Pile Base Research Articles

Bearing capacity of tapered piles in clay under undrained condition

ABSTRACT Based on the lower bound limit analysis, the bearing capacity of a tapered pile in clay is computed. The numerical analysis is performed for various parameters such as embedment length to base diameter ratio (Lp /D 0), taper angle (β), a factor m for the linear variation of cohesion, and adhesion factors (αb and αs ). The results are presented in the form of bearing capacity factors Nct b, Nct s and Nct which represent resistances due to pile base, shaft and total load carrying capacity, respectively. The factor Nct b is found to be decreasing, while the factors Nct s and Nct are increasing, due to an increase in β. The increases in Nct s and Nct are found to be significant for smaller β (between 1–3°) and larger Lp /D 0. The bearing capacity factors are significantly affected by undrained cohesion. It is expected that the results of the present analysis will be helpful to the practicing engineers.

An Innovative Experimental Setup for Characterizing Friction Fatigue during Cyclic Jacking of Piles in Dense Sand

AbstractIn this study, an innovative experimental setup for model pile tests was developed to characterize friction fatigue in sand during cyclic jacking. In the experimental setup, a high-performance precision electric linear actuator was used to control jacking of the model piles. P-wave tomographic imaging was used to characterize the associated changes in the distribution of the P-wave velocities in the soil, and tactile pressure sensors were utilized to monitor related variations in stresses in the soil surrounding the pile. Measurements obtained from the experiments allow us to explore the behavior of fiction fatigue from a different perspective, especially from the viewpoint of stress changes in the soil surrounding the pile. It was found that for a soil element surrounding the pile in a jacking cycle, the maximum values of the stationary radial and hoop stresses and the ultimate radial and hoop stresses in that soil element are reached when the pile penetrates to nearly the same depth, which is therefore defined as the transition depth. For the soil elements at the same depth, such a transition depth increases with increasing distance from the pile centerline. When the pile base gradually penetrates through the transition depth, these stresses in the soil elements surrounding the pile will exceed the peak value, which in turn leads to a reduction in the ultimate unit shear resistance (τf), giving rise to friction fatigue. Based on these experimental findings, a simple model is also proposed to explain friction fatigue.

An analytical solution for integrity detection of a floating pile embedded in saturated viscoelastic half-space

A new mathematical model of a floating pile embedded in a viscoelastic saturated soil for low-strain integrity detection is proposed using the theory of porous media. The saturated surrounding soil is divided into Novak’s thin layers along the pile length and a homogeneous half-space underlying the pile base to consider the effect of excitation frequency on the dynamic stiffness of the soil beneath the pile base. And the corresponding analytical solutions for the dynamic impedance and the reflected wave signal of vertical velocity at the pile head are derived and verified by comparing its reduced solution with the existing solutions for the end-bearing pile. In addition, an extensive parametric analysis is further conducted to investigate the effects of the slenderness ratio of pile, the modulus ratio of pile to the surrounding soil, and the permeability coefficient of saturated soil on the vertical vibration characteristics of the pile–soil interaction system.

The Loading Test on the Singe Pile with Pile Cap in Transparent Soil Model

Pile-cap-soil interaction is important to understand the load transfer mechanisms of pile foundations. However, studies on pile-cap-soil interactions are quite limited. This article reports a series of small-scale model tests in laboratory that was carried out on the single piles with and without pile caps. Transparent soils made of fused quartz and refractive index–matching fluids are employed to represent natural angular sand. Pile cap effects, diameter effects, and pile length effects are investigated. Elastic load limits are found to increase linearly with pile cap area, pile length, and pile diameter for the tested pile models. Soil deformation around the pile head is greatly influenced by the pile cap size, pile diameter, and pile length. Soil deformation at the pile head can be described by Terzaghi’s bearing capacity failure theory. The soil particles below the pile cap next to the pile body move downward, which might reduce the shaft friction or induce the negative shaft friction. All the loading tests show that the pile cap can increase the pile’s bearing capacity. For small-diameter model piles, soil deformation is centered below the pile base, no sliding surfaces are formed at the pile base when settlement S = 4 mm. For large-diameter piles, it is possible that a bearing capacity failure forms two sliding surfaces on the left and right of the pile base. This study indicates that the appropriate usage of the bearing resistance of soils below the pile cap can increase the bearing capacity of pile foundations. This study reveals the soil deformation below the pile cap, which benefits the utilization of the bearing resistance of pile caps. The soil deformation zone at the pile head and around the pile base is also investigated.

Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement

The assimilation of sulfate by Martian melts could explain the highly oxidized state of some Martian nakhlite meteorites, such as those paired with MIL 03346 (MIL 090030, MIL 090032, and MIL 090136). Here, a combination of new sulfur isotope data, mineral composition and abundance data, and consideration of mineral textures is used to link assimilation of surface-derived Martian sulfate to oxidation of nakhlite melts. The magnitudes of the mass independent sulfur isotope signatures (negative Δ33S) and the abundance of sulfide minerals accounts for much of the added oxygen implied by the occurrence of abundant skeletal titanomagnetite in the MIL pairs. Assimilation and reduction of sulfate amounts equivalent to that from 10′s of centimeters of Martian sediment are required to account for an oxidation front extending ∼1 m into the flow, a position previously proposed for MIL 03346, and implies a position at the bottom, rather than the top of a nakhlite flow. A similar positional and amount constraint is required for an alternative path for assimilation of sulfate from sulfate-rich brine. Assimilation and reduction of sulfate is therefore inferred to play a critical role in establishing both the enrichment in skeletal titanomagnetite within the lower portion of the nakhlite pile and the large Δ33S anomalies of the MIL pairs. Other nakhlites with smaller Δ33S anomalies and less titanomagnetite would occupy positions farther away from the source of sulfate.

Испытания и расчет железобетонных висячих свай по несущей способности сваи и грунта основания

Испытания и расчет железобетонных висячих свай по несущей способности сваи и грунта основания

On the Stress-Strain State and Load-Bearing Strength of Argillite-Like Clays and Sandstones

The development of the stress-strain state of the soil mass, represented by argillite-like clays and sandstones, at the base of bored end-bearing piles is examined. A method is developed for conducting experimental studies. Stamp tests showing the load-settlement relation were performed and three phases of development of the stress-strain state were identified. Recommendations are formulated for designing bases comprised of argillite-like clays and sandstones.

Design of deep foundation for Osijek city water treatment plant

AbstractWater Treatment Plant for the city of Osijek is situated on the riverbank of Drava River. The soil at the location consists of alluvial deposits with layers of soft soil to the depth of 16 m. One part of the construction area is covered with 4 m high fill material. For heavy loaded structures and large area basins and tanks, deep foundation was designed with full displacement concrete piles. The piles of d=40 cm are installed by using lost cone technique down to 2 m in the bearing stratum of dense sand. Bearing capacity of the piles is calculated according to geotechnical investigation works which consists of geotechnical borings, laboratory tests, in‐situ SPT and CPTU. The calculation methodology is given, regarding the selection of design values for pile skin and base resistance. The effect of addition filling on the construction area is evaluated by using finite element method in Plaxis 2D, to calculate the negative skin friction on the piles. After the pile construction, pile capacity was tested by dynamic load test. The comparison of predicted and tested results is given in the paper.

Field and petrological study of metasomatism and high-pressure carbonation from lawsonite eclogite-facies terrains, Alpine Corsica

This study presents new field and petrological data on carbonated metasomatic rocks from the lawsonite-eclogite units of Alpine Corsica. These rocks form along major, slab-scale lithological boundaries of the subducted Alpine Tethys plate. Our results indicate that a large variety of rocks ranging from metamafic/ultramafic to metafelsic can react with carbon-bearing fluids, leading to carbon sequestration at high-pressure conditions. The process of carbonation includes both replacement of silicates by high-pressure carbonate, and carbonate veining. The field, microstructural and mineralogical data strongly suggest that the metasomatism was mediated by the infiltration of external fluids of mixed origin, including both mafic/ultramafic and metasedimentary sources. Our results support the following three-step evolution: (i) Release of aqueous fluids by lawsonite and/or antigorite breakdown at depth; (ii) Fluid channelization along the base of the metasedimentary pile of the subducted lithospheric plate and related reactive fluid flow leading to carbonate mineral dissolution; (iii) Further interactions of the resulting carbon-bearing fluids with slab-forming rocks at depths of ca. 70 km and carbonation of pre-existing silicate-rich lithologies. This study highlights the importance of carbonate-bearing fluids evolving along down-T, down-P paths, such as along slab-parallel lithological boundaries, for the sequestration of carbon in subduction zones, and suggests that similar processes may also operate in collisional settings.

