Temporary construction

Timbering (formwork) of trenches is the temporary support of the sides of an excavation with timber or steel to prevent the earth from collapsing and to protect workers. It is needed when the trench is deeper than about 1.5 m or the soil is loose, wet or surcharged.

Timbering in firm soil

• Stay bracing: vertical boards (poling boards) 200 x 40 mm are placed at about 2-3 m intervals on both sides; they are held apart by horizontal struts and, in places, by walings. Used for depths up to 2 m in fairly firm soil.
• Box sheeting (poling boards): vertical or horizontal boards placed at 1-2 m centres, held by walings and cross struts.

Timbering in loose soil

• Vertical sheeting: boards placed close to each other vertically with horizontal walings and struts; used for loose soil, depth up to 3 m.
• Runners and sheet piling: boards are driven ahead of excavation in very soft or running soil; used for depths over 3 m.

   ground level
  |<--- trench width --->|
  |poling   strut   poling|
  |board  ====o====  board|
  |   |  waling      |    |
  |   |========o=====|    |
  |   |              |    |
  |___|______________|____|

Components: poling boards, struts (props, adjustable with wedges), walings, runners, and cleats. Precautions: inspect daily, keep spoil heaps 1 m or more from the edge, fix struts tightly, and provide ladders and drainage.

Shoring is the temporary support given to an unsafe wall, building or structure to prevent it from collapsing, using inclined, horizontal or vertical timber or steel members, until permanent repair or reconstruction is done.

Types of shoring

1. Raking shore Raking (inclined) shore: inclined members (rakers) support a wall from the outside. Rakers are at 60-70 degrees to the ground and are fixed at the top to a wall plate (with needles) bolted to the wall, and at the bottom to a sole plate resting on a firm base. Cleats and braces hold the members together.

        wall plate
   wall |==|\ needle
   |    |  | \ raker
   |    |  |  \ cleat
   |    |  |   \
   |    |  |    \
 --+----+--+-----\--- ground
                sole plate

Types: simple (single raker), compound/double (two or more rakers on different levels), and multiple raking shores for high walls (up to three storeys).

2. Flying shore Flying (horizontal) shore: used when two parallel walls with a narrow gap (3-9 m) between them are to be supported, e.g., when the building between them is demolished. Horizontal members (horizontal shores) are fixed between the two walls with wall plates, needles, cleats and struts, and no part touches the ground, hence "flying".

   wall plate         wall plate
 |   ||  horizontal shore  ||   |
 |   ||=====================|| |
 |   || \ strut     strut / || |
 |   ||  \  needle     /    || |
 |   |    \_________/       | |
 wall                      wall

Single flying shore is used for a gap up to about 9 m; double flying shore for greater heights. The system is cheaper than raking shores and keeps the ground clear.

3. Dead shore Dead (vertical) shore: used to support the floors and roofs above when a wall is removed or an opening is made at lower storeys, or when the lower wall is repaired. It transfers the vertical load to the ground.

It consists of vertical posts (dead shores) on a sole plate at the bottom, a needle (horizontal beam) passing through the wall at the top, braces, cleats and wedges to take the weight.

        floor above
   ____|==needle==|____
   wall| |      | |wall
   wall| | post | |
   wall| | post | |
       |_|______|_|
       sole plate

Definition

Underpinning is the process of strengthening or deepening the foundation of an existing building by extending it to a firmer or deeper stratum, or enlarging the base, so that it can carry the load safely.

Necessity

• Foundation has settled or is weak due to poor soil or an overload.
• A building is to be raised (extra storeys) and loads increase.
• Adjacent deep excavation or new basement lowers the support (e.g. neighbouring building).
• A change in water table, scouring or earthquake damage reduces bearing capacity.
• Faulty or shallow original foundation, or damage by roots, mining, or subsidence.

