Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support

APPENDIX C. GUIDE CONSTRUCTION SPECIFICATION FOR DEEP MIXING

Deep Mixing Guide Construction Specification

Commentary: This guide provides information that must be considered to responsibly develop specifications for a successful deep mixing project. Each specification developed must be written carefully to reflect the site- and project-specific conditions and requirements. Suggested specification language is shown in normal text, and commentary is noted in italics. The commentary is intended to highlight project-specific items the engineer should consider when writing a specification. The commentary is listed at the beginning of each section and relates to the group of provisions that follow the commentary. The commentary must be removed before the specification can be used for a project.

Suggested tolerances and requirements are provided in the commentary; however, these generic requirements must be tailored to the project needs and be sufficiently flexible to accommodate differences in equipment and methods without limiting competition or imparting unnecessary or unachievable restrictions while still achieving the design intent.

Because a wide variety of DMMs are available and the quality of deep mixed soils are heavily dependent on the contractor's equipment and methods, a pure method specification is virtually never used for deep mixing projects. Instead, a hybrid specification is recommended, as discussed in chapter 9.

For simplicity, the term "contractor" in this specification refers to the company responsible for the construction of the deep mixing work. In practice, this company may be either a GC or a DMM subcontractor. If a DMM subcontractor is used, the terms GC or DMM contractor must be used to clearly identify the relative responsibilities.

The term "engineer" in this specification refers to the owner's representative. This individual may be an employee of the owner or may be a subcontractor/subconsultant.

PART 1-GENERAL

1.1 Scope

The contractor should furnish all labor, equipment, and materials necessary to plan, design, and construct the deep mixing and associated testing, monitoring, sampling, and recording to meet the performance requirements outlined in these plans and specifications.

1.2 References

The following publications form a part of this specification to the extent indicated by the references. The latest publication as of the issue date of this specification should govern, unless indicated otherwise.

1. Federal Highway Administration. (2012). Deep Mixing Manual for Embankment and Foundation Support, U.S. Department of Transportation, Washington, DC.
2. ASTM C150. (2012). "Standard Specification for Portland Cement," Book of Standards Volume 04.01, ASTM International, West Conshohocken, PA.
3. ASTM C192. (2012). "Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory," Book of Standards Volume 04.02, ASTM International, West Conshohocken, PA.
4. ASTM C618-08a. (2012). "Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete," Book of Standards Volume 04.02, ASTM International, West Conshohocken, PA.
5. ASTM C821-09. (2009). "Standard Specification for Lime for Use with Pozzolans," Book of Standards Volume 04.01, ASTM International, West Conshohocken, PA.
6. ASTM C989-09. (2012). "Standard Specification for Slag Cement for Use in Concrete and Mortars," Book of Standards Volume 04.02, ASTM International, West Conshohocken, PA.
7. ASTM D2166. (2006). "Standard Specification for Unconfined Compressive Strength of Cohesive Soil," Book of Standards Volume 04.08, ASTM International, West Conshohocken, PA.
8. ASTM D4380. (2012). "Standard Test Method for Density of Bentonitic Slurries," Book of Standards Volume 04.08, ASTM International, West Conshohocken, PA.
9. ASTM D5084. (2010). "Standard Test Method for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter," Book of Standards Volume 04.08, ASTM International, West Conshohoken, PA.

1.3 Definitions

The technical and construction terms used in this specification are outlined in this section.

Admixtures: Ingredients in the grout other than binder, bentonite, and water. Admixtures can be fluidifiers, dispersants, or retarding, plugging, or bridging agents that permit efficient use of materials and proper workability of the grout.

Bentonite: Ultra-fine natural clay principally comprising sodium cation montmorillonite.

Binder:Chemically reactive material (i.e., lime, cement, gypsum, blast furnace slag, flyash, or other hardening reagents) that can be used for mixing with in situ soils to strengthen the soils and form DMM columns. Also referred to as stabilizer or reagent. In U.S. practice, binder slurry is frequently referred to as grout or slurry.

Binder content: Ratio of weight of dry binder to dry weight of soil to be treated.

Binder factor: Ratio of weight of dry binder to volume of soil to be treated.

Binder factor in-place: Ratio of weight of dry binder to volume of mixture, which is the volume of the soil to be treated plus the volume of the slurry for the wet method or the volume of the dry binder for the dry method.

Binder slurry: Stable colloidal mixture of water, binder, and admixtures that assists in loosening the soils for effective mixing and strengthening the in situ soil upon setting.

BRN: Total number of mixing blade rotations per meter of shaft movement. BRN has been developed for ensuring uniformity of products produced only by WRE/ DRE systems. For horizontal cutter systems (e.g., CSM), revolutions per minute are typically reported as an indicator of mixing energy (not applicable for chainsaw-type mixers (e.g., TRD)).

Column: Pillar of treated soil produced in situ by a single installation process using a mixing tool, typically a rotating auger, to make a round column. A rectangular barrette produced by "element" and "wall," which are related geometric terms.

Deep mixing equipment: Deep mixing equipment with various mixing tools including single vertical shaft mixing tools, multiple vertical shaft mixing tools, horizontal rotating circular cutters, chainsaw-type cutters, etc.

DMM: In situ ground treatment in which soil is blended with cementitious and/or other binder materials to improve strength, permeability, and/or compressibility characteristics (synonymous terms (some proprietary) include DSM, deep mixing, CDSM, and soil cement mixing).

Dry mixing: Process of mechanical disaggregation of the soil in situ and its mixing with binders with or without fillers and admixtures in dry powder form. Binders are delivered primarily on tool retrieval.

Element:This is an inclusive term that refers to a DMM element produced by a single stroke of the mixing tools at a single equipment location. A column produced by a single-axis machine, a set of overlapping columns produced by a single stroke of a multiple shaft mixing tool, and a rectangular barrette produced by a mixing tool with horizontal axis rotating cutter blades are each considered an element. An element consisting of overlapping columns produced by a single stroke of a multiple-shaft mixing tool is sometimes referred to as a "panel." A chainsaw-type mixing tool that travels as it mixes produces a continuous wall, which is not an element.

Engineer: The representative of the design engineer or of the project owner (owner). This person may either be a subconsultant to the owner or a member of the owner's staff.

Filler: Non-reacting materials (i.e., sand, limestone powder, etc.).

Mix design: Ratios of soil, binder, water, and additive quantities required to meet the design requirements of the project.

Mixing process: Mechanical disaggregation of the soil structure and dispersion of binders and fillers in the soil.

Mixing tool: Equipment used to disaggregate the soil and distribute and mix the binder with the soil. Consists of one or several rotating units equipped with several blades, arms, and paddles with or without continuous or discontinuous flight augers, horizontal rotating cutter blades, or chainsaw-type cutters.

