Grading, Leveling, and Compaction

Levelling, Grading, and Compaction

Chapter Introduction

This chapter covers the essential skills of the tractor-loader-backhoe (TLB) operator in levelling, grading, and compaction. These operations are the core of the trade and are thoroughly assessed on the Red Seal exam. You must master not only the technical movements, but also the physical principles, slope calculations, and Canadian standards that govern this work. This chapter is structured to follow the logical progression of a job site: preparation, execution, verification, and correction.

1. Fundamental Principles of Levelling

1.1 Key Definitions

Levelling is the operation that gives the ground a flat surface or a specified slope. The following distinctions are made:

Rough levelling: first pass to remove excess soil or fill depressions. Typical tolerance of ±50 mm.

Fine levelling: final pass to achieve the required precision. Typical tolerance of ±10 mm.

Grading: the action of making a surface horizontal (0% slope).

Cross slope: inclination perpendicular to the axis of the road or structure, expressed as a percentage.

Longitudinal slope: inclination along the length, also expressed as a percentage.

1.2 The Reference System: The Benchmark

The benchmark (BM) is a fixed point whose elevation is precisely known. It is typically installed by a land surveyor and marked by a permanent reference point (nail, monument, marker). On a job site, you must:

15.Locate the BM before any levelling work.

16.Protect the BM from damage caused by machinery.

17.Never move the BM without written authorization from the site supervisor.

Levelling readings are taken using an optical or digital level. The fundamental formula is:

Elevation of target point = BM elevation + Backsight − Foresight

Where:

Backsight: reading on the level rod placed on the BM.

Foresight: reading on the level rod placed on the point to be determined.

1.3 Calculating Slopes

Slope is expressed as a percentage (%) and is calculated as follows:

Slope (%) = (Elevation difference / Horizontal distance) × 100

Example: for a 2% slope over a distance of 25 m, the elevation difference is:

Elevation difference = 2% × 25 m = 0.02 × 25 = 0.50 m

The following table gives elevation differences for various slopes and distances:

Slope (%)	Distance 10 m	Distance 20 m	Distance 30 m	Distance 50 m
0.5%	0.05 m	0.10 m	0.15 m	0.25 m
1%	0.10 m	0.20 m	0.30 m	0.50 m
2%	0.20 m	0.40 m	0.60 m	1.00 m
3%	0.30 m	0.60 m	0.90 m	1.50 m
5%	0.50 m	1.00 m	1.50 m	2.50 m

Golden rule: a 1% slope corresponds to an elevation difference of 10 mm per metre. This quick conversion is frequently used in exam calculations.

1.4 Levelling Instruments

The TLB operator must know how to use:

The optical level: an instrument fixed on a tripod, providing a horizontal reference plane.

The graduated level rod: a rod graduated in metres and centimetres, held vertically on the point to be measured.

The laser level: emits a horizontal or inclined plane detectable by a receiver cell mounted on the blade or bucket. It enables continuous automated levelling.

The hand level: a compact instrument for quick checks.

Exam trap: the rotating laser level emits a reference plane, but the receiver cell must be calibrated relative to the blade position. A calibration error of 5 mm on the cell translates to a 5 mm error over the entire levelled surface.

2. Levelling Techniques with the Tractor-Loader-Backhoe

2.1 Machine and Site Preparation

Before any levelling operation:

42.Check tire condition: uneven pressure (±10 kPa between the rear tires) will affect levelling accuracy.

43.Inspect the bucket: wear on the teeth and cutting edge affects precision. Worn teeth create grooves.

44.Check the linkages: play in the boom and bucket pins causes height variations.

45.Determine the direction of work: levelling is generally done in reverse with the bucket, or in forward gear with the blade if the machine is equipped with one.

46.Water the soil if necessary: dry, dusty soil reduces the visibility of reference marks.

2.2 Bucket Levelling (Basic Technique)

The bucket levelling technique is the most common for the TLB:

49.Initial position: the bucket is slightly tilted forward (attack angle of approximately 15° to 20°).

50.Lowering the bucket: lower the bucket until the cutting edge touches the ground at the starting point.

51.Depth adjustment: use the lift lever to control the cutting depth. The recommended maximum cutting depth is 50 to 75 mm per pass for fine levelling.

