Deep Foundations On Bored And Auger Piles PdfBy Terplitima In and pdf 11.05.2021 at 04:58 6 min read
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- Challenges to Quality Control in Bored Cast-In-Situ Piling in Growing Urban Environment
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Challenges to Quality Control in Bored Cast-In-Situ Piling in Growing Urban Environment
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. These aspects are discussed in the presented paper. Rapid urbanization of cities with increasing population has necessitated construction of high rise residential and office buildings.
The building foot-prints are small which result in imposing high loads columns which in turn are required to be supported on pile foundations. Bored cast-in-situ piling becomes the most suitable piling system. In urban environment the roads are small, traffic is heavy, there are restrictions on timings for movement of construction machinery and with all these limitations, speedy progress is required.
Geotechnical consultants and piling contractors face tremendous challenges in ensuring quality in piling work. The challenges relate to all aspects of piling work such as equipment selection for pile boring, pilebore retention, pile tip zone cleaning, forming of stipulated socket length meeting the pile termination criteria and concreting without interruptions.
Challenges also exist when piles are used for shoring to protect the excavations for deep basements. Use of micropiles for supporting building loads or for excavation shoring bring in further challenges.
In congested urban environment all these methods encounter problems which affect pile installation and its quality. In small and narrow access urban plots, this method can be used. It is slow and uses temporary mild steel M. It is this aspect of use of a temporary casing that throws in a major challenge. This is due to the difficulties in casing extraction owing to large frictional resistance on its outer surface caused by surrounding soil.
Permanent M. Thus with short casing, the pile bore at lower depth remains vulnerable to caving resulting in necking, bulging and even loss of concrete in pile shaft Figs. Consequently piles have to be either discarded or derated. Their long term durability also remains suspect due to reduction in concrete cover. Problem increases in high sulphate bearing and high chloride soils which are aggressive to concrete and reinforcement.
In urban area, space restriction often does not permit such an arrangement. Besides, the site gets very slushy and muck disposal is delayed due to difficulties in its handling. The environmental norm does not allow slurry disposal in municipal drains.
DMC method therefore is the least preferred one in urban areas. Use of bio-degradable polymer fluid is an option to bentonite slurry but at present it is not popular with piling contractors due to higher cost and lack of adequate training in its use.
Due to their fast operation, giving rapid progress in piling work, use of hydraulic rotary auger rigs is preferred and its adoption is becoming more and more common. But there are many issues of quality control, which get overlooked affecting piling quality. In this paper, these issues have been more specifically elaborated. These issues relate to a selection of rotary rig, b local geological factors, c pile bore stability, d pile shaft integrity, e pile tip zone cleaning, and f concreting without interruptions.
These are discussed below and case studies are presented to highlight the same. This should normally be done based on the type of rock, its strength, extent of fracturing and grade of weathering. The required rock socket length also, has to be kept in mind.
Site access will also dictate the selection of rig. Due to extensive piling work that is presently going on, rotary rigs are in high demand and the piling contractor tends to use the available rig, either his own or a hired one, overlooking the need for selection of an appropriate rig for the rock type and its insitu rock mass condition.
Similar is the case when site is filled with boulders. The boulders tend to fall in pile bore and boring tends to deviate from verticality. Piling contractors need to seek guidance from the rig manufacturers on selection of piling rig, cutting tools etc. Typical guidance from one such manufacturer is given below in Fig.
Very often local geological factors are overlooked in piling work. For example, the present day Mumbai Fig. Far away from the present sea shore we find reverse sequence of deposits, i. This can happen if site in the past was near the island shore. Implication of this deposit sequence is often overlooked.
Fast rotary augering relies on temporary cohesion in upper sandy strata and formation of slurry due to lower marine clay for stabilizing the pile bore. This makes the pile bore prone for slumping. Many piles had to be discarded or drastically derated and due to smaller foundation footprint, positioning of new piles became extremely difficult. New piles had to have permanent M. The Mumbai geology also adds to surprises due to presence of volcanic ash, weak Tuff, Breccia, Intertrappean Shale in Basalt or Trachyte rock mass.
Selection of pile boring rig needs careful study of borehole and other geotechnical investigation data. Presence of Basaltic dykes altogether removes the need for piling even in a small plot, where some columns would still need piles. This problem occurs even in rotary piling method, like in Chisel—Bailor method, when a relatively short temporary casing is used.
Bentonite slurry for pile bore stability is avoided due to space constraints and environmental restriction. Use of polymer fluid is a good option but not many piling contractors use it. Polymer fluid is biodegradable, thus environmental friendly, quantity required is much less than bentonite which partly offsets its high cost and it is more efficient in trapping the bored fine muck and its removal. The slurry can be directly discharged in nearby municipal drains which removes a major hassel in disposing the site slush.
