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4C h a p t e r 2 A literature review was completed to identify similar reports and systems previously developed for geoconstruction tech- nologies. Two broad concepts are discussed herein. First, lit- erature that focuses on previously programmed systems for geoconstruction technologies is presented. Second, literature describing the geotechnical design process and the imple- mentation of a geoconstruction technology is reviewed. The literature search revealed the commitment of the national research sponsor, the Transportation Research Board (TRB), to compiling and disseminating information regard- ing problem foundations for highway embankments. In 1966, Highway Research Record 133 contained five reports on the use of sites with soft foundations. From this record, Moore (1966) summarized the New York State Department of Public Works procedures for dealing with foundation problems. In 1975, National Cooperative Highway Research Program (NCHRP) Synthesis of Highway Practice 29: Treatment of Soft Founda- tions for Highway Embankments provided the first compre- hensive review of the design process philosophy, treatment methods, special considerations, subsurface investigation and testing, and foundation treatment design (Johnson, 1975). In 1989, NCHRP Synthesis of Highway Practice 147: Treatment of Problem Foundations for Highway Embankments expanded the 1975 Synthesis to include more treatment methods and also included a section on construction and performance monitoring (Holtz, 1989). previously programmed Systems Automated systems for various aspects of geotechnical engi- neering were found during the study. Toll (1996b) reviewed systems that have been developed for geotechnical applica- tions. By 1996, more than 103 knowledge-based applications had been developed in the field of geotechnical engineering (Toll, 1996a). Previous systems included expert systems, deci- sion support systems, knowledge-based systems, and neural network approaches. Toll (1996b) summarizes the Geotech- nical areas where knowledge-based systems have been devel- oped as follows: ⢠Site characterization 44 Site investigation planning, 44 Interpreting ground conditions, 44 Soil classification and parameter assessment, and 44 Rock classification and parameter assessment. ⢠Foundations 44 Conceptual design of foundations, 44 Detailed design, 44 Pile driving, 44 Foundation construction, and 44 Foundation problems. ⢠Slopes 44 Soil slopes and 44 Rock slopes. ⢠Earth retaining structures. ⢠Tunnels and underground openings. ⢠Mining. ⢠Liquefaction. ⢠Ground improvement. ⢠Geotextiles. ⢠Groundwater and dams. ⢠Roads and earthworks. Rule-based systems dominated the earlier systems, with more complex systems being developed more recently. The previously programmed systems described in this section are presented chronologically. Improve Chameau and Santamarina (1989) presented the knowledge- based system, Improve, for the selection of soil improvement methods. This system approaches the process of selection as Background
5being similar to a classification problem (e.g., analogous to soil classification and mineral identification). The system uses a knowledge representation structure based on âwindowsâ together with a best-first search algorithm. A window refers to a possibility number that characterizes an object with respect to the variable of interest and is a fuzzy set. The search algo- rithm includes a preprocessor, classification system, case- based system, and postprocessor. The preprocessor collects the required input to form a stack of windows and then compares the input stack to the windows stack with each technology. An acceptability value is determined from this comparison to identify the most suitable technologies. More than 40 technol- ogies, listed below, were considered in the system (Chameau and Santamarina, 1989): ⢠Densification blasting ⢠Blasting and vibratory rollers ⢠Vibratory probe ⢠Vibratory probe and vibratory rollers ⢠Vibro compaction ⢠Vibro compaction and vibratory rollers ⢠Compaction piles ⢠Heavy tamping ⢠Heavy tamping and vibratory rollers ⢠Vibratory rollers ⢠Preloading ⢠Preloading and drains ⢠Surcharge fills ⢠Surcharge fills and drains ⢠Dynamic consolidation ⢠Electroosmosis ⢠Drains ⢠Particulate grouting ⢠Chemical grouting ⢠Pressure injected lime ⢠Displacement grout ⢠Electrokinetic injection ⢠Jet grouting ⢠Remove and replace ⢠Admixture stabilization ⢠Displacement blasting ⢠Prewetting loess ⢠Prewetting swelling clay ⢠Structural fill ⢠Lightweight fill ⢠Mix-in-place piles ⢠Mix-in-place walls ⢠Heating ⢠Freezing ⢠Stone columns ⢠Root piles ⢠Soil nailing ⢠Strip reinforcement ⢠Moisture barriers ⢠Geotextiles ⢠Berms The project-specific information used to sort the geo- construction technologies is as follows: ⢠Type of project ⢠Environmental freedom ⢠Time available ⢠Importance of increasing strength ⢠Importance of reducing deformation ⢠Importance of modifying permeability ⢠Position (depth) of layer ⢠Distance to the neighbor/layer depth ⢠Structure width/layer depth ⢠Special soil type ⢠Particle size ⢠Relative density ⢠Saturation conditions ⢠Stratum (covered