Penetration (downstroke): Stage/phase of mixing process cycle in which the mixing tool is delivered to the appropriate depth (disaggregation phase) for withdrawal injection and disaggregation and mixing for penetration injection. (Not applicable for chainsaw-type mixers (TRD)).

Penetration/retrieval speed: Vertical movement per unit time of the mixing tool during penetration or withdrawal. (Not applicable for chainsaw-type mixers (TRD)).

Restroke: Additional penetration and withdrawal cycle of the mixing tool to increase the binder content and/or the mixing energy. (Not applicable for chainsaw-type mixers (TRD).)

Retrieval: Withdrawal of mixing tool from bottom depth to the ground surface. Binder may be injected during retrieval, which also imparts additional mixing energy.

Rotation speed: Number of revolutions of the mixing tool per unit time.

Soil-cement: Product of DMM consisting of a mixture of the in situ soil and binder. Also referred to as treated soil or deep mixed material. "strength" usually means shear strength, but during QC/QA, "strength" usually means unconfined compressive strength. For clarity, the intended type of strength should always be identified when using this term.

Stroke: One complete cycle (penetration and withdrawal) of the mixing process.

Volume ratio: Ratio of the volume of slurry injected (in wet mixing) to the volume of soil to be treated.

Wall: Group of overlapping elements arranged to form a continuous wall. Continuous walls can also be constructed using a chainsaw-type of mixing device. Walls can be referred to as shear walls, cutoff walls, or excavation support walls depending on the application. A shear wall can also be referred to as a buttress.

Water: Fresh water that is free of deleterious substances that adversely affect the strength and mixing properties of the grout and is used to manufacture grout.

Water-to-binder ratio: Weight of water added to the dry binder divided by the weight of the dry binder. In wet mixing, the water-to-binder ratio of the slurry is determined from the weights of water and dry binder used to manufacture the slurry in a plant at the ground surface. In either wet or dry mixing, the total water-to-binder ratio is the weight of water in the mixture divided by the weight of dry binder. For wet mixing, the total water-to-binder ratio is the weight of slurry water plus the weight of soil water divided by the weight of dry binder. For dry mixing, the total water-to-slurry ratio is the weight of soil water divided by the weight of dry binder.

Wet mixing: Process of mechanical disaggregation of the soil in situ and its mixing with slurry consisting of water and binders with or without fillers and admixtures. Binder is delivered on mixing tool penetration for vertical and horizontal axis mixing tools.

Withdrawal (upstroke): Stage or phase of retrieval of the mixing tool in which the final mixing occurs for penetration injection and initial mixing for withdrawal injection. Disaggregation occurs during the penetration for both penetration injection and withdrawal injection. (Not applicable for chainsaw-type mixers (TRD).)

Withdrawal rate: The average up-hole retrieval rate of the mixing tool.

1.4 Project Description and Performance Requirements

Commentary: In this section, the project purpose should be outlined, including the identifiers for the embankment, abutment, culvert, retaining wall to be supported using a deep mixed foundation, project location, roadway section number, county, State, etc. The overall structure dimensions and layout may be highlighted by reference to the plans.

The information provided in this section is critical to the contractor's understanding of the project, upon which the contractor will determine the preferred DMMs and materials to be used. The specification requires the DMM contractor to construct the deep mixed material (mix design and mixing process) to meet the strength and permeability requirements outlined in the engineer's design. Except for a design-build project or an alternative design submission, the geotechnical design should be carried out by the engineer before the DMM project is allowed for bid and construction. The specification should outline the minimum and/or maximum allowed values for certain geometric parameters to afford the contractor flexibility in construction while still assuring that the final DMM product will satisfy the requirements for performance.

The following items must be outlined based on the requirements for a particular project:

1. Particular DMM schedule information (e.g., preloading or phasing schedule). If particular schedule requirements are associated with the DMM, care must be taken to check the overall specification package for consistency with scheduling requirements presented in other sections.
2. Requirements of structural reinforcement, if any (material grade and installation procedure for installation, including pile caps).
3. Spoil handling requirements.
4. Environmental restrictions (i.e., noise, vibrations, emissions, etc.).
5. Maximum allowable displacement of adjacent structures.

A.  The purpose of the project is to provide support for __________.

B.  Allowable geometric parameters for DMM construction are outlined in table 25.

Table 25. Allowable geometric parameters for DMM construction.

C.  Layouts and sizes of deep mixing elements that adhere to the minimum and maximum values of the parameters listed in table 25 and included in the plans and/or specifications will be deemed acceptable to meet the requirements of the engineer's design, and additional design calculations will not be required. If layouts and element sizes do not adhere to these requirements, design calculations must be prepared and stamped by a professional engineer registered in the jurisdiction where the project is located and retained by the contractor. The calculations must be submitted to the engineer for review and possible approval after the contract is awarded. The owner/engineer is not obligated to accept designs that fall outside the geometric limits in the plans and specifications.

1.5 Qualifications of Contractor

Commentary: The following personnel are typically involved in a DMM project:

• The project manager is the contractor representative responsible for the overall direction of the DMM project, including site operations, technical acceptability, project billing, and reporting. The project engineer and the project superintendent ordinarily report to the project manager.
• The project engineer is responsible for supervising the QC technicians' work, providing technical support to the QC technician, and reviewing production records and QC/QA data to ensure the quality of the DMM work.
• The project superintendent oversees construction operations, equipment, and material supply; collects and compiles daily production reports; and ensures QC activities are conducted in accordance with project requirements. The project superintendent and the project engineer may work together on QC activities and documentation.
• The DMM equipment operator is responsible for operating the equipment during construction.
• On large, complex, or critical deep mixing projects, the contractor or the owner, and sometimes both, employs a deep mixing specialist or a review board to provide advice, review, and assistance with dispute resolution.

A.  The DMM contractor must have previous successful experience with DMM projects for the soil conditions and project scope similar to that of the project being bid (contractor provides project description(s) and reference list).

B.  The DMM contractor must assign a project manager who has had significant experience on at least five DMM projects (contractor provides the number of years/projects, project description(s), and reference list).

C.  The DMM contractor must assign a project engineer to supervise the construction of the DMM work. The project engineer must have had significant experience on at least five DMM projects (contractor provides the number of years/projects, project description(s), and reference list). For a design-build project, the DMM contractor must assign a professional engineer who is registered in the jurisdiction in which the project is located to supervise the design and preparation of the drawings and to review QC/QA records and as-built drawings to confirm that the DMM work meets the design intent.

D.  The DMM contractor must assign a full-time project superintendent with at least five projects and at least 130,000 yd³ (100,000 m³) of total treatment volume in DMM construction (contractor provides the number of years/projects, project description(s), and reference list).

