INTRODUCTION

Shallow foundations represent the simplest form of load transfer from a structure to the

ground beneath. They are typically constructed with generally small excavations into the ground,

do not require specialized construction equipment or tools, and are relatively inexpensive. In

most cases, shallow foundations are the most cost-effective choice for support of a structure. A

shallow foundation is also known as an open foundation, since such foundation is constructed by

open excavation. Hence those foundations, which have depth even greater than its width, but are

constructed by way of open excavation also come under ‘shallow foundations’. Shallow

foundation can divided into three types such as pad footing, strip footing and raft footing.

Pad foundation tend to be the simplest and cheapest foundation type and are used when

the soil is relatively strong or when the column loads are relatively light. They are usually square

or rectangular on plan, of uniform thickness and generally of reinforced concrete. They can be

stepped or haunched, if material cost outweigh labour costs. The reinforcement can vary from

nothing at one extreme through to a heavy steel grillage at the other, with lightly reinforced

section being the most common.

PAD FOOTING

Strip footings are commonly used for the foundations to load bearing walls. They are also

used when pad foundations for number of columns in line are so closely spaced that the distance

between the pads is approximately equal to the length of the side of pads. It is usually more

economic and faster to excavate and cast concrete in one long strip, than as a series of closely

spaced isolated pads. They are also used on weak ground to increase the foundation bearing area.

STRIP FOOTING

A mat foundation consists of a single heavily reinforced concrete slab, which underlies

the entire structure or a major portion of the structure. It also known as Raft foundation. Mat

foundations are often economical when spread footings would cover more than about 50 percent

of the footprint of the plan area of a structure. A mat typically supports a number of columns

and/or walls in either direction or a uniformly distributed load. The principal advantage of a mat

foundation is its ability to bridge over soft spots and reduce differential movement. Structures

founded on relatively weak soils or light weight structures may be economically supported on

mat foundations. Column and wall loads are transferred to the foundation materials through the

mat foundation. Mat foundations distribute the loads over a large area, thus reducing the intensity

of contact pressures.

MAT/RAFT FOUNDATION

WORK PROCEDURE

Even though shallow foundation has a several types with different characteristics which pad

foundation, strip foundation, and mate or raft foundation but the work procedure is still same.

The procedure are such a sequence below;

1. Site clearing

2. Setting out

3. Excavation

4. Waterproofing

5. Installation(formwork, support, strut, spacer block, rebar, starter bar, and other services

involved)

6. Carried out inspection

7. Concreting

8. Concrete curing

9. Dismantling formwork

10. Backfilling foundation

11. Compacting backfilled foundation

2.1 Site Clearing

Before the construction of the shallow foundation is doing, the location of the

construction site must be clear such as trees get cut down and thrown up to the roots before the

construction is start. After the site clearing is done, fill and compacted soil work will do to obtain

a the compact and flat platform surface so that it is not will be easily damaged for access roads to

facilitate entry and exit machineries to construction sites.

2.2 Setting Out

The position for the shallow foundation will be set accurately by surveyors and marked

using the baseline for the building according to plan layout on the drawing, for example

rectangular shape of building four corners then we marking the four corners of the building that

has been offset at least 2 meter to the behind of the line gridline and so the peg would be more

durable.

The profile board to be installed around the building site based on the baseline and the

fence height profile should be at the level of finish floor level and the level of finish floor level

should be marked on the peg. Pull the thread between 2 gridline to get the intersection point for

pad footing and mark it on the ground. The surveyor is required to obtain assurance that the pad

footing position is right.

2.3 Excavation Of Footing

After already identified the actual position of the pad footing, the excavation work is

carried out according to the size and depth required. Excavation work should be done below lean

concrete level.

2.4 Waterproofing

Waterproofing is done to avoid concrete loosing water-cement ratio during concreting

work. There are two common technique to do the water proofing work which by using plastic

sheet. Lean concrete to be poured after the excavation work is completed, lean concrete thickness

is in the range of 50mm or according to the required specifications. Lean concrete works

required is to get a flat platform and hard surface for ease of installation work of reinforcement

bar carried out and it also serves to prevent moisture in the concrete is reduced due to seep into

the ground.

2.5 Installation

After water proofing work done such as lean concrete, then it comes to installation work.