52.Movement: move forward at a constant speed (2 to 4 km/h). Excessive speed creates waves; overly slow speed leaves humps.

53.Visual control: observe the bucket edge and the ground behind the machine to detect irregularities.

54.Dumping: when the bucket is full, transport the soil to the disposal area or truck.

Professional tip: for precise levelling, use the float function on the hydraulic control valve. This function allows the bucket to follow the ground contour without the operator constantly correcting the height.

2.3 Sloped Levelling

For sloped surfaces (roads, sidewalks, ditches):

58.Set up the laser level with the programmed slope (e.g., 2%).

59.Mount the receiver cell on the bucket arm.

60.Make a first pass to approximate the slope line.

61.Correct high and low areas by referring to the cell readings.

62.Verify with the level rod every 10 to 15 metres.

Caution: levelling a cross slope on terrain with a longitudinal slope requires a double correction. The laser must be programmed for the cross slope, and the operator must visually compensate for the longitudinal slope.

2.4 Precision Levelling (±10 mm Tolerance)

For finishing work (foundations, slabs, sidewalks):

66.Use the bucket float mode.

67.Reduce the cutting depth to 10-20 mm per pass.

68.Work back and forth with successive passes overlapping by 50%.

69.Check with the 3 m straightedge: place the straightedge on the surface; the maximum gap under the straightedge must not exceed 10 mm.

70.Correct high spots with the bucket in a scraping position (attack angle of 5° to 10°).

3. Compaction

3.1 Physical Principles of Compaction

Compaction is the operation that increases soil density by reducing voids between particles. It improves:

Bearing capacity (ability to support loads).

Stability (resistance to deformation).

Impermeability (reduced water infiltration).

Maximum dry density (MDD) is the highest density a soil can achieve for a given moisture content. It is determined by the modified Proctor test (ASTM D1557) or the standard Proctor test (ASTM D698).

Optimum moisture content (OMC) is the moisture content at which the MDD is achieved. Compaction must be performed at a moisture content close to the OMC, generally between OMC − 2% and OMC + 1%.

3.2 The Proctor Test: Essential Concepts

The Proctor test involves compacting a soil sample in a standardized mould, with a specified compaction energy, at different moisture contents. The compaction curve (dry density as a function of moisture content) is then plotted.

Parameter	Standard Proctor (ASTM D698)	Modified Proctor (ASTM D1557)
Compaction energy	600 kN·m/m³	2700 kN·m/m³
Hammer mass	2.5 kg	4.54 kg
Drop height	305 mm	457 mm
Number of layers	3	5
Blows per layer	25	25
Typical use	Backfill, light foundations	Roads, dams, heavy structures

Typical site requirement: compaction must achieve 95% of the MDD (modified Proctor) for backfill under foundations, and 98% for road base layers.

3.3 Degree of Compaction

The degree of compaction (or compaction percentage) is calculated as follows:

Degree of compaction (%) = (Field dry density / Maximum dry density) × 100

Example: if the MDD is 2.10 t/m³ and the field dry density measured is 2.00 t/m³, the degree of compaction is:

Degree = (2.00 / 2.10) × 100 = 95.2%

This result satisfies the 95% requirement but not the 98% requirement.

3.4 Compaction Methods

For a TLB, compaction is mainly done with:

Vibratory plate compactor: for confined areas (trenches, foundations). Maximum layer thickness of 150 to 200 mm.

Vibratory roller compactor: for large surfaces. Layer thickness of 200 to 300 mm.

Sheepsfoot compactor: for cohesive soils (clays). Layer thickness of 200 to 250 mm.

The TLB can also be used with a plate compactor mounted on the arm for narrow trenches.

3.5 Layer Thickness and Number of Passes

The following table provides general recommendations:

Soil Type	Layer Thickness (mm)	Number of Passes (vibratory plate)	Number of Passes (vibratory roller)
Sand and gravel	200-300	2-3	3-4
Silt	150-200	3-4	4-5
Clay	150-200	4-5	5-6
Organic soil	Not compactable	—	—

Important rule: each layer must be compacted before placing the next layer. Compacting a thick 600 mm layer in a single pass is ineffective and is a common error.