E.   The DMM contractor must provide at least one DMM equipment operator with at least 1 year of experience with the equipment and DMM construction (contractor provides the number of years/projects, project description(s), and reference list).

F.   Written requests for substitution of these key personnel must be submitted prior to personnel changes. Documentation must be submitted to the owner that demonstrates that the substitute meets the requirements listed. Substitution may not be made until written approval is provided by the owner.

1.6 Available Information

Commentary: The subsurface conditions expected can significantly impact the contractor's choice of equipment, methods, materials, bidding process, and contract administration. Experience has proven the advantages of using a geotechnical baseline report in successful projects. It is the owner's responsibility to divulge knowledge of potentially difficult ground conditions that could result in avoidable differing site conditions claims. However, the information should not be written in an exculpatory manner that expressly intends to transfer the risk or responsibility unfairly from the owner to the contractor. It is the contractor's responsibility to anticipate and allow for typical variability in subsurface conditions as discussed in the geotechnical reports. Information on writing effective geotechnical baseline reports is provided by Essex.⁽¹³⁷⁾ Important geotechnical information includes, at a minimum, soil type, density, strength, plasticity, moisture content, and gradation for each stratum to be mixed. If organic soils are encountered, the organic content should be measured on selected samples and reported.

In some situations, deep mixing may have been performed at nearby sites, but no information is available because the owner, engineer, and contractor are private entities different from those involved in the current project.

Available information developed by the owner or by the owner's duly authorized representative (engineer) includes the following items:

• Geotechnical reports No.(s) ________ titled ________, dated ________.
• Pre-production deep mixing test program reports No.(s) ________ titled ________, dated ________.
• Deep mixing reports from adjacent sites reports No.(s) ________ titled ________, dated ________.

1.7 Construction Site Survey

Commentary: The location of both active and abandoned buried utilities at the site can have a significant impact on the design and construction of deep mixing works. Careful consideration of the presence and location of all utilities is required.

A.  Prior to bidding, the contractor should review the available subsurface information and visit the site to assess the site geometry, equipment access conditions, location of existing structures, and above-ground utilities and facilities.

B.  The contractor should field locate and verify the locations of all utilities prior to starting work. The contractor should maintain uninterrupted service for those utilities designated to remain in service throughout the work. The contractor should notify the engineer of any utility locations different from those shown in the plans that may require relocation of deep mixed elements or structure design modification. Subject to the engineer's approval, the contractor should be compensated for additional costs of element relocation and/or structure design modifications resulting from utility locations different from those shown in the plans.

1.8 Submittals

A.  Contractor experience profile: The contractor must submit documentation evidencing the experience requirements outlined in section 1.5.

B.  Bench-scale testing report: The contractor must submit results from bench-scale tests conducted. The report should provide all data collected, including, at a minimum, descriptions of sampling techniques used, boring logs, classifications of all major soil strata to be mixed, site groundwater conditions, binder materials used, mixed design proportions, laboratory mixing techniques used, and curing curves for unconfined compressive strength versus time for each major soil type. Discussion of tests results should be provided, including proposed mix designs for use in the field.

C.  Field validation program plan: At least 30 days before the start of the field validation program, the contractor should submit a field validation program plan that contains descriptions of the construction procedures, equipment, and ancillary equipment to be used for mixing and binder proportioning and injection; mix design parameters and associated soil strata to be evaluated; operational and material parameters to be monitored during field validation; layout of the DMM elements to be constructed; a summary of QC/QA samples to be collected and tested; and examples of the forms that will be used to document the work.

D.  Deep mixing work plan: Based on the results of the preconstruction testing (bench-scale and field validation program), at least 30 days prior to the start of deep mixing work, the contractor must submit a deep mixing work plan for review and approval. This plan must include the following items:

• Detailed descriptions of sequence of construction and all construction procedures, equipment (catalog cut sheets), and ancillary equipment to be used to penetrate the ground, proportion and mix binders, and inject and mix the site soils.
• Proposed mix design(s), including binder types, additives, fillers, reagents, and their relative proportions, and the required mixing time, water-to-binder ratio of the slurry (for wet mixing), binder factor (for dry and wet mixing), and volume ratio (for wet mixing) for a deep mixed element.
• Proposed injection and mixing parameters, including mixing slurry rates, slurry pumping rates, air injection pressure and volume flow rates, mixing tool rotational speeds, and penetration and withdrawal rates.
• Methods for controlling and recording the verticality and the top and bottom elevation of each element.
• The necessary procedure and measurement to confirm the end-bearing when DMM elements are required to penetrate into a bearing layer,.
• Working drawings and calculations for the DMM elements showing the site location of the DMM project as well as the dimensions, layout, and locations of all DMM elements. Drawings should indicate the identification number of every element if a multi-shaft mixing tool is used and every column if a single-auger mixing tool is used. Calculations and drawings should demonstrate that the element layout, depth, and quantity meet the specification requirements. For a design-build project, the design calculations should be performed by a professional engineer who is registered in the jurisdiction in which the project is located. He/she will also prepare, stamp, and sign the drawings.
• DMM schedule information (e.g., preloading or phasing schedule).
• Sample daily production report, including the items described in section 1.8.
• Details of all means and methods proposed for QC/QA activities, including surveying, process monitoring, sampling, testing, documenting, and marking schedule milestones.
• Names of any subcontractors used for QC/QA activities. An independent laboratory must be used for QC/QA testing and must be approved by the owner/engineer.

E.   Material certifications: Certificates of compliance must be submitted as proof of conformance to materials standards and requirements for each truckload of binder, admixtures, and steel, as needed.

F.   Production records: By the end of the next business day following each deep mixing shift, the contractor should submit a daily production report in the approved format. The report should be completed and signed by the contractor's project superintendent. The report should contain at a minimum the following information:

