Chow and Herbich’s study in 1978 is the first in the literature introducing wave scour at pile groups. To the authors’ knowledge, Sumer and Fredsøe (1998) is the first comprehensive study in regular wave scour around pile groups. The study by Sumer and Fredsøe (1998) investigated wave scour around groups of two piles, three piles and square group of 4x4 piles. However, their experiments focused on a small gap between piles (G /D smaller than 2 with a majority of the experiments with G/D smaller than 1). A gap to diameter ratio of G/D of 1 means that center to center spacing between piles is 2. The small gap to pile diameter ratio is important in case of piles used as a breakwater. In many applications for marine structures such as jetties, seawalls and offshore structures, G/D ratio is 2 or higher. This is to enable easy pile driving and to reduce the effect of soil-pile-soil interaction.
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Abstract: To a practicing foundation engineer, the performance of batter piles under seismic conditions still remains a questionable prospect. The contradictory findings reported by various investigators with regard to the performance of batter piles add to this dilemma. This calls for a rigorous three-dimensional investigation to evaluate seismic behaviour of batter pile groups. In this study, a comparative assessment of three-dimensional seismic behaviour of 2 x 2 vertical and batter pile groups (batter angle 150) was carried out in Finite Element (FE) software package ANSYS. The effects of centre to centre spacing of piles and soil modulus values were investigated. Idealized soil profiles having constant and triangular variation of soil modulus were adopted for the study. Results of analyses for both vertical and batter pile groups are presented in terms of dynamic stiffness and kinematic interaction factors. Results suggest that the horizontal dynamic stiffness of the batter pile groups is higher in comparison to the vertical pile groups in most of the cases considered in the present study. However, vertical dynamic stiffness of batter pile groups is slightly lesser in comparison to the vertical pile groups. Moreover kinematic interaction factors for the batter pile groups for various cases are either comparable or smaller to that of the vertical pile groups. This indicates better seismic performance of batter pile groups in comparison to that of the vertical pile groups.To demonstrate the importance of the findings, a five-storied portal frame structure supported separately on vertical and batter pile group was considered. Time history record of N-S component of El-Centro earthquake (1940) was adopted for the study. The effects of dynamic stiffness and kinematic interaction factors for different configurations of vertical and batter pile groups on the seismic response of the superstructure are highlighted.
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Onshore and offshore spills contaminate soil. This basically takes place due to oil exploration, transportation, production and processing leakage of diesel products from oil tankers, spills due to vehicular accidents, from buried pipelines. In addition to environmental concerns for ground water pollution, oil contamination brings adverse effect on basic geotechnical properties of foundation soil. Thus main aim of the study was to discover the influence of oil contaminated sandy soil on the lateral behavior of pile groups. Small scale test model tests were performed on a single pile and pile groups. The investigation was carried out by varying the percentage of oil content, the thickness of the contaminated layer and the type of oil (Mobil oil) and pile group configuration .For matching the field conditions, contaminated sand layers was prepared by mixing the sand with oil content 0-5% with regard to dry soil. The results from the study can be used for the geotechnical purpose and can benefit engineers for safe and economic construction of a structure on the contaminated sand.
This basically takes place due Onshore and offshore spills, oil exploration, transportation, production and processing leakage of diesel products from oil tankers, spills due to vehicular accidents, from pipelines beneath ground. In addition to environmental concerns for ground water pollution, oil contamination brings adverse effect on basic geotechnical properties of foundation soil. Thus main aim of the study was to discover the influence of oil contaminated sandy soil on the lateral behavior of pile groups. Small scale test model tests were performed on pile groups and on a single pile. The investigation was carried out by varying the percentage of oil content, the thickness of the contaminated layer and the type of oil (Mobil oil, Diesel) to find out suitable pile group configuration .For matching the field conditions, contaminated sand layers was prepared by mixing the sand with oil content 0-5% with regard to dry soil.
