Short Piles Research Articles

Centrifuge modelling of piled foundations in swelling clays

A study aimed towards assessing the variation in shaft capacity of piled foundations in swelling clays is presented. At the clay's in-situ water content, the results of pull-out tests on short-length piles revealed no dependency of shaft capacity on overburden stress. Conversely, after achieving a targeted value of swell, a strong dependency on overburden stress was observed. In upper portions of the profile where swell can occur relatively freely, swell-induced softening results in a reduction in pile shaft capacity. However, at greater depths where swell is largely suppressed, so too are the effects of swell-induced softening. For this reason, shaft capacity at depth was found to remain relatively constant before and after swell. The results of an instrumented pile test revealed an overriding dependency of lateral induced swell pressure on the magnitude of heave which has occurred. Irrespective of the level of overburden stress, lateral pressures against the pile were found to increase at early stages of the swelling process, but then reduce as swell continued and softening began to occur. Such a result highlights the importance of carefully considering the level of swell at which shaft capacity should be assessed if a conservative design is to be obtained.

Numerical investigation on the responses of existing single piles due to adjacent twin tunneling considering the lagging distance

This paper presents an assessment of the influence of the lagging distance between two horizontal tunnel faces of the side-by-side twin tunnels on the responses of the adjacent existing single pile by a series of three-dimensional numerical analyses. Two different relative positions between the pile tip and the tunnel are considered to cover the short and long pile behaviors. The responses of the existing pile in terms of pile head settlement, axial force, lateral movement and bending moment are considered and discussed. The numerical results indicate that the lagging distance between twin tunnel faces significantly affects not only the soil movements but also the responses of the existing single pile. The critical case that produces unsatisfactory pile responses due to twin tunneling is when the lagging distance between the second tunnel and the preceding tunnel equals to the shield length. It is recommended that the lagging distance be not less than three times of shield length when the two tunnels need to be concurrently excavated.

Investigation on the long-term strain of geogrid in GRPS embankment under cyclic loading

Geogrid is a horizontal reinforcement material that is used in geosynthetic-reinforced pile-supported (GRPS) embankments in freeways with soft soil. Nevertheless, the long-term deformation mechanics of geogrid in the GRPS embankment under cyclic loading is not clear enough. This paper presents a laboratory model study of a GRPS embankment to study the long-term geogrid strain under cyclic loading. The effects of parameters such as number of load cycles, load frequency, geogrid layer numbers, and length of supporting piles on the long-term strain of geogrid were investigated. The results showed that geogrid strain increased with the number of load cycles, mainly developed in the first 10 000 load cycles and increased slowly in the later period. When the frequency was increased from 1 to 5 Hz, geogrid strain increased dramatically. When compared with the condition of a single geogrid layer, the upper layer of two geogrid layers caused a less geogrid strain. Compared with long piles and short piles GRPS embankments, a sufficient membrane effect of geogrid was found for long-short piles GRPS embankments. Finally, the 95% prediction interval proposed in this paper could be expressed using a logarithmic function, providing a theoretical foundation for future engineering applications.

Predicting driving transferred energy: case studies of steel piles

ABSTRACT This paper application of a method developed in Brazil for predicting driving transferred energy. The method was recently developed in Brazil and was used in short piles in 2019. In this more recent paper, it was sought to extend the application of the method to long piles (Pile length > 30 m) in soils of different characteristics. It is based on the pile measurements of permanent and elastic displacements during driving and calibration of the site-specific λ coefficient. The article validates the methodology in a case study of two sites with 159 dynamic tests of steel-driven piles in the cities of Santos (SP) and Itaguaí (RJ). Through calibration of λ, the energy predictions showed a good correlation to those obtained from the dynamic tests. There is an additional contribution to the original author’s analysis – increasing the previous testing database – about the correlation between λ and the pile length, as the study includes piles from 36 to 60 m in length – a range that was not included during the author’s first method evaluation. Its major advantage is allowing effective energy estimations in non‑instrumented piles as it is not practical to monitor every single pile of a construction driving site to assess the transferred energy. The presented method is useful in the practice of driven foundation and its quality control.

Analysis of the effects of isolation piles on the basal stability of foundation pits against upheaval based on continuous velocity fields.

