por What is the pit?
The test pit It is the excavation of a test well to directly observe the surface of a piece of land and take a sample to analyze the composition and nature of the soil. The main objective is to carry out a geotechnical survey of the land, to assess if it is in condition for the use for which it is intended (mining, planting, construction, etc.).
This type of procedure is carried out through the implementation of conventional mechanical techniques, which facilitate direct observation of the soil and the implementation of some field tests.
It is a simple but very effective exploration method, since it allows to inspect the soil conditions in an expedited manner.
The test holes are intended to analyze the stratification; therefore, they must be deep enough for this. The excavation is usually square and must allow the entry of some people inside.
Test pit characteristics
Drilling holes are quick and easy to make, as well as being extremely reliable in terms of the results obtained. Therefore, it is one of the preferred methods when evaluating the surface conditions of a terrain.
The most outstanding characteristics of the soil survey by test pits are detailed below:
– Given the simplicity of the procedure, test pits can be implemented in all types of terrain, and under a significant diversity of geological conditions.
– Excavation is carried out using standard mechanical methods, such as: backhoe loaders.
– The depth of the pits depends on the scope of the exploration; It is limited by the groundwater table. That is, the height of the well will depend on the distance to which the water is in the subsoil, with the surface of the land as a reference. Sometimes the depth does not exceed 5 meters; in exceptional cases it reaches 10 meters.
– The characteristics of the excavation vary depending on the soil: if they are cohesive soils and the well is less than 3 meters deep, secondary supports (bracing) are implemented to guarantee stability. If they are cohesionless soils, it will suffice to dig leaving a steep slope on the walls of the test hole.
– A standard pit area is usually 0.8 meters wide by 1 meter long. Less than this is not recommended, in order to properly observe the soil walls and verify bedding.
– It is suggested that, when a new layer of terrain is glimpsed, the excavation area is reduced and platforms approximately 30 centimeters long are left to easily recognize the soil strata.
– A good practice is to discard material from the excavation that has samples of different types of soil to its credit. This material is considered contaminated, for the purposes of soil analysis.
– The specific technical information must be reported under a control format that records the depth of the pit and the presence of leaks and/or irregularities. The geological, mineralogical and physical characteristics of the soil and the components found in each stratum are also documented. The photographic record is essential.
– Pits should not remain open for a long period of time. After sampling and documentation of the area has been completed, the test pit must be backfilled and compacted to avoid potential hazards in the work area.
– For the physical-chemical analysis of the soil, it is suggested to take a sample from each soil stratum, starting in the deepest stratum and sweeping from the bottom to the top of the test pit. It is likely that the upper layers were disturbed by material from other layers at the time the test hole was excavated.
In this case, one must be very meticulous when taking the sample, and investigate in an uncontaminated area. A hole can even be dug deeper into some stratum if necessary, all to ensure sample integrity.
– When compared with other types of methodologies, the test pits bring with them a significant risk for the executing personnel. Workers must wear personal protective equipment and comply with applicable safety regulations in the event of landslides or collapse of the side walls of the hole during excavation.
Types of test pits
In essence, two types of test pits are distinguished, depending on the results to be obtained from the analysis:
Test pits for routine soil analysis
Before starting work in the adjacencies of a piece of land, the soil conditions must be evaluated and it must be verified if these are the ideal ones for the objective to be achieved.
In this case, a reconnaissance tour is carried out in the area and test holes are dug in locations conducive to investigation.
These locations must be separated from each other (depending on the terrain conditions) and once the soil analysis has been carried out, they must be completely covered.
Test pits for case analysis
These types of test pits dig in search of a specific aspect and, consequently, are only carried out in a particular area of the land.
For example, this type of test pits is applicable to fields that present vegetative development problems in a specific sector and not in the entire object field.
Moisture monitoring is also considered a case analysis test pit. In the latter case, if the ground conditions are homogeneous, the test pit result can be extrapolated to the rest of the ground.
What are the pits used for?
The test pits are extremely useful when evaluating the conditions of a land for construction works, planting and mining, among other applications.
Given the characteristic of the procedure, the test pits are applicable to all types of terrain, respecting the differences between the different types of soil. Test pits are particularly recommended in cohesive and heterogeneous terrain.