Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support
CHAPTER 2. TERMINOLOGY
Terms specific to laboratory testing, treated soil properties, design, construction, and contracting/procurement are defined in this section. These terms are currently used and accepted by the U.S. construction industry.
Various definitions of the same terms are often used in U.S. practice. Using a variety of terms can be misleading, and this practice has caused contractual difficulties and confusion. A single preferred term is provided for each item. Duplicate terms are shown in parenthesis following the preferred term to promote understanding, but use of the preferred term is recommended.
- 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.
- Blade rotation number (BRN): Total number of mixing blade rotations per meter of shaft movement. BRN has been developed to ensure uniformity of products produced by wet rotary end (WRE)/dry rotary end (DRE) systems. Refer to chapter 11 for indepth descriptions of WRE and DRE classifications. For horizontal cutter systems (e.g., cutter soil mixing (CSM)), revolutions per minute are typically reported as an indicator of mixing energy. Note that BRN is not applicable for chainsaw-type mixers (e.g., trench cutting and remixing deep wall method (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 twin horizontal mixing shafts is also a column. See “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 or 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 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: Dependent on application, various strengths may be used to assess the quality of deep mixed material. For design, 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 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 mixing with slurry consisting of water and binders with or without fillers and admixtures. In most cases, 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.