Difference Between Shallow and Deep Foundation

Looking for the Difference Between Shallow and Deep Foundation? Then you came to the right place. Deep and shallow foundations are one of the most important parts of a structure.

These are responsible for transferring the total loads that the structure has to the ground and at the same time are responsible for providing stability. Foundations are classified into two parts, which are deep and superficial. These are used taking into account the depth they must have to provide stability to the construction.

Differences Between Shallow and Deep Foundation

The foundations deep and superficial have several differences. These differences can be evidenced in their definition, in the depth they need, their cost, feasibility, the mechanism they have for the transfer of loads, the advantages, the disadvantages, the types that each one has, among others. In this article we are going to tell you in more detail about each of these differences that we mentioned above.

Definition of deep and shallow foundations

The deep foundations are the base that is installed at a greater depth and is responsible for transferring the loads of the structures that it supports to the soil strata that have a great bearing capacity. On the other hand, shallow foundations are those that are installed near the surface of the earth or are responsible for transferring loads at a shallow depth.

Depth they need

In the case of shallow foundations, they have shallow depths that are generally 3 meters or in other cases the depth of the foundations is less compared to the base of the structure. However, in the case of deep foundations, their perforations are larger compared to shallow foundations, this is because in many cases piles are used to support the structures and these have a usual length of 15 to 60 meters.

Cost of deep and shallow foundations

Deep foundations are more expensive compared to shallow foundations because more resources are used for their installation, such as machines, materials, transport of materials, among others.

Feasibility of its construction

Deep foundations have a more complex construction process, for this reason they have a more complex construction feasibility compared to shallow foundations.

Mechanism how they transfer their loads

Deep foundations transfer their loads using shaft friction or in other cases through final capacity. In the case of shallow foundations, these are responsible for transferring their loads mainly through the end of the bearing.

Advantages that each one offers

Deep foundations are characterized in that they can be installed at a greater depth, they provide lateral support and resist lifting, they are effective when shallow foundations cannot be built, they are capable of supporting considerable loads, etc. On the other hand, shallow foundations are more available, require less labor, their construction procedure is characterized by being simple and at a very low cost, etc.

Disadvantages they present

Deep foundations have several disadvantages, among the most considerable being that they require qualified work, their construction procedure is more complex, they can take a long time and some types of deep foundations are not flexible. For its part, the disadvantages of shallow foundations can be observed thanks to the fact that they allow settlements that are generally applied for light constructions, they are weak against lateral loads, among others.

Types of shallow and deep foundations you can count on

On the side of the deep foundations you can count on the dock bases, the piles, the Caissons, among others. With regard to deep foundations, you can find isolated footings, slab base, combined footings, etc.

These are the main differences that you can find with shallow and deep foundations, it is important that you know very well the terrain and the type of structure that you are going to build so that in this way you can choose the type of foundation that best suits your project.

The material presented is important data information, which is very much needed in construction design in general, the author describes the theory and discussion in a simple but complete and structured manner in order to facilitate understanding of the theory given.

The structure of the building consists of structural elements that are in the underground part, and structural elements that are at the top of the building, in a construction building, both buildings and bridges, there are so-called upper and lower buildings, one of the civil buildings is the foundation element that is located. In the sub-building, when we encounter the term foundation, we will certainly ask in our minds, What is meant by the foundation ?, what things need to be considered in choosing the type of foundation?

Definition of Foundation

The foundation is one of the structural elements under the building which is directly related to the soil which functions to transmit the load from the structure above it to the supporting soil layer or the rock under it. The foundation is said to be the lowest part of the building, therefore the loads from the building above it such as dead load, live load, wind load are transferred through the horizontal or vertical structural elements to the foundation, which is then continued to the subgrade.

Foundation Classification

1) Shallow Foundation

There are two classifications of foundations, namely shallow foundation and deep foundation. Shallow foundation is defined as a foundation that supports the load directly, such as: tread foundation, longitudinal foundation and raft foundation. Shallow foundations are used when the soil depth is not too deep, namely between 0.6 to 2 meters, and the soil bearing capacity is relatively good (> 2.0 kg / cm2). In general, shallow foundations provide cheaper costs than other types of foundations.

