Model Pile Groups Research Articles

Experimental Evaluation of Load Distribution between Piles in Case of Block Failure

In this study, the load distribution of the piles in the pile group was investigated in the case of the pile raft foundations failure under the effect of vertical loads in cohesive soils. For this purpose, loading tests were carried out on model pile groups in the laboratory. In addition, the effects of these conditions on the load distribution between the piles were examined by changing the pile spacing and soil properties. As a result of the experiments, it was determined that the piles in the corner region carried more load than the ones in the center region in small settlement amounts as in the literature. However, it has been determined that as the amount of settlement in the pile foundation increases, the soil between piles behaves like a block and approaches failure, and the piles in the center region of the pile group carry more load. As a result of excessive settlement, a fracture surface formed around the block and therefore the corner piles of the block began to carry less load. It has been determined that failure analyses should be performed considering the load carried by the corner piles after failure due to excessive settlement.

Bearing capacity of piles in unsaturated soil from theoretical and experimental approaches

Research in unsaturated soil mechanics has considerably developed in the past decades, through the simultaneous development of experimental investigations and theoretical analyses. A fundamental property of unsaturated soil is the ability to store and release water.In this study, an attempt was made to compare the results of bearing capacity of model pile groups constructed in saturated soil prepared at two dry densities and unsaturated soil, with results from theoretical approach (conventional and modified) α, β and λ methods. Square aluminum model piles of 20 x 20 mm in cross section and 200 mm in length were used. The piles were arranged in six group configurations, single, 2×1, 3×1, 2×2, 3×2, and 3×3, groups in addition to pull out test at which the pile is designed to verify this purpose. All groups have the same spacing, which is equal to 3 pile diameters (60 mm). The results showed that using the β method gives the value of ultimate capacity close to the experimental results for saturated and unsaturated tests, while the theoretical results showed overestimation when using other two methods. The results of load displacement curves for piles embedded in soil having three different properties indicate an increase in the ultimate pile load carrying capacity with increase in the number of piles for different soil properties. This increase however, is not linear and gives a high value when the soil becomes in unsaturated state compared to the soil in saturated state.

Experimental Investigation of Single Model Pile and Pile Group Behavior in Saturated and Unsaturated Sand

AbstractThe research focus of this paper is directed to investigate the behavior of a single model pile and pile groups in sand under both saturated and unsaturated conditions. Forty different mode...

Seismic behaviour of soft clay and its influence on the response of friction pile foundations

In recent years, much of the research in geotechnical earthquake engineering has focused on liquefaction of loose, saturated sands and silts. However, the dynamic behaviour of soft, clayey soils and their interaction with pile foundations during the earthquakes have received relatively little attention. In this study, an attempt is made to investigate the dynamic behaviour of soft clay and its interaction with pile foundations during earthquakes using high gravity centrifuge testing. A model single pile and two sets of 3 × 1 row model pile groups with different pile spacing were embedded in soft kaolin clay and tested under the action of model earthquakes at 50 times the earth’s gravity. The strength and stiffness of clay were evaluated using a T-bar test and an air hammer device respectively. The focus of this research is to investigate the dynamic response of friction piles in soft clay. However, this depends on the dynamic response of the soft clay layer around the pile. To this end, one-dimensional ground response analysis was performed using DEEPSOIL software to emphasise the importance of non-linear analysis in characterising the seismic behaviour of soft clays. It will be shown that clay response depends both on the earthquake intensity and the shear strength and stiffness of the clay layer. This has a direct bearing on the response of single piles and pile groups, with larger amplification occurring for small intensity earthquakes and attenuation occurring for stronger earthquakes.

Behavioural analysis of vertical and batter pile groups under vertical and lateral loading in sand

Laboratory model tests were carried out to study the behaviour of vertical piles and batter pile groups under vertical and lateral load. The model pile groups were made up of mild steel rod of 8-mm diameter. Parameters such as degree of batter and different length to diameter ratios of 7.50, 15.00 and 22.50 were considered in this study. The size of the model tank was 1000 mm × 1000mm × 800 mm. Experiments were performed on 3 × 3 model pile groups with a row of batter piles both positive and negative in addition to vertical pile groups with batter angle 0° in sandy soil subject to vertical and lateral loads. It was observed that the behaviour of vertical pile groups and group of piles with batter piles were similar but it showed substantial variation in the capacity of pile groups. Results indicated that the load–settlement relationships were non-linear for all model pile groups both under vertical and lateral loading. Numerical FEM analysis using ABAQUS/CAE 6.11 was also used to compare and validate the load carrying capacity of pile groups obtained from the experimental model tests.