Methods of underpinning

1. Pit method (pier method): The wall is divided into 1-1.5 m sections. Pits are dug below the old footing in alternate sections (the others stay in place), the soil is excavated to the required depth and filled with concrete or masonry, and a gap of about 75 mm is left under the old foundation, then packed with dry mortar or wedges. This is repeated with the next sections.
2. Pile method: Piles (bored or driven) are installed on both sides of the wall and connected by cross beams (needles) below the wall. Useful when good soil is deep.
3. Pretest method: Hydraulic jacks apply a test load to piles, then wedges are inserted to avoid later settlement.
4. Chemical (grouting) method: Cement or chemical grout is injected into weak soil to increase bearing capacity.
5. Cantilever/needle beam method: Needle beams carry the wall's load so the footing can be rebuilt below.
6. Jet grouting / micropile method for tight spaces.

Procedure of the pit method (most common)

1. Study the soil and the structure, and support the building by shoring if necessary.
2. Dig the first pit below the footing, in sections about 1-1.5 m wide, leaving alternate sections untouched.
3. Dig to the design depth, with timbering support if needed.
4. Fill with PCC or masonry in cement mortar (1:4) up to about 75 mm below the old foundation.
5. Pack the gap with dry cement-sand mortar (1:1) or wedges and leave to set for 3-4 days.
6. Repeat for the intermediate sections, in a planned order.
7. Backfill and compact.

   wall
   ||||||  old footing
   ||||||====|  pit (section 1)
          |  new masonry/concrete
          |  packing (75 mm gap)
          |__ firm stratum

Temporary construction means structures built only for a limited period to help the construction of a permanent building, and removed after use. Examples are scaffolding, formwork, shoring, underpinning and timbering of trenches.

Types

1. Scaffolding: a platform at height for workers and materials. Types are single (brick layer's), double (mason's) and cantilever scaffold.

   Single scaffold        Double scaffold
   wall |  ledger         wall |  | ledger
   putlog==|--|           ---- |--|--|
        standard          standard x2

2. Formwork (shuttering): moulds of timber, plywood or steel that hold the wet concrete until it hardens (for footings, columns, beams, slabs).

   column form: [ sheathing ]
     | yoke | yoke |   props & wedges

3. Shoring: temporary support to an unsafe wall or structure by raking, flying or dead shores.

        wall plate
   wall |\ raker

4. Underpinning: strengthening of an existing foundation by extending it to a deeper or firmer layer.

5. Timbering of trenches (formwork for excavation): supports for the sides of a trench using poling boards, struts and walings.

6. Centering: temporary support for arches, vaults and domes.

7. Dewatering/cofferdams for foundation work in water.

Formwork (shuttering) is the temporary mould into which wet concrete is poured and kept until it gains enough strength to support itself. Materials are timber, plywood, steel or aluminium.

Formwork for beam

• Beam bottom (soffit) plank: 25-40 mm thick board, as wide as the beam, supported on head trees/props at 0.6-1.2 m spacing on sole plates and wedges.
• Beam sides (cheeks): vertical boards fixed on both sides with cleats and struts at 0.6-0.9 m spacing, to hold the sides in place.
• Props are braced against each other horizontally and diagonally.

Formwork for slab

• Sheathing/decking: plywood or boards (18-25 mm).
• Joists (75 x 50 mm at 400-500 mm) under the sheathing, supported on runners (beams) and props (vertical posts, steel or ballies) at 1-1.2 m with sole plate and wedges for easy removal.
• Edges closed by a side form (stop board).

 Beam & slab form (section)
   ___slab sheathing_________
   ___joists |  |  |  |  ___
        |cheek| beam |cheek|
        |     |soffit|     |
        |    head tree     |
        |      prop        |
        |_____ sole plate__|

Striking time (IS 456): sides of beams, columns and walls 16-24 hours; slab soffits (props left) 3 days; slab (props) 7 days up to 4.5 m span; beam soffit (props left) 7 days; beam soffit up to 6 m span, 14 days. Surfaces should be oiled for easy removal.

Scaffolding is a temporary framework of timber, bamboo or steel erected beside a building so that workers and materials can be placed at height while the structure is built, repaired or cleaned.

