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30 C h a p t e r 5 Introduction Extensive literature reviews and data mining on each technol- ogy were performed to complete project Tasks 9, 10, 11, and 12 (see Chapter 1). A common methodology was developed, refined, and used for all 46 technologies of Elements 1, 2, and 3. This process has resulted in the creation of project technical summaries, task reports, and products and tools. The distinction between items is their intended use. The tech- nical summaries and the task reports are complete with the Phase 2 final submission and will not be updated or revised in the future. The technical summaries and task reports were used to develop the products and tools. The project products and tools are the primary user items on the Geotechnical Solutions for Transportation Infrastructure website. These products and tools are living documents. They will be updated and revised as appropriate during the beta testing phase of the website, and routinely when the website is fully opera- tional. Additional documents will be added to the website (e.g., case histories) as it is used. The technical summaries and assessment task reports sys- tematically organized and evaluated the background infor- mation on each technology, in a consistent format. These comprehensive technical summaries (CTS) and task reports are project working documents, and are not tools to engineer ground improvement works. Additionally, project working document reports on technology evaluation and on product development have been prepared and document the develop- ment, formatting, and review process for the technical sum- maries and assessment tasks, and for the products and tools, respectively. These reports document research and develop- ment information, and are not primary user tools. Thus, the project working documents and reports will not be available on the Geotechnical Solutions for Transportation Infrastruc- ture website. The methodology employed to develop the technical sum- maries and the task reports is summarized in the following subsections. Additional details are contained the respective project documentation report. technical Summaries and task reports Task 9 is the development of a catalog of materials and sys- tems for rapid renewal projects. The materials and systems are the 46 technologies. Each technology was individually researched to gather the information needed to develop a technologies catalog (i.e., the Geotechnical Solutions for Transportation Infrastructure website). The keystone component in creating the catalog is the CTS developed for each technology. The CTS, a detailed literature review summary for a given technology, is the first document produced for a technology. Its purpose is to serve as the pri- mary document on a given technology for completion of the Phase 2 R02 project tasks. Each respective CTS is a working document that contains source materials for completing Phase 2 Tasks 9, 10, 11, and 12. Subsequent documents, reports, and products for a technology were developed on the basis of information contained within the CTS. The reports and prod- ucts that flowed from the CTS (for each technology) are illus- trated in Figure 5.1. A design and quality control and quality assurance (QC/QA) assessment and a specification assessment report were prepared for each individual technology. The design and QC/QA assess- ment reports are detailed assessments of design methods and QC/QA procedures for a given technology. Existing specifica- tions for a given technology are assessed in the specification assessment reports. The CTS, design and QC/QA assessment, and specification assessment reports provided the background information to develop the end user products and tools. Thus, the project working documents/reports are not available on the Geotechnical Solutions for Transportation Infrastructure website. Development of Background Information
31 Comprehensive technology Summary Purpose of the CTS The CTS is a detailed literature review summary for a given technology. Its purpose is to serve as the primary, or keystone, document on a given technology for completion of the Phase 2 R02 project tasks. The format of the CTS was developed to organize information into categories applicable to different aspects of engineering with a ground improvement technol- ogy. This categorized information was then used to produce project reports and products, as discussed in the following subsections. Information Gathered in the CTS Literature for the CTS came from a wide variety of sources. Capturing literature that transportation agency engineers routinely rely on was given high priority. Sources included the following: ⢠Federal Highway Administration (FHWA) design and guideline manuals ⢠American Association of State Highway and Transporta- tion Officials (AASHTO) manuals and specifications ⢠Transportation Research Record: Journal of the Transporta- tion Research Board ⢠National Cooperative Highway Research Program (NCHRP) reports ⢠NCHRP Synthesis of Highway Practice Literature was also gathered from university research reports and papers, conference technical papers, journal technical papers, and the like. Additionally, example specifications were gathered from individual STAs. For the identified technologies, a comprehensive set of ref- erences was collected and is detailed in the Phase 1 Literature Review Database document. This database was placed on a web-based searchable system