File Name: deep foundations on bored and auger piles .zip
Experimental and numerical analyses of a deep foundation containing a single defective pile. Paulo J. Olavo F.
- Deep foundation
- Challenges to Quality Control in Bored Cast-In-Situ Piling in Growing Urban Environment
A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site.
There are many reasons that a geotechnical engineer would recommend a deep foundation over a shallow foundation, such as for a skyscraper. Some of the common reasons are very large design loads, a poor soil at shallow depth, or site constraints like property lines. There are different terms used to describe different types of deep foundations including the pile which is analogous to a pole , the pier which is analogous to a column , drilled shafts, and caissons.
Piles are generally driven into the ground in situ ; other deep foundations are typically put in place using excavation and drilling. The naming conventions may vary between engineering disciplines and firms. Deep foundations can be made out of timber , steel , reinforced concrete or prestressed concrete.
Prefabricated piles are driven into the ground using a pile driver. Driven piles are constructed of wood, reinforced concrete, or steel. Wooden piles are made from the trunks of tall trees. Concrete piles are available in square, octagonal, and round cross-sections like Franki piles. They are reinforced with rebar and are often prestressed.
Steel piles are either pipe piles or some sort of beam section like an H-pile. Historically, wood piles used splices to join multiple segments end-to-end when the driven depth required was too long for a single pile; today, splicing is common with steel piles, though concrete piles can be spliced with mechanical and other means. Driving piles, as opposed to drilling shafts, is advantageous because the soil displaced by driving the piles compresses the surrounding soil, causing greater friction against the sides of the piles, thus increasing their load-bearing capacity.
Driven piles are also considered to be "tested" for weight-bearing ability because of their method of installation; thus the motto of the Pile Driving Contractors' Association is "A Driven Pile Is a Tested Pile!
Foundations relying on driven piles often have groups of piles connected by a pile cap a large concrete block into which the heads of the piles are embedded to distribute loads that are greater than one pile can bear.
Pile caps and isolated piles are typically connected with grade beams to tie the foundation elements together; lighter structural elements bear on the grade beams, while heavier elements bear directly on the pile cap. A monopile foundation utilizes a single, generally large-diameter, foundation structural element to support all the loads weight, wind, etc. A large number of monopile foundations  have been utilized in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water subsea locations.
A transition piece complete with pre-installed features such as boat-landing arrangement, cathodic protection , cable ducts for sub-marine cables, turbine tower flange, etc. An additional layer of even larger stone, up to 0. Also called caissons , drilled shafts , drilled piers , cast-in-drilled-hole piles CIDH piles or cast-in-situ piles, a borehole is drilled into the ground, then concrete and often some sort of reinforcing is placed into the borehole to form the pile.
Rotary boring techniques allow larger diameter piles than any other piling method and permit pile construction through particularly dense or hard strata. Construction methods depend on the geology of the site; in particular, whether boring is to be undertaken in 'dry' ground conditions or through water-saturated strata. Casing is often used when the sides of the borehole are likely to slough off before concrete is poured.
For end-bearing piles, drilling continues until the borehole has extended a sufficient depth socketing into a sufficiently strong layer. Depending on site geology, this can be a rock layer , or hardpan, or other dense, strong layers.
Both the diameter of the pile and the depth of the pile are highly specific to the ground conditions, loading conditions, and nature of the project. Pile depths may vary substantially across a project if the bearing layer is not level. Drilled piles can be tested using a variety of methods to verify the pile integrity during installation.
The larger base diameter allows greater bearing capacity than a straight-shaft pile. These piles are suited for expansive soils which are often subjected to seasonal moisture variations, or for loose or soft strata. They are used in normal ground condition also where economics are favorable. Under reamed piles are used in black cotton soil: This type of soil expands when it comes in contact with water and contraction occurs when water is removed.
