Understanding Soil Types and Foundation Engineering
Types of Land
Classification by RQD (%), one considers the following types of terrain in its initial state, in excavations:
- Excellent or Hard: Attackable with machinery and/or scaler, but not billed as a land of transit, broken rocks, soil, very compact, and so on.
- Good Quality: Attackable with a machine.
- Medium Quality: Attackable with beaks, but not with the shovel, as semicompact clays with or without gravel or gravel.
- Poor Quality: Attack with the shovel, and loose soils, topsoil, sand, etc.
- Very Poor Quality
For the sake of digging and a very large, for safety purposes, we classify land according to the organoleptic reason making done in the field into three categories:
- Stable (rock, marl, etc.).
- Shortly Stable (gravel, clay, trawling grounds, etc.).
- Loose (loose gravel, sand, etc.).
The rocky terrain for those who need or use explosives to dig drum machines do not give problems from the standpoint of security. In rock sound is not needed any special precaution to maintain the walls in excavations. What we must eliminate those blocks are unstable, regardless of their size, and whose fall could cause accidents.
In the rest of the land, to have security guarantees, it must give the walls a certain slope, generally, in the excavations to build in urban areas can never take it for lack of space, which forces us to yokes.
Elements for Grounding Aggressive in Field
The types of land seen before, are not pure in nature, but mixed in different proportions and may contain also other elements that may be aggressive for the foundation, among which we mention the following:
- Plasters (sulfates): React with wet cement and corrode unprotected reinforcement.
- Salts (chlorides): React with wet cement and corrode unprotected reinforcement.
- Cal (carbonates): React with wet cement.
- Organic Matter: Are the decomposition products (ammonia and nitrous) that react with the cement.
- Pure Water (melting): They have high solubility, dissolving the components of cement.
Factors that Modify the Characteristics of Land
There are a number of circumstances, which almost always involve water, which may eventually change the characteristics of a field, such as variations in water level, broken pipes buried underground, spill decks, etc.
These include water, by itself, can occur for example:
- Volume changes in expansive clays.
- Drag incoherent materials on land while in motion.
- Landslides in stratified terrains, especially in the case of silt or clay and filtered water to the contact face of the strata, which cancels the frictional forces.
Water can also change the terrain by the aggressive elements containing (sulfates, carbonates, chlorides, organic matter, etc.). As in the case of wastewater from industry.
Equally important is the action of roots in certain species of great development that may affect the stability of small buildings.
Classification of Slopes Depending on the Terrain
When we start digging we are breaking a balance between a system, sometimes very complex forces or stresses.
If we carry out the excavation of dry sand grains from the walls slide toward the bottom and stops moving when you get a certain angle of repose. This angle is independent of the height of the slope. If you do the same operation on a clay can get some depth with nearly vertical walls. In this case, we could see that angle of repose varies with altitude.
Between pure sand and clay, there is a wide range of soils with different coefficients of friction and cohesion.
Experience teaches us that the soil tends always to restore this balance that we are breaking. In some cases, this makes it immediately, if the sand, in others it is slower and can take hours, days, months or even years.
If we knew this time we could make the excavation safe. But the restoration of this balance depends on multiple factors that we can only obtain a thorough study of the soil.
Among these factors we have:
- Angular internal friction
- Size and kind of grain
- Shear
- Consistency
- Moisture
- Density
- Permeability
- Stability
- Stratigraphy, dip and fault
- Lateral pressure field
- Existing Pipes
- Vibrations in the vicinity
In general, it is necessary yokes where we give a slope of land equal to or greater indicated in the table.
Depth Review of Excavation
Definition
It’s called critical depth Hc excavation of land, to the maximum depth that can dig in stable vertical wall without any fortification.
As a rule guidance we have the following:
HC in m Terreno
- Arena grava 1.00
- Arena cohesiva 1 soils, 25
- Arcillosos 1, 50
- Muy compact, no rocks and hammers rompedores 1, 80
- Muy compact, no rock. With bars, picks and cuñas 2, 00
- Compactos, with machinery and without obreros 3, 00
Recognition of Terrain: Terrain Geotechnical Study
Its object is to know the nature and properties of the ground to define the most suitable type of foundation and the stratum is going to be supportive.
A first information can be obtained from the study of local experiences, and the behavior of foundations of nearby buildings.
In some cases, and in the case of minor construction may be sufficient, but in general, it is necessary to use systems of local knowledge, from which it is possible to determine the position of the firm stratum of land on which to build without exceeding allowable pressure and with few seats compatible with the tolerances of the structure.
For reasons of time, often the geotechnical study performed after the construction project, which provided a foundation is made to transmit to a given pressure field. In these cases, the work allows us to monitor compliance with field data considered in the Project and shall otherwise modify the foundation and, in extreme cases, to the structure.
We must appreciate that the geotechnical study of the ground can prevent costly accidents and motivated by a poor or inadequate foundation, leaving more than justify its cost. Promotion in public buildings and homes of Official Protection these studies are mandatory, and has published a basic rule that if compulsory extended to all types of buildings.
Surface Foundations
- Spread footing.
- Brake Eccentric
- Brake cable-stayed.
- Brake foundation beams.
- Brake runs.
- Slabs of thickness.
- Slabs with capitals.
- Ribbed slabs.
- Floating slabs.
Deep Foundations
- Prefabricated piles.
- Piles spot.