Parts of scaffolding

• Standards (uprights): vertical posts that carry the load to the ground, 1.5-2.4 m apart.
• Ledgers: horizontal members parallel to the wall joining the standards.
• Putlogs (transoms): horizontal members at right angles to the wall; one end rests on the ledger and the other in the wall.
• Braces: diagonal members for stability (facade and cross braces).
• Guard rails and toe boards: at the edge for safety.
• Boards/planks: the working platform, on putlogs.
• Base plates (sole plates): spread load on the ground.
• Ties and clamps/couplers: connect scaffold to the structure and members to each other.

    guard rail ----------------------
     toe board        board on putlogs
        |     putlog  ___|____
   wall |   ----|----|  ledger
   wall |          | |
   wall |   brace /  | standard
   wall |        /   |
   _____|______/_____|_____
            base plate

Shoring is the temporary support given to an unsafe wall, building or structure to prevent it from collapsing, using inclined, horizontal or vertical timber or steel members, until permanent repair or reconstruction is done.

Types

• Raking (inclined) shore
• Flying (horizontal) shore
• Dead (vertical) shore

Flying shore

Flying (horizontal) shore: used when two parallel walls with a narrow gap (3-9 m) between them are to be supported, e.g., when the building between them is demolished. Horizontal members (horizontal shores) are fixed between the two walls with wall plates, needles, cleats and struts, and no part touches the ground, hence "flying".

   wall plate         wall plate
 |   ||  horizontal shore  ||   |
 |   ||=====================|| |
 |   || \ strut     strut / || |
 |   ||  \  needle     /    || |
 |   |    \_________/       | |
 wall                      wall

Single flying shore is used for a gap up to about 9 m; double flying shore for greater heights. The system is cheaper than raking shores and keeps the ground clear.

Parts: wall plates, needles, horizontal shores, struts, cleats and straining pieces. Use: when buildings on each side of the gap are to be supported, such as after demolition of the building between them, or alteration of one wall.

Shoring is the temporary support given to an unsafe wall, building or structure to prevent it from collapsing, using inclined, horizontal or vertical timber or steel members, until permanent repair or reconstruction is done.

Necessity (conditions for shoring)

• A wall is bulging, leaning or cracked and may collapse.
• Adjacent building is being demolished or an excavation is made nearby.
• Foundation of the building is weakened (settlement, flood, underpinning work).
• Alterations: removing a wall, opening or pier, which carries load above.
• Damage from earthquake, fire, or vehicle impact.

Types of shoring

1. Raking shore: Raking (inclined) shore: inclined members (rakers) support a wall from the outside. Rakers are at 60-70 degrees to the ground and are fixed at the top to a wall plate (with needles) bolted to the wall, and at the bottom to a sole plate resting on a firm base. Cleats and braces hold the members together.

        wall plate
   wall |==|\ needle
   |    |  | \ raker
   |    |  |  \ cleat
   |    |  |   \
   |    |  |    \
 --+----+--+-----\--- ground
                sole plate

Types: simple (single raker), compound/double (two or more rakers on different levels), and multiple raking shores for high walls (up to three storeys).

2. Flying shore: Flying (horizontal) shore: used when two parallel walls with a narrow gap (3-9 m) between them are to be supported, e.g., when the building between them is demolished. Horizontal members (horizontal shores) are fixed between the two walls with wall plates, needles, cleats and struts, and no part touches the ground, hence "flying".

   wall plate         wall plate
 |   ||  horizontal shore  ||   |
 |   ||=====================|| |
 |   || \ strut     strut / || |
 |   ||  \  needle     /    || |
 |   |    \_________/       | |
 wall                      wall

Single flying shore is used for a gap up to about 9 m; double flying shore for greater heights. The system is cheaper than raking shores and keeps the ground clear.

3. Dead shore: Dead (vertical) shore: used to support the floors and roofs above when a wall is removed or an opening is made at lower storeys, or when the lower wall is repaired. It transfers the vertical load to the ground.

It consists of vertical posts (dead shores) on a sole plate at the bottom, a needle (horizontal beam) passing through the wall at the top, braces, cleats and wedges to take the weight.

        floor above
   ____|==needle==|____
   wall| |      | |wall
   wall| | post | |
   wall| | post | |
       |_|______|_|
       sole plate

Underpinning is the process of strengthening or deepening the foundation of an existing building by extending it to a firmer or deeper stratum, or enlarging the base, so that it can carry the load safely.

It is carried out by digging below the old foundation in short sections and building new concrete or masonry up to the base of the old footing, so that the load is shifted to a deeper or firmer stratum.