and was used by the project team in Phase 2 work. To categorize the literature, a matrix of relevant categories was developed for each technology and then populated by the research team members. Twenty-two categories were included in the matrix for each technology, including technology over- view, site characterization, analysis techniques, design proce- dures, design codes, construction methods, construction time, equipment/contractors, contracting, QC/QA, perfor- mance criteria, monitoring, geotechnical limitations, non- geotechnical limitations, case history, environmental impacts, initial cost, life-cycle cost durability, and reliability. The tech- nology matrix is contained in the Bibliography product for each technologyâwhich is contained on the Geotechnical Solutions for Transportation Infrastructure website. Reports and Products The CTS is the keystone project working document for a given technology. Additional project working documents and several end user products were developed for each technology based on the CTS. The project products, or user tools, are those items that are posted on the Geotechnical Solutions for Transportation Infrastructure website. These are tools for use by agency personnel on their upcoming projects. It is planned Figure 5.1. Reports and products that flowed from the CTS. Comprehensive Technology Summary Report Design & QC/QA Assessment Report Specification Assessment Report Cost Estimating Report Photographs Product Design Guidance Product QC/QA Assessment Product Cost Information Products Specifications Product Case History Products Bibliography Product Technology Fact Sheet Product
32 that these products and tools will be refined and updated during the beta testing program of Phase 3 and with contin- ued use of the fully released website. The reports, products, and tools that flowed from the CTS (for each technology) are illustrated in Figure 5.1. CTS Format A consistent format was developed to produce a CTS for each technology. The template provides format and instructions for completion of the CTS. There is no page or length limit for a CTS. The following items are to be provided: ⢠Definition and description of the technology ⢠Applicability screening parameters for the technology ⢠Case history summaries ⢠Summary of design procedures ⢠Summary of QC/QA procedures ⢠Cost information ⢠Summary of available specifications ⢠Technology matrix ⢠Bibliography The technology matrix and bibliography are part of an ini- tial or draft CTS. They are not included in the final project CTS document or report. The technology matrix and bibli- ography become a website product, which should be updated as necessary. This template should also be used to develop any and all additional, future technology CTSs. This will provide consis- tent assessments of technologies and consistency in the devel- opment of technology screening tools and end user products and tools. assessment of Design Methods and QC/Qa procedures Purpose of Assessment Design procedures of one form or another already exist for many of the R02 technologies. Some technologies already have well-established design procedures, some have various published design procedures, some have proprietary design procedures, and others have developing design procedures. Some technologies have worthwhile analysis procedures that are not integrated into comprehensive design procedures. To avoid excluding such material, the design assessment included both design and analysis procedures. There are also many technologies for which establishing suitable QC/QA procedures is arguably the critical limiting fac- tor preventing more widespread application of the technolo- gies. Providing clear, precise, and effective guidelines for QC/ QA procedures will remove an important source of uncertainty that currently makes some designers hesitant to apply these technologies. The purpose of the assessment of design methods and of QC/QA procedures (design and QC/QA assessment) is to gather design/analysis methods and QC/QA procedures, and then critique and compare these two. The design and QC/QA assessment project working document provides the basis for development of the end user tools and products. Information Assessed Design methods and QC/QA procedures for the assessment came from various sources. Capturing literature that trans- portation agency engineers routinely rely on was a high pri- ority. This included the following: ⢠FHWA design and guideline manuals ⢠AASHTO manuals and specifications ⢠Transportation Research Record: Journal of the Transporta- tion Research Board ⢠NCHRP reports ⢠NCHRP Synthesis of Highway Practice Literature was also gathered from university research reports and papers, conference technical papers, journal technical papers, and the like. The design and QC/QA assessment critiques and charac- terizes the design and analysis methods and QC/QA proce- dures that were identified in the CTS document. There is no length limit for an assessment. The design and analysis por- tion of the assessments includes the following: ⢠Listing of all input and output parameters for each design/ analysis method, in matrix form. In the matrix, specific input and output items appropriate for a particular tech- nology are arranged in the following categories: perfor- mance criteria and indicators, subsurface conditions, loading conditions, material characteristics, geometry, and construction techniques. ⢠Comparative assessment of all design/analysis methods, in matrix form. The matrix contains four sections: design/ analysis procedures, references, applications, and assessment of design/analysis procedure. ⢠Comparative characterization of all design/analysis meth- ods, in matrix and comment forms. This includes a descrip- tive summary of each method, categorized ratings on each method, and comments on the ratings. The QC/QA portion of the assessment also uses a matrix to systematically organize and evaluate information on existing procedures. The matrix has six sections: QC/QA methods, ref- erences, QC/QA objectives, applicability to QC and QA, assess- ment of QC/QA methods, and usefulness of QC/QA method