The upper bound limit analysis method is one of the main approaches to check the basal stability of foundation pits against upheaval. However, existing studies have often failed to consider the effects of external supporting structures, including isolation piles and others, on basal stability against upheaval. This study derives a formula for the coefficient of basal stability against upheaval under the action of isolation piles by simplifying the pile-soil relationship and systematically examines the impact of isolation pile parameters on basal stability against upheaval using the theory of continuous velocity fields and the upper bound limit analysis method. A comparison of simulation results indicates that this technique can accurately identify the variation trend of basal stability against upheaval under the influence of isolation piles and achieve high calculation precision under the operating conditions of wide foundation pits and short isolation piles. Accordingly, a moderate increase in isolation pile parameters produces a significant supporting effect for narrowed foundation pits. Whereas for wide foundation pits, the supporting capacity of isolation piles can be maximized when pile length equals excavation depth.

РІЗНИЦЯ В РОБОТІ КОРОТКИХ І ДОВГИХ ПАЛЬ У СКЛАДІ СТОВПЧАСТОГО ПАЛЬОВОГО ФУНДАМЕНТУ ЗА РЕЗУЛЬТАТАМИ ФІЗИЧНОГО МОДЕЛЮВАННЯ

In the work, on the basis of physical modeling on small-scale models, the joint operation of piles and a low grid as part of a pile foundation was investigated and analyzed. The operation of a grid without piles and a grid with different numbers of piles of two standard sizes was considered separately. The force in thepiles of the bush was monitored using tensometric equipment. The nature of changes in the share of the grid and realization of the load-bearing capacity of piles in the foundation with changes in their number and length in the group with constant dimensions of the grid were considered. The possible load-bearing capacity of the bush was analyzed according to two theoretical hypotheses: as the sum of the load-bearing capacities of single piles without taking into account the grid plate and as the sum of the load-bearing capacities of single piles and the load-bearing capacity of the grid plate as a foundation for shallow laying without piles. Failure to take into account the work of the grid as part ofthe foundation gives underestimated values of the loads on the bush, and taking into account the work of the grid without adjusting for the redistribution of forces between the elements of the bush during pile placement leads to an overestimation of the load-bearing capacity of the bush. When evaluating the bearing capacity of a bush through the bearing capacity of its individual elements, it is necessary to proceed from the degree of realization of these bearing capacities in the composition of the bush.The efficiency of using short piles compared to long pileswas evaluated

An analysis of static loading tests on short bored pile in tropical soil

An analysis of static loading tests on short bored pile in tropical soil

Computational modeling of the axial behavior of corroded and buckled short steel piles strengthened using concrete-filled GFRP jackets

Steel columns or piles commonly used in bridges and marine structures in various parts of the world exhibit insufficient strength due to increased load demands or section loss due to corrosion. The latter issue can cause unexpected buckling of these columns. In this study, the repair of corroded and buckled short steel piles using concrete-filled GFRP jackets was numerically simulated to better understand the overall effectiveness of the method and the influence of the parameters involved. Thirteen steel piles used in this study had different degradation characteristics to investigate the section losses affecting the axial capacity and failure modes. The parameters considered included the presence or absence of concrete steel reinforcement (rebar), the diameter of the rebar, the number of GFRP layers, the location of the worn zone in the steel section and the severity of the section loss. The numerical models were validated using these experimental results of the repaired specimens from the authors’ earlier work on the topic. The main contribution of this study is in the development of the numerical models that can very accurately simulate the ultimate strength and damage behavior of retrofitted piles that are heavily corroded and buckled. The validated models were used in a parametric study to understand the effects of different levels of concrete strength, or corrosion of the piles in the flanges, the web, or both. The results of the parametric study provided further understanding of the structural behavior of degraded and strengthened steel piles.

Analytical interpretation and numerical analysis of multiple energy pile thermal response tests

Thermal response tests (TRT) are an essential in situ test for the sizing of ground source heat pump systems. Its application on energy piles is becoming an established practice, involving key differences in relation to testing boreholes. Recently, group TRTs emerged as an alternative to testing single short energy pile elements. This work assesses the execution and interpretation of those tests through different analytical heat transfer models implemented in a unit-response calculation methodology. To assess the suitability of the method, a comprehensive parametric analysis using a validated numerical model is undertaken, considering different energy pile sizes, thermal properties for both concrete and soil and group pile arrangements. The analytical methodology is validated against experimental and numerical results, and then tested to interpret the numerically simulated TRTs using a curve fitting algorithm. The broad parametric investigation and the evaluation of the capacity of different analytical methods on modelling each scenario provide directions to execute and interpret group TRTs. The soil effective thermal conductivity and energy pile thermal resistance are obtained with less than 5% precision error for most scenarios and less than 10% considering all scenarios. These results can be further improved with specific individual G-functions for the pile elements, that can be implemented on the proposed methodology.