Types of temporary construction in buildings:

1. Scaffolding (single, double, cantilever, trestle, steel).
2. Formwork or shuttering (foundation, column, beam, slab, wall).
3. Shoring (raking, flying, dead).
4. Underpinning.
5. Timbering of trenches (excavation support).
6. Centering for arches and vaults.
7. Cofferdams and dewatering systems.
8. Temporary sheds, ramps and hoardings.

Temporary structures are used because many building operations cannot be done safely or at all without them:

• Safe working at height: scaffolding gives masons and painters a stable platform.
• Shaping concrete: formwork gives the wet concrete its shape until it gains strength.
• Protecting the excavation: timbering prevents collapse of the trench sides and protects workers.
• Supporting weak structures: shoring and underpinning protect adjacent walls and buildings during excavation, repair or alteration.
• Speed and economy: formwork can be reused many times, scaffolds are cheap and removable.
• Quality: proper support gives correct alignment, level and finish of the work.

They are dismantled once the permanent work is complete and can bear its own load.

Temporary construction is any support, framework or structure that is put up for a limited period to help the construction, repair or alteration of a permanent building, and is removed when its purpose is served.

Types

1. Scaffolding Scaffolding is a temporary framework of timber, bamboo or steel erected beside a building so that workers and materials can be placed at height while the structure is built, repaired or cleaned.

• Single (brick layer's) scaffold: one row of standards joined by ledgers, putlogs resting on the wall.
• Double (mason's) scaffold: two rows of standards, used for stone masonry where holes in the wall are not allowed.
• Cantilever scaffold: needles projecting from the wall support the platform where ground support is not possible.

  single           double          cantilever
  wall|--ledger    wall| |--|      wall|=needle=>
      |putlog          |putlog          |  platform
      |standard      2 standards      struts /

2. Formwork: moulds of timber, plywood or steel that give shape to concrete.

3. Shoring: raking, flying and dead shores that support unsafe walls.

   wall plate / raker / sole plate

4. Underpinning: strengthening foundation by deeper or wider construction.

5. Timbering of trenches: poling boards, struts and walings to hold trench sides.

Requirements of temporary construction

• Strength and stability: must carry all dead, live and impact loads, with a factor of safety (generally 4).
• Rigidity: minimal deflection and no sway.
• Safe and sound materials: good timber without defects, steel free from rust.
• Easy erection and dismantling: quick work and re-use.
• Economy: low cost, light weight and possible re-use.
• Safety: guard rails, toe boards, ladders, access and inspection.
• Correct alignment and tight joints (formwork is leakproof).
• Foundation: firm, level sole plates.

Formwork (shuttering or centering) is a temporary mould, made of timber, plywood, steel or aluminium, into which fresh concrete is placed to get the required shape. It stays until the concrete gains enough strength.

Requirements

• Strong enough to carry the weight of wet concrete, workers and vibrations.
• Rigid and stable, with little deflection.
• Tight joints, to stop leakage of cement slurry.
• Easy to erect, strip and re-use.
• Inner surface smooth, treated with mould oil.
• Economic and accurate in dimensions.

Types by material

Timber, plywood, steel, aluminium, plastic and fibreglass.

Components

Sheathing, studs/joists, walings, props, braces, ties, sole plates and wedges.

Stripping time (IS 456)

Vertical sides: 16-24 hours; slab soffit: 3 days (props left); beam soffit: 7 days; props to slabs up to 4.5 m span: 7 days, over 4.5 m: 14 days.

Both are methods of timbering trenches to hold the sides of the excavation.

Stay bracing

Used in fairly firm soil for depths up to about 2 m. Vertical boards (poling boards, 200 x 40 mm) are placed at 2-3 m centres on opposite faces of the trench and kept apart by horizontal struts (props). The poling boards are placed at intervals, leaving the soil between exposed. The struts are fixed at 1.2-1.5 m centres vertically, and can be wedged.

   |board   strut   board|
   |  |==========|  |
   |  |          |  |
   |  |==========|  |   (soil between boards
   |__|__________|__|    left unsupported)

Vertical sheeting

Used in loose soil and for depths up to 3 m (or more). Vertical boards (sheeting), 25-40 mm thick, are placed side by side touching each other, so the whole face is covered. They are held by horizontal walings (120 x 120 mm) on the inside, with struts across the trench at about 1.2-1.5 m c/c.

   |sheet|waling|  strut  |waling|sheet|
   ||||||=====o===========o=====||||||
   ||||||                      ||||||
   ||||||=====o===========o=====||||||

Difference: stay bracing leaves gaps between boards, while vertical sheeting gives continuous support. Sheeting is thus used for looser soil.

