3.9 mixing energy resources used for operating machinery 3.10 mixing process de: Mischvorgang involves mechanical disaggregation of the soil structure, dispersion of binders and fillers
General
4.1.1 Prior to the execution of the work, all necessary information shall be provided
The information must encompass any legal or statutory restrictions, the positioning of main grid lines for layout, the condition of nearby structures, roads, and services, as well as an appropriate quality management system that includes supervision, monitoring, and testing.
The site conditions must include relevant details such as the site's geometry, including boundary conditions, topography, access, slopes, and headroom restrictions Additionally, it should address existing underground structures, services, known contamination, and archaeological constraints Environmental restrictions, such as noise, vibration, and pollution, must also be considered, along with any future or ongoing construction activities like dewatering, tunneling, and deep excavations.
Particular requirements
The article should include details about prior experience with deep mixing or specialized geotechnical projects near the site, along with field test results that validate the design Additionally, it must address any underground contamination or hazards that could impact the execution methods, work safety, or the disposal of excavation materials from the site.
The instructions include a reporting procedure for unforeseen circumstances or conditions that differ from the design assumptions, a reporting method for observational design approaches, notification of any construction phasing restrictions, and a schedule for testing and acceptance procedures for materials used in the project.
4.2.3 Any additional or deviating requirements falling within the permission clauses given in this document shall be established and agreed upon before the commencement of the works
General
5.1.1 The depth and the extent of any investigations shall be sufficient to allow determination of the ground conditions in accordance with the requirements of EN 1997-1
5.1.2 Laboratory and field investigations shall comply with prEN 1997-2 and the relevant European Standard EN 196-1 to -8, EN 196-21, EN 197-1 and -2, EN 451, EN 459-1 and -2, ENV 10080, EN 12716,
When assessing the scope of the site investigation, it is essential to consider relevant experience from executing comparable deep mixing projects under similar conditions near the site.
5.1.4 The site investigation report shall be made available together with all relevant data known to affect the choice of method
5.1.5 Boreholes or trial pits shall be suitably sealed not to affect groundwater movement and/or subsequent deep-mixed column construction and performance.
Specific information
5.2.1 Identification and classification of soil shall comply with EN ISO 14688-1 and EN ISO 14688-2.
The site investigation report must include essential information about ground conditions for deep mixing, as outlined in EN 1997-1 Key details should cover the composition, lateral extent, thickness, and firmness of the surface stratum, including tree roots and fill Additionally, it should address the presence of cobbles, boulders, cemented layers, or underlying rock that may pose challenges during execution or necessitate the use of specialized methods or tools.
EN 791,ˆEN ISO 14688-1 and EN ISO 14688-2‰ c) presence of swelling soil (montmorillonite); d) cavities, voids or fissures; e) piezometric levels of groundwater, its variation and possible artesian pressure;
5.2.3 When relevant, the following additional information should be provided:
5.2.3.1 Physical and state characteristics: a) consistency limits; b) classification; c) density; d) grain size distribution; e) mineralogy; f) natural water content; g) organic content
5.2.3.2 Mechanical characteristics: a) deformation and consolidation; b) strength (shear, compressive and tensile); c) permeability
5.2.3.3 Environmental, chemical and biological characteristics: a) groundwater quality (e.g contamination, aggressiveness, chemistry, pH- value, type and concentration of ions and metals (reference measurements); b) contamination test data; c) leaching tests.
5.2.4 The ground level and location at any point of investigation or testing should be established relative to the recognised national datum or to a fixed reference point.
General
6.1.1 Construction of deep mixing involves the addition of a binder and, if needed, one or more of the following components to the soil: a) admixture; b) water; c) filler; d) structural reinforcement
All materials and products used in deep mixing must comply with the applicable European Standards In cases where these standards are unavailable, adherence to national standards and guidance is required.
6.1.3 All materials and products used shall comply with local environmental regulations.
6.1.4 All materials and products used shall comply with the design specifications
6.1.5 Appropriate tests shall be provided in order to ensure compliance with the design specifications for materials not covered by existing standards
6.1.6 The sources of supply materials shall be documented and shall not be changed without prior notification.
Special considerations
6.2.1 Water from other sources than recognised potable water shall be tested to determine whether or not it is suitable for the intended use
6.2.2 Environmentally significant traces of chemical substances in materials and products may be present as normally occurring impurity, and their environmental impact may need to be assessed
General
The in-situ strength of columns is affected by various factors, including soil properties, mixing conditions, tools, processes, curing conditions, binder type and quantity, and ground conditions Accurately estimating field strength during the design stage can be challenging Therefore, it is crucial to assess and confirm field strength through laboratory mixing tests, accumulated experience, field trials, and verification tests If the design requirements are not met, modifications should be made accordingly.
The execution of deep mixing projects requires a multi-phase geotechnical design that is often iterative The primary goal is to create technical documents that ensure construction adheres to safety, serviceability, economy, and durability, while considering the anticipated service life It is advisable for the design team to remain involved throughout the construction process.
The geotechnical design for deep mixing projects must adhere to ENV 1991, EN 1997-1, and prEN 1997-2 standards Key parameters influencing the stability and settlement of the treated ground are summarized in informative Annex B.
7.1.4 Reference to relevant experience is permitted if appropriate verification has been undertaken (e.g by penetration tests, pressuremeter tests or other tests)
A comprehensive method statement must be developed for the deep mixing works, outlining the project's location and objectives It should specify the required design life, identify potential construction phase restrictions, and highlight any hazards related to the execution of the works.
7.1.6 When there is some latitude in the selection of materials, the method statement shall emphasise the particular requirements, which can influence the final selection
7.1.7 Preliminary design can be based on tests of laboratory mixed samples and comparable experience, taking into account the difference in characteristics between laboratory mixed samples and treated soilin-situ.
NOTE For guidance, reference is made to Annex B
Testing alone may not adequately confirm the effectiveness of the treatment; therefore, proper supervision, monitoring, and documentation are essential An observational approach is typically suitable, and the design process is generally not finalized until sufficient site experience has been acquired.
Additional design considerations
When conducting deep mixing works, it is essential to consider loading conditions, climatic effects, hydraulic conditions, and the acceptable limits for settlement, heave, and distortion of structures and services that may be impacted.
7.2.2 The design should identify and take into account environmental restrictions on construction, such as noise, vibration, pollution of air and water and impact on adjacent structures
To ensure the end-bearing capacity of the column, it is essential to specify an appropriate mixing tool and process to prevent the creation of a remoulded zone at the column's base.