Permanent pile liners, going up to the start of rock socket, made from woven or non-woven polypropylene can be very effectively used to ensure pile shaft integrity, particularly in bouldery fill or in very soft clays.
The liners are wound around the reinforcement cages and the cages are lowered in the pile bores stabilized either by bentonite slurry or by temporary M. The alternative of using permanent M. Apart from economy, geofabric liners increase the pile concrete durability in aggressive environment. The liners however have to be properly designed to withstand fluid concrete pressure and have toughness to prevent their puncturing in bouldery zone. With LDPE melt coat on the outer surface of these liners, negative skin friction can be virtually eliminated in soft clays.
Geofabric liners have been successfully used in bored piles installed in soft clays in Uran, Nhava Sheva, Navi Mumbai and in bouldery strata of Eksar, Borivali. This is an issue which really needs to be carefully attended to in piling construction. Due to a small footprint of high rise building, there is a need to adopt high pile capacities, nearly reaching to their structural capacities.
Normally tip zone has to be cleaned twice. First, when pile boring is completed and second, just prior to concreting after the reinforcement cage is lowered and tremie is inserted.
While the first cleaning is generally done with a cleaning bucket, the need for the second cleaning is questioned and even dispensed with. This is particularly so when pile boring is done with rotary rigs. Bentonite or polymer fluid slurry tank and pumping arrangements are absent in rotary piling method and tremie flushing is not carried out prior to concreting.
The reinforcement cage scraps the sides of pile bore, when permanent liner is absent, and this deposits the muck at the base of pile. Compressed airlift flushing method suggested by Datye [ 1 ] as illustrated in Fig. Its use at one of the sites can be seen in Fig. This is an issue in deep weathered rocks with variable weathering grades. The boreholes show low core recovery and poor RQD. Deciding pile termination criterion is a challenge.
The guidelines given below would be useful in ensuring piling quality and optimization in their lengths using one of the two criteria detailed below, viz. Both these methods have been incorporated as a quality control tool for Piling in rocks in IRC: [ 2 ]. In rocks, wherein the socket is formed by chiseling, Datye and Karandikar [ 3 ] proposed a simple method based on Chiseling Energy Concept for the pile termination.
The response of founding rock strata is expressed in terms of Energy Level, E, Eq. Capacity estimation based on these parameters is conservative. The chisel energy response data can be plotted depth wise side by side with the nearby bore log and hours of chiseling.
The pile termination zone can be decided to further optimize the chiseling effort while also ensuring the pile capacity. With use of rotary piling, the energy concept is modified as given in Eq. As the resistance to rock cutting increases, RPM decreases and Kelly bar pressure is required to be increased, increasing the Torque. Piling manufacturers can furnish Torque-RPM curve specific to the machine used. Some contractors install torque meters on the control panels of hydraulic rigs to measure the torque.
Based on borelog and rock quality data, manufacturers can suggest the most suitable rig to be used. Both these methods are mainly recommended for deciding pile termination during execution. PPR should not be used to compute pile capacity.
See Fig. From Chisel Energy or PPR values it is also possible to assess the time for pile boring and forming required rock socket length. To highlight the challenges and problems in urban environment, all the case studies in this paper are taken for sites in Mumbai. At one of the multistoried building sites Typical borelog in Fig. Although bentonite stabilization was initially specified, piling was allowed without its use.
IP51 actually showed complete absence of concrete in the pile toe.
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Experimental and numerical analyses of a deep foundation containing a single defective pile. Paulo J. Olavo F. E-mail: osvaldocivil ufrn. E-mail: rpcunha unb. E-mail: pjra g. The methodologies for designing pile foundations can be complex since the simultaneous interactions among the block, piles and surrounding soil should be taken into account.
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. The design of foundation systems is an engineering process which therefore involves a simplistic modelling of the more complex real world. With reference to pile foundations, pile design always involves calculation of the axial bearing capacity of the single pile.
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. These aspects are discussed in the presented paper. Rapid urbanization of cities with increasing population has necessitated construction of high rise residential and office buildings.
ABSTRACT: Static pile load test results of ten large diameter bored piles founded in the multi-layered soils of Bangkok are discussed in this.
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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.
It was written by the following authors: William F. Van Impe , Peter van Impe. Other books on similar topics can be found in sections: Medicine , Technology , Science. The book was published on
Emeritus Professor Alain Holeyman
Парень загородил ему дорогу. - Подними. Беккер заморгал от неожиданности. Дело принимало дурной оборот. - Ты, часом, не шутишь? - Он был едва ли не на полметра выше этого панка и тяжелее килограммов на двадцать. - С чего это ты взял, что я шучу. Беккер промолчал.
Шаги быстро приближались.