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Journal of Arid Land
Journal of Arid Land  2025, Vol. 17 Issue (5): 644-663    DOI: 10.1007/s40333-025-0100-0    
Research article     
Mechanical properties of surface soil in alpine meadow and its relationship with soil cracking in Qinghai Province, China
ZHANG Hailong1, ZHU Haili1,2,*(), WU Yuechen1, XU Pengkai1, HONG Chenze1, LIU Yabin1,2, LI Guorong1,2, HU Xiasong1,2
1School of Geological Engineering, Qinghai University, Xining 810016, China
2Key Laboratory of the Cenozoic Resources and Environment on the North Rim of the Qinghai-Xizang Plateau, Xining 810016, China
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Abstract  

Surface soil cracking in alpine meadows signifies the transition of degradation from quantitative accumulation to qualitative deterioration. Quantitative research remains insufficient regarding changes in the mechanical properties of degraded meadow soils and the mechanical thresholds for cracking initiation. This study explored the relationships between surface cracking and the physical properties, tensile strength, and matrix suction of root-soil composites in alpine meadow sites with different stages of degradation (undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD)) under different water gradients (high water content (HWC), medium water content (MWC), and low water content (LWC)) corresponding to different drying durations at a constant temperature of 40.0°C. The Huangcheng Mongolian Township in Menyuan Hui Autonomous County, Qinghai Province, China was chosen as the study area. The results indicated that as the degradation degree of alpine meadow intensified, both water content of root-soil composite and the fine grain content of soil decreased. In contrast, the root-soil mass ratio and root area ratio initially increased and then decreased with progressive degradation. Under a consistent water content, the tensile strength of root-soil composite followed a pattern of MD>HD>LD>UD. The peak displacement of tensile strength also decreased as the degradation degree of alpine meadow increased. Both the tensile strength and matrix suction of root-soil composite increased as root-soil water content decreased. A root-soil water content of 30.00%-40.00% was found to be the critical threshold for soil cracking in alpine meadows. Within this range, the matrix suction of root-soil composite ranged from 50.00 to 100.00 kPa, resulting in the formation of linear cracks in the surface soil. As the root-soil water content continued to decrease, liner cracks evolved into branch-like and polygonal patterns. The findings of this study provide essential data for improving the mechanical understanding of grassland cracking and its development process.

Key words： degradation      alpine meadow      root-soil composite      tensile strength      matrix suction      grassland crack     
Received: 26 January 2025      Published: 31 May 2025
Corresponding Authors: *ZHU Haili (E-mail: qdzhuhaili@163.com)
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ZHANG Hailong
ZHU Haili
WU Yuechen
XU Pengkai
HONG Chenze
LIU Yabin
LI Guorong
HU Xiasong
Cite this article:

ZHANG Hailong, ZHU Haili, WU Yuechen, XU Pengkai, HONG Chenze, LIU Yabin, LI Guorong, HU Xiasong. Mechanical properties of surface soil in alpine meadow and its relationship with soil cracking in Qinghai Province, China. Journal of Arid Land, 2025, 17(5): 644-663.

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http://jal.xjegi.com/10.1007/s40333-025-0100-0     OR     http://jal.xjegi.com/Y2025/V17/I5/644

