Text 4. Different types of house foundations

Text 3. FROST HEAVING

Reading Practice

Read through text 3 (Frost Heaving) and then choose the best sentence given below to fill in each of the blanks.

E.g.: 1- e

Frost heaving can damage houses, barns, sheds, roadways, concrete slabs, basically anything that is connected to the Earth in a place where the ground freezes. (___1___) The problem is, the lifting may not be equal around the structure.

Frost heaving (or a frost heave) results from ice forming beneath the surface of soil during freezing conditions in the atmosphere. The ice grows in the direction of heat loss (vertically toward the surface), starting at the freezing front or boundary in the soil. (___2___). The growing ice is restrained by overlying soil, which applies a load that limits its vertical growth and promotes the formation of a lens-shaped area of ice within the soil. Yet the force of one or more growing ice lenses is sufficient to lift a layer of soil, as much as 30 cm or more. (___3___).

The dominant cause of soil displacement in frost heaving is the development of ice lenses. During frost heave, one or more soil-free ice lenses grow, and their growth displaces the soil above them. (___4___).

Frost heaving requires a frost-susceptible soil, a continual supply of water below (a water table) and freezing temperatures, penetrating into the soil. (___5___) Silty and loamy soil types, which contain fine particles, are examples of frost-susceptible soils.

Non-frost-susceptible soils may be too dense to promote water flow (low hydraulic conductivity) or too open in porosity to promote capillary flow. (___6___). These soils contain small amounts of fine particles and their pore sizes are too open to promote capillary flow.

Sentences to choose from:

a) Differential frost heaving can crack pavements and damage building foundations.

b) Examples include dense clays with a small pore size and therefore a low hydraulic conductivity and clean sands and gravels

c) Frost-susceptible soils are those with pore sizes between particles and particle surface area that promote capillary flow.

d) It requires a water supply to keep feeding the ice crystal growth.

e) Just as the phrase implies, the frost heaves, or lifts things up.

f) These grow with the continual addition of water from a groundwater source lower in the soil structure, below the freezing line in the soil.

Read text 4 divided into parts. Find answers to the questions which come before each of the coming passages.

1. Which defects are more common, troubles with walls or with foundations?

Foundation construction is an integral part of home building. It is what the whole house rests on. A firm foundation is a must, so don't use sand. In most construction, concrete is used as foundation. It is laid into a trench up to 3 or 4 feet deep, and provides a very solid foundation for whatever building material used. The foundation is the most critical part of any structure. The structural failures due to faulty workmanship or to an insufficient thickness of the walls are rare in comparison with those due to defective foundations.

2. What factor is important to consider besides the soil type?

There are many different types of foundations. The most typical foundation is made up of a footing which is the portion of the steel reinforced concrete on the undisturbed soil. Waterproofing and drainage are typically applied at the exterior of the foundation and footing. This is particularly important when building in wet soils.

The choice of a home foundation depends on the soil type of the construction site. Homes that are built on poor soil conditions may require a deep foundation, whereas most sites only require a shallow foundation. Climate is another factor to consider when choosing a foundation. Some types of foundations do not perform well in flooding or cold temperatures.

3. Can poured concrete foundations be good in cold climates?

A poured concrete foundation is the most common type of home foundation. A concrete slab foundation is formed by pouring a few inches of concrete with thicker edges to provide support. The slab normally rests on a bed of crushed gravel to improve drainage. The slab is poured all at one time and is ideal for use in areas where the ground does not freeze in the winter.

4. What helps to support frost-protected foundations from frost damage?

As the name suggests, a frost-protected foundation protects concrete from damage due to extreme temperatures. A T-shaped foundation is the traditional choice for cold areas. This foundation method provides extra support for a concrete slab foundation with concrete footings that extend below the frost line. A frost-protected shallow foundation (FPSF) provides protection without digging below the frost line. FPSF utilizes insulated concrete to protect a slab foundation from frost damage. Frost-protected shallow foundations are used in over 5,000 buildings in the United States, as well as over a million homes in Sweden, Finland and Norway.

5. What are the advantages of wood for permanent foundations?

Permanent wood foundations have been used since the 1960s, and manufacturers are now recommending treated plywood and lumber as an alternate material for crawl space, basement and stem wall foundations. The foundations are made of preservative-treated wood that is very lightweight, decay-resistant and easy to install. A permanent wood foundation does not require concrete pouring or casting, which makes the process much more convenient. Additionally, the foundations are easy to insulate and moisture-resistant. More than 300,000 houses in the United States utilize permanent wood foundations.

6. What types of raised foundations are there?

Raised foundations are necessary in coastal areas that receive large amounts of rain and are prone to flooding. Raised foundations require careful planning, because they must be able to both support the home and provide protection from moisture. There are two types of raised foundations: pier-and-beam and stem wall. A pier-and-beam foundation uses concrete or brick blocks that are reinforced with footings. The blocks are placed approximately 8 to 12 inches apart and raise the home above the flood line. A stem wall foundation is similar, except that the footings are continuous rather than spaced.

Дата добавления: 2014-12-23