pile is very similar to that for two piles with side-by-side arrangement. This is because the side-by-side reduction factor due to group interaction is negligible if the spacing is greater than three times the pile diameter [Group] . For the same lateral loading, pile group with tandem ar- rangement has less displacement than that for pile group with side-by-side arrangement. For relatively small lat- eral loads on the group (F < 100 kN) no major differ- ences in the normalized pile head displacement (y/d) are found due to pile group arrangement. The impact of pile arrangement is more pronounced with the increase in la- teral loading due to the nonlinearity in the pile-soil sys- tem. For single pile and pile groups with different arran- gements, scour increases the pile head displacement. For the same lateral loading, piles with tandem arrangement even when scour is considered has lower displacement than the piles with side-by-side arrangement with no scour. This is due to the greater reduction in group effi- ciency for side-by-side arrangement compared to the re- duction in group efficiency for tandem arrangement.
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The above five groups are detailed enough to distinguish between different pile diameters since the all and only SC180 piles are included in the Pink and Purple groups. The lengths of the piles placed in the lower left corner of the layout, however is sensibly lower than the rest of the piles of the same group, hence in step II, three additional groups are added as shown in Figure 3 using the red and grey (having length 4.2 m versus 5.5 m for the yellow group) and orange colours (length 5.5 m versus 6.5 m of no colour group). Evaluation of the computational Step II a) to e) are shown in Table 3 and Table 4.
The use of pile foundations is increasing day by day due to non-availability of suitable land for construction. Heavy multi-storied building are being constructed, and load from these structures can not be directly transferred to ground due to low bearing capacity issue and stability issues of building during lateral load application. So, demand for use of pile foundations are increasing day by day.The scope of present work was to study experimentally the behavior of pile groups in sandy soil under combined uplift and lateral loading for various parameters.
Fleming et al (2009) discussed the failure of a pile group and stated that independent calculations should be made of both the block capacity and the individual pile capacities, to ensure that there is an adequate factor of safety against both modes of failure. The axial capacity of a group failing as a block may be calculated the same way as for a single pile but using the group perimeter, P, and area, A, for the whole block when calculating its shaft and base contributions. It should be noted that the settlement needed to mobilise the base capacity of the block will usually be very large (i.e. 5 to 10 % the width of the group). Therefore, if the benefits of any base capacity can be exploited in perimeter groups then it is probable that these settlements will also be large. The increased settlement necessary to fully mobilise the base capacity may limit the application of perimeter groups, except for less sensitive structures. However, it should be noted that there were no signs of significant base capacity mobilisation from the numerical modelling. This was also the case in the centrifuge experiments (Rose, 2012).
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Few study of pile cap resistance against lateral load was found in the literature and the findings from these few previous studies indicate that the lateral load resistance provided by pile caps can be very significant, and that in some cases the cap resistance is as large as the resistance provided by the piles themselves. Mokwa (1999) concluded that the pile caps provide significant resistance to lateral load and it was approximately 50 percent of the overall lateral resistance of the pile group foundations. It was found in the literature that the initial study of this phenomenon was carried out by Beatty (1970). He tested two 6 pile groups of step tapered piles and determined that approximately 50 percent of the applied lateral load was resisted by passive pressure on the pile cap. Mokwa (1999) and Mokwa and Duncan (2001) investigated about influence of pile cap under lateral load. He performed full-scale
In order to evaluate the effect of moving rate of ground surface causing a sliding for single pile and pile groups, four tests were conducted in PLAXIS 3D for each case (single pile, 2x1 pile group, 1x2 pile group and 2x2 pile group). In all cases, the lateral soil movement rates were selected as (5, 7.5, 10 and 12.5 mm/min). In all tests the length to diameter ratio (L/D=30) was used, loose sand was used with relative density of 30 % and for pile groups (pile spacing to the diameter ratio) S/D equals 3.
