This specification covers the materials, execution, testing, and quality control for all earthwork operations on the project site. Earthwork is the first construction scope to begin and the last to be fully closed out — it directly conditions every subsequent scope, from foundations and utilities to paving and landscaping. Errors in earthwork, particularly inadequate compaction or failure to honor geotechnical recommendations, propagate forward through the project as structural distress, settlement, utility misalignment, pavement failure, and warranty claims. The investment in doing earthwork correctly is always less than the cost of remediation.
This standard addresses site clearing and demolition of existing improvements, cut and fill grading operations, excavation by type and purpose, classification of materials encountered, fill and backfill materials and placement, compaction requirements, subgrade preparation, groundwater management and dewatering, temporary excavation support, and erosion and sediment control throughout the construction period. All work shall conform to the recommendations of the geotechnical investigation report prepared for this project, and in cases of conflict between this standard and the geotechnical report, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
The Contractor shall recognize that the geotechnical investigation report is based on a limited number of borings and test pits that characterize but do not fully describe the subsurface. Actual conditions encountered may differ from those reported. The Contractor shall promptly notify the Engineer of Record of any differing site condition that materially affects work under this specification, including unexpected groundwater, rock, soft or organic soils, buried utilities, obstructions, or contaminated materials not identified in the geotechnical report.
Coordinate work under this specification with Cast In Place Concrete for foundation bearing surface preparation and concrete placement over prepared subgrades, with Below Grade Waterproofing for backfill restrictions adjacent to waterproofed foundation walls, with Aggregate Base Course for subbase and base course work under pavements, and with Storm Drainage for pipe trench requirements and inlet protection.
Equipment, materials, testing, and execution shall comply with the latest adopted edition of the following standards. Where project documents, adopted codes, and referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard | Title |
|---|---|
| ASTM D698 | Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft³) |
| ASTM D1557 | Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft³) |
| ASTM D1556/D1556M | Standard Test Method for Density and Unit Weight of Soil in Place by Sand-Cone Method |
| ASTM D2167 | Standard Test Method for Density and Unit Weight of Soil in Place by the Rubber Balloon Method |
| ASTM D2216 | Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass |
| ASTM D2487 | Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) |
| ASTM D2488 | Standard Practice for Description and Identification of Soils (Visual-Manual Procedures) |
| ASTM D4318 | Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils |
| ASTM D6938 | Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth) |
| ASTM D7928 | Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis |
| ASTM C136/C136M | Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates |
| IBC Chapter 18 | Soils and Foundations (International Building Code, currently adopted edition) |
| OSHA 29 CFR 1926 Subpart P | Excavations (Safety and Health Regulations for Construction) |
| EPA NPDES CGP | Construction General Permit (National Pollutant Discharge Elimination System) |
| AASHTO T 99 | Standard Method of Test for Moisture-Density Relations of Soils Using a 2.5-kg Rammer and a 305-mm Drop |
| AASHTO T 180 | Standard Method of Test for Moisture-Density Relations of Soils Using a 4.54-kg Rammer and a 457-mm Drop |
The Contractor shall submit the following for the Engineer of Record's review prior to beginning work. Excavation and fill operations shall not proceed on any portion of the site until the submittals relevant to that portion are reviewed and returned. Submittal review does not relieve the Contractor of responsibility for compliance with contract documents.
Prior to substantial completion the Contractor shall provide the following:
The Owner shall retain a licensed geotechnical engineer of record to provide construction observation and materials testing services for earthwork. The geotechnical engineer shall observe subgrade conditions at the base of every foundation excavation before concrete or fill is placed, observe proof-rolling operations, evaluate any differing site condition reported by the Contractor, interpret the project geotechnical report in light of actual conditions, and direct adjustments to materials or procedures when warranted. The geotechnical engineer's authority to halt earthwork operations that do not conform to the recommendations of the geotechnical report is binding on the Contractor.
The Contractor shall designate a competent person as defined in OSHA 29 CFR 1926 Subpart P to be present at all excavation work exceeding 5 feet in depth. The competent person shall classify soils, evaluate excavation stability, inspect the excavation daily and after every rain event or other occurrence that could affect stability, and direct immediate corrective action when hazardous conditions are observed. The Contractor shall not substitute personnel without ensuring that the replacement meets the competent person qualification.
