Soils Mechanical Grain Classification (nfm)

Field identification procedures (excluding particles > 7.5cms & basic frictions on estimated weights

Group symbol

Typical names

permeability if compacted

Coarse grain soils

Gravels

more than half of coarse friction

clean gravel

(little or no lines)

wide range in grain size & substantial amounts of intermediate particle size

CW

well graded gravels,gravel sand mixtures, little or no line

pervious

predominantly one size or a range of sizes with some intermediate size missing

GP

poorly graded gravels, gravel-sand mixtures, line or not

very pervious

gravel with fines

(lines)

non plastic fines

GM

silty gravels poorl graded gravel-sand-salt mixtures

semi pervious

plastic fines

GC

clayey gravels, poorly graded gravel sand clay mixtures

impervious

Sands (more than half of coarse friction

clean sands

wider range in grain sizes and substantial amounts of all intermediate particle sizes

SW

well graded sands, gravelly sands, little or no lines

pervious

predominantly one size or a range of sizes with some intermediate sizes missing

SP

poorly graded gravelly sands little or no lines

pervious

non plastic fines

SM

silty sands poorly graded sand salt mixtures

semipervious

sands with fines

plastic fines

SC

claysands poorly graded sand-salt mixtures

impervious

Fine grains soils

more than half is smaller than

Identification procedures on fraction smaller than n°sieve size

dry strength (crushing characteristics)

dilatancy (reaction to shaking

Toughtness (consistency near plastici -ty limit

Silts and clays (liquid limit less than 50

none to slight

quick to slow

none

ML

inorganic silt and very fine sands, rocks, lime, silty or clayey fine sands with slight plasticity

semiperviour

medium to high

none to very slow

medium

CL

inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays lean clays

imp

slight to medium

slow

slight

OL

organic silts & organics silt-clay of low plasticity

semiimpervious

Silts and Clays

liquid limit greater than 50

slight to medium

slow to none

slight to medium

MH

inorganic silts, micaceous or diatomaceous fine sandy or silty soils,elastic silte

semi -impervious

high to very high

none

high

CH

inorganic clays of high plasticity fat clays

impervious

medium to high

none to very slow

slight to medium

OH

organic clays of medium to high plasticity

imp

Highly organic soil

Readily identified by color, odor, spongy feel and fibrous texture

Pr

pest ans other highly organic

Soils Hydrologic Properties

Soil Permeability

Site Classification

coeffi- cient of permea- bility k

relative permea- bility

Soil type

site

class

general conditions required for such classification

conditions found during site classification survey

that are indicative of the class

cm/sec

field pum -ping test, relia -ble if well done

cons tant head perm- eame -ter liable

com- puta- tion from grain size

relative to water table level

relative to surface water accumulation

10

high

clean gravel

soil type

ter- rain

rain or irrigation

1

high

coarse sand

A- severe

water table frequently above bottom of the system

ground -water within 0.3 m of bottom of system

any

any

any

0.1

medium

rollig head permeameter

reliable

medium sands

water table occasionally above bottom of the system and surface water accumulates & remains for long periods of soil surrounding the system

ground -water within 0.3 m of bottom of system

GC, SC, CL, CH, OH

Any

Any

0.01

medium

fine sand, sands&gravels mixtures

B - bad

water table occasional above bottom of the system and surface water accumulates & remains for short periods

ground -water within 1.5m of bottom of system

GW, GP, SW, SP,

GM, SM, ML, OL, MH

any

any

0.001

medium

very fine sand

water table never above the bottom of the system but surface water accumulates and remains for long periods in soil surrounding the system

no ground water encoun -tered

GC, SC, CI, CH, OH

any

7.6 cms or > / month or 50cms / year

0.0001

low

un- relia- ble

silty sand, organic silt

C - moderate

water table never above the bottom of the system but surface water accumulates and remains for long periods in soil surrounding the system

no ground water encountered

GM, SM, ML, OL, MH

any

7.6 cms or > / month or 50cms / year

0.00001

low

silt, glacial till

GC, SC, CL, CH, OH

any except low areas

< 7.5cms / month or > 50cms/year

0.000001

low

silty clay

D - mild

water table never above the bottom of the system and surface water does not accumulate and remain in soil surrounding the system

