SAFE BEARING CAPACITY OF SOIL

 SBC OF SOIL

The safe bearing capacity of soil is defined as the maximum load per unit area that the soil can bear without any displacement or settlement. This is measured in terms of kilograms per square centimeter. If the load exceeds this mark, the soil will start to displace or break. This will lead to structure settlement, which can end up in destructive results.

Formula:
Safe bearing capacity of soil = (ultimate bearing capacity)/(Cross-section area x Factor of safety)

          *The ultimate bearing capacity of the soil - the point at which the soil starts to displace under load. Any soil can take up to a certain amount of load only, after which it starts to settle or displace.

           *The cross-section area is the area of soil on site on which the tests are being performed. It can be a square meter in general practice.

          *The factor of safety indicates how safe the soil capacity results must be before considering a certain type of construction. Naturally, it depends upon the type of building being constructed. It is kept at 2 for general civil constructions and 3 for high-rise or heavy constructions.

Testing Procedures for Soil Bearing Capacity: 

Drop Weight Method is the easiest and it is a tried and tested true test.

Drop Weight Test:

1. Dig up a pit down to the foundation depth.

2. Find a heavy perfectly cube-shaped object. Stone blocks work best. Measure its precise weight.

3. Lift the cube up to a predetermined height directly over the pit. This must be precise as well.

4. Drop the cube in the pit, and then carefully lift it out without disturbing the impression made by the block.

5. Measure the depth of the impression made by the block.

6. Repeat the above process several times and take the average value.

Example:

Weight of the block: 1.2 kg
Height of drop: 120cm
Depth of impression: 1.6cm
Cross section: 20 sq.cm.
Factor of safety: 2

Therefore, ultimate bearing capacity = (1.2 x 120)/1.6 = 90

And, safe bearing capacity of soil = 90/(20 x 2) = 2.25 kg/cm².

Safe Bearing Capacity (SBC) values for different types soils: 

(The values below are probable only and to use for preliminary design of structures.)

Soft,wet or muddy clay: 0.5 kg/cm²
Black cotton soil: 1.5 kg/cm²
Loose gravel: 2.5 kg/cm²
Compacted clay: 4.5 kg/cm²
Soft rocks: 4.5 kg/cm²
Compacted gravel: 4.5 kg/cm²
Hard rocks: 33.0 kg/cm²
Coarse sand: 4.4 kg/cm²
Medium sand: 2.45 kg/cm²
Fine sand: 4.45 kg/cm²

KNOW ABOUT CONCRETE COVER AND COVER BLOCKS

 CONCRETE COVER AND COVER BLOCKS

NOMINAL COVER (or Clear Cover)

Nominal cover is the design depth of concrete cover to all steel reinforcements, ,including links. It is the dimension used in design and indicated in the drawings. It shall be not less than the diameter of the bar.

Nominal Cover to Meet Durability Requirement

Minimum values for the nominal cover of normal weight aggregate concrete which should be provided to all reinforcement, including links depending.on the condition of exposure described below:

Exposure	Nominal Cover in mm ( not less than)
Mild	20
Moderate	30
Severe	45
Very Severe	50
Extreme	75

NOTES

1. For main reinforcement up to 12 mm diameter bar for mild exposure the nominal cover may be
reduced by 5 mm.

2. Unless specified otherwise, actual concrete cover should not deviate from the required nominal cover by +I0 mm

3. For exposure condition ‘severe’ and ‘very severe’, reduction of 5 mm may be made, where cpncrete grade is M35 and above.

 * However for a longitudinal reinforcing bar in a column nominal cover shall in any case not be less than 40 mm, or less than the diameter of such bar. In the case of columns of minimum dimension of 200 mm or under, whose reinforcing bars do not exceed 12 mm, a nominal cover of 25 mm may be used.

 * For footings minimum cover shall be 50 mm.

