Graded Soils / And What ???

I decided to take a minute to gather my thoughts and read some of your coments as to get a feel for what you need and how I might better assist in these matters of construction. The field is huge, it's hard to say. So leave a clue, that I might work with.

Help Me to Help You!!!!

And I purpose to stop jumping around so much, you know it's easy to get off the subject, and on to a subject utterly unrelated, you just can't help it. And I'm not trying to make excuses it's just a fact, when your full and running over with ??( WELL FORGET IT ) you loose control.

Ok I want to close on soil, but I can't just yet!

When the soil sample is taken, it will consist of a mixture of every type and composition of the soil ie, it will be composed of gravel, sand, silt, and clay. And it is described by the most predominate part, ie. Is it predominately gravel, sand, silt, or clay. So it's description references the mixture with the most prevalent part; by saying the soil is a gravelly sand, it means, sand mixed with gravel, or a silty sand would be a sand mixed with silt or clayey sand, that is sand mixed with clay.

These classification of soils are critical for engineers to be able to identify problem soils.

Classifications of soils developed by the American Society for Testing and Materials (ASTM) standards are D 2487 and D 2488. And the Unified Soil Classification System ( USCS ) are used to describe the grain size of a soil.

ASTM Terminology

Coarse-Grained Soils More than 50% retained on a 0.075 mm(#200) sieve.
Fine-Grained Soils 50% or more passes a 0.075 mm (#200) sieve.
Gravel Material passing a 75 mm (3 inch) sieve and retained on a 4.75 mm (#4) sieve.
Coarse Gravel Material passing a 75 mm (3 inch) sieve and retained on a 19.0 mm (3/4 inch) sieve.
Fine Gravel Material passing a 19.0 mm (3/4 inch) sieve and retained on a 4.75 mm (#4) sieve.
Sand Material passing a 4.75 mm sieve (#4) and retained on a 0.075 mm (#200) sieve.
Coarse Sand Material passing a 4.75 mm sieve (#4) and retained on a 2.00 mm (#10) sieve.
Medium Sand Material passing a 2.00 mm sieve (#10) and retained on a 0.475 mm (#40) sieve.
Fine Sand Material passing a 0.475 mm (#40) sieve and retained on a 0.075 mm (#200) sieve.
Clay Material passing a 0.075 mm (#200) sieve that exhibits plasticity, and strength when dry.
Silt Material passing a 0.075 mm (#200) sieve that is non-plastic, and has little strength when dry.
Peat Soil of vegetable matter.

Letter Definition:

(G) Gravel, (S) Sand, (M) Silt, (C) Clay, (O) Organic

(P) Poorly graded-uniform particle sizes. (W)Well graded diversified particle sizes. (H) High plasticity. (L) Low plasticity.

This is the soils classification systems most used in construction, engineering, and geology. It broadly breaks down soils to these two classifications (1) Granular: ( Coarse- grained soils more than 50% of coarse fractions retained on a #200 sieve. )

This granular group symbols are "GW": Well-graded gravels and gravel-sand mixtures, with 5% fines or no fines, and are gravels that, 50% or more of course fractions are retained on a #4 sieve, called Clean gravels. "GP": Poorly-graded gravels and gravel-sand mixtures with 5% fines or no fines. Then there are Gravel with 5 to 15% fines, and this group GM; Silty gravels, gravel-sand-silt mixtures. And "GC";Clayey gravels, gravel-sand-clay mixtures. "GW-GM"; Well-graded gravel with silt. "GW-GC"; Well-graded gravel with clay. "GP-GM"; Poorly-graded gravel with silt. "GP-GC"; Poorly-graded gravel with clay.

Fines are defined by the American Association of State Highway and Transportation Officials ( AASHTO M 147 ) as natural or crushed sand passing the #10 sieve and mineral particles passing the #200 sieve.

Don't forget to drop me a note!!

Thanks in advance.

0

Posted in Soil, Uncategorized.

Tagged with american society for testing and materials, problem soils, soil classification system, unified soil classification system.

4 comments

By Keith Bray – February 26, 2010

Granular Soil Uses

THAT'S GOOD DIRT

Alrighty Then; We were discussing granular graded soils, and we ended with a brief look at classification charts (schemes); ASTM, USCS, and the AAHTO and ( a lot of other acronyms we haven't looked at ), said these standards are used by our engineers in determining soil types.

We also mentioned, that soils are in combinations of each other with diverse compositions and varying consistencies. The granular soils are for the most part non-plastic, meaning; no bonding agent or attraction of particles, and no shear strength if unconfined; the particles don't sticktogether that well but, are preferred in construction use, over the cohesive (clay) types, and that's because of their distinctive characteristic like; stability, excellent drainage capability, low frost heave, best back-fill potential, dense, coarse-grained, and resistance to foundation settlement, and typical high bearing capacity. Building codes often list maximum bearing capacities for soils of general classes that may be used without soil testing in light frame construction. But these are generic and may lead to erroneous conclusions regarding the true load-carrying capability of the soil at a specific site, and so these should be used with caution.

Presumptive Bearing Values of Foundation Materials

Class of materials Bearing Pressure lb./sq.ft.

Crystalline bedrock 12,000
Sedimentary rock 6,000
Sandy gravel or gravel 5,000
Sand, silty sand, clayey sand, silty gravel, clayey gravel 3,000
Clay, sandy clay, silty clay, clayey silt 2,000

No Problem Construction Soil

Soils that are dense, coarse-grained, and properly drained. Cause very few problems in light buildings for slab-on-grade foundations.

The soils here have excellent bearing capacity, and they are not subject to significant volumetric change (we will see this later). Gravels, occur in a dense state and not likely to settle, or prone to pose that problem. The settlement that does occur is very sudden and happens immediately when the load is applied.

During trenching and grading operations, other precautions need to be heeded, ie; the natural confinement of the soil should not be disturbed, (except when compacting);, because further disturbance of the soil bed would necessitate measures that half to be taken to increase the necessary lateral support, ie; (earth retention systems; soil stabilization systems; water and Portland Cement for bonding).

Lateral displacement, is horizontal movement of soil, displaced by compression of heavy loads or the foundation. Generally this is not a problem in light frame construction. Lateral displacement is more likely to occur under heavy building loads and this problem is addressed in the foundation design. At any rate, the bearing soil must be undisturbed and stable.

Soils acceptable for use in the construction of fills, back-fills, and embankments for commercial, institutional, and industrial buildings and for large multifamily housing projects are generally limited to those in the GP, GM, GC, SP, and SC categories.

General back-filling outside of the structures is generally limited to those soil classified as GP, GM, GC, SP, and SM. However, in certain situations, some other classifications may be permitted, but that decision should be left to a competent soil engineer, and in all circumstances additional liquid limit and plastic limit requirements will apply.

Gravel and sands; The shear strength of these soils depend solely upon the internal friction between grains. Generally speaking, bearing strength is high and foundation failure is relatively infrequent. The sudden settlement that does occur takes place immediately upon application of the load and does not materially effect the foundation. The shear strength increases as the grain size increases and a well graded soil is best.

They do not hold water at all, with the exception of some sands and silts, which do exhibit a weak tendency to bond together with a negative water charge, but will easily collapse. You'll notice this while excavating in a sandy soil type; the sides will hold for some time and then start dropping off as the soil becomes unsaturated and then falls apart or collapses. It is very permeable and excellent material to use for drainage.