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Novak and Aboul-Ella (1978) derived dynamic stiffness and damping for a single pile based on the dynamic soil reactions to pile displacements assuming that soil consists of infinitely thin layers extending horizontally to infinity. The methodology is best suited for high frequencies. In the low frequency range, as the frequency approaches zero, the horizontal and vertical soil stiffness become zero. To correct for this, the theory is modified to match more rigorous solutions by choosing a minimum cutoff frequency below which the soil stiffness is taken as constant and the damping is taken as linear. For pile groups, the foundation stiffness and damping are then calculated by superposition method (Novak and Mitwally, 1990) in which the interaction between each two piles is used to derive the flexibility matrix from which the group stiffness and damping are calculated. The interaction between two piles are obtained by curve- fitting to the published static and dynamic group factors available in the literature for small pile groups. This procedure has been implemented in DYNA5 program. It is noted that the accuracy of this procedure for large pile groups is dependent on the group factors formulated from published results.
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The nature of the loading and the kind of soil around the pile, are major factors in determining the response of an isolated single pile and the pile groups. The influence caused by the settlement of the supporting ground on the response of framed structures was often ignored in structural design . Soil settlement is a function of the flexural rigidity of the superstructure . The structural stiffness can have a significant influence on the distribution of the column loads and moments transmitted to the foundation of the structure. The effect of interaction between soil and structure can be quite significant [9, 10]. Interaction analyses have been reported in numerous previous studies such as Meyerhof (1947, 1953), Chamecki (1956), Morris (1966), Lee and Harrison (1970), Lee and Brown (1972), and even a few studies in the recent past such as Deshmukh and Karmarkar (1991), Noorzaei et al. (1995), Srinivasa Rao et al. (1995), Dasgupta et al. (1998) and Mandal et al. (1999). The common practice of obtaining foundation loads from the structural analysis without allowance for foundation settlement may, therefore, result in extra cost that might have been avoided had the effect of soil-structure interaction been taken into account in determining the settlements [11, 12&13]. This requires that the engineers not only understand the properties of the ground but they also need to know how the building responds to deformation and what the consequences of such deformation will be to the function of the building. In this regard, many analytical works have been reported on the building frames founded on pile groups by Buragohain et al. (1977), Ingle and Chore (2007), Chore and Ingle (2008a, b) and chore et al. (2009, 2010). But no significant light was thrown in the direction of experimental investigation of the effect of soil interaction on building frames founded on pile groups [14, 15&17].
Piles are commonly connected using a raft to maintain group action and ensure overcoming any expected differential settlement. Although the raft is indirect contact with subsurface strata, conventional design system ignores the load transferred from raft to the soil due to this contact and encounter on the pile group bearing capacity and settlement. However, piled raft foundations that are not directly rested on soil such as the bases of the bridges and in case of settlement or scoured of soil underneath the raft do not take much attention. In the present study, the effect of group efficiency as well as the load distribution of the friction along the pile shaft the load transferred to the tip of the pile and load transferred to soil underneath pile cap in pile groups in cohesion less soil have been presented. The piles were tested in a setup under compressive axial loads. Load at pile tip and the strain along the piles as well as the pile head loads were measured simultaneously. Furthermore, the load under pile cap transferred directly through pile cap to soil has been measured. The program consisted of installing test piles in dense sand, placing piles in a soil chamber subjected to compressive axial load. However, three groups of testing were performed in axial compression. First group load test was carried out on single pile. Second group is four pile caps rested on soil. Third group is four pile caps non-rested on soil. The load capacity of the piles was established and the load distributions along pile walls were determined at various depths. In addition, the loads at pile tip and underneath the pile cap were measured by load cells. It was found that the group efficiency of pile groups cap of four pile rested on soil is more than that pile group cap of four pile non-rested on soil. The group efficiency was found to be ranging between 1.25 to 1.65. The load transferred to soil underneath pile cap was found to be 8 % from the ultimate load capacity. The settlement of pile groups for piles cap rested on soil is less than that for pile cap non-rested on soil. Finite element analysis gives values of settlement less than experimental test results. Fair agreement has been obtained between finite element analysis and experimental test results.