Formwork for excavation (timbering)

It is the temporary support of the sides of a trench or pit to prevent the earth from falling, and to protect the workers. It is used when depth exceeds 1.5 m.

For firm soil:

• Stay bracing: vertical poling boards at 2-3 m centres, held apart by cross struts, for up to 2 m depth.
• Box sheeting (poling boards): boards at about 1.2-2 m spacing, with walings and struts.

For loose soil:

• Vertical sheeting: closely placed vertical boards, with horizontal walings and struts, for up to 3 m depth.
• Runners: boards driven ahead of the excavation for soft, running soil (3-6 m depth).
• Sheet piling: timber or steel sheets driven to depth for deep excavation.

   |poling|   strut   |poling|
   |board |==========|board |
   |      | waling   |      |

Formwork for RCC construction

Formwork is a temporary mould of timber, plywood or steel into which concrete is cast, and which is removed after the concrete has hardened.

Principal requirements:

• Strong and stable to carry the loads of wet concrete, workers and equipment without sagging.
• Rigid, correct in shape, line and level.
• Joints tight, no leakage of cement grout.
• Smooth surfaces, oiled for easy stripping.
• Quick and easy to erect and strip, without damaging concrete.
• Economical and re-usable.
• Supports on firm base with sole plates and wedges.
• Proper striking time as per IS 456.

Scaffolding is a temporary framework of timber, bamboo or steel erected beside a building so that workers and materials can be placed at height while the structure is built, repaired or cleaned.

Types of scaffolding

1. Single (brick layer's) scaffold: A single row of standards is placed 1.2-1.5 m from the wall, joined by ledgers. Putlogs rest on the ledgers at one end and are fixed in the wall holes at the other end. Used in brick masonry.

  wall |           ledger
  wall |--putlog---|---
  wall |           |
  wall |         standard
  wall |           |

2. Double (mason's) scaffold: Two rows of standards, the first 20-30 cm from the wall, the second about 1.2-1.5 m away, joined by ledgers and putlogs resting on the two ledgers. Used for stone masonry, where holes cannot be made in the wall.

  wall | std  ledger  std
  wall | |=putlog=====| |
  wall | |            | |
  wall | |  braces X  | |

3. Cantilever scaffold: Needles projecting out of the wall (through holes) carry the platform, with struts. Used when the ground is unsuitable for standards.

4. Suspended scaffold: A platform hangs from the roof by ropes or chains, raised and lowered. Used for painting and repairs.

5. Trestle scaffold: Movable platform on ladders or trestles; for inside work up to 5 m.

6. Steel (tubular) scaffold: Steel tubes with couplers; strong, fast to assemble, re-usable and used for high buildings.

7. Patented scaffold: Manufactured frames with special couplings.

Why temporary construction is necessary

• Gives workers and materials a safe, stable platform at height.
• Supports weak walls and trenches during work.
• Provides the shape for concrete until it hardens.
• Allows work on deep foundations and repair of old structures.
• Increases safety, speed and quality of work.

Single and double scaffolding

  SINGLE                      DOUBLE
  wall |__ledger__            wall |  ledger  ledger
  wall |--putlog (in wall)    wall |==putlog on both==|
  wall |   standard           wall |  std      std
  wall |   standard           wall |  std      std

Constructional details: standards are fixed on sole plates, ledgers are lashed or clamped at 1.2-1.8 m height, braces (diagonal) are provided on the face and cross braces for stability, boards 40 mm thick are fixed on the putlogs, and guard rails and toe boards are provided.

Double scaffolding

Also called a mason's scaffold. Two rows of standards are put up, the first close to the wall (about 20-30 cm) and the second at 1.2-1.5 m. Ledgers join the standards, putlogs rest on both rows (not in the wall), and braces make the frame rigid. It is used for stone masonry and heavy work where holes in the wall are not allowed.

  wall |std  ledger  std
  wall |  |=putlog====|
  wall |  |  boards   |
  wall |  | /brace    |
  wall |__|/__________|__ sole plate

Use: stone masonry, tall buildings, heavy work.

