Shoring Shapes and Sizes: Key Considerations for Technicians

Shoring shapes and sizes determine whether a support system fits the structure, carries the load, and stays stable throughout the work. This guide explains the key considerations for technicians, covering the shapes used in shoring, the sizes that matter, and the checks that keep work accurate.

Introduction: Why Shoring Shapes and Sizes Matter

Shoring supports structures and excavations that have become unstable. Moreover, it carries the weight of walls, floors, and soil that could otherwise collapse. Consequently, the shape and size of each member directly affect safety.

In addition, wrong dimensions cause serious problems. For instance, an undersized raker buckles under load, and a badly angled shore transfers force in the wrong direction. Therefore, technicians must treat every dimension as critical.

This guide therefore covers the standard shapes, the sizes that matter most, and the preparation details that keep shoring accurate.

The Relationship Between Drawing and Shoring

Shoring dimensions come directly from the design or working drawing. Therefore, technicians must read the drawing correctly before cutting or assembling anything.

Span and Height

The span is the clear distance the shore must bridge. Moreover, the height is the vertical distance from the base to the point of support. Together, these two dimensions determine the length and angle of the shore.

Angle of Inclination

Raker shores must sit at an angle between 30 and 60 degrees. Exceeding these limits places excessive pressure on other shoring components and may cause failure.

Point of Contact

Raker shores should contact the wall at approximately two-thirds of the way up. Consequently, the load transfers efficiently without overstressing the wall.

Depth and Width Ratios

Flying shores should have a depth not less than one-third of the clear span. In addition, their width should be not less than one-fifth of their length.

Standard Shoring Shapes

Shoring shapes fall into several standard categories. Each shape demands its own fabrication and installation approach.

1. Inclined (Raker) Shapes

Raker shores form an inclined line between the ground and the wall. They suit vertical or near-vertical walls that need external support.

For these shapes, check the angle carefully. Moreover, install rakers in pairs and lace them together.

2. Horizontal (Flying) Shapes

Flying shores form a horizontal line between two parallel walls. They suit cases where an intermediate building has been removed or has collapsed.

For these shapes, check the depth and width ratios. In addition, install struts and braces to stiffen the shore.

3. Vertical (Dead) Shapes

Dead shores form vertical posts that support needles. They suit opening formation, underpinning, and rebuilding defective lower walls.

For these shapes, check plumbness carefully. Moreover, tighten jacks gradually so the load transfers without shock.

4. Needle Shapes

Needles are horizontal beams that pass through a wall. They support the upper portion of the wall while the lower part is altered.

For these shapes, check the pocket depth and the bearing length. In addition, support both ends firmly with dead shores or jacks.

5. Trench Shoring Shapes

Trench shoring forms a rectangular box within the excavation. It consists of sheeting, walings, and struts.

For these shapes, check the trench width and depth. Moreover, space struts according to the soil type and depth.

6. Sheet Pile and Soldier Pile Shapes

Sheet piling forms a continuous interlocking wall. Soldier piles form vertical columns with lagging between them.

For these shapes, check the embedment depth. In addition, verify the alignment and interlock of adjacent sheets.

Standard Shoring Sizes

Shoring sizes follow standard sections in many countries. Therefore, understanding standard sizes speeds up assembly and reduces cutting waste.

Timber Sizes

Timber members for shoring follow standard sections:

Sole plates and wall plates – 75 mm × 150 mm, 100 mm × 150 mm
Rakers – 100 mm × 100 mm, 150 mm × 150 mm
Needles – 150 mm × 150 mm, 200 mm × 200 mm
Dead shores (posts) – 100 mm × 100 mm, 150 mm × 150 mm
Walings – 75 mm × 150 mm, 100 mm × 150 mm
Struts – 100 mm × 100 mm, 150 mm × 150 mm
Sheeting boards – 50 mm × 200 mm, 50 mm × 250 mm

Steel and Aluminium Sizes

Steel and aluminium shoring members follow proprietary sizes:

Hydraulic cylinders – various diameters and stroke lengths
Soldier piles – standard I-beam sections
Sheet piles – standard interlocking sections
Walings – standard channel or box sections

Plywood Sizes

Plywood sheeting for shoring follows standard panel sizes:

2440 mm × 1220 mm
2400 mm × 1200 mm
1800 mm × 900 mm

Assessment Sizes from the TVET CDACC

The TVET CDACC practical assessment specifies particular sizes. Therefore, technicians should practise these dimensions:

Trench – 1000 mm × 600 mm
Column formwork – 300 mm × 300 mm × 2000 mm
Scaffold framework – 1050 mm, 750 mm, and 1000 mm dimensions
Brace spacing – 500 mm intervals

Size Tolerances in Shoring

Perfect accuracy is impossible, so standards define acceptable tolerances. Moreover, tolerances tell the technician when to correct and when to accept.