So that cracks appear in the construction done on such clay. An under reamed pile is used in the base to remove this defect. An augercast pile, often known as a continuous flight augering CFA pile, is formed by drilling into the ground with a hollow stemmed continuous flight auger to the required depth or degree of resistance. No casing is required. A cement grout mix is then pumped down the stem of the auger.
While the cement grout is pumped, the auger is slowly withdrawn, conveying the soil upward along the flights. A shaft of fluid cement grout is formed to ground level. Reinforcement can be installed. Recent innovations in addition to stringent quality control allows reinforcing cages to be placed up to the full length of a pile when required.
Augercast piles cause minimal disturbance and are often used for noise-sensitive and environmentally-sensitive sites. Augercast piles are not generally suited for use in contaminated soils, because of expensive waste disposal costs. In cases such as these, a displacement pile like Olivier piles may provide the cost efficiency of an augercast pile and minimal environmental impact. In ground containing obstructions or cobbles and boulders, augercast piles are less suitable as refusal above the design pile tip elevation may be encountered.
In drilled pier foundations, the piers can be connected with grade beams on which the structure sits, sometimes with heavy column loads bearing directly on the piers. In some residential construction, the piers are extended above the ground level, and wood beams bearing on the piers are used to support the structure.
This type of foundation results in a crawl space underneath the building in which wiring and duct work can be laid during construction or re-modelling. In jet piling high pressure water is used to set piles. Micropiles, also called mini piles, are often used for underpinning.
They are also used to create foundations for a variety of project types, including highway , bridge and transmission tower projects. They are especially useful at sites with difficult or restricted access, or with environmental sensitivity. Installation of micropiles through top soil, sand and cobblestones overburden and into soil rock can be achieved using air rotary or mud rotary drilling, impact driving, jacking, vibrating or screwing machinery.
The use of a tripod rig to install piles is one of the more traditional ways of forming piles. Although unit costs are generally higher than with most other forms of piling, [ citation needed ] it has several advantages which have ensured its continued use through to the present day.
The tripod system is easy and inexpensive to bring to site, making it ideal for jobs with a small number of piles. Sheet piling is a form of driven piling using thin interlocking sheets of steel to obtain a continuous barrier in the ground. The main application of sheet piles is in retaining walls and cofferdams erected to enable permanent works to proceed.
Normally, vibrating hammer, t-crane and crawle drilling are used to establish sheet piles. As the excavation proceeds, horizontal timber sheeting lagging is inserted behind the H pile flanges. The horizontal earth pressures are concentrated on the soldier piles because of their relative rigidity compared to the lagging. Soil movement and subsidence is minimized by maintaining the lagging in firm contact with the soil.
Soldier piles are most suitable in conditions where well constructed walls will not result in subsidence such as over-consolidated clays, soils above the water table if they have some cohesion, and free draining soils which can be effectively dewatered, like sands. Unsuitable soils include soft clays and weak running soils that allow large movements such as loose sands. It is also not possible to extend the wall beyond the bottom of the excavation, and dewatering is often required.
Screw piles , also called helical piers and screw foundations , have been used as foundations since the mid 19th century in screw-pile lighthouses. The screw distributes the load to the soil and is sized accordingly.
Suction piles are used underwater to secure floating platforms. Tubular piles are driven into the seabed or more commonly dropped a few metres into a soft seabed and then a pump sucks water out at the top of the tubular, pulling the pile further down.
The proportions of the pile diameter to height are dependent upon the soil type. Sand is difficult to penetrate but provides good holding capacity, so the height may be as short as half the diameter. Clays and muds are easy to penetrate but provide poor holding capacity, so the height may be as much as eight times the diameter. The open nature of gravel means that water would flow through the ground during installation, causing 'piping' flow where water boils up through weaker paths through the soil.
Therefore, suction piles cannot be used in gravel seabeds. In high latitudes where the ground is continuously frozen , adfreeze piles are used as the primary structural foundation method. Adfreeze piles derive their strength from the bond of the frozen ground around them to the surface of the pile. Adfreeze pile foundations are particularly sensitive in conditions which cause the permafrost to melt.