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A numerical approach to solve the soil-pile-structure interaction problem is presented. The soil-pile simulation approach consists of Green’s functions formulation to simulate distributed loads and improve the near field compliance calculation over the traditional transmitting boundaries formulation to simulate concentrated loads. A comparison of free field displacements demonstrates the suitability of distributed loads over concentrated loads for the compliance calculation to simulate piles, as concentrated loads do not provide adequate free field displacements along the vertical line under the load. Green’s functions formulation for ring and disk loads are selected for the soil-pile-structure simulation. Piles are simulated with modified version of beam elements, accounting for the displaced soil. The numerical approach is generalized to a combination of single piles, pile groups of single or multiple cross sections, and shallow foundations, subjected to seismic loads or any other kind of dynamic loads. The numerical approach is implemented in SC-SASSI, taking advantage of high computational speed through High Performance Computing capabilities, as well as flexible and automated postprocessing tools. Highlights from a comprehensive verification program that demonstrates the correct design and implementation of the pile element in SC-SASSI are discussed. A companion paper discusses benchmark results (impedance functions) of this implementation derived for various pile foundations.
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By analyzing the obtained data, it can be found that in groups of two, three and four piles, the initial loads applied on the piled foundation is born in 58% (average value) by pile groups; regarding the foundation composed of one pile, the load is mostly born by the deep foundation element (≅ 99%). From the fourth loading stage on, the participation of pile groups increases, considering that 78% of the total load applied on the piled foundation starts to be born by the piles and only 22% by the shallow foundation element (raft). According to the graph in Figure 19, the lateral friction of piles can be considered the main aspect responsible for the increase in pile group performance, with little tip strength participation being registered (Figure 20).
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As a result the model piles were made of solid aluminium rod of 10mm diameter and 220mm length (Figures 3.42 and 3.43). The model piles were embedded 200mm into the clay corresponding to 12m long piles at prototype scale at 60g (Figure 3.44). The model pile foundations were installed in holes pre bored into the clay at 1g prior to placing the assembled model onto the centrifuge swing. The holes were excavated using 10mm and 5mm outside diameter thin wall stainless steel tubes (see Figures 3.45 and 3.46) which were guided using jigs shown in Figures 3.47 and 3.48. Prior to placing the foundations in the hole a small amount of clay slurry was placed in the base of the hole using a syringe (see Figure 3.49). The clay slurry was used to ensure that the pile was in good contact into clay. In order to release trapped air a 0.5mm deep by 1mm wide channel was machined on one side of each pile (see Figure 3.50). For the mini-piles 5mm diameter and 100mm, 120mm, 200mm and 220mm long solid aluminium rods were used (see Figures 3.51, 3.52 and 3.53). The length of the mini-piles was varied depending whether their function was sacrificial and in providing a general stiffness effect or if they were to be loaded. The scale factors for centrifuge model testing are shown in Table 3.2. For the details of individual centrifuge model tests see Table 3.4.
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Dumping areas represent a stable hazard. To clarify the formation mechanism of dumping piles on dumping area stability, an investigation in open pit mine was performed. Moreover, experiments with gravel were conducted based on the research site conditions. The geological conditions, dumping operation, and waste particle size distribution were investigated in the Heidaigou open pit mine. Particle size distribution, dumping height, dumping volume, and floor inclination were varied to examine their effects on a single pile formation. The design of blasting can be modified to make the particle size of waste smaller. The volume of the bucket does not have a pronounced ef- fect on dumping pile repose angle, capacity of dumping pile, and dumping area stability. The smal- ler the floor inclination, the better it is. Two measures are proposed to increase the kinetic force of friction between waste material and floor surface. The interval distance, dumping volume and dumping height were also varied to examine the interaction between the formations of multiple piles. The dumping width should be decided through optimization efficiency of bulldozer and dumping device in bucket wheel excavator-belt-stacker dumping operation and dragline dumping operation. Moreover, the volume of the bucket does not have a pronounced interaction effect. In the dumping operation, the work amount of bulldozer decreases as dumping pile increases. The design of the dumping operation must consider the total efficiency of ground leveling operation and forming dumping the area.
