件PLAXIS3D建立三维数值模型并对基桩沉降综合分析，结果表明，在已施工完成桩基上方大面积堆土可引起基桩较大沉降，地表及桩顶最大沉降均位于堆土中心，沉降最大与最小的两基桩上部负摩阻力相差一倍；按区域分析，大面积无序堆土引起基桩整体沉降趋势符合软土地区的沉降规律；各基桩产生较大离散性主要因素包括堆土厚度、堆土面积、堆土时间、排水条件、桩穿越土层情况、桩端下卧层的土层情况等。本研究为类似工程积累了经验。Abstract: A large-scale construction project needs to mound soil over a large area on the constructed foundation pile due to the change of excavation conditions. Large-area mounded soil will cause the settlement of group foundation piles. After the excavation of foundation trench, the settlement of foundation piles is discrete, and the maximum settlement of foundation piles is as high as 670 mm, the maximum extreme value of settlement between foundation piles in single buildings is as high as 510 mm, which far exceeds the standard calculation value, thus the settlement attribution is controversial. Using the finite element software PLAXIS3D, a three-dimensional numerical model was set up and comprehensive analysis of pile settlement was carried out. The results show that large area soil mounded above the completed pile foundation can cause large settlement of the foundation pile. Maximum settlement of ground surface and pile top are located at the center of the mounded soil, negative friction of two piles with maximum and minimum settlement is doubled; According to regional analysis, the overall settlement trend of pile caused by large area disorderly mounded soil conforms to the settlement law in soft soil area; The main factors of large dispersion of each foundation pile include: the height, area and time of the mounded soil, drainage conditions, soil layer conditions of pile crossing, soil layer conditions of underlying layer at pile end, etc. This research has accumulated experience for similar projects.
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表 1 各楼栋桩数及基桩沉降
区域 栋号 最大堆土厚度/m 沉降范围/mm 沉降平均值/mm 总桩数 洋房 1# 0（堆土后施工） 10～50 19.3 151 2# 0（堆土后施工） 10～50 16.7 151 19# 0（堆土后施工） 10～50 16.86 151 11# 4.0 60～180 101 179 18# 4.0（出入口位置） 55～390 159 179 20# 4.0 60～200 112 133 别墅 40# 2.8 55～130 91 57 41# 4.0（出入口位置） 160～670 249 57 42# 4.0 50～210 125 57 43# 4.0 110～620 222 57 44# 2.8 60～290 185 47 45# 4.0 50～370 218 57 46# 4.0 50～370 216 57 47# 2.8 120～200 136 57 
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表 2 别墅区域桩长平均桩顶沉降对比表
栋号 13 m桩平均桩顶沉降/mm 19 m桩平均桩顶沉降/mm 40# 78.7 100 41# 264.6（大） 230.3 42# 158.3（大） 101.5 43# 248.3（大） 206.1 44# 241.5（大） 144.1 45# 245.8（大） 197.9 46# 205.8 226.9 47# 112.9 153.9
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表 3 土层分布及物理力学参数
土层名称 层厚
/m天然重度
γ/（kN·m−3）黏聚力
c′/kPa内摩擦角
φ′/（°）参考割线模量
E50/MPa参考切线模量
Eoed/MPa加卸载模量
Eur/MPa初始剪切模量
G0/MPa剪应变
γ0.7黏土 6.2 17.9 21.1 13.0 3310 3310 13.2×103 39.7×103 0.2×10−3 粉质黏土 6.8 19 22.5 13.1 3900 3900 15.6×103 46.8×103 0.2×10−3 粉质黏土 9 19.7 27.5 16.6 4850 4850 19.4×103 58.2×103 0.2×10−3 粉质黏土 13 19.5 28.9 15.7 4710 4710 18.8×103 56.6×103 0.2×10−3 粉质黏土 25 19.8 28.5 16.5 5020 5020 20.1×103 60.2×103 0.2×10−3
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