Soil testing

Once opened, the sample is photographed, examined, and described in order to perform a preliminary characterization.
During this phase, the following are determined:

• The lithology of the sample
• The color, using the Munsell Rock Color Chart
• Particle size, assessed visually or with the aid of lenses and a microscope
• The presence of carbonates, using a 10% HCl solution
• Consistency and shear strength of cohesive soils, using penetrometers and pocket shear devices

The procedure complies with the following standards:
ASTM D2573-08
ASTM D2488
ASTM WK27337

Natural Water Content is one of the fundamental physical properties of great geotechnical interest. The test consists of determining the water content of a soil sample in its as-received condition.

The procedure complies with the following standards:
ASTM D2216
EN ISO 17892-1:2014/2022
EN ISO 17892-2:2014/2022

A physical property that defines the mass of soil or rock per unit volume. It can be used as an index of material density under natural conditions.

The procedure complies with the following standards:
ASTM D2216
EN ISO 17892-1:2014/2022
EN ISO 17892-2:2014/2022

This physical property can be defined as the average value of the unit weight of the granular particles that compose the material. Determining this property allows for the calculation of various other parameters useful for classification and geotechnical characterization.

The procedure complies with the following standards:
ASTM D854 – 92
EN ISO 17892-3:2015

Porosity and void ratio are two important parameters used to characterize a material. Porosity expresses the percentage of empty space present within a given volume of material, while the void ratio is the ratio between the volume of voids and the volume of solids.

Sieve analysis allows the evaluation of the coarser particle sizes (gravels and sands) that make up a soil. By using metal sieves, each with different mesh sizes (opening of the sieve’s metal mesh), the particles constituting the examined sample are separated to assess the distribution of different sizes. Finer particles (silts and clays), on the other hand, are treated by sedimentation.

The procedure complies with the following standards:
ASTM D422 – 63
EN ISO 17892-4:2016
AGI Recommendations – 1993

To evaluate the size of the finer particles (silts and clays) that make up the soil, particle size analysis by sedimentation is performed. Particle sizes are determined indirectly by measuring the sedimentation time within a cylinder, where the fine material is dispersed in distilled water.

The procedure complies with the following standards:
ASTM D422 – 63
EN ISO 17892-4:2016
AGI Recommendations – 1993

The evaluation of the minimum water content at which the soil flows under a small applied pressure, behaving like a fluid, is carried out using the Casagrande cup device.

The procedure complies with the following standards:
ASTM D4318 – 17
UNI EN ISO 17892-12:2018
AGI Recommendations – 1993

The evaluation of the minimum water content at which the soil can be plastically deformed is performed manually. The operator, by varying the sample’s water content, rolls cylindrical threads approximately 3 mm in diameter and observes the point at which the material begins to crack.

The procedure complies with the following standards:
ASTM D4318 – 17
UNI EN ISO 17892-12:2018
AGI Recommendations – 1993

The laboratory evaluation of the shrinkage limit is performed by measuring the linear and/or volumetric changes of the sample while varying its water content. This procedure allows the determination of the minimum water content below which the soil no longer undergoes volume reduction upon drying.

The procedure complies with the following standards:
ASTM D0427 – 04
ASTM D4943 – 02

The ELL test (Free Lateral Expansion Test) allows the determination of the undrained shear strength of cohesive soil. A cylindrical specimen (from 38 mm to 100 mm in diameter), obtained from an undisturbed sample, is subjected to an axial load until failure, thereby determining the soil’s undrained shear strength.

The procedure complies with the following standards:
ASTM D2166 – 00
EN ISO 17892-7:2018

The test is used to experimentally determine the failure envelope and the corresponding parameters. For each soil sample, three specimens are prepared; each specimen is consolidated and brought to failure by shearing under three different vertical loads.

The procedure complies with the following standards:
ASTM D3080 – 11
EN ISO 17892-10:2018
AGI Recommendations (1993)

Shear strength, for most materials, reaches a peak value and then decreases, maintaining a lower limit value known as residual strength. The evaluation of this residual strength is often of significant geotechnical interest.

The procedure complies with the following standards:
ASTM D3080 – 11
EN ISO 17892-10:2018
AGI Recommendations (1993)

A soil specimen is placed in the oedometer, where a vertical load is progressively applied. From the moment the vertical pressure is applied, the vertical settlements of the specimen are measured. During the same test and on the same specimen, multiple compression stages are carried out with increasing pressures, leaving each load in place for the time required (24–48 hours) for the settlements to stabilize.

This procedure allows the execution of multiple load increments, and for each increment it is possible to determine both an oedometer consolidation curve and an oedometer compressibility curve. From the obtained curves, several geotechnically important parameters can be derived, including:

• Consolidation velocity
• Magnitude of settlements
• Corresponding void ratio
• Preconsolidation pressure
• Primary consolidation coefficient Cv (Casagrande and Taylor methods)
• Secondary consolidation coefficient (Casagrande method)
• Compressibility coefficient
• Compressibility index

The procedure complies with the following standards:
ASTM D2435 – 11
EN ISO 17892-5:2017
AGI Recommendations (1993)

Also known as swelling tests, these are performed to investigate the behavior of cohesive soils regarding the relaxation of geostatic stresses and volume increase due to water absorption. From the test, it is possible to obtain the following values:

• Swelling pressure
• Swelling strain
• Swelling curve (Huder-Amberg)

The procedure complies with the following standards:
ASTM D2435 – 11
EN ISO 17892-5:2017
AGI Recommendations (1993)

In these tests, drainage is prevented both during the application of isotropic pressure and axial loading. Under these conditions, water content, void ratio, and effective stresses remain constant throughout the test. The shear strength measured in this way is independent of the applied isotropic pressure and is expressed in terms of total stresses.