Cantilever scaffolding

Cantilever scaffolding is a scaffold in which the platform is carried on needles (projecting beams) that cantilever out from the wall, instead of standards resting on the ground. It is used when the ground cannot support standards (e.g. along a road, a basement or a soft or sloping ground), or when the building is on a street where the pavement must remain free.

Parts: needles (steel/timber beams), struts or braces, standards on the needles, ledgers, putlogs, boards and guard rails.

Types:

1. Needle (built-up) type: needles pass through holes in the wall and are anchored inside by counterweight or by tying to the floor.
2. Truss-out type: needles are supported by inclined struts fixed on the wall.

    wall |=====needle=====>  platform boards
    wall |  \               |guard rail
    wall |   \ strut        |standard
    wall |    \ 
    wall |_____\

Use: where the ground cannot support standards, or in busy streets.

Cantilever scaffolding is a scaffold in which the platform is carried on needles (projecting beams) that cantilever out from the wall, instead of standards resting on the ground. It is used when the ground cannot support standards (e.g. along a road, a basement or a soft or sloping ground), or when the building is on a street where the pavement must remain free.

Parts: needles (steel/timber beams), struts or braces, standards on the needles, ledgers, putlogs, boards and guard rails.

Types:

1. Needle (built-up) type: needles pass through holes in the wall and are anchored inside by counterweight or by tying to the floor.
2. Truss-out type: needles are supported by inclined struts fixed on the wall.

    wall |=====needle=====>  platform boards
    wall |  \               |guard rail
    wall |   \ strut        |standard
    wall |    \ 
    wall |_____\

Temporary construction work is any support structure built for a short period to help in the construction, repair or alteration of a permanent building, such as scaffolding, formwork, shoring and underpinning.

Brick layer's (single) scaffold

  wall |           ledger
  wall |--putlog----|----
  wall |          standard
  wall |          brace
  wall |_______ sole plate

Parts: standards, ledgers, putlogs, braces, boards, guard rails and sole plate.

Dead shore

        floor above
   _____|==needle==|____
   wall | |      | | wall
   wall | |post  | |
   wall | |      | |
        |_|sole__|_|

Parts: needle, vertical posts (dead shores), braces, cleats, head plates, sole plate and wedges.

Why shoring is necessary

• A wall is bulging, leaning or cracked and may collapse.
• Adjacent building is being demolished or an excavation is made nearby.
• Foundation of the building is weakened (settlement, flood, underpinning work).
• Alterations: removing a wall, opening or pier, which carries load above.
• Damage from earthquake, fire, or vehicle impact.

Raking shore versus flying shore

 RAKING                    FLYING
   wall|\                 wall||====shore====||wall
   wall| \ raker                \ strut / 
 ______|__\_____sole       

Types of shoring

1. Raking (inclined) shore
2. Flying (horizontal) shore
3. Dead (vertical) shore

Raking shore

Raking (inclined) shore: inclined members (rakers) support a wall from the outside. Rakers are at 60-70 degrees to the ground and are fixed at the top to a wall plate (with needles) bolted to the wall, and at the bottom to a sole plate resting on a firm base. Cleats and braces hold the members together.

        wall plate
   wall |==|\ needle
   |    |  | \ raker
   |    |  |  \ cleat
   |    |  |   \
   |    |  |    \
 --+----+--+-----\--- ground
                sole plate

Types: simple (single raker), compound/double (two or more rakers on different levels), and multiple raking shores for high walls (up to three storeys).

Parts: wall plate, needles, rakers, cleats, braces, sole plate and wedges. Use: to support an external wall that is leaning, bulging or undergoing alteration, where open ground is available. Spacing: rakers are placed at 3-4.5 m c/c along the wall.

Shoring is the temporary support given to an unsafe wall, building or structure to prevent it from collapsing, using inclined, horizontal or vertical timber or steel members, until permanent repair or reconstruction is done.

