GDS dynamic triaxial apparatus and nuclear magnetic resonance analyzer were used to analyze the pore characteristics of the improved soil under different confining pressures and frequencies and the hysteretic curve morphology under dynamic cyclic loads, which were compared with the original expansive soil. The pore characteristics were analyzed by NMR signal distribution curve, and the morphology of hysteretic curve was quantitatively analyzed by the dip degree of long axis, hysteretic circle area, plastic deformation and fullness degree. The test results show that the total amount of pores in the improved soil and the original expansive soil decrease with the consolidation and cyclic load progression, while the pore size gradually compresses. The total amount and size of pores in the improved soil are close to the original soil. High confining pressure leads to the improved soil porosity reduction and make the strain become smaller under the same dynamic load condition. High frequency loading reduces the strain of the improved soil, and the number of pores and pore diameter in the soil increase correspondingly. The inclined degree of the long axis of hysteretic curve of improved soil gradually decreases and tends to be gentle with the increase of loading series and the development of dynamic strain, while the area of hysteretic circle, plastic deformation and fullness degree all show an upward trend. The increase of confining pressure and frequency increases the inclination degree of long axis, hysteretic circle area and fullness degree of the improved soil under the same dynamic strain condition. Different confining pressure and frequency have little influence on the development of plastic deformation in the early stage of dynamic strain development. High confining pressure and high frequency under the same dynamic strain correspond to higher plastic deformation when a critical point is exceeded.
Tab.1Basic physical-mechanical parameters of expansive soil
组别
试样编号
Ve/%
σ3/kPa
f/Hz
σd/kPa
1
1-1
15
50
1
30~120
1
1-2
15
100
1
30~120
1
1-3
15
150
1
30~120
2
2-1
15
100
1
30~120
2
2-2
15
100
2
30~120
2
2-3
15
100
3
30~120
3
3-1
0
100
1
30~120
Tab.2Dynamic triaxial cyclic loading test plan
组别
试样编号
Ve /%
真空饱和
σ3=100 kPa条件下是否固结
4
4-1
15
是
否
4
4-2
15
是
是
5
5-1
0
是
否
5
5-2
0
是
是
Tab.3Supplement NMR test protocol
Fig.1Schematic diagram of quantitative parameters of hysteretic curve morphology
Fig.2NMR signal distribution curve of modified soil at different test stages
Fig.3NMR signal distribution and dynamic stress-strain curve of improved soil under different confining pressure and frequency
Fig.4Variation curve of long axis tilt degree of hysteretic curve with dynamic strain
Fig.5Variation curve of hysteretic curve area with dynamic strain
Fig.6Variation curve of hysteretic curve area with dynamic stress
Fig.7Variation curve of unclosed degree of hysteretic curve with dynamic strain
Fig.8Variation curve of fullness of hysteretic curve with dynamic strain
Fig.9NMR signal distribution curve and dynamic stress-strain curve at different test stages before and after modification
Fig.10Variation curve of main parameters of hysteretic curve with dynamic strain before and after soil improvement
特征参量曲线
土样
A
B
C
R2
k-εd
原膨胀土
?72.378
395.765
?0.125
0.9935
k-εd
改良土
?18.109
215.491
?0.251
0.9985
S-εd
原膨胀土
?0.873
833.168
1.919
0.9996
S-εd
改良土
?1.224
820.726
2.205
0.9993
εp-εd
原膨胀土
?2.387
0.239
1.758
0.9997
εp-εd
改良土
2.976
0.413
2.016
0.9993
α-εd
原膨胀土
?2.763
2.869
0.001
0.7689
α-εd
改良土
?0.021
0.125
0.245
0.9936
Tab.4Fitting parameters of hysteretic curve morphological characteristic parameters
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