5.6 Chemical testing of soil and groundwater

5.6.1 Requirements for all chemical tests Scope

(1) Although the detailed chemical composition of soil is often of limited interest for civil engineering purposes, the presence of certain chemical constituents in soil can be very significant, for example for the durability of the geotechnical structure.

(2) Routine chemical testing in a soil laboratory is usually limited to organic content (loss on ignition, total organic content, organic matter), carbonate content, sulfate content, pH value (acidity or alkalinity) and chloride content. This standard deals with these five chemical tests only.

NOTE 1 Annex N provides more details on each chemical test and its interpretation, and some guidelines.

NOTE 2 There are other chemical components that may cause an environment very aggressive to steel and concrete, for example sulfide, magnesium and ammonium. The corresponding chemical testing is not covered in this standard.

NOTE 3 Corrosiveness to sleet constructions in soil is usually evaluated by means of electrical resistivity tests and determination of the redox potential (not covered in this standard), pH, chlorides and sulfate determinations. Objective

(1) The purpose of the chemical tests described herein is to classify the soil and to assess the detrimental effect of the soil and groundwater on concrete, steel and the soil itself. The tests are not intended for environmentally related purposes. Requirements

(1)P The following requirements shall be specified for all chemical tests:

  • the samples to be tested;
  • the number of samples to be tested;
  • the test procedures to be applied;
  • the pre-treatments including treatment of oversize particles (i.e. D > 2 mm);
  • the number of tests per stratum and number of duplicate tests;
  • the number of separate tests for the determination of a mean value;
  • the format of reporting;
  • the required supplementary classification tests for each test or series of tests.

(2)P The proper procedures of mixing, riffling and quartering shall be strictly followed in order to avoid inconsistent results.

(3) Disturbed soil samples may be used for the chemical tests, but particle size and water content need to be representative of the field conditions (Quality Classes 1 to 3).

(4) For the determination of organic content, the particle size distribution only needs to be representative (Quality Class 4).

NOTE Recommended test procedures arc available in Annex N. Evaluation of test results

(1)P The test results shall be reviewed together with the geological description and the prevailing environment.

(2)P Where appropriate, account shall be taken of recognised classifications in terms of the parameter measured.

5.6.2 Organic content determination Objective

(1) Organic content tests are used to classify the soil. In soil with little or no clay particles and carbonate content, the organic content is often determined from the loss on ignition at a controlled temperature. Other suitable tests can also be used. For example, organic content can be determined from the mass loss on treatment with hydrogen peroxide (H2O2), which provides a more specific measure of organics.

(2) The presence of organic matter can have undesirable effects on the engineering behaviour of soil. For example, the bearing capacity is reduced, the compressibility is increased, swelling and shrinkage potential is increased due to organic content. Gas can lead to large immediate settlements and can affect the consolidation coefficients and shear strength derived from laboratory tests. Organic mutter is detrimental for the stabilisation of soil used for roads and is usually associated with low pH and at times with presence of sulfates which can have negative effects on foundations. Requirements

(1)P For each test or series of tests, in addition to the list in, the following shall be specified:

  • the drying temperature;
  • the ignition temperature;
  • the required corrections for bound water, carbonates, etc.;
  • the factor used for converting carbon content into organic content.

(2)P Non-homogeneous samples require larger specimens and the appropriate apparatus. Correspondingly larger crucibles shall be used.

(3)P The loss on ignition shall be reported as a percentage of original dry matter, also giving the drying temperature, ignition temperature and drying and ignition times.

(4)P The organic content shall be reported as a percentage of original dry matter, also giving the method of determination. Evaluation of test results

(1) In clays and silty soil with moderate organic content, the errors involved in the correction for bound water or carbonates can be so large that special testing methods are necessary.

5.6.3 Carbonate content determination Objective

(1) The carbonate content is used as an index to classify natural carbonate soil and rock or as an index to indicate the degree of cementation.

(2) Measurement of the carbonate content depends on the reaction with hydrochloric acid (HCl) which liberates carbon dioxide. It is usually assumed that the only carbonate present is calcium carbonate (CaCO3). The carbonate content is calculated from the content of carbon dioxide measured on treatment of the soil with HCl. Requirements

(1)P The soil shall be assessed visually before the selection of the appropriate pre-treatment.

(2) When appropriate, large initial samples can be used to cope with non-homogeneous carbonate distribution in soil and rock. Representative test samples can be established by crushing and riffling.

(3)P The carbonate content shall be reported as a percentage of the original dry matter. Evaluation of tests results

(1)P Some carbonates, e.g. dolomite, neednot dissolve using the standard solution of hydrochloric acid during the specified time. Special methods shall be used for soil or rock types containing such carbonates.

5.6.4 Sulfate content determination Objective

(1) The objective of the test is to determine the sulfate content as an index for the possible detrimental effect of the soil on steel and concrete. All naturally occurring sulfates, with rare exceptions, are soluble in hydrochloric acid. Some are soluble in water.

(2) The acid-soluble sulfate content is referred to as the total sulfate content, as distinct from the water-soluble sulfate content. It is important to appreciate which value is relevant.

(3) Groundwater containing dissolved sulfates, especially sodium and magnesium sulfates, can attack concrete and other materials placed in the ground or on the ground surface. Classification of soil and groundwater in terms of sulfate content is therefore necessary so that suitable precautionary measures can be taken, if required. Requirements

(1)P It shall be specified for each test or group of tests, whether acid- or water-soluble sulfate is required for the test, in addition to the items listed in

(2)P Non-homogeneous soil containing visible crystals of gypsum require large samples, which shall be crushed, mixed and riffled to provide representative test specimens. A visual assessment is needed before selecting the appropriate specimen preparation method. Evaluation of test results

(1)P The content in SO2-3 or SO2-4 shall be reported as a percentage of dry substance or in grams per litre, relating to acid- or water-soluble sulfate,

5.6.5 pH value determination (acidity and alkalinity) Objective

(1) The pH value of groundwater or solution soil in water is used to assess the possibility of excessive acidity or alkalinity. Requirements

(1)P The following shall be specified for each test or group of tests, in addition to the general requirements for chemical testing:

  • whether or not the soil shall be dried;
  • the ratio of soil to water.

(2)P Standard buffer solutions shall be used for calibration of the pH meter.

(3)P The pH value of the soil suspensions or the groundwater shall be reported. The test method shall be stated. Evaluation of test results

(1) The evaluation should consider that, in some soil, the measured values can be influenced by oxidation.

5.6.6 Chloride content determination Objective

(1) The objective of the test is the determination of the water-soluble or acid-soluble chloride content so that the salinity of the pore water or soil can be assessed. The results provide an index for the possible effect of the groundwater towards concrete, steel, other materials and soil. Requirements

(1)P The following shall be specified for each test or group of tests, in addition to the items listed in

  • whether water-soluble or acid-soluble chlorides shall be determined;
  • whether or not the soil shall be dried.

(2)P After drying, the soil shall be mixed thoroughly to redistribute any salts which may have mi stilted to form a surface crust. Evaluation of test results

(1)P The chloride content in grams per litre or as a percentage by dry mass of the soil shall be reported. The test procedures used shall state whether water-soluble or acid-soluble chlorides have been determined.

Eurocode 7: Geotechnical design — Part 2: Ground investigation and testing