Objectives

• To prevent collapse of a weak, leaning or cracked wall.
• To support adjoining buildings during demolition or excavation.
• To support the structure above while the lower part is altered or underpinned.
• To carry loads temporarily during repair or extension.
• To give safety to people and property.

Types

1. Raking shore Raking (inclined) shore: inclined members (rakers) support a wall from the outside. Rakers are at 60-70 degrees to the ground and are fixed at the top to a wall plate (with needles) bolted to the wall, and at the bottom to a sole plate resting on a firm base. Cleats and braces hold the members together.

        wall plate
   wall |==|\ needle
   |    |  | \ raker
   |    |  |  \ cleat
   |    |  |   \
   |    |  |    \
 --+----+--+-----\--- ground
                sole plate

Types: simple (single raker), compound/double (two or more rakers on different levels), and multiple raking shores for high walls (up to three storeys).

2. Flying shore Flying (horizontal) shore: used when two parallel walls with a narrow gap (3-9 m) between them are to be supported, e.g., when the building between them is demolished. Horizontal members (horizontal shores) are fixed between the two walls with wall plates, needles, cleats and struts, and no part touches the ground, hence "flying".

   wall plate         wall plate
 |   ||  horizontal shore  ||   |
 |   ||=====================|| |
 |   || \ strut     strut / || |
 |   ||  \  needle     /    || |
 |   |    \_________/       | |
 wall                      wall

Single flying shore is used for a gap up to about 9 m; double flying shore for greater heights. The system is cheaper than raking shores and keeps the ground clear.

3. Dead shore Dead (vertical) shore: used to support the floors and roofs above when a wall is removed or an opening is made at lower storeys, or when the lower wall is repaired. It transfers the vertical load to the ground.

It consists of vertical posts (dead shores) on a sole plate at the bottom, a needle (horizontal beam) passing through the wall at the top, braces, cleats and wedges to take the weight.

        floor above
   ____|==needle==|____
   wall| |      | |wall
   wall| | post | |
   wall| | post | |
       |_|______|_|
       sole plate

Objectives of shoring

• To prevent collapse of a weak, leaning or cracked wall.
• To support adjoining buildings during demolition or excavation.
• To support the structure above while the lower part is altered or underpinned.
• To carry loads temporarily during repair or extension.
• To give safety to people and property.

Dead shore

Dead (vertical) shore: used to support the floors and roofs above when a wall is removed or an opening is made at lower storeys, or when the lower wall is repaired. It transfers the vertical load to the ground.

It consists of vertical posts (dead shores) on a sole plate at the bottom, a needle (horizontal beam) passing through the wall at the top, braces, cleats and wedges to take the weight.

        floor above
   ____|==needle==|____
   wall| |      | |wall
   wall| | post | |
   wall| | post | |
       |_|______|_|
       sole plate

Parts: needle, vertical posts, braces, cleats, wedges, head plate and sole plate. Procedure: holes are made in the wall at floor level for needles, the needle is fixed and wedged, posts are put under the needle on a sole plate, wedges are driven to take load, and then braces are fixed. After this, the lower wall can be removed or altered safely. Use: when the wall below is removed or altered, or an opening is made, in multi-storey buildings.

Shoring

Shoring is the temporary support given to an unsafe wall, building or structure to prevent it from collapsing, using inclined, horizontal or vertical timber or steel members, until permanent repair or reconstruction is done. Types: raking, flying and dead shores.

   wall plate
   wall |\ raker
   wall | \
   _____|__\_ sole plate

Scaffolding

Scaffolding is a temporary framework of timber, bamboo or steel erected beside a building so that workers and materials can be placed at height while the structure is built, repaired or cleaned. Types: single, double, cantilever, suspended, trestle and steel scaffolds.

   wall |    ledger
   wall |-putlog--|
   wall |      standard

Why they are used

• Safe working platform at height for masons, painters and plasterers (scaffolding).
• Safe movement of materials and workers.
• Preventing collapse of weak walls and adjoining buildings during excavation, demolition or repair (shoring).
• Support during alteration of the structure, such as removing a wall or an opening.
• Increases the speed and quality of work and reduces accidents.

Underpinning is the process of strengthening or deepening the foundation of an existing building by extending it to a firmer or deeper stratum, or enlarging the base, so that it can carry the load safely.