The procedure complies with the following standards:
ASTM D2850 – 15
EN ISO 17892-8:2018
AGI Recommendations (1993)

In this test, during the consolidation phase of the soil specimen, the dissipation of pore water pressures and volume changes are monitored to determine the effective stresses acting on the soil skeleton. In the failure phase, an increasing vertical stress is applied until the specimen reaches its maximum strength. During this phase, the generated pore water pressures are measured. By repeating the test on different specimens consolidated under varying stress states, it is possible to correlate the shear strength with the applied effective stresses and obtain the failure envelope known as the shear strength envelope. From this, key geotechnical parameters such as the effective shear strength angle and cohesion can be derived.

The procedure complies with the following standards:
ASTM D4767 – 11
EN ISO 17892-9:2018
AGI Recommendations (1993)

In this test, during the consolidation phase of the soil specimen, the dissipation of pore water pressures and volume changes are monitored to determine the effective stresses acting on the soil skeleton. The failure phase, where an increasing vertical load is applied, is conducted at a controlled rate to allow the dissipation of pore water pressures, thus measuring the volume change. By repeating the test on different specimens consolidated under varying stress states, it is possible to correlate the shear strength with the applied effective stresses and obtain the envelope known as the shear strength or failure envelope. From this, important geotechnical parameters such as the effective shear strength angle and cohesion can be derived.

The procedure complies with the following standards:
ASTM D7181 – 11
EN ISO 17892-9:2018
AGI Recommendations (1993)

The variable head permeameter is typically used for testing fine-grained materials with medium to low permeability, as the equipment characteristics allow for easy measurement of hydraulic head and time over a wide range of permeability coefficient values, k. The test consists of measuring the volume of water that flows through the soil sample in a time interval t under the action of a variable hydraulic head h.

The procedure complies with the following standards:
ASTM D2434 – 00
EN ISO 17892-11:2019

The constant head permeameter is typically used for testing coarse-grained materials such as gravel and clean sands, characterized by high permeability. The test consists of measuring the volume of water that flows through the soil sample over a time interval t under the action of a constant hydraulic head h.

The procedure complies with the following standards:
ASTM D2434 – 00
EN ISO 17892-11:2019

For clayey or generally fine-grained soils characterized by low permeability values, direct measurements are performed using an oedometer cell. The test can be conducted simultaneously with the incremental load oedometer test; in fact, at the end of each consolidation stage, the permeability measurement is taken. The test consists of reading the water levels in the measuring burette connected to the oedometer cell at predetermined time intervals.

The procedure complies with the following standards:
ASTM D2435 – 11
EN ISO 17892-5:2017
AGI Recommendations (1993)

Similarly to oedometer tests, direct permeability measurements can also be performed at the end of the consolidation phase in triaxial tests. These tests are typically conducted on fine-grained materials with low permeability.

The procedure complies with the following standards:
ASTM D4767 – 11
ASTM D7181 – 11
EN ISO 17892-9:2018
AGI Recommendations (1993)

The test consists of compacting layers of soil placed in a cylindrical mold by the free fall of a rammer. During the test, it is possible to vary the water content of the soil samples, the compaction energy, the number of blows per soil layer, or the thickness of the layers. From the results obtained, the effectiveness of compaction can be assessed (understood as the artificial increase of soil density through mechanical means).

The procedure complies with the following standards:
ASTM D1557 – 02
ASTM D698 – 00
ASTM D558 – 04

The CBR test measures the bearing capacity of a soil under specific density and moisture conditions. The test is performed by penetrating a steel piston with standardized section and weight into a compacted soil sample contained in a mold, at a constant rate. The force required to maintain the constant penetration rate is measured. From the test, the load-penetration curve is obtained, allowing the calculation of the California Bearing Ratio (CBR).

The procedure complies with the following standards:
ASTM D1883 – 05
EN ISO 13286-47 – 2012
CNR-UNI 10009 (1964)

The purpose of this test is to estimate the content of organic impurities within soils of various grain sizes. It is applicable both in geotechnical engineering and in assessing the quality of construction materials such as cements and mortars.

The procedure complies with the following standard:
ASTM C40 / C40M

In the fields of Earth, Environmental, and Agronomic Sciences, calcimetry is the most widely used, efficient, and rapid method to determine total carbonate content in rocks and soils. However, samples with low carbonate content may present reliability issues. The “total carbonate” analysis aims to determine the quantity of all carbonates present in the soil (CaCO3, MgCO3, Na2CO3, etc.), although the result is conventionally expressed as calcium carbonate (CaCO3) since it predominates and the analytical method does not distinguish among different carbonate forms. Therefore, soil carbonate content is usually reported as a percentage of calcium carbonate (%CaCO3). The test is conducted using the Früling-Dietrich Calcimeter.

The testing method complies with the following standards:

AGI Recommendations (2011)
ARPAV – Interpretation of Soil Analysis, Tool for Environmental Sustainability
Method 9 – Official Gazette Supplement, General Series No. 121, 1992

The test consists of filling a standard-sized mold with a sand sample, which is then subjected to a uniform load and vibration for a specified period. The measurement of the resulting settlement allows determination of the maximum dry density and the minimum void ratio achieved.

The procedure complies with the following standard:
ASTM D4253