1 Scope

1.1 This standard covers the design-build specialty ground improvement scope: site investigation supplementation, ground improvement design, installation, and in-place verification of aggregate piers, deep and mass soil mixing, and jet grouting used to improve native soils beneath shallow foundations, slabs-on-grade, embankments, and pavement subgrades.

NOTE Ground improvement is a composite-soil strategy: discrete reinforcing or stabilizing elements are installed on a grid through inadequate native soil so that the treated zone, acting together with the soil between elements, carries shallow-foundation loads at a higher allowable bearing pressure and with less settlement than the untreated soil would. (1.2)

NOTE It is selected where native soils cannot support shallow foundations directly but where mass over-excavation and replacement, or driven deep foundations to competent strata, are slower or more costly than improving the soil in place. (1.3)

NOTE Two mechanistic families are covered. (1.4)

NOTE Granular reinforcement methods (rammed aggregate piers, vibro stone columns, vibro replacement) build stiff, free-draining columns of compacted crushed stone that reinforce and densify the surrounding soil and, below the water table, provide drainage paths that aid liquefaction resistance. (1.4.1)

NOTE Cementitious stabilization methods (deep soil mixing, mass soil mixing, jet grouting) blend or inject a cement or lime binder into the soil in place to create columns, panels, or treated blocks of hardened soil-cement with engineered strength and stiffness. (1.4.2)

NOTE Controlled modulus columns (CMC) and other rigid inclusions occupy a gray area: they are thin grout or concrete columns that act structurally as small piles bearing through a load transfer platform, closer to deep foundations than to composite ground improvement. (1.5)

NOTE Controlled modulus columns and rigid inclusions are specified under Deep FoundationsDeep Foundations (Piles and Drilled Piers)Resolves to the current edition.sync/deep-foundations unless the project geotechnical engineer of record explicitly classifies them as ground improvement for the specific site. (1.5.1)

NOTE Where ground improvement supports a shallow foundation system, the foundation itself (footing sizing, bearing pressure selection, reinforcement) is specified under Shallow FoundationsShallow Foundations (Spread and Strip Footings)Resolves to the current edition.sync/shallow-foundations; this standard delivers the improved bearing condition that foundation design assumes. (1.6)

NOTE Method selection, target performance, and element layout are site-specific and depend on a project geotechnical investigation; this standard establishes the performance framework, submittal requirements, materials, installation controls, and verification testing common to all covered methods. (1.7)

2 Referenced Standards

2.1 Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited or the authority having jurisdiction has adopted a different edition.

2.2 Where referenced standards conflict, the more stringent requirement shall govern unless the geotechnical engineer of record directs otherwise in writing.

Standard	Title
ICC IBC Chapter 18	International Building Code, Soils and Foundations (Section 1808 special foundation systems)
ASTM D1143/D1143M	Standard Test Method for Deep Foundations Under Static Axial Compressive Load
ASTM D4832	Standard Test Method for Preparation and Testing of Soil-Cement Slurry Test Cylinders
ASTM D2166/D2166M	Standard Test Method for Unconfined Compressive Strength of Cohesive Soil
ASTM D6913/D6913M	Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis
ASTM C131/C131M	Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact (Los Angeles Machine)
ASTM D4945	Standard Test Method for High-Strain Dynamic Testing of Deep Foundations
ASTM D2573/D2573M	Standard Test Method for Field Vane Shear Test in Cohesive Soil
ASTM D1586/D1586M	Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils
ASTM D5777	Standard Guide for Using the Seismic Refraction Method for Subsurface Investigation
FHWA NHI-16-027	Ground Modification Methods Reference Manual, Volume I (Federal Highway Administration)
UFGS 31 62 50	Unified Facilities Guide Specification, Densified Aggregate Piers
ACI 207.1R	Guide to Mass Concrete
ACI 228.1R	Report on Methods for Estimating In-Place Concrete Strength
AASHTO R 69	Determination of Ground Modification Method and Design Parameters

NOTE FHWA NHI-16-027 and UFGS 31 62 50 are publicly available reference documents that establish the design methodology, material requirements, and quality control practices on which the requirements of this standard are based; they may be cited directly by the engineer in project-specific design. (2.3)