3.6 Compaction Control

Compaction control is performed using:

102.Sand cone test (ASTM D1556): reference method, destructive.

103.Rubber balloon densitometer test (ASTM D2167): alternative reference method.

104.Nuclear test (ASTM D6938): rapid, non-destructive method, but requires calibration.

105.Dynamic cone penetrometer test: indirect method, used for rapid checks.

Testing frequency: generally one test per 500 m² of compacted surface, or one test per 150 m³ of backfill, depending on contract specifications.

3.7 Trench Compaction

Trench compaction (for water supply, sewer lines, etc.) is a special case:

109.Initial backfill: up to 300 mm above the pipe, compacted by hand or with a light vibratory plate to avoid damaging the pipe.

110.Intermediate backfill: in 150 to 200 mm layers, compacted with a vibratory plate.

111.Final backfill: up to the surface, compacted in 200 to 300 mm layers.

Typical requirement: the degree of compaction must be 95% of the MDD (standard Proctor) for trenches under roads, and 90% for trenches off-road.

4. Applicable Canadian Standards and Codes

4.1 Canadian Electrical Code, Part I

The Canadian Electrical Code, Part I (CE Code) governs the installation of underground conduits. Although it is an electrical code, it contains requirements related to excavation and backfilling of trenches for electrical conduits.

Rule 8-200 of the CE Code specifies the burial depth requirements for conduits. For example, conduits must be buried at a minimum depth of 600 mm below finished grade, unless otherwise specified. This depth influences the trench depth you must excavate and backfill.

4.2 CSA B149.1 — Natural Gas and Propane Installation Code

The CSA B149.1 standard (Natural Gas and Propane Installation Code) contains requirements for the installation of underground gas piping. The relevant clauses for the TLB operator include:

Clause 6.8: minimum burial depth for gas piping (generally 600 mm below finished grade).

Clause 6.9: trench backfilling — backfill must be free of stones, debris, and materials that could damage the pipe.

Clause 6.10: backfill compaction — backfill must be compacted to ensure uniform support of the pipe.

Exam point: backfill around a gas pipe must be placed in layers of 150 mm maximum and compacted manually or with light equipment up to 300 mm above the pipe.

4.3 CSA A3000 — Certification of Aggregates

The CSA A3000 standard (Certification of Aggregates) defines requirements for aggregates used in construction. Although this standard is primarily intended for aggregate producers, the TLB operator must know that:

Aggregates for backfill must conform to the specified gradation.

Organic matter content must be limited (generally less than 1%).

Aggregates must not contain sulphates in harmful quantities.

4.4 Civil Engineering Regulations (National Research Council Standards)

The National Research Council of Canada (NRC) publishes standards for civil engineering work, including:

NRC-CGSB 8.1: test methods for soil compaction.

NRC-CGSB 8.2: modified Proctor test.

These standards are frequently cited in construction specifications and exams.

5. Safe Work Procedures

5.1 Trench Safety

The Canada Occupational Health and Safety Regulations (COHSR) require that trenches deeper than 1.2 m be shored, shielded, or sloped. Key requirements:

Trenches from 1.2 m to 3 m: shoring or shielding mandatory, or sloping at a maximum angle of 45° (1:1 slope).

Trenches deeper than 3 m: shoring design by an engineer.

Access: a ladder or ramp must be available within 8 m of any worker in the trench.

Inspection: trenches must be inspected daily and after each rain or event that could affect stability.

5.2 Compaction Safety

Never stand on a running plate compactor.

Wear hearing protection (the noise of a vibratory compactor exceeds 90 dB(A)).

Check for buried utilities before compacting (a compactor can damage an unprotected pipe).

5.3 Levelling Safety

Never work under a suspended load.

Check machine stability on slopes (the TLB has a high centre of gravity).

Use seat belts and the rollover protective structure (ROPS) at all times.

6. Practical Calculations for the Exam

6.1 Calculating Backfill Volume

The volume of backfill required for a trench is calculated as follows:

Volume (m³) = Width (m) × Depth (m) × Length (m)

Example: a trench 0.6 m wide, 1.5 m deep, and 30 m long:

Volume = 0.6 × 1.5 × 30 = 27 m³

Swell factor: excavated soil occupies more volume than in-situ soil. The swell factor varies by soil type:

Soil Type	Swell Factor
Dry sand	1.10
Gravel	1.15
Topsoil	1.25
Clay	1.30
Rock	1.50

Thus, to backfill the 27 m³ trench, approximately 27 × 1.25 = 33.75 m³ of loose topsoil will be required.