Fig. 1 Location of Menyuan Hui Autonomous County in Qinghai Province (a) and location of the study area in Huangcheng Mongolian Township, Menyuan Hui Autonomous County (b). DEM, digital elevation model.
Fig. 2 Developmental morphological of surface cracks in alpine meadows. (a), linear fracture; (b), dendritic fracture; (c), polygonal fracture.
Degradation degree Dominant species Coverage of Gramineae and Cyperaceae (%) Vegetation coverage (%) Status of surface crack
Undegraded (UD) Kobresia humilis (C. A. Mey. ex Trautv.) Serg., Elymus nutans Griseb., and Poa crymophila Keng 73.00-85.00 95.00-100.00 The meadow surface layer doesn't exhibit apparent crack.
Lightly degraded (LD) Kobresia pygmaea C. B. Clarke, Poa crymophila Keng, and Saussurea pulchra Lipsch 62.00-72.00 80.00-95.00 Simple linear cracks can be observed.
Moderately degraded (MD) Kobresia pygmaea C. B. Clarke, Gentiana dahurica Fischer, and Saussurea pulchra Lipsch 45.00-58.00 60.00-85.00 Branch-like cracks can be observed and the crack area doesn't exceed 5.00% of the total plot area.
Heavily degraded (HD) Potentilla bifurca L., Anaphalis lactea Maxim. and Carex capillifolia (Decne.) S. R. Zhang 30.00-43.00 40.00-60.00 Irregular polygonal cracks can be observed, accompanied by bare ground and collapse areas around the cracks.
Table 1 Basic characteristics of alpine meadow sites with different degrees of degradation in the study area
Fig. 3 Field sampling. (a), soil physical properties samples; (b), plant root parameters; (c), tensile and matrix suction samples.
Fig. 4 Evaporation rate curve (a) and water content curve (b) of root-soil composite sample determined by this study. UD, undegraded; LD, lightly degraded; MD, moderately degraded; HD, highly degraded.
Fig. 5 Schematic diagram of test process. (a), field sampling; (b), drying experiment and tensile test; (c), matrix suction test. HWC, high water content; MWC, medium water content; LWC, low water content.
Degradation degree ρd (g/cm3) wsr (%) wr (%) ws (%) Rs (%) RAR (%)
UD 0.39±0.03 93.40±7.21 140.42±13.55 56.39±5.70 13.58±2.12 14.75±2.05
LD 0.57±0.02 76.25±5.37 113.30±14.14 47.82±6.52 16.45±1.48 18.11±1.42
MD 0.60±0.01 48.86±10.47 82.63±11.27 35.50±3.90 22.29±5.52 32.31±18.48
HD 0.66±0.02 38.56±12.73 31.34±1.44 33.34±3.93 12.80±1.56 17.37±12.49
Table 2 Basic characteristics of root-soil composite in alpine meadows with different degrees of degradation
Degradation degree Granule composition (%) Cu Cc Gradation type Soil type
>0.250 mm 0.075-0.250 mm <0.075mm
UD 34.05±12.56 41.25±10.36 23.70±6.56 8.78 1.93 Well-graded SS
LD 36.60±14.11 53.21±12.29 13.93±8.42 3.69 1.17 Poorly-graded CS
MD 53.04±20.53 39.03±18.46 7.93±6.53 4.44 0.96 Poorly-graded CS
HD 61.35±22.95 29.95±17.34 10.25±4.34 7.45 0.78 Poorly-graded CS
Table 3 Basic characteristics of sand particle at the upper soil layer in alpine meadows with different degrees of degradation
Fig. 6 Tensile stress-displacement curve of root-soil composite under different water content gradients. (a), LWC; (b), MWC; (c), HWC.
Fig. 7 Stage classification diagram of tensile stress-displacement curve under LWC condition. (a), elastic deformation stage (Stage I); (b), elastic-plastic deformation stage (Stage II); (c), root fracturing and local soil failure stage (Stage III); (d), overall failure stage (Stage IV); (e), tensile stress-displacement curve.
Fig. 8 Matrix suction characteristic curve of root-soil composite with different degrees of degradation. (a), UD; (b), LD; (c), MD; (d), HD.
Fig. 9 Rate of change in matrix suction of root-soil composites with different degrees of degradation
Fig. 10 Relationship among root-soil water content, matrix suction and tensile strength. (a), fitting surface diagram; (b), simulation formula between tensile strength and matrix suction.
Fig. 11 Variation trend in matrix suction and tensile strength of root-soil composites from different degrees of degradation with water content (a) and root content (b) changes.
Fig. 12 Images of crack development in root-soil composites during drying process
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