Comparing the Response of Static Loading Tests on Two Model Pile Groups in Soft Clay

Static load test program was performed on a single pile and two 16-pile groups with equal and different pile lengths. The soil profile consists of sand fill to 0.5 m depth placed on a thick deposit of soft, normally consolidated and compressible clay. The closed end steel pipe piles in 60 mm diameter were installed from 1.5 m through 2.1 m depth within soft clay deposit. The center-to-center distance of piles in group is about 3 times of pile diameter. The strain gages were installed at one level above and two through four levels below ground surface. Tests were carried out about 7 days after driving by method of a series of load increments placed every 5-min until plunging failure occurred. The load at plunging failure for the single pile, the equal-length pile group and the different-length pile group were about 3, 40 and 48 kN, respectively. The movements at start of failure were about 12, 18, and 17 mm, respectively. The analysis of strain gage measurements indicates that the load distribution on piles in the different-length pile group has become significantly uniform.

CYCLIC LATERAL RESPONSE OF MODEL PILE GROUPS FOR WIND TURBINES IN CLAY SOIL

Due to the large diameter and the cyclic loading, it is necessary to investigate the lateral response of pile groups for wind turbines in clay soil. This paper presents an experimental research on 2x2 model pile groups embedded in different types of clay soil, relatively density of 90% and 10%, subjected to one-way lateral cyclic loading. Analysis on the experimental results, such as load–deflection curves and bending moment profiles, were processed. It is found that the magnitude of the head level deflections and the maximum bending moment increased with the number of loading cycles. The group interaction effect under cyclic lateral loading is more significant in loose soil.

Response of Pile Groups Driven in Sand Subjected to Combined Loads

Although the loads applied on piles are usually a combination of both vertical and lateral loads, very limited experimental research has been done on the response of pile groups subjected to combined loads. Due to pile–soil–pile interaction in pile groups, the response of a pile group may differ substantially from that of a single pile. This difference depends on soil state and pile spacing. This paper presents results of experiments designed to investigate pile interaction effects on the response of pile groups subjected to both axial and lateral loads. The experiments were load tests performed on model pile groups (2 × 2 pile groups) in calibration chamber sand samples. The model piles were driven into the sand samples prepared with different relative densities using a sand pluviator. The combined load tests were performed on the model pile groups subjected to different axial load levels, i.e., 0 (pure lateral loading), 25, 50, and 75% of the ultimate axial load capacity of the pile groups, defined as the load corresponding to a settlement of 10% of the model pile diameter. The combined load test results showed that the bending moment and lateral deflection at the head of the piles increased substantially for tests performed in the presence of axial loads, suggesting that the presence of axial loads on groups of piles driven in sand is detrimental to their lateral capacity.

Response of Single and Grouped Pile Subjected to Lateral Load in Cohesionless Soil

Piles are generally required to transfer load from a superstructure through weak or compressible strata, or through water, on to stiffer and less compressible soils and rock. The pile behavior is very important in Soil-Pile interaction (as known Kinematic Interaction) so that grouped and single pile behavior differs owing to the impacts of the pile-to-pile interaction. In this research presents a series of experimental investigations carried out on single and group pile subjected to monotonic lateral loadings. The aluminum model piles were tested in the different relative densities in Johor Bahru sand. The sand samples were prepared by using the newly designed Mobile Pluviator adopted the air pluviation method. The different configurations of model pile groups for embedded length-to-diameter ratio equal to 32 into loose and dense sand spacing from 3 to 6 pile diameter (D) were conducted. The ultimate lateral load is increased 53% in increasing of s/d from 3 to 6 owing to effects of sand relative density. A ratio of s/D more than 6d is large enough to eliminate the pile-to-pile interaction and the group effects. It may be more in the loose sand.

Effect of Loading Direction on the Response of Laterally Loaded Pile Groups in Sand

AbstractPrevious experimental studies on laterally loaded pile groups usually applied loading along the direction parallel to the edge of the pile cap. This study aims to determine the effects of the loading direction on the response of laterally loaded pile groups through a comprehensive experimental investigation. Model pile groups with different configurations embedded in sand were subjected to lateral loads along various horizontal directions. The results show that the loading direction has a predominant effect on the evolution and eventual distribution of force among piles in the pile group, the bending responses along the piles, and the total lateral resistance of the pile group. These results can be attributed to different group-interaction effects under different loading directions. For both square and rectangular configurations, the pile groups provide the largest total lateral resistance along the diagonal direction. The effect of the loading direction on the response of the pile group is affect...