7.2.4 The specified column or wall layout and tolerances should take into account the limitations of the mixing equipment
7.2.5 take into account the angular deviation and the positional tolerances
7.2.6 Amendments necessitated by unforeseen circumstances, such as essential changes in ground or hydraulic conditions, shall be reported immediately
7.2.7 Suitable protection and testing should be specified when treated soils are likely to be exposed to freeze/thaw cycles
When designing columns, it is essential to account for the consequences of exposure to chemical and physical effects Special attention must be given to long-term durability, especially in marine environments or contaminated ground conditions.
Selection of the binder and the additives
7.3.1 The site and ground conditions and the nature and properties of the soil to be treated shall be considered in the selection of binder
7.3.2 The efficiency of the binder and the admixture shall be studied by laboratory and/orin-situ tests of the treated soil, taking into account the prescriptions given in 7.4.
Laboratory and in-situ mixing and treatment tests
Preliminary trials and tests of the treated soil are essential to ensure that the design requirements can be met, as the properties of the treated soil are affected by various factors, including the execution process.
When analyzing treated soil, it is important to recognize that laboratory test results may overstate the potential outcomes in the field This discrepancy can be attributed to factors such as more intensive mixing techniques used in the lab and differing curing conditions.
When examining treated soil, it is essential to consider the improvement over time, which is influenced by the type and amount of binder used, as well as the curing process.
For grid type or block type or overlap columns, the specified spacing between the columns shall ˆ
‰ condition When studying the effect of time on trial mix specimens, considerations should be given to the effect of curing conditions (temperature, curing under water, preloading etc.).
7.4.4 Sequence and rate of execution, setting and hardening time, and diameter of the columns shall be considered in order to avoid local soil failure or unacceptable settlement or heave
In cases where deep mixing is employed to immobilize contaminants or stabilize waste deposits, it is essential to conduct site-specific test programs to address potential unpredictable interactions between the binder and the in-situ material.
Design statement
The design output must clearly outline the performance objectives and geometry of the treatment, including material specifications and additional details such as work phasing Key information should encompass specifications for deep mixing work, column requirements (including strength, deformation characteristics, and permeability), the width of overlaps between adjacent columns, and tolerances for length, diameter, inclination, and plan position It should also detail installation boundaries and geometry through setting out drawings, a construction program with a time schedule for loading and preloading, and any necessary construction phasing restrictions Furthermore, a schedule for testing and acceptance procedures for materials, along with monitoring requirements during execution, should be included The design must specify structural reinforcement requirements (material class and installation procedure) and the timeline for installation, as well as toe penetration into bearing or impermeable strata Lastly, a reporting procedure for unforeseen circumstances or differing conditions from the design assumptions should be established, particularly if an observational procedure is implemented.
7.5.2 Whenever acceptance is defined on the basis of tests of core samples, the design shall specify location, age at test, coring equipment and procedure
For mechanical tests on treated soil, it is essential to define the testing conditions and acceptance criteria for the samples Tolerances related to specified performance parameters must take into account the effectiveness of the proposed test methods, particularly when these methods are indirect, as outlined in Annex B.
7.5.4 Limiting values of critical geotechnical design parameters shall be stated, as well as steps to be taken if values are likely to be exceeded
7.5.5 Any additional or deviating requirements, falling within the permission clauses given in the standard,shall be established and agreed upon before the commencement of the work
Method statement
Before executing deep mixing, a comprehensive method statement must be provided, detailing the identification, objectives, and scope of the work It should include a soil description in accordance with EN ISO 14688-1:2002 and EN ISO 14688-2:2004, the shape of the deep mixing column, and the specific deep mixing method to be employed Additionally, the statement must outline the mixing tool's specifications, including the shape, dimensions, and configuration of the rotating units, as well as the working procedure for penetration, retrieval, and mixing sequence Installation accuracy, deep mixing parameters such as binder type and composition, and precautions against heave and settlement are also essential The document should address site installation areas, plant and equipment, spoil management, and quality control procedures as per the contract Furthermore, it must include protocols for handling interruptions, potential modifications to deep mixing parameters, verification testing methods, and necessary working documents, along with a safety and environmental risk assessment.
Preparation of the site
The preparation must align with design specifications and environmental site conditions, ensuring proper access for machinery, thorough excavation, cleaning, and leveling of the working platform Additionally, it is essential to establish adequate ground bearing capacity for equipment, along with effective receipt, quality control, and storage of materials.
8.2.2 All materials and products for deep mixing delivered to the site shall be identified and checked against the design specifications (see 6.1.2)
8.2.3 The binders shall be protected from ingress of moisture or air that could otherwise detrimentally affect their use and/or performance.
Field trials
In the absence of comparable previous experience, it is essential to conduct representative field trials to verify that the design requirements can be met These trials should utilize the same equipment, materials, techniques, and procedures planned for the main execution of the work, allowing for the establishment of critical control values.
The execution control values must encompass the penetration and retrieval speed of the mixing tool, the rotation speed of the mixing tool's rotating unit(s), the air pressure for dry mixing, and the feed rate of the binder or slurry.
In specific situations, it is essential to monitor additional parameters that directly affect the quality and performance of the work For example, overlapping width is crucial when a wall is used for containment, and torque is significant when columns are anchored in rigid strata.
Execution tolerances
General
8.4.1.1 Before the installation of the columns, the position of each column shall be located and identified
8.4.1.2 The columns shall be constructed within the geometrical tolerances set in the design
8.4.1.3 Verticality and inclination measurements can be carried out by means of inclinometers.
Quality control and quality assurance
A comprehensive quality plan must be established, outlining the methods and frequency of inspections throughout the construction and verification phases, as well as the procedures for addressing any non-conformities (refer to EN ISO 9000) Additionally, the quality plan should specify all essential documents, including drawings, method statements, and plans, required for the successful execution of the project.
The tests on the treated soils, as detailed in section 9.3, must be conducted using the testing methods outlined in Annex B, in accordance with the design specifications provided in sections 7.4 and 9.3.
8.5.3 If the conditions encountered during execution do not correspond with those expected in the design, this shall be reported immediately to those responsible for the project.
Deep mixing
General
8.6.1.1 The execution of deep mixing can be carried out by either dry or wet mixing These two methods are described in detail in Annex A.
