+---
+title: Site Grading and Subgrade Preparation
+category: Sitework
+toc_depth: 3
+description: >
+ When to use: Rough and finish grading of site surfaces — building pads, pavement subgrades, lawn and landscape areas, swales, berms, and drainage courses — from completion of mass earthwork through final subgrade preparation ready to receive aggregate base, slab-on-grade, pavement, or topsoil. Covers topsoil stripping and stockpiling, cut/fill grading to design contours, proof-rolling, scarification and recompaction, moisture conditioning, select/structural fill under building pads, and fine grading to trade tolerances on commercial, institutional, industrial, and residential projects.
+ Not intended for: Mass earthwork and cut/fill haul (sync/earthwork); aggregate base over prepared subgrade (sync/aggregate-base-course); clearing and grubbing (sync/site-clearing); erosion and sediment controls during grading (sync/erosion-and-sediment-control); chemical or geosynthetic soil modification as the primary strategy (sync/soil-stabilization); cast-in-place site concrete on the subgrade (sync/site-concrete-structures); under-slab vapor barriers (sync/vapor-barriers-under-slab).
+---
+
+# Scope {toc}
+
+## This standard covers grading and subgrade preparation of site surfaces from the completion of mass earthwork through delivery of a tested, accepted subgrade ready to receive aggregate base, slab-on-grade, pavement, or topsoil. {note}
+
+## The work begins where bulk cut and fill has established approximate grade and ends at the subgrade surface that subsequent trades build on. {note}
+
+## Both rough grading (establishing design contours and elevations) and finish grading (trimming the subgrade to the tolerances required by the next trade) are included; some projects keep these as separate operations but this standard treats them as one continuous scope through subgrade acceptance. {note}
+
+## The Contractor shall strip and stockpile reusable topsoil before grading the areas beneath it.
+
+## The Contractor shall grade all site surfaces to the lines, grades, and contours shown on the drawings.
+
+## The Contractor shall scarify, moisture-condition, and recompact subgrade soils to the densities required for the surface they support.
+
+## The Contractor shall proof-roll the completed subgrade and correct soft or yielding areas before any base, slab, or pavement is placed.
+
+## The Contractor shall fine-grade finished surfaces to the tolerances of the trade that follows.
+
+## The following adjacent scopes are governed by separate standards and are excluded here: mass earthwork and cut/fill volumes [[sync/earthwork]], aggregate base course over the prepared subgrade [[sync/aggregate-base-course]], clearing and grubbing that precedes grading [[sync/site-clearing]], temporary erosion and sediment controls [[sync/erosion-and-sediment-control]], chemical or geosynthetic soil modification as a primary strategy [[sync/soil-stabilization]], cast-in-place site concrete on the subgrade [[sync/site-concrete-structures]], and under-slab vapor barriers [[sync/vapor-barriers-under-slab]]. {note}
+
+# Governing Documents {toc}
+
+## The project geotechnical report is the primary governing document for this work; it defines the soil zones, compaction criteria, moisture windows, over-excavation rules, and allowable bearing values for the specific site. {note}
+
+## Where the geotechnical report and this standard differ, the geotechnical report governs for soil-specific criteria and this standard governs for procedure, testing, and submittal requirements. {note}
+
+## The current geotechnical report shall be on site and available to the Contractor and the testing agency throughout grading operations.
+
+## The Contractor shall follow the recommendations of the geotechnical report as supplemented by these requirements.
+
+## The parameters stated in this standard are typical defaults for use when a project-specific geotechnical report has not yet established a value; they do not override a value set by the geotechnical engineer of record. {note}
+
+# Referenced Standards {toc}
+
+## Work shall comply with the latest adopted edition of each of the following unless a specific edition is cited or the geotechnical report pins a different edition.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the geotechnical engineer of record directs otherwise in writing.
