Geotechnical prospecting

Drilling Boreholes can be either with continuous or discontinuous sampling, dry or fluid drilling, using appropriate samplers or simply with destructive drilling without sample collection (hollow boring, drag bit with wash boring, etc.).

In the Cable Percurssion works, as its name implies, the borehole is obtained by striking the bottom of the hole with cutting steel pieces, which will destroy the soil matrix and cleaning it from the bottom of the hole, with the aid of cutters, shells and chiselling tools. The bore hole is usually stabilized with casing tubes and a stabilizing fluid

The Standard Penetration Test (SPT) is a dynamic test consisting of stick a standardized sampler at the bottom of a bore hole, cleaned and stabilized. The driving is done by using a pylon weighing 63.5 kgf which falls freely from a height of 30 “on a stopper which in turn is connected to a train of rods, the tip of which is the standardized sampler.

The test is composed of two phases: in the first the sampler is nailed 15 cm, registering the respective number of blows; To this phase, as a rule, the soils in question are disturbed, so that the value obtained at this stage is indicative only. In the second phase, the sampler is drived plus 30 cm. The result of the SPT test is the number of blows obtained. If after 60 blows (Portuguese practice), the penetration does not reach 30 cm, the test is terminated by measuring the penetration obtained.

In order to obtain certain physical and mechanical parameters, of some types of soil, undisturbed samples are collected with suitable samplers, which are later duly sealed, trying to minimize the alteration of the sample during collection, transport and extraction manipulation, thus allowing the soil to maintain its structure and moisture content as much as possible, until the preparation of the respective test.

Continuous dynamic probing tests consist of determining the number of strokes (N) of a mass pestle (M) in free fall from a height (H) on the assembly formed from top to bottom by a stop, a train of Rods and a conical tip (whose area is A-base), so that a certain length of penetration (L) occurs.

A summary table with the characteristics of the standard dynamic tests is presented below.Type of test .

The electrical resistivity in soils and rocks, can be used for various purposes, such as the design of grounding systems in electrical projects, corrosion studies, etc. In the case of geology\geotechnics, included in the area of geophysics, it allows to obtain projections on the physical properties of the soil\rock in a quick, non-evasive way, allowing the coverage of relatively large extensions, being a method widely used to identify, for example, karsification phenomena \ voids in rock masses formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. Within its applications, the technique also allows the prospection of groundwater.

The soil thermal resistivity test measures the ability of the soil to conduct or dissipate heat. A correct understanding of the thermal properties of a soil or soil layer made is important for the design and installation of underground pipelines and transmission cables, to optimize their design and avoid premature failures.

The plate load test basically consists of loading a steel plate placed at the level where the actual load will be applied and recording the settlements corresponding to successive load increments.

The test allows obtaining parameters such as the Young´s modulus (E), modulus of subgrade reaction (K), CBR value, and the ultimate load capacity of the soil, generally by extrapolation.

We proceed to the installation of piezometric tubes by taking advantage of the drilling hole made or by making holes dedicated to the installation of piezometers or monitoring holes. Piezometers are aquifer observation holes. They serve to monitor water levels in aquifers, to evaluate their hydrostatic pressure and contamination levels of aquifers, as well as to allow the collection of a water sample for later analysis.

Parallel to the field work, through the collection of samples, disturbed or “undisturbed”, laboratory tests may be carried out to complement information on their identification and the physical, chemical and mechanical characteristics of the soils.

Sondasol’s laboratory covers the following areas:

• Identification tests – grain size, Atterberg limits, moisture content, etc…;
• Tests for compaction control – Proctor and CBR;
• Shear and stress-strain tests, consolidation, expansion, collapsibility;
• Chemical tests to evaluate soil and water aggressiveness;
• Thermal resistivity tests.