Materials include in installation work are such rebar, spacer block, formwork, support/strut,

form-tie, starter bar and any other services attach to foundation. Sequence of work are such as

follow;

i. Install main formwork surrounding the footing as an actual size

ii. Install support for the formwork to stabilize the main frame.

Formwork

Formwork means the surface of the form and framing used to contain and shape wet concrete

until it is self-supporting. Formwork includes the forms on or within which the concrete is

poured and the frames and bracing which provide stability. Although commonly referred to as

part of the formwork assembly, the joists, bearers, bracing, foundations and footings are

technically referred to as false work.

Design

The design of the final concrete structure can have a major effect on the ease of formwork

construction and the health and safety of people during construction. Generally the more basic

and simple the final concrete structure, the safer it is to construct, erect and dismantle the

formwork.

An experienced formwork designer should be consulted during the design of in-situ concrete

structures to enable the health and safety risks during formwork construction and dismantling to

be considered in the design.

The formwork designer must be competent in formwork design including documenting

temporary work platforms and special equipment needed for safe formwork construction on-site.

A designer may use a technical standard or a combination of standards and engineering

principles relevant to the design requirements as long as the outcome is a design that meets

regulatory requirements.

Formwork should be:

Rigid, watertight, braced and tied together to maintain position and shape during

construction , and

Able to be removed easily and safely without damaging the formed concrete, or have

components that remain as part of the finished structure so the rest can be removed

without damaging the structure.

GUIDE TO FORMWORK

Formwork drawings should include details of

Formwork and formwork joints

Sealing procedures

Ties

Size and spacing of framing

Details of proprietary fittings or systems proposed to be used, and

Air breakers, if used.

The formwork designer should determine the vertical pour rates for walls, columns and other

vertical concrete elements before completing the formwork design. Details of the construction

method and erection sequence should be included on the formwork drawings where appropriate.

Where special methods like external vibration are involved the formwork design should allow

for any resulting additional structural loads. Variations to a design of a system should be checked

and verified in writing by a designer, engineer or other competent person.

iii. After that, prepare and install spacer block on the lean concrete inside of

formwork. Thickness of the spacer block is depends on drawings specification.

iv. Short way rebar then install before the long way

v. After that, long way bar was install and tighten with the short way by spacing

provided on specification.

vi. Starter bar then install and tighten with the foundation rebar. Make sure lapping of

the starter bar for upper structure enough as per drawings.

vii. After that is installation of other services that attach/punch through such as

sewerage pipe and cable for electrical used.

viii. Then for bigger foundation, install form tie or strut to strengthen the formwork or

prevent formwork failure and concrete bulging.

However sequence of installation work was not necessary to follow as state above. It depends on

site condition that influence flow of work. Some criteria that may affect the flow of work is

materials, man power, weather, and also logistic on site.

2.6 INSPECTION OF WORK

When To Call For Inspection

When all form-work (boxing) has been completed, footings have been excavated and

reinforcement is in place.

What We Will Look At

Check that the siting of the building conforms with the building consent site plan. Boundaries

must be identified by location of boundary pegs or by survey. With building projects that are

critical in respect to distance from boundaries, height or daylighting requirements, building set

out must be confirmed by survey.

Footings are appropriate size and excavated to solid

Reinforcing is in place (size, spacing, laps and cover) adequately tied and secured and

conform with consent documents for ring foundations; sub-floor vents

That minimum floor levels/ground clearances can be achieved against datum

Advise on next inspection

What You Should Do

Ensure that boundaries are adequately defined

Ensure that building set out complies with consent documents

If required, a surveyors report is available

Approved plans and supporting documents are on site

Don’t put us and the contractor under pressure by ordering concrete until after the

inspection has been carried out

After all installation work have done, then inspection will be carry out before ordering a

concrete. Criteria that will be checked during inspection are:

i. Rebar

ii. Starter bar

iii. Spacer block

iv. Size

v. Level

vi. Position

vii. Cleanliness

viii. Materials for concreting work

ix. Manpower

After inspection done, then concreting work will be proceed.

2.7 CONCRETING OF SHALLOW FOUNDATION

The design of the foundations will need to be approved by the Local Authority (Client

representative). The plans submitted for approval will detail the type and depth of the

foundations. However, prior to concreting the foundations, the excavation works will need to be

inspected and approved by the District Surveyor. Many factors have to be taken into account but,

during his site visit he will be establishing that the base of the trench is of good load bearing

capacity and that there are no adverse factors such as nearby trees which may affect the

foundations. Trees can draw a large amount of moisture from the surrounding ground and the

height and species of nearby trees will be taken into consideration so that there is no risk of

ground movement.

