SOIL TYPES


Soil designations are those given in ASTM D 2487. The native soil surrounding the pipe trench should be identified and classified prior to calculations.

For design purposes, soils are grouped into two general types, Normal Soils and Highly Plastic Soils.

NORMAL SOILS


Soils referred to here as "normal" include all granular soils and CL and ML in areas unlikely to become saturated, such as arid or semi-arid regions. When CL and ML are near saturation they should be classed as Highly Plastic soils and the pipe should be bedded in granular material, GP, SP or better.

In all Normal Soils calculations, the pipe is assumed to be embedded and backfilled with native soil removed from the trench, free from organic material and large stones. In all Highly Plastic soil calculations, the pipe is assumed to be surrounded with granular material, GP, SP or better.

GW - Well graded gravels and gravel-sand mixtures, little or no fines.

SW - Well graded sands and gravelly sands, little or no fines.

GP - Poorly graded gravels and gravel-sand mixtures, little or no fines.

SP - Poorly graded sands and gravelly sands, little or no fines.

GM - Silty gravels, gravel-sand-silt mixtures.

SM - Silty sands, sand-silt mixture.

GC - Clayey gravels, gravel-sand-clay mixtures.

SC - Clayey sands, sand-clay mixtures.

CL - Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays. Assumed to be in arid or semi-arid regions above the water table.

ML - Inorganic silts, very fine sands, rock flour, silty or clayey fine sands. Assumed to be in arid or semi-arid regions above the water table.

HIGHLY PLASTIC SOILS


(Use GP or SP embedment soils. Type 4 or type 5 trench is recommended.)

CL - Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays, near saturation. Pipe should be surrounded with granular material, GP, SP or better.

ML - Inorganic silts, very fine sands, rock flour, silty or clayey fine sands, near saturation. Pipe should be surrounded with granular material GP, SP or better.

CH - Inorganic clays of high plasticity, fat clays. Pipe should be surrounded with granular material GP, SP or better.

MH - Inorganic silts, micaceous or diatomaceous fine sands or silts, clastic silts. Pipe should be surrounded with granular material GP, SP or better.