• Project name.
• Day, month, year, and time of work shift (beginning and end).
• Name of field superintendent in charge of the work for the contractor.
• Deep mixing equipment (rig number) in operation during the shift and specific activities conducted by said equipment.
• Type of mixing tool.
• Treatment zone and reference drawing number.
• Elevation of top and bottom of treatment zone.
• Element number, diameter, and location coordinates.
• Date and time (start and finish) of element.
• Location of each completed column/element installed during the work shift and all zones completed to date on a plan of suitable scale to clearly show the location of the elements. Frequently, the owner/engineer will specify this scale at 1 inch = 10 ft or 1 inch = 20 ft, depending on the size of the elements and the amount of detail necessary.
• Mix design (not applicable for dry mixing).
• Slurry specific gravity measurements (not applicable for dry mixing).
• Binder slurry injection rate (gal/min (L/min)) plotted at each 3-ft (1-m) depth interval for the full depth of the treated zone. Variations in volumes should be noted (not applicable for TRD).
• Mixing tool rotation speed in revolutions per minute versus depth.
• Penetration/withdrawal rates of the mixing tool in ft/min (m/min) plotted at each 3 ft (1 m) of depth (not applicable for TRD).
• Element verticality measurements.
• Plots of BRN and binder factor versus depth for each element plotted at least every 3 ft (1 m) of depth. The total number of rotations should be reported for CSM (not applicable for TRD).
• For TRD, the vertical and horizontal rates of cutter chain travel should be reported along with the slurry injection rate. From these data, the average binder factor as a function of position can be calculated and reported.
• A description of obstructions, interruptions of binder injections, or other difficulties during installation and their resolution.
• Other pertinent observations including but not limited to binder escapes, ground settlement or heave, collapses of the treatment zone, and any unusual behavior of any equipment during the deep mixing process.
• For both wet grab samples and coring, provide collection date, time, plan location, elevation, and identification numbers of all deep mixed samples, including unsuccessful attempts to retrieve samples.
• For coring operations, provide the coring method, equipment, and personnel; recovery percentage and percent treatment (percent of run length that is treated) for each core run; sample collection, handling, and storage details; and name of person responsible for logging and collecting cores and samples to be tested.
• Quantities of all binder materials delivered to the site plus a reconciliation showing the amount actually injected.
• Summary of any down time or other unproductive time including time, duration, and reason.
• Detailed results of all testing.

G.  QC/QA records: Calibration data must be submitted for all measurement devices used for binder production, deep mixing operational monitoring, and laboratory testing. Within 3 business days of completing any QC/QA testing, the contractor should submit the test results, including original data sheets from the laboratory and an evaluation of the compliance of the test results with project acceptance criteria. Equipment should be calibrated prior to initial use and repeated every 3 months.

H.  As-built field measurement data:

Commentary: As-built measurement data can be required at the end of the project or after a phase of the project is completed, depending on project size and layout.

After completion of the project, the contractor must submit as-built field measurement data indicating surveyed as-built plan locations of each DMM element, including the element center (per site specific coordinates), the element dimension, the column verticality, and the top and bottom elevations of each element to the accuracy required by the project specifications.

1.9 Preconstruction Meeting

Commentary: Contractor attendance at the preconstruction meeting should be mandatory. The date, time, and location of the meeting should be included in this section.

The contractor is required to attend a pre-construction meeting on ____________.

PART 2-Materials and Equipment

2.1 Materials

Commentary: If use of onsite site water is permitted, the specifications should describe the source. The owner may want to specify the types of materials to be used for mixing. Alternatively, the owner may specify what materials and methods are not permitted (e.g., for environmental or cost reasons).

A.  Cement binder materials should conform to ASTM C150 low-alkali type II PCC. Type III PCC should not be used. Slag cement should conform to ASTM C1157. All cement should be homogeneous in composition and properties and should be manufactured using the same methods at each plant by each supplier. Tricalcium aluminate content should not exceed 8 percent.

B.  Water used in drilling, mixing cement grout, and other applications should be potable.

C.  Admixtures will not be allowed unless the contractor submits documentation demonstrating the effects of the admixture and the admixture is approved by the engineer.

D.  Binder slurry should be a stable homogeneous mixture of approved binder, approved admixtures, and water. The ratios of various components may be proposed for modifications by the contractor but should not be implemented until reviewed and accepted by the engineer. Any proposed deviations from the submitted and approved mix design should be resubmitted for the engineer's approval. Revalidation through laboratory or field testing is necessary for changes that exceed 10 percent of previously approved mix designs. Regardless of such changes, the contractor is responsible for satisfying the acceptance criteria.

E.   Soil-binder mixture should be a stable mixture of binder slurry and in situ soil. The contractor should propose the ratios and quantities of various components.

2.2 Equipment

Commentary: DMM equipment varies greatly, and the selection of mixing method and equipment is typically left to the contractor. The engineer may specify the general capacity requirements of the equipment and level of monitoring required to evaluate conformance with the specification. Different levels of monitoring equipment are available, ranging from manually to fully automated control and recording.

A.  Deep mixing equipment should be of sufficient size, capacity, and torque to perform the required deep mixing to the desired depths. Characteristics of deep mixing equipment are as follows:

• The equipment should be capable of advancing through previously installed elements to achieve designed overlapping or remixing as needed and be sufficient to maintain the necessary revolutions per minute and penetration rate at the maximum depth to achieve thorough mixing.
• The mixing and injection equipment should be sufficient to adequately blend and distribute the binder with the in situ soils to provide the required strength.
• The mixing tools should be adequately marked to allow the engineer to confirm the penetration depth to within 1 ft (0.3 m) during construction. If rigs with varying mixing tool lengths are used, the shortest tools should extend to the lowest element termination elevations indicated in the plans.
• All equipment should have monitoring equipment to permit accurate and continuous monitoring, recording, and controlling of mixing tool depth, location, binder volume flow rates and factors, binder injection pressures and quantities, tool rotational speeds, tool advancement, and withdrawal rates.
• The monitoring equipment should be calibrated at the beginning of the project, and the data should be submitted to the owner. Calibration should be repeated every 3 months.
• The owner/engineer should have access to monitoring equipment.

B.  Binder materials handling and storage:

Commentary: Binder may be produced using either batching or a continuous mixing process, depending on the project size and production rate. The means used to prepare and pump the slurry (wet mixing) or convey the dry binder (dry mixing) to the injection point should be identified. Controls to ensure the proportioning or a monitoring system for proportion verification must be used, especially for continuous mixing processes. Calibration is required for slurry proportioning methods that do not rely on weighing each component for each batch. State emissions requirements must be considered. Air quality permits for material storage may be required in certain States.

• The contractor should measure, handle the transport, and store bulk binder in accordance with the manufacturer's recommendations.
• Dry materials should be stored in dry containers. The binder should be adequately protected from moisture and contamination while in transit and when stored at the project site.
• Dry materials should be transported to the project site and placed in the onsite storage tanks using a closed system. Any air evacuated from the storage tanks during the loading process should be filtered before being discharged to the atmosphere.
• Material that has become caked due to moisture absorption should not be used. Binder materials containing lumps or foreign matter of a nature and in amounts that may be deleterious to the injection operation should not be used. In each instance in which the binder source is changed, the batch plant silos should be completely emptied before storing binder from the new source. Mixing binders from different sources in the same silos is not permitted.
• Equipment used for proportioning during binder production should be calibrated prior to initial use and repeated every 3 months or every time the batch plant is relocated, whichever is sooner. Calibration records must be submitted to the owner in accordance with section 1.8.
• Positive displacement pumps should be used to transfer the slurry to the injection point. The contractor should demonstrate that the equipment can uniformly deliver binder at suitable rates in accordance with the construction plan.