Where the adopted building code or the structural drawings require special inspection for earthwork, the Owner shall retain a special inspector approved by the Authority Having Jurisdiction. The special inspector shall perform periodic and continuous observation as required by the inspection program, document observations and test results, and report non-conformances to the Owner and to the Engineer of Record. Special inspection under the building code does not relieve the Owner's geotechnical engineer of record of the separate obligation described above.
Prior to beginning earthwork operations the Contractor shall participate in a pre-construction conference attended by the Contractor's superintendent responsible for earthwork, the Owner's geotechnical engineer of record, the Owner's special inspector, and the Engineer of Record. The conference shall review the geotechnical report recommendations, the compaction requirements and testing program, the excavation safety plan, the dewatering plan, the erosion and sediment control plan, the requirements for dealing with differing site conditions, and the lines of communication for field decisions.
Compaction testing frequencies shall conform to the geotechnical engineer's recommendations. In the absence of project-specific direction, minimum testing frequencies shall be as follows: one test per 2,500 square feet of fill surface per lift for areas under footings, slabs, and pavements; one test per 100 linear feet of trench per lift for utility trenches; and one test per 500 square feet of fill surface per lift for general site grading not within a building footprint. The geotechnical engineer shall increase testing frequency in areas showing variability or failing tests.
Modified Proctor (ASTM D1557) shall be used for structural fill under foundations, floor slabs, and pavements, and for all trench backfill under or adjacent to structures. Standard Proctor (ASTM D698) may be used for general site grading, landscaped areas, and non-structural fill remote from buildings and utilities. When in doubt, use Modified Proctor — specifying the wrong test method is one of the most common earthwork errors. A compaction result referenced against the wrong Proctor value is meaningless.
The nuclear gauge method (ASTM D6938) is the standard production testing method because it is fast and non-destructive, allowing the same location to be re-tested after additional compaction effort if the first test fails. The sand cone method (ASTM D1556/D1556M) is the reference method for calibration and for locations where nuclear gauge use is restricted or impractical. The testing technician shall perform gauge count standard checks at the beginning and end of each testing session in accordance with ASTM D6938.
All soils encountered during excavation and all imported fill materials shall be classified in accordance with ASTM D2487, using the Unified Soil Classification System (USCS). Visual identification in the field shall conform to ASTM D2488. Where the geotechnical engineer determines that laboratory testing is needed to confirm field classification, tests shall include gradation per ASTM C136/C136M and ASTM D7928, and Atterberg limits per ASTM D4318. USCS classification governs the acceptability of materials for specific fill applications as described below.
The USCS designation shall be recorded on all field logs, boring logs, and test pit logs. It is not sufficient to describe soils generically as "good," "bad," or "clay" — the USCS symbol (GW, GP, GM, GC, SW, SP, SM, SC, ML, CL, MH, CH, OL, OH, PT) provides a precise, universally understood language that carries information about drainage, compressibility, and suitability for specific applications.
For payment and excavation planning purposes, materials encountered shall be classified as follows. The Contractor shall notify the Engineer of Record when material of a different classification than anticipated is encountered, before changing excavation methods.
Soil: Naturally occurring or previously placed earth material that can be excavated with conventional earthmoving equipment (hydraulic excavators, dozers, motor graders, scrapers) without blasting or special treatment. Includes clay, silt, sand, gravel, and mixtures thereof, and previously placed fill. Soil is the expected material for the majority of earthwork on most projects.
Soft Rock / Rippable Rock: Material that cannot be efficiently excavated with conventional earthmoving equipment but can be broken and removed by ripping with a heavy dozer-mounted ripper, or by hoe-ramming. Includes weathered or highly fractured rock, shale, hardpan, cemented gravels, and caliche. Classification requires judgment by the geotechnical engineer based on observed seismic velocity, rock quality designation, and equipment performance.
Rock: Solid material of mineral origin that cannot be excavated by ripping and requires drilling and blasting, hydraulic breaking, or other special methods for removal. Classification as rock shall be confirmed by the geotechnical engineer.
Unsuitable Material: Material that is unacceptable as a foundation bearing surface or as fill regardless of classification, including organic soils, topsoil, peat and muck, material with organic content by weight greater than 3 percent, frozen material, materials with liquid limit greater than 50 or plasticity index greater than 25 (unless specifically evaluated by the geotechnical engineer for a particular application), and materials with a swell potential that exceeds the bearing capacity design assumptions.