33 for application. Generally, all the desired outputs from design procedures (from the first matrix in this document) should be subject to QC/QA activities and should be reflected in the QC/ QA matrix. Report and Products A design and QC/QA assessment project working report has been prepared for each technology. The assessments and characterizations in the design and QC/QA assessment are used to develop the design guidance and the QC/QA proce- dures tools and products for the Geotechnical Solutions for Transportation Infrastructure website. assessment of existing Specifications Purpose of Assessment Several specifications exist for many of the R02 technologies. Most technologies already have well-established STA specifi- cations or guideline specifications, though some have propri- etary specifications, and a few emerging technologies do not have a generic specification. The purpose of the assessment of existing specifications (specification assessment) is to gather existing specifications; critique, characterize, and compare these; and provide recom- mendations on specification preparation for a technology. Information Assessed Individual specifications for the specification assessment came from diverse sources. This included the following: ⢠FHWA design and guideline manuals ⢠AASHTO manuals and specifications ⢠Standard specifications and special provisions from indi- vidual STAs ⢠NCHRP reports and NCHRP Synthesis of Highway Practice The specification assessment critiques and characterizes the specifications that were identified in the CTS document. There is length limit for an assessment. The specification assessment also uses a matrix to systematically organize and evaluate information. The matrix is used to assess existing specifications for clarity, risk allocation, ability to be fairly bid, constructability, QC/QA verification, and completeness. Report and Product A specification assessment project working document has been prepared for each technology. The assessment and char- acterization in the specification assessment is used to develop the specifications guidance tool or product for the Geo- technical Solutions for Transportation Infrastructure website. review processes Typically, lead authorship of a CTS, design and QC/QA assess- ment report, and specification assessment report was given to one or two of the student researchers. One of the principal investigators served as a mentor and as the primary reviewer of each draft CTS. Additional reviewers included other principal investigators, advisory board members, and outside technical experts. The top of each document shows the lead author or authors, the mentor or primary reviewer, and any additional reviewers. Usually, the same authors, mentors, and reviewers were used on all three documents for a given technology. Two additional reviews were completed in the fall of 2011. A peer review process was completed by student researchers. These student researchers reviewed the documents, reports, and products for all 46 technologies. This peer review focused on consistency between technologies and within products of an individual technology. This was followed by reviews performed by the technology mentor or primary reviewer and by Vernon Schaefer and Ryan Berg, the R02 project managers. These were reviews of all the final documents, reports, and products for a particular tech- nology. The primary focus of these reviews was consistency within all the technology products, documents, and reports. Development projects Nine development projects were completed during the research to fill knowledge gaps for specific technologies and applications. The decision-making process to select these specific topics for advancement was documented in the Phase 1 report. A brief summary of each project follows. A separate report for each project has been prepared. The R02 development projects are the following: ⢠Review and update of settlement methods for stone columns ⢠Development of a design procedure for vibro concrete columns ⢠Assessment of design of shoot-in soil nailing ⢠Guidelines for reinforced soil facing ⢠Review of existing design methods and development of a recommended design method for column-supported embankments ⢠Use of multiple technologies for stabilizing soft soils ⢠Performance verification of stabilized subgrades ⢠Comparison of surface compaction technologies through a compaction roadeo ⢠Assessment of geocell-reinforced recycled asphalt pavements