Structural, metamorphic and geochronological insights on the Variscan evolution of the Alpine basement in the Belledonne Massif (France)

A structural and petrochronological study was carried out in the southern part of the Belledonne crystalline massif. A first tectonometamorphic event, Dx, corresponds to the eastward thrusting of the Chamrousse ophiolitic complex characterized by a low-temperature–moderate-pressure metamorphism reaching 0.535 ± 0.045 GPa and 427.5 ± 17.5 °C. A subsequent D1 deformation is defined by a penetrative S1 foliation that mostly dips toward the west and displays an E–W- to NE–SW-trending mineral and stretching lineation L1. D1 is associated with a top-to-the east shearing and is responsible for the crustal thickening accommodated by the eastward nappe stacking and the emplacement of the Chamrousse ophiolitic complex upon the Rioupéroux-Livet unit. This event is characterized by an amphibolite facies metamorphism (0.58 GPa ± 0.06; 608 ± 14 °C) that attains partial melting at the base of the nappe pile (0.78 ± 0.07 GPa; 680.5 ± 11.5 °C). LA-ICP-MS U-Pb dating of monazite grains from the mica schists of the Rioupéroux-Livet unit constrain the age of D1 to 337 ± 7 Ma. The D2 tectono-metamorphic event is characterized by NE–SW trending, upright to NE-verging synfolial folding. Folding associated with D2 is pervasively developed in all lithotectonic units with the development of a steeply-dipping S2 foliation. In particular, D2 involves the uppermost weakly metamorphosed Taillefer unit. LA-ICP-MS U-Pb dating performed on detrital zircon grains shows that the Taillefer conglomerates was deposited during the Visean. A zircon SIMS U-Pb age of 352 ± 1 Ma from a plagioglase-rich leucocratic sill of the Rioupéroux-Livet unit is interpreted as the age of magmatic emplacement. Our results suggest that the D2 event took place between 330 Ma and 310 Ma. We propose a new interpretation of the tectonometamorphic evolution of the southern part of the Belledonne massif, focusing on the Middle Carboniferous stages of the Variscan orogeny.

Calculation of the natural oscillation frequency of the submerged basement subject to pulsed loading

The aim of work. To determine the dynamic stiffness at considering vertical and horizontal vibrations of embedded foundations on a conventional and pile base, the possibility of using formulas obtained within the framework of the wave model and SP 26.13330.2012 is considered. Solution technique. Depending on deepening changes, the natural-vibration frequencies of the system oscillations are calculated. The obtained results are compared with the experimental data obtained in a series of impulse dynamic loads performed on foundation models in semi-real conditions. The values of the transverse wave velocities were determined directly on the experimental range from the results of measurements. Results. It is determined that deepening leads to an increase in the frequencies of natural oscillations, both pile foundations and shallow foundations. Full penetration helps to increase natural-vibration frequencies. For horizontal oscillations more than 1.6 times, for vertical oscillations up to 1.4 times. The influence of deepening on shallow foundations is more significant. The advantage of the calculations results and their high agreement with the values obtained during the experiments in the framework of the wave model in comparison with the method from SP 26.13330.2012 is shown. It allows to reliably determining the amplitude-frequency characteristics of the foundations. The results determined in accordance with SP 26.13330.2012, have significantly lower values of the natural-vibration frequencies and do not fully take into account the influence of deepening. The maximum difference with the experimental data for vertical vibrations for a foundation on piles and for a shallow foundation is 33 %. In case of horizontal fluctuations, the maximum differences are from 20 % for a shallow foundation and up to 27 % for a pile foundation.

Probabilistic assessment of pile capacity based on CPTu probing including random pile foundation depth

The modern recognition of subsoil with the use of CPTu static probes allows to obtain detailed information necessary for the designing. Registered basic two quantities, i.e. cone resistance qc and friction on the sleeve fs, often become direct data, which allow to estimate bearing capacity of the base and the side surface of the pile. Direct methods use similarity of the pile work and piezo-cone work during the examination. An important design stage is the appropriate development of measurement data prior to the commencement of the procedure of determining the pile bearing capacity. Algorithms generated on the basis of empirical experiments are often applied with the simultaneous use of test loads. The probabilistic approach is also significant, because it enables objective assessment of the reliability level of performed design calculations. This work contains an analysis of the impact on the estimated bearing capacity and reliability of a pile of variable random depth of the pile base. It also includes the determination of probabilities of obtaining the assumed safety index for the designed solution at random foundation depth.

A simplified nonlinear calculation method to describe the settlement of pre-bored grouting planted nodular piles

The pre-bored grouting planted nodular (PGPN) pile is a type of composite pile foundation that is considered to be environmentally friendly and economical. A simplified approach, which considers the two interfaces of the pile shaft, was proposed to analyze the load-displacement response of a single PGPN pile. An elastic-failure model, based on the shear test results, was used to simulate the shearing behavior of the concrete-cemented soil interface. A hyperbolic nonlinear model, considering the influence of cement paste injection, was created to simulate the behavior between the skin friction and the relative displacement developed along the cemented soil-soil interface. A linear model and a nonlinear model that considers the reduction in the shearing stiffness were used to simulate the PGPN pile base load-displacement responses in a field test and in a model test, respectively. Comparisons between the calculated and measured load-displacement responses revealed relatively good agreement. The proposed approach is thus shown to be efficient and suitable for the analysis of a single PGPN pile embedded in layered soils, and is used to analyze the factors influencing its behavior. Enlarged cemented soil base is considered to be effective in promoting the behavior of a short PGPN pile, while increasing the diameter of cemented soil along the shaft is efficient in promoting the compressive bearing capacity of a long PGPN pile.

