Soil improvement and ground modification methods chapter 1 what is “ground improvement

Soil improvement and ground modification methods chapter 1 what is “ground improvement Soil improvement and ground modification methods chapter 1 what is “ground improvement Soil improvement and ground modification methods chapter 1 what is “ground improvement Soil improvement and ground modification methods chapter 1 what is “ground improvement Soil improvement and ground modification methods chapter 1 what is “ground improvement Soil improvement and ground modification methods chapter 1 what is “ground improvement Soil improvement and ground modification methods chapter 1 what is “ground improvement

CHAPTER What is “Ground Improvement?” In this chapter, the subject of ground improvement is introduced along with a discussion of the engineering parameters that can be addressed and a brief history of ancient practices An overview of the objectives of designing a ground improvement plan is provided with a description of how ground improvement methods may be implemented into a project The general categories and objectives of ground improvement techniques are also described 1.1 INTRODUCTION While one of the most important criterion for establishing the value of a parcel of land has often been expressed as “location, location, location,” the practical and economic feasibility of developing and building upon the land must be at least of equal (or greater) importance When one considers developing a site either for construction, rehabilitation, preservation/protection, or other use, there needs to be consideration given to the effects of loads imposed and the behavior or response of the ground and soil to those loads In some cases, the loads may be man-made, while in others forces of nature may be the driving mechanism Either way, there are some fundamental engineering parameters that generally fall under the expertise of geotechnical engineers that can be evaluated and analyzed to predict what effects a variety of possible loading conditions may have on the ground These engineers spend much of their careers devising solutions to prevent deleterious effects (or worse, failures) from occurring Most commonly, these effects can be related to a limited number of soil behaviors or responses now reasonably well understood by geotechnical engineers These include: shear strength of soils, responsible for sustaining loads (static and dynamic) without excessive deformation or failure; compressibility of soils, which manifests in settlement, slumping, and volume change of soil masses; permeability of soils, which is the rate at which a fluid may flow through the void (open) spaces in a soil mass; and shrink/swell potential in soils, which is a phenomenon whereby a soil mass may substantially change volume typically associated with intake or loss of moisture Other properties, such as stiffness, durability, erodibility, and creep, are also of relative importance depending on the specifics of the application Soil Improvement and Ground Modification Methods © 2015 Elsevier Inc All rights reserved Soil improvement and ground modification methods 1.2 ALTERNATIVES TO “POOR” SOIL CONDITIONS A soil or site may be considered “poor” if it fails to have minimum required engineering properties and/or has been evaluated to provide inadequate performance for the design requirements A soil may be considered “marginal” if it possesses near the minimal requirements When “poor” or inadequate soil and/or site conditions prevail, one must consider the available alternatives for the situation These alternatives may include: (1) Abandon the project This might be considered a practical solution only when another suitable site can be found and no compelling commitments require the project to remain at the location in question, or when the cost estimates are considered to be impractical (2) Excavate and replace the existing “poor” soil This method was common practice for many years, but has declined in use due to cost restraints for materials and hauling, availability and cost of select materials, and environmental issues (3) Redesign the project or design (often including structural members) to accommodate the soil and site conditions A common example is the use of driven piles and drilled shafts to bypass soft, weak, and compressible soils by transferring substantial applied loads to a suitable bearing strata (4) Modify the soil (or rock) to improve its properties and/or behavior through the use of available ground improvement technologies Ground improvement methods have been used to address and solve many ground condition problems and improve desired engineering properties of existing or available soils In addition, they have often provided economical and environmentally responsible alternatives to more traditional approaches There are a number of terms that have been used to describe making changes to the ground and/or soil to improve them for engineering purposes These include: soil improvement, ground improvement, ground modification, soil stabilization, and so forth Various authors have attempted to define these terms to differentiate between them, but, generally, there is such overlap between the applications that the terms are often used interchangeably In general, ground/soil improvement is a process carried out to achieve improved geotechnical properties (and engineering response) of a soil (or earth material) at a site The processes can be achieved by methods that can be considered to fall into one of three categories: (1) modification without the addition of any other material, (2) modification including adding certain materials to the soil/ground, or (3) modification by providing reinforcement or “inclusions” into the soil/ ground What is "ground improvement?" The purpose of soil and ground Improvement is essentially to alter the natural properties of soil (and/or