荆条根系的固土功能随土壤含水率的变化

doi:10.11707/j.1001-7488.20200620

摘要/Abstract

摘要：

目的: 分析原状根土复合体和素土的黏聚力和内摩擦角随土壤含水率的变化规律，探索植物根系破坏方式与土壤含水率的关系，为动态分析降雨过程中边坡稳定性提供理论基础。方法: 选择北方常见灌木种荆条，在降雨后的不同时期，在预先挖好的土壤剖面取得原状根土复合体和素土样本，测定其抗剪强度指标：黏聚力c和内摩擦角φ，并辅以重塑的根土复合体和素土样本作为对比。结果: 1)荆条单根拔出强度随土壤含水率增高呈单峰曲线变化，土壤体积含水率约18%时达到最大值。2)植物根系可以显著提高土壤的抗剪强度，其中原状和重塑根土复合体黏聚力分别比原状和重塑素土高出约15.8 kPa和7.5 kPa，内摩擦角最大高出约3.1°和1.1°。3)根土复合体的黏聚力和内摩擦角与土壤体积含水率大体呈负相关。随着土壤含水率从约13%增高到约40%，原状和重塑的根土复合体样品中的土壤黏聚力的最大增加值分别降至5.9 kPa和2.6 kPa。原状根土复合体内摩擦角最大增加值降至0.1°，重塑土复合体则升至1.8°。结论: 根系可以同时提高土壤的黏聚力和内摩擦角，根系对土壤的加固效果随土壤含水率的升高而大幅度降低。因此建议在降雨较多的地区或季节，植物根系固土护坡能力应该更保守地进行评估。本研究可为土壤含水率在内的根系固土动态模型的建立提供理论依据。

关键词: 根系黏聚力增强值, 土壤体积含水率, 拔出强度, 根土复合体, 根面积比率

Abstract:

Objective: Rainfall is one of the important causes of slope instability. It is generally believed that plant roots can effectively reinforce soil and increase slope stability. In general,shallow landslides occur during and shortly after precipitation events. The function of soil reinforcement and its change dependent upon the soil volumetric water contents remain poorly studied because of the complex root-soil interactions and difficulty of the underground observations. This study investigated the influence of soil moisture on soil cohesion and internal friction angle,and identified the root failure mode under different soil moisture,which aims to expand our knowledge about the dynamics of slope stability during rainfall. Method: In this study,a common shrub species (Vitex negundo) in north China was selected. In different periods after rainfall,the undisturbed root-soil composite samples and plain soil samples without roots were collected from soil profiles. The shear strength of the undisturbed root-soil composite and plain soil samples were measured for calculating the cohesion (c) and internal friction angle (φ). Here,remolded samples of root-soil composite and plain soil were also tested for comparison. Result: 1) The increase of root pullout strength of V. negundo exhibited a single peak curve with the soil volume water content,and the strength reached the maximum value when the soil volume water content was about 18%. 2) Plant roots were able to significantly reinforce the soil. Compared with root free soil,the cohesion of the undisturbed and remolded root soil composite increased by 15.8 and 7.5 kPa,and the internal friction angle increased by 3.1° and 1.1°,respectively. 3) The cohesion and friction angle of rooted soil were negatively correlated with soil water content,generally. With the increase of soil moisture from 13% to 40%,the additional cohesion of undisturbed and remold samples decreased to 5.9 and 2.6 kPa,respectively. Additional internal friction angle of the undisturbed samples decreased to 0.1°,while that of remold samples increased to 1.8°. Conclusion: Plant roots can play an important role on both cohesion and internal friction angle,however,the reinforcement provided by roots would be decrease significantly with precipitation-driven water content increase. Thus,it is suggested that in the area or season with heavy rainfall,the additional cohesion provided by roots should be evaluated more conservatively. This study provides a theoretical basis for establishing a dynamic root reinforcement model considering soil moisture.

Key words: addition cohesion of root, soil volume water content, pull-out strength, root-soil composite, root area ratio

中图分类号:

S714.7

朱锦奇,苏伯儒,王云琦,王玉杰,李云霞. 荆条根系的固土功能随土壤含水率的变化[J]. 林业科学, 2020, 56(6): 202-208.

Jinqi Zhu,Boru Su,Yunqi Wang,Yujie Wang,Yunxia Li. Variation of Soil Reinforcement of Vitex negundo Root with Soil Moisture[J]. Scientia Silvae Sinicae, 2020, 56(6): 202-208.

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土层深度 Soil depth/m	土壤密度 Soil density/(g·cm^-3)	紧实度 Compactness/kPa	黏聚力 Cohesion/kPa	内摩擦角 Internal friction angle/(°)	根系面积比率 Root area ratio(%)
0.1~0.2	1.29±0.26	72.00±19.63	15.36±5.21	22.70±2.71	0.196 7±0.017 1

黏聚力增强值 Addition cohesion/kPa	土壤体积含水率Soil volumetric water content(%)
黏聚力增强值 Addition cohesion/kPa	15	20	25	30	35	40
原状根土复合体Undisturbed root-soil composite	15.42	10.75	10.64	8.21	4.60	6.81
重塑根土复合体Remolded root-soil composite	5.98	6.91	5.92	4.71	2.96	2.46
模型计算值Estimated value of model	28.42	26.31	24.18	25.74	24.46	25.11
k′	0.54	0.41	0.44	0.32	0.19	0.27

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