Typical tolerances include:

Dimensions – ±5 mm to ±10 mm for most members.
Plumbness – not more than 1 in 500, or as specified.
Level – ±5 mm over a 3 m length.
Angle of rakers – within 5 degrees of the design angle.
Bearing length – full contact with the sole plate or wall plate.

Always check the project specification, because tolerances vary with the member and the standard applied.

Getting the Details Right: Step-by-Step

Accurate shoring results from a sequence of checks. Therefore, follow these steps for every shore.

Step 1: Extract Dimensions from the Drawing

First, read all dimensions from the design or working drawing. Note spans, heights, angles, and member sizes. Moreover, record any special notes on bearing or fixing.

Step 2: Convert Design Sizes to Cutting Sizes

Next, convert design sizes to cutting sizes. Allow for bearing lengths, laps, and joint details. Furthermore, subtract for any rebates or notches.

Step 3: Cut Members Accurately

Then, measure and mark each member before cutting. Use a try square to mark right angles. Moreover, cut on the waste side of the line so the finished size stays correct.

Step 4: Check Angles Before Installation

Raker shores must sit at the correct angle. Therefore, set out the angle on the ground before cutting. In addition, check the angle with a sliding bevel or protractor.

Step 5: Check Plumbness and Level During Installation

During installation, check plumbness with a plumb bob or spirit level. Moreover, check levels at the base and at the point of contact. Correct any error before tightening braces.

Step 6: Check Bearing and Contact

Confirm that each member bears fully on its support. In addition, check that wall plates contact the wall evenly. Consequently, the load distributes without local crushing.

Step 7: Record and Verify

Finally, record the checked dimensions. Where the specification requires it, obtain verification before loading.

Factors That Affect Shoring Dimensions

Several factors influence the final size of shoring members. Therefore, technicians must allow for each one.

Deflection under load – members bend, so stiffness matters.
Joint thickness – wedges and packing add to the overall size.
Moisture – timber swells when wet, so allow for expansion.
Temperature – heat and cold affect steel and timber dimensions slightly.
Ground settlement – the base may settle, so re-check after loading.
Wall movement – the structure may shift, so monitor with crack gauges.

Common Mistakes with Shoring Shapes and Sizes

Many shoring failures trace back to simple dimensional errors. Therefore, avoid the following common mistakes.

Confusing span with member length.
Setting rakers outside the 30 to 60 degree range.
Cutting on the wrong side of the line.
Neglecting to check depth and width ratios for flying shores.
Ignoring specified tolerances.
Failing to allow for bearing lengths.
Using undersized members for the load.
Failing to check plumbness after tightening.
Making changes on site without approval.

Shoring Shape and Size Checklist

Before loading, confirm the following items.

□ Span and height match the drawing
□ Raker angle is between 30 and 60 degrees
□ Wall contact is at two-thirds height
□ Flying shore depth and width ratios are correct
□ Needle pockets and bearing lengths are correct
□ Member sizes match the design
□ Plumbness is within tolerance
□ Levels are correct at base and contact
□ Bearing is full and even
□ Wedges and jacks are tight
□ Bracing and lacing are complete
□ Inspection is recorded

Conclusion

Shoring shapes and sizes decide whether a support system fits the structure and carries the load safely. When technicians extract dimensions correctly, set the right angles, and check plumbness, level, and bearing, they produce accurate work.

Moreover, tolerances exist for a reason. Therefore, technicians should check against them and correct errors before loading. As a result, shoring performs reliably, and structures remain stable throughout the work.

Frequently Asked Questions

What angle should raker shores be installed at?

Raker shores should sit at an angle between 30 and 60 degrees. Exceeding these limits places excessive pressure on other shoring components and may cause failure.

Where should raker shores contact the wall?