NOTE 1 Deep mixing is executed by mechanical disaggregation of the soil using mainly vertical movement of rotating mixing unit(s) and introduction of a binder, which is homogenised with the soil during the penetration and/or retrieval The execution of deep mixing can be carried out either by dry or wet mixing These two methods are described in detail in Annex A
NOTE 2 In the dry mixing method, the medium of transportation of the binder is normally compressed air
NOTE 3 In the wet mixing method, the medium of transportation of the binder is normally water
8.6.1.2 The equipment and the mixing tool shall be correctly positioned at each column location in accordance with the execution tolerances specified in the design
8.6.1.3 The quantity of binder along the column shall be measured during installation of each column
8.6.1.4 Equipment used for recording of the supplied quantity of binder or solids for the slurry shall be calibrated
8.6.1.5 Any spoil generated shall be collected and disposed of in accordance with the legal or statutory requirements.
Dry mixing
8.6.2.1 The execution procedure of dry mixing shall follow the specifications given in the design
NOTE 1 The installation is usually carried out according to the following procedure:
⎯ the mixing tool is correctly positioned;
⎯ the mixing shaft penetrates to the prescribed depth of treatment with simultaneous disaggregation of the soil by the mixing tool;
After achieving the specified treatment depth, the shaft is retracted while simultaneously injecting the binder in granular or powdered form into the soil A horizontally rotating mixing tool then blends the soil with the binder effectively.
NOTE 2 The binder may also be injected and mixed with the soil during the penetration stage
8.6.2.2 The equipment and mixing tools shall be compatible with the execution procedure, the depth of the soil to be treated and the execution tolerances specified in the design
NOTE When the binder is injected and mixed with the soil during the penetration stage, the injection outlet shall be positioned at, or under, the mixing tool
8.6.2.3 The rotation speed of the rotating unit(s) and the rate of penetration and retrieval of the mixing tool shall be adjusted to produce sufficiently homogeneous treated soil
NOTE 1 Current penetration or retrieval rates of mixing shaft are usually 10 mm/rev to 50 mm/rev and the blade rotation numbers are usually 200 to 500
NOTE 2 The amount of mixing work involved in producing a dry-mixed column depends on the type and quantity of binder and type of soil Cement as binder requires a higher mixing energy than lime only
8.6.2.4 In dry mixing the air pressure shall be kept as low as possible during the mixing process to avoid problems of air entrainment and ground movements.
NOTE If the air pressure is too low, the binder may not spread into the whole cross-sectional area of the column
8.6.2.5 The amount of binder and the air pressure shall be monitored during installation of the columns
8.6.2.6 Mixing energy should be monitored to achieve uniform treated soil.
Wet mixing
8.6.3.1 The execution procedure of wet mixing shall take into account the specifications given in the design
NOTE The installation is usually carried out according to the following procedure:
⎯ the mixing tool is correctly positioned;
After achieving the designated treatment depth, the shaft is retracted, and in certain instances, the slurry is simultaneously injected into the soil and blended with it.
8.6.3.2 The equipment and the mixing tools shall be compatible with the execution procedure, the depth of soil to be treated and the execution tolerances specified in the design
NOTE 1 For machines with the outlet below the mixing tool, the slurry shall not be added during the retrieval phase
NOTE 2 Whereas a continuous flight auger may be sufficient for predominantly granular soils, cohesive soils require more sophisticated mixing tools The rotary drives, turning the shaft, need to have enough power to destroy the matrix of the soil for intimate mixture with the slurry
8.6.3.3 The rotational speed of the rotating unit(s) and the rate of penetration and retrieval of the mixing tool shall be adjusted to produce sufficiently homogeneous treated soil
NOTE Current rotation speed of the mixing blades are usually 25 rev./min to 50 rev./min and the blade rotation numbers usually greater than 350
8.6.3.4 During mixing the slurry shall be delivered by pumping in a continuous flow to the soil to be treated
8.6.3.5 The wet mixing process may be interrupted on condition that the slurry has not begun to harden and the mixing tool starts again at least 0,5 m in the soil already treated
8.6.3.6 Restroking may be used to redistribute slurry to a certain portion of the treated column, re-fluidise a portion of the stratum on the penetration or as a means of keeping the rotating units in motion during a hold or waiting period
8.6.3.7 The density of the slurry shall be tested by a suitable device at least twice per working shift at each batching/mixing plant In the case of manual batching, the frequency of testing shall be increased.
Installation of structural reinforcement
8.7.1 Structural reinforcement (steel bars, steel cages or steal beams) may be installed into the fresh mixed-in-place columns or elements.
NOTE The aid of a vibrator may be required for the installation process
8.7.2 Any structural reinforcement shall be installed in accordance with the specifications of the design (see 7.5.1 h)).
General
9.1.1 The extent of testing and monitoring should be given in the specifications of the design
Before starting the work, it is essential to establish specific procedures for verification, control, and acceptance The mixing shaft must reach the designated treatment depth while simultaneously disaggregating the soil using the mixing tool and/or injecting a slurry, typically consisting of cement along with potential fillers and additives.
Supervision
9.2.1 In order to check that construction complies with the design and other contract documents, qualified personnel experienced in the technique shall be in charge of the execution work
9.2.2 Where unforeseen conditions are encountered or new information about soil conditions become available, they shall be reported immediately in accordance with the specified information procedures(see 7.5.1 j).
Testing
The verification of compliance with design assumptions must assess the strength characteristics, deformation properties, and homogeneity of the columns, as well as their length, diameter, permeability, inclination, and overlap when applicable.
9.3.2 The extent and the methods of performance testing shall be defined before the commencement of the deep mixing works in each individual case (type of application and specified tests)
The extent and methods of performance testing for treated soil are determined by the specific application and functional requirements Informative Annex B provides guidance on suitable testing methods, including unconfined compression tests, triaxial tests, oedometer tests, column penetration tests, reverse column penetration tests, CPTU tests, pressuremeter tests, and seismic tests.
9.3.3 Quality control tests should be uniformly distributed both in time and between the mixing tools utilised
Control tests must encompass a sufficient number of columns to accurately determine the distribution and average properties of each significant soil stratum involved in deep mixing operations.
9.3.5 The number of columns to be tested should be decided in each individual case, taking into account the purpose and the extent of the treatment, and the application
In relevant applications such as immobilisation, containment, and retaining walls, it is essential to conduct appropriate chemical tests These tests should include the determination of chemically active substances, pH value, carbonate content, and levels of chloride, sulphate, and sulphide.