3 Submittals

3.1 Action Submittals

3.1.1 The specialty ground improvement contractor shall submit the following action submittals for review before mobilizing:

Ground improvement design report and calculations, stamped and signed by a professional geotechnical engineer licensed in the project jurisdiction, demonstrating that the design satisfies the specified bearing capacity, settlement, and (where applicable) liquefaction-resistance criteria
Treatment layout drawings showing element type, diameter, depth, grid spacing, and area replacement ratio for each foundation, slab, and embankment area
Equipment data describing the installation rig, mandrel or auger or jet-grout monitor, tamper or vibrator, and instrumentation used to record installation parameters
For aggregate piers and stone columns: aggregate source, gradation test results, and Los Angeles abrasion results
For deep soil mixing and jet grouting: binder type and source, mix design, target binder dosage, water-cement ratio, and trial-mix or bench-scale unconfined compressive strength results
Load test plan identifying proof and verification test locations, reaction arrangement, loading schedule, and acceptance criteria
Quality control plan describing installation parameter recording, aggregate or spoil volume tracking, and field acceptance testing
Spoil and grout-return management and disposal plan for wet soil mixing and jet grouting

Action submittals requiredcheckbox

☑ Stamped ground improvement design report and calculations

☑ Treatment layout drawings (type, diameter, depth, spacing, replacement ratio)

☑ Installation equipment data

☐ Aggregate gradation and LA abrasion results

☐ Binder mix design and trial-mix UCS results

☑ Load test plan

☑ Quality control plan

☐ Spoil and grout-return management plan

3.1.2 The ground improvement design report shall be stamped and signed by a professional geotechnical engineer licensed in the project jurisdiction.

3.1.3 The treatment layout shall identify each element by type, diameter, design depth, grid spacing, and area replacement ratio.

3.1.4 The contractor shall not mobilize installation equipment until the ground improvement design report has been reviewed and accepted.

3.2 Informational Submittals

3.2.1 The contractor shall submit the following informational submittals:

Qualifications of the installing contractor and the licensed geotechnical engineer of record for the ground improvement design
Supplementary geotechnical investigation data (borings, cone penetration tests, laboratory results) used to support the design where the project geotechnical report is insufficient
Preconstruction survey of adjacent structures, slabs, and utilities within the zone of influence
Manufacturer or system-licensor installation procedures for proprietary aggregate pier, soil mixing, or jet grout systems

Informational submittals requiredcheckbox

☑ Contractor and engineer-of-record qualifications

☐ Supplementary geotechnical investigation data

☑ Preconstruction adjacent-structure and utility survey

☐ System-licensor installation procedures

3.3 Closeout Submittals

3.3.1 The contractor shall submit the following closeout submittals before final acceptance:

As-built installation records for every element, including location, depth, and recorded installation parameters
Aggregate volume-per-foot logs (granular methods) or binder dosage and spoil-return logs (cementitious methods) for each element
Load test reports with measured load-settlement data and the engineer's interpretation against acceptance criteria
Core test reports (unconfined compressive strength) for deep soil mixing and jet grout verification
Post-improvement in-situ verification test results (SPT, CPT, or field vane) where specified
Letter of certification from the geotechnical engineer of record that the installed ground improvement satisfies the design intent

Closeout submittals requiredcheckbox

☑ As-built installation records (all elements)

☑ Aggregate volume or binder dosage logs

☑ Load test reports with interpretation

☐ Core UCS test reports (cementitious methods)

☐ Post-improvement in-situ verification results

☑ Engineer-of-record certification letter

4 Quality Assurance

4.1 Installer Qualifications

4.1.1 The ground improvement contractor shall be a specialty firm regularly engaged in the installation of the specified method, with documented experience on at least three projects of comparable scope, soil conditions, and element depth completed within the preceding five years.

4.1.2 The ground improvement design shall be performed by, or under the responsible charge of, a professional geotechnical engineer licensed in the project jurisdiction.

4.1.3 Where a proprietary aggregate pier, soil mixing, or jet grout system is used, the installing crew shall be trained and licensed by the system developer.