34 Settlement Analysis of Stone Columns Stone column technology lacks a standard design procedure for accurately estimating settlements. The R02 project team believes that current methods for estimating settlements of stone col- umns are conservative. An extensive literature review was con- ducted to identify case histories where stone columns were used to reduce settlements. Case histories selected for evaluation had sufficient information provided for analysis and had data on settlements measured in the field. Based on analyses using three methods of estimating settlements and the measured settle- ments in the field, a statistical analysis was completed to evalu- ate the accuracy of each method. A parametric study of the procedures was conducted to assess the critical design inputs. The report of this study provides a listing of case histories that document the successful and unsuccessful implementa- tion of this technology, a summary of the settlement analysis procedures considered in this study, and a presentation of the comparisons between calculated and measured settlements. The work completed as part of this project may be used in the future to identify or develop a preferred procedure for esti- mating settlement of stone column reinforced sites. The pre- ferred procedure could be an existing method or some modification of an existing method. It is recommended that this report be made available for download (in PDF format) from the Geotechnical Solutions for Transportation Infrastructure website, specifically, from the aggregate columns document page. This will allow the user to learn about the various methods available for estimat- ing settlements for stone columnâreinforced ground. Design Procedure for Vibro Concrete Columns Vibro concrete columns (VCCs) are a foundation solution that can be used to improve load capacity and reduce settlements. Columns are constructed using a procedure similar to that for dry, bottom-feed dry stone columns but use concrete instead of stone. Advantages over stone columns are that VCCs dem- onstrate higher load capacity and they can be used in soils not suitable for stone columns (e.g., peat and compressible clay). VCC technology lacks a standard design methodology, so VCCs are currently designed using modified drilled shaft or driven pile design methods. Drilled shaft design methods tend to over predict capacity, while driven pile methods tend to under predict capacity. To promote VCCs as a rapid and cost-effective technology, it is necessary to provide a standard design methodology that more accurately predicts capacity. The objectives of the VCC development project are to assess current design procedures based on available load test data and, to the extent possible, develop a standard design meth- odology for VCCs that more accurately predicts capacity. Efforts have included the review of available literature on VCCs, collection of VCC case histories with load test data, and review of failure criteria for piles. A stand-alone VCC capacity program has been developed for easy calculation and comparison of design capacities. The program allows the user to input soil profile and column information, and it automatically determines capacity based on several drilled shaft and driven pile design methods. Results from the pro- gram will be compared with actual VCC load test data to evaluate the individual methodsâ accuracy and applicability to VCC design. A manual to explain the use of the program and the design method calculations has also been prepared. It is recommended that this report be made available for download (in PDF format) from the Geotechnical Solutions for Transportation Infrastructure website, specifically, from the VCC document page. This will allow the user to more accurately and efficiently design VCCs. Assessment of Design of Shoot-In Soil Nailing Roadway widening and new roadway construction projects in rough terrain often require retaining walls. Drilled and grouted soil nails have been a traditional reinforcement method for these situations. In recent years, shoot-in or launched soil nails have become a viable alternative form of retaining wall and slope reinforcement in both temporary and permanent appli- cations. This technology is directly applicable to Element 2, roadway and embankment widening. Other launched soil nail uses include bluff stabilization, micropiling, and excavation shoring. Launched soil nailing is a relatively new technology devel- oped in the United Kingdom in the early 1990s. A compressed air cannon, typically mounted on a traditional tracked excava- tor, uses pressures approaching 2,500 psi to launch the nails into the ground in a single blow at speeds in excess of 200 mph. Groups of these nails can be quickly installed to support retain- ing walls or unstable slopes. The soil nails used are typically 1½-in. diameter, 20-ft long steel or steel-tipped fiberglass tubes. After installation, an inner reinforcing steel bar is inserted and the annular spacing is filled with grout to transfer longitudinal shear stresses to the reinforcement and to provide corrosion protection for the steel. The tubes can also be perforated to allow for pressure injected grout to permeate into the surround- ing soil and further increase the soil bond to the nail. Advan- tages of launched soil nailing include rapid installation and cost savings. Also, because the soil nail launcher can be mounted various highly mobile equipment, this technology can be applied in hard-to-access areas and in areas with narrow right- of-ways, with minimal disturbance to the surrounding area. For the shoot-in soil nailing technology, the project goal is to review the different existing design methodologies and