+
+| Standard | Title |
+|----------|-------|
+| ASTM D698 | Laboratory Compaction Characteristics of Soil Using Standard Effort |
+| ASTM D1557 | Laboratory Compaction Characteristics of Soil Using Modified Effort |
+| ASTM D1556/D1556M | Density and Unit Weight of Soil in Place by Sand-Cone Method |
+| ASTM D6938 | In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth) |
+| ASTM D2216 | Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass |
+| ASTM D4318 | Liquid Limit, Plastic Limit, and Plasticity Index of Soils |
+| ASTM D2487 | Classification of Soils for Engineering Purposes (Unified Soil Classification System) |
+| AASHTO T 99 | Moisture-Density Relations of Soils Using a 2.5 kg Rammer and a 305 mm Drop |
+| AASHTO T 180 | Moisture-Density Relations of Soils Using a 4.54 kg Rammer and a 457 mm Drop |
+| AASHTO M 147 | Materials for Aggregate and Soil-Aggregate Subbase, Base, and Surface Courses |
+| ACI 117 | Specification for Tolerances for Concrete Construction and Materials |
+| IBC 2021 | International Building Code (Chapter 18, Soils and Foundations) |
+
+## ASTM D698 (Standard Proctor) and ASTM D1557 (Modified Proctor) define two different compaction efforts; a percent-of-maximum-dry-density requirement is meaningless unless the Proctor method is named. {note}
+
+## AASHTO T 99 and T 180 are the AASHTO equivalents of ASTM D698 and D1557 and apply where the authority having jurisdiction or a DOT controls access roads or parking that connect to the public right-of-way. {note}
+
+# Submittals {toc}
+
+## Action Submittals {toc}
+
+### The Contractor shall submit the following action items for review before grading begins:
+
+- Source, classification (ASTM D2487), and Atterberg limits (ASTM D4318) for any imported select or structural fill
+- Proctor curve (ASTM D698 or D1557, with method A/B/C identified) for each soil type to be compacted
+- Grading plan and sequence, including topsoil stripping limits and stockpile locations
+- Proposed compaction equipment for each soil type (vibratory, sheepsfoot/padfoot, pneumatic)
+- Manufacturer data and certification for any separation geotextile
+
+```datasheet
+label: Action Submittals
+type: checkbox
+options:
+ - Imported fill source, USCS classification, Atterberg limits
+ - Proctor curve per soil type (method identified)
+ - Grading plan and sequence
+ - Compaction equipment list
+ - Geotextile data and certification
+default:
+ - Imported fill source, USCS classification, Atterberg limits
+ - Proctor curve per soil type (method identified)
+ - Grading plan and sequence
+```
+
+## Informational Submittals {toc}
+
+### The Contractor shall submit the following informational items during the work:
+
+- Field density test reports (ASTM D6938 or D1556) for each lift and test location
+- Proof-rolling observation reports identifying any soft areas and corrective action taken
+- Over-excavation and replacement records where unsuitable material was removed
+- Subgrade acceptance documentation signed by the geotechnical engineer of record
+
+```datasheet
+label: Informational Submittals
+type: checkbox
+options:
+ - Field density test reports
+ - Proof-rolling observation reports
+ - Over-excavation and replacement records
+ - Subgrade acceptance documentation
+default:
+ - Field density test reports
+ - Proof-rolling observation reports
+ - Subgrade acceptance documentation
+```
+
+# Quality Assurance {toc}
+
+## Testing Agency {toc}
+
+### An independent geotechnical testing agency shall perform all compaction, moisture, and density testing.
+
+### The testing agency shall be engaged and paid by the Owner unless the Contract Documents assign that responsibility otherwise. {note}
+
+### The testing agency shall report results to the Owner, the geotechnical engineer of record, and the Contractor within the timeframe established at the preconstruction meeting.
+
+### Field density testing shall be performed by the nuclear method (ASTM D6938) or the sand-cone method (ASTM D1556).
+
+### The nuclear gauge shall be correlated to the sand-cone method when results are disputed or when the geotechnical engineer requires verification. {note}
+
+## Subgrade Approval {toc}
+
+### The geotechnical engineer of record shall approve the prepared subgrade before any aggregate base, slab, or pavement is placed over it.
+
+### Self-certification of subgrade acceptance by the Contractor in lieu of geotechnical engineer approval is not permitted; the approval is the Owner's quality-assurance checkpoint and may not be waived by the Contractor. {note}
+
+## Testing Frequency {toc}
+
+### Field density tests shall be taken at the frequency below, with at least one test per lift in each defined area and additional tests wherever the testing agency observes a change in material or compaction.