or uncovered) ⢠Stage (built or not built) ⢠Is surface above water? ⢠Is surface treatment possible? ⢠Is layered construction possible? ⢠Duration of improvement (permanent or temporary) ⢠Equipment particular to each alternative ⢠Materials required by each method The knowledge in the system was acquired from Robert Holtz. Holtz also provided performance feedback that resulted in a systematic consideration of technical limitations of the possible methods. Additionally, common practice does pose some constraints on the applicability of a method (Chameau and Santamarina, 1989). Chameau and Santamarina (1989) also noted that a geo- technical expertâs comprehension of a problem is affected by a large number of factors, including factors that are case-specific, context-dependent, and subjective. Geotechnical experts make decisions based on the recollection of previous cases, which is relevant in geotechnical engineering where an emphasis is placed on experience. Systems such as Improve can help bring the state of the art to practice and train professionals, recog- nize gaps in knowledge, and transfer the knowledge and accu- mulated experience of a few to a large number of practitioners. Soil improvement can be readily distilled into a decision sup- port system because it is a well-defined domain, the selection of methods is well documented by the job characteristics and the required soil improvement, documented cases exist, and qualitative variables enter the decision process (Chameau and Santamarina, 1989).
6Expert System for Preliminary Ground Improvement Selection Motamed et al. (1991) developed an expert system for pre- liminary ground improvement selection (ESPGIS), which is based on a knowledge-based expert system (KBES). The sys- tem is menu-driven and can advise the user in selecting a ground improvement method or evaluate the userâs preselected method. Motamed et al. (1991) indicate that KBES applica- tions have been implemented in all areas of civil engineer- ing, with 76 operational prototype expert systems reported by 1987. Ground improvement in the United States has not been fully accepted as common practice because of the nature of the construction industry, resulting in a slow transfer of technol- ogy from the specialty contractor to the designer. A time lag in the range of 5 to 10 years exists between the introduction of a method and the subsequent widespread acceptance. The development of the system is presented in five stages, as illustrated in Figure 2.1. First, the problem is defined conceptu- ally, the user group is defined, and the need for an expert opin- ion is documented. Second, the problem is accurately defined. Third, the knowledge base is acquired from experts and other knowledgeable sources. Fourth, a tool is selected based on the requirements of the problem domain. Fifth, coding and testing of the system is completed. The preliminary selection of ground improvement meth- ods is not performed until the need for such modification is realized. The preliminary selection is based on the nature of the improvement and on physical subsurface, surface, and surrounding characteristics of the site. In developing the knowl- edge base for ESPGIS, published information and contractorâs literature was used extensively. Motamed et al. (1991) included the following methods in ESPGIS: ⢠Dynamic compaction ⢠Vibro compaction ⢠Vibro replacement ⢠Compaction grouting ⢠Preloading ⢠Wick drains ⢠Ground anchors ⢠Minipiles ⢠Slurry walls ⢠Diaphragm walls ⢠Chemical grouting ⢠Slurry grouting ⢠Freezing ⢠Jet grouting ⢠Lime injection Geotechnical experts were not actively engaged in the devel- opment process. The selection of an expert system shell (ESS) was an important in the success potential of a KBES system. The system was coded using VP-Expert in an MS-DOS based system (Motamed et al., 1991). International Knowledge Data Base for Ground Improvement Geosystems Yoon et al. (1994) developed an International Knowledge Data Base for Ground Improvement Geosystems (IKD-GIGS), which was to aid rational selections, design, and construction of ground improvement technologies. DiMillio (1999), in A Quarter Century of Geotechnical Research, states that the Fed- eral Highway Administration (FHWA) joined forces with the International Center for Ground Improvement Technology in Brooklyn, New York, to develop this system. This system was intended to provide a comprehensive, user-friendly database where a user could retrieve information on possible technolo- gies by viewing similar case histories, problems encountered, possible remedial action schemes, comparative cost data, speci- fications and codes, and quality control and quality assurance (QC/QA). Yoon et al. (1994) included the following ground improvement technologies in IKD-GIGS: ⢠Ground improvement technologies 44 Dynamic consolidation 44 Vibro compaction 44 Vacuum consolidation 44 Drainage 44 Preloading 44 Blasting 44 Heating 44 Freezing 44 Stone and lime columns 44 Electrochemical treatment ⢠Ground reinforcement technologies 44 Reinforced soils 44 GeosyntheticsFigure 2.1. Stages in building a KBES. Source: After Motamed et al., 1991.