2.3 Products

Commentary: The product requirements will be verified by laboratory and field testing to confirm the parameters assumed in the design. It is critical that the design criteria be verifiable by measurements and testing and that all results be used to verify that the specification requirements have been satisfied or to provide measurement data for payment. It is important for the owner/engineer to understand which design parameter or payment item is being confirmed by each test to avoid unnecessary testing.

A.  Geometric tolerance: DMM elements installed should meet the geometric tolerance outlined in section 3.6.

B,  Strength: The strength of treated soils should meet the strength criteria outlined in section 3.6.

C.  Uniformity: The uniformity of treated soils should meet the uniformity criteria outlined in section 3.6.

PART 3-EXECUTION

3.1 General

Deep mixed elements should be constructed to the lines, grades, and cross sections indicated in the plans and should meet the strength and uniformity requirements specified in section 3.6. The contractor should establish consistent procedures during construction to ensure that the acceptance criteria are satisfied. The procedures should be established based on the results of the field validation program.

3.2 Field Validation Program

Commentary: The contractor should determine and demonstrate the field mixing parameters that reliably produce mixed soil satisfying the specification requirements. Based on a review of the results of the field validation program, the contractor may propose changes to the originally intended means, methods, and materials. These changes to the installation procedures must be agreed on by the owner prior to production. It is important to recall that the strength of laboratory- and field-mixed materials will differ.

Sometimes, a contractor may install two test elements to become familiar with the soils and operational parameters. Only one full-depth core should be required from each group of elements installed using the same mixing parameters.

A.  Prior to production, the contractor must construct a test section at the location shown in the plans to verify that the contractor's proposed equipment, procedures, and mix design can uniformly mix the onsite soils and achieve the product requirements outlined in the acceptance criteria in section 3.6.

B.  The contractor should submit the results of the field validation program to the owner as outlined in section 1.8.

C.  Laboratory bench-scale testing should be used to identify initial mix designs for use in the field validation program. Bulk soil samples from the site should be obtained by the contractor. A suite of three mix designs is required for each major soil stratum encountered to the expected termination depth of the elements.

D.  The test section should be installed at the location indicated in the plans. The contractor should submit a plan drawing showing the locations of the test section elements. At least three elements should be installed with different mixing parameters for each element. Each element should extend from the top elevation to the bottom elevation (or required penetration into bearing layer) if different mixing parameters are used. At least one full-depth core should be obtained from each element or group of elements installed using the same mixing parameters.

E.   The contractor should obtain full-depth core samples from the test elements in accordance with the QC/QA requirements outlined in section 3.6. Test samples should be submitted to an approved independent laboratory for testing. The contractor may propose other sampling techniques to obtain continuous samples of the deep mixed material which, if approved by the engineer, could be submitted as further evidence of compliance with the acceptance requirements.

3.3 Binder Preparation (Wet Method)

A.  The contractor should mix dry binder and water in the slurry plant to produce a uniform suspension of binder in the water.

B.  The slurry should be held in the agitation tank for a maximum holding time of 4 h. Holding time is calculated from the beginning of the initial mixing.

C.  Slurry density must be measured in accordance with the requirements outlined in section 3.6. If the slurry density is outside the tolerance required by the mix design, the contractor should recalibrate monitoring equipment and perform additional testing as required by the engineer at no additional cost to the owner. The contractor may also adjust binder or water quantities appropriately and retest at no additional cost to the owner. The specific gravity of the binder slurry measured during production may not deviate by more than 3 percent from the established specific gravity.

D.  Monitoring data should be recorded in the daily production report.

3.4 Locating Elements

Commentary: The delay and standby procedures to be used when obstructions are encountered must be defined clearly. It is not always practical for the contractor to maintain production by moving to a different section of the site and continuing deep mixing while an obstruction is being investigated. Redrilling hardened elements with high target strengths may be impractical in some cases, so it is important that the columns/elements be located accurately by the contractor.

A.  Before beginning installation, the contractor should accurately stake the location of the deep mixed elements shown in the plans using a licensed surveyor. The contractor should provide an adequate method for locating elements to allow the engineer to verify the as-built location of the elements during construction. The contractor will not be compensated for elements that are located outside of the tolerances specified in section 3.6. The owner will review the location of misaligned elements to determine if the elements interfere with the proposed construction. If the owner determines that misaligned elements will interfere with construction, the contractor should correct the alignment. The method of correction should be submitted by the contractor to the owner/engineer for review and approval.

B.  If an obstruction is encountered that prevents drilling advancement, the contractor should immediately notify the engineer and investigate the location and extent of the obstruction using methods approved by the engineer. The contractor should propose remedial measures to clear the obstruction for approval by the engineer. The contractor will be compensated for removal or clearing of obstructions with prior approval from the owner. If the element cannot be installed at the design location due to obstructions, the element should be relocated as directed by the engineer.

3.5 Mixing

A.  The equipment, installation procedures, materials, and sampling and testing methods established during the field validation program should be used for production. The contractor may request that the established mix design, equipment, installation procedure, or test methods be modified; however, the engineer may require additional testing or a new test section at no additional cost to the owner to verify that acceptable results can be achieved. The contractor should not employ modified mix designs, equipment, installation procedures, or sampling and testing methods until approved by the engineer in writing.

B.  If the contractor must modify established methods due to equipment breakdowns, manpower changes, or improved conditions, a new test section should be installed at no cost to the owner. If the owner requests modifications to the means and methods for design or other reasons (e.g., site conditions differ from what were encountered during the geotechnical explorations and the preproduction test program), the contractor should be compensated for new test sections.

C.  Installation of each column should be continuous. If an interruption of more than 1 h occurs, the element should be remixed while injecting binder at the design rate for the entire height of the element at no additional cost to the owner.

D.  Binder slurry injection rate: The contractor should record in the daily production report on a real-time basis the weight of dry binder or the volume of binder slurry injected for each 3 ft (1 m) (measured vertically) during penetration and withdrawal for each element. If the weight of dry binder or the volume of binder slurry injected per vertical foot (meter) is less than the amount required to meet the binder factor or volume ratio established during the field validation program, the element should be remixed, and additional binder should be injected at the design binder injection rate to a depth at least 3 ft (1 m) below the deficient zone at no additional cost to the owner. The binder factor should be recorded and plotted versus depth, and the records should be visible to the operator on a screen during construction so that proper adjustments may be made in real time.

E.   Rotational speed and penetration/withdrawal rates: The necessary rotational speeds and penetration/withdrawal rates for the various soil layers encountered should be determined during the field validation program. The penetration and withdrawal rates must be monitored on a real-time basis. If the BRN is more than 15 percent below the value determined to be reliably acceptable from the field validation program, the column/element section must be remixed while injecting grout at the design binder injection rate.

