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- Herausgeber: Bentham Science Publishers
- Kategorie: Fachliteratur
- Sprache: Englisch
Ground Improvement Techniques for Sustainable Engineering explores modern methods for enhancing soil strength and stability, emphasizing sustainable solutions in geotechnical engineering. This comprehensive book addresses challenges such as weak soils, low bearing capacity, and settlement issues while aligning with the Sustainable Development Goals (SDGs). It bridges traditional methods with cutting-edge advancements, providing an all-encompassing guide to ground improvement techniques. Key topics include compaction, soil stabilization, lime soil, stone columns, preloading with vertical drains, geosynthetics, soil nailing, micropiles, and ground anchors. Theoretical insights are paired with practical applications and case studies to demonstrate how these methods support resilient infrastructure while promoting environmental stewardship. Key Features: - Coverage of classical and advanced ground improvement techniques. - Integration of theoretical foundations, practical case studies, and innovative solutions. - Focus on sustainability in geotechnical engineering practices. Readership: Ideal for civil engineers, geotechnical experts, researchers, and students.
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Veröffentlichungsjahr: 2025
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PREFACE
In the evolving landscape of geotechnical engineering, the application of ground improvement techniques has become indispensable. Also, this domain has witnessed bountiful innovations in recent decades. With the increasing demand for construction using soil as an engineering material on less-than-ideal grounds, these techniques are essential, and they focus on enhancing the bearing capacity and reducing the settlement of weak soils, thereby ensuring the structural integrity and longevity of engineering projects resting over the soil. This book delves into the expansive subject of ground improvement techniques with special emphasis on techniques supporting Sustainable Development Goals (SDG). It offers a comprehensive exploration of methods designed to reinforce soft clays and loose sands, materials often deemed challenging due to their low bearing capacities and susceptibility to considerable settlement under stress.
This textbook presents readers with an extensive range of ground improvement methods, including compaction and stabilization, preloading and sand drains, lime-soil and stone columns, electro-osmosis, and grouting, as well as the use of geosynthetics and heavy tamping. Each approach is thoroughly examined, detailing its utility, efficacy, and scientific basis. The aim is to provide a wealth of knowledge for practitioners, scholars, and students that encompasses theoretical foundations, practical applications, and the most recent advancements in the field. This book delves into how these challenging conditions can be tackled through densification, dewatering, chemical stabilization, and other innovative techniques, thus transforming problematic soils into suitable foundations for construction. From conventional compaction methods to pioneering approaches involving geosynthetics, the content is designed to reflect the durable and cutting-edge strategies in ground improvement.
As we delve into the chapters, detailed discussions on techniques such as dynamic compaction, chemical stabilization, and stone-column installation provide insights into the complex processes and engineering principles involved. Additionally, modern challenges and solutions, such as the use of soil nails, micropiles, and ground anchors, demonstrate the adaptable and forward-thinking nature of geotechnical engineering. This book is an endorsement of the wide range of ground improvement techniques and serves as a guide towards their optimal and well-informed application in the pursuit of durable and resilient infrastructure development.
We are pleased to introduce this book, which is intended to serve as a helpful resource for individuals involved in the commendable pursuit of enhancing the land to promote human progress while preserving the Earth's well-being.
Enhancing Soil Density through Compaction
Thotakura Vamsi Nagaraju,Gobinath RavindranAbstract
Soil compaction is a key technique widely used in pavement and embankment construction. It is crucial to increase soil density and mechanical stability, enhance soil load-bearing capacity, and reduce the void ratio. This chapter delves into soil compaction, beginning with its basic premise as a mechanical method to enhance soil density by decreasing the air voids among soil particles, thus reinforcing the soil structure. The discourse differentiates between static and dynamic compaction, tailored for various soil types and project demands, where static compaction employs gradual pressure, and dynamic compaction involves vigorous impacts or vibrations. The efficacy of these methods is influenced by critical factors, such as soil moisture content and soil type (clay, silt, or sand), which dictate the compaction approach. The analysis extends to factors that impact compaction, highlighting the roles of soil texture, moisture, compaction energy, and equipment in achieving the desired compaction results. The discussion progresses to compaction control mechanisms, underscoring the need for real-time monitoring and adjustments to meet compaction goals while preventing soil overcompaction and damage. By providing an exhaustive understanding of soil compaction, this chapter aims to serve as an invaluable guide, shedding light on its practices, influences, and management strategies to optimize compaction in construction.