Dynamic response of a pile embedded in elastic half space subjected to harmonic vertical loading

An analytical method is developed to investigate the dynamic response of a pile subjected to harmonic vertical loading. The pile is modeled as a one-dimensional (1D) elastic rod. The elastic soil is divided into a homogeneous half space underlying the base of pile and a series of infinitesimally thin layers along the vertical shaft of pile. The analytical solution for the soil-pile dynamic interaction problem is obtained by the method of Hankel transformation. The proposed solution is compared with the classical plane strain solution. Arithmetical examples are presented to demonstrate the sensitivity of the vertical impedance of the pile to relevant parameters.

Interesting Developments in Testing Methods Applied to Foundation Piles

Both: piling technologies and pile testing methods are a subject of current development. New technologies, providing larger diameters or using in-situ materials, are very demanding in terms of providing proper quality of execution of works. That concerns the material quality and continuity which define the integral strength of pile. On the other side we have the capacity of the ground around the pile and its ability to carry the loads transferred by shaft and pile base. Inhomogeneous nature of soils and a relatively small amount of tested piles imposes very good understanding of small amount of results. In some special cases the capacity test itself form an important cost in the piling contract. This work presents a brief description of selected testing methods and authors remarks based on cooperation with Universities constantly developing new ideas. Paper presents some experience based remarks on integrity testing by means of low energy impact (low strain) and introduces selected (Polish) developments in the field of closed–end pipe piles testing based on bi-directional loading, similar to Osterberg idea, but without sacrificial hydraulic jack. Such test is suitable especially when steel piles are used for temporary support in the rivers, where constructing of conventional testing appliance with anchor piles or kentledge meets technical problems. According to the author’s experience, such tests were not yet used on the building site but they bring a real potential especially, when the displacement control can be provided from the river bank using surveying techniques.

Measurement on soil deformation caused by expanded-base pile in transparent soil using particle image velocimetry (PIV)

A new small-scale geotechnical physical model in 1-g and unconfined condition, combining the transparent soil, close-range photogrammetry and particle image velocimetry (PIV), was employed, which provides a non-intrusively internal deformation measurement approach to monitor the internal deformation of soil caused by expanded-base pile jacking with casing. The transparent soil was made of fused quartz and its refractive index matched blended oil, adding reflective particles (glass beads). Close-range photogrammetry was employed to record the images of the process of casing jacking and extraction in transparent soil, allowing the use of Matlab-based Geo-PIV to figure out the displacement field converted from image space to object space. Analysis of test results indicates that the maximum displacement caused by casing jacking for expanded-conical-base pile is decreased by 29% compared with that for expanded-flat-base pile. The main movement happens at the early stage of casing extraction. The maximum displacement caused by casing extraction for the conical base is about 43% of that for the flat base, while the affected zone caused by casing extraction for the conical base accounts for about 1/3 of that for the flat base. The contraction for horizontal displacements tends to decrease with the depth increasing. By contrast, the contraction under pile base decreases with the increasing of displacement. The displacements generated by jacking a conventional pile having a diameter equal to the casing diameter of the expanded-base pile were comparable to the net displacement taking place due to expanded-base pile installation for the conical base pile.

Geochemistry and toxicity of a large slag pile and its drainage complex in Sudbury, Ontario

Slag piles from mining activities are common worldwide, but in contrast to mine tailings the environmental impact of runoff from slag piles is less documented. This study was designed to assess the geochemistry and potential toxicity of water draining a large, 62.2ha slag pile in Sudbury, Ontario. The Coniston slag pile contains 12–20Mt of slag from smelting local Ni-Cu ore between 1913 and 1972. Slag leaching experiments confirmed slag is a source of sulphate (SO4), heavy metals (including Fe, Al, Ni, Co, Cu, Zn, Pb, Cr, Mn) and base cations (Ca, K, Mg, Na). Concentrations of some metals draining through slag in column experiments were similar to concentrations measured at the base of the slag pile, although base cations, SO4 and pH were much higher, possibly because of water inputs interacting with the surrounding basic glaciolacustrine landscape. The high pH rapidly precipitates metals, leading to high accumulations in surface sediments in the pond-wetland complex draining from the pile. Away from the pile's base, vegetation cover increases, which increases dissolved organic carbon (DOC) and nutrient concentrations in runoff along with metals with strong binding affinities (e.g. Cu). Total metal concentration in water and sediment exceed provincial guidelines, particularly near the slag pile, however WHAM7 modeling indicated the free metal ion concentration in water is very low. Nevertheless, 48-h toxicity experiments showed that water with greater concentrations of solutes collected close to the slag negatively impacts D. magna, suggesting water draining the slag pile can adversely impact biota in nearby drainage areas.