+
+```datasheet
+label: Field density test frequency — building pad subgrade
+type: select
+unit: SF per test per lift
+options:
+ - "2,500"
+ - "5,000"
+ - "10,000"
+default: "2,500"
+```
+
+```datasheet
+label: Field density test frequency — pavement subgrade
+type: select
+unit: SF per test per lift
+options:
+ - "2,500"
+ - "5,000"
+ - "10,000"
+default: "5,000"
+```
+
+```datasheet
+label: Field density test frequency — fill placement
+type: select
+unit: CY of fill per test
+options:
+ - "500"
+ - "1,000"
+ - "2,000"
+default: "1,000"
+```
+
+# Topsoil Stripping and Stockpiling {toc}
+
+## Topsoil is the organic-rich surface horizon; it is unsuitable as structural fill or subgrade but valuable for finish grading of landscaped areas, so it is stripped and preserved rather than mixed into the cut. {note}
+
+## The Contractor shall strip topsoil from all areas to be graded, filled, or paved before those operations begin.
+
+## Topsoil shall be stripped to the full depth of the organic horizon as encountered, not to a fixed nominal depth, where the horizon is deeper than the value below.
+
+## Topsoil shall not be intermixed with subsoil, unsuitable material, or debris during stripping or stockpiling.
+
+## Stockpiles shall be located clear of drainage courses, the building footprint, and traffic, and shall be protected from erosion in accordance with [[sync/erosion-and-sediment-control]].
+
+## Stockpile height shall be limited because piles that are too tall compact their own lower lifts, exclude oxygen, and kill the soil organisms that make topsoil valuable for reuse. {note}
+
+```datasheet
+label: Topsoil stripping depth (nominal; verify against actual organic horizon)
+type: range
+unit: in
+min: 4
+max: 12
+step: 1
+default: 6
+```
+
+```datasheet
+label: Maximum topsoil stockpile height
+type: range
+unit: ft
+min: 6
+max: 10
+step: 1
+default: 8
+```
+
+# Subgrade Soil Material {toc}
+
+## Native Soil Subgrade {toc}
+
+### Native subgrade is the in-place soil scarified, moisture-conditioned, and recompacted without import; it is the default where the geotechnical report confirms the native material is suitable. {note}
+
+### Native subgrade soils shall be free of organic matter, debris, frozen material, and particles larger than permitted by the lift thickness and compaction equipment.
+
+### Native soils classified by ASTM D2487 as highly organic (PT) or as high-plasticity clay or silt (CH, MH) shall not be used as building pad subgrade unless the geotechnical report specifically accepts them.
+
+## Select and Structural Fill {toc}
+
+### Select granular fill is imported clean borrow used to replace over-excavated unsuitable native soil; structural fill is engineered fill placed in controlled lifts to build a building pad to design elevation. {note}
+
+### Imported select fill shall classify as GW, GP, SW, or SP by ASTM D2487 unless the geotechnical report accepts a different gradation.
+
+### Granular subbase fill shall meet the gradation and quality requirements of AASHTO M 147 where used as a working course or under pavement.
+
+### Structural fill shall be placed only on a subgrade that has been proof-rolled and accepted, and shall be the soil type and gradation specified in the geotechnical report.
+
+```datasheet
+label: Subgrade configuration
+type: radio
+options:
+ - Native soil — scarify, moisture-condition, recompact in place
+ - Select granular fill — over-excavate unsuitable native and replace
+ - Structural fill pad — engineered fill in controlled lifts to design elevation
+ - Geotextile-separated — separation fabric on soft native before granular working course
+default: Native soil — scarify, moisture-condition, recompact in place
+```
+
+```datasheet
+label: Imported select fill classification (ASTM D2487)
+type: checkbox
+options:
+ - "GW — well-graded gravel"
+ - "GP — poorly graded gravel"
+ - "SW — well-graded sand"
+ - "SP — poorly graded sand"
+default:
+ - "GW — well-graded gravel"
+ - "SW — well-graded sand"
+```
+
+## Geotextile Separation {toc}
+
+### A nonwoven separation geotextile is placed on a soft native subgrade before a granular working course to keep the soft soil from pumping up into and contaminating the granular layer. {note}
+
+### Where the geotechnical report requires it, separation geotextile shall be placed on the prepared native subgrade before the granular working course.