35 generate a technical evaluation report analyzing the design, construction, performance, and quality assurance aspects of the technology. A report detailing the technology back- ground, applications, QC/QA procedures, and materials and equipment has been completed. Three design methodologies were examined: the FHWA method, the French method, and a method developed by Soil Nail Launcher, Inc. These meth- ods were analyzed and compared via an ongoing literature review and sample soil nail wall designs. It is recommended that this report be made available for download (in PDF format) from the Geotechnical Solutions for Transportation Infrastructure website, specifically, from the shoot-in soil nailing document page. This report will give general technology background for new users and provide guidance on available design methods. Guidelines for Reinforced Soil Facing Reinforced soil slope (RSS) technology uses geosynthetic or steel reinforcing elements within a soil slope to create a stable slope at a steeper slope angle than traditional, unreinforced slopes. Steepened slopes are desirable in some transportation applications. Typical RSS facing ranges vegetation and bio- engineered faces to flexible armor systems. The purpose of RSS facing is to minimize erosion, protect the reinforcing elements, and contribute to the aesthetic quality of the structure. With- out proper design and detailing of the RSS face, soil raveling, soil sloughing, erosion, or surficial slope failures may occur. Typically, soil reinforcement manufacturers or vendors develop RSS-specific facing details and guidelines as an integral part of an RSS product. A project owner or DOT may choose to incorporate additional criteria or design considerations to the facing selection. Some facing details are well documented and established and others are not. The lack of accessible, docu- mented, and proven facing details and designs continues to sig- nificantly limit the use of RSS by state DOTs. The objective of this project is to develop comprehensive guidelines for reinforced soil slope facing and a catalog of design and construction details. The proposed document will include facing and vegetation selection guidelines, example specifications, design and construction details, and mainte- nance recommendations. The final report will be available in hard copy and electronic formats with drawings and details available in various program formats. Various detail drawings and manufacturer literature have been collected from members of the Geosynthetic Materials Association (GMA) and from other industry sources. These resources were used to generate standard facing details for common facing types that could be used by DOTs. The report provides a description of each facing type and project criteria that are considered when selecting a facing. Several detail drawings have been developed. It is recommended that this report be made available for download (in PDF format) from the Geotechnical Solutions for Transportation Infrastructure website, specifically, from the RSS document page. This will allow the user to learn about facing types and selection alongside the design, QC/QA, and specifications documents. Development of a Recommended Design Method for Column-Supported Embankments When an embankment is required over ground that is too soft or compressible to provide adequate support, columns of strong material can be placed in the soft ground to provide the necessary support by transferring the embankment load to a firm stratum. Several types of columns may be used for this technology, such as aggregate columns, deep-mixing- method columns, and traditional piles. A load transfer plat- form or bridging layer, consisting of compacted select fill with or without geosynthetic reinforcement, may be con- structed immediately above the columns to help transfer the load from the embankment to the columns. A literature review revealed 12 design procedures for column-supported embankments (CSEs). CSEs have the advantages of more rapid single-phase con- struction, reduced total and differential settlements, and pro- tection of adjacent facilities and embankments. The major obstacle preventing widespread use of CSEs is the lack of standard design procedures. The goal of this research was to validate, improve, or develop one or more successful design procedures for widespread use in transportation projects. A CSE test facility with a 30-ft by 30-ft test area was designed and constructed for the purpose of evaluating the arching and load transfer to the columns that occurs within the embank- ment. The test process involves an innovative use of geofoam for temporary support during embankment construction. After completion of CSE construction, the geofoam was dis- solved to remove embankment support between precast con- crete columns to simulate the settlement of soft soil. Five instrumented CSE tests were conducted from April to October 2010 using a total of approximately 2,100 tons of fill material. The key results of the CSE tests and resulting data analysis are the following: ⢠The critical height for 6-ft center-to-center spacing of 2-ft- diameter round columns in a square array is approximately 6.5 ft without trafficking loads and 7.5 ft after trafficking with a small skid-steer, rubber-tired loader. The critical height is the embankment height above which differential surface settlements were not observed. ⢠The Adapted Terzaghi and Hewlett and Randolph Meth- ods for determining the vertical stress on the geosynthetic reinforcement are consistent with the test results.