4.2 Geotechnical Investigation

4.2.1 A pre-construction geotechnical investigation conducted in accordance with IBC Section 1803 shall provide subsurface data sufficient to support the ground improvement design, including borings or cone penetration tests to a depth below the deepest element and laboratory classification and strength testing of the affected strata.

NOTE The geotechnical investigation underpinning the ground improvement design must be specific to the site and adequate in depth and density; existing borings that are too sparse or too shallow are not acceptable as the sole basis of design, because element type, depth, and spacing all derive from the site soil profile. (4.2.2)

NOTE Ground improvement under IBC Section 1808 is an alternative foundation system with no prescriptive code path: there is no table to size elements from, so a project-specific geotechnical report and engineer approval are mandatory rather than optional. (4.2.3)

4.2.4 The contractor shall not reuse an element layout from another project without site-specific geotechnical justification.

4.3 Engineer Coordination

4.3.1 The allowable bearing capacity assumed by the ground improvement design shall match the bearing pressure used in the shallow foundation design under Shallow FoundationsShallow Foundations (Spread and Strip Footings)Resolves to the current edition.sync/shallow-foundations, confirmed in writing before installation.

NOTE A mismatch between the bearing pressure stated in the geotechnical report and the bearing pressure shown on the structural drawings is a persistent source of requests for information and rework; reconciling the two values before installation closes that gap. (4.3.2)

4.3.3 Value engineering that changes element type, depth, spacing, or area replacement ratio shall be re-analyzed and accepted in writing by the geotechnical engineer of record before implementation.

NOTE Reducing the element grid or depth as a deductive alternate without re-analysis by the geotechnical engineer of record voids the performance basis of the design and typically voids any settlement or bearing warranty; cost savings that bypass the engineer are not savings. (4.3.4)

5 Performance Requirements

5.1 Performance Basis

NOTE This standard is written as a performance specification: the engineer states the required end result (allowable bearing capacity, settlement limits, and liquefaction-resistance target where applicable) and the specialty contractor designs the method, layout, and element details to achieve it. (5.1.1)

NOTE Aggregate pier and soil mixing work is inherently specialty-contractor-driven, so a performance specification that fixes the target and leaves the means to the design-build contractor is generally more defensible and easier to administer than a rigid procedural specification that dictates equipment and sequence. (5.1.2)

NOTE A purely prescriptive specification that locks the method and grid is appropriate only for rammed aggregate piers on well-characterized sites where the engineer has performed the composite design; for stone columns, soil mixing, and jet grouting the design should remain with the specialty contractor. (5.1.3)

5.1.4 The improved ground shall achieve the specified allowable bearing capacity for the supported element type.

Allowable bearing capacity, improved composite groundrange

psf

20003000400060008000

5.1.5 The supported foundation type shall be identified so that the bearing target and element layout can be coordinated with the structural design.

Supported foundation / structure typeradio

● Slab-on-grade

○ Spread footings

○ Combined footings / mat

○ Embankment / fill support

○ Pavement subgrade

5.2 Settlement Criteria

5.2.1 Settlement of the improved ground under design service loads shall not exceed the specified total and differential settlement limits.

NOTE Settlement limits are commonly expressed two ways: a total settlement cap (often about 1 inch for slabs and 0.5 to 1 inch for spread footings) and a differential settlement ratio between adjacent supports (commonly L/480 to L/240 for structural frames), with the structural engineer setting the governing values for the specific frame. (5.2.2)

Maximum total settlement under design loadrange

in

0.50.7511.5

Maximum differential settlement ratio between supportsselect

L/480

L/360

L/240

5.2.3 Post-improvement settlement under design load shall not exceed the fraction of the unimproved settlement assumed in the design.

NOTE Granular reinforcement typically reduces post-improvement settlement to about 30 to 60 percent of the unimproved settlement; the design report shall state the settlement reduction the layout is intended to achieve so that it can be verified against load test results. (5.2.4)

5.3 Liquefaction Resistance

5.3.1 Where the design intent includes mitigation of liquefiable soils, the improved ground shall achieve the specified post-treatment density or penetration resistance, and that resistance shall be verified by post-treatment testing rather than assumed from the pre-treatment design.