 For Minimum values of nominal cover of normal-weight aggregate concrete to be provided to all reinforcement including links to meet specified period of fire resistance, refer in code section - 26.4.3

--------------------------------

There is no maximum cover, but the combination of inherent shrinkage and other factors may make excessive cover break away from underlying concrete 

Minimum Concrete Cover for Reinforcement

Below are the specifications for reinforcement cover for different structural members in different conditions.

a) At each end of reinforcing bar, concrete cover not less that 25 mm or less than twice the diameter of the bar should be provided.

 b) For a longitudinal reinforcing bar in a column, concrete cover not less than 40 mm not less than the diameter of such bar should be provided. In case of columns of minimum dimension of 20 cm or under, whose reinforcing bars do no not exceed 12 mm, concrete cover of 25 mm to be used for reinforcement. 

c) For longitudinal reinforcing bars in a beam, not less than 30 mm or less than the diameter of the bar.

 d) For tensile, compressive shear or other reinforcements in a slab or wall not less than 15 mm, not less that the diameter of such bar. 

e) For any other reinforcement not less than 15 mm, concrete cover not less than the diameter of such bar.

 f) For footings and other principal structural members in which the concrete is deposited directly against the ground, cover to the bottom reinforcement shall be 75 mm. If concrete is poured on a layer of lean concrete, the bottom cover maybe reduced to 50 mm. 

g) For concrete surfaces exposed to the weather or the ground after removal of forms, such as retaining walls, grade beams, footing sides and top etc. cover should not be less than 50 mm.

 h) Increased cover thickness shall be provided as indicated on the drawings, for surfaces exposed to the action of harmful chemicals (or exposed to earth contaminated by such chemicals), acid, alkali, saline atmosphere, sulphur, smoke etc.

 i) For liquid retaining structures, the minimum cover to all steel shall be 40mm or the diameter of the main bar, whichever is greater. In the presence of sea water and oils and waters of a corrosive character the covers, shall be increased by 10 mm.

 j) Protection to reinforcement in case of concrete exposed to harmful surroundings may also be given by providing a dense impermeable concrete with approved protective coatings. In such a case the extra cover mentioned in (b) & (i) above may be reduced.

 k) The correct cover shall be maintained by cement mortar cubes (blocks) or other approved means. Reinforcements for footings, grade beams and slabs on a sub-grade shall be supported on precast concrete blocks as approved by EIC. The use of pebbles or stones shall not be permitted. 

l) The minimum clear distance between reinforcing bars shall be in accordance with IS:456 – 2000 or as shown in drawing.

Minimum Clear Cover for Reinforcement

Footings	50 mm
Raft Foundation - Top	50 mm
Raft Foundation – Bottom / Sides	75 mm
Strap Beam	50 mm
Grade Beam	20 mm
Column	40 mm
Shear walls	25 mm
Beams	25 mm
Slabs	15 mm
Flat Slab	20 mm
Staircase	15 mm
Retaining wall – on earth	20 / 25 mm
Water Retaining structures	20 / 30 mm

Effective cover 

Effective cover = nominal cover + half dia of reinforcement

CONCRETE COVER BLOCKS

Cover block is a precast concrete block to provide the necessary cover or spacing for the

reinforcement bars from the formwork. PVC or Plastic Cover blocks are also available.

By placing Cover blocks, rebar gets proper bonding with concrete and saved from  corrosion.

The distance between the two cover blocks depends upon the diameter of the rebar, the type of  RCC structure, and rebar directions (longitudinal or transverse). When the rebar diameter increases there will be less sagging and hence the number of cover blocks requirement becomes less as the bar dia. increases.

Average distance between Cover blocks

 Slabs - For 8mm - 60 cm and for 10mm - 70 cm. For 100 Sqm, approx. 280 nos. required for 8 mm bars and approx. 210 nos. required for 10 mm bars.

Columns - all sides, for 12mm - 20mm - 60 -90 Cm and above 20mm - 100 cm spacing required.

Beams - 12mm - 20 mm - 40 -70 Cm and above 20 mm - 80 Cm required.

Footings - 60 - 70 Cm required

Various types of Cover blocks

Single Cover spacers, Multiple Cover Spacers and Circular Spacers are in precast concrete blocks.

Clip Spacers, wheel spacers and chair spacers are PVC material blocks.