Topsoil is the upper zone of naturally occurring soil containing organic matter, root systems, and biological activity. Topsoil shall be stripped from all areas to be occupied by fills, structures, pavements, and utility trenches. Stripping depth shall be as indicated on the grading drawings or as directed by the geotechnical engineer in the field, typically 4 to 12 inches depending on site conditions.
Stripped topsoil shall be stockpiled separately from other excavated material for later use in landscaping and permanent vegetative stabilization, unless the geotechnical report indicates that site topsoil is unsuitable for reuse. Topsoil stockpiles shall be located outside of fill areas and drainage swales, protected from erosion with perimeter silt fence, and seeded or covered if stockpiled for more than 30 days.
Site clearing shall be performed within the limits as indicated on the site plan and demolition drawings. The Contractor shall stake clearing limits before beginning work and shall protect trees and vegetation designated for preservation with protective fencing installed at the drip line. No equipment shall operate, no material shall be stockpiled, and no soil shall be compacted within the drip line of trees designated for preservation.
Existing structures, pavements, curbs, walks, underground utilities, and other improvements within the work area shall be demolished and removed as shown on the drawings and as required for the work. The Contractor shall verify the locations of all underground utilities before demolition begins, using utility locates (one-call) and hand-digging as required within tolerance zones. Existing underground storage tanks, septic systems, wells, and similar structures shall be decommissioned and removed in accordance with applicable regulations before earthwork proceeds; the Contractor shall notify the Owner immediately if any previously unidentified underground storage tank or regulated structure is discovered.
Demolished concrete and masonry shall be removed from the site. Concrete rubble shall not be used as fill unless specifically approved in writing by the Engineer of Record, limited to applications where the material can be adequately compacted and tested, and prohibited beneath buildings and slabs.
The Contractor shall immediately notify the Owner and Engineer of Record upon discovery of any subsurface obstruction, buried structure, contaminated material, or other condition not shown on the contract documents. Work in the affected area shall be suspended until the Engineer of Record issues written direction. The Contractor shall not remove, disturb, or backfill around any discovered condition pending direction, except as required for immediate safety.
Excavation shall be performed to the lines, grades, and dimensions shown on the drawings or directed by the Engineer of Record, with the following tolerances unless otherwise noted: plus or minus 0.10 foot vertically for unformed excavation. Excavated material suitable for reuse as structural fill shall be stockpiled separately from unsuitable material and protected from contamination, precipitation, and excessive drying. All excavated material not to be reused shall be removed from the site and legally disposed.
The Contractor shall maintain all excavations in a dry condition and in a stable configuration. Standing water shall not be permitted in excavations at the time fill or concrete is placed. The bottom of all excavations shall be observed by the geotechnical engineer of record before placing fill, concrete, or other materials. The Contractor shall not proceed past the geotechnical engineer's observation without written authorization.
Mass grading operations remove soil and rock from areas to be lowered in elevation to achieve design grade, or strip and stockpile topsoil, or provide material for placement as fill elsewhere on the site. Cut areas shall be shaped to drain away from any exposed subgrade. Where cut slopes are required, temporary and permanent slope angles shall conform to the geotechnical report recommendations.
Temporary cut slopes shall be classified and designed in accordance with OSHA 29 CFR 1926 Subpart P, Appendix B. OSHA soil type classifications (Type A, B, C) are distinct from USCS classifications and are used specifically for determining safe temporary slope angles and excavation support requirements. The competent person shall determine the OSHA soil classification for every excavation based on visual and manual tests described in OSHA Appendix A.
Wet or overloaded cut slopes that begin to move or ravel shall be immediately brought to the attention of the competent person and the geotechnical engineer. The Contractor shall not allow personnel to work below an unstable cut slope.
Structural excavation is excavation performed to create space for foundations, pits, grade beams, retaining walls, and similar structures. Structural excavation shall be performed to the neat lines and grades shown on the structural drawings, plus working space required for forming and waterproofing.