36 ⢠The Parabolic Method for determining the tension and strain in the geosynthetic reinforcement is consistent with the test results. ⢠The load-displacement compatibility approach by Filz and Smith incorporates soft-soil support and is consistent with the test results when the load is shared between the con- crete columns and the geofoam before it is dissolved. The method developed by Filz and Smith also uses the Adapted Terzaghi and Parabolic Methods and forms the basis of the recommended design procedure contained in the report. It is recommended that this report be made available for download (in PDF format) from the Geotechnical Solutions for Transportation Infrastructure website, specifically from the CSE document page. The report includes a literature review of design procedures and a complete description of the CSE facility and tests, as well as a recommended design procedure, specification, and QC/QA procedures. Integrated Technologies for Embankments on Unstable Ground The SHRP 2 R02 information and guidance system allows users to input project requirements and constraints, and from that obtain a list of potentially applicable ground improve- ment technologies. It provides users with a list of technologies, but it does not directly inform users of possible situations where the combination of technologies may be beneficial for their project. The objective of a separate white paper on integrated tech- nologies for unstable ground is to assist in achieving the goal of the SHRP 2 R02 program more efficiently and effectively by using two or more technologies at a site. The white paper includes a discussion of benefits that com- bining multiple technologies may provide over the use of a single technology. In addition, it lists the SHRP 2 Elements 1 and 2 technologies that can be used to improve unstable ground under embankments and potential combinations of these tech- nologies. Finally, case histories of successful combinations are summarized and links to additional references provided. The summaries illustrate where and why specific combinations have been used. A summary list of technology combinations is pro- vided. This white paper has been developed to be used in con- junction with the information and guidance system. The white paper is hyperlinked throughout the Geotechnical Solutions for Transportation Infrastructure website. Performance Verification of Stabilized Subgrades Chemical stabilization of subgrades can improve the support conditions under pavements with increased strength/stiffness and resistance to seasonal changes, which should, in turn, contribute to better long-term performance of pavements. The MechanisticâEmpirical Pavement Design Guide (MEPDG) provides typical elastic modulus values and empirical equa- tions to estimate elastic modulus values of stabilized soils for use in design. The modulus values provided in the guide are based on laboratory measurements obtained in short-term. The design also recommends typical deteriorated elastic mod- ulus values for stabilized subgrades. Long-term changes in the performance characteristics of the stabilized subgrade layers are not considered in the design because of performance uncertainty and lack of quantitative long-term performance data. To remedy this, performance data on test sections that are at least 10 years old is crucial to gain understanding on the long-term strength, stiffness, and mineralogical and micro- structural characteristics of chemical stabilized subgrades. The main objectives of the project were to (a) document engineering properties (in situ strength and stiffness) and min- eralogical and microstructural characteristics of chemically stabilized subgrades that are at least 10 years old, in compari- son with natural subgrades at the same sites, and (b) under- stand factors that contribute to long-term engineering behavior of stabilized subgrade. In situ strength and stiffness character- istics were measured using falling weight deflectometer (FWD), light weight deflectometer (LWD), static plate load test (PLT), and dynamic cone penetrometer (DCP) tests [to determine California bearing ratio (CBR)], and laboratory tests on soil samples obtained from the field. Mineralogical and micro- structural analysis was performed using scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). Nine test sections were selected to assess engineering prop- erties of old stabilized subgrades in Texas, Oklahoma, and Kansas. The selection of the test sites was based on the type of subgrade, availability of old construction records, and age. Subgrades at six of these sites were stabilized with lime and the other three with fly ash. Eight test sites were over 10 years old, and one test site was approximately 5 years old. Eight sites consisted of flexible pavement supported on base and stabilized subgrade or just stabilized subgrade; one site con- sisted of concrete pavement supported on cement-treated base and stabilized subgrade. In situ and laboratory testing and data analysis for all test sites have been completed and a data report has been gener- ated. Some significant findings from the field and laboratory testing are as follows: ⢠FWD testing conducted showed nonuniform conditions at each site. Analyses are being performed to determine the influence of various parameters (i.e., pavement thickness, age of stabilized subgrade, thickness of stabilized subgrade, and moisture content) on the relationship between sub- grade CBR and FWD surface deflections.
