WUS Austria

 

Settlement of soil

 

By    Sloboda Danijela                              Teachers: Dr Petar Santrac

        Zavisic Bojan                                                   Dr Ruza Ostrogonac-Seserko

        Vlaovic Goran

        Merkovic Ivan

 

Settlement of soil (how and why it happens)

Any structure built on soil is subject to settlement. Some settlement is inevitable and, depending on the situation, some settlements are tolerable.

In designing a structure it is commonly assumed that the foundation will not move. Correspondingly, if cracks appear in the structure it is assumed that the foundation did move and that this is the sole cause of cracking.

As building loads are applied to the ground an "immediate" settlement occurs as a result of instantaneous compression of the soil. Most immediate settlement may be accommodated within the structure as it is built, and fortunately much of the differential movement occurs at this stage. Under certain conditions, however, fine-grained soils will continue to compress under constant load for many years. This long-term compression is called "consolidation" settlement and is caused by the squeezing out of water from the pores in the clay.

Differential settlement occurs for a number of reasons:

- Local variations in soil compressibility,

- Variation in thickness of compressible soil,

- Differences in footing sizes and pressures,

- Variation in applied loads,

- Overlapping stresses,

- Differences in depth of embedment of footings.

-Soil Permeability

-Soil Drainage

-Load to be placed on the soil

-History of loads placed upon the soil (normally or over-consolidated?)

-Water Table

Types of Settlement

There are three basic types of settlement: uniform settlement, tilt, and non-uniform settlement

 

 

Types of geotechnical testing

The most common types of geotechnical testing used to evaluate the modulus of the soil are penetration tests such as the Standard Penetration Test (SPT) or the Static Cone Penetration Test (CPT).

The standard penetration test (SPT) is the most commonly used in situ test. However, cone penetration test (CPT) is becoming increasingly popular as an in situ test for site investigation and geotechnical design.

There are number of testing but we are going just to name some of them:

-analytic and numeric methods

-

-

Lines of equal vertical stress caused by surface loads

 

Figure


 1. Lines of equal vertical stress caused by surface loads.

 

 

To decreases future settlements we have to compacted soil, and here are some of machines which we can do that:

 

 

Settlement of structures

-The Palace of Fine Arts in Mexico City, for example, built sometime between 1900 and 1934; it was a magnificent and strongly built structure. It was built on grade, level with the square and other buildings nearby.  But because of loose sand permeated with water in the subsurface, the massive structure sunk more than 340, 8 cm into the ground!  (Luckily, it settled evenly minimizing structural damage.)   Believe it or not, in the 1960's the building moved again.  This time it moved 365, 76 cm up!  The weight of skyscrapers being built around the Palace had pushed the subsurface water and soil around sufficiently to raise the building.

 

 

- In Winnipeg, an extension to a church was built over an area in which the trees were cut down immediately before construction. The floor slab for the addition, which rested directly on the ground, was heaved 15, 24 cm in two years, giving an annoying discontinuity between the old and new sections.

-It is common in many of the heavy clay regions of Canada for shallow foundations to move up or down by several inches.

 

 

Solution for settlement of soil

-One of the solutions is so called floating foundation. The word "floating" is used in its literal sense. When a body floats in water, it displaces a volume of water the weight of which is equal to the weight of the floating body.

The Post Office Building in Albany, New York, was one of the pioneer North American buildings to be so founded. There are now some Canadian buildings floating on the soil beneath them, notably a fine multi-storey building in Ottawa founded on clay.

 

-examples of pile foundation and there range of max load


Pile type

 

Description of use and availability

Range of Maximum Load
 (KN)

Timber

Depends on wood (tree) type. Lengths in the 15 to 18 m are usually available in most areas; lengths to about 25 m are available but in limited quantity; lengths up to the 30 m are available, but supply is very limited.

100-300

Steel H and pipe

Unlimited length; "short" sections are driven and additional sections are field-welded to obtain a desired total length.

 

Steel shell, cast-in-place

Typically to between 30 to 40 m, depending on shell type and manufacturer-contractor.

250- 700

Precast concrete

Solid, small cross-section piles usually extend into the 15 to 18 m, depending on cross-section shape, dimensions, and manufacturer. Large-diameter cylinder piles can extend to about 60 m long.

 

Drilled-shaft, cast-in-place concrete

Usually in the 15 to 25 m, depending on contractor equipment.

 

Bulb-type, cast-in-place concrete

Up to about 30 m.

600-9000

Composite

Related to available lengths of material in the different sections. If steel and thin-shell cast-in-place concrete are used, the length can be unlimited; if timber and thin-shell cast-in-place concrete are used, lengths can be on the order of 45 m.

250- 600

 

Pisa’s Tower

This is the monument that, among the others of the "Piazza dei Miracoli", stirs the imagination of everybody, from the old to the young. Firstly we like to give you some information and events regarding its long history.

The construction of this imposing mass was started in the year 1174 by Bonanno Pisano. When the tower had reached its third storey the works ceased because it had started sinking into the ground. The tower remained thus for 90 years. It was completed by Giovanni di Simone, Tommano Simone (son of Andreo Pisano), crowned the tower with the belfry at half of 14th century.

The top of the Leaning Tower can be reached by mounting the 294 steps which rise in the form of a spiral on the inner side of the tower walls.

This very famous work is of Romanesque style, and as already stated dates back to the year 1174. Cylindrical in shape it is supplied whit six open galleries.

This monument is not lacking in elegance and lightness due to the arcades and open galleries between one storey and another. Although it can be considered a real masterpiece of architecture, this monument is mostly famous for its strong inclination. Regarding this inclination it can be safely stated that it is undoubtedly due to a sinking of the ground right from the time of its construction. Therefore, the assumption of those who desire to imagine that great tower was built inclined is entirely without foundation.

 

 

-It is one of the most famous buildings in the   world. It has been built before hundreds years ago. When three tops were over, they started to swoop, so the tower started to list. Engineer, who ganged its loch, says that the tower all the time tends, it lurches for 2,5cm.Stalian expect that the tower won't tumble.

 

Even today the great mass continues to sink very slowly. It is a question of about 1 mm. every year. Since nobody can state with mathematical security that this sinking will continue in the future at the present yearly rate, without its ceasing, remedies by means of adequate measures, based on scientific studies and projects, are under consideration. In the meantime supervision with instruments of very high precision is continuously being carried out.

 

These procedures and associated theoretical considerations of soil action constitute the modern science of Soil Mechanics. The proper application of the results of such scientific studies now enables the foundation engineer to design a foundation for any given combination of loads on even the most unpromising soil, as also upon soils that have not caused problems when utilized in more pragmatic ways.