NOTE Specifying aggregate piers in liquefiable granular soils on the strength of the pre-treatment design alone is a recognized pitfall: densification and drainage performance vary with as-installed conditions, so post-treatment CPT or SPT verification is required to confirm the improvement actually occurred. (5.3.2)

Liquefaction mitigation requiredradio

● Not required

○ Required, verified by post-treatment SPT

○ Required, verified by post-treatment CPT

6 Method Selection

NOTE The installation method shall be selected to suit the native soil type, groundwater depth, headroom and access constraints, and target performance, and shall be documented in the ground improvement design report. (6.1)

NOTE Method selection is the first and most consequential decision: cohesive versus granular soils, the depth to groundwater, overhead and lateral access limits, and the governing performance target (bearing, settlement, or liquefaction) each push toward a different family of methods, and the wrong choice cannot be corrected by adjusting spacing. (6.1.1)

Ground improvement methodradio

● Rammed aggregate piers (drill-and-ram)

○ Rammed aggregate piers (displacement)

○ Vibro stone columns / vibro replacement

○ Vibro compaction (granular soils, no aggregate)

○ Deep soil mixing, wet method

○ Deep soil mixing, dry method

○ Mass soil mixing

○ Jet grouting, single-fluid

○ Jet grouting, triple-fluid

6.2 Granular Reinforcement Methods

NOTE Rammed aggregate piers are built by drilling or displacing a cavity and ramming successive lifts of crushed stone with a beveled tamper that both compacts the aggregate and prestresses and densifies the surrounding soil; they suit cohesive and mixed soils and are the method most commonly specified by owners with a prescriptive specification. (6.2.1)

NOTE Displacement (no-spoil) rammed aggregate piers form the cavity by pushing soil aside rather than augering it out, which suits loose granular soils below the water table where an open hole would collapse. (6.2.2)

NOTE Vibro stone columns (vibro replacement) use a vibrating probe to form a stone column in soft cohesive soils below the water table, by either a wet (jetted) or dry (bottom-feed) process; they reach greater depths than rammed piers and provide both reinforcement and drainage. (6.2.3)

NOTE Vibro compaction densifies clean loose granular soils with a vibrating probe and does not add aggregate or form a column; it is a densification method, not a reinforcement method, and is ineffective in cohesive soils. (6.2.4)

NOTE Vibro stone columns shall not be specified in stiff cohesive soils with undrained shear strength above approximately 50 kPa (1,000 psf) without a constructability review by the specialty contractor, because dense or stiff soil may resist the lateral expansion the column needs to mobilize its capacity. (6.2.5)

6.3 Cementitious Stabilization Methods

NOTE Wet-method deep soil mixing blends a cement slurry into the soil with single- or multi-axis augers to form overlapping columns or panels of hardened soil-cement; it suits a wide range of soils and reaches the greatest depths of the covered methods. (6.3.1)

NOTE Dry-method deep soil mixing injects dry cement or lime powder into the soil through a rotating auger and relies on the soil's own water for hydration; it suits high-water-content cohesive soils where adding slurry water is undesirable. (6.3.2)

NOTE Mass soil mixing overlaps soil-mix columns in a grid or block pattern to treat a continuous volume of soil, used for widespread settlement control beneath structures or for environmental containment. (6.3.3)

NOTE Single-fluid jet grouting injects high-pressure grout through a rotating monitor to erode and mix the soil into a column; it produces smaller-diameter columns and is precise in restricted-access work and adjacent to existing structures. (6.3.4)

NOTE Triple-fluid jet grouting pre-cuts the soil with water shrouded by air before injecting grout, producing the largest column diameters where wide treatment from a single drill location is required. (6.3.5)

6.3.6 Cementitious methods shall not be used on a contaminated site until the spoil and grout-return handling has been coordinated with abatement scope under Hazardous Material AbatementHazardous Material AbatementResolves to the current edition.sync/hazardous-material-abatement and any required environmental permitting is in place.

7 Elements and Materials

7.1 Aggregate Pier and Stone Column Elements

7.1.1 Element diameter, design depth, grid spacing, and area replacement ratio shall be as shown on the accepted treatment layout for each foundation and slab area.

