What do you know about (Shallow foundations) in structure and bridges?

 Thank you my dear brother ,,,,, Shallow Foundations: These types of foundations are so called because they are placed at a shallow depth (relative to their dimensions) beneath the soil surface. Their depth may range from the top soil surface to about3 times their breadth .They include footings (spread and combined), and soil retaining structures (retaining walls, sheet piles, excavations and reinforced earth). There are several others of course. The design of shallow foundations is becoming an attractive choice for supporting highway bridge  structures. The settlement of structures built on soil is a subject of considerable interest to practicing engineers since excessive settlements can lead to serviceability problems or even failure states in the structural foundations. Therefore, the design of shallow foundations is most often governed by settlement requirements. Reliability based approach can be applied for designing shallow foundations for which their design needs knowledge about the distribution of settlement under a given footing. The performance of geotechnical structures, including shallow foundations depends mostly on loads and soil properties, which are the random variables described by statistical parameters. However, most of the current research efforts have been focused on the reliability models for the superstructure components with less attention paid to the substructure and foundations. The random variables and limit state functions for shallow foundations are very different from those for superstructures such as bridges or buildings.. 

Thanks for invitation,

Shallow foundations are constructed relatively close to the ground level. Shallow foundations can only be used where the soil at that level is capable of adequately supporting the load. They are founded at a minimum depth in the UK to resist damage from frost, and in cohesive soils, for example clays, the presence of nearby trees can significantly affect the depth of the foundation.

Shallow foundations can be sub-divided into the following main types;• Strip foundations (footings) – a linear foundation which generally support walls.• Pad foundations – a discrete square or rectangular foundation supporting columns or piers.• Raft foundations – a large single foundation supporting a whole structure.

Shallow foundations are generally constructed using in-situ concrete but some substructure elements can alternatively be constructed in precast concrete in part or whole to improve speed of construction on site.

:if I understand your question, you talk about semi deep foundation

A semi-deep foundation is a one-time work; generally reinforced concrete for transmitting the loads of a structure such as a building, at the ground, to a depth of about3 to6 m

This type of foundation is used when shallow foundations can not be realized and deep foundations are not needed, avoiding excessive cost

Often, these wells can be dug hydraulic excavator, allowing the company to achieve shell of the structure without using a specialized company, as in the case of deep foundations

This type of foundation also helps guard against freezing phenomenon and soil thaw

Here in Algeria, the main methods of implementation of the soles and the sizing calculation rules are respectively described in the Unified Technical Document

 

 

Shallow foundations, often called footings, are usually embedded about a metre or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials) which extend below the frost line and transfer the weight from walls and columns to the soil or bedrock.

Another common type of shallow foundation is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface. Slab-on-grade foundations can be reinforced mat slabs, which range from25 cm to several meters thick, depending on the size of the building, or post - tensioned slabs, which are typically at least20 cm for houses, and thicker for heavier structures.

 

Shallow foundations distribute live and dead loads that the structure transmits through its support elements on a rather large surface that supports those charges.

Shallow foundations are considered when they are between0.50 m. and4 m. deep, when the depth of the foundation is smaller than the width of that foundation,and when the allowable stresses of the different soil layers, which are on the footing, make possible to support the building directly without excessive deformation on the surface on which the foundation rests, that may affect the functionality of the structure; otherwise, deep foundations will be made.

It should be considered the possibility of having different types of soil in the same area for our building where will be located; this can cause dangerous differential deformations in spite of the fact that the total deformation values are admissible, so we have to be careful!

 

In important structures such as bridges, we have to ensure that foundation is supported deep enough without damages. Bridge construction can present extraordinary difficulties. Usually the foundations for the piers must rest on bedrock, and often under water. One technique for working in these conditions is by means of a cofferdam and the other technique is the use of the pneumatic caisson.

 

And finally I can tell you that there are several kind of shallow foundations:

1) Isolated footings

2) Adjoining footings ( rigid  and flexible)

3) Slabs

 

I recommend you the following spanish author: Jose Antonio Jimenez Salas. His complete book compilation about Geotechnics and Foundations is one of the best in the world. You can check as well this book “A short Course on Foundations Engineering” by  Simons, N.E. & Menzies, B.K. (1975).

Combined Strip Spread Footings Combined Strip Spread Footings

-- Length (L) to width (B) ratio, L/B Length (L) to width (B) ratio, L/B

Spread Footing Design Procedure Spread Footing Design Procedure

Geotechnical design of spread footing is a Geotechnical design of spread footing is a

two part process two part process

First Part: First Part:

-- Establish an allowable stress to prevent shear Establish an allowable stress to prevent shear

failure in soil failure in soil

Second Part: Second Part:

-- Estimate the settlement under the applied stress Estimate the settlement under the applied stres

This is a type of foundation where the depth/breadth ration is less than4

deep foundation is meaning piles foundation or similar system which transfer the loads to suitable soil  level

shallow foundation  is direct support of the foundation to the suitable soil 

Thank you for the good question.

Engineers should explore the effects of regional geology on bridge foundation, including the variety of soil conditions found beneath foundations. They learn about shallow and deep foundations, as well as the concepts of bearing pressure and settlement.

Engineering Connection

The findings from geological site surveys are important to geotechnical and structural engineers who design bridges, buildings and other land structures. These engineers investigate the subsurface conditions of the area and the risks imposed by those conditions on various foundations. Having an understanding of the soil type and geological setting helps engineers select building materials that make a structure more likely to remain standing over time, taking into account technical, economic and environmental factors.

 

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standard Network (ASN), a project of JES & Co. (www.jesandco.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

Click on the standard groupings to explore this hierarchy as it applies to this document.

 

 

G. Structures rest on a foundation. (Grades6 -8) [2000] ...show

• I. Buildings generally contain a variety of subsystems. (Grades6 -8) [2000] ...show

Pre-Req Knowledge

Engneers should have some previous knowledge of bridges, including a familiarity with bridge types and loads, as introduced in the first two lessons of the Bridges unit.

Learning Objectives

After this lesson, students should be able to:

• Define and describe a foundation for a structure.
• Describe two basic types of foundations: shallow and deep.
• Discuss several factors that engineers must consider when designing foundations for a bridge, include soil conditions, materials and forces.

A shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, rather than to a subsurface layer or a range of depths as does a deep foundation. Shallow foundations include spread footing foundations, mat-slab foundations, slab-on-grade foundations, pad foundations, rubble trench foundations and earthbag foundations.

LOWER BELOW THE EARTH SURFACE IS BETTER FOR FOUNDATIONS BECAUSE OF THE COMPRESSION CAUSED BY THE WEIGHT OF THE EARTH AT THE TOP.