744 Fiber reinforcement 44 Texsol 44 Mechanically stabilized embankments 44 Anchorages 44 Nails 44 Pinpiles 44 Diaphragm walls ⢠Ground treatment technologies 44 Compaction grouting 44 Jet grouting 44 Permeation grouting 44 Hydrofracture grouting 44 Compensation grouting 44 Fissure grouting 44 Bulk grouting 44 Slabjacking 44 Deep soil mixing 44 Shallow soil mixing The system was programmed using a DOS-based system to facilitate the program operating on a personal computer. A rela- tional database system was selected to implement IKD-GIGS because the software was economical, popular, powerful, and easy to use. The database included a compendium of national and international codes of practice, a collection of monitored case histories, and information on instrumented structures. As of 1999, the system contained more than 200 documented records of ground improvement case histories from 15 coun- tries. Yoon et al. (1994) described the initial phase of work and indicated that IKD-GIGS was to be developed through multiple phases. During the development of this SHRP 2 R02 Phase 2 project, the IKD-GIGS system could not be located. Soil and Site Improvement Guide Sadek and Khoury (2000) developed a selection system as part of a specialized geotechnical engineering soil improve- ment course at the American University of Beirut. The main objective of the system was to enhance the quality of the teach- ing and learning process as it relates to soil improvement. The end product provided a system for learning about different techniques, their advantages and limitations, their applicability under certain conditions, and the associated costs. Seventeen ground modification methods were included in the program and broken into four categories: ⢠Densification 44 Dynamic deep compaction 44 Surcharging 44 Vibro compaction 44 Vibro replacement 44 Compaction grouting 44 Accelerated consolidation/wick drains ⢠Adhesion 44 Cement grouting 44 Chemical grouting 44 Slurry grouting 44 Freezing ⢠Reinforcement 44 Minipiles 44 Soil nailing 44 Soil and rock anchors ⢠Physicochemical 44 Electroosmosis 44 Lime treatment 44 Soil mixing 44 Vitrification The Soil and Site Improvement Guide software was devel- oped by using Microsoft Visual Basic and queried a database developed with Microsoft Access (Sadek and Khoury, 2000). Geotechnical Design process review The SHRP 2 R02 project is applicable to a wide range of proj- ects, from embankments to retaining walls to pavement foun- dations. Each project will have a unique design process. The literature identified in this section provides some background to the geotechnical design process. Treatment of Problem Foundations for Highway Embankments Holtz (1989) addresses the treatment of problem foundations for highway embankments. A list of questions, which begins the process of evaluating project conditions and geoconstruction technologies, is presented in Table 2.1. Table 2.2 describes some of the factors involved in constructing embankments on prob- lem soils. Figure 2.2 illustrates the process of incorporating geotechnical information into project planning. Preliminary Ground Improvement Selection Beyond the intricacies of the expert system, the overall ground improvement process is discussed and divided into four parts, as shown in Figure 2.3 (Motamed et al., 1991). The four parts are geotechnical study and evaluation, design and performance prediction, performance of ground improvement, and project evaluation. The geotechnical study and evaluation is typically conducted by the geotechnical engineer and the specialty con- tractor. Design and performance predictions are prepared if ground improvement is required. At this stage, the specialty contractor prepares detailed designs, work plans, schedules, and estimates. Once construction begins, the process is measured by previously set or established quality control criteria. Project evaluation is the degree to which the groundâs performance
8Table 2.1. Questions Involved in Constructing Highways on Problem Foundations Question Remarks Elevated structure or embankment? Will the embankment be stable? What is the probability and cost of failure? Can an embankment provide a satisfactory riding surface? Can added cost of elevated structure be justified? How much time is available for construction? What are relative maintenance costs? What is the economic/design life of the structure? Can, or should, postconstruction embankment settlements be accepted? Will settlements be uniform or irregular? Should design remove all primary settlements and reduce secondary compression settlements? Source: Holtz, 1989. Table 2.2. Factors Involved in Constructing Embankments on Problem Foundations Item Remarks Additional construction costs Substantial; may be as much as several million dollars per mile. Safety and public relations Excessive postconstruction differential settlements may require taking part of roadway out of service for maintenance. ⢠Serious safety hazard for heavily traveled roads. ⢠Major inconvenienceâpublic relations problems. Maintenance cost May be large ⢠More expensive construction may minimize post construction maintenance. ⢠Maintenance costs are sometimes regarded as deferred construction costs. Environmental considerations May determine type of highway construction and possible alternatives for foundation treatment. Foundation stability during construction Detailed subsurface investigations, laboratory and in situ tests, and design studies required. Tolerable postconstruction total and differential settlements Appropriate criteria not well formulated; subjective; depends on engineering and public attitudes. Structure versus embankment An important decision affecting both construction and maintenance costs. Construction time available Some alternatives may be eliminated by need for early completion date. Source: Holtz, 1989. conforms to the required performance and often includes test- ing of the ground (Motamed et al., 1991). Guidelines on Ground Improvement for Structures and Facilities The U.S. Army Corps of Engineers described factors to con- sider in assessing, designing, and selecting which technique(s) to use for a particular project (U.S. Army Corps of Engineers, 1999). The first area discussed is described as âdesign con- siderations and parametersâ and considers site constraints, subsurface conditions, scheduling, budget, and availability of contractor. The second area is described as âdesign proce- duresâ and includes the following steps: 1. Select potential improvement methods. 2. Develop and evaluate remedial design concepts. 3. Choose methods for further evaluation. 4. Perform final design for one or more of the preliminary methods. 5. Compare final designs and select the best one. 6. Field test for verification of effectiveness and development of construction procedures. 7. Develop specifications and QC/QA programs.