Concrete Specification

Also included in the plans approved by the Local Authority will be the specification for the

concrete mix to be used for the foundations. Mix ratios are commonly specified as a proportion

of cement : sand : aggregate. Typically this will be 1:3:6 for foundations such as those shown in

the accompanying pictures. This mix is 1 part cement : 3 parts sharp sand : 6 parts aggregate. In

practice, it is often easier to order ballast where the sand and aggregate is pre mixed. When using

readymix, mixes are specified by grade. You must ensure that the mix you use is as specified in

the approved documents.

Mixing Concrete Versus Ready Mix

Mixing the concrete by hand would not be practical for this job - even mixing concrete with a

mixer is a labour intensive process. Having concrete delivered by a ready mix lorry is the most

practical solution for anything more than a small volume. When ordering the concrete you will

need to specify what mix you require as well as agree a time slot for delivery. The amount of

concrete you are ordering will affect the price and remember that you may have to pay a

surcharge for any cubic metres less than a full load. There are also other preparations you will

need to make aside from ensuring that the work is absolutely ready before the lorry arrives. You

need to be sure that there will be room for the lorry to park up as near to the work as possible –

the less barrowing the better. Talk to neighbours and if needs be mark out an area of the street

with cones in advance. The last thing you want is a load of concrete turning up and not being

able to offload it. The access route between the lorry and the foundation trenches should be

completely clear so that a steady flow of barrow loads can go back and forth.

Barrowing and Pouring Concrete

When the lorry arrives, make sure that you have enough people ready to barrow the

concrete to the excavations. You cannot expect the lorry to hang about so, if needs be, rope in a

few helpers. As a rough guide, a cubic metre of concrete is about 25 barrow loads and weighs

over 2 tonnes. The driver will set up the chute so that the concrete can be discharged into the

barrows. Hold the barrow steady as it is loaded – concrete is heavy and can easily tip the barrow

as it drops in.

Remember that concrete can cause alkali burns so wear protective gear and avoid skin

and eye contact. The easiest way to work is have one person working the concrete as it is tipped

into the trench and two or three people barrowing it from the lorry. Work the concrete so that it

fills all the space without leaving any pockets, voids or trapped air. Use a shovel to work it into

place. The level for the top of the concrete should be clearly marked on site so you know when

you’ve reached it. Once the trench has been filled to this level, tamp the surface with a batten so

that it is flat and level ready to receive the brickwork when it has set.

As soon as all the concrete has been poured, clean up the area. There will inevitably be a

few slops and spills along the way and this will set hard if it’s not cleared up straight away. Use a

shovel to pick up any spilled concrete then thoroughly hose the area down. Make sure you

include the street where the lorry was loading the barrows.

2.8 CURING OF SHALLOW FOUNDATION

Curing is the maintenance of a satisfactory moisture content and temperature in concrete for a period of time immediately following placing and finishing so that the desired properties may develop . The need for adequate curing of concrete cannot be overemphasized. Curing has a strong influence on the properties of hardened concrete; proper curing will increase durability, strength, watertightness, abrasion resistance, volume stability, and resistance to freezing and thawing and deicers.

Curing Methods And Materials

Concrete can be kept moist (and in some cases at a favorable temperature) by three curing methods:

Methods that maintain the presence of mixing water in the concrete during the early hardening period. These include ponding or immersion, spraying or fogging, and saturated wet coverings. These methods afford some cooling through evaporation, which is beneficial in hot weather.

Methods that reduce the loss of mixing water from the surface of the concrete. This can be done by covering the concrete with impervious paper or plastic sheets, or by applying membrane-forming curing compounds.

Methods that accelerate strength gain by supplying heat and additional moisture to the concrete. This is usually accomplished with live steam, heating coils, or electrically heated forms or pads. The method or combination of methods chosen depends on factors such as availability of curing materials, size, shape, and age of concrete, production facilities (in place or in a plant), esthetic appearance, and economics.

As a result, curing often involves a series of procedures used at a particular time as the concrete ages. For example, fog spraying or plastic covered wet burlap can precede application of a curing compound. The timing of each procedure depends on the degree of hardening of the concrete needed to prevent the particular procedure from damaging the concrete surface

How Long Should a Concrete Foundation Cure Before Erecting the Building?