37 ⢠The in situ elastic modulus of chemical-stabilized sub- grades determined from the static PLT varied from 7 MPa to 317 MPa at the nine test sites. The MEPDG recom- mended typical modulus value for lime-stabilized soils is 310 MPa with a range of 240 MPa to 413 MPa, and a dete- riorated modulus value for lime-stabilized soil is 103 MPa. Two of the six lime-stabilized subgrade sites tested showed modulus < 103 MPa (note that MEPDG does not provide typical values for fly ashâstabilized subgrades). ⢠Field results indicated that the elastic modulus value deter- mined in the field is dependent on the test method used. On average, LWD and the back-calculated FWD modulus were about 0.7 times and 8.3 times the static PLT modulus, respectively. This divergence in calculated modulus values is an important aspect to consider when selecting design values and establishing QC/QA target values. ⢠The ratio of LWD modulus of stabilized subgrade and natural subgrade varied from about 4 to 11. Similarly, CBR ratios between stabilized and natural subgrade ranged from about 2.2 to 7.4. Results indicated that these ratios are influ- enced by the thickness of the stabilized layers (the lower the thickness, the lower the ratio). It is recommended that the detailed report generated from this study be made available for download (in PDF format) from the Geotechnical Solutions for Transportation Infra- structure website, specifically, from the Chemical Stabilization of Subgrade and Base Courses technology page. The report will consist of case study information for each test site along with analysis of the field and laboratory results. This report provides significant new information on the performance of chemical-stabilized layers for use in pavement design. Comparison of Compaction Technologies Through a Compaction Roadeo A comprehensive review of literature, a detailed assessment of several technical obstacles that interfere with more widespread use, and evaluation of mitigation strategies and action items in terms of benefit-to-cost (B/C) ratio for each of the Ele- ment 3 technologies were completed. Three compaction tech- nologies received high B/C ratios: rapid impact compaction (RIC), intelligent compaction (IC), and high energy impact roller (IR). One major obstacle for widespread implementa- tion of RIC, IC, and IR technologies was identified as lack of well-documented and accessible case histories with benefits related to construction cost, time, efficiency, and effectiveness in consistently obtaining design properties, using these tech- nologies compared to traditional compaction methods. Con- ducting compaction roadeo field demonstration projects is an effective mitigation strategy to overcome this obstacle. A field demonstration was originally intended to develop detailed case history information for different material and subsurface conditions (e.g., lift thicknesses) comparing the relative com- paction efficiency, time, and cost by using the different com- paction technologies. However, unavailability of equipment at the time of this project limited use of IC and traditional com- paction technologies. The demonstration did include use of geosynthetic and geocells reinforcement technologies. The main objectives of the project were to (a) evaluate the use of IC technology with on-board computer display system for compacted fill QC/QA testing; (b) evaluate compaction influence depth under the IC roller; (c) evaluate differences in engineering properties between different types of geosynthetic- and geocell-reinforced fill test sections along with unreinforced fill test sections by using different QC/QA testing methods; (d) evaluate differences in the in-ground dynamic stresses under the roller between different test sections; and (e) provide hands-on experience with IC technology and various QC/QA testing technologies, and various geosynthetic and geocell re inforcement products to researchers and practitioners. The compaction roadeo field demonstration was con- ducted on the Highway 9B reconstruction project in Jackson- ville, Florida, from May 16 to 20, 2011. A Caterpillar CS74 vibratory smooth drum self-propelled IC roller weighing about 34,000 lb was used on the project. Field testing involved construction and testing of five test beds (TBs) on the project site with poorly graded sand embankment fill (A-3) material. TB1 involved constructing six test sections, which included three different geosynthetic reinforcement (biaxial grid, poly- propylene combigrid, woven polypropylene fabric) sections, two geocells reinforcement sections (6 in. and 4 in.), and one control section. TB2 involved compacting a thick loose lift (3 ft deep) in two sectionsâone with BX grid reinforcement and one without