+
+### Geotextile shall be overlapped at all seams by the manufacturer's recommended lap, and not less than 12 in., on a prepared surface free of protruding stone or debris.
+
+```datasheet
+label: Separation geotextile required
+type: radio
+options:
+ - "Not required"
+ - "Required on soft native subgrade only"
+ - "Required across full building pad"
+ - "Required across full site"
+default: "Not required"
+```
+
+# Compaction Requirements {toc}
+
+## Compaction Standard {toc}
+
+### The Proctor method is the reference maximum dry density against which field density is measured; naming it (D698 Standard vs. D1557 Modified) is mandatory because the two efforts yield different maximum densities for the same soil. {note}
+
+### When ASTM D1557 (Modified Proctor) is specified, the test method (A, B, or C) shall be identified because the method depends on maximum particle size and an unspecified method causes testing disputes. {note}
+
+### The compaction reference standard for each soil shall be as established by the geotechnical report.
+
+```datasheet
+label: Compaction reference standard
+type: radio
+options:
+ - "ASTM D1557 (Modified Proctor)"
+ - "ASTM D698 (Standard Proctor)"
+ - "AASHTO T 180 (Modified)"
+ - "AASHTO T 99 (Standard)"
+default: "ASTM D1557 (Modified Proctor)"
+```
+
+```datasheet
+label: Modified Proctor test method (when D1557 specified)
+type: radio
+options:
+ - "Method A"
+ - "Method B"
+ - "Method C"
+default: "Method C"
+```
+
+## Required Density by Zone {toc}
+
+### Compaction shall be specified by zone rather than as a single site-wide value; a uniform high value over-compacts landscape soil so plants cannot establish, while a single low value under-protects the building pad against settlement. {note}
+
+### The building pad subgrade shall be compacted to the percentage of maximum dry density below over the depth specified by the geotechnical report, typically the top 12 in.
+
+### The pavement subgrade shall be compacted to the percentage of maximum dry density below over its upper layer, typically the top 6 in.
+
+### Landscaped and other non-structural areas shall be compacted to the lower percentage below so as not to inhibit plant establishment.
+
+```datasheet
+label: Building pad subgrade compaction (% of max dry density)
+type: range
+unit: "%"
+min: 90
+max: 100
+step: 1
+default: 95
+```
+
+```datasheet
+label: Pavement subgrade compaction (% of max dry density)
+type: range
+unit: "%"
+min: 90
+max: 100
+step: 1
+default: 95
+```
+
+```datasheet
+label: Landscaped / non-structural area compaction (% of max dry density)
+type: range
+unit: "%"
+min: 85
+max: 95
+step: 1
+default: 90
+```
+
+## Moisture Conditioning {toc}
+
+### Soil compacted dry or wet of optimum moisture cannot reach its maximum dry density and settles later; the specification must state an acceptable moisture window and require correction by wetting or aeration when soil falls outside it. {note}
+
+### Subgrade and fill soils shall be moisture-conditioned to within the window below of optimum moisture content (ASTM D2216) at the time of compaction.
+
+### Soil that is too wet shall be aerated, disked, or dried, and soil that is too dry shall be uniformly wetted and mixed, before compaction proceeds.
+
+```datasheet
+label: Moisture window — cohesive soils (relative to optimum)
+type: range
+unit: "% of optimum"
+min: -3
+max: 4
+step: 1
+default: 0
+setpoints: [-2, 2]
+```
+
+```datasheet
+label: Moisture window — granular soils (relative to optimum)
+type: range
+unit: "% of optimum"
+min: -3
+max: 3
+step: 1
+default: 0
+setpoints: [-3, 3]
+```
+
+## Lift Thickness {toc}
+
+### Loose lift thickness is limited so the compaction equipment's energy reaches the bottom of the lift; granular soil with a vibratory roller tolerates thicker lifts than cohesive soil compacted with a sheepsfoot or padfoot roller. {note}
+
+### Fill shall be placed in horizontal loose lifts not exceeding the thickness below for the soil type and compaction equipment, and each lift shall be compacted and accepted before the next is placed.