Final trimming of the bearing surface at the bottom of structural excavation shall be performed by hand or by a smooth-bucket excavator, removing no more than necessary to achieve a clean, undisturbed bearing surface at the design elevation. Over-excavation of foundation bearing surfaces is a common and costly error — once the bearing stratum is loosened or saturated, it cannot be simply re-compacted to the same condition. If the bearing surface is inadvertently over-excavated, or if soft, loose, or otherwise unsuitable material is encountered at the bearing elevation, the geotechnical engineer shall be consulted before proceeding. Remedial options may include further over-excavation and replacement with lean concrete or compacted structural fill, subgrade improvement, or foundation redesign.
The bearing surface at the bottom of structural excavation shall be proof-rolled or probed by the geotechnical engineer before any concrete or fill is placed. Soft, yielding, or pumping areas shall be undercut and replaced. The Contractor shall provide the geotechnical engineer at least 24 hours notice before each bearing surface will be ready for observation.
Trench excavation serves utility installation, including water supply, sanitary sewer, storm drainage, electrical conduit, gas, and communications. Trench excavation shall conform to the alignment, depth, grade, and bedding requirements shown on the utility drawings.
Trench width shall be the minimum necessary for safe worker access and utility installation and bedding placement, but not less than the pipe outside diameter plus 12 inches on each side for pipes up to 24 inches in diameter. Unnecessarily wide trenches increase the volume of backfill and the potential for consolidation settlement. Trenches shall be excavated to stable, undisturbed material; where unstable trench bottom conditions are encountered, the geotechnical engineer shall evaluate the need for over-excavation and replacement with crushed stone or other suitable material.
Trench sidewalls shall be stable during the time workers are in the trench. Every trench 5 feet or deeper shall have a protective system as required by OSHA 29 CFR 1926 Subpart P. The Contractor shall not permit workers in an unprotected trench 5 feet or deeper for any reason, including hand trimming, pipe laying, or inspection.
Where excavation extends below the groundwater table, the Contractor shall manage groundwater by dewatering as described in the dewatering section of this specification. Excavation into groundwater without effective dewatering causes piping, boiling, and bottom heave that destroys the integrity of the bearing surface and is an immediate safety hazard. The Contractor shall not allow workers in an excavation where active groundwater inflow is occurring and the bottom is not stable.
Stockpiles of excavated material shall be located at least 2 feet from the edge of any excavation for stockpiles less than 5 feet high, and farther for taller stockpiles, to prevent surcharge-induced slope failure into the excavation. Stockpile heights shall not exceed the maximum for the soil type unless the geotechnical engineer approves a higher stockpile with appropriate side slopes. Stockpiles shall be protected from excessive drying, wetting, or freezing that would render the material unsuitable for its intended reuse.
All excavations 5 feet or deeper shall be protected by a sloping/benching system or a support system designed to prevent cave-in, as required by OSHA 29 CFR 1926 Subpart P. Protective systems shall be selected from the OSHA-tabulated options (sloping per Appendix B, timber shoring per Appendix C, aluminum hydraulic shoring per Appendix D) or shall be designed by a registered professional engineer. The competent person shall evaluate soil conditions and select or confirm the appropriate protective system for each excavation. Selection of a protective system is the responsibility of the Contractor; the Engineer of Record's review of the excavation safety plan does not constitute approval of the protective system design.
Where excavation support is designed by the Contractor's engineer, the design shall account for: soil type and stratification based on the project geotechnical report, groundwater level and hydrostatic pressure, surcharge loads from stockpiles, equipment, and adjacent structures, and any restrictions on ground movement that protect adjacent foundations, utilities, or improvements. The Owner's Engineer of Record shall be consulted before any designed support system is installed that affects permanent structures or existing improvements.
When excavating adjacent to existing buildings, foundations, pavements, or utilities, the Contractor shall evaluate whether the excavation will undermine the support of adjacent improvements. No excavation that removes lateral or vertical support from an existing foundation shall be performed without either underpinning the existing foundation or designing and installing a temporary support system adequate to prevent movement. IBC Chapter 18 requires that excavation near any foundation not reduce vertical or lateral support without prior protection of the affected foundation.
The Contractor shall monitor any existing structures adjacent to deep excavations for signs of movement or distress. Pre-construction condition surveys shall be performed on adjacent structures within a distance equal to the depth of excavation, and the Contractor shall maintain records sufficient to defend against claims of damage.