For direct dimensional planning, it can be determined by the formula:

D/B ≤ 1-4

Where:

D = Depth of foundation is measured from foundation base to soil surface

B = width of the foundation base

While the area of ​​the foundation base is calculated in such a way that the pressure that occurs on the subgrade does not exceed the allowable capacity of the soil α ≤ α , and the area of ​​the foundation base is determined by the formula:

A = P / α

With:

A = Area of ​​foundation base

P = the load acting on the column supported by the foundation

α = pressure on the ground

Dimensional planning of the foundation is most economical if it is made in such a way that the resultant forces acting through the center of weight of the foundation base. The following illustrates the variety of the tread foundation. The Telapak Foundation is divided into two, namely the pedestal foundation and the plate / raft / mat foundation.

  1. a) Focus Foundation Includes:

– Continuous foundation

– Combination foundation

– Local foundations

  1. b) Foundation plate / raft / mat Includes:

– Flat Plate

– Plates with a thickness below the column

– Plates with two -way confection beams

– Flat plate with short columns

– Plates with cellular structure

– Floating plate foundation

  1. c) Supporting Capacity of Shallow Foundations

The ultimate bearing capacity (qult) is defined as the maximum load per unit area where the soil still supports the load without experiencing collapse.

Terrazaghi formula

qult = C. Nc + yb. Nq. Df + 0.5.yb. B. Ny

Where:

qult = ultimate bearing capacity of the foundation

C = Soil Cohesion

Yb = Soil Volume Weight

Df = depth of foundation

B = width of foundation is considered to be 1 meter

Nc, Nq, Ny = Terrazaghi bearing capacity is determined by the magnitude of the inner shear angle after we get the ultimate bearing capacity of the soil (qult).

The next step to calculate the carrying capacity of the land permit, namely:

q = qult/SF

Where:

q = Carrying capacity of land permit

qult = Ultimate soil bearing capacity

SF = Safety factor is usually taken three values.

2) Deep Foundation

Deep foundations are defined as foundations that transmit the load of the building to hard soil or rocks that are located relatively far from the surface, the foundation pile piles and foundation piles are deep foundations that are commonly used in the field, except for the process of mobilizing vehicles with difficult terrain, the use of bore piles as an alternative. the use of deep foundations. The deep foundation is used if a hard soil layer or a layer of soil with adequate bearing capacity is at a deep enough soil depth from the surface and in the topsoil in the form of soft soil, so that it requires the foundation to be staked to reach the hard soil layer.

  1. a) Supporting Capacity of Deep Foundations

The bearing capacity calculation associated with the planning process must pay attention to the condition of the pile in the soil layer, whether the pile is held at the end (point bearing pile) or is held back by the attachment between the pile and the ground (friction pile) and is held at the end (point bearing pile). This type of pillar is inserted into the hard soil layer so that the load of the building is borne by this layer. This hard soil layer may consist of any material, from hard clay to fixed rock.

Determining the carrying capacity is done by looking at what type of soil is in the hard soil layer. If the hard soil layer is hard rock, then determining the bearing capacity becomes easy, namely calculating the strength of the pile itself or from the stress value obtained on the pile material. If the hard soil layer is in the form of clay, hard or sand, the bearing capacity of the pile is very dependent on the properties of the soil layer (especially on its density), in this case a good and simple way for this purpose is by means of sondir.

By using sondir data, it can be seen at what depth the pile must be inserted and the bearing capacity at that depth. The carrying capacity can be calculated directly from the highest cone value from the sondir result through the equation:

Q pole = A pole/3

Where:

Q pole = carrying capacity of balance (kg)

A pole = Surface area of ​​the pile (cm2)

P = Value of conus sondir result (kg / cm2)

3 = Safety factor