F.   Vertical alignment: The contractor should monitor and control the vertical alignment of the mixing tool stroke in two directions (longitudinal and transverse to the element alignment). Vertical alignment should be maintained within 1 percent of plumb during the element installation.

G.  Element top and bottom elevations:

Commentary: The termination depth of DMM elements is designed to meet the foundation requirements of the structure, as discussed in chapter 6. For designs that specify the top and bottom elevations of the DMM elements, the constructed elements must extend from the specified bottom elevation or lower to the specified top elevation or higher. The specified top and bottom elevations may vary across the site depending on in situ ground conditions and facility requirements.

For sites that have a well-defined competent bearing stratum, the necessary bottom elevation can be based on refusal criteria determined from penetration speed, vertical load from the mixing tool, mixing energy, and/or power consumption needed for mixing tool penetration. The refusal criteria can be developed during the field validation program by installing test columns within 5 ft (1.5 m) of an existing boring and recording the operational parameters encountered when the intended competent stratum is reached as indicated in the adjacent boring. If mix designs or operational procedures are modified during production, refusal criteria must be reestablished.

The total depth of penetration can be measured either by observing the length of the mixing shaft inserted below a reference point on the mast or by subtracting the exposed length of shaft above the reference point from the total shaft length. The contractor is responsible for achieving the specified top and bottom elevation requirements and for recording the actual elevations. However, remedial measures for elements of insufficient depth could significantly and adversely impact project costs and schedule, and it is helpful for the engineer to observe and confirm the column termination depth during construction. The mixing equipment must be adequately marked to allow QA personnel to confirm the penetration depth. The depth may also be determined by instrument and displayed in real time. The contractor should measure and record top and bottom elevations in the daily production report (see section 1.8).

If the depth to the competent soil layer at the bottom of the DMM element is found to be different from that indicated on the plans, the engineer may direct the contractor to shorten or deepen the element. The contractor should be compensated based on the decreased or increased amount of deep mixing as the engineer varies the termination depths. The contractor should not, however, be compensated for any portions of the elements that are above the top elevations or below the bottom elevations shown on the plans that are not approved by the engineer.

• Elements should be installed in accordance with the line and grades shown in the plans.
• The total depth of penetration should be measured either by observing the length of the mixing shaft inserted below a reference point on the mast or by subtracting the exposed length of shaft above the reference point from the total shaft length. Care should be taken to note ground surface heave that may affect reference points for measuring mixing shaft length. The contractor should note and record on the daily production report the final depth of the stroke. The equipment should be adequately marked to allow the engineer to confirm the penetration depth during construction.
• If the elevations of the top of competent soils are found to be different from those estimated, the engineer may direct the contractor to shorten or deepen the elements. Measurements of torque, down pressure, and/or the change in rotational speed may be used as indications of termination depth if a suitable correlation can be develop by the contractor to the satisfaction of the engineer. The contractor will be compensated based on the decreased or increased amount of deep mixing as termination depths vary. The contractor should not be compensated for any portions of the elements that are above the top elevations or below the bottom elevations shown on the plans unless approved by the engineer.

H.  Bottom mixing:

Commentary: Bottom mixing is generally required to provide an adequate level of mixing in the lower portion of the DMM column. Bottom mixing may be conducted by lifting the mixing tool approximately 5 to 10 ft (1.5 to 3 m) above the element bottom elevation while maintaining mixing action and repenetrating to the element bottom elevation. The zone and procedure of bottom mixing is established during the field validation program. (Bottom mixing is not applicable for TRD.)

The contractor should conduct bottom mixing as established in the field validation program.

I.    Control of spoils:

Commentary: The contractor's selection of means and methods can be heavily influenced by the requirements and procedures for handling spoils. Spoils may be handled in several different ways. Often, spoils are contained at the ground surface until they are sufficiently cured to be stockpiled and used for engineered fill. If unacceptably high pH levels preclude the use of spoils as fill, removal and offsite disposal may be necessary.

The contractor should control and dispose of all waste materials produced as a result of the mixing operation in accordance with the project requirements. The areas designated in the plans should be used for containing and processing the spoils.

3.6 QC

A.  The contractor should provide all the personnel and equipment necessary to implement the QC/QA requirements of the project. The engineer will review daily production reports and QC/QA test reports to verify that QC/QA procedures are being properly implemented.

B.  Deep mixing work plan: The contractor's deep mixing work plan should include descriptions of all QC/QA activities and reporting as outlined in section 1.8. After the field validation program is conducted, the contractor may revise the QC/QA procedures, if approved by the engineer. The contractor should maintain the established and approved QC/QA procedures throughout production to ensure consistency in the deep mixing installation and to verify that the work complies with all requirements indicated in the approved working drawings.

C.  Daily production records should be submitted as outlined in section 1.8.

D.  Binder slurry density: The contractor should measure the specific gravity of the binder slurry at least twice per shift per slurry plant using the methods outlined in ASTM D4380 (not appropriate for dry mixing). The specific gravity of the binder slurry measured during production may not deviate by more than 3 percent from the established specific gravity. If the slurry density deviates by more than 3 percent, the contractor should recalibrate monitoring equipment and perform additional testing as required by the engineer at no additional cost to the owner. The contractor may also adjust binder or water quantities appropriately and retest at no additional cost to the owner.

E.   The contractor should make simple routine checks of material quantities such as counting the number of bags or truckloads of binder materials that have been used. These quantities should be recorded in the daily production report.

F.   Wet sampling and testing (not appropriate for dry mixing):

Commentary: Some deep mixed material may not be able to be wet grab sampled because either the mixture is too stiff or the material may not flow back into the void left after the sampler is extracted, possibly leaving a damaged element.

• The contractor should perform all wet sampling in the presence of the engineer. The contractor should notify the engineer at least 1 business day in advance of beginning sampling operations.
• The contractor should propose locations for wet sampling while considering input from the owner/engineer. Sample locations should be distributed uniformly both laterally and vertically within the deep mixed zone. Sampling depths should be selected to ensure that wet samples are retrieved from every main soil stratum underlying the site.
• The contractor should report the information required in the daily production report (see section 1.8) for all attempts, successful and unsuccessful, to obtain wet samples.
• The contractor should collect a minimum of three wet bulk samples (each sample is taken at one selected depth at one location) for each mix design used in each test section. At least one wet bulk sample (one selected depth at one location) should be collected from within each main soil layer from elements produced using each mix design.
• One wet bulk sample (one selected depth at one location) should be retrieved every 2 production days or for every 2,000 yd³ (1500 m³) of treated soil, whichever produces the higher sampling frequency.
• Wet bulk samples should be collected using a bailer-type sampling tool or similar.
• Eight test specimens from each wet bulk sample should be made with 3-inch (76-mm) diameter and 6-inch (152-mm) length, using the following general procedures (detailed procedures on specimen preparation are outlined in appendix A):
  1. Pour the sample into a container, screening for oversized lumps (gravel versus unmixed soil). Place the sample in specimen molds in three to five layers. Tap, vibrate, or rod the specimens to remove trapped air bubbles. Use care to avoid additional mixing or kneading action as much as possible on the sample during screening and specimen preparation so that the sample is representative of in-place mixing conditions.
  2. Measure and describe the volume and composition of oversized lumps.
  3. Seal the specimen to prevent moisture from entering or leaving, and store the specimen in a humid environment in accordance with ASTM C192.
  4. The engineer may request additional test specimens for QA testing.