COMPLETE GUIDE TO GROUTING

 GROUTING

Grouting is generally a mixture of cement, sand and water or chemical used to fill gaps or used as reinforcement in existing structures.

The purpose of grouting can be either to strengthen a formation or to reduce water flow through it. It is also used to correct faults in concrete and masonry structures

Applications of grouting

1.   For grouting machine foundation, base plate, bearing and column joints in precast construction

2.   It is used for filling voids, gaps and cavities in the concrete

3.   Grouting is done for filling the voids between the rock face and lining in tunnel work

4.   It is used for fixing tendons post-tensioned in prestressed concrete construction.

5.   It is used for repairing pavement and ground below the foundation.

6.   It is used for repairing cracks in concrete and defects in masonry

 7.  Also, for fixing ground anchors for concrete pile wall.

The process of grouting consists of filling pores or cavities in soil or rock with a liquid form material to decrease the permeability and improve the shear strength by increasing the cohesion when it is set. Cement base grout mixes are commonly used for gravely layers or fissure rock treatment.

TYPES OF GROUTS

1. Cementitious Grouts

Cementitious grout is used to create a solid bearing surface between structural baseplates and base foundations. It enables even dispersal of the load into the existing concrete slab. Cementitious grout is suitable for a range of different bedding and fixing applications.

a) Ordinary Portland cement grouting

It is commonly used for repairing concrete cracks. Since they have the particulate size of 15 microns they can help in filing the wider cracks.

b) Micro-fine cement grouting

Finely ground slag, fine fly ash, or Portland cement are mixed with water to allow penetration into the fine cracks. They have the particulate size in the range of 6 to 10 microns.

 c) Ultra-fine cement grouting

This grout is used for sealing the very fine hairline like cracks and have the particulate size of 3 to 5 microns. They are used for stabilizing waste plumes.

d) Sanded grout 

Sanded grout is most commonly used for ceramic tile, stone and any tile with a grout joint or larger. It is composed of Portland cement, sand and other additives, it is mixed with water and troweled into the grout joint, where it takes approximately 24 hours to dry.

For joints 3.175 to 9.525 mm (1/8 to 3/8”) wide, fine sanded grout

For joints 9.525 to 12.7 mm (3/8 to 1/2”) wide, Coarse sand will be used.

e) Unsanded grout 

Unsanded grout, commonly called “wall grout,” is essentially sanded grout without the sand. It is used on ceramic tile and polished marble with grout joints smaller than 1/8 inch.

f) Latex modified grout

Sanded grouts may be formulated with a latex polymer additive, either included in the dry mix or added in as the grout is mixed with water.

2. Chemical grouts

Chemical grouts are an emulsion of water and liquid resin. Chemical grouting requires injection of specially formulated chemical grouts into finer cracks that cannot be possible by cement grouts. Some of the popular ones are epoxy, acrylic and furan resin grouts.

a) Epoxy grout 

Epoxy grout is strong and durable. It is highly resistant to stains, cracks, chemicals, harsh weather conditions, and climate changes. These characteristics make epoxy grout the only way to go if you’re looking for the most durable, efficient way to do tile work.

b) Acrylic grout 

With acrylic grout is that you don’t have to cover the entire work surface. You can just apply it in the joints between the tiles. The silicone additive, which comes premixed with Portland cement grout, aid¬s in greater adhesion. Because of its stability in freezes and thaws, it can be used outdoors, making it perfect for deck or garage projects.

c) Furan grout 

Furan grout is similar to epoxies, but are composed of polymers of furfuryl alcohol, which are highly resistant to chemical action. Furans are two-component systems that contain a furan resin and a filler powder with an acid catalyst. It is the acid catalyst that causes the furan resins to cure, forming a thermosetting resin that has unsurpassed chemical, physical and thermal-resistance.

