Mechanical Properties and Water Holding Characteristics of Initially Isotropic Soils and Transversely Isotropic Soils
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摘要: 为了探讨不同初始状态下非饱和黄土的力学性质和水量变化规律之间的差异，提出了制备各向同性及横观各向同性试样的方法，用改进的非饱和土三轴仪对制备的各向同性、横观各向同性及常规重塑试样进行了72个三轴固结排水剪切试验. 试验结果表明：对不同削样角度的各向同性试样进行试验验证，发现其近似各向同性；3种不同初始状态下各向同性非饱和试样的破坏应力最大，横观各向同性非饱和试样次之；横观各向同性试样在剪切阶段的初始切线模量最大，其他两组试样的初始切线模量较小且近似相等；各向同性试样及横观各向同性试样在剪切的初始阶段均有轻微的剪胀现象，常规重塑试样均处于剪缩状态；不同初始状态下的各非饱和试样在剪切阶段吸力变化对排水的影响并不显著，其中横观各向同性试样的偏应力-含水率关系曲线的斜率绝对值最小，其他两组试验的斜率几乎相同，各向同性、横观各向同性及常规的重塑试样的力学特性及持水特性不尽相同. 本文的研究成果可为不同初始状态下各模型的建立及工程应用提供有益的参考.Abstract: In order to investigate the difference between the mechanical properties and water quantity variation of unsaturated loess under different initial conditions, a method for preparing isotropic and transversely isotropic specimens was suggested. An improved triaxial apparatus for unsaturated soils was used to carry out 72 consolidated drained triaxial tests on prepared isotropic, transversely isotropic and regular specimens. Isotropic samples with different cutting angles were studied experimentally and found to be approximately isotropic. For three different initial states, the failure stress of the isotropic unsaturated specimen is the largest, followed by that of the transversely isotropic unsaturated specimen; the initial tangent modulus of the transversely isotropic specimen is the largest at the shear stage, while those of the other two groups are smaller and approximately equal. Both the isotropic and transversely isotropic specimens have slight dilatancy at the initial stage of shear, while all ordinary remoulded specimens are in the state of shear contraction. Under different initial conditions, the change of the suction of unsaturated samples has little effect on the drainage, the absolute slope value of the deviator stress-water content curve of the transversely isotropic sample is the lowest, and those of the other two groups are almost the same. The mechanical properties and water holding characteristics of the isotropic, transversely isotropic and ordinary remoulded specimens are different. The research results obtained may provide a useful reference for the establishment of different models of soil under different initial conditions and for various engineering applications.
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图 1 不同角度各向同性试样切削过程
Figure 1. Cutting process of isotropic specimens with different angles
图 2 各向同性试样q-
$ {\varepsilon _{\rm a}}$ 关系曲线Figure 2. Relation curves of q-
${\varepsilon _{\rm a}}$ for isotropic specimens
图 3 各向同性试样
${\varepsilon _{\rm{a}}}$ -${\varepsilon _{\rm{v}}} $ 关系曲线Figure 3. Relation curves of
${\varepsilon _{\rm{a}}}$ -${\varepsilon _{\rm{v}}}$ for isotropic specimens
图 4 横观各向同性 −K0预固结试样及常规重塑试样的
$q$ -$ {\varepsilon _{\rm{a}}}$ 及${\varepsilon _{\rm{a}}} $ -$ {\varepsilon _{\rm{v}}}$ 关系曲线Figure 4. Relation curves of
$q$ -$ {\varepsilon _{\rm{a}}}$ and${\varepsilon _{\rm{a}}}$ -${\varepsilon _{\rm{v}}}$ for transversely isotropic specimens and remolded samples
图 5 起始切线模量随净围压的变化
Figure 5. Variation of
$\lg ({E}/{P_{\rm{a}}})$ with$\lg (p/{P_{\rm{a}}})$ 
图 6 3组试样的q-
$ w$ 关系曲线Figure 6. Relation curves of q-
$ w$ for different group specimens表 1 土样的基本物理指标
Table 1. Physical parameters of soil samples
相对密度ds 塑限wp/% 液限wL/% 最大干密度
${\rho _{{\rm d}\max }}$/（g•cm−1）最优含水率wop/% 2.71 17.3 31.1 1.91 12.5 
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表 2 试验研究方案
Table 2. Experimental research programs
试验组别 试验简称 控制竖向压力/kPa 削样角度/（°） 控制净围压/kPa 控制基质吸力/kPa 1 各向同性试验 0 100、200、300 50、100、200 45 60 90 2 K0CD试验 100 100、200、300 0、50、100、200 200 3 CD试验 100、200、300 0、50、100、200
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表 3 土样的强度参数
Table 3. Strength parameters
吸力/kPa 净围压p/kPa qf/kPa pf/kPa φ/（°） c/kPa 各向
同性K0CD
试验CD
试验各向
同性K0CD
试验CD
试验各向
同性K0CD
试验CD
试验各向
同性K0CD
试验CD
试验0 100 367.7 201.3 226.6 167.1 31.39 26.51 41.63 16.11 200 596.2 400.9 398.7 333.7 300 831.0 521.5 593.7 473.8 50 100 341.5 312.1 276.0 213.8 204.0 192.0 26.61 28.93 27.13 58.08 37.25 30.98 200 524.1 503.8 424.5 374.7 367.9 341.5 300 665.4 686.9 610.8 521.8 529.0 503.6 100 100 399.0 333.0 325.5 229.7 211.0 208.3 28.44 30.04 28.21 67.07 42.07 47.90 200 564.3 557.7 525.1 388.1 385.9 375.0 300 768.4 733.0 683.8 556.1 544.3 527.9 200 100 447.4 433.3 409.3 249.1 244.4 236.4 31.35 31.61 29.2 70.56 62.61 67.50 200 704.9 666.0 605.4 435.0 422.0 410.7 300 892 873.8 790.3 602.7 591.3 563.4
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表 4 剪切过程中土样的q-w关系曲线的斜率
Table 4. Slope of the q-w relation curve of soil samples in the shear process
试样 吸力/kPa 净围压/kPa $\alpha$/（× 10–5） 各吸力下$\alpha$的平均值/（× 10–5） 平均值/（× 10–5） 各向同性 50 100 –3.27 –2.68 –2.62 200 –2.63 300 –2.15 100 100 –3.09 –2.61 200 –2.48 300 –2.26 200 100 –3.30 –2.56 200 –2.39 300 –2.00 横观各向同性 0 100 –4.98 –4.43 –1.55 200 –4.06 300 –3.72 50 100 –2.16 –1.55 200 –1.33 300 –1.16 100 100 –1.44 –1.52 200 –1.84 300 –1.27 200 100 –1.63 –1.59 200 –1.69 300 –1.45 重塑 0 100 –6.82 –5.46 –2.59 200 –5.05 300 –4.50 50 100 –3.02 –2.47 200 –2.49 300 –1.89 100 100 –2.95 –2.48 200 –2.49 300 –1.99 200 100 –3.20 –2.83 200 –2.78 300 –2.52
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