INTRODUCTION
The soil compaction improves the physical characteristics of the soil by reducing its permeability and compressibility and increasing its strength and load-bearing capacity [1]. Long before the fundamentals of soil mechanics were properly investigated, this fundamental knowledge of how soil responds to compaction was well known. In the past, those who built roads had an innate understanding that building roads with compacted soil produced higher-quality surfaces [2]. Soil compaction is still essential in modern civil engineering, particularly in the transportation industry. The Proctor curve, which first appeared in 1933 and supported scientific understanding of compaction processes, represented a significant advance in know-how and ability to optimize soil compaction [3]. Later, the California Bearing Ratio (CBR) test was introduced, which improved soil engineering even more and significantly contributed to the area. The fact that
these inventions are still being used as industry standards speaks much about their continued usefulness and their robustness [4]. Soil behavior under loading in compacted and uncompacted conditions is an area of research undertaken by numerous researchers [3, 4].
Although analyzing the behavior of compacted soils under varying external and environmental stresses appears simple, it is a challenging task for engineers in the field. For example, the interaction with air conditions can majorly impact compacted soil and result in various behavioral patterns. Plastic deformation is demonstrated by swelling and collapsing once the soil is moist and splitting as the soil dries [5]. Moreover, soaking and drying cycles can cause changes in density in compacted soil [6, 7]. To ensure the endurance and strength of the infrastructure (see Fig. 1), it is imperative to understand these intricate reactions to apply soil compaction techniques in civil engineering projects efficiently [8].
Fig. (1)) Structure exposed with and without compaction.Since the Roman era, soil compaction techniques have been essential for improving the ground in road construction. Higher-standard roads became necessary in the early 18th century as the interurban movement gained strategic importance [9]. France established the School for Bridges and Roads and the Engineering Corps to undertake research in this area [10]. Renowned 1765 alumnus Pierre-Marie Tresaguet revolutionized road pavement designs by including subbase layers, a technique he took cues from Roman engineering practices [11]. Similarly, Thomas Telford and John Metcalf used comparable design concepts in Britain. The use of huge stones for the pavement foundation posed a considerable obstacle to their designs, making construction time and expense prohibitive [11]. John McAdam addressed this problem by suggesting the use of smaller rock layers, which allowed for the creation of a denser layer that,viaparticle interlocking, offered support comparable to a massive stone foundation [12].
In early road construction, most soil compaction was done manually, with mechanized methods being rare. The need for durable road surfaces led to innovations in compaction machinery. In France, horse-drawn rollers were used for soil compaction, but the introduction of steam rollers in 1860 marked a significant improvement [13]. In the U.S., the sheep foot roller, inspired by the natural soil compaction from animals used in dam building in England, was developed in the 1820s. Early models applied substantial pressure but were relatively lightweight. With the advent of internal combustion engines in 1876, rollers could manage heavier loads, enhancing compaction efficiency [14]. Post-World War II, vibratory compaction technology became the standard, with vibrating rollers particularly effective for achieving high-density compaction in granular pavement layers [14]. This evolution highlights the shift from manual labor to advanced mechanical systems, improving road construction methods and infrastructure durability.
Over the last decade, numerous countries have significantly developed high-speed railways and metropolitan pavements, enhancing global transportation infrastructure [15]. This expansion has driven advances in design, construction, and maintenance technologies, focusing on strict safety and performance standards such as minimal subgrade settlement and reduced subgrade heave after construction.
To meet these challenges, innovative solutions have emerged, including the use of advanced subgrade fill materials and ground improvement techniques. For example, modern machinery for compacting subgrade soils, particularly vibratory rollers, has improved stability and efficiency. Current advancements in road compaction equipment include the development of automated, intelligent, and GPS-integrated vibratory rollers [16]. These intelligent machines feature adjustable modes and are at the forefront of road compaction technology. Additionally, the integration of the Internet of Things (IoT) and the management of compaction parameters allow for real-time analysis and optimization of compaction processes [16]. This chapter explores various types of compaction methods, their field applications, and the latest technological advancements, focusing on factors influencing compaction performance and outcomes.