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Based on test observations of real shear behavior of pile caps, this paper develops an efficient tool for general daily design application, through solving a two-way statically determinate grillage model. A well verified linear load-deflection relationship for one-way RC deep beams is adopted as the constitutive relationship for the grillage elements. A VBA Userform based design software has been developed, enabling designers to obtain within seconds for each cap, the shear capacity, full field distribution of reinforcement stress and cap deflection at any design loading including the failure load. Therefore, the new method is more accurate and time efficient than the existing design tools. The proposed method has been verified for four-pile caps under wall loading but also innovates a pathway that is versatile for analyzing a wide range of two-way RC deep structural elements under various loading conditions, for which no previous international study has been performed.
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Pile Foundations are the most common type of deep foundations and are used for various conditions which include loose soil, huge loads from structure, lack of space for shallow foundation and many others. The bearing capacity of a pile foundation is directly related to the embedded length and reduction in the effective depth of the foundation may cause significant reduction in strength and thus compromises the safety of the structure. Hence it is beneficial to evaluate the effective embedded length of pile using Non-Destructive Evaluation (NDE). The analysis of unknown foundation has been a long addressed problem. Several methods have been developed for finding the unknown depth of the already installed pile foundation. The idea of using lateral impact inducing flexural waves, rather than the conventional longitudinal waves from the impact echo method, was apparently first conceived by Holt and Douglas . Longitudinal waves generally contain the least of the total energy imparted from impact and are non-dispersive in nature. Surface and bending waves contain most of the energy imparted from impact and are dispersive in nature. The analysis of non-dispersive waves is much easier compared to dispersive waves, but the pile tip reflection might not be seen due to low energy of the longitudinal waves. Also, the top of the pile is inaccessible to produce longitudinal waves in an existing pile. Thus flexural wave based NDT is chosen, due to the higher energy and ease of creation of the wave.
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Abstract: A pre-construction site investigation was carried out in a marshy stream channel and adjoining areas for a proposed building site to characterize the subsurface subgrades and recommend foundation design for which proposed structures include a 1-floor 39.7m x 33.7m hostel, a 20.5m x 10.0m 4-bedroom duplex and a 1- floor 2-bedroom block of flats measuring 28.2m x 11.5m with 1.5 factored design dead + live load data as 2700tons, 655tons and 1270 tons respectively. Field investigations include boring of 10 boreholes to a depth of 10m using auger and sounding of 6 cone penetration tests using a 2.5tons mechanical cone penetrometer. The results indicate a soft clay layer existing from ground surface to a depth varying from 1.0m – 1.1m in the stream channel and 0.60m – 0.70m on the adjoining land. These clays are extra-sensitive to sensitive high compressibility Kaolin clays (CH – OH, MH - OH) with undrained shear strength varying from 42 – 75.0KN/m 2 , angle of internal friction ranging from 0 - 3 0 with cone resistance values of 3.0 – 11.0 Kg/cm 2 . Swell potential ranges from 11.45 – 30.64%, swell index from 0.44 – 0.57, activity from 7.0 – 11.0 and swelling pressure 4.776KPa – 4.890KPa. Below this depth a harder clay layer occurs to a depth of between 4.5m – 5.2m and is proposed to found the structures. Pre-consolidation pressures determined from Oedometer test on undisturbed clay samples retrieved from the centre of the second clay layer varies from 125.0KPa – 162.5KPa and Overconsolidation ratios from 2.75 – 6.40 depicting overconsolidation while water table corrected bearing capacities indicates a favourable fully compensated depth of 1.2m for the building foundations. However excessive total settlement determined using Boussinesq’s average vertical stress ranges from 180.1cm - 211.1cm on adjoining land and 160 -111.9cm on the stream channel under the worst case scenario for the structures necessitating further depth compensation to 2.0m. This yielded a reduction in settlement varying from 8.0% to 9.9% on the stream channel and 16.7% - 18.4% on the adjoining land. Rate of settlement depicts that it will take 6.655 and 28.65 years after construction to achieve 50% and 90% settlement under the worst case scenario. Below these clays are loose to medium density sands of varying grain sizes. Load transfer to these sands through pile foundations was considered using the cone penetrometer as a load test to derive unit toe bearing capacities of piles which embedment depth of 11.0m was recommended.
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