An experimental study of the stress-strain relationship of different excavation paths for soft soil K0 consolidation
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摘要:
基坑开挖过程中不同部位的土体会因不同的卸荷力学行为而表现出动态的破坏特性。为研究基坑土体开挖过程中复杂的卸荷应力路径，利用TSZ-1S应力控制式三轴仪分别对湖相沉积的泥炭质土进行固结不排水及K0固结下的加、卸荷试验，并按侧向、轴向、轴侧向同时卸荷等不同卸荷条件制定试验方案，模拟基坑开挖过程中不同部位土体卸荷路径下的应力-应变曲线、卸荷剪切破坏时的强度及初始切线模量等的变化规律。试验结果表明：土体的应力-应变特性与应力路径密切相关，各路径下应力-应变曲线都近似呈双曲线型；卸荷剪切破坏时强度明显低于加荷破坏。对不同卸荷路径下初始切线模量（Ei）的研究发现，Ei受侧向卸荷影响较大，卸荷后Ei有所提高，轴向卸荷对其影响较小。对各应力-应变曲线进行归一化处理，构建了考虑不同归一化因子的归一化方程，以该方程为基础对不同应力路径下的泥炭质土进行归一化处理，并对结果进行了验证，效果良好。本研究可为泥炭质土场地上基坑在不同卸荷路径下的变形参数和本构关系的研究提供参考。
Abstract:In the process of foundation pit excavation, the soil mass in different parts shows dynamic destruction characteristics due to diverse unloading mechanics. In order to study the complex unloading stress path in the foundation excavation, the TSZ-1S stress control triaxial compression apparatus is used to carry out the loading and unloading tests of the lacustrine sedimentary peat soil under the conditions of consolidation undrained and K0 consolidation, respectively, and the test scheme is formulated according to different unloading conditions such as lateral, axial and axial lateral meantime unloading, so as to simulate the stress-strain curves of soil under different unloading paths in the foundation excavation and the variation laws of strength and initial tangent modulus under unloading shear failure. The test results show that the stress-strain characteristics of soil are closely related to the stress path, and the stress-strain curves under each path are approximately hyperbolic. The strength of unloading shear failure is significantly lower than that of loading failure. The study of initial tangent modulus Ei under different unloading paths shows that Ei is greatly affected by lateral unloading, Ei increases after unloading, and axial unloading has little effect on it. The stress-strain curves are normalized, and the normalization equation of peat soil considering different normalization factors is constructed. Based on this equation, the peat soil under different stress paths is normalized, and the results are verified. The results of this work can provide reference for the study of deformation parameters and constitutive relations of foundation pits on peat soil sites under different unloading paths.
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Key words:
- peat soil /
- unloading path /
- K0 consolidation /
- stress-strain /
- starting tangent modulus /
- normalization
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表 1 不同卸荷路径下三轴剪切试验方案
Table 1. Triaxial shear test schemes under different unloading paths
试验分组 σ3/kPa 固结方式 卸荷路径 剪切路径 ① 100 等向固结 无 σ3不变，σ1
逐渐增大150 225 ② 100 K0固结 无 150 225 ③ 100 K0固结 σ3每级减10 kPa至破坏 σ1不变，σ3
逐渐减小150 σ3每级减15 kPa至破坏 225 σ3每级减20 kPa至破坏 ④ 100 K0固结 σ3=100→90→80→70→
60→80→100σ3不变，σ1
逐渐增大150 σ3=150→135→120→
105→90→120→150225 σ3=225→205→185→
165→145→185→225⑤ 100 K0固结 每级σ3变化与④组一致，σ3减小时沿K0线减小σ1，后恢复至初始状态 150 225 ⑥ 100 K0固结 σ1=133→128→123→
118→113→123→133150 σ1=200→192→185→
177→170→185→200225 σ1=300→290→280→
270→260→280→300注：σ1、σ3分别表示大、小主应力。 
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表 2 Ei与σm拟合表达式及参数值
Table 2. Ei and σm fitting expressions and parameter values
试验组 σm/kPa Ei/MPa R2 表达式 ① 100 33.84 0.998 
150 44.27 225 57.84 ② 111 31.91 0.958 
167 39.60 250 67.98 ③ 111 23.02 0.986 
167 27.37 250 31.68 ④ 111 62.77 0.945 
167 69.69 250 110.87 ⑤ 111 57.01 0.947 
167 75.76 250 88.18 ⑥ 111 30.62 0.999 
167 43.98 250 64.31
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