9.3.7 Where overlap is an essential part of the design, the width of the overlapping portion between adjacent columns shall be checked
NOTE The width of overlapping can be verified by the use of inclinometers during penetration and retrieval and by drilling across the columns or visual inspection
9.3.8 Columns exposed as retaining elements shall be visually inspected for nonhomogeneities during excavation.
Monitoring
9.4.1.1 The following construction parameters and information shall be monitored continuously during execution, or at least at a depth interval of 0,5 m (see Table 1)
Air tank pressure Slurry pressure; air pressure (if any)
Penetration and retrieval rate Penetration and retrieval rate
The rotation speed measured in revolutions per minute (revs/min) is crucial during both penetration and retrieval processes Additionally, the quantity of binder and slurry applied per meter of depth plays a significant role in ensuring effective operations during these phases.
NOTE In certain applications, especially where wall continuity is important, it is required to monitor positioning and verticality of the mixing tool
Monitoring machine operation parameters, including power consumption and the penetration resistance of the mixing tool, can provide limited insights into soil type and groundwater conditions.
9.4.1.3 The construction process shall be controlled and relevant construction parameters as well as information concerning the ground conditions and construction tolerances shall be monitored during execution
9.4.1.4 The execution should be monitored automatically, preferably with the aid of a computerised system.
In a computerized system, key parameters such as feed pressure, feed rate, mixing tool type, binder factor, binder content, and water/binder ratio are meticulously recorded Each installed column generates a printout, enabling early assessment of whether adjustments to the installation technique are necessary or if additional columns should be added.
Performance of the treated soil
9.5.1 Vertical and lateral movements of the ground should be monitored by appropriate methods For certain applications, other parameters, such as pore water pressure, should be monitored
9.5.2 Deviations from specified design limits shall be reported.
Other aspects
9.6.1 Monitoring instruments shall be installed early enough to have stable reference values before the start of the work.
Records during construction
10.1.1 Records shall be made of relevant aspects of the construction: execution of columns, tests and observations as described in Clause 9 and these shall be available at the site
10.1.2 The following execution parameters shall be recorded during execution (see Table 2)
Date and time of execution Date and time of execution
Column reference number Column reference number
Shape of mixing shaft and tool Shape of mixing shaft and tool
The penetration and retrieval rate, measured in mm/rev or speed in m/min, is crucial for assessing performance Additionally, the rotation speed during both penetration and retrieval, expressed in rev/min, plays a significant role in optimizing efficiency.
Binder type and composition Binder type and composition
The quantity of binder and slurry used per meter of depth is crucial during both penetration and retrieval processes Additionally, maintaining construction tolerances, including verticality, diameter, and setting out, is essential for ensuring structural integrity and compliance with project specifications.
Sequence and timing Sequence and timing
Top and toe level Top and toe level
Records at the completion of the work
Records of the as-built works must include comprehensive documentation such as: a) the records specified in section 10.1; b) detailed information on the as-built columns, including test results and any deviations from the design drawings and specifications; c) specifics regarding the materials and products utilized; and d) relevant details about the geotechnical soil conditions.
General
11.1.1 Only those aspects of site safety and protection of the environment that are specific to deep mixing, are considered in this chapter
11.1.2 All relevant European and national standards, specifications and statutory requirements regarding safety and environment during execution of the work shall be respected.
Safety
Special emphasis must be placed on processes involving personnel working near heavy equipment and tools, particularly when operating mixing equipment, which poses significant hazards It is crucial to prioritize the safety of individuals in the vicinity of rotating machinery Additionally, all material and product handling should strictly adhere to the manufacturer's safety guidelines.
Environmental protection
11.3.1 Construction should identify and take into account environmental restrictions such as noise, vibrations, pollution of air and water and impact on adjacent structures.
Impact on adjacent structures
When sensitive structures or unstable slopes are located near the site or within the potential impact area of installation works, it is essential to closely monitor and document their condition both before and during the installation process.
Practical aspects of deep mixing
Introduction
Deep mixing aims to enhance soil properties, such as increasing shear strength and reducing compressibility, by incorporating chemical additives that react with the soil This improvement is achieved through processes like ion exchange on clay mineral surfaces, bonding soil particles, and filling voids with chemical reaction products The technique is categorized based on the type of binder used—such as cement, lime/cement, and additives like gypsum or fly ash—and the mixing method, which can be wet or dry, rotary or jet-based, auger-based, or blade-based.
Deep mixing originated in Sweden and Japan during the late 1960s, with dry mixing using granular quick lime implemented in Japan by the mid-1970s Around the same time, Sweden adopted dry mixing with powdered lime to enhance the settlement characteristics of soft, plastic clays Additionally, wet mixing with cement slurry was introduced in Japan during the same period Since then, deep mixing techniques have expanded globally, and more recently, the combination of cement and lime with materials such as gypsum, fly ash, and slag has been introduced.
Since their inception, deep mixing methods have evolved significantly, with advancements in equipment and modifications to hardening agents Extensive research and practical experience have led to their widespread acceptance across various countries Additionally, increasing environmental awareness has prompted the adoption of deep mixing techniques for the remediation and containment of contaminated sites.
Recent advancements in hybrid techniques have emerged by integrating deep mixing with various soil improvement methods, including jet grouting and surface mixing machinery Terashi (2001) provides a summary of the technological developments over the past 25 years A generic classification of the equipment is illustrated in Figure A.1.
Fields of application
Deep mixing has diverse applications for both temporary and permanent projects, applicable in both terrestrial and marine environments The primary uses include reducing settlement, enhancing stability, and providing containment solutions.
Execution
General
The execution process typically involves three key stages: positioning, penetration, and retrieval During the penetration phase, mixing tools cut and disaggregate the soil to the required treatment depth In the retrieval phase, a binder is injected into the soil at a consistent flow rate while maintaining a steady retrieval speed The mixing blades operate in a horizontal plane, effectively combining the soil with the binder Some machine variations allow for binder injection during both the penetration and retrieval phases.
Figure A.1 — General classification of equipment used by the deep mixing methods included in the Code and by hybrid mixing methods not included
To minimize ground movement during execution, specialized mixing tools are employed Deep mixing can be performed using two methods: dry mixing, where the binder is introduced via air, and wet mixing, which utilizes a slurry form of the binder.
In dry mixing, the binder typically consists of a blend of unslaked lime and cement, or a combination of cement, lime, gypsum, blast furnace slag, and pulverised fuel ash (PFA) in either granular or powdered form Air is utilized to incorporate the binder into the soil, which must have a moisture content of at least 20%.
Figure A.2 — Applications of deep mixing for various purposes
In wet mixing the most common binder is cement
Dry mixing enhances the properties of cohesive soil, while wet mixing is used to improve granular materials Additionally, dry mixing can be effective in preventing liquefaction in loose granular soils for specific applications.
