11.1 Types of deep foundations (piles, drilled shafts, caissons)
5 min read•august 16, 2024
Deep foundations are crucial for supporting structures in challenging soil conditions. They transfer loads to stable layers deep underground, ensuring stability for buildings and infrastructure.
Types of deep foundations include , , and . Each has unique advantages and is chosen based on soil conditions, loads, and site constraints. Understanding these options is key for effective foundation design.
Deep Foundation Types and Applications
Types of Deep Foundations
Top images from around the web for Types of Deep Foundations
Drilling of foundation piles that will support a personnel… | Flickr View original
Is this image relevant?
USARPAC 1st Caisson Drilling | The U.S. Army Corps of Engine… | Flickr View original
Is this image relevant?
USARPAC 1st Caisson Drilling | The U.S. Army Corps of Engine… | Flickr View original
Is this image relevant?
Drilling of foundation piles that will support a personnel… | Flickr View original
Is this image relevant?
USARPAC 1st Caisson Drilling | The U.S. Army Corps of Engine… | Flickr View original
Is this image relevant?
1 of 3
Top images from around the web for Types of Deep Foundations
Drilling of foundation piles that will support a personnel… | Flickr View original
Is this image relevant?
USARPAC 1st Caisson Drilling | The U.S. Army Corps of Engine… | Flickr View original
Is this image relevant?
USARPAC 1st Caisson Drilling | The U.S. Army Corps of Engine… | Flickr View original
Is this image relevant?
Drilling of foundation piles that will support a personnel… | Flickr View original
Is this image relevant?
USARPAC 1st Caisson Drilling | The U.S. Army Corps of Engine… | Flickr View original
Is this image relevant?
1 of 3
- Deep foundations transfer loads from superstructure to deeper, more competent soil or rock strata
- Piles serve as slender, column-like elements driven or installed into the ground to support structures
- Drilled shafts (bored piles) function as large-diameter cylindrical foundations constructed by drilling a hole and filling it with reinforced concrete
- Caissons act as hollow structures sunk into the ground and filled with concrete, used for deep foundations in water or unstable soils
- operate as small-diameter (typically less than 300 mm) reinforced piles drilled into various soil and rock conditions
Applications and Selection Factors
- Support high-rise buildings, bridges, offshore structures, and structures on weak or compressible soils
- Choice of deep foundation type depends on soil conditions, structural loads, site constraints, and economic considerations
- Piles excel in supporting structures in areas with poor surface soil conditions (coastal areas)
- Drilled shafts prove effective for heavy loads and when minimal ground disturbance required (urban environments)
- Caissons perform well in marine environments and for structures requiring large lateral load resistance (bridge piers)
- Micropiles offer solutions for limited access areas or retrofitting existing structures (historic building foundations)
Construction Methods for Deep Foundations
Pile Installation Techniques
- methods include impact (diesel hammers, hydraulic hammers) or vibratory techniques
- Jacking involves pushing piles into the ground using hydraulic jacks
- Screwing utilizes helical piles rotated into the soil
- In-situ techniques encompass cast-in-place concrete piles (auger cast piles, continuous flight auger piles)
- Driven piles made of various materials timber (for light structures in marine environments), steel (H-piles for deep penetration), and precast concrete (for heavy loads and corrosive environments)
Drilled Shaft and Caisson Construction
- Drilled shaft construction involves excavating a cylindrical hole using specialized drilling equipment (rotary drilling rigs, bucket augers)
- Reinforcement cage placement follows excavation, ensuring proper alignment and cover
- Concrete filling completes the shaft, often using tremie methods for underwater concrete placement
- Caisson construction typically involves sinking a prefabricated hollow structure through soil or water
- Sinking achieved using caisson's weight, additional ballast, or hydraulic jacks
- Slurry techniques employed in unstable soil conditions for both drilled shafts and caissons
- Bentonite slurry maintains borehole stability during excavation
- Polymer slurries used for temporary support in certain soil types
Quality Control and Environmental Considerations
- Integrity testing methods include sonic logging, thermal integrity profiling, and pile dynamics analysis
- Load testing verifies design assumptions and confirms foundation capacity (static load tests, dynamic load tests)
- Environmental factors considered noise restrictions (urban areas), vibration limits (near sensitive structures)
- Potential damage to adjacent structures mitigated through pre-construction surveys and vibration monitoring
- Construction methods adapted to minimize environmental impact (low-noise pile installation techniques, containment systems for drilling fluids)
Load Transfer Mechanisms in Deep Foundations
End-Bearing and Skin Friction
- End- transfers load through the tip of the deep foundation element to underlying competent soil or rock layer
- Skin friction (shaft resistance) transfers load along the sides of the deep foundation element through friction or adhesion with surrounding soil
- Relative contribution of end-bearing and skin friction varies depending on foundation type, soil conditions, and installation method
- Piles in cohesionless soils (sand, gravel) typically develop significant skin friction
- Piles in cohesive soils (clay) may rely more on end-bearing capacity
- Drilled shafts often utilize both end-bearing and skin friction, distribution depends on shaft geometry and soil profile
- Caissons primarily rely on end-bearing capacity, especially when founded on bedrock, but may also develop skin friction along their sides
Soil-Structure Interaction and Load Distribution
- Load transfer affected by soil properties (strength, stiffness) and foundation characteristics (surface roughness, shape)
