1. Foundation & Timbering of Trenches
Lahiru Rajapakshe
33136
Diploma in QS

2. Content Foundation Function of foundation Types of foundation
To where each type of foundation can apply
De wattering of foundation trenches
Damp proofing course
Timbering of trenches

3. 01.Foundation Definition of foundation
Foundation is the lower portion of the building usually located below ground level, which transmits the loads of the super structure to the supporting soil. A foundation is therefore that part of the structure which is in direct contact with the ground to which loads are transmitted.

4. Foundations mainly can devided into two. Shallow Foundation
Shallow foundation are those foundations in which the depth at which the foundation is placed is less than the width of the foundation (D < B). Shallow foundations are generally termed as spread footing as they transmit the load of the super structure laterally into the ground.
Deep Foundation
Deep Foundation are those foundations in which the depth of the foundation is greater than its width (D>B). The D/B ratio is usually 4-5 for deep foundation. Unlike shallow foundation, the deep foundation transmits the load of the superstructure vertically to the rock strata lying deep. Deep foundations are used when the shallow foundation cannot support the load of the structure.

5. 2.Function of foundation
1. Reduction of load intensity
Foundation distributes the loads of the super structure, to a larger area so that the intensity of the load at its base (i.e. total load divided by the total area) does not exceed the safe bearing capacity of the sub-soil.
2. Even distribution of load
Foundations distribute the non-uniform load of the super structure evenly to the sub soil. For example, two columns carrying unequal loads can have a combined footing which may transmit the load to sub soil evenly with uniform soil pressure. Due to this, unequal or differential settlements are minimized.
3. Provision of level surface
Foundation provide leveled and hard surface over which the super structure can be built.
4. Lateral stability
It anchors the super structure to the ground, thus imparting lateral stability to the super structure. The stability of the building, against sliding and overturning, due to horizontal forces (such as wind, earthquake etc.) is increased due to foundations.
5. Safety against undermining
It provides the structural safety against undermining or scouring due to burrowing animals and flood water.
6. Protection against soil movements
Special foundation measures prevents or minimizes the distress (or cracks) in the super structure, due to expansion or contraction of the sub soil because of moisture movement in some problematic soils.

6. 3.Types of foundation Strip foundation Rubble foundation
Colum foundation
Pad foundation
Short bored foundation
Pile & beam foundation
Raft foundation
Step foundation

7. Strip Foundation
Strip foundations are a type of shallow foundation that are used to provide a continuous, level strip of support to a linear structure such as a wall or closely-spaced rows of columns built centrally above them.Strip foundations can be used for most subsoils, but are most suitable for soil which is of relatively good bearing capacity. They are particularly suited to light structural loadings such as those found in many low-to-medium rise domestic buildings - where mass concrete strip foundations can be used. In other situations, reinforced concrete may be required.
Typical strip foundation measurements are as follows:
Single storey building: 450 mm wide and at least 200 mm deep.
Two storey building: 600 mm wide and 200 mm deep.
The underside of strip foundations should be deep enough to avoid frost action; for example, at least 450mm unless they are bearing on rock, and at least 1m on high shrinkage clays.
Deep strip foundations may be necessary where soil with a suitable bearing capacity is deeper.
Wide strip foundations may be required where the soil is soft or of a low bearing capacity, so as to spread the load over a larger area. Wide strip foundations will typically require reinforcement

8. .

9. Reinforced beam and concrete strip foundation
Plain concrete strip foundation
Reinforced concrete strip foundation
Reinforced beam and concrete strip foundation

10. 2.Rubble foundation.
The rubble trench foundation, an ancient construction ,is a type of foundation that uses loose stone or rubble to minimize the use of concrete and improve drainage. It is considered more environmentally friendly than other types of foundation because cement manufacturing requires the use of enormous amounts of energy. However, some soil environments are not suitable for this kind of foundation; particularly expansive or poor load-bearing (< 1 ton/sf) soils. A rubble trench foundation with a concrete grade beam is not recommended for earthquake prone areas
A foundation must bear the structural loads imposed upon it and allow proper drainage of ground water to prevent expansion or weakening of soils and frost heaving. While the far more common concrete foundation requires separate measures to insure good soil drainage, the rubble trench foundation serves both foundation functions at once.
To construct a rubble trench foundation a narrow trench is dug down below the frost line. The bottom of the trench would ideally be gently sloped to an outlet. Drainage tile, graded 1":8' to daylight, is then placed at the bottom of the trench in a bed of washed stone protected by filter fabric. The trench is then filled with either screened stone (typically 1-1/2") or recycled rubble. A steel-reinforced concrete grade beam may be poured at the surface to provide ground clearance for the structure.