Uplift resistance of belled and multi-belled piles in loose sand

In this study, a series of small scale tests are conducted on belled and multi-belled piles in dry loose sand. The installed piles were carefully instrumented with several LVDTs, strain gauges, and a load cell. Results recorded from a laboratory model tests were used to investigate the potential benefits of installing belled and multi-belled piles in increasing the uplift load capacity and also to reduce vertical ground deformation adjacent to the pile. Finite element modeling (FEM) is also performed to assess the soil particle movement, inside the glass box, during pile uplift displacement. The results unveils that increasing the number of wings will not always increase the uplift resistance of piles. For instance, in comparison with the straight pile, the uplift resistance increases up to 60% when the belled installed at the pile base and it decreases about 4% when installed at the depth equal to 33% of the pile length. In addition, for a similar uplift displacement, the pile with installed belled at the base could reduce 75% of the ground surface deformation, comparing to the straight pile.

Effect of cavities on the behaviour of laterally loaded pile in sand

This paper sheds the light on the interaction between piles under lateral loading conditions embedded in sandy soils and adjacent to cavities. The experimental study comprised a full laboratory testing programme carried out on small scale piles embedded in a soil mass with predetermined cavities. The experimental model has the capability to investigate the effect of different cavity locations on the ultimate pile resistances, bending moment along the pile length and pile rotation with the y-axis. Eighteen cavity locations were chosen in order to obtain a thorough investigation on how the ultimate load capacity of single piles is affected by their presence in sandy soil. It is concluded that reductions in pile capacities caused by cavity presence was ranged from 0 to 43.3% for the active side of pile while on the passive side was from 1.8 to 22%. No effect on pile capacities was registered for cavities located under the pile base. Pile settlement, bending moment and rotation values were also influenced by the presence of cavities in different ratios.

Efficient Low-pH Iron Removal by a Microbial Iron Oxide Mound Ecosystem at Scalp Level Run.

Acid mine drainage (AMD) is a major environmental problem affecting tens of thousands of kilometers of waterways worldwide. Passive bioremediation of AMD relies on microbial communities to oxidize and remove iron from the system; however, iron oxidation rates in AMD environments are highly variable among sites. At Scalp Level Run (Cambria County, PA), first-order iron oxidation rates are 10 times greater than at other coal-associated iron mounds in the Appalachians. We examined the bacterial community at Scalp Level Run to determine whether a unique community is responsible for the rapid iron oxidation rate. Despite strong geochemical gradients, including a >10-fold change in the concentration of ferrous iron from 57.3 mg/liter at the emergence to 2.5 mg/liter at the base of the coal tailings pile, the bacterial community composition was nearly constant with distance from the spring outflow. Scalp Level Run contains many of the same taxa present in other AMD sites, but the community is dominated by two strains of Ferrovum myxofaciens, a species that is associated with high rates of Fe(II) oxidation in laboratory studies.IMPORTANCE Acid mine drainage pollutes more than 19,300 km of rivers and streams and 72,000 ha of lakes worldwide. Remediation is frequently ineffective and costly, upwards of $100 billion globally and nearly $5 billion in Pennsylvania alone. Microbial Fe(II) oxidation is more efficient than abiotic Fe(II) oxidation at low pH (P. C. Singer and W. Stumm, Science 167:1121-1123, 1970, https://doi.org/10.1126/science.167.3921.1121). Therefore, AMD bioremediation could harness microbial Fe(II) oxidation to fuel more-cost-effective treatments. Advances will require a deeper understanding of the ecology of Fe(II)-oxidizing microbial communities and the factors that control their distribution and rates of Fe(II) oxidation. We investigated bacterial communities that inhabit an AMD site with rapid Fe(II) oxidation and found that they were dominated by two operational taxonomic units (OTUs) of Ferrovum myxofaciens, a taxon associated with high laboratory rates of iron oxidation. This research represents a step forward in identifying taxa that can be used to enhance cost-effective AMD bioremediation.