- Stress distribution in soil around deep foundation influences load-carrying capacity
- Negative skin friction can develop in settling soils, adding load to the foundation element
- Group effects, such as overlapping stress zones and reduced efficiency, considered for closely spaced deep foundations
- Load transfer in layered soils complex, requiring careful analysis of each stratum's contribution
- Dynamic load transfer (seismic events, machine vibrations) differs from static load transfer, necessitating specialized analysis
Deep Foundation Systems: Advantages vs Limitations
Driven Pile Systems
- Advantages
- High load-carrying capacity achieved through densification of surrounding soil
- Quick installation process increases construction efficiency
- Quality control facilitated by uniform manufacturing processes (precast concrete, steel piles)
- Limitations
- Noise and vibration issues during installation may restrict use in urban areas
- Potential for damage to adjacent structures if not properly managed
- Limited ability to penetrate very dense soils or bedrock without pre-drilling
Drilled Shaft Systems
- Advantages
- Large diameters and depths achievable, allowing for high load-carrying capacity
- Minimal vibration and noise during installation suitable for urban environments
- Ability to visually inspect soil conditions during drilling process
- Limitations
- Require specialized equipment and expertise for installation
- Construction process can be slowed by unexpected soil conditions or groundwater issues
- Quality control challenges in ensuring proper concrete placement and shaft integrity
Caisson Systems
- Advantages
- Well-suited for deep water applications (offshore structures, bridge foundations)
- Can resist large lateral loads due to their size and mass
- Ability to be prefabricated off-site, potentially reducing on-site construction time
- Limitations
- Costly and time-consuming to construct, especially for deep installations
- Challenges in achieving proper sealing against water ingress during sinking process
- Limited to specific soil conditions and project types due to size and installation requirements
Micropile Systems
- Advantages
- Low vibration installation ideal for work near existing structures
- Can be used in limited access areas or for retrofitting existing foundations
- Versatile in various soil and rock conditions due to drilling installation method
- Limitations
- Generally lower load-carrying capacity compared to larger deep foundation types
- Higher cost per unit of load-carrying capacity compared to conventional piles
- May require a large number of micropiles to support heavy loads, increasing complexity
Key Terms to Review (21)
AASHTO: The American Association of State Highway and Transportation Officials (AASHTO) is an organization that develops technical standards for highway design, construction, and maintenance across the United States. AASHTO provides guidelines that play a crucial role in ensuring the safety and efficiency of transportation infrastructure, including roadways and bridges, which directly relates to both shallow and deep foundation design practices.
Aci: Aci refers to the Allowable Compression Index, which is a critical factor in geotechnical engineering used to assess the compressibility of soil under vertical loading. It helps engineers determine how much settlement can occur when a load is applied to the ground, playing a vital role in the design of deep foundations such as piles, drilled shafts, and caissons. Understanding aci is essential for ensuring that structures are built on stable foundations that can adequately support their weight over time.
Axial Load Capacity: Axial load capacity refers to the maximum load that a deep foundation can support along its axis without experiencing failure. This capacity is crucial for ensuring the stability and safety of structures, as it helps determine how much weight a foundation can bear based on its design and the materials used. Understanding axial load capacity is essential for selecting appropriate foundation types, including piles, drilled shafts, and caissons, as each has different capabilities and methods of load transfer.
Bearing Capacity: Bearing capacity is the ability of soil to support the loads applied to it without experiencing failure or excessive settlement. This concept is crucial in determining the suitability of different foundation types, ensuring that structures can be built safely and sustainably, taking into account various factors like soil conditions and load distributions.
Boring: Boring is a technique used in geotechnical engineering to create holes in the ground for the purpose of site investigation and foundation design. This process allows engineers to gather important information about soil and rock properties, which is essential for assessing the suitability of a site for construction projects. By obtaining samples from various depths, engineers can analyze the ground conditions and make informed decisions regarding the type of foundations to use, whether it's piles, drilled shafts, or caissons.
Caissons: Caissons are large, watertight structures used as foundations for bridges, buildings, and other heavy structures, typically constructed underwater or in areas with high water tables. They are designed to support the weight of the superstructure and prevent settlement by transferring loads to stable soil or bedrock beneath the water surface. Caissons can be open or closed at the top, and their construction involves excavation and placement of concrete or other materials to create a robust foundation.
Cohesive soil: Cohesive soil is a type of fine-grained soil that exhibits strong inter-particle attraction, primarily due to its clay content, which allows it to retain shape and resist deformation when subjected to external forces. This soil is significant in various engineering applications due to its unique properties, such as high plasticity and compressibility, influencing factors like drainage, load-bearing capacity, and stability in construction projects.