Dewatering removes groundwater from excavations to maintain dry working conditions, prevent bottom heave and piping, and allow compaction of fill to meet density requirements. The Contractor shall provide dewatering systems capable of maintaining the water level at least 2 feet below the working level in every excavation, unless the geotechnical report indicates that a lower drawdown is required.
The Contractor shall maintain dewatering continuously during all excavation and fill operations until the fill or structure has progressed to a height where groundwater no longer affects compaction or bearing capacity. Dewatering shall not be discontinued abruptly; if dewatering equipment fails, the Contractor shall immediately notify the Engineer of Record and take emergency measures to prevent flooding of the excavation. Groundwater shall not be discharged in a manner that causes erosion, flooding, or contamination of adjacent properties; all dewatering discharge shall comply with applicable NPDES permit conditions and local stormwater regulations.
Where dewatering causes settlement of adjacent soils or structures, the Contractor shall stop dewatering, notify the Owner and Engineer of Record, and not resume until a revised dewatering plan is approved. Fine-grained soils are susceptible to consolidation settlement when groundwater is permanently lowered; the effect on adjacent improvements shall be evaluated by the geotechnical engineer before dewatering begins in such soils.
Fill materials shall be free of organic material, frozen lumps, ice, snow, debris, and other deleterious matter. All fill material sources — whether excavated from the site or imported — shall be evaluated and approved by the geotechnical engineer before placement. The Contractor shall not change material sources without re-evaluation and approval.
Structural fill is used beneath foundations, floor slabs, pavements, and other load-bearing applications where settlement or inadequate bearing capacity would cause structural damage. Structural fill shall be granular or low-plasticity cohesive material with the following properties unless the geotechnical report specifies otherwise:
Where the geotechnical report indicates that on-site soils are not suitable as structural fill, or where the volume of suitable material is insufficient, the Contractor shall import approved granular fill. Imported structural fill shall be certified by a qualified laboratory prior to delivery. Certification shall include gradation analysis per ASTM C136/C136M and ASTM D7928, Atterberg limits per ASTM D4318, and Proctor test per ASTM D1557, performed on a sample representative of the import source.
Select granular fill is a high-quality, free-draining material used for pipe bedding, drainage layers under slabs, and applications where low compressibility and positive drainage are required.
Controlled Low-Strength Material (CLSM), also known as flowable fill, is a self-compacting cementitious fill that may be used as an alternative to compacted fill in confined spaces, around complex structures, or where compaction is not feasible. CLSM shall be used only where approved by the Engineer of Record. CLSM mix design shall achieve a 28-day compressive strength of 30 to 200 psi where future excavation may be required, or up to 1,200 psi where re-excavation is not anticipated.
General site fill is used in areas remote from structures where settlement over time is acceptable, such as landscaped areas and non-traffic areas beyond the building footprint. General site fill may include cohesive soils with higher plasticity than structural fill, provided the material is free of organics and debris.
General site fill shall not be used within 10 feet of building foundations or within any utility trench or pavement subgrade zone unless specifically approved by the geotechnical engineer.
The following materials shall not be used as fill in any application:
The Contractor shall submit laboratory test results for each fill source — both on-site stockpiles and import sources — before that material is placed. Test results shall include USCS classification, gradation, Atterberg limits, and Proctor compaction curve. If the source material changes in character during production (e.g., a stockpile contains zones of different material), additional testing shall be performed. The geotechnical engineer shall be notified of any material change that may affect suitability.
Compaction is the densification of soil by mechanical energy that reduces void space, increases dry density, and reduces future settlement potential. The energy is delivered by compaction equipment — vibratory rollers, tamping foot rollers, plate compactors, and pneumatic rollers — and the effectiveness depends on equipment type, lift thickness, number of passes, and most critically, on the moisture content of the soil relative to its optimum.
Compaction shall be performed in uniform horizontal lifts of the thickness specified herein, using equipment appropriate for the soil type and application. No fill shall be placed on frozen subgrade, and no compaction shall be performed on material that is frozen.
Lift thickness shall not exceed the capability of the compaction equipment to achieve uniform density through the full lift depth. A common compaction error is placing lifts that are thicker than the equipment can penetrate, producing a dense top crust that passes density testing while the lower portion remains loose. The geotechnical engineer may require proof of uniform compaction by performing density tests at mid-lift depth where there is reason to suspect layering.