Furan grout is commonly used to grout brick pavers and quarry tile and it is also recommended in areas exposed to chemicals and grease. The tile surfaces may be smooth, non-skid, or abrasive, depending on the intended use for the floor. The tile or brick surfaces must receive a wax coating to protect them from staining prior to the installation of furan

3. Polyester grouts

For decades, grouting has been the most popular soil stabilization method. Some additives, as well as cement and polymeric materials, are also widely used as grout mixtures in order to lower costs and achieve the best engineering properties with early strength gain. Unconfined compression and dynamic tests of grouted granular soils were conducted with different mixtures to evaluate the feasibility of using polyester, red mud and micronized clay as grouting materials. This type of grouts advances with increasing additive percentages and curing time. Polyester grout is used for anchoring to impart strength to foundations that must be achieved in limited available space.

4. Non-shrink grout

Non shrinking grout

Non-shrink grouts are hydraulic cement grout that, when hardened under stipulated test conditions, does not shrink, so its final volume is greater than or equal to the original installed volume. It is often used as a transfer medium between load-bearing members. This grout often sets rapidly. It is a pre-mix product that needs only to be mixed with [water] which includes ingredients to compensate against cement stone shrinkage

G1 Grout

It is mainly used for steel structures, small pumps, ships, towers and all other non-vibration machinery. It should be cementitious, nonshrinkable and free flow with compressive strength equal or greater than the foundation’s concrete, but not less than 30n/mm2 in 7 days and 40n/mm2 in 28 days.

G2 Grout

It is generally used for prefabricated concrete structures, compressors, heavy equipment subjected to vibration and for massive structure’s column bearing plates. Minimum compressive strength should be 50N/mm2 in 7 days and 60n/mm2 in 28 days. The grout’s flexibile strength should not exceed 9n/mm2 in 28 days.

It should be cementitious, nonshrinkable high strength grout.

Mixing of grout

Mixing of grouting powder with water can be done mechanically using an electric drill

For Flowable grouting – Water:Powder = 0.14 to 0.16 by weight (4.2 to 4.8 litres water for 30 Kg bag)

For Pourable grouting – Water:Powder = 0.12 to 0.14 by weight (3.6 to 4.2 litres water for 30 Kg bag)

The minimum mixing time is 3 minutes

5. Bituminous grouting

In this method, hot bitumen is used as a grouting material. Hot bitumen is employed associated with solidify based suspension grout. this is often never really grout from spreading and to create the mechanical quality of the finished result.

A hard-oxidized environment friendly, having a high solidification point is used for grouting.

Process of bituminous grouting

Firstly, the bitumen is heated up to 200 degrees Celsius. At this time the grout has a dynamic viscosity in the range 15 to 100 cp.

Unlike another grouting, the hot bitumen’s curing is thermally driven. This hot bitumen turns from its fluid state to a highly viscous elastoplastic state, when it is injected into medium saturated water. Finally, when this is injected the pass is plugged.

6. Resin grouting

In traditional resin grout, it is the composition of epoxy resin mixed with the filler. But new type of water-based resin has been recently developed that is better than the traditional ones.

It is also known as penetration grouting and is the most conventional grouting for use. This grouting method is used in non-cohesive soil, sand, and other porous media for filling cracks and joints.

It is injected inside the porous medium without disturbing its original structure. It is commonly used in soil and rock deposits to change its geotechnical properties.

There are two types of Permeation grouting injecting system:

• Circulating grout system

• Direct grout system

Types of Grouting based on the the Process

1) Compaction grouting

 Compaction grouting is done to strengthen the subsurface or surface of the permeable soil to reduce the voids and sinkholes.

It is driven to the depth through the drill. Cement, sand, fly ash, and water is then placed from bottom to top according to the pressure criteria. After each step, the drill is lifted up until it is fully taken out. This grouting is commonly called low mobility grouting

2) Bentonite grouting

Bentonite is made up of the clay having thixotropic properties that is a highly water-resistant gel which forms the permanent barrier to water flow when mixed with additives.

This method is used in the soil particles that cannot accept the cement grouting. This is commonly used for plugging old wells.

It is composed of 50 pounds of powdered bentonite to 34 gallons of water in which 50 pounds of washed sand is added.