Underground contamination, including old refuse heaps, industrial waste, and chemical products, can pose hazards that impact construction methods, work safety, and the disposal of excavation materials Additionally, obstructions like boulders and tree roots can hinder the efficiency of deep mixing processes Prior to commencing construction, it is essential to determine the desired quality of the columns, following the execution principles outlined in Figure A.3.
Dry mixing
Dry mixing is normally carried out in accordance with some general principles, summarised in Figure A.4.
The flow chart illustrates that the binder is introduced into the soil in a dry state using compressed air Currently, there are two primary techniques for dry mixing: the Nordic technique and the Japanese technique.
Figure A.3 — Principles of execution of deep mixing
Figure A.4 — Flow chart for the execution of dry mixing
The installation is carried out according to the following procedure, from left to right:
1) the mixing tool is correctly positioned;
2) the mixing shaft penetrates to the desired depth of treatment with simultaneous disaggregation of the soil by the mixing tool;
3) after reaching the desired depth, the shaft is withdrawn and at the same time, the binder in granular or powder form is injected into the soil;
4) the mixing tool rotates in the horizontal plane and mixes the soil and the binder;
5) completion of the treated column
In the Nordic countries, specialized equipment can install columns to a depth of 25 meters, typically with diameters ranging from 0.6 to 1.0 meters These columns can be inclined at angles of up to 70° from the vertical The machines feature a single mixing shaft with an injection outlet located at the mixing tool, allowing for precise monitoring and, in some cases, automatic control of mixing energy and binder quantity to ensure uniform soil treatment.
During the retrieval phase, the mixing tool is drilled to the desired depth, and a specific amount of binder is introduced through an inner tube connected to the mixing tool The soil and binder are thoroughly mixed by continuously rotating the mixing tool If necessary, both phases can be repeated at the same location.
To achieve uniform mixing in dry-mixed columns, it is essential to adjust both the rotation speed of the mixing tool and the withdrawal speed The mixing work required varies based on the binder type, binder quantity, and soil type Notably, using cement as a binder necessitates more mixing energy than using lime alone Additionally, specialized equipment has been designed to effectively contain air and dust during the mixing process.
Execution machines come in various designs, featuring either one or two mixing shafts Each shaft is equipped with multiple blades ranging from 0.8 m to 1.3 m in diameter, capable of installing columns up to a depth of 33 m Typically, the binder used in these machines is cement powder, which is delivered to the mixing machine via compressed air.
A bellows covering the mixing shaft prevents air scatter from the ground, while the mixing tool, consisting of multiple stacks of mixing blades, ensures uniformity in the treated column Injection outlets are strategically placed above and below the mixing blades on the shaft A steel bar maintains the distance between two mixing shafts and, along with additional freely rotating mixing blades, helps prevent soil from adhering to the driven components Automatic control of air pressure and binder quantity is implemented to achieve homogeneity in the treated column.
The binder is injected during the penetration stage or both during the penetration and retrieval stages
Table A.1 — Comparison of the Nordic and Japanese dry mixing techniques
Equipment Details Nordic technique Japanese technique
Mixing machine Number of mixing shafts 1 1 to 2
Diameter of mixing tool 0,4 m to1,0 m 0,8 m to1,3 m
Position of binder outlet The upper pair of mixing blades Bottom of shaft and/or mixing blades (single or multiple)
The batching plant offers a supplying capacity ranging from 50 kg/min to 300 kg/min, with typical execution values for Nordic and Japanese techniques detailed in Table A.2 The variable pressure is noted to be between 200 kPa and a specified limit.
Table A.2 — Typical execution values of the Nordic and Japanese dry mixing techniques
Mixing machine Nordic technique Japanese technique
Penetration speed of mixing shaft 2,0 m/min to 6,0 m/min 1,0 m/min to 2,0 m/min
Retrieval speed of mixing shaft 1,5 m/min to 6,0 m/min 0,7 m/min to 0,9 m/min
Rotation speed of mixing blades 100 revolutions/min to
200 revolutions/min 24 revolutions/min to
Blade rotation number 1) 150 per m to 500 per m 274 per m
Amount of binder injected 100 kg/m 3 to 250 kg/m 3 100 kg/m 3 to 300 kg/m 3
Retrieval (penetration) rate 10 mm/rev to 30 mm/rev 10 mm/rev to 35 mm/rev.
Injection phase Typically during retrieval Penetration and/or retrieval
Wet mixing
Wet mixing is carried out in accordance with some general principles, which can be summarised as shown in Figure A.6.
Figure A.6 — Flow chart for the execution of wet mixing
In wet mixing, the binder typically consists of cement slurry, to which filler materials like sand and additives can be incorporated as needed The amount of slurry used may differ based on the depth of the mix Additionally, for machines with an outlet positioned below the mixing tool, the slurry does not need to be added during the retrieval phase.
1) Blade rotation number means the total number of mixing blades passing during 1 m of shaft movement and is defined by the equation T= ΣM N ( d V d +N u V u ), where T= blade rotation number (n/m), ΣM = total number of mixing blades,
The rotational speed of the blades during penetration is denoted as \$N_d\$ (rev./min), while the mixing blade penetration velocity is represented by \$V_d\$ (m/min) The rotational speed during retrieval is indicated as \$N_u\$, and the mixing blade velocity during retrieval is \$V_u\$ In cases where injection occurs solely during retrieval, the value of \$N\$ is set to zero.
Flight augers are effective for granular soils, but finer and stiffer materials necessitate advanced mixing tools equipped with variously shaped mixing and cutting blades Additionally, the rotary drives must possess sufficient power to break down the soil matrix, ensuring a thorough blend with the slurry.
The strength and permeability of a mortar-like mixture, formed from various soils and slurries, are significantly influenced by factors such as soil composition, including fines and organic content, clay type, grain shape, size distribution, and hardness Additionally, the type and quantity of binder used, along with the mixing procedure, play crucial roles in the hydration process that leads to hardening.
The wet mixing process may be paused as long as the slurry remains un-hardened, and the mixing tool must resume at least 0.5 meters into the previously treated soil.
Pumps for transport of the slurry to the outlet need to have sufficient capacity (delivery rate and pressure) to safely deliver the design quantity of slurry
Wet mixing is common in Central and Southern Europe, North America and Japan
In Europe, the installation of wet-mixed columns is performed using either flight augers—available in continuous or sectional, single or multiple configurations—or blades, depending on the specific ground conditions and intended applications.
In reinforced soil wall structures, the installation of steel bars, cages, or beams into freshly mixed columns is essential, often necessitating the use of a vibrator to ensure proper placement.