A novel short pile foundation system bonded to highly cemented layers for settlement control

While design methods of deep foundations are mainly developed for homogenous soil deposits, the presence of highly cemented layers could lead to underestimation of resistance and overestimation of settlement of pile foundations. This study presents a novel approach using competent caliche layers bonded to the top and bottom of a continuous flight auger (CFA) pile as a new composite foundation system named caliche stiffened pile (CSP). The key objective is to optimize the required pile length in a cost-effective approach without ameliorating soil properties. Settlements of the CSP foundation for a high-rise building were monitored and full-scale tests were conducted to measure piles’ capacity. Finite element back analyses were performed to avoid adverse effect of sample disturbance in settlement calculations. A back calculation of a test fill embankment was performed to determine soil stiffness parameters by simulating an unscheduled imposed load to the structure. Impacts of the CSP on controlling the settlement of pile foundation and optimizing the required pile length are investigated using finite element analysis and a parametric study. The proposed CSP foundation can reduce the CFA pile settlement significantly in the presence of caliche layers with thickness equal or greater than a pile diameter at CFA pile head and toe, where the CSP is located.

Experimental Study on the Dynamic Characteristics of a New Long-Short Pile Composite Foundation under Long-Term Train Load

Long-short pile composite foundation (PC-LSPCF) composed of part-screw pile and cement-soil compaction pile is a new railway foundation treatment method, which has been widely used in high-speed railway construction projects in China. To explore the dynamic characteristics and deformation characteristics of railway PC-LSPCF under long-term train loads, the dynamic characteristics of long piles, short piles, and soil between piles under long-term train loads are tested by an indoor dynamic model test. The dynamic amplification of pile and soil under dynamic load and the temporal and spatial distribution of peak response are analyzed, and the stress and deformation development mechanism of PC-LSPCF under cyclic loading of large-cycle trains is revealed. The results show that the neutral point of the long pile is at 1/2 of the pile length and that of the short pile is at 3/8 of the pile length. The part-screw pile has a certain absorption effect on vibration energy. The deformation of a long-short pile composite foundation under long-term train loads can be divided into three stages: extreme growth, transition, and stability. The train speed is negatively correlated with the cumulative settlement of the long-short pile composite foundation. The higher the train speed, the smaller the cumulative settlement, and the smaller the number of cycles of the N-S curve entering the gentle period. As the number of train cyclic loads increases, the load-sharing relationship of the long pile-short pile-soil system will be redistributed. The research results have important reference significance for the optimization design of high-speed railway foundation treatment.

Adaptability Evaluation of Rotary Jet Grouting Pile Composite Foundation for Shallow Buried Collapsible Loess Tunnel

The deformation control effect of loess tunnel composite foundation plays an important role in optimization design and reinforcement effect evaluation. Systematically evaluate the adaptability of the composite foundation of jet grouting pile in shallow collapsible loess tunnel. Taking the shallow buried section of Fujiyao Tunnel with a buried depth of 20 m as an example, using MIDAS finite element numerical simulation software, the foundation deformation control during construction and settlement control after construction are systematically studied, the differential deformation control is analyzed, and the reinforcement effect of the tunnel bottom is evaluated. The results show that the uplift displacement can be controlled by changing the pile length and increasing the replacement ratio. The combination of long and short piles can significantly reduce the uneven settlement and plastic zone of the foundation. The uneven settlement of 9 mm can be used as the evaluation index of the composite foundation reinforcement effect in a shallow buried section of the loess tunnel.

An extension of Broms’ theory to unsaturated soils

This paper presents an analytical method to predict the horizontal capacity of piles in unsaturated soils. The method extends the well-known Broms approach to account for the combined effect of the groundwater table and the apparent cohesion of the unsaturated soil above it. Similar to the original formulation of Broms, the present method calculates the maximum horizontal force and bending moment that can be sustained by the pile for two different head fixities (i.e. free-head and restrained-head) as a function of non-dimensional parameters that depend on the geometry and flexural resistance of the pile (i.e. yielding moment), the soil resistance and the type of failure mechanism (i.e. short, intermediate or long pile). Compared to Broms’ solution, the method introduces additional non-dimensional parameters that relate the water retention behaviour of the soil to the geometry of the pile. The proposed formulation accurately predicts the lateral capacity of piles as experimentally measured in previous works. Results confirm that consideration of the partially saturated state of the soil above the groundwater table is essential for a reliable estimate of the horizontal capacity of piles.