G.  Coring:

Commentary: The coring frequency should be selected by the engineer during the design stage based on considerations of project size, criticality, and complexity. The selected coring frequency can be stated in the specifications either as a percentage of elements or as a combination of the percentage of elements and the treatment area, depending on the project needs.

For production elements on typical DMM projects, one full-depth continuous core should be made for every 3 percent of elements. For smaller, more critical, or more complex projects or at more critical locations within otherwise typical projects such as at structure foundations, the engineer could specify that more elements be cored, up to 4 percent of the total production elements. For a larger, less critical, and less complex project, such as a large DMM embankment foundation project in similar subsurface soils along the entire alignment, the engineer could specify that 2 percent of the production elements be cored. At a minimum, five production elements should be cored at full depth so that a reasonable amount of data is collected, even for small projects.

Some deep mixing equipment produces a relatively large treated area in each element, whereas other equipment produces a relatively small treated area in each element. For example, if the same project were done using two different mixing machines that both produce 3-ft (1-m)-diameter columns and the same column overlap is used but one machine is single-axis and the other is a six-axis machine, then up to six times as many cores would be necessary for the single-axis machine as for the six-axis machine when the number of cored elements is specified on a percentage basis. A justification for requiring a smaller number of cores for equipment that produces larger treatment areas per element is that the same binder factor, mixing parameters, and blending action apply to the entire area treated. Nevertheless, an engineer may want to consider adding a treatment area criterion to the percentage criterion for determining the number of elements to be cored so that a sufficient amount of data can be collected even if the contractor uses equipment that produces a large treated area per element. For example, an engineer may want to specify that full-depth coring be done on 2.5 percent of elements or for every 1,000 ft² (93 m²) of treated ground, whichever produces the greater number of cores. In this example, the 2.5 percent criterion would control for all types of elements that produce a treated area smaller than 25 ft² (2.3 m²) after accounting for overlaps between elements, and the 1,000 ft²(93m²) criterion would control for all types of elements that produce a treated area larger than 25 ft² (2.3 m²) after accounting for overlaps between elements.

For TRD or cutoff walls, every 1,000 yd³ (750 m³) of treated soil or every 300 ft (90 m) of wall in horizontal direction should be cored. For small sized projects, at least five elements should be cored to provide a reasonable amount of information for evaluation of deep mixing work.

• The contractor should perform all coring operations in the presence of the engineer. The contractor should notify the engineer at least 1 business day in advance of beginning sampling operations.
• The contractor should determine the time interval between element installation and coring except that the interval should be no longer than required to conduct 28-day strength testing.
• The full-depth samples should be obtained along a vertical alignment located one-fourth of a column diameter from the column center. If it is difficult to avoid drilling out of the column at this coring location, the contractor may drill one-fourth of a column diameter along the centerline of an element or shear wall so the core enters the adjacent column in the same element.
• Core samples should be retrieved using standard triple-tube or equivalent continuous coring techniques.
• Samples should have a diameter of at least 2.5 inches (65 mm), and each core run should be at least 3 ft (1 m) in length.
• For each field validation test section, the contractor should collect at least one full-depth core for each mix design at locations defined by the owner/engineer.
• The contractor should collect one full-depth core from 3 percent of elements or 860 ft² (79 m²) of treated area, whichever produces a larger number of cored elements. The cores should be drilled at locations defined by the owner/engineer. An element is defined as the treated soil produced by one setup of either a single- or multiple-axis machine.
• The contractor should photograph each core run.
• Upon retrieval, the contractor should provide the cores to the engineer for logging and test specimen selection.
• Following logging, the engineer will select at least five specimens from each full-depth continuous core for strength testing. Each test specimen should have a length-to-diameter ratio of 2 or greater.
• Immediately following logging and test specimen selection by the engineer, the contractor should seal the entire full-depth sample, including the designated test specimens, in plastic wrap to prevent drying and transport the sealed sample to the laboratory. The samples should be protected against drying and mechanical damage prior to and during transport.
• The samples should be stored in a moist room in accordance with ASTM C192 until the test date.
• Samples must not be submerged in water during curing unless they are sealed in a water-tight plastic bag (e.g., a Ziploc® bag) with as much air removed as possible prior to sealing to void swelling.
• The contractor should retain portions of the samples that are not tested until completion and acceptance of all DMM work for possible future inspection and confirmation testing by the engineer. If a large volume of samples cannot be reasonably stored on the job site, cores from columns deemed satisfactory may be disposed of prior to project completion if approved by the engineer.
• All core holes should be filled with cement grout that will obtain a 28-day unconfined compressive strength equal to or greater than the 28-day unconfined compressive strength of the deep mixed material.

H.  Strength testing:

• Strength testing should be conducted by an independent testing laboratory retained by the contractor and approved by the engineer.
• Testing for unconfined compressive strength should be conducted in accordance with ASTM D2166, except that loading should continue on all specimens until the cylinders break sufficiently to examine the interior of the specimen.
• The broken specimen should be photographed so that the engineer may document any apparent segregation, lenses, and pockets in the specimen.
• For field validation testing, unconfined compressive strength testing should be performed on specimens from wet grab samples 3, 7, 28, and 56 days or more after mixing.
• For full production work, unconfined compressive strength testing should be performed on specimens from wet grab samples 7 and 28 days after mixing.
• For specimens obtained by coring, unconfined compressive strength testing should be performed 28 days after mixing.
• Laboratory permeability testing should be performed on cylinders at 7 and 28 days for the test section and usually only at 28 days for the production elements. Laboratory permeability testing should be conducted in accordance with ASTM D5084.

I.    Uniformity evaluation: The contractor should provide the continuous core samples to the engineer for logging and assessing uniformity in accordance with the acceptance criteria outlined in section 3.6.

J.    Both the contractor's testing and the engineer's testing (if performed) must demonstrate that the required strengths are met prior to accepting the work. The contractor should conduct additional coring and testing required to demonstrate the acceptability of the DMM product due to non-conformance at no additional cost to the owner.