In Japan, the wet mixing technique is commonly employed for both terrestrial and marine constructions For on-land projects, machines equipped with one to four mixing shafts are utilized, featuring multiple stacks of mixing blades to ensure uniform treatment of the column A steel bar maintains the distance between the mixing shafts, while additional freely rotating mixing blades help prevent soil from clinging to the driven blades and shaft.
The machine features automatic control of blade rotation and binder quantity to ensure uniformity in the treated column It is equipped with multiple mixing blades ranging from 1.0 m to 1.6 m in diameter and can install columns to a maximum depth of 48 m Additionally, the shaft is designed with mixing blades positioned at various levels.
In marine construction, large execution vessels are employed for the efficient treatment of significant soil volumes These vessels are equipped with essential facilities, including a mixing machine, batching plant, storage tanks, and a control room Typically, marine work machines feature multiple mixing shafts, and the advanced deep-mixing machines available in Japan can create columns with cross-sectional areas ranging from 1.5 m² to 6.9 m², reaching depths of up to 70 m below sea level.
2 Mixing blades 5 Stabilising agent plant
Figure A.7 — Japanese vessel for execution of marine wet mixing
Typical mixing conditions are shown in Tables A.3 and A.4
Table A.3 — Major capacity and execution of European and Japanese wet mixing techniques
Equipment Details On land, Europe On land, Japan Marine, Japan
Mixing machine Number of mixing rods 1 to 3 1 to 4 2 to 8
Diameter of mixing tool 0,4 m to 0,9 m 1,0 m to 1,6 m 1,0 m to 1,6 m
Maximum depth of treatment 25 m 48 m 70 m below sea level
Position of binder outlet Rod Rod and blade Rod and blade
Injection pressure 500 kPa to 1 000 kPa 300 kPa to 600 kPa 300 kPa to 800 kPa Batching plant Amount of slurry storage 3 m 3 to 6 m 3 3 m 3 3 m 3 to 20 m 3
Binder storage tank Maximum capacity 30 t 50 t to 1 600 t
Table A.4 — Typical execution values of European and Japanese wet mixing techniques
Mixing machine On land, Europe On land, Japan Marine, Japan
Penetration speed of mixing shaft 0,5 m/min to 1,5 m/min 1,0 m/min 1,0 m/min
Retrieval speed of mixing shaft 3,0 m/min to 5,0 m/min 0,7 m/min to 1,0 m/min 1,0 m/min
The rotation speed of mixing blades ranges from 25 rev/min to 50 rev/min, with variations of 20 rev/min to 40 rev/min and 20 rev/min to 60 rev/min Additionally, the blade rotation number for continuous flight augers is consistently 350 per meter.
Amount of binder injected 80 kg/m 3 to 450 kg/m 3 70 kg/m 3 to 300 kg/m 3 70 kg/m 3 to 300 kg/m 3 Injection phase Penetration and/or retrieval Penetration and/or retrieval Penetration and/or retrieval
Patterns of installation
Deep mixing utilizes various column installation patterns, such as equilateral triangular or square arrangements, depending on the intended purpose For stability in cuts or embankments, columns are typically arranged in walls that are perpendicular to the anticipated failure surface Overlapping columns is crucial for containment applications and is common in block, wall, and grid installations U-shaped, elliptical, or circular column patterns effectively create barriers against horizontal forces like earth pressure and slip surfaces To minimize settlement, overlapping columns are installed in a sequence to form interlocking walls.
Figure A.8 — Examples of treatment patterns in dry mixing
Figure A.9 — Block type pattern in dry mixing with overlapping columns
Figure A.10 — Examples of treatment patterns in wet mixing on land
Figure A.11 — Examples of treatment patterns in marine conditions
Hybrid methods
Hybrid methods, which incorporate deep mixing techniques, are continually evolving to address specific ground conditions and foundation challenges These methods typically blend hydraulic and mechanical mixing approaches Notable hybrid methods that have gained acceptance among contractors include mass stabilization and jet grouting combined with mechanical mixing.
In challenging soil conditions, such as peat, gyttja, organic clay, and soft clay deposits, mass stabilization is often necessary, treating the entire soil mass to depths typically ranging from 2 to 3 meters, with a maximum treatment depth of 5 meters Unlike column stabilization machines, mass stabilization machines utilize a conventional excavator fitted with a mass stabilization mixer, where the binder is introduced to the mixing head as the mixer rotates and moves both vertically and horizontally.
4 Mass stabilised peat, gyttja or clay
Figure A.13 — Two types of mass stabilisation A.3.5.3 Jet grouting combined with mechanical mixing
A novel method has been introduced that merges the benefits of mechanical mixing with jet grouting, utilizing machines equipped with a mixing shaft and jetting nozzles This innovation allows for the creation of columns that exceed the diameter of the mixing tool, while also facilitating the overlapping of treated columns The diameter of these columns can be adjusted through the use of jetting or by opting not to jet Detailed information on the jet grouting technique is provided.
A novel low-displacement deep-mixing method has been introduced in Japan to minimize lateral displacements during construction This technique involves the installation of an earth auger screw on the upper part of the mixing shaft, which effectively removes soil to the ground surface By extracting a soil volume equivalent to the injected cement slurry, the method significantly reduces the displacement of surrounding ground and nearby structures.
The Cut-Mix-Injection (Frọs-Misch-Injektionsverfahren) is an innovative German technique that utilizes a specialized machine, known as the Frọsmaschine, to mix loose soil with cement slurry in deep strips This off-road, caterpillar track-driven FMI machine features a driver cabin, power train, and a cutting tree equipped with rotating blades powered by dual chain systems The cutting tree, which can be inclined up to 80° and positioned perpendicularly to the operational direction, mixes the soil in-situ rather than excavating it The machine's driving speed, cutting depth, and cement injection rate are all controlled by a computer, ensuring precision and efficiency in the mixing process.
The cutting tree is equipped with an injection pipe and outlets, allowing for the distribution of cement slurry mixed at a separate site With an average supply rate of 100 m³/h, this method enables soil treatment to a maximum depth of 9 meters The cutting width is 1.0 meters down to 6 meters and narrows to 0.5 meters at a depth of 9 meters.
Construction considerations
Deep mixing techniques are essential for addressing slope stability issues and protecting sensitive structures These methods effectively reduce settlement and enhance stability, preventing negative impacts on nearby constructions Additionally, deep mixing serves as a supporting wall in deep excavations, as illustrated in Figure A.14.
