(Tổng hợp) BS 1377 – phương pháp phân loại và gọi tên đất

Very coarse soils BOULDERS > 200 mm COBBLES 60 – 200 mm   Coarse soils G GRAVEL coarse 20 – 60 mm medium 6 – 20 mm fine 2 – 6 mm S SAND coarse 0.6 – 2.0 mm medium 0.2 – 0.6 mm fine 0.06 – 0.2 mm Fine soils M SILT coarse 0.02 – 0.06 mm medium 0.006 – 0.02 mm fine 0.002 – 0.006 mm C  CLAY < 0.002 mm

Sieve mesh size (mm) Mass retained (g) Percentage retained Percentage finer (passing) 14.0 0 0 100.0 10.0 3.5 1.2 98.8 6.3 7.6 2.6 86.2 5.0 7.0 2.4 93.8 3.35 14.3 4.9 88.9 2.0 21.1 7.2 81.7 1.18 56.7 19.4 62.3 0.600 73.4 25.1 37.2 0.425 22.2 7.6 29.6 0.300 26.9 9.2 20.4 0.212 18.4 6.3 14.1 0.150 15.2 5.2 8.9 0.063 17.5 6.0 2.9 Pan 8.5 2.9 TOTAL 292.3 100.0

 

The soil comprises: 18% gravel, 45% coarse sand, 24% medium sand, 10% fine sand, 3% silt, and is classified therefore as: a well-graded gravelly SAND

Low plasticity	wL = < 35%
Intermediate plasticity	wL = 35 – 50%
High plasticity	wL = 50 – 70%
Very high plasticity	wL = 70 – 90%
Extremely high plasticity	wL = > 90%

 

[The range of G_s for common soils is 2.64 to 2.72]

BS description system

A recommended protocol for describing a soil deposit uses nine characteristics; these should be written in the following order:

compactness
loose, dense, slightly cemented
bedding structure
homogeneous or stratified; dip, orientation
discontinuities
spacing of beds, joints, fissures
weathered state
degree of weathering
colour
main body colour, mottling
grading or consistency
well-graded, poorly-graded; soft, firm, hard
SOIL NAME
GRAVEL, SAND, SILT, CLAY; (upper case letters) plus silty-, gravelly-, with-fines, etc. as appropriate
soil class
(BSCS) designation (for roads & airfields)  SW = well-graded sand
geological stratigraphic name
(when known)  London clay

Not all characteristics are necessarily applicable in every case.

Example:
(i) Loose homogeneous reddish-yellow poorly-graded medium SAND (SP), Flood plain alluvium
(ii) Dense fissured unweathered greyish-blue firm CLAY. Oxford clay.

British Soil Classification System

The recommended standard for soil classification is the British Soil Classification System, and this is detailed in BS 5930 Site Investigation. Its essential structure is as follows:

Soil group		Symbol		Recommended name
Coarse soils			Fines %
GRAVEL	G	GW	0 – 5	Well-graded GRAVEL
		GPu/GPg	0 – 5	Uniform/poorly-graded GRAVEL
	G-F	GWM/GWC	5 – 15	Well-graded silty/clayey GRAVEL
		GPM/GPC	5 – 15	Poorly graded silty/clayey GRAVEL
	GF	GML, GMI…	15 – 35	Very silty GRAVEL [plasticity sub-group…]
		GCL, GCI…	15 – 35	Very clayey GRAVEL [..symbols as below]
SAND	S	SW	0 – 5	Well-graded SAND
		SPu/SPg	0 – 5	Uniform/poorly-graded SAND
	S-F	SWM/SWC	5 – 15	Well-graded silty/clayey SAND
		GPM/GPC	5 – 15	Poorly graded silty/clayey SAND
	SF	SML, SMI…	15 – 35	Very silty SAND [plasticity sub-group…]
		SCL, SCI…	15 – 35	Very clayey SAND [..symbols as below]
Fine soils		>35% fines	Liquid limit%
SILT	M	MG		Gravelly SILT
		MS		Sandy SILT
		ML, MI…		[Plasticity subdivisions as for CLAY]
CLAY	C	CG		Gravelly CLAY
		CS		Sandy CLAY
		CL	<35	CLAY of low plasticity
		CI	35 – 50	CLAY of intermediate plasticity
		CH	50 – 70	CLAY of high plasticity
		CV	70 – 90	CLAY of very high plasticity
		CE	>90	CLAY of extremely high plasticity
Organic soils	O			[Add letter ‘O’ to group symbol]
Peat	Pt			[Soil predominantly fibrous and organic]