Study on the Evaluation Method of Subgrade Slope Green Protection Effect in Dry-Hot Valley of Sichuan-Tibet Railway

Table 2

Indexes’ standard level.

Indexes		Excellent	Good	General	Poor	Very poor
Volumetric weight of soil (g cm^−3)		<1.1	1.1∼1.2	1.2∼1.3	1.3∼1.4	>1.4
Total soil porosity (%)		>60	60∼56	56∼52	52∼50	<50
Organic matter content (g kg^−1)		>23.2	17.4∼23.2	11.6∼17.4	3.5∼11.6	<3.5
Duration of soil PWP (month)		<2	2∼5	5∼7	7∼9	>9
Soil infiltration rate (mm h^−1)		>30	20∼30	10∼20	5∼10	<5
Content of mineral nutrients (g kg^−1)	Total N (g·kg^−1)	>2.0	1.5∼2.0	1..0∼1.5	0.75∼1.0	<0.75
	Available P (P2O5) (g kg^−1)	>0.015	0.01∼0.015	0.005∼0.01	0.002∼0.005	<0.002
	Available K (K2O) (g kg^−1)	>0.1	0.08∼0.1	0.06∼0.08	0.04∼0.06	<0.04
Ability of soil to preserve moisture and fertility		Very strong	Strong	Medium	Weak	Very weak
Soil expansion and contraction		Very weak	Weak	Medium	Strong	Very strong
Coverage of vegetation (%)		>90	80∼90	70∼80	50∼70	<50
Vegetation survival rate (%)		>90	80∼90	70∼80	50∼70	<50
Incidence of pests and diseases in vegetation (%)		<20	20∼40	40∼70	70∼90	>90
Vegetation species richness index		>1.0	0.8∼1.0	0.6∼0.8	0.4∼0.6	<0.4
Rationality of vegetation spatial collocation		Extremely reasonable	Reasonable	Medium	Unreasonable	Extremely unreasonable
Ability of vegetation to resist drought and heat		Very strong	Strong	Medium	Weak	Very weak
Vegetation tolerance to barrenness		Very strong	Strong	Medium	Weak	Very weak
Slope resistance to leaching erosion		Very strong	Strong	Medium	Weak	Very weak
Antiscouring ability		Very strong	Strong	Medium	Weak	Very weak
Ability of slope to protect against wind and sand		Very strong	Strong	Medium	Weak	Very weak
Slope resistance to natural disasters		Very strong	Strong	Medium	Weak	Very weak
Ability of slope to prevent water and soil loss		Very strong	Strong	Medium	Weak	Very weak