Soil compaction achieves its maximum density at optimum moisture content, as determined by the Proctor test. Soil that is too dry will not compact fully regardless of roller passes; soil that is too wet will pump under roller traffic and cannot achieve the required density without drying. Both conditions are common causes of compaction failures.
The Contractor shall measure soil moisture before compaction using a nuclear gauge per ASTM D6938 or by laboratory determination per ASTM D2216. If fill is too dry, it shall be wetted uniformly using water trucks or sprinklers and allowed to condition before compaction begins; surface wetting without adequate mixing does not bring the full lift to optimum moisture. If fill is too wet, it shall be aerated by discing, blading, or windrowing until moisture falls within the acceptable range; the Contractor shall not attempt to compact overly wet material in the expectation that density testing will pass.
Highly plastic clays are particularly difficult to moisture-condition because they absorb and release water slowly. Such soils may require extended conditioning periods or should be replaced with more workable material.
Structural fill placed beneath footings, grade beams, mat foundations, and foundation walls shall be compacted to a minimum of 95 percent of Modified Proctor maximum dry density (ASTM D1557) unless the geotechnical report specifies a higher value. The geotechnical engineer shall determine the required bearing capacity from the project report and shall direct the compaction criterion accordingly. For highly loaded foundations or expansive soil conditions, compaction to 98 or 100 percent of Modified Proctor may be required.
Fill beneath floor slabs, concrete pavements, and asphalt pavements shall be compacted to a minimum of 95 percent of Modified Proctor maximum dry density unless the structural drawings specify a higher value. The top 6 inches of subgrade immediately beneath the slab or base course shall be compacted to not less than 95 percent of Modified Proctor.
Trench backfill within the footprint of any structure, within 5 feet of any foundation, or within any pavement area shall be compacted to a minimum of 95 percent of Modified Proctor maximum dry density. Trench backfill in unpaved areas remote from structures shall be compacted to a minimum of 90 percent. Initial backfill directly over pipe shall be hand-tamped or lightly compacted with small equipment to avoid pipe damage; after the initial backfill covers the pipe crown by 12 inches, heavier equipment may be used.
Fill in landscaped areas, turf areas, and other non-traffic, non-structural areas shall be compacted to a minimum of 90 percent of Standard Proctor (ASTM D698) maximum dry density. This value provides adequate stability for surface drainage and vehicle access without over-compacting areas that will be planted.
Compaction equipment shall be selected based on soil type and application. Vibratory smooth-drum rollers are effective for granular materials. Tamping foot (sheepsfoot) rollers are effective for cohesive fine-grained soils. Plate compactors and jumping jack tampers are used in confined areas and around utilities where large rollers cannot operate. The compaction equipment shall be of adequate size to achieve the required density in the specified lift thickness; light equipment used on heavy lifts will not achieve required compaction regardless of passes.
Compaction equipment shall not operate within 5 feet of any foundation wall, retaining wall, buried structure, or buried utility without the approval of the Engineer of Record, because heavy vibratory equipment transmits dynamic loads that can crack concrete, displace reinforcement, or damage flexible pipe. In the zone within 5 feet of any structure, compaction shall be performed with hand-operated vibratory plate compactors or jumping jack tampers in lifts not exceeding 6 inches. The Contractor shall verify that the approved compaction equipment achieves the required density in confined zones by performing test strips before committing to full production.
When a field density test fails to achieve the required percent compaction, the Contractor shall immediately cease filling the affected area, scarify and rework the failing lift, adjust moisture content if needed, re-compact, and request re-testing at the same location before proceeding. A single passing test after a failure does not eliminate the need to understand why the failure occurred. The geotechnical engineer shall evaluate patterns of repeated failure, which may indicate that the material is unsuitable, the moisture is persistently out of range, or the equipment is inadequate, and shall direct corrective action.
The Contractor shall not hide failed test results or attempt to proceed past a failing test based on verbal assurances. All test results, including failures, shall be documented, and the corrective action shall be recorded before the next test in the same area.
The bearing surface for every spread footing, strip footing, mat foundation, and grade beam shall be observed by the geotechnical engineer of record before any concrete, lean fill, or other material is placed. The observation shall confirm that the bearing elevation matches the design, that the material is the bearing stratum identified in the geotechnical report, and that there are no soft spots, disturbed zones, or groundwater that would compromise bearing capacity.