Between 3 and 9 days

Concrete should be allowed to cure from anywhere between three and nine days,

depending upon the temperature and moisture levels, according to the National Ready

Mixed Concrete Association. Lower temperatures and higher moisture levels result in a

longer curing time.

Seven to 28 days

According to Concrete Network, concrete should be allowed to cure for at least seven

days before it's built on. However, waiting longer will greatly reduce the risk of the

concrete cracking. Concrete continues to cure up to 28 days after it is poured, at which

point it reaches maximum strength.

Bottom Line

When a contractor or engineer is in charge of a project, follow the professional's advice,

since the result of curing is his responsibility, according to Builder Bill. For small,

nondocumented jobs, wait a minimum of three days—although seven days is better,

Builder Bill advises.

2.9 DISMANTLING FORMWORK OF SHALLOW FOUNDATION

Dismantling formwork should be done at least 12 hours after concreting or depends on

specification. Dismantling formwork of foundation can be done before cube test has pass

because it can give a better concrete curing after backfilling.

ERECTING, ALTERING AND DISMANTLING FORMWORK AND FALSEWORK

Formwork and false work should be systematically erected and dismantled by competent and tied in progressively to stabilize the structure in accordance with the designer’s or manufacturer’s instructions. Prefabricated formwork and false work should be erected and used in accordance with the manufacturer’s instructions.

Where scaffolding is used to construct formwork and false work it must comply with the requirements for scaffolding including using licensed of scaffolder.

Safe systems of work should be developed depending on the type and complexity of the formwork and false work design. The system of work should seek to eliminate or minimize risks, for example to:

Minimize working at height by assembling components on the ground

Provide safe temporary work platforms where work at height is required

Provide for the safe handling and operating of plant and equipment—large structures may require scaffolding or mobile plant to be located on suspended floors

Provide suitable plant and material handling, placement and storage arrangements to minimize manual tasks, and

Include regular inspection and maintenance.

Erecting formwork and false work safely

Erecting formwork and false work safely will include preparing the foundations and footings where required, and erecting, altering and dismantling the formwork and false work including for adequate access and work platforms in a way that minimize risk to workers and people who may work on or near the formwork and false work.

2.10 BACKFILLING OF FOUNDATIONS

There are four key elements to proper backfilling:

Protecting the foundation wall from damage during backfilling

Using the right backfill materials

Compacting the backfill

Final finishing the subgrade to ensure that water drains away from the foundation

Done correctly, these four steps help to ensure that a well-built basement functions the way it’s

supposed.

Protecting the foundation during backfilling

The surest way to protect foundations from damage during backfilling is to backfill only after the

basement floor slab and the first-floor deck are in place. For the deck, sill plates should be bolted

down and joists nailed to the sill plate. This provides the restraint needed to make the

foundations strong enough to resist earth pressures caused by backfilling.

Choosing the right backfill material

Some people recommend backfilling with a free- draining granular material. When you dig a

hole in the ground for a foundation, water moves toward the hole just as it does in a well. A

granular fill makes it easier for water to move toward the foundation wall. And if the drain tile

system gets plugged, that could cause problems. avoid backfilling with large clumps of clay or

with soil full of roots, tree branches, or other organic materials .These materials won’t compact

well and will hold a lot of water even if the ground slope is steep enough to carry surface water

away from the house. Splash blocks for downspouts don’t usually carry water more than a foot

or two away from the foundation So most of the water that comes off the roof may still end up

next to the foundation if the backfill is porous.

2.11 COMPACTING THE BACKFILL

Compaction is needed to reduce the amount of soil settlement that occurs with time. Failure to

compact the soil can cause basement leakage even before the house is completed. In this case,

during rainy weather, water collected in the trough caused by settlement and started leaking

through shrinkage cracks in the foundation wall. Correcting the faulty drainage stopped the

leaking. Be careful when compacting backfill. Some compactors are powerful enough to damage

the foundation. One way to avoid this problem is to place the backfill in 6-inch-thick lifts and

have the laborers tamp it with foot pressure or hand rammers. Vibrating plate compactors also

can be used for granular backfill without damaging the foundation. It takes more time to compact

thin layers, but the method provides insurance against foundation damage and against call-backs

related to drainage problems.

3.0 CONCLUSION

Shallow foundation has 3 major types which are pad foundation, strip foundation, and raft

foundation.