The chemical reactions between the soil and the binder generate an increase of the ground temperature, which goes on until the chemical reactions are terminated
When operating mixing equipment, it is crucial to prioritize safety due to the highly exothermic reaction between unslaked lime and moisture or water, which can cause rapid volumetric expansion and potentially lead to fire or explosion Given that both unslaked lime and cement are caustic and toxic, it is essential to wear protective gear, including tight eye-shields, gloves, and masks, to ensure safety during handling.
The possibility that the execution of deep mixing will cause ground displacements, affecting stability condi-
Ensuring the stability of road embankments is crucial, particularly for high embankments, to prevent uneven settlement at bridge abutments Additionally, the stability of cut slopes must be maintained while minimizing the impact of nearby construction activities It is essential to consider braced excavation earth pressure and potential heave, as well as the lateral resistance of pile foundations Furthermore, evaluating the bearing capacity of sea walls and breakwaters is vital for structural integrity and safety.
Figure A.14 — Diversified application of deep mixing - After CDM Association [23]
General
Scope
This annex addresses key design aspects, including process design development, binder selection, and both laboratory and field testing, as well as how column layout and performance impact design For detailed principles and methods of geotechnical design, please refer to EN 1997-1.
As deep mixing is a ground improvement process, design encompasses two distinct aspects:
⎯ functional design describes the way in which the treated soil and the untreated soil interact to produce the required overall behaviour;
⎯ process design describes the means by which the required performance characteristics are obtained from the treated soil by selecting and modifying the process control parameters.
Application
The scope of the application of deep mixing is to handle and solve problems associated with the following aspects:
⎯ settlement reduction (e.g of embankments and structures);
⎯ improvement of stability (structures and embankments);
⎯ support of slopes and excavations;
⎯ improvement of bearing capacity and reduction of settlement and lateral spreading due to dynamic and cyclic loading (e.g in seismic regions);
⎯ immobilisation and/or confinement of waste deposits or polluted soils;
⎯ reduction of vibrations and their effects on structures and human beings.
Design principles
Deep mixing ground treatment must be carefully designed and executed to ensure that the supported structure remains suitable for its intended use throughout its lifespan It should reliably withstand all expected actions and influences during both execution and use, meeting the necessary serviceability and ultimate limit state requirements for cost-effectiveness and durability.
The requirements for the serviceability and ultimate limit states are to be specified by the client The design shall be in accordance with the requirements put forward in EN 1997-1.
Iterative design, which involves analyzing results from various testing methods, plays a crucial role in the design process This approach emphasizes key factors essential for the effective implementation and objectives of deep mixing.
The design is made for the most unfavourable combinations of loads, which could occur during construction and service
The deep mixing process can lead to a temporary reduction in resistance to failure due to excess pore water pressure and soil displacements To enhance stability, mixed-in-place columns must be strategically arranged to prevent potential weakness in some columns from negatively impacting overall stability Stability analysis should consider the differing stress-strain relationships between treated and untreated soil Key parameters for excavation support include the compressive strength of the treated soil and the concept of arching An iterative process that integrates functional and process design is illustrated in Figure B.1.
Figure B.1 — Iterative design process, including laboratory testing, functional design, field trials and process design
Execution process of deep mixing
Standardized laboratory tests, also known as laboratory mixing tests, are essential for determining the appropriate binder type and dosage for construction projects, taking into account each representative soil layer Typically, there is a discrepancy between laboratory strength and field strength, making it crucial to base preliminary process design on laboratory results, databases, and similar experiences Prior to construction, deep mixed test columns are created for field trials to verify that the selected binder, dosage, and mixing energy achieve the necessary strength and uniformity If the field trials do not meet the design requirements, both the functional and process designs must be reevaluated.
Choice of binder
In deep mixing, the selection of binders, typically cement or a combination of lime and cement for dry mixing, is crucial and influenced by soil conditions and project objectives It is essential to test binders with the specific soil to be treated for any deep mixing project A summary of commonly used binders can be found in Table B.1.
Table B.1 — Binders commonly used in dry mixing
Clay Lime or lime/cement
Quick clay Lime or lime/cement
Organic clay and gyttja Lime/cement or cement/granulated blast furnace slag or lime/gypsum
Peat Cement or cement/granulated blast furnace slag or lime/gypsum/cement
Sulphate soil Cement or cement/granulated blast furnace slag
Silt Lime/cement or cement
In wet mixing, cement is typically the primary binder, although specially formulated binders are utilized for highly organic or very soft, water-saturated soils For applications where lower strength is desired, mixtures of fly ash, gypsum, and cement can be employed Additionally, bentonite is commonly added to enhance the rheology and stabilize slurry mixes.
Testing
General
The testing method for deep mixing must be tailored to its specific purpose For reducing settlement, the focus is on the elastic modulus value, while enhancing stability and minimizing failure risk requires attention to the strength of the columns Additionally, for the immobilization and confinement of waste deposits or contaminated soil, the key factors are the overlapping and low permeability of the columns.
Laboratory testing
Laboratory testing is essential for evaluating soil treatment options and assessing the effectiveness of deep mixing techniques This process involves analyzing both laboratory-mixed soil samples and samples collected from different depths within installed columns.
Laboratory mixed samples enable the investigation of the optimal quantity and type of binder, as well as the ideal combinations of binder, filler, and admixture Additionally, they help determine the necessary binder factor and water-to-binder ratio needed to effectively stabilize soil for its intended use.
For the laboratory investigation of soil/binder samples, reference is given to the following procedures included in the Design Guide from [6]:
1) laboratory procedure for preparation and storing of test samples of soil stabilised by binders for Deep Mixing, Column applications;
2) laboratory procedure for preparation and storing of test samples of soil (especially peat) stabilised by lime and cement-type materials for mass stabilisation applications
NOTE Laboratory procedure for preparation and storing of test samples of soil for Japanese dry and wet mixing methods have been standardised by the Japanese Geotechnical Society.
The relationship between the strength properties of laboratory mixed samples and their performance in field conditions is often unpredictable When there is substantial experience regarding the correlation of strength characteristics between laboratory samples and columns installed in soil of the same geological origin, a conservative correlation coefficient can be utilized It is essential to use the same type of mixing tool, binder, and binder content as those used in the reference object to ensure accuracy.
Core samples are obtained using rotary core drilling equipment and are essential for analyzing deformation characteristics, strength, and uniformity of soil The selection of coring technique and core diameter is influenced by the soil's strength and grading, with triple tube samplers being ideal for soft soils For construction projects, a minimum of three core borings is recommended, extending to the full depth of treatment The rate of strength gain differs between dry and wet mixing, influenced by moisture content and binder hydration characteristics, while temperature also plays a crucial role in strength development The hydration effect of the binder on ground temperature is affected by factors such as binder type, content, and treated soil volume Additionally, sample disturbance can significantly impact sample characteristics, making it important to complement core sampling with other testing methods.