Methodology for calculating the settlement of pile-raft foundations and foundations strengthened with piles

In the case of using pile technology in the construction and reconstruction of buildings and structures, the issue of assessing the settlement of foundations arises quite sharp-ly. Modern regulatory documents do not reflect reliable methods for calculating the settlement of pile-raft foundations, especially if short piles are used (with a pile length of 3-10 m). The ar-ticle provides a calculation methodology that makes it possible to assess the settlement of foundations, taking into account the distribution of loads between the piles and the raft (strengthened foundation), not only for cases of pile-raft foundations with a low raft, but also for cases of strengthening existing foundations with piles. The proposed technique allows the use of standard (including those reflected in the normative documentation) methods for calcu-lating the settlement, resulting in deformations close to the real ones.

The effect of changing the structural scheme of reinforcing strip foundations with short piles

In the work, mathematical modeling of the reinforcement of the strip foundation of shallow laying with short piles is performed in two variants: reinforcement at the level of the sole of the existing foundation, reinforcement from the soil surface. For comparison, short piles of different lengths are considered in both versions. In order to verify the possibility of determining the bearing capacity of the reinforced foundation as a conditional foundation of shallow laying, mathematical modeling of the conditional foundation was performed for both variants of the design solution. In mathematical modeling, not only the length varies, but also the pitch of the reinforcement piles, as well as soil conditions. The obtained results were analyzed with a comparison of all options.
 The results of the calculations showed that when using short piles, it is effective to switch to the reinforcement option, when there is no need to dig trenches to the level of the sole of the existing foundation, with the placement of the riser of the newly created foundation at the level of the paving or floor. This option excludes time-consuming work of manual digging of trenches, and also allows you to perform reinforcement work not with small grabs, but in an arbitrary manner. In general, this makes it possible to significantly reduce costs of labor, time and money.
 Research has established that increasing the pitch of the piles leads to a decrease in the bearing capacity of the reinforced foundation for both short and long piles, and the consideration of the foundations as conditional arrays is most consistent with the option with a pile pitch of 3d (600 mm).
 The results of the calculations also showed that the bearing capacity of the reinforced foundation, obtained by modeling in Plaxis, exceeds the bearing capacity calculated according to the recommendations of the standards. Therefore, the implementation of the load-bearing capacity of the piles and grillage of the newly created pile foundation during reinforcement improves the joint operation of its elements.

Lateral deformation and buckling analysis of piles including shear effects: Numerical analysis

Piles are one-dimensional (1D) beam–column elements used to support tall buildings, onshore and offshore structures, bridges, wind turbines, etc. In practice, piles are commonly designed using the Euler–Bernoulli Theory. However, this theory is only considered appropriate for long, slender piles because it neglects the contribution of the shear deformation on the pile response. The effect of the shear deformation might be of importance in short, rigid and large-diameter piles such as monopiles, and it should be considered in the analysis. In geotechnical engineering, studies addressing this effect and its interaction with the surrounding soil are scarce and very limited. The aim of this work is to conduct a parametric study to investigate the influence of the shear deformation, semi-rigid connections and pile/soil stiffness ratio on the head deflection, head rotation and first-mode of critical load of an embedded pile. For this purpose, the well-known commercial FE software SAP2000 is employed. Four examples are presented to show the effect of the shear deformation on reinforced concrete (RC) and hollow circular piles embedded in either homogeneous or non-homogeneous soil. For lateral deformation analysis, it is found that deflections and rotations at the pile head considerably increase when the shear deformation is taken into account and they are of most significance at low values of pile/soil stiffness ratios. For buckling analysis, Timoshenko’s theory shows that the critical load notably increases as the stiffness of the surrounding soil increases and, regardless of the soil/pile stiffness ratio, it rapidly decreases as the shear stiffness of the pile decreases.