Loose material, disturbed soil, and standing water shall be removed before observation. If the bearing stratum is exposed more than 2 hours in advance of concrete placement, the top 2 to 3 inches shall be re-trimmed immediately before placement to remove desiccated crust in fine-grained soils or disturbed material in granular soils. In freezing weather, bearing surfaces shall be protected from frost and shall be confirmed unfrozen by the geotechnical engineer before concrete is placed.
Proof rolling consists of driving a fully loaded, rubber-tired vehicle over the prepared subgrade surface to identify soft, pumping, or yielding areas that indicate inadequate bearing or insufficient compaction. Proof rolling shall be performed on all areas to receive structural fill under foundations or slabs, on all subgrades to receive base course under pavements, and at any location where the geotechnical engineer suspects inconsistent subgrade conditions.
The geotechnical engineer shall observe all proof rolling. Areas that exhibit more than 0.5 inch of deformation, rut, or pumping shall be undercut to competent material and replaced with approved structural fill or otherwise stabilized as directed by the geotechnical engineer. The Contractor shall not proceed with fill placement or base course until all failing areas have been remediated and re-proof-rolled.
Where the subgrade is soft, wet, or otherwise unable to support compaction equipment or proof-rolling, the geotechnical engineer shall evaluate stabilization options. Options include:
Lime and cement treatment requires a mix design developed by a qualified laboratory, field application with calibrated equipment, and curing before the treated layer is loaded. Treated layers shall be re-tested before being loaded to confirm achievement of the target unconfined compressive strength.
Where slabs on grade are designed with a capillary break layer, the layer shall consist of clean crushed stone with less than 5 percent fines (USCS SP or GP), placed and compacted in a single layer of the thickness shown on the drawings.
The capillary break layer shall be placed after the subgrade has been proof-rolled and accepted by the geotechnical engineer. The layer shall be compacted with a vibratory plate compactor to a stable surface and shall not be over-compacted to the point of crushing aggregate. The layer shall not be contaminated with fines from traffic before the vapor retarder and concrete are placed.
Construction activities that disturb 1 acre or more of land — or less if part of a common plan of development that totals 1 acre or more — require coverage under the EPA Construction General Permit (CGP) or the applicable state NPDES stormwater permit before grading begins. The Contractor shall obtain all required stormwater permits, prepare a Stormwater Pollution Prevention Plan (SWPPP) in accordance with the permit requirements, and maintain the SWPPP on site at all times for inspection.
The SWPPP shall describe every Best Management Practice (BMP) to be used, the location of each BMP shown on a site map, the sequence of installation relative to grading operations, the maintenance and inspection protocol, and the basis for determining when the permit can be terminated at project completion. The SWPPP shall be updated when conditions change, when BMPs prove ineffective, or when new areas of disturbance are added.
The perimeter of the site shall be protected by sediment controls installed before grading begins, to intercept sediment-laden runoff before it leaves the site. Silt fence, fiber wattles, rock check dams, and sediment basins are common perimeter controls, each suited to different slope conditions and drainage areas.
Silt fence shall be installed by slicing the fabric into the soil using a mechanical device or by digging a 6-inch trench, inserting the fabric, and backfilling; fabric simply staked to the surface without embedment will fail in the first rain event. Silt fence shall be inspected after every rain event and repaired or replaced when sediment accumulation reaches one-third of the exposed fabric height.
A stabilized construction entrance shall be provided at every point where construction vehicles enter or exit the site onto a public road, to remove mud and sediment from tires before vehicles reach the pavement.
The stabilized entrance shall extend from the public road into the site at least 50 feet, or the full length of the ingress/egress zone if shorter. Where vehicles track mud onto public roads despite the stabilized entrance, the Contractor shall arrange for street sweeping at a frequency that prevents sediment buildup.
Disturbed slopes shall be protected from erosion by temporary seeding, erosion control blankets, compost applications, or other approved methods when the slope will be exposed for more than 7 days on slopes steeper than 3:1 or more than 14 days on slopes 3:1 or flatter. Temporary seeding with fast-germinating annual grasses provides cost-effective erosion protection for exposed slopes during construction.
All storm drain inlets within or immediately downslope of the construction area shall be protected with inlet protection devices to prevent sediment from entering the storm drainage system. Inlet protection shall be installed before grading begins in the contributing drainage area.