K.  Geometric acceptance criteria:

Commentary: The overlap between any two adjacent elements should be as specified by the design engineer based on analyses of vertical shearing, as described in chapter 6, and considering common tooling in the deep mixing industry. Overlap up to 20 percent of the cross-sectional area of a single column has been specified for shear walls. The amount of overlap and the vertical tolerance are interdependent, and both acceptance criteria should be considered together. The design effects of overlaps are discussed in chapter 6.

• The engineer should make the sole determination as to whether the test results satisfy the geometric acceptance criteria.
• The horizontal alignment of the DMM element should be within 4 inches (100 mm) of the planned location at the top of design DMM layout.
• The overlap between any two adjacent elements should be at least _____ percent (to be defined by the engineer) of the cross sectional area of a single column.
• Vertical alignment within 1 percent of plumb should be maintained during the DMM column installation.
• The top of the column should extend upward to the designated elevation or higher.
• The bottom of the DMM column should extend at least to the depth indicated on the construction drawings or to a specified penetration into the bearing layer or as modified by the engineer in the field.

L.   Strength acceptance criteria:

Commentary: The acceptance criteria must reflect the level of risk and tolerances of the structure and the expected behavior of the deep mixed material. For example, strength criteria are critical for highly loaded individual deep mixed elements that serve as abutment support but may be less stringent for elements that are installed with a high area replacement ratio for embankment support. Acceptance criteria should be modified to accommodate these differences. A statistical approach to assessing strength criteria is preferred to an average or minimum unconfined compressive strength to avoid impact by inordinately high or low values.

Since deep mixing is an in situ ground engineering technique, the deep mixed soil product will vary based on characteristics of the native soil, construction methods, operational parameters, binder characteristics, and curing conditions. The acceptance criteria for the strength of deep mixed material are outlined in section 3.6. The acceptance criteria outline the acceptable variability of measured deep mixed soil strength relative to the product requirements.

The proposed mix design and installation procedures will vary based on the stringency of the acceptance criteria. It is critical to establish acceptance criteria based on the risk and criticality of the structure and the factor of safety assumed during design. Very tight acceptance criteria leave a relatively small margin for variability (e.g., a minimum unconfined compressive strength that must be met with no accommodation for test results that fall below the minimum is not an appropriate specification approach). The contractor must propose a mix design that produces a product that will consistently exceed the product requirement by a sufficient margin to avoid non-conformance. Over-conservatism produced by unnecessarily strict acceptance criteria results in additional materials and mixing energy that will be reflected in the contractor's bid price. Unit weight is typically not a criterion for acceptance of DMM work.

• The engineer should make the sole determination as to whether the test results satisfy the following strength acceptance criteria.
• The specified unconfined compressive strength of the deep mixed material as determined by ASTM D2166 at 28 days curing time should be _____ psi (to be defined by the engineer).
• 80 percent of unconfined compressive strength test results as determined by ASTM D2166 from each tested deep mixed element should equal or exceed the specified strength. If a strength specimen falls below the specified strength due to an obviously unrepresentative lump of unmixed soil in the specimen, the engineer has the option to select another specimen from the same core run and allow the contractor's laboratory to test the replacement specimen and substitute the strength from the replacement specimen for the strength from the unrepresentative specimen that failed to satisfy the strength requirement. Only one such retest will be allowed per core run.
• To prevent a weak layer at one elevation in the DMM foundation system, strengths below the specified strength are not permitted within 10 ft (3 m) of the same elevation in more than two nearby cored elements. "Nearby cored elements" refer to cored elements without an intervening cored element that has a passing test result in the suspect elevation zone.
• 90 percent of all of the test results across the site should equal or exceed the specified strength.

M.  Uniformity criteria:

• The engineer should make the sole determination as to whether the test results satisfy the uniformity acceptance criteria.
• Full-depth continuous core samples retrieved by the contractor from the DMM element should be used to evaluate uniformity.
• Core recovery (expressed as a percentage) should be reported for each run and is equal to the total length of recovered core divided by the total core run length. Length of recovered core includes lengths of treated and untreated soil.
• Percent treatment is calculated as the total length of recovered core minus the sum of the lengths of unmixed or poorly mixed soil regions or lumps that extend across the entire diameter of the core divided by the total core run length expressed as a percentage. Percent treatment must be at least 80 percent for every 5 ft (1.5 m) core run. If 80 percent treatment cannot be confirmed by coring in coarse sandy or gravelly soil, optical televiewer logs can be used to confirm uniformity.
• If the contractor uses core runs shorter than 5 ft (1.5 m) (e.g., 3 ft (1 m)), then the recovery and percent treatment can be calculated taking into equal amounts of core run length on either side of the short core run length to make up a total 5-ft (1.5-m) run length for calculation purposes

N.  Non-conformance:

• The contractor is responsible for correcting the location or alignment of misplaced elements that will adversely affect the project quality. The contractor should correct misaligned elements that interfere with the project in a manner acceptable to the owner.
• If the strength and uniformity acceptance criteria are not achieved for production elements, the contractor should submit a proposed plan for investigating, remixing, or repairing failed sections for review and approval by the engineer.
• To prove acceptability of the failed element, the contractor may core elements on both sides of the failed element. If those two cores meet the criteria, then the element should be accepted. If the additional cores fail, then the contractor can propose additional investigations and remedial measures, which the engineer will review and has the option to accept or reject depending on whether the proposed remedial measures meet the design intent. Examples of such investigations and remedial measures include the following:
  • In the case that the treated soil meets the uniformity criteria but fails to meet the strength criteria, the elements or zone could be assigned a lower strength level. The contractor could propose installing additional elements to compensate the strength required by the design intent. If the treated soil fails to meet the uniformity criteria, the elements need to be remixed or replaced.
  • If the treated soil that failed to meet the uniformity criteria is concentrated in a narrow elevation range forming weak planes or zones, the contractor could propose redrilling and remixing to 3 ft (1 m) below the deficient zone. If redrilling and remixing cannot be done efficiently, the contractor must replace the elements to the full depth. If the treated soil in the narrow elevation meets the uniformity criteria but fails to meet the strength criteria, the contractor could propose to redrill and remix the deficient zone or to assign a lower strength level to the deficient zone and install additional elements to compensate for the strength deficiency.
  • If the treated soil that failed to pass cannot be isolated in a specific zone, the contractor must provide remedial measures for all elements constructed during all rig shifts that occurred between passing elements.
  • Remedial measures are subject to coring and application of the specification acceptance criteria.

Part 4-Measurement and Payment

Commentary: Contractor payment may be made as a percentage of completion to accommodate time lag in acceptance of work due to awaiting test results. Payment may be made when production is 50 percent complete and 50 percent upon submittal of acceptable test results.

Measurement and payment items are detailed in table 26.

Table 26. Measurement and payment items for DMM contracts.