3) Fracture grouting

In this method, grout uses the low viscosity grouts that splits by hydraulic fracture under the high pressure and enters into the cracks by creating the lenses. It is also known as compensation grouting and is commonly used for structural releveling.

Procedure of hydraulic fracture:

In this method, a hydraulically pressurized liquid composed of water, sand, and chemical mixture is used to fracture the rock. Artificial cracks are provided with pre-split holes. Then, the grout is passed down the holes.

The casing is inserted to the fracture section and grouted. A pressurized fluid carrier is inserted into the opening casing and spread throughout fractures. The casing remains open after fracturing.

4) Jet grouting in construction

This is a process of creating soil concrete column or jet grouted column using high-pressure jet through the nozzle in a borehole.

The specially designed drill stem and the monitor are raised and rotated at slow, smooth, and constant speed cutting the soil with water or/and air at high pressure to create the soil concrete column. The end product is then cemented round column. This grout is effective for almost soil.

Procedure of jet grouting:

1. Initially, the hole is drilled in the required place and depth.

2. The drill is done until a weak subsoil exists. It may be up to 10 to 20 cm.

3. Then, equipment is placed in the hole to conduct an injection process that consists of a jet grouting string of almost 7 to 10 cm.

4. The string consists of a nozzle to have an injection on high velocity, having a diameter of 1 to 10mm.

5. Then, the string is raised and rotated to seal the whole column with soil and the fluid system. Now, the jetting starts. The string is raised when the fluid is injected. For every raising, there is rotation performed smoothly and constantly. This gives a perfectly refined grouting column.

Types of jet grouting system

1. Single

2. Double

3. Triple fluid system.

Application of jet grouting

• Horizontal barriers

• Groundwater control

• Tunneling

• Supporting excavation

• Underpinning

Jet grouting steps

Types of Grout for Ceramic Tile 

There are four basic types of grout:

• Unsanded Grout

• Finely Sanded Grout

• Quarry TypeGrout

• Epoxy Grout

1. Unsanded Grout

This is used for wall tiles where the grout joint is less than 1/8” wide.

2. Finely Sanded Grout

This is used for floor tiles where the joints are 1/8” to 3/8” wide.

3. Quarry Type Grout

• This is the same as finely sanded grout for ceramic tiles except that a coarser grade of sand is used.

• The quarry-type grout is used for joints that are 3/8” wide to 1/2” wide such as those used with Terracota / Saltillo tiles.

4. Epoxy Grout

• This consists of an epoxy resin and hardener.

• Epoxy grout for ceramic tile is highly resistant to stains and chemicals and has a tremendous bonding strength.

• It is ideal for countertops and other areas susceptible to stains.

IS code for grouting

A fundamental requirement of a grout is that it shall develop adequate gel strength after a control- Page 11 IS 14343 : 1996 lable interval of time. This should be determined by relevant test procedures.

Applications of Grouting

(Courtesy: sika.com)

GUIDE TO FORMWORKS, FALSE WORKS & SCAFFOLDING

 FORMWORK, FALSE WORKS & SCAFFOLDING

FORM WORKS

Formwork is the process of making a temporary mould into which concrete is poured and formed. Formwork plays a key role in concrete construction. They mould the concrete to the desired size & shape, control its alignment and position. 

Requirements of a Good Formwork

Formwork also carries the weight of freshly placed concrete and itself besides live load due to materials, equipment and workmen. Therefore Formwork should be strong enough to withstand all types of dead and live loads. . The design of formwork should be easy to handle , quick erection and removal. joints between formwork must have tight enough to prevent leakage of grout.

Formwork should be rigidly constructed and efficiently propped and braced both horizontally and vertically, so as to retain its shape. Construction of formwork should permit removal of various parts in desired sequences without damage to the Concrete.

The formwork should be accurately to the desired line and levels should have plane surface. The material of the formwork should not warp or get distorted when exposed to the elements.

