Enhancement Effect of Phragmites australis Roots on Soil Shear Strength in the Yellow River Delta

Xinyue Li, Kai Jin, Peng Qin, Chunxia Liu, Xiuzhi Zhu, Yuyang Zhang and Quanli Zong ()
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Xinyue Li: College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109, China
Kai Jin: College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109, China
Peng Qin: College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109, China
Chunxia Liu: College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109, China
Xiuzhi Zhu: College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109, China
Yuyang Zhang: College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109, China
Quanli Zong: College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109, China

Sustainability, 2024, vol. 16, issue 23, 1-17

Abstract: Soil erosion is one of the causes of ecosystem fragility in the Yellow River Delta. Plant roots can improve soil shear strength and effectively prevent soil erosion. However, there are no studies on soil shear strength in the Yellow River Delta. In this study, Phragmites australis (PA) root–soil composites with different root area ratios (RARs) (RARs = 0%, 0.06%, 0.14%, 0.17%, 0.19%, 0.24%, 0.36%) were prototypically sampled from the Yellow River Delta. Direct shear tests of root–soil composites were performed by a ZJ-type (three-speed) strain-controlled direct shear apparatus. The normal stresses were 25, 50, 100, and 200 kPa, and the shear rate was 1.2 mm/min. The results showed that PA roots significantly increased soil shear strength and cohesion with maximum growth rates of 219.0% and 440.1%, respectively. An optimal RAR of 0.14% in the range of 0~0.36% maximized the shear strength and cohesion of the root–soil composites. The internal friction angles of root–soil composites with different RARs did not differ significantly from those of the rootless soil. This indicates that the increase in shear strength was mainly due to an increase in cohesion. In addition, overall shear failure was the primary failure mode of rootless soil, with the roots pulled out of the soil in the root–soil composite failure mode. It is important to note that the root is deflected during shear in the direction opposite to the direction of the shear stress. These findings deepen our understanding of the effect of vegetation roots on soil shear characteristics and provide a scientific basis for the protection of bank slopes, soil and water conservation, and vegetation restoration in the Yellow River Delta.

Keywords: Phragmites australis; undisturbed root–soil composites; root content; shear strength (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2024
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