The mechanism of the plant roots' soil-reinforcement based on generalized equivalent confining pressure

Ping Guo; Zhenyao Xia; Qi Liu; Hai Xiao; Feng Gao; Lun Zhang; Mingyi Li; Yueshu Yang; Wennian Xu

doi:10.7717/peerj.10064

The mechanism of the plant roots' soil-reinforcement based on generalized equivalent confining pressure

PeerJ. 2020 Sep 29:8:e10064. doi: 10.7717/peerj.10064. eCollection 2020.

Authors

Ping Guo^#^{1

2}, Zhenyao Xia^#^{1

2}, Qi Liu³, Hai Xiao^{1

2}, Feng Gao¹, Lun Zhang¹, Mingyi Li^{1

2}, Yueshu Yang^{1

2}, Wennian Xu^{1

2}

Affiliations

¹ Key Laboratory of Geological Hazards on Three Gorges Reservoir Area (China Three Gorges University), Ministry of Education, Yichang, China.
² Engineering Research Center of Eco-environment in Three Gorges Reservoir Region, Ministry of Education, China Three Gorges University, Yichang, China.
³ Key Laboratory of Mountain Hazards and Earth Surface Process, Institute of Mountain Hazards and Environment, CAS, Chengdu, China.

^# Contributed equally.

Abstract

Background: To quantitatively evaluate the contribution of plant roots to soil shear strength, the generalized equivalent confining pressure (GECP), which is the difference in confining pressure between the reinforced and un-reinforced soil specimens at the same shear strength, was proposed and considered in terms of the function of plant roots in soil reinforcement.

Methods: In this paper, silt loam soil was selected as the test soil, and the roots of Indigofera amblyantha were chosen as the reinforcing material. Different drainage conditions (consolidation drained (CD), consolidation undrained (CU), and unconsolidated undrained (UU)) were used to analyse the influences of different root distribution patterns (horizontal root (HR), vertical root (VR), and complex root (CR)) and root contents (0.25%, 0.50%, and 0.75%) on the shear strength of soil-root composites.

Results: The cohesion (c) values of the soil-root composites varied under different drainage conditions and root contents, while the internal friction angle (φ ) values remain basically stable under different drainage conditions. Under the same root content and drainage conditions, the shear strength indexes ranked in order of lower to higher were HR, VR and CR. The GECP of the soil-root composites with a 0.75% root content was 1.5-2.0 times that with a 0.50% root content and more than 5 times that with a 0.25% root content under the CD and CU conditions. The GECP in reinforced soil followed the sequence of CD > CU > UU. The GECP of the plant roots increased as confining pressure increased under CD and CU conditions while showed a complex change to the confining pressure under the UU condition.

Conclusion: It was concluded that the evaluation of plant root reinforcing soil based on GECP can be used to measure effectively the influences of roots on soil under different drainage conditions and root distribution patterns.

Keywords: Drainage condition; Generalized equivalent confining pressure; Root distribution patterns; Shear strength indexes; Soil-root composite.

Grants and funding

This study was financially supported by the National Key Research & Development Plan of China (2017YFC0504902), Research Fund for Excellent Dissertation of China Three Gorges University (2020BSPY003), the National Natural Science Foundation of China (41807068), the CRSRI Open Research Program (CKWV2018488/KY), and the open fund of Key Laboratory of Geological Hazards on Three Gorges Reservoir Area, Ministry of Education (China Three Gorges University) (2018KDZ06). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.