no ground water encountered

GW, GP, SW, SP

any

any

0.0000001

0.00000001

0.000000001

practically impervious

fairly relia- ble

computation from test data (reliable)

impervious soils e.g. homogeneous clays below some of weathering

GM, SM, ML, OL, MH

any except low areas

<7.5cm

/month or < 50cms/year

Suggested Boring Program for Various Engineering Structures

Structure

Number of boring spacing

Depth of borings

Remarks

Rigid Frame structure

1 boring per 230 m2 of ground floor area

1.5 times the minimum dimension of footing below the base of the footing

Pile footings 1.5 times the minimum dimension of animaginary footing located at 2/3 of the expected depth of piles

cohesive soil: - continuous undisturbed samples for the first 3m - intermittent samplesat 1.5 to 3 m intervals thereafter - sample at every change of soil type

cohesionless soils: - obtain undisturbed samples (if possible) or condutct in situ soundings such as SPT or CPT tests

Continuous truss (girder) type bridge

minimum of 1 boring at every pier/footing

1.5 times the minimum dimension of footing below the base of the footing

Piles footings 1.5 times the minimum dimension of an imaginary footing located 2/3 of the expected depth of piles

cohesive soils: pier size < 50m2 - continuous undisturbed samples at each pier

pier size: 50 - 100m2 2 continuous undistubed samples at each pier

pier size: 100- 250m2 4 continuous undistubed samples at each pier; more: minimum of 5 samples

cohesionless soils: obtain undisturbed samples or soundings as for cohesive soils

competent rock: trace formation at each pier, if in doubt of rock quality, drill at least 6 m into formation

Levees

leeve high: 3 - 5m space boring at 300m intervals

Depth of boring: 6m

cohesive soils: continuous undisturbed samples

cohesionless soils: continuous undisturbed sample or soundings

locate borings along centerline of proposed structure

Levees

leeve high: 6 - 12m space boring at 230m intervals

Depth at least equal to height of leeve

Levees

leeve high: 12 - 18m space boring at 150m intervals

Depth at least equal to height of leeve

Earth dam preliminary investigation

depth at least equal to height of dam or twice the maximum head,whichever is greater. Trace the top of the impervious zone

mximum stree occurs approximately at mid point of slope between the centerline and toe of proposed structure. Establish a square grid pattern of borings located upstream and downstream of dam centerline near midpoint of slope in a direction with respect to dam centerline

Earth dam primary investigation

trace the limits of various strata e.g. sand; - treat power plants, spillways and other control structures asrigid frame structures; - obtain adequate subsurface data to define the character of the abutments

Earth dams

Obtain in situ permeability and pore pressure measurments

cohesive soils continuous undisturbed samples

cohesionless soils: continuous undisturbed samples or soundings

borrow pit

use a 60m grid spacing

maximum depth to water table or sorking depth of equipment

disturbed samples are satisfactory; may use augers to obtain samples

roads 2 lane highways

1 boring / 150m along centerline and at each major change of soil profile

For excavation and level terrain: 3 m below level finished grade. For compacted embankment: treat asfor leeves

For rock extend 0.75m into rock

cohesive soil: continuous undisturbed samples

cohesionless soils: continuous undisturbed samples or soundings

roads: multilane highways

1 boring /75m centerline, borings may be staggerred

airfield

preliminary investigation

place borings at 300m intervals in asquare grid patterns to a depth of 6m, sample may be disturbed, site facilities based upon preliminary investigation

airfield

primary investigation

runways

2 lines in a square grid pattern of 30m on either side of runway centerline to a depth of 6m or 1.5m into rock

airfield

primary investigation

taxiway

place borings at 60 - 75m intervals along centerline to depth of 6m

airfield

primary investigation

apron

place borings in a 60 - 75m square grid to a depth of 6m

houses

1 boring/ 750m2 in new subdivision

to unweathered rock of 4.5m whichever is lesser

obtain sample at 1.5m interval using undistributed sampling techniques for cohesive soils or undisturbed or sounding for cohesion less soils