Types of Formwork 

Formwork based on Materials	Formwork based on Shape
1            Timber Formwork   2            Plywood Formwork 3            Steel Formwork 4            Aluminium Formwork 5.           Plastic Formwork	Column Formwork                    Beam Formwork                    Slab Formwork                    Wall Formwork

Timber Formwork

The timber used for formwork should be well seasoned and light in weight. It should have smooth and even surface on all the sides which comes in direct contact with concrete. The timber should be free from loose knots and easily workable with nails without splitting.

Plywood Formwork

The Plywood should be boiling waterproof grade. Plywood shuttering is durable under alternate wetting and drying conditions. Plywood has a hard surface and it possesses adequate strength to withstand a load of concrete and the forces caused by pouring of concrete and vibrations.

Plywood formwork is very economical as it can be use repeatedly, depending upon the care taken during erection and dismantling.

Steel Formwork

Steel formwork formed by steel panels fabricated with angles and thin steel plates. Steel panels can e fabricated in any modular shape or size, mostly circular and curved.

Steel panels are stronger, durable and have longer life span. These can be insttalled and dismantled easily with great speed. They do not shrink or warp. 

Compared to Plywoog, steel is costly. Initial investment will be high, but easy to maintain. Steel panels are  heavy in weight and needs lifting equipment.

Aluminium Formwork

Formed with Aluminium panels, this formwork increases the speed of construction and saves time and labour. Aluminium Formwork can be reused up to 250 times. Though initial cost is high, cost effective in building large number of symmetrical structures. Skilled labours are required for erection, alignment and maintenance.

Holes caused during formwork by wall tie should be grouted properly, or else there will be a leakage problem in the future.

Mivan Company Ltd. from Malaysia is manufacturing aluminium formworks. Mivan formworks are widely used in mass residential units. It is economical and useful for fast construction.

Plastic Formwork

Plastic formwork is assembled either from interlocking panels or from a modular system and is used for relatively simple concrete structures. It is not as versatile as timber formwork due to the prefabrication requirements. It is used for concrete columns and piers and stays in place, acting as permanent axial and shear reinforcement for the structural member. It also provides resistance to environmental damage for both the concrete and reinforcing bars.

Column Formwork

Column box or shuttering for columns is made of Plywood sheets or Steel sheets fabricated with adequate stiffeners. A thin films of oil or grease should be applied to inner surface of the shuttering to enable easy removal of the column after the concrete hardens. Plastic Panels also can be used for Column shuttering.

Column Formwork is to be designed to be able to accommodate relatively high fresh concrete pressures as comparatively small cross-sections are concreted quickly.

Beam Formwork

Formwork for beams takes the form of a three-sided box which is supported and propped in the correct position and to the desired level. Beam formwork is generally formed with either timber or metal panels. It should be built up tightly and sustained competently and braced both horizontally and vertically with the intension of preserving its shape.

The joints in the formwork should be firm against seepage of cement grout. The formwork should be arranged correctly to the preferred line and levels with plane surface. It should be supported with firm base.

Slab Formwork

Components of slab formwork are formwork panels, joists, Props, bracing and other supporting materials that enables the concrete to be poured and set above the ground. Slab formwork essentially supports the weight of the concrete during the curing process and when the concrete slab is positioned on permanent supports.

There are a variety of materials used in slab formwork, including plywood, timber, metal, aluminium, and sometimes even plastic components that are used to shape and give strength to the concrete.

Wall Formwork

Formwork for a concrete wall is normally built up on both sides of the wall. Reinforcement bars are laid on wires before the spreaders are placed and the wall is tied. The studs are approximately 600 mm apart. All studs are braced.

Formworks for wall are subjected to relatively lower lateral prssure than Column forms due to their large cross sectional area. Wall Formwork panels should be checked for adequate tying and bracing. Form panels should be checked for adequate tying and bracing.

Centring and Shuttering

Centring - formwork which supports the horizontal surface such as Beam, Slab bottom is known as Centring.

Shuttering - Formwork which supports the vertical surface such as Columns, Shear walls is known as Shuttering.

But Centring and Shuttering have no significant difference between them.

Major Companies manufacturing Form works are MIVAN, PERI, DOKA, COFFOR etc.

Stripping : Operation of removing formwork is known as Stripping or De-shuttering. 