SOIL COMPACTION TESTS
Soil density is one important parameter to consider when designing engineered soil. To understand the behavior of soil in the field, it is imperative to study the same in the laboratory (see Fig. 2). This is done by multiple laboratory experiments, out of which the Proctor compaction test is most widely used across the globe due to its versatility and prediction efficiency.
Fig. (2)) Soil density with compaction.Proctor Compaction Test
This test was devised in 1933 by a scientist named Proctor [17]. It falls under the type of dynamic compaction. The test basically consists of compacting a soil sample in a 1000 cm cylindrical mold volume with a rammer weighing 2.5 kg and falling from a height of 30 cm. The soil is compacted into three layers, and each layer is given 25 blows with the rammer [17]. Therefore, the total compaction energy imported to the soil is approximately 600 kg-cm. Also, there is a heavy compaction test in which the compaction energy (27560 kg-cm) is higher due to the weight of the rammer (4.5 kg) and drop height of 450 mm; the soil is compacted with 5 layers, the number of blows per layer is kept as same.
The result of the compaction test is generally plotted in the form of water moisture content - dry density curve, which is called the compaction curve because it looks like an inverted U-curve. Fig. (3) shows the standard Proctor compaction curve for a soil sample. It shows that dry density increases with increasing water content and peaks at a particular water content and thereafter decreases even through an increase in water content. The dry density is called maximum dry density (MDD), and the water content corresponding to it is called optimum moisture content (OMC). Sometimes, relationships between dry density and water content are drawn in the form of lines for a constant degree of saturated or a constant % air void.
Fig. (3)) Compaction curve.When the degree of saturation becomes 100%, then 0% of air voids will be there, which is marked as the zero air voids line (ZAVL). This line is generally known to be only a theoretical line because neither in the field nor in the laboratory can soil be compacted to such a degree that its air voids can completely become zero [17]. ZAVL falls outside the compaction curve. Sometimes, compaction tests are done with increased compaction energy, as mentioned. Fig. (4) shows the results of an increase in the compaction energy. The compaction curve for the modified test is shifted upward and toward the left, thus indicating that the dry density increases for all the water contents and the OMC decreases.
FACTORS AFFECTING COMPACTION
Soil is a granular material and contains multiple phases (air, solid, and water). Numerous factors affect soil compaction, a critical step in pavement construction procedures. Comprehending these variables is crucial to attaining the intended soil characteristics and to guarantee the stability and longevity of soil architectures. The following factors affect the affect compaction in the manner described.
Fig. (4)) Compaction curves with varying compaction energy.Water Content
At low water content, there is low inter-particle repulsion and depression in the diffuse double layer. Hence, clay particles get attracted to each other, making it one another, which renders it difficult for them to roll to new positions under the blows of compaction. Hence, the soil sample cannot be compacted to higher densities. As the water content increases, a diffuse double layer develops, and their inter-particle repulsion increases. Hence, it is easy for clay particles to roll over one another to new positions under the blows of compaction. Therefore, it is evident that dry density increases with higher water content. However, this phenomenon can be observed only up to OMC because beyond OMC, air voids remain almost constant, and water voids keep increasing. Therefore, the dry density decreases beyond the OMC.
Compaction Energy
Whatever may be the type of soil, the role of an increase in compaction energy is to increase the dry density of all water content levels. Whatever the compaction water content, if the compaction energy is increased, the dry density increases significantly because the solid particles are brought closer to one another than at lower compaction energy for the same water content. Fig. (2) shows the compaction curves to increase the compaction energy. As the compaction energy increased, the dry density increased for all water contents. However, the effect of an increase in compaction energy is more pronounced on the dry of optimum than on the wet of optimum (WOP) because, as can be seen, the compaction curves shift upward and towards the left. Hence, with an increase in compaction energy, OMC decreases, and MDD increases. The line joining peak points is called the line of optimums. Fine-grained soils are often field compacted using various equipment, with a considerable variation in compaction energy. Therefore, acquiring the compaction characteristics at various compaction energies is necessary. From a practical point of view, it is crucial to understand the behavior of compaction and its features in fine-grained soils at varying levels of compaction energy. Among the first to examine the impact of compaction intensity on the maximum dry unit weight was McRae in 1958 [18]. He created the compaction classification index, which helps estimate the approximate amount of compaction work that will probably be needed on any given soil in the field and set compaction needs for various soil types.