6.2 Calculating the Number of Compaction Passes

The number of passes required to achieve the specified degree of compaction depends on:

Layer thickness.

Soil type.

Compactor type.

Moisture content.

As a general rule, successive passes are made until the density increase between two consecutive passes is less than 1%. This method is called the density increment method.

6.3 Calculating a Ditch Slope

For a drainage ditch with a longitudinal slope of 0.5% over a length of 80 m:

Elevation difference = 0.005 × 80 = 0.40 m

The ditch bottom must therefore drop 400 mm over the 80 m length.

7. Pitfalls to Avoid

Here are the most frequent errors on the Red Seal exam on this topic:

174.Confusing slope and elevation difference: slope is a ratio (percentage), while elevation difference is a vertical distance (in metres). Never mix them in calculations.

175.Forgetting the swell factor: the volume of soil to be transported is not equal to the trench volume. Always apply the swell factor.

176.Neglecting moisture content: compacting soil that is too dry or too wet will not achieve the required density. Moisture content must be close to the OMC.

177.Compacting in a single thick layer: compaction energy does not penetrate sufficiently into thick layers. Respect the maximum thicknesses indicated.

178.Ignoring CE Code and CSA B149.1 requirements: burial depths and backfilling methods are regulated. Do not treat them as suggestions.

179.Confusing standard Proctor and modified Proctor: the compaction energy differs by a factor of 4.5. Compaction requirements (95% or 98%) always refer to a specific test.

180.Forgetting the final verification: after levelling, always check with a 3 m straightedge and a level. A surface that appears flat to the naked eye may have deviations of 30 mm.

181.Working without a reference point: never begin levelling without having identified the BM and reference points. A 10 mm reading error multiplies over the entire surface.

182.Underestimating the importance of compaction under pipes: poorly compacted backfill under a pipe causes differential settlement and pipe failure.

183.Not accounting for TLB reach: the TLB has a limited reach (approximately 4 to 5 m for the backhoe). For large surfaces, use a bulldozer or motor grader.

8. Summary

Concept	Key Point
Levelling	Operation to achieve a flat or sloped surface. Tolerance: ±50 mm (rough), ±10 mm (fine).
Benchmark (BM)	Fixed reference point of known elevation. Never move it.
Levelling formula	Target elevation = BM elevation + Backsight − Foresight.
Slope calculation	Slope (%) = (Elevation difference / Distance) × 100. 1% = 10 mm/m.
Compaction	Increasing soil density by reducing voids.
Proctor test	Determines maximum dry density and optimum moisture content.
Degree of compaction	(Field dry density / MDD) × 100. Requirement: 95% or 98% depending on use.
Layer thickness	150-300 mm depending on soil type and equipment.
CE Code, Rule 8-200	Minimum burial depth for electrical conduits: 600 mm.
CSA B149.1, Clauses 6.8-6.10	Gas pipe depth, backfilling, and compaction.
Swell factor	1.10 (sand) to 1.50 (rock). Apply to calculate the volume of soil to transport.
Trench safety	Trenches > 1.2 m: shoring, shielding, or sloping mandatory.

Key points to remember for the exam:

188.Master the levelling formula and slope calculations. These questions appear regularly.

189.Know the difference between standard Proctor and modified Proctor, and the associated compaction requirements.

190.Memorize the minimum burial depths from the CE Code (600 mm) and CSA B149.1 (600 mm).

191.Always apply the swell factor in volume calculations.

192.Respect maximum layer thicknesses for compaction.

193.Check moisture content before compacting: it must be close to the OMC.

194.Use the 3 m straightedge to verify flatness after fine levelling.

195.Never neglect trench safety: shoring, shielding, or sloping depending on depth.

This chapter covers all the theoretical and practical knowledge required to succeed on the exam questions on levelling, grading, and compaction. Carefully review the sections on Canadian standards and calculations, as they form the basis of the long-answer questions. Good luck with your preparation!