9Soil Improvement Holtz et al. (2001) discussed the following nine factors to consider in assessing which technique(s) may be the most appropriate: ⢠Operational criteria for the facility ⢠Area, depth, and total volume of soil to be treated ⢠Soil type and its initial properties, depth to water table ⢠Availability of materials ⢠Availability of equipment and required skills ⢠Construction and environmental factors, such as site acces- sibility and constraints ⢠Local experience and preference, politics and tradition ⢠Time available ⢠Cost Source: After Motamed et al., 1991. Figure 2.3. Stages of a ground improvement project. Source: Holtz, 1989. Figure 2.2. Requirements for input of geotechnical information into the corridor planning phase when problem soils are present.
10 Key Elements in Deep Vibratory Ground Improvement Bell (2004) discusses the importance of the construction tech- nique in regard to deep vibratory ground improvement. Bell states, âDeep vibratory ground improvement is best under- stood as a process rather than a product. It can be applied most effectively if all the elements of the process are understood in relation to each other, and if each is given proper attention at all stages.â The sequence set forth is apparently chronological, but this may not always be the case. The following key elements are identified in the selection and implementation process: 1. Site evaluation 2. Ground investigation 3. Development of concept 4. Design 5. Construction technique 6. Process evaluation 7. Commissioning and maintenance Ground Improvement Methods Elias et al. (2006a) describe the following sequential process for the selection of candidate ground improvement methods for any specific project. The steps in the process include evaluations that proceed from simple to more detailed, allowing for the best method to emerge. The process is described as follows: 1. Identify potential poor ground conditions, their extent, and type of negative impact. Poor ground conditions are typi- cally characterized by soft or loose foundation soils, which, under load, would cause long-term settlement or construc- tion or postconstruction instability. 2. Identify or establish performance requirements. Perfor- mance requirements generally consist of deformation lim- its (horizontal and vertical), as well as some minimum factors of safety for stability. The available time for con- struction is also a performance requirement. 3. Identify and assess any space or environmental constraints. Space constraints typically refer to accessibility for con- struction equipment to operate safely and environmental constraints may include the disposal of spoil (hazardous or not hazardous) and the effect of construction vibrations or noise. 4. Assessment of subsurface conditions. The type, depth, and extent of the poor soils must be considered, as well as the location of the groundwater table. It is further valuable to have at least a preliminary assessment of the shear strength and compressibility of the identified poor soils. 5. Preliminary selection. Preliminary selection of potentially applicable method(s) is generally made on a qualitative basis, taking into consideration the performance criteria, limitations imposed by subsurface conditions, schedule and environmental constraints, and the level of improve- ment that is required. Table 7-23 in Elias et al. (2006a), which groups the available methods in six broad catego- ries, can be used as a guide in this process to identify pos- sible methods and eliminate those that by themselves, or in conjunction with other methods, cannot produce the desired performance. 6. Preliminary design. A preliminary design is developed for each method identified under preliminary selection and a cost estimate prepared based on the data in Table 7-24 in Elias et al. (2006a). The guidance in developing prelimi- nary designs is contained within each technical summary. 7. Comparison and selection. The selected methods are then compared, and a selection is made by considering perfor- mance, constructability, cost, and other relevant project factors. Some Ground Improvement Techniques in the Urban Environment Serridge (2006) developed Figure 2.4 to describe the key aspects for achieving a successful ground improvement proj- ect and provides a detailed discussion on the process with case histories. Geosynthetic Design and Construction Guidelines Holtz et al. (2008) presents the following steps for designing a reinforced soil slope. 1. Establish the geometric, loading, and performance require- ments for design. 2. Determine the subsurface stratigraphy and the engineer- ing properties of the in situ soils. 3. Determine the engineering properties of the available fill soils. 4. Evaluate design parameters for the reinforcement (design reinforcement strength, durability criteria, and soil- reinforcement interaction). 5. Determine the factor of safety of the unreinforced slope. 6. Design reinforcement to provide stable slope. 44 Method A: Direct reinforcement design. 44 Method B: Trial reinforcement layout analysis. 7. Select slope face treatment. 8. Check external stability. 9. Check seismic stability. 10. Evaluate requirements for subsurface and surface water control. 11. Develop specifications and contract documents.