+
+```datasheet
+label: Maximum loose lift thickness — granular fill (vibratory roller)
+type: range
+unit: in
+min: 6
+max: 12
+step: 1
+default: 8
+```
+
+```datasheet
+label: Maximum loose lift thickness — cohesive fill (sheepsfoot/padfoot roller)
+type: range
+unit: in
+min: 6
+max: 8
+step: 1
+default: 6
+```
+
+# Subgrade Preparation {toc}
+
+## Scarification and Recompaction {toc}
+
+### Scarifying the exposed subgrade and recompacting it removes the loose, disturbed surface left by earthwork and gives a uniform density at the top of the subgrade, which is where settlement matters most. {note}
+
+### The exposed subgrade shall be scarified to a uniform depth, moisture-conditioned, and recompacted to the required density for its zone before fill or surfacing is placed.
+
+```datasheet
+label: Scarification depth before recompaction
+type: range
+unit: in
+min: 6
+max: 12
+step: 1
+default: 8
+```
+
+## Benching of Fill Slopes {toc}
+
+### Where fill is placed against an existing slope, the slope is cut into level steps (benches) so the new fill keys into the old ground instead of sliding along a smooth inclined contact. {note}
+
+### Fill placed against existing slopes steeper than the value below shall be benched into the existing ground in level steps as the fill is brought up.
+
+```datasheet
+label: Existing slope steeper than this requires benching (H:V)
+type: select
+options:
+ - "5H:1V"
+ - "4H:1V"
+ - "3H:1V"
+default: "5H:1V"
+```
+
+## Over-Excavation and Replacement {toc}
+
+### When proof-rolling or density testing reveals unsuitable material below grade, the depth of over-excavation and the acceptable replacement material must be defined in advance, or every soft spot becomes a change order and an RFI. {note}
+
+### Where unsuitable material is identified, the Contractor shall over-excavate to the depth directed by the geotechnical engineer and replace it with compacted select or structural fill.
+
+### Over-excavated areas shall be proof-rolled at the base of excavation before replacement fill is placed.
+
+### Where native soils across the site are uniformly poor and chemical or mechanical modification is the primary remedy, that work shall be performed under [[sync/soil-stabilization]] rather than specified inline here, to avoid contradictory requirements. {note}
+
+# Proof Rolling {toc}
+
+## Proof-rolling drives a heavy loaded truck over the completed subgrade to find soft or yielding areas that lift-by-lift density testing can miss; it is performed after mass earthwork is complete and before base or slab placement. {note}
+
+## The completed subgrade shall be proof-rolled in the presence of the testing agency or geotechnical engineer before any base, slab, or pavement is placed.
+
+## Proof-rolling shall use a loaded tandem-axle dump truck of the gross vehicle weight below, making at least the number of passes below in a pattern that covers the full area.
+
+## Areas that rut, pump, or deflect more than the depth below under a loaded wheel shall be over-excavated and replaced or otherwise corrected as directed by the geotechnical engineer.
+
+```datasheet
+label: Proof-roll vehicle gross weight
+type: range
+unit: ton GVW
+min: 20
+max: 25
+step: 1
+default: 20
+```
+
+```datasheet
+label: Proof-roll minimum passes
+type: range
+unit: passes
+min: 2
+max: 4
+step: 1
+default: 2
+```
+
+```datasheet
+label: Rut depth triggering over-excavation
+type: range
+unit: in
+min: 0.5
+max: 1.5
+step: 0.25
+default: 1
+```
+
+# Finish Grading and Tolerances {toc}
+
+## Finish grading trims the accepted subgrade to the elevation and smoothness the next trade needs; tolerances differ by surface because a building pad, a paved subgrade, and a lawn each have different downstream sensitivity. {note}
+
+## Finished surfaces shall be graded to the tolerances below, measured against the project surveyor's benchmark.
+
+## Where the civil drawing tolerance and the ACI 117 tolerance for soil immediately below a slab-on-ground conflict, the tighter tolerance governs below the slab and the structural slab specification shall be checked to confirm which applies. {note}
+
+## The finished subgrade shall be free of ruts, humps, depressions, and loose material at the time it is handed off to the next trade.