Inlet protection devices shall be inspected after every rain event and cleaned when sediment accumulates to one-half the device capacity. Clogged inlet protection that blocks drainage and causes ponding presents a flooding risk and shall be cleaned immediately.
All erosion and sediment control BMPs shall be inspected by the Contractor's designated responsible party at least weekly and within 24 hours after any rain event of 0.5 inch or greater. Inspection records shall document the condition of each BMP, any deficiencies noted, and corrective actions taken. Corrective actions shall be completed within 24 hours of inspection unless weather prevents it, in which case they shall be completed as soon as practicable.
At project completion, all temporary erosion and sediment control BMPs shall be removed and disturbed areas stabilized with permanent vegetation or hardscape. Temporary BMPs shall not be removed until the areas they protect have achieved permanent stabilization. Silt fence fabric and other synthetic materials shall be collected and disposed of properly; they shall not be buried in place.
Field compaction testing shall be performed by the Owner-retained special inspection or geotechnical firm. Testing is Owner-retained because the testing entity must be independent of the Contractor — Contractor-retained testing for compaction acceptance is not acceptable for structural applications. The Contractor shall cooperate fully with the testing agency, provide access to all fill areas, and provide information about lift locations, material types, and moisture conditioning operations.
The testing agency shall use nuclear density gauge testing per ASTM D6938 as the primary production method, with sand cone tests per ASTM D1556/D1556M for verification or calibration. The nuclear gauge shall be standardized at the beginning and end of each shift. Gauge count standard results shall be recorded and compared to the reference standards. If count ratios fall outside acceptable limits, the gauge shall be recalibrated before testing continues.
Minimum testing frequencies, in the absence of project-specific geotechnical recommendations, shall be:
For each distinct fill material on the project, a Proctor reference curve (maximum dry density vs. moisture content) shall be established by laboratory testing before that material is placed in the field. Field density results are meaningless without an accurate reference Proctor. If visual observation by the geotechnical engineer suggests that the material being placed has changed from the material on which the reference Proctor was performed, the geotechnical engineer shall direct verification testing on the new material before compaction acceptance continues.
Where the structural design is based on a minimum allowable bearing pressure, the geotechnical engineer of record shall confirm that the bearing material at the foundation bearing elevation is consistent with the material on which the design bearing pressure is based. Consistency is established by visual observation, standard penetration test blow counts from boring logs, hand penetrometer readings, or dynamic cone penetrometer testing in the bearing surface, as appropriate to the material type. The geotechnical engineer's written observation report for each foundation bearing elevation shall be provided to the Owner and Engineer of Record and retained in the project file.
In addition to Proctor and density testing, the geotechnical engineer may direct gradation and Atterberg limits tests on fill materials at any time during construction to confirm continued conformance to the approved material description. Testing shall be performed when material appearance changes, when a new stockpile or import delivery is initiated, or when compaction testing shows unexplained variability that may indicate a material change. Test frequency shall be as directed by the geotechnical engineer.
All field testing data shall be recorded on forms that include: project name, test date, test location (plan coordinates or station and offset, plus depth or lift number), material description, moisture content, wet density, dry density, percent compaction relative to the applicable Proctor, and pass/fail determination. The testing agency shall provide results to the Owner and Contractor within 24 hours of testing. Failing tests shall be flagged immediately and shall not be buried in a batch report delivered days later — the Contractor must have immediate notice to stop work and address the failure.
The Contractor shall warrant earthwork operations, including achievement of specified grades, compaction of all fill and backfill, and the performance of erosion and sediment control measures, for the project warranty period beginning at substantial completion. Warranty obligations include correction of settlement, heaving, erosion, or other defects attributable to non-conforming earthwork operations.
The warranty does not relieve the Contractor of liability for concealed non-conforming work discovered after the warranty period expires, nor does it limit the Owner's remedies for latent defects. Settlement or structural distress discovered after the warranty period that is attributable to inadequate compaction or non-conforming fill materials shall be evaluated by the geotechnical engineer and may constitute a latent defect extending beyond the warranty term.
Settlement monitoring pins or monuments shall be installed where directed by the geotechnical engineer to provide objective data on fill performance during the warranty period. Readings shall be taken at the intervals specified by the geotechnical engineer and reported to the Owner. Accelerated settlement that exceeds the predicted range shall be reported immediately.