Soil Type
In general, sandy soils are easier to compact than clayey soils due to their higher void ratio and other attributes. There is a difference in the way in which sandy soil and clayey soil respond to compaction. The compaction curves for sandy and clay soil are shown in Fig. (5). When a proctor compaction test is performed on fine sand, the densities obtained by the sand at low water contents are lower than the density of the sand in the air-dried condition. At lower water content, capillary tension develops in the fine sand, increasing its volume. Therefore, the sand attains low densities. Further, the capillary forces acting in the upward direction oppose the compaction effort.
Admixture
The addition of other materials, known as admixtures, improves soil compaction characteristics. The most used admixtures for soil improvement are lime, cement, bitumen, etc. The density achieved depends on the type and amount of admixture. Fig. (6) shows the effect of additives on compaction characteristics.
Fig. (5)) Compaction curves with varying soil types. Fig. (6)) Compaction curves with varying cement content.EFFECT OF COMPACTION ON SOIL PROPERTIES
The engineering properties of the soil are improved by compaction. Desirable properties are achieved by properly selecting the soil type, mode of placement, and method of compaction. It is the duty of the engineer to understand the properties and finalize suitable compaction methods according to the nature of the soil and project requirements. Table 1 shows the effect of compaction on the properties of the soil.
Soil Structure
The dry side is optimum, the water content is low, and the attractive forces are more predominant than the repulsive forces, resulting in flocculated structures. As the water content increases beyond the OMC, repulsive forces increase, and particles become oriented in a dispersed structure.
Permeability
The permeability of the soil depends on the size of the gaps. Soil permeability decreases with increasing water content. There is an improved orientation of particles and a corresponding reduction in the size of voids that causes a decrease in permeability.
Swelling
The swelling of compacted clays is greater for those compacted dry of optimum. They have a relatively greater deficiency of water and, therefore, have a greater tendency to adsorb water and thus swell more. Certain types of soil contain minerals that exhibit high levels of swelling, including montmorillonite, and these soils need to be carefully handled.
Shrinkage
The dry soil of the optimal shrinks less in drying compared to compacted WOP. The compacted WOPs in the soil shrink more because the soil particles in the dispersed structure have a nearly parallel orientation of the particles and can pack more effectively. Maintaining a constant moisture level in expansive soils is crucial, as variations in water content can lead to significant swelling and shrinkage. This characteristic is particularly challenging for engineers, as the impact of moisture fluctuations on expansive soils can lead to substantial volume changes. Such alterations are most pronounced in regions experiencing seasonal wet and dry periods [19].
Compressibility
The flocculated structure developed on the dry side offers greater resistance to compression than the dispersed structure on the WOP. Consequently, the soil on the dry side is less compressible. The compressibility of the soil depends on several other factors. It increases with increasing degrees of saturation.
Porewater Pressure
A sample compacted on dry soil with optimum density has a low water content. Therefore, the pore water pressure developed for the soil compacted dry of optimum is less than that for the same soil compacted WOP.
Stress-strain Relationship
The dry side of the optimum: The soil compacted on the dry side of the optimum allows a steeper stress-strain curve; the modulus of elasticity is high and has a brittle failure.
WOP: The soil compacted on WOP allows for a flatter stress-strain curve; the modulus of elasticity is low, and failure in this occurs at a large stress and is of plastic-type.
Shear Strength
The shear strength of the soil increases with an increase in the compaction effort until a critical degree of saturation is reached. With a further increase in the compaction effort, the shear strength decreases. The shear strength of the compacted soil depends on soil type, molded water content, drainage condition, and method of compaction.