Observation of Ground Movement with Existing Pile Groups Due to Tunneling in Sand Using Centrifuge Modelling

In developing urban areas, there are unavoidable interactions between existing structures and new construction such as tunnelling through pre-existing pile foundations. An accurate prediction of the ground deformation due to tunnelling is necessary to assess potential damage to those existing structures. Two dimensional tunnelling model tests were carried out to study the movement of both soil surface and subsurface layers of dry Toyoura sand with two pile groups of different length at both sides of the tunnel. The model pile group has four piles with spacing and diameter ratio of 5. The tunnelling process was simulated by reducing the diameter of the model tunnel with initial diameter of 70 mm for various ground loss values at 100g centrifugal acceleration. The induced soil movement and displacement of pile foundation were observed using the particle image velocity technique and displacement transducers. The test cases were conducted at two different tunnel cover depth and diameter ratios (C/D = 1.5 and 2.5) and three different horizontal distances between the pile groups and the tunnel. Tunnel machine showed good agreement of soil movements with the results from real site construction at small ground loss ratios. The cases with the pile group induced larger maximum settlement in the vertical direction than the cases without piles. There was an effect of the pile groups on the ground movement at the location more than five times pile diameter away from the piles in the longitudinal direction.

Response of 1 × 2 pile group under eccentric lateral loading

A large scale model test of a 1×2 pile group was conducted in silts to investigate its behavior under eccentric lateral loading. The model pile group consisted of two well instrumented steel piles and was installed in a large soil tank with a close spacing of three-pile diameters on centers. The test results revealed that the eccentricity of lateral loads had limited effect on the overall performances of the 1×2 pile group, but significantly contributed to the unevenness of internal forces of the individual piles. The coupling effect between the lateral deflection and torque gave rise to the substantial increase in the torsional resistance of individual piles within the group, comparing to that of a torsionally loaded single pile. The contribution provided by the torsional resistances of individual piles in resisting the external torque continually decreased when the applied lateral load increased. In addition, a three-dimensional finite-element analysis for the pile group was performed and the simulated response was found to be in good agreement with the measured test results. Based on the same model, more cases with different loading conditions were further analyzed. It could be concluded from the analyses that the layout of individual piles within the group obviously affected the behavior of the 1×2 pile group under eccentric lateral loads.

Effect of Compressive Load on Uplift Capacity of Pile Groups in Sand

An experimental cum analytical study has been carried out to quantify the effect of compressive load due to stage construction on uplift capacity of model pile groups embedded in sand. Pull out tests were conducted by placing a static compressive load of 0, 25, 50, 75, and 100% of their ultimate capacity in compression on pile groups of different configuration and length to diameter ratio embedded in sand. The experimental results indicated that the presence of compressive load on the pile group decreases the net uplift capacity of the group and the decrease depends on the magnitude of the compressive load. Based on the experimental results a semi empirical method has been suggested to predict the net uplift capacity of a group of piles in the presence of compressive loading. The predictions are found to be in good agreement with the measured values validating the developed method of analysis.

An Experimental Study on Pile Spacing Effects under Lateral Loading in Sand

Grouped and single pile behavior differs owing to the impacts of the pile-to-pile interaction. Ultimate lateral resistance and lateral subgrade modulus within a pile group are known as the key parameters in the soil-pile interaction phenomenon. In this study, a series of experimental investigation was carried out on single and group pile subjected to monotonic lateral loadings. Experimental investigations were conducted on twelve model pile groups of configurations 1 × 2, 1 × 3, 2 × 2, 3 × 3, and 3 × 2 for embedded length-to-diameter ratio l/d = 32 into loose and dense sand, spacing from 3 to 6 pile diameter, in parallel and series arrangement. The tests were performed in dry sand from Johor Bahru, Malaysia. To reconstruct the sand samples, the new designed apparatus, Mobile Pluviator, was adopted. The ultimate lateral load is increased 53% in increasing of s/d from 3 to 6 owing to effects of sand relative density. An increasing of the number of piles in-group decreases the group efficiency owing to the increasing of overlapped stress zones and active wedges. A ratio of s/d more than 6d is large enough to eliminate the pile-to-pile interaction and the group effects. It may be more in the loose sand.

Cam Elyaf Takviyeli Plastik Profilli Pasif Kazik Grup Davranişinin Deneysel Olarak İncelenmesi

Experimental Investigation of Glass Fiber Reinforced Plastic Profiled Passive Pile Group Behavior In this study, the use of glass fiber reinforced plastic (GFRP) profiled passive piles in slope stability is investigated and it is aimed to contribute to the literature as the first model study regarding this topic. A special experimental setup is designed in order to model pile groups subjected to soil movement under its own weight. Soil pressure distributions acting on instrumented GFRP pile groups are examined for various pile spacings. As a result of experiments, it is revealed that the loads acting on piles increase with decreasing pile spacing due to soil arching. Experimentally determined soil pressure distributions are compared with the soil pressure values calculated by analytical methods.