11 Geotechnical Aspects of Pavements Christopher et al. (2010) outlines two procedures for using geosynthetic reinforcement for base reinforcement and stabili- zation. The following design approach is for base reinforce- ment using geosynthetics, which is summarized from AASHTO 4E and defined by a traffic benefit ratio (TBR) or base-course reduction ratio (BCR). 1. Initial assessment of applicability of the technology 2. Design of the unreinforced pavement 3. Definition of the qualitative benefits of reinforcement for the project 4. Definition of the quantitative benefits of reinforcement (TBR or BCR) 5. Design of the reinforced pavement using the benefits defined in Step 4 6. Analysis of life-cycle costs 7. Development of a project specification 8. Development of construction drawings and bid documents 9. Construction of the roadway Christopher et al. (2010) also outline the design of the geosynthetic for stabilization using the design-by-function approach in conjunction with AASHTO M288, in the steps from FHWA HI-95-038 (Holtz et al., 1998). A key feature of this method is the assumption that the structural pavement design is not modified at all in the procedure. A limited sum- mary of the procedure outlined in Christopher et al. (2010) is as follows: 1. Identify properties of the subgrade, including CBR, loca- tion of groundwater table, AASHTO or Unified Soil Clas- sification System (USCS) classification, and sensitivity. 2. Compare these properties to those appropriate for stabi- lized subgrade conditions (Christopher et al., 2010; Holtz et al., 2008), or with local policies. Determine if a geo- synthetic will be required. 3. Design the pavement without consideration of a geo- synthetic, using normal pavement structural design procedures. 4. Determine the need for additional imported aggregate to ameliorate mixing at the base/subgrade interface. If such DESIGN EXECUTION SUCCESSFUL COMPLETION Source: After Serridge, 2006. Geotechnical Risk Management Building Design Team Design Stage Performance Criteria Trial Interpretation Dealing with Unkown Additional SI Design Principles Monitoring Preliminary Design Design and Intefacing Testing Site Investigation (SI) Preliminary Trials Design Changes Execution Stage GROUND MODEL Figure 2.4. Steps for achieving successful ground improvement implementation.
12 aggregate is required, determine its thickness, t1, and reduce the thickness by 50%, considering the use of a geosynthetic. 5. Determine additional aggregate thickness t2 needed for establishment of a construction platform. The FHWA pro- cedure requires the use of curves for aggregate thickness versus the expected single tire pressure and the subgrade bearing capacity. 6. Select the greater of t2 or 50% of t1. 7. Check filtration criteria for the geotextile to be used. For geogrids, check the aggregate for filtration compatibility with the subgrade, or use a geotextile in combination with the grid meeting the project requirements. 8. Determine geotextile or geogrid survival criteria. The design is based on the assumption that the geosynthetic cannot function unless it survives the construction process. Principles and Application of Ground Improvement in Asia Raju (2010) provides a few factors to consider in the impor- tant decision of choosing which method to use: ⢠Suitability of the method ⢠Technical compliance ⢠Availability of QC/QA methods ⢠Availability of material ⢠Time ⢠Cost ⢠Convenience ⢠Protection of the environment For additional discussion on each of these factors, please refer to the source.