Multi-directional T-EMSD-based p-y model for recent loading history effects on lateral response of short pile and caisson in undrained clays

Rigid foundations supporting offshore wind turbines (OWT) like short piles and caissons can sustain multi-directional lateral loading. Moreover, the monotonic and cyclic response of these foundations can be affected by recent loading history aligned along directions different from the present one. To represent such recent loading history effects, a multi-directional p-y model is proposed for rigid foundations in undrained clays. The model is constructed by extending the uni-directional p-y model previously proposed by the authors based on Total-displacement-loading Extended Mobilisable Strength Design (T-EMSD) approach, and thus considering site-specific soil stress-strain relations and foundation geometries. The crux of the extension is to combine bounding surface plasticity and radial mapping with a moving projection center. The former effectively couples p-y response along orthogonal directions, while the latter is crucial for representing the influences of loading direction reversal and recent loading history effects. The proposed p-y model is evaluated against existing centrifuge tests and finite element analysis (FEA) of this work. Lastly, the proposed p-y model and FEA are used in parallel to highlight the effects of loading path rotation on monotonic and cyclic accumulative foundation response. These comparative analyses indicate that the proposed p-y model can reasonably represent recent loading history effects.

Assessment of Earth Retaining Performance for Long-Short Piles Composite Structures from Field Experiments and Numerical Analysis

Retaining pile structure is commonly utilized in excavation maintenance design. In recent years, the long-short combined retaining piles have received more and more attention. According to the actual deep excavation engineering, the working mechanism of the long-short, long-double-short, and long-triple-short combined retaining piles was tested in the field. Based on the field test parameters, the finite element model of the test area was established and the simulation results were verified, and the effects of short pile length and pile spacing on bending moment, horizontal displacement of piles, surface settlement, and excavation bottom heave were further investigated. The results show that the bending moment of the long pile is larger than the short pile. The bending moment of the long pile and short pile increases gradually with the increase in the number of short piles. When the combination changes from combination 1 to 3, the peak moment of the long pile and short pile increases by 15.8% and 15.2%, respectively. The maximum displacement is near the pile top, combination 3 has the largest horizontal displacement, and the peak displacement of the long pile and the short pile is 17.21 mm and 17.87 mm, respectively, but almost no effect exists on the horizontal displacement below the excavation bottom. In addition, reducing short pile length and increasing pile spacing will increase bending moment and horizontal displacement of the long and short piles to a certain extent, and this phenomenon is mainly concentrated above the excavation bottom, the influence of short pile length and pile spacing on surface settlement and excavation bottom heave can be ignored.

Numerical investigation of the effect of particle gradation on the lateral response of pile in coral sand

This paper addresses the effect of particle gradation on the lateral response of pile in coral sand foundation through numerical method. Firstly, the parameters of Hypoplastic (HP) constitutive model were calibrated by a series of laboratory tests and show obvious difference in value between fine and coarse coral sand. Subsequently, a 50 g centrifuge test and 1g model pile test were carried out to verify the numerical model and calibrated parameters. Afterward, numerical analyses were systematically conducted to investigate the influence of particle gradation, buried depth, and relative density on the lateral response of pile. The lateral load–displacement response, deflection and bending moment of pile, and soil resistance were analyzed and discussed in detail. Numerical results show that the bearing capacity of pile and soil resistance in coarse sand are greater than those in fine coral sand when the relative density is 25 % or 50 %. However, when the relative density is 75 %, the bearing capacity of pile and soil resistance in fine sand present significantly greater values than those in coarse sand under higher lateral displacement level. Moreover, the difference in lateral response of pile between coarse and fine coral sand is more significant in looser sand or shorter pile.

Experimental investigation of local scour around two submerged short square piles under tandem, side-by-side and staggered arrangements in steady current

This research investigates the effects of the arrangement of two submerged square piles on water flow induced local scour topography at the sand-covered bed in steady current under clear water scour condition. The height of each pile is the same as its boundary length. Experimental tests were conducted for G/D = 1 to 5 under the tandem arrangement and G/D = 1 and 2 under side-by-side (SBS) and staggered arrangements, where G is the gap between the two piles and D is the boundary length of the square piles. Results showed that in the tandem arrangement, the scour of the upstream pile is similar to that of a single pile, but the scour of the downstream pile goes through three stages: scour, backfill and re-scour. The backfill stage is caused by the downstream motion of the sand dunes generated from the upstream pile. In the SBS arrangement, the evolution of scour of each pile is similar to that of a single pile. However, the scour rates at the two inner upstream corners of the piles are slowed down by the sand dune between the gap at G/D = 1. In the staggered arrangement, the maximum scour depth of the downstream pile is greater than that of the upstream pile because the flow is accelerated twice from the corners of the two piles, respectively. The maximum scour depth at the SBS and staggered arrangements at G/D = 1 and 2 are slightly greater than that of a single pile, while the maximum scour depth of the tandem arrangement at G/D = 1 to 5 is similar to that of a single pile.