Order and method of removing Formwork

• Shuttering forming vertical faces of walls, beams and Column sides should be removed first. Shuttering forming soffit to slab should be removed next
• Shuttering forming soffit to beams, girders or heavily loaded members should be removed at the end.
• Time of removal of formwork depends on type of Cement, ratio of Concrete mix and weather condition.
• Over loaded, misaligned formwork, Inadequate bracing, improper stripping are some of the reasons for formwork failures.

Stripping Time as per IS 456:2000 (For OPC Cement)

Description Of the Structural Member	Minimum Time Period
Walls, columns and vertical sides of beams	16 to 24 hours
Slabs (props left under)	3 days
Beam soffits (props left under)	7 days
Removal Of Props To Slabs
(a)   Spanning up to 4.5 m	7 days
(b)   Spanning over 4.5 m	14 days
Removal Of Props To Beams And Arches
(a) Spanning up to 6 m	14 days
(b) Spanning over 6 m	21 days

 FALSE WORK

A transitory Support system for the permanent structure until it can withstand its own weight is called as False work. Falsework may be required to support steel and timber frameworks and masonry arches as well as in situ and precast concrete construction like Flyover, box girder bridge, culverts, etc. False works have Props or Scaffolding only.

SHORING

Shoring is the process of temporarily supporting a building, vessel, structure, retaining wall or trench with shores (props) when in danger of collapse or during repairs or alterations. Shoring comes from shore, a timber or metal prop.

Professionals use shoring to fix unstable walls, demolish structures, change existing walls, construct new walls and repair cracked or broken walls or foundations. When deciding which type of shoring to use, professionals take several variables into consideration, like the soil located on the site, the proximity of the site to other structures and the environment of their worksite, like if it's wet, dry or near a body of water.

Shoring is often used to provide lateral support:

• To walls undergoing repair or reinforcement.
• During excavations.
• To prevent walls bulging out.
• When an adjacent structure is to be pulled down.
• When openings in a wall are made or enlarged.
• Temporary vertical supports to Bridges also.

Types of Shoring

• Horizontal shoring or flying shoring
•  Vertical shoring or dead shoring
•  Inclined Shoring or raking shoring

STAGING

Staging is a temporary member which is used to support formwork (either it may be for centering or shuttering). It is done by props, jacks, H frames, cup lock system, wooden ballies, etc. Staging should be firm enough so that during concreting it should properly hold the concrete & shuttering so that shuttering does not bulge of settle.

SCAFFOLDING

Scaffolding is a fixed / movable platform used to lift, support, and supply materials during a construction, repair or cleaning of a structure. In Construction, they are usually used for activities such as Plastering, Painting, Brick work at heights, etc.

 In addition, it also provides some degree of support for a standing structure during the construction phase.

Types of Scaffolding

• Single Scaffolding.
• Double Scaffolding.
• Cantilever Scaffolding.
• Suspended Scaffolding.
• Trestle Scaffolding.
• Steel Scaffolding.
• Patented Scaffolding.
• Wooden Gantries Scaffolding.

Single Scaffolding
Single Scaffolding is generally used for brick masonry Construction, It is made of only one row. It comprises of putlogs, standards, ledgers, etc. that are corresponded to the wall within a distance of 1.2m. The standards are placed at a distance of 2–2.5m. Ledgers connect the standards at vertical interval of 1.2 to 1.5 m. Putlogs are taken out from the hole left in the wall to one end of the ledgers. Putlogs are placed at an interval of 1.2 to 1.5 m.

Double Scaffolding

Normally used for the construction work of stone masonry, plastering, the double scaffolding is also called “mason’s scaffolding”. This scaffolding is made by two rows to support. The first row is 20–30cms away from the wall and the 2nd row is put almost 1m away from the row so that they can form a stiff support for the construction work.

Cantilever Scaffolding

This a type of scaffolding in which the standards are supported on series of needles and these needles are taken out through holes in the wall. This is called single frame type scaffolding. In the other type, needles are strutted inside the floors through the openings and this is called independent or double frame type scaffolding. Care should be taken while construction of cantilever scaffolding.