The strength characteristics and elastic modulus (E col) of samples are typically assessed through unconfined compression tests However, the presence of cracks in the samples can influence the results In cases where cracks are visible, triaxial testing is recommended, as outlined in prEN 1997-2.
The compression modulus \( M_{col} \) of the samples is determined through œdometer tests, as outlined in prEN 1997-2 For evaluating the settlement behavior of stabilized soil, the elastic modulus of the column is a more accurate representation than the œdometer modulus Relying on the œdometer modulus for settlement analysis can result in an underestimation of long-term settlement.
Hydraulic conductivity tests necessitate specialized equipment since there is no standard apparatus available Nevertheless, permeability can be estimated through back-calculation using the coefficient of consolidation obtained from oedometer tests.
Wet grab sampling is a crucial component of the European wet method, conducted before the initial setting of treated soil Samples are collected from specific depths using a sampling tool, typically at a rate of one sample per 500 m³ of treated soil or daily The process involves lowering a wet grab sampling device to the desired depth, capturing the fluid sample, sealing the device, and bringing the sample to the surface for processing into cylinders for testing These samples are then cured at a specified temperature in standard-sized molds, cylinders, or cubes Testing occurs after 7 and 28 days of curing, with the differing curing conditions of in-situ treated soil and wet grab samples affecting their strength and rate of strength increase.
Field testing
In-situ tests are essential due to uncertainties about laboratory-determined column characteristics To assess column uniformity, methods such as sounding, core boring, or lifting entire columns can be employed Evaluating the mechanical and hydraulic conductivity properties of the columns necessitates specialized equipment Typically, a field trial test involves installing two to three columns with varying binder content.
Field-testing plays a crucial role in establishing construction control criteria for deep mixing Key control values include the penetration and retrieval rates of the mixing tool, its rotation speed and torque, as well as the overlapping width and binder/slurry delivery rate To ensure a column is founded on a solid bearing stratum, it is essential to measure torque and changes in penetration resistance to determine the critical construction control values.
B.5.3.2 Direct determination of mechanical properties
Pressuremeter tests, as outlined in prEN 1997-2, are essential for assessing the shear strength and compressibility of soil columns These tests necessitate the preboring of a hole in the column to facilitate the insertion of the pressuremeter.
Geophysical tests are essential for assessing the properties of treated soil under dynamic conditions and for evaluating the integrity of columns They also facilitate the indirect determination of deformation modulus and strength Nevertheless, the interpretation of geophysical test results remains a subject of ongoing research.
B.5.3.3 Investigation of uniformity and indirect determination of mechanical properties
CPT tests, or conventional cone penetration tests, are utilized to assess the strength parameters and continuity of columns However, the CPT method has certain limitations, particularly regarding its ability to maintain verticality compared to column penetration tests Additionally, due to the size of the cone, CPT only evaluates a small portion of the column's volume, often necessitating stepwise preboring to ensure the cone remains within the column during testing.
Static/dynamic penetration tests, which are a combination of penetration and hammering test, are useful for treated soil with unconfined compressive strength ≤ 4 MPa
The column penetration test involves pressing a probe into the center of a column at a speed of approximately 20 mm/s while continuously recording penetration resistance This method is suitable for columns up to 8 m in length with unconfined compressive strength less than 300 kPa For longer columns, preboring a vertical hole in the center—without percussion—can prevent the probe from exiting the column into the surrounding soil With preboring, the test can be effectively applied to columns with unconfined compressive strengths ranging from 600 kPa to 700 kPa, extending to depths of 20 m to 25 m.
By the reverse column penetration test the uniformity of the column can be determined along its whole length
In this test, a probe equipped with vanes similar to those used in the column penetration test is connected to a wire rope that extends from the bottom of the column to the ground surface The wire rope must have a minimum strength of 150 kN The column's strength is determined by measuring the resistance encountered when the probe is withdrawn at a speed of approximately 20 mm/s The vane type should align with recommendations for the column penetration test This method serves to assess the variability of the column's strength with depth rather than providing a direct measurement of shear strength, and it is currently under development.
Pressure-permeameter tests are used in a similar way as the pressuremeter and can serve as a basis for determination of the permeability of the column in radial direction
Various types of field tests can be used to assess the hydraulic properties in the field However, no standard equipment exists for determination of the permeability
2 Tube, d y = 36 mm threaded on easing
4 Internally threaded casing on sounding rod
Figure B.2 — Vanes used in the conventional (left) and the reverse column penetration tests
Correlation of various properties of treated soil
Field strength and laboratory strength
Variations in mixing methods and curing conditions lead to differences between field and laboratory mixed soils Laboratory testing procedures differ between Europe and Japan, as outlined in Clause 5, and the use of distinct mixing tools in each region complicates the comparison of field and laboratory strength Nevertheless, utilizing the same mixing tools within a standardized quality control system allows for a meaningful comparison of field- and laboratory-treated soils, drawing on accumulated experience.
Based on Swedish dry mixing practices in soft plastic clays, the strength ratio between field and laboratory-mixed samples ranges from 0.2 to 0.5 In contrast, granular soils tend to exhibit a significantly higher strength ratio, primarily influenced by the fines content present in the soil.
The Cement Deep Mixing Method (CDM) is the most prevalent wet mixing technique in Japan, with the CDM association implementing quality control procedures and setting a minimum blade rotation speed In contrast, the Dry Jet Mixing Method (DJM), which is the typical dry mixing method, utilizes mixing tools produced by the same manufacturer Data accumulated from Japanese experiences with both CDM and DJM on land is illustrated in Figure B.3, while Figure B.4 specifically summarizes the findings related to CDM works.
Figure B.3 — Relation between strength results of field and laboratory tests for on-land constructions [19]
1 Unconfined compressive strength of in-situtreated soil, q uf , MPa
2 Unconfined compressive strength of laboratory treated soil,q ul , MPa
Figure B.4 — Relation between strength results of field and laboratory tests for marine constructions [5]
Correlation between mechanical characteristics and unconfined compressive strength
In design, it is essential to obtain values for bending strength, tensile strength, modulus of elasticity, and permeability These properties can be derived from core samples of in-situ treated soil following construction.
During the design phase, it is essential to utilize values derived from a trustworthy database The Japanese wet mixing method is supported by extensive data compiled by the Coastal Development Institute of Technology in Japan.