If a building is constructed improperly then it can will the ground below, resulting in a failure of the foundation system. Vibrated stone columns are a ground improvement technique where columns of coarse aggregate are placed in soils with poor drainage or bearing capacity to improve the soils. Specific to marine structures, hospital piles also known as gallow piles are built to provide temporary support to marine structure components during refurbishment works.
For example, when removing a river pontoon, the brow will be attached to hospital pile to support it. They are normal piles, usually with a chain or hook attachment. These methods of retaining wall construction employ bored piling techniques, normally CFA or rotary.
They provide special advantages where available working space dictates that basement excavation faces be vertical. Both methods offer technically effective and offer a cost efficient temporary or permanent means of retaining the sides of bulk excavations even in water bearing strata.
When used in permanent works, these walls can be designed to accommodate vertical loads in addition to moments and horizontal forces. Construction of both methods is the same as for foundation bearing piles. Contiguous walls are constructed with small gaps between adjacent piles. The size of this space is determined by the strength of the soils.
Secant pile walls are constructed such that space is left between alternate 'female' piles for the subsequent construction of 'male' piles. The male pile is the one where steel reinforcement cages are installed, though in some cases the female piles are also reinforced. Hard refers to structural concrete and firm or soft is usually a weaker grout mix containing bentonite.
Where party wall agreements allow, ground anchors can be used as tie backs. A slurry wall is a barrier built under ground using a mix of bentonite and water to prevent the flow of groundwater.
Extensive bored cast-in-situ piling work is being carried out in growing metropolitan and other large cities for foundations of multi-storeyed office and residential buildings, flyovers and for retaining deep excavations for basements. Geotechnical consultants and piling contractors face tremendous challenges in urban environment in ensuring quality in piling work. The challenges relate to all aspects of piling work such as pile-bore retention during boring, pile tip zone cleaning, deciding socket lengths in deep weathered rocks, meeting the pile termination criteria, concreting without interruptions etc. In case of shoring piles for basement excavations, installation of anchors adds to a further challenge since they would penetrate in adjoining plot. Micropiles are also being extensively used without regard to their inherent limitations in installation and load carrying capacity.
This paper presents a process of pile foundation design since the planning of soil exploration, consideration of design parameter and related laws or regulations. The questionnaire was used to interview the target group. And pointed out the issues to be aware of the context and conditions of the study area. The study concluded that. The wash boring method is mostly used for drilling exploration and field testing using SPT. The parameters of shear strength design transformed by using N-value. Consideration of settlement is based on the principle of piling on hard clay.
Original contributions Gharsallaoui, H. Pile end bearing capacity in rock mass using cavity expansion theory, Journal of Rock Mechanics and Geotechnical Engineering , 12 5 , Bearing capacity of surface foundations resting on Hoek - Brown materials using equivalent Mohr - Coulomb parameters, Geotechnical Engineering foundation of the future - Proceedings of the 17th European Conference on Soil Mechanics and Geotechnical Engineering , September , Reykjavik, Iceland, Sigursteinsson, H. End bearing response of open-ended pipe piles embedded in rock, International Journal of Rock Mechanics and Mining Sciences , , Shear strength degradation of vibrated dry sand, Soil Dynamics and Earthquake Engineering , 95 ,
Challenges to Quality Control in Bored Cast-In-Situ Piling in Growing Urban Environment
The work at hand attempts to propose a local pile design method based on pile load test results for a reference site. Such LPDM is simply based on the identification of three dimensionless quantities, such as the capacity ratio CR, the stiffness ratio SR, and the group settlement ratio. To prove the LPDM reliability, experimental data collected during years in the Neapolitan area Italy have been used to obtain the abovementioned coefficients. The satisfactory agreement between the geometry in the original design of piles and the one obtained by applying the LPDM proves that the proposed methodology may be very helpful for preliminary design, allowing for reasonable accuracy while requiring few hand calculations.
It was written by the following authors: William F. Van Impe , Peter van Impe.