NOTE Element diameter is commonly 18 inches for rammed aggregate piers (the most frequent size), increasing to 24 to 30 inches for heavier loads and 30 to 48 inches for vibro stone columns; the design depth extends to a competent stratum or refusal and at least 1.5 times the footing width below bearing elevation. (7.1.2)

Aggregate pier / stone column diameterselect

18

24

30

36

48

Element design depthrange

ft

860

Default: 20 ft

Per drawings — geotechnical profile / boring logs

Element grid spacing (on center)range

ft

412

Default: 6 ft

Per drawings — treatment layout plan

7.1.3 The area replacement ratio (ratio of element cross-sectional area to tributary area) shall be as required by the design to achieve the specified bearing and settlement performance.

NOTE Area replacement ratios commonly run 10 to 35 percent, with a design optimum often near 20 to 25 percent for soft clay sites; the ratio is the principal lever the designer uses to trade element count against performance. (7.1.4)

Area replacement ratio (As/A)range

%

1035

Default: 25 %

7.1.5 Aggregate for piers and stone columns shall be crushed stone graded in accordance with ASTM D6913/D6913M, of nominal 0.75 to 1.5 inch size.

7.1.6 Aggregate shall contain no more than 5 percent passing the No. 200 sieve.

NOTE Fines content must be controlled because the column's drainage function (especially for liquefaction mitigation and for stone columns below the water table) depends on the aggregate staying free-draining; excess fines clog the column and defeat the drainage path. (7.1.7)

7.1.8 Aggregate shall have a Los Angeles abrasion loss of no more than 50 percent when tested in accordance with ASTM C131/C131M.

Aggregate nominal sizeselect

0.75

1.0

1.25

1.5

Maximum aggregate fines (passing No. 200 sieve)range

%

35

Default: 5 %

7.2 Deep Soil Mixing and Jet Grout Elements

7.2.1 Soil-mix and jet grout column diameter, design depth, and grid or panel layout shall be as shown on the accepted treatment layout.

NOTE Wet-method single-axis soil-mix columns are most commonly 24 to 36 inches in diameter; multi-axis soil-mix walls run 36 to 60 inches; single-fluid jet grout columns run 18 to 36 inches and triple-fluid jet grout columns run 48 to 78 inches. (7.2.2)

Soil-mix / jet grout column diameterrange

in

2436486078

7.2.3 The binder type and dosage shall be selected for the in-situ soil chemistry and the target unconfined compressive strength, and shall be confirmed by trial-mix or bench-scale testing before production.

NOTE The binder is commonly Portland cement (Type I/II, or Type III where high early strength is needed), sometimes blended with slag or lime; in-situ soil chemistry governs the choice because organics, sulfates, or low pH can inhibit cement hydration and, if unaddressed, cause complete column failure, which is why trial-mix testing is mandatory rather than advisory. (7.2.4)

Binder typeradio

● Portland cement Type I/II

○ Portland cement Type III (high early strength)

○ Cement-slag blend

○ Cement-lime blend

○ Lime (dry method)

Binder content (cement) per cubic meter of treated soilrange

kg/m³

150350

Default: 225 kg/m³

Water-cement ratio (wet method)range

ratio

0.81.5

Default: 1 ratio

7.2.5 Soil-mix and jet grout columns shall attain the specified unconfined compressive strength at the specified age when tested in accordance with ASTM D4832.

NOTE Target unconfined compressive strength is commonly 50 to 150 psi (345 to 1,034 kPa) for settlement control in soft clay and 100 to 300 psi (690 to 2,069 kPa) for structural load transfer, with environmental containment work often requiring at least 50 psi; the design report shall state the governing target and age. (7.2.6)

Target unconfined compressive strength (UCS) at 28 daysrange

psi

50100150200300

7.3 Load Transfer Platform

7.3.1 A compacted granular load transfer platform shall be placed over the improved zone where required by the design to redistribute structure loads across the element grid and the intervening soil.

