Field Soil Description ASTM 2487 [PDF]

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Field Soil Description ASTM 2487 - 2488



COLOUR Color varies widely in earth materials but often provides a useful means of identification for geologic and engineering purposes. The presence of organic matter,certain minerals, and some types of weathering can often be readily detected by color.



ANGULARITY Angularity is a descriptor for coarse-grained materials only. The angularity of the sand (coarse sizes only), gravel, cobbles, and boulders, are described as angular, subangular, subrounded, or rounded .A range of angularity may be stated, such as: sub-rounded to rounded



S



DESCRIPTION



CRITERIA



Angular



Particles have sharp edges and relatively plane side with unpolished surfaces



Sub angular



Particles are similar to angular, but have rounded edges



Sub rounded



Particles have nearly plane sides but have well rounded corners and edges



Rounded



Particles have smoothly curved sides no edges



PARTICLE GRADATION SCALE AND SHAPE For gravel and sand-size components, describe the range of particle sizes within each component as defined in the previous terminology paragraph. Descriptive terms, sizes, and examples of particle sizes are shown in. Describe the maximum particle size found in the sample. For reporting maximum particle size, use the following descriptors and size increments: For example: "maximum particle size 35 mm" "maximum particle size 400 mm" If the maximum particle size is sand size, describe as fine, medium, or coarse sand; for example, maximum particle size, medium sand. If the maximum particle size is gravel size, describe the maximum particle size as the smallest sieve opening that the particle would pass. If the maximum particle size is cobble or boulder size, describe the maximum dimension of the largest particle.



SHAPE The particle shape shall be described as follows where length, width, and thickness refer to the greatest, intermediate, and least dimensions of a particle, respectively. Flat Elongated Flat and elongated



Particles with width/thickness > 3 Particles with length/width > 3 Particles meet criteria for both flat and elongated



ODOR Describe the odor if organic or unusual. Soils containing a significant amount of organic material usually have a distinctive odor of decaying vegetation. This is especially apparent in fresh samples, but if the samples are dried, the odor often may be revived by heating a moistened sample. If the odor is unusual, such as that of a petroleum product or other chemical, the material should be described and identified if known. The material may be hazardous, and combustion or exposure should be considered.



MOISTURE CONTENT The moisture content is the ratio of the weight of water contained in the soil to the dry weight of the soil solids. A certain compaction density may be specified, and the moisture content at the time of compaction is critical.



DESCRIPTION Dry Moist Wet



CONDITION No sign of water and soil dry to touch Signs of water and soil is relatively dry to touch Signs of water and soil definitely wet to touch; granular soil exhibit



HCL REACTION Calcium carbonate is a common cementing agent. The reaction with dilute hydrochloric acid is important in determining the presence and abundance of calcium carbonate. DESCRIPTION



CRITERIA



None



No visible reaction



Weak



Some reaction with bubbles forming slowly



Strong



Violent reaction, with bubbles forming immediately



CEMENTATION Describe the cementation of intact soils as weak, moderate, or strong, DESCRIPTION



CRITERIA



Weak



Crumbles or breaks with handling or little finger pressure



Moderate



Crumbles or breaks with considerable finger pressure



Strong



Will not crumble or break with finger pressure



CONSISTENCY With increasing water content, a solid clay mass changes consistency and passes from a solid state, through a semisolid and plastic state, to a liquid state. The moisture contents, expressed in percent of dry weight,at which the mass passes from one of these stages of consistency to another are known as the Atterberg limits or limits of consistency



COHESIVE SOIL (SILT AND CLAY)



DESCRIPTION



SPT



Pocket



(N=blows/ft) penetrometer



Unconfined compressive Strength (UCS)



CRITERIA



(MPa) Very soft



0.62



Indented with difficulty by thumbnail



NON COHESIVE SPT



TERM



(N=blows/ft)



RELATIVE DENSITY (%)



TACTILE TEST



Very loose



VL



85



Hard Picking



STRUCTURE The descriptors presented are for soils only; they are not synonymous with descriptors for rock. TERM



DESCRIPTION



Homogeneus



The total lack of visible bedding and the same colour and appearance throughout



Bedding



The presence of layer



Fissured



Breaks along definite planes of fracture with little resistance to fracturing



Polished



Fracture planes are polished or glossy



Slickensided



Blocky



Fracture planes are striated Cohesive soil that can be broken down into small angular lumps which resist further breakdown



lensoidal



Discontinuous pockets of a soil within different soil mass



DRY STRENGTH After removing particles > No. 40 sieve size, mold a pat of soil to the consistency of putty, adding water if necessary. Allow the pat to dry completely by oven, sun, or air drying, and then test its strength by breaking and crumbling between the fingers. This strength is a measure of the character and quantity of the colloidal fraction contained in the soil. The dry strength increases with increasing plasticity. DESCRIPTION