+
+```datasheet
+label: Building pad subgrade tolerance
+type: range
+unit: ft
+min: 0.05
+max: 0.10
+step: 0.01
+default: 0.10
+```
+
+```datasheet
+label: Pavement subgrade tolerance
+type: range
+unit: ft
+min: 0.03
+max: 0.10
+step: 0.01
+default: 0.05
+```
+
+```datasheet
+label: Lawn / landscape area tolerance
+type: range
+unit: ft
+min: 0.05
+max: 0.15
+step: 0.01
+default: 0.10
+```
+
+```datasheet
+label: Subgrade tolerance immediately below slab-on-ground (ACI 117)
+type: radio
+options:
+ - "± 3/4 in."
+ - "± 1/2 in."
+ - "± 1 in."
+default: "± 3/4 in."
+```
+
+# Drainage and Slopes {toc}
+
+## Positive drainage on the finished subgrade prevents water from ponding against structures and soaking the subgrade before it is covered; minimum grades are set so even survey tolerance does not create a flat or reverse slope. {note}
+
+## The finished subgrade shall slope away from buildings at not less than the minimum grade below.
+
+## All graded surfaces shall maintain at least the absolute minimum positive grade below so that no area ponds water.
+
+## Swales, berms, and drainage courses shall be graded to the lines and inverts shown; their alignment and extent are coordinated on the drawings [[drawing: grading and drainage plan]].
+
+## Unretained fill side slopes shall not be steeper than the maximum below unless a flatter slope is required by the geotechnical stability analysis.
+
+```datasheet
+label: Minimum grade away from building (finished pad subgrade)
+type: range
+unit: "%"
+min: 1
+max: 3
+step: 0.5
+default: 2
+```
+
+```datasheet
+label: Absolute minimum positive grade (any graded surface)
+type: range
+unit: "%"
+min: 0.5
+max: 2
+step: 0.5
+default: 1
+```
+
+```datasheet
+label: Maximum unretained fill side slope (H:V)
+type: select
+options:
+ - "2H:1V"
+ - "2.5H:1V"
+ - "3H:1V"
+default: "2H:1V"
+```
+
+# Bearing and Pavement Design Inputs {toc}
+
+## Allowable bearing pressure and subgrade modulus are design inputs the geotechnical report provides; the values below are presumptive defaults (IBC 2021 Table 1806.2 lists presumptive bearing values) for use only until the report establishes site-specific numbers. {note}
+
+## The prepared building pad subgrade shall provide the allowable bearing pressure required by the foundation design, as confirmed by the geotechnical engineer.
+
+## The prepared pavement subgrade shall provide the subgrade modulus (k-value) assumed in the pavement design.
+
+```datasheet
+label: Minimum allowable bearing pressure — light commercial pad (presumptive)
+type: range
+unit: psf
+min: 1500
+max: 3000
+step: 250
+default: 2000
+```
+
+```datasheet
+label: Design subgrade modulus (k-value) — prepared granular subgrade
+type: range
+unit: pci
+min: 100
+max: 200
+step: 25
+default: 125
+```
+
+# Subgrade Protection {toc}
+
+## A subgrade that is fine-graded and accepted can still be ruined if construction traffic from other trades ruts or remolds it, especially in wet weather; the specification has to limit traffic or call for a protective course. {note}
+
+## The Contractor shall protect the accepted subgrade from construction traffic, ponding water, and weather until it is covered by the next layer.
+
+## Construction traffic shall be kept off the finished subgrade, or routed over a granular working course or geotextile-separated layer where traffic cannot be avoided.
+
+## Subgrade that is rutted, remolded, softened, or otherwise disturbed after acceptance shall be reworked, recompacted, and re-tested at the Contractor's expense before the next layer is placed.
+
+```datasheet
+label: Subgrade protection method
+type: radio
+options:
+ - "Traffic limitation only — keep equipment off finished subgrade"
+ - "Granular working course over finished subgrade"
+ - "Geotextile separation plus granular working course"
+default: "Traffic limitation only — keep equipment off finished subgrade"
+```
+
+# Cold Weather and Frozen Ground {toc}
+
+## Frozen soil cannot be compacted to a stable density and thaws to a soft, weak condition, so it is excluded as both a working surface and a fill material. {note}
+
+## Fill shall not be placed on frozen subgrade.
+
+## Frozen soil shall not be used as fill.
+
+## Subgrade that has frozen after acceptance shall be allowed to thaw, then re-proof-rolled and re-tested before the next layer is placed.