NOTE Omitting the load transfer platform is a common pitfall: the granular working mat (often with geogrid reinforcement) is what spreads load from the structure across the stiff elements and the softer soil between them, and without it most of the composite-system benefit is lost. (7.3.2)

Load transfer platform thicknessrange

in

1224

Default: 18 in

Geogrid reinforcement in load transfer platformradio

● Not required

○ Biaxial geogrid, 40 kN/m minimum tensile strength

○ Biaxial geogrid, design strength per layout

8 Installation

8.1 General

8.1.1 Installation shall follow the accepted ground improvement design, treatment layout, and quality control plan.

8.1.2 A preconstruction survey of adjacent structures, slabs, and utilities within the zone of influence shall be performed and documented before installation begins.

NOTE Aggregate pier, soil mixing, and jet grout installation can cause ground heave, vibration, and lateral soil displacement; a documented preconstruction survey of adjacent foundations and buried utilities establishes the baseline needed to detect and attribute any damage. (8.1.3)

8.1.4 The contractor shall stop ground improvement work and notify the engineer when hazardous soil or groundwater is encountered, and shall not resume until abatement clearance is obtained under Hazardous Material AbatementHazardous Material AbatementResolves to the current edition.sync/hazardous-material-abatement.

8.2 Aggregate Pier and Stone Column Installation

8.2.1 Each element shall be installed to the design depth or to refusal on a competent stratum, whichever is reached first, and the as-installed depth shall be recorded.

8.2.2 Aggregate shall be placed and compacted in controlled lifts using the tamper or vibrator energy specified by the system, and the compaction effort or energy shall be recorded for each element.

8.2.3 The volume of aggregate placed shall be recorded as cubic feet per linear foot for every element.

NOTE Aggregate volume tracking is the only field record that proves an element was fully built; without volume-per-foot logs there is no objective basis to reject an under-installed pier, and quality control collapses to a top-of-pier elevation check that cannot detect a hollow or under-filled column. (8.2.4)

8.2.5 An element whose recorded aggregate volume deviates from the design volume by more than 15 percent shall be re-evaluated by the engineer before acceptance.

8.2.6 For elements installed below the water table, the bottom-bulb densification shall achieve at least the minimum dynamic penetration acceptance specified by the design (commonly 15 blows per 45 mm per UFGS 31 62 50).

Aggregate volume deviation triggering re-evaluationrange

%

1020

Default: 15 %

8.3 Soil Mixing and Jet Grout Installation

8.3.1 Each soil-mix or jet grout column shall be installed at the binder dosage, injection pressure, withdrawal rate, and rotation specified by the accepted design, and these parameters shall be recorded for every column.

8.3.2 Soil-cement spoil and grout returns shall be contained, characterized, and disposed of in accordance with the accepted spoil management plan.

NOTE Wet soil mixing and jet grouting generate significant volumes of soil-cement spoil and grout return; disposal must be planned and permitted before mobilization, because on contaminated sites the returns may be a regulated waste and an unplanned spoil stream can halt the work. (8.3.3)

8.3.4 Overlap between adjacent columns in walls, grids, and mass-mix blocks shall be maintained within the tolerance required by the design to ensure continuity of the treated mass.

8.4 Curing and Loading Sequence

8.4.1 A minimum waiting period shall elapse between element installation and footing excavation or load application, as required for the method and binder.

NOTE Premature loading before strength gain is a recurring field problem; aggregate piers can typically accept footing construction within about 24 hours, while soil-mix and jet grout columns require 7 to 28 days of curing depending on the binder and target strength before load is applied. (8.4.2)

Minimum waiting period before load applicationselect

24 hours (aggregate piers)

7 days (soil mixing / jet grout, early strength)

14 days (soil mixing / jet grout)

28 days (soil mixing / jet grout, full strength)

9 Testing and Verification

9.1 Load Testing

9.1.1 A load test program shall be performed to confirm the load-deformation behavior of representative elements against the design assumptions.

NOTE The program distinguishes proof tests (loading representative production elements to a multiple of design load to confirm acceptable behavior) from verification tests (loading a sacrificial or pre-production element to a higher multiple to validate the design model); both follow ASTM D1143/D1143M loading and measurement protocols adapted to single elements. (9.1.2)

9.1.3 Proof tests shall load the element to between 150 and 200 percent of design load.

9.1.4 Verification tests shall load the element to between 200 and 300 percent of design load.

9.1.5 The number and location of proof and verification tests shall be as specified, with a minimum of one verification test per project and proof tests distributed across the treated area.

