CHARACTERIZATION TESTS USEFUL IN DETERMINING CHEMICAL PROPERTIES

Technical Note DOER-C2

May 1999

The CBR is used to determine resistance to penetration of a material (subgrades or bases) before

its ultimate shearing modulus is reached. Its primary use has been in the design of flexible

pavements for airfields located in areas where frost action is not a controlling factor. Since moisture

content affects the results, tests must be conducted using a moisture content that approximates the

moisture content anticipated at the site where the pavement is to be constructed. Values obtained

usually range from 3 to 80 depending on the type of material tested.

Consolidation Tests. Consolidation tests are needed to estimate the readjustment or plastic

deformation likely to occur when soil is subjected to increasing pressures or loads and to determine

the compressibility of the dredged material (compressibility index Cc). It is a rate process based

on the time required for pore fluid, either water or air, to flow out of soil pores (void-ratio reduction).

The rate of consolidation is dependent on (a) the degree of saturation, (b) the coefficient of soil

permeability, (c) the nature of pore fluid (air or water), and (d) the distance the pore fluid has to

travel for equilibrium to occur. The amount of consolidation or settlement likely to occur must be

determined before dredged material is used as a base or subgrade.

Shear Strength. The behavior of dredged material under a load is a measure of its shear strength.

Before a dredged material can be used for construction purposes, its shear strength must be

determined ( e.g., weight-bearing capacity and stability of earthen slopes are directly related to shear

strength). Three tests are generally used to determine shear strength: (a) the unconsolidated,

undrained (UU) test, (b) the consolidated, undrained (CU) test, and (c) the consolidated, drained

(CD) test. The methods and appropriate characterization tests for determination of geotechnical

and engineering properties of dredged material are listed in Table 1.

CHARACTERIZATION TESTS USEFUL IN DETERMINING CHEMICAL PROPERTIES

pH. The chemical properties of dredged material are interrelated, but pH is one of the most useful

and informative parameters in characterizing those properties. It is a measure of the concentration

and activity of ionized hydrogen (H ) in the dredged material/soil solution. The pH affects the

chemical properties of dredged material, including (a) surface charge of organic matter, clay, or

mineral particles, (b) solubility, mobility, and toxicity of contaminants (e.g., metals, organics),

equivalents (liming requirements), and (e) nutrient availability. pH values are "beacons" that point

to potential corrective actions: pH < 4.0 is indicative of the presence of free acids (e.g., sulfates or

nitrates); pH < 5.5 indicates that toxic amounts of exchangeable aluminum, iron, or manganese may

be present; pH values between 7.8 and 8.2 are indicative of large accumulations of bicarbonate ions.

pH is a useful tool for determining the kinds of analyses or corrective action(s) needed before

dredged material can be used in beneficial ways.

Calcium Carbonate Equivalent. The calcium carbonate equivalents (lime requirements) and

pH are closely related parameters. The calcium carbonate equivalent is an indicator of the amount

of lime required to neutralize any acidity present in order to maintain the desired pH. If large

concentrations of sulfides are present in the dredged material, heavy lime application may be

required to neutralize the acidity produced from the oxidation of sulfides to sulfates. The need for

lime can usually be determined by the calcium carbonate equivalent, which is expressed in terms

of lime (CaCO3/100 g of dredged material). Agricultural lime is the most commonly used basic