reinforcement. TBs 3, 4, and 5 involved mapping production areas using the IC roller and selecting test locations based on the color-coded on-board display unit in the roller for in situ testing. Field testing involved obtaining roller-integrated compaction measurements dur- ing compaction/mapping process, and point tests, including dynamic cone penetrometer (DCP) test, static cone pene- trometer test (CPT), static plate load test (PLT), falling weight deflectometer (FWD) test, light weight deflectometer (LWD), nuclear gauge (NG), and sand cone density. In addition, all the sections of TB1 were instrumented with piezoelectric earth pressure cells (EPCs) to monitor in-ground total vertical and horizontal stresses before, during, and after compaction. It is recommended that the detailed field data report gen- erated from this study be made available for download (in PDF format) from the Geotechnical Solutions for Transpor- tation Infrastructure website, specifically, from the Intelligent Compaction, Geosynthetic Reinforcement in Pavement Sys- tems, and Geocell Confinement in Pavement systems pages. The results from this report will allow users to learn about
38 differences in in situ soil characteristics with different geo- synthetic and geocell reinforcement methods, compaction influence depth under vibratory compacted roller used on the project, and usefulness of application of IC technology for QC/QA. Assessment of Geocell-Reinforced Recycled Asphalt Pavements Geocell confinement technology uses geocell at the bottom portion of bases and subbases or on the top of subgrade in unpaved roads and some paved roads to construct stable pave- ment systems with less base or subbase thickness than tradi- tional unreinforced pavement systems. The purpose of using geocell in pavement systems is to provide lateral confinement to infill materials, increase the stiffness and shear strength of the reinforced fill, distribute the wheel load to a wider area, and reduce rutting and other pavement distresses. Typically, geocell manufacturers or vendors provide specifications for the use of geocell in pavement applications. The lack of a well-developed design method, defined economical benefits, a well-developed QC/QA methods, documented case histories, and difficulties in compaction limit the use of geocell in pavement systems. The objective of this project was to explore the possibility of geocell confinement of recycled asphalt pavement (RAP) as a base course material in pavement systems. The development document includes a comprehensive literature review for geocell-confined pavement systems, and experimental study of geocell-reinforced RAP bases for unpaved and paved roads. Various specifications have been collected from industry sources, and a comprehensive literature review has been con- ducted. The experimental studies on the creep and cyclic behavior of geocell-reinforced RAP bases over subgrade for unpaved roads have been completed. The development project summary report provides a brief review and description of geocell technology for RAP bases, summarizes the experimen- tal results and findings, and provides recommendations. It is recommended that this report be made available for download (in PDF format) from the Geotechnical Solutions for Transportation Infrastructure website, specifically, from the Geocell Confinement in Pavement Systems document page. This will allow the user to learn about possible use of geocell with RAP as reinforced bases for unpaved and paved roads. Future Work As previously noted, the CTSs, design and QC/QA assess- ment reports and specification assessment reports are Phase 2 project work documents and reports. These are not primary products and tools and, therefore, will not be available on the Geotechnical Solutions for Transportation Infrastructure website. These documents will not be updated. End user products developed from these documents and posted on the Geotechnical Solutions for Transportation Infrastructure website will be updated as needed. Future work will include the addition of technologies to the Geotechnical Solutions for Transportation Infrastructure website. The process of adding a technology will start with the development of a CTS, with bibliography and literature matrix included. Then, design and QC/QA assessment and specification assessment reports will be prepared. The detailed templates and instructions for these documents developed in Phase 2 will be used to help ensure consistent information gathering, evaluation, and summarizing processes. The CTS, design and QC/QA assessment report, and specification assessment report will be used to develop the Geotechnical Solutions for Transportation Infrastructure website products and tools for a new technology.