Pit method (pier method)

1. The wall is divided into sections of 1-1.5 m width.
2. A pit is dug under the old foundation in alternate sections, and the wall is supported if needed.
3. The pit is dug down to a firm stratum and filled with PCC or masonry in cement mortar (1:4) up to about 75 mm below the old footing.
4. The gap is packed with dry cement-sand mortar (1:1) or slate pieces, rammed, and left 3-4 days to set.
5. The same is repeated for the intermediate sections, then the pits are backfilled.

   wall
   |||||| old footing
   ||||||===| pit
          | new concrete
          | 75 mm packing
          |_ firm soil

Definitions

• Scaffolding: a temporary framework of timber, bamboo or steel erected beside a building so that workers and materials can be placed at height while the work is done.
• Underpinning: the process of strengthening or deepening the foundation of an existing building by extending it to a firmer or deeper stratum, or enlarging the base, so that it can carry the load safely.
• Shoring: the temporary support given to an unsafe wall or structure by inclined, horizontal or vertical members to prevent it from collapsing.

Methods of underpinning

1. Pit method (pier method): The wall is divided into 1-1.5 m sections. Pits are dug below the old footing in alternate sections (the others stay in place), the soil is excavated to the required depth and filled with concrete or masonry, and a gap of about 75 mm is left under the old foundation, then packed with dry mortar or wedges. This is repeated with the next sections.
2. Pile method: Piles (bored or driven) are installed on both sides of the wall and connected by cross beams (needles) below the wall. Useful when good soil is deep.
3. Pretest method: Hydraulic jacks apply a test load to piles, then wedges are inserted to avoid later settlement.
4. Chemical (grouting) method: Cement or chemical grout is injected into weak soil to increase bearing capacity.
5. Cantilever/needle beam method: Needle beams carry the wall's load so the footing can be rebuilt below.
6. Jet grouting / micropile method for tight spaces.

Procedure of the pit method

1. Study the soil and the structure, and support the building by shoring if necessary.
2. Dig the first pit below the footing, in sections about 1-1.5 m wide, leaving alternate sections untouched.
3. Dig to the design depth, with timbering support if needed.
4. Fill with PCC or masonry in cement mortar (1:4) up to about 75 mm below the old foundation.
5. Pack the gap with dry cement-sand mortar (1:1) or wedges and leave to set for 3-4 days.
6. Repeat for the intermediate sections, in a planned order.
7. Backfill and compact.

Underpinning is needed in the following cases.

• Foundation has settled or is weak due to poor soil or an overload.
• A building is to be raised (extra storeys) and loads increase.
• Adjacent deep excavation or new basement lowers the support (e.g. neighbouring building).
• A change in water table, scouring or earthquake damage reduces bearing capacity.
• Faulty or shallow original foundation, or damage by roots, mining, or subsidence.

Underpinning is the process of strengthening or deepening the foundation of an existing building by extending it to a firmer or deeper stratum, or enlarging the base, so that it can carry the load safely.

Necessity: weak or settled foundation, extra load on the building, nearby deep excavation, damage by flood or earthquake, or change in the water table.

Methods: pit method, pile method, pretest method and chemical grouting.

Pit method: pits are dug below the footing in alternate sections about 1-1.5 m wide, filled with concrete to about 75 mm below the old footing, the gap is packed with dry mortar, then the remaining sections are done.

   wall
   |||||| old footing
   ||||||==| new pier
          | 75 mm packing

Flying (horizontal) shore: used when two parallel walls with a narrow gap (3-9 m) between them are to be supported, e.g., when the building between them is demolished. Horizontal members (horizontal shores) are fixed between the two walls with wall plates, needles, cleats and struts, and no part touches the ground, hence "flying".

   wall plate         wall plate
 |   ||  horizontal shore  ||   |
 |   ||=====================|| |
 |   || \ strut     strut / || |
 |   ||  \  needle     /    || |
 |   |    \_________/       | |
 wall                      wall

Single flying shore is used for a gap up to about 9 m; double flying shore for greater heights. The system is cheaper than raking shores and keeps the ground clear.

Parts: wall plates, needles, horizontal shores, struts, cleats and straining pieces.