Generally cantilever scaffoldings are used under conditions such as

• When the ground does not having the capacity to support standards,
• When the Ground near the wall is to be free from traffic,
• When upper part of the wall is under construction.

Suspended Scaffolding

This one is used for the painting, cleaning and repair purposes for the exteriors of the house. The working platform of the scaffolding is suspended from the roofs through wires or chains and it can be pulled up or down depending on the area of the work carried out in the construction sites.

Trestle Scaffolding

This is mostly used for interiors work like paintings, cleaning, repairs, etc. This type of scaffolding is made in a way that it is supported on movable tripods or ladders and can be used up to 5 meters in height.

Steel Scaffolding

The steel scaffoldings are made of steel tubes and are joined by couplers or fittings that are also of steel materials. It is very easy to work on such type of scaffoldings as they have better robust, superior and durable characteristics. Also, it is easy to dismantle or erect such scaffoldings. But it is a bit costly as compared to the other types of scaffoldings.

Patented Scaffolding

Patented scaffoldings are readymade scaffoldings which are available in the market.  These are made up of steel but these are equipped with special couplings and frames etc., The working platform of the patented scaffolding is set in the brackets in a way that it is adjustable to required extents

Wooden Scaffolding

Wooden scaffolding can be used in the construction or repair of both large and small buildings. These scaffoldings are not as stable as scaffolds made from other materials. Bamboo scaffolding is widely used in Hong Kong and Macau, with nylon straps tied into knots as couplers. In India, bamboo or other wooden scaffolding is also mostly used, with poles being lashed together using ropes made from coconut hair (coir).

SLIP FORM

Slip form is a method of construction in which concrete is poured into the top of a continuously moving formwork. As the concrete is poured, the formwork is raised vertically at a speed which allows the concrete to harden before it is free from the formwork at the bottom. Slip form is most economical for structures over 7 storeys high such as bridges and towers, as it is the fastest method of construction for vertical reinforced concrete structures, but it can also be used for horizontal structures such as roadways.

As long as there is a regular shape or core, formwork can be used for a smooth, continuous pour that requires no joints. The formwork supports itself on the core rather than relying on other parts of the building or permanent works, and rises at a rate of about 300 mm per hour.

The concrete to be used needs to be workable enough to be placed into the form and consolidated by vibration, yet quick-setting enough to emerge from the form with strength. The concrete must be constantly monitored for its setting rate to ensure the forms are not being raised too fast.

Usually, the formwork has three platforms:

• Upper platform: This acts as a storage and distribution area.
• Middle platform: This is the main working platform and sits at the top of the poured concrete level.
• Lower platform: This provides access for concrete finishing.

It is essential that the middle supporting platform is rigid so that all parts of the structure move simultaneously. The shuttering can drag if there is inconsistency in the rate at which the platform is moving which can cause difficulties.

The types of structure that are most commonly constructed used slip forming techniques include:

• Service cores for commercial buildings
• Lift and stair shafts
• Silos
• Chimneys
• Concrete gravity structures such as oil platforms
• Bridge pylons and piers
• Mine headgear towers
• Shaft linings
• Surge shafts
• Liquid containment vessels

Advantages of slip forming

• Slip forming can achieve high production rates, however, once continuous concreting has begun there is little flexibility for change and so very careful planning is required.
• Crane use is minimised.
• Only minimal scaffolding and temporary works are required allowing the construction site to be less congested, and so safer.
• The exposed concrete can be finished at the bottom of the rising formwork.
• Slip form systems require a small but skilled workforce on site.
• There is flexibility in that tapering structures with wall reductions (either gradual, over a short distance, or stepped) can be achieved

Cost of Formworks

• For normal works cost of formwork is about 30%-40% of the concrete cost.
• For special works cost of formwork is about 50%-60% of the concrete cost.

 Formwork cost is controlled by the following factors

•  Formwork Material cost
•  Formwork erecting cost
•  Formwork removal cost
•  Formwork jointing cost (Nails and Cables)
• Labor charges.