Drilled shafts: Drilled shafts, also known as auger cast piles or drilled piers, are a type of deep foundation that is constructed by drilling a hole into the ground and then filling it with concrete. This method provides a strong support structure for buildings and other heavy loads, making them a preferred choice in areas where soil conditions are challenging. Drilled shafts can reach considerable depths and are often used in combination with other foundation types, such as piles and caissons, to ensure stability and load distribution.
Driving: Driving refers to the process of installing deep foundation elements, such as piles, drilled shafts, and caissons, into the ground to provide structural support for buildings and other constructions. This technique is crucial for transferring loads from a structure down to stronger soil or bedrock layers, ensuring stability and safety. Understanding driving is essential for evaluating how these foundation types interact with various soil conditions and construction methods.
Dynamic load test: A dynamic load test is a method used to evaluate the load-bearing capacity of deep foundations, such as piles and drilled shafts, by applying a sudden load and measuring the resulting response. This testing technique helps to assess how foundations will behave under real-world conditions, including impacts from seismic activity or heavy loads. The results can provide important insights into the structural integrity and performance of foundation systems in various geological contexts.
Granular soil: Granular soil refers to a type of soil that is composed primarily of larger particles, such as sand and gravel, which have little to no cohesion. This type of soil is essential for various geotechnical applications because of its drainage properties and the ability to compact effectively under load. Its characteristics play a critical role in seepage analysis, foundation design, bearing capacity, and stabilization techniques.
Grouting: Grouting is a construction technique used to fill voids and improve the strength and stability of soil or rock by injecting a fluid material, such as cement or epoxy, into the ground. This process enhances load-bearing capacity, reduces permeability, and can be crucial in stabilizing deep foundations, mechanical stabilization, and reinforcement techniques.
Lateral load capacity: Lateral load capacity refers to the ability of a deep foundation to resist horizontal forces acting on it, such as wind or seismic loads. This capacity is crucial for ensuring the stability of structures that may be subjected to lateral forces, especially in areas prone to high winds or earthquakes. Understanding lateral load capacity is essential for designing safe and effective deep foundations like piles, drilled shafts, and caissons.
Load requirements: Load requirements refer to the specific forces and stresses that structures, such as deep foundations, must safely support during their service life. These requirements dictate how much weight the foundation must bear from the structure above, including live loads, dead loads, and environmental loads. Understanding these requirements is crucial for ensuring that deep foundations like piles, drilled shafts, and caissons are designed effectively to prevent structural failure and ensure stability.
Micropiles: Micropiles are small-diameter, high-strength structural elements that are drilled and grouted into the ground to provide foundation support or soil stabilization. They can be used to reinforce slopes, support new structures, or stabilize existing ones by transferring loads through weaker soil layers to more stable strata. Their versatility makes them suitable for various applications, including retrofitting and stabilizing slopes.
Pile spacing: Pile spacing refers to the distance between individual piles in a deep foundation system, which is crucial for ensuring stability and load distribution. Proper pile spacing allows for effective transfer of loads to the soil while minimizing potential issues like overlapping shear zones and compromising the integrity of the surrounding soil. The design of pile spacing is influenced by factors such as pile type, soil conditions, and the overall load requirements of the structure.
Piles: Piles are long, slender columns made of materials like concrete, steel, or wood that are driven deep into the ground to provide foundational support for structures. They are essential in transferring the load of a building to deeper, more stable soil layers, especially when surface soils are weak or unstable. This method is vital for ensuring stability and durability in construction projects where traditional shallow foundations would fail.
Settlement: Settlement refers to the gradual downward movement or sinking of the ground surface due to various factors, such as load from structures, changes in moisture content, and soil compaction. Understanding settlement is crucial in geotechnical science because it affects the stability and safety of structures, particularly when considering the soil's behavior under different loading conditions and construction methods.
Shaft Design: Shaft design refers to the engineering process of determining the size, shape, and structural integrity of the vertical components of deep foundations, specifically piles, drilled shafts, and caissons. This design is crucial for ensuring that the shafts can adequately support the loads imposed by structures above while also resisting lateral forces from soil and water. The shaft must effectively transfer loads into the surrounding soil or rock to achieve stability and prevent settlement or failure.
Site conditions: Site conditions refer to the physical characteristics of a location where construction is planned, including soil type, groundwater levels, and environmental factors. Understanding site conditions is crucial because they directly affect the design and performance of foundations, both shallow and deep. Factors such as soil bearing capacity, settlement potential, and presence of fill materials play a significant role in determining which foundation type is most suitable for a specific site.
Static load test: A static load test is a method used to determine the load-carrying capacity of deep foundations by applying a vertical load to the foundation element and measuring the resulting displacement. This testing process is crucial for ensuring that foundations, such as piles, drilled shafts, and caissons, can support the anticipated loads from structures above. The results help engineers assess both the performance of the foundation under static conditions and its suitability for construction projects.