Number of proof testsrange

tests

16

Default: 2 tests

Number of verification testsrange

tests

13

Default: 1 tests

Proof test load (percent of design load)range

%

150200

Default: 150 %

Verification test load (percent of design load)range

%

200300

Default: 200 %

9.1.6 A load test element shall not be loaded before the minimum waiting period for the method and binder has elapsed.

9.2 Core and In-Situ Verification

9.2.1 Soil-mix and jet grout columns shall be verified by coring and unconfined compressive strength testing of the recovered soil-cement in accordance with ASTM D4832, at the frequency specified in the quality control plan.

NOTE Where low or variable core strengths are encountered, the engineer may interpret in-place strength using methods consistent with ACI 228.1R before accepting or rejecting affected columns. (9.2.2)

9.2.3 Where the design relies on densification or strength gain in the native soil, pre- and post-improvement in-situ testing shall document the change, using SPT (ASTM D1586/D1586M) for granular soils and field vane shear (ASTM D2573/D2573M) for cohesive soils.

NOTE For large soil-mix programs, the engineer may specify seismic refraction (ASTM D5777) as a supplementary geophysical check of treatment continuity. (9.2.4)

9.2.5 High-strain dynamic testing in accordance with ASTM D4945 may be specified as a supplementary quality check for deep soil-mix columns.

Core UCS testing frequency (cementitious methods)select

1 core per 1,000 cubic yards treated

1 core per 50 columns

1 core per 25 columns

Post-improvement in-situ verificationradio

● Not required

○ Post-improvement SPT (granular soils)

○ Post-improvement CPT (granular soils)

○ Post-improvement field vane shear (cohesive soils)

9.3 Acceptance

9.3.1 Ground improvement shall be accepted only after load test results, core or in-situ verification results, and installation records have been reviewed by the geotechnical engineer of record against the specified acceptance criteria.

9.3.2 Elements that fail to meet the acceptance criteria shall be supplemented, replaced, or otherwise remediated by means designed and accepted by the geotechnical engineer of record at no additional cost to the owner.

10 Coordination

NOTE Ground improvement bearing capacity and settlement assumptions shall be coordinated with the shallow foundation design under Shallow FoundationsShallow Foundations (Spread and Strip Footings)Resolves to the current edition.sync/shallow-foundations and confirmed before installation. (10.1)

NOTE Mass earthwork, site grading to working-platform elevation, and engineered fill above the improved zone are specified under EarthworkEarthworkResolves to the current edition.sync/earthwork and shall be coordinated so the working platform is in place before installation and the load transfer platform is built on a prepared subgrade. (10.2)

NOTE Performance monitoring of the improved ground during and after construction (settlement plates, inclinometers, piezometers) is specified under Geotechnical Instrumentation And MonitoringGeotechnical Instrumentation and MonitoringResolves to the current edition.sync/geotechnical-instrumentation-and-monitoring; this standard's testing requirements cover construction verification, not long-term monitoring. (10.3)

NOTE Where the project also includes thin-layer chemical or mechanical subgrade stabilization for pavement, that work is specified under Soil StabilizationSoil Stabilization and ModificationResolves to the current edition.sync/soil-stabilization and is distinct from the deep ground improvement covered here. (10.4)

NOTE Sequencing with hazardous material abatement under Hazardous Material AbatementHazardous Material AbatementResolves to the current edition.sync/hazardous-material-abatement shall be documented where soil mixing or jet grouting is performed on a contaminated site, so that spoil and grout-return handling, permitting, and clearance are resolved before and during installation. (10.5)

11 Warranty

11.1 The specialty ground improvement contractor shall warrant that the installed ground improvement was designed and built to achieve the specified bearing capacity and settlement performance, for the period required by the contract.

NOTE The performance warranty is predicated on the design as accepted; any field change to element type, depth, spacing, or replacement ratio that was not re-analyzed and accepted in writing by the geotechnical engineer of record voids the warranty for the affected area. (11.1.1)

11.2 The warranty shall remain in effect notwithstanding the owner's acceptance of load test and verification results.