CRITERIA



None



The dry specimen crumbles into powder with mere pressure of handling



Low



The dry specimen crumbles into powder with some finger pressure



Medium



High



Very high



The dry specimen breaks into pieces or crumbles with considerable finger pressure The dry specimen cannot be broken with finger pressure The dry specimen cannot be broken between the thumn and a hard surface



DILATANCY (Reaction to shaking) After removing particles > No. 40 sieve size, prepare a pat of moist soil with a volume of about 0.5 in 3 Add enough water, if necessary, to make the soil soft but not sticky. Place the pat in the open palm of one hand and shake horizontally, striking vigorously against the other hand several times. A positive reaction is the appearance of water on the surface of the pat, which changes to a livery consistency and becomes glossy. When the sample is squeezed between the fingers, the water and gloss disappear from the surface, the pat stiffens, and it finally cracks or crumbles. The rapidity of appearance of water during shaking and of its disappearance during squeezing assist in identifying the character of the fines in a soil. Very fine clean sands give the quickest and most distinct reaction, whereas a plastic clay has no reaction. Inorganic silts, such as rock flour, show a moderately quick reaction. DESCRIPTION



CRITERIA



None



No visible change in the specimen



Slow



Water appears slowly on the surface of the specimen during shaking and does not disappears slowly upon squeezing



Rapid



Water appears quickly on the surface of the specimen during shaking and disappears quickly upon squeezing



TOUGHNESS Following the completion of the dilatancy test, the test specimen is shaped into an elongated pat and rolled by hand on a smooth surface or between the palms into a thread about 1⁄8 in. (3 mm) in diameter. (If the sample is too wet to roll easily, it should be spread into a thin layer and allowed to lose some water by evaporation.) Fold the sample threads and reroll repeatedly until the thread crumbles at a diameter of about 1⁄8 in. The thread will crumble at a diameter of 1⁄8 in. when the soil is near the plastic limit. Note the pressure required to roll the thread near the plastic limit. Also, note the strength of the thread. After the thread crumbles, the pieces should be lumped together and kneaded until the lump crumbles. Note the toughness of the material during kneading. Description



Criteria Low



Medium



High



Only slight pressure is required to roll the thread near the plastic limit. The thread and the lump are weak and soft Medium pressure is required to roll the thread to near the plastic limit. The thread and the lump have medium stiffness Considerable pressure is required to roll the thread to near the plastic limit. The thread and the lump have very high stiffness



PLASTICITY Description



CRITERIA



Non plastic



A 3mm thread cannot be rolled at any water content



Low



The thread can barely be rolled and the lump cannot be formed when drier than plastic limit



Medium



The thread is easy to roll and not much time is required to reach the plastic limit. The thread cannot be rerolled after reaching the plastic limit. The lump crumbles when drier than the plastic limit



High



It takes considerable time rolling and kneading to reach the plastic limit. The thread can be rerolled several times after reaching the plastic limit. The lump can be formed without crumbling when drier than the plastic limit



Identification of Organic Fine-Grained Soils If the soil contains enough organic particles to influence the soil properties, classify the soil as an organic soil, OL or OH. Organic soils usually are dark brown to black and usually have an organic odor. Often organic soils will change color, (black to brown) when exposed to air. Organic soils normally do not have high toughness or plasticity. The thread for the toughness test is spongy. In some cases, further identification of organic soils as organic silts or organic clays, OL or OH is possible. Correlations between the dilatancy, dry strength, and toughness tests with laboratory tests can be made to classify organic soils in similar materials. TERM Topsoil



Organic clay, silt or sand



DESCRIPTION Surficial soil layer that may contain living matter Contain finely devided organic matter, may have distinctive smell



Peat



Consist predominantly of plant remains, firm: fibres already compressed together, Spongy: Very compressible and open structure, Plastic: Can be moulded in hand and smears in fingers, Fibrous: plant remains recognisable and retain some strength



Roolets



Fine, partly decomposed roots, normally found in the upper part of a soil profile or in a redeposited soil



Carbonaceous



Discrete particles or hardened plant material