Set of operations carried out at the site of the future construction, aiming at determining the nature and characteristics of the land, its layout and accidents with interest for this work / project.
At the end of the survey is usually drawn up a report that can be simply factual or with technical advice and its recommendations and parameters of the soil.
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.
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.
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 bentonite.
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.).
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.
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.
Aiming to guarantee the quality and load capacity of deep foundations – piles, pegs, rods, molded wall, etc. It is desirable that non-destructive and / or disabling tests (experimental elements) be carried out ensuring the quality of execution and the carrying capacity. For example, a stake may be well executed, but its load capacity may not be the expected, and the reverse situation is also possible.
Non – destructive test, which requires – preferably – prior preparation during the execution of the pile or element to be tested. This test consists of lowering an ultrasonic emitter and receiver, in parallel, by two hollow conduits located inside a pile. The time taken to traverse the distance between them, as well as the energy, are recorded.
In the case of wave path defects such as soil inclusions, voids, etc., the test plot will reflect the variation and the depth to which this occurs.
Non-destructive, fast and economical test. The principle of integrity (or sonic) testing is based on the mechanical impulse generated by the impact of a hammer and is described as a shock wave, or acoustic wave. Wave expansion occurs rapidly from the point of impact and propagates through the pile like a flat wave. The wave will go through the pile in the form of energy and if the pile is homogeneous it will go through this at constant speed. By monitoring the pilehead response to the initial impact and to any return reflection, some inferences and conclusions about the properties of buried and inaccessible piles based on an understanding of the physical principles involved can be drawn. The integrity of the pile, its length, cross-section variations, changes in the quality of the concrete, etc. can be obtained from the test.
In Europe, this type of test already takes about 25 years of experience, and has always obtained good results with its use.
Parallel to the sonic or ultrasonic quality tests, which will give us information about the execution quality of the piles, it will be possible to verify (static load test) or estimate (dynamic load test) the load capacity of a pile.
Static load tests allow a load versus settling curve to be obtained up to the workload or up to the last value. However, it is expensive because of the preparation of the reaction structure which requires anchoring systems (anchors, micro-piles or piles).
The dynamic load tests are an essay that aims mainly to determine the breaking capacity of the pile-soil interaction, for static axial loads. It differs from traditional static load tests by the fact that the load is applied dynamically, by means of blows from an appropriate percussion system.
The measurement is made by installing sensors on the pile shaft, in a section located at least twice the diameter below its top. The signal from the sensors is sent by cable to the equipment, which stores and processes the signals “online”.
It has the advantage of being a less expensive test and execution time, enabling its application in a larger number of piles, which better characterizes the variability of pile resistance and, thus, provides conditions for the reliability analysis.
As geotechnical consultants, we prepare reports following geotechnical prospecting, regarding aspects like, excavation works, foundations, slopes, containment structures, etc.
We execute and supervise, in partnership with Structural engineering specialists, projects of geotechnical scope.
Special Foundations are systems formed by the structural element of a building that lies below the ground, with the main function of safely supporting the loads of a building for a resistant layer of soil. Special Foundations can be made from different methods.
Lateral Support with concrete soldier piles, is a fast and economical method of lateral support, applicable to a wide range of geological – geotechnical conditions.
The concrete soldier piles can be composed of contiguous piles – close or very close (tangents) or secants (intercept), in the latter case, the need to make the primary piles first without any type of reinforcement (plastic – soft, without structural function) and then secondary piles that will intercept the primaries and will be properly armed with the steel reinforcement.
The piles can be executed with a Kelly bar or continuous flight auger (CFA), and the resulting wall is stabilized by anchors or by permanent slab systems supported by stakes or temporary micro-piles.
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