rock) and/or control the behavior of a geotechnical feature or earthwork in order to improve the behavior and performance of a project Among the properties that are usually targeted for improvement are: • Reducing compressibility to avoid settlement • Increasing strength to improve stability, bearing capacity, or durability • Reducing permeability to restrict groundwater flow • Increasing permeability to allow drainage • Mitigating the potential for (earthquake-induced) liquefaction Each of these fundamental improvements may be achieved by a variety of methods that will be described in this text Improvements will be done during one of three phases of a project: Preconstruction improvements are often the most desirable and cost-effective These types of improvements would be done to prepare a site for construction and would generally be a part of the planning and design to ensure the success of a project Examples of preconstruction improvements are ground densification, preconsolidation, drainage, dewatering and modification of hydraulic flows, planned underpinning, and various grouting techniques Part-of-construction improvements are those improvement techniques that are done during the construction of the project and could become permanent components of a project Examples of part-of-construction improvements are compacted gravel columns, shallow soil treatment (including gradation control, shallow compaction, and treatment with admixtures), ground freezing, construction with geosynthetics, soil nails, tie-backs and anchors for cuts, excavation, lightweight fills (including geofoam), and so on Earthwork construction may involve a number of different methodologies and improvement processes for achieving one or more improvement objectives These would include engineered fills such as constructed slopes and embankments, retaining wall backfill, and roadways These would also be encompassed under the category of part-ofconstruction improvements Postconstruction improvements are done after completion of the construction phase of a project and are often remedial processes These applications can be very costly, but are used as last choice alternatives to rectify problems encountered after (or long after) the completion of a project or to stabilize natural features that have failed or become hazardous Examples include methods to stabilize settlement problems, failed or near-failure slopes, seepage problems, and so forth Processes used for postconstruction improvements include grouting, soil nails, drainage, dewatering and modification of hydraulic flows, and so on 6 Soil improvement and ground modification methods 1.3 HISTORICAL SOIL AND GROUND IMPROVEMENT The fundamental idea of improving the engineering properties of soils or modifying earth materials to perform a desired function is not new Some of the basic principles of ground improvement, such as densification, dewatering, and use of admixtures, have existed for thousands of years The use of wood and straw inclusions mixed with mud for “Adobe” construction has been reported for civil works in ancient times of Mesopotamia (the productive “fertile triangle” formed between the Tigris and Euphrates rivers, now Iraq) and ancient Egypt (BCE) Written works from Chinese civilizations (3000-2000 BCE) described use of stone and timber inclusions (ASCE, 1978) Lime mixed with soil was used in construction with Rome’s famous Appian Way, built around 600 AD during the height of the Roman Empire That roadway has endured the test of time and is still fully functional today An early application soil improvement by addition of infilling material was reportedly used for seepage control in construction of gravelly/rockfill dams in Egypt around 1900, where fine-grained soil was sluiced into the coarse aggregate to lower permeability As many of the soil and ground improvement techniques fall in a relatively new area of geotechnical specialization with only a limited database of case histories, some would argue that some methods are the “interaction of engineering science and experience-based technologies” (Charles, 2002) Burland et al (1976) described the implementation of ground treatment in a “rational context” with the basic stages: (1) Define the required ground behavior for a particular use of the ground (2) Identify any deficiencies in the ground behavior (3) Design and implement appropriate ground treatment to remedy any deficiencies While these steps may seem very simple and obvious, they are the essential basics to follow when addressing a site for new construction But in the current field, we must also consider treatment techniques that can be used to remediate existing construction and/or to rehabilitate sites for rebuilding or new types of construction not considered feasible previously REFERENCES ASCE, 1978 Soil improvement: history, capabilities and outlook Report by the Committee on Placement and Improvement of Soils, Geotechnical Engineering Division ASCE, 182 pp What is "ground improvement?" Burland, J.B., McKenna, J.M., Thomlinson, M.J., 1976 Preface: ground treatment by deep compaction Geotechnique 25 (1), 1–2 Charles, J.A., 2002 Ground improvement: the interaction of engineering science and experience-based technology Geotechnique 52 (7), 527–532 http://www.astm.org/Standards (accessed 02.11.14.)  ... soil nails, drainage, dewatering and modification of hydraulic flows, and so on 6 Soil improvement and ground modification methods 1. 3 HISTORICAL SOIL AND GROUND IMPROVEMENT The fundamental idea... on Placement and Improvement of Soils, Geotechnical Engineering Division ASCE, 18 2 pp What is "ground improvement? " Burland, J.B., McKenna, J.M., Thomlinson, M.J., 19 76 Preface: ground treatment... making changes to the ground and/ or soil to improve them for engineering purposes These include: soil improvement, ground improvement, ground modification, soil stabilization, and so forth Various