Taking or obtaining samples is the procedure that consists of collecting representative parts, portions or elements of a piece of land, from which a geotechnical recognition of the same will be carried out.
The samples are representative portions of the land that are extracted to carry out laboratory tests. Depending on the way they are obtained, they can be generally classified into two types:
Samples obtained in pits
They are taken from pieces of soil torn up by the excavator shovel, placing it in bags. If the aim is to obtain soil moisture, the sample can be stored in a watertight container or paraffin container.
The sample should be stored at room temperature.
They require surface cleaning prior to taking the sample, and subsequent waxing of the faces of the sample, in which the soil is in contact with the outside. They can be:
Block: hand carving an approximately cubic block, with dimensions greater than 15 or 20 cm. The quality of this sample is excellent.
Cylindrical: by manually tapping a cylindrical sampler with a diameter of no less than 15 cm.
Samples obtained in surveys
Obtained from control pieces or SPT test samples. Analogously to the case of altered samples obtained in pits, the same considerations are taken into account.
They are obtained through appropriate samplers. The most commonly used are the thick-walled open samplers and the thin-walled or Shelby sampler. Also, in soils very sensitive to the alteration inherent to the maneuver, the thick or thin wall piston sampler can be used.
The most frequently used is the first of those mentioned. It consists of a thick-walled cylindrical tube fitted with a separable shoe. The rest of the tube is split (by two generators), for the subsequent extraction of the sample once taken. Inside, a thin jacket is housed, which is generally made of PVC, although it can be metallic, where the sample is introduced to be sent to the laboratory, having previously waxed the end faces to avoid moisture loss.
In soft soils, the thickness of the footing causes a strong alteration of the sample. To avoid this, the thin-walled sampler, also called Shelby, is used. In this case, no jacket is inserted inside the sampler, but the sample is sent to the laboratory in the same Shelby tube, suitably capped and waxed.
Tampered samples
Introduction
Taking or obtaining samples is the procedure that consists of collecting representative parts, portions or elements of a piece of land, from which a geotechnical recognition of the same will be carried out.
The samples are representative portions of the land that are extracted to carry out laboratory tests. Depending on the way they are obtained, they can be generally classified into two types:
Samples obtained in pits
They are taken from pieces of soil torn up by the excavator shovel, placing it in bags. If the aim is to obtain soil moisture, the sample can be stored in a watertight container or paraffin container.
The sample should be stored at room temperature.
They require surface cleaning prior to taking the sample, and subsequent waxing of the faces of the sample, in which the soil is in contact with the outside. They can be:
Block: hand carving an approximately cubic block, with dimensions greater than 15 or 20 cm. The quality of this sample is excellent.
Cylindrical: by manually tapping a cylindrical sampler with a diameter of no less than 15 cm.
Samples obtained in surveys
Obtained from control pieces or SPT test samples. Analogously to the case of altered samples obtained in pits, the same considerations are taken into account.
They are obtained through appropriate samplers. The most commonly used are the thick-walled open samplers and the thin-walled or Shelby sampler. Also, in soils very sensitive to the alteration inherent to the maneuver, the thick or thin wall piston sampler can be used.
The most frequently used is the first of those mentioned. It consists of a thick-walled cylindrical tube fitted with a separable shoe. The rest of the tube is split (by two generators), for the subsequent extraction of the sample once taken. Inside, a thin jacket is housed, which is generally made of PVC, although it can be metallic, where the sample is introduced to be sent to the laboratory, having previously waxed the end faces to avoid moisture loss.
In very hard clay soils or in rocks, sampling tubes cannot be introduced by means of pressure or percussion: in the case of very firm clays, the introduction of the sampling tube by means of a large number of blows causes the total alteration of the soil. Therefore, the sample must be obtained with the drilling battery. If this hard soil or rock requires water for advancement, (and this may result in alteration of the sample), a double core tube should be used. The control that is going to be sent as a sample to the laboratory must be wrapped in mesh and subsequently waxed.
An altered sample is defined as one where part or all of it has suffered an alteration such that it has lost the structure it had in-situ. These samples do not truly represent the engineering properties of resistance and permeability of the soil. An unaltered sample is generally used for soil identification and characterization processes. The unaltered samples are also used to prepare laboratory specimens and evaluate their permeability and mechanical resistance properties, when the soil is used as a construction element.
They are made up of disintegrated or fragmented material, in which no special precautions are taken to preserve the characteristics of structure and humidity; However, on some occasions it is useful to know the original water content of the soil, for which the samples are packaged and transported appropriately.
They can be obtained from an excavation, from a face, either from a bench or from drilling carried out to depth with special tools. The samples must be representative of each layer that is crossed, until reaching a depth that may correspond to the lowest level of exploitation, the level of groundwater or the level to which it is necessary to extend the study.
In soft soils, the thickness of the footing causes a strong alteration of the sample. To avoid this, the thin-walled sampler, also called Shelby, is used. In this case, no jacket is inserted inside the sampler, but the sample is sent to the laboratory in the same Shelby tube, suitably capped and waxed.
In very hard clay soils or in rocks, sampling tubes cannot be introduced by means of pressure or percussion: in the case of very firm clays, the introduction of the sampling tube by means of a large number of blows causes the total alteration of the soil. Therefore, the sample must be obtained with the drilling battery. If this hard soil or rock requires water for advancement, (and this may result in alteration of the sample), a double core tube should be used. The control that is going to be sent as a sample to the laboratory must be wrapped in mesh and subsequently waxed.
An altered sample is defined as one where part or all of it has suffered an alteration such that it has lost the structure it had in-situ. These samples do not truly represent the engineering properties of resistance and permeability of the soil. An unaltered sample is generally used for soil identification and characterization processes. The unaltered samples are also used to prepare laboratory specimens and evaluate their permeability and mechanical resistance properties, when the soil is used as a construction element.
They are made up of disintegrated or fragmented material, in which no special precautions are taken to preserve the characteristics of structure and humidity; However, on some occasions it is useful to know the original water content of the soil, for which the samples are packaged and transported appropriately.
They can be obtained from an excavation, from a face, either from a bench or from drilling carried out to depth with special tools. The samples must be representative of each layer that is crossed, until reaching a depth that may correspond to the lowest level of exploitation, the level of groundwater or the level to which it is necessary to extend the study.