11. The rubble-trench foundation is a relatively simple, inexpensive, and environment-friendly alternative to a conventional foundation, but may require an engineer's approval if building officials are not familiar with it. Frank Lloyd Wright used them successfully for more than 50 years in the first half of the 20th century, and there is a revival of this style of foundation with the increased interest in green building.
If an insulated slab is to be poured inside the grade beam, then the outer surface of the grade beam and the rubble trench should be insulated with rigid XPS foam board, which must be protected above grade from mechanical and UV degradation.

12. 3.Colum foundation

15. 4. To where each type of foundation can apply

16. 5. De wattering of foundation trenches

17. 6.Damp proofing course
Damp proofing in construction is a type of moisture control applied to building walls and floors to prevent moisture from passing into the interior spaces. Damp problems are among the most frequent problems encountered in homes.
Damp proofing is accomplished several ways including:
A damp-proof course (DPC) is a barrier through the structure designed to prevent moisture rising by capillary action such as through a phenomenon known as rising damp. Rising damp is the effect of water rising from the ground into property.The damp proof course may be horizontal or verticalA DPC layer is usually laid below all masonry walls, regardless if the wall is a load bearing wall or a partition wall.
A damp-proof membrane (DPM) is a membrane material applied to prevent moisture transmission. A common example is polyethylene sheeting laid under a concrete slab to prevent the concrete from gaining moisture through capillary action. A DPM may be used for the DPC.
Integral damp proofing in concrete involves adding materials to the concrete mix to make the concrete itself impermeable.

18. Surface coating with thin water proof materials for resistance to non-pressurized moisture such as rain water or a coating of cement sprayed on such as shotcrete which can resist water under pressure.
Cavity wall construction, such as rainscreen construction, is where the interior walls are separated from the exterior walls by a cavity.
Pressure grouting cracks and joints in masonry materials.
Materials widely used for damp proofing include
Flexible materials like butyl rubber, hot bitumen, plastic sheets, bituminous felts, sheets of lead, copper, etc.
Semi-rigid materials like mastic asphalt
Rigid materials like impervious bricks, stones, slates, cement mortar or cement concrete painted with bitumen, etc.
Stones
Mortar with waterproofing compounds
Coarse sand layers under floors
Continuous plastic sheets under floors

19. Masonry construction
A DPC is a durable, impermeable material such as slate, felt paper, metal, plastic or special engineered bricks bedded into the mortar between two courses of bricks or blocks. It can often be seen as a thin line in the mortar near ground level. To create a continuous barrier, pieces of DPC or DPM may be sealed together. In addition, the DPC may be sealed to the DPM around the outside edges of the ground floor, completely sealing the inside of the building from the damp ground around it.
In a masonry cavity wall, there is usually a DPC in both the outer and inner wall. In the outer wall it is normally 150 millimetres (5.9 in) to 200 millimetres (7.9 in) above ground level (the height of 2-3 brick courses). This allows rain to form puddles and splash up off the ground, without saturating the wall above DPC level. The wall below the DPC may become saturated in rainy weather. The DPC in the inner wall is usually below floor level, (under a suspended timber floor structure), or, with a solid concrete floor, it is usually found immediately above the floor slab so that it can be linked to the DPM under the floor slab. This enables installation of skirting boards above floor level without fear of puncturing it. Alternatively, instead of fitting separate inner and outer DPCs, it is common in commercial housebuilding to use a one-piece length of rigid plastic, (albeit an angled section), which fits neatly across the cavity and slots into both walls (a cavity tray). This method requires the need for weep vents to enable rainwater ingress to drain from the cavities otherwise rising dampness could occur from above the DPC.

20. 7. Timbering of trenches

23. Wall Footing
This type of foundation runs continuous along the direction of the wall and helps to transmit the load of the wall into the ground. Wall footing are suitable where loads to be transmitted are small and are economical in dense sands and gravels. In this type of foundation the width is 2-3 times the width of the wall at ground level. Wall footing may be constructed through stone, brick, plain or reinforced cement concrete.