Experimental Investigations on the Behaviour of Pile Groups in Clay Under Lateral Cyclic Loading

This paper presents the results of two-way cyclic lateral load tests carried out on model pile groups embedded in soft marine clay. The tests are conducted on 1 × 2, 2 × 2 and 3 × 3 pile groups having length to diameter ratio (L/D) of 15, 30 and 40 with the spacing to diameter ratio (S/D) of 3, 5, 7 and 9. The experimental results are presented in the form of load–deflection curves and bending moment profiles. Cyclic group efficiency, critical spacing, critical cyclic load level and cyclic p-multipliers are evaluated. It is found that the lateral capacity of the 3 × 3 group reduces by about 42% after 50 cycles of loading. The cyclic p-multipliers of 3 × 3 pile group are found to be 0.41, 0.25 and 0.29 for leading, intermediate and rear rows respectively. The test results are compared with the numerical analysis carried out by p–y method using GROUP program. The analysis carried out with experimentally evaluated p-multipliers predicts load—deflection and bending profiles of pile groups reasonably well, but underestimates the depth to maximum bending moment by about 15%.

Load Tests of Piled Raft Models with Different Pile Head Connection Conditions and Their Analyses

A series of experimental and analytical studies on the behaviours of model pile groups and model piled rafts in dry sand subjected to static vertical loading and static cyclic horizontal loading were carried out in order to investigate the influence of various pile head connection conditions between the raft and the piles on the behaviours of the foundations models and to examine the applicability of an simplified analytical method to simulate the load tests. In the load tests, the behaviours of the model foundations were investigated in detail, with particular focus on cyclic horizontal loading, and behaviour such as horizontal stiffness and the rotation of the foundation, the load proportions between the raft and the piles, and the bending moments and shear forces generated in the piles. A simplified three-dimensional deformation analysis method was used to simulate the experiments.

Group Interaction Effects on Laterally Loaded Piles in Clay

This paper presents the results of static lateral load tests carried out on 1×2 , 2×2 , 1×4 , and 3×3 model pile groups embedded in soft clay. Tests were carried out on piles with length to diameter ratios of 15, 30, and 40 and three to nine pile diameter spacing. The effects of pile spacing, number of piles, embedment length, and configuration on pile-group interaction were investigated. Group efficiency, critical spacing, and p multipliers were evaluated from the experimental study. The experimental results have been compared with those obtained from the program GROUP. It has been found that the lateral capacity of piles in 3×3 group at three diameter spacing is about 40% less than that of the single pile. Group interaction causes 20% increase in the maximum bending moment in piles of the groups with three diameter spacing in comparison to the single pile. Results indicate substantial difference in p multipliers of the corresponding rows of the linear and square pile groups. The predicted field group be...

Seismic Bearing Capacity of Piles in Liquefiable Soils

An investigation into the base capacity of piles in passing through loose, liquefiable sand and founded in underlying dense sand is presented based on the results of a series of dynamic centrifuge tests on instrumented model pile groups. Excess pore pressures equal in magnitude to the initial effective vertical stress were observed to be generated in the bearing layer of dense sand at both shallow (15 m) and deep (26 m) depths. This induced a dramatic reduction in base capacity and consequently, large settlements of the piles by as much as ~5 D 0 . A spherical cavity expansion solution for base capacity was validated against measured values showing good agreement, provided that excess pore pressure and dynamic shear stiffness in the bearing layer are known. A simple closed-form relationship, applicable to end-bearing piles, between the degree of liquefaction and the initial pile static safety factor was then developed against plunging failure at the pile base which can be used in design.

Liquefaction-Induced Settlement of Pile Groups in Liquefiable and Laterally Spreading Soils

The results of a series of dynamic centrifuge tests on model pile groups in (level) liquefied and laterally spreading soil profiles are presented. The piles are axially loaded at typical working loads, which has enabled liquefaction-induced settlements of the foundations to be studied. The development of excess pore pressures within the bearing layer (dense sand) was found to lead to a reduction in pile capacity and potentially damagingly large coseismic settlements. As the excess pore pressure increased, these settlements were observed to exceed postshaking downdrag-induced settlements, which occur due to the reconsolidation of liquefied sand around the pile shaft. In resisting settlement, the pile cap was found to play an important role by compensating for the capacity lost by the piles. This was shown to be achieved by the development of dilative excess pore pressures beneath the pile cap within the underlying loose liquefied sand which provide increasing bearing capacity with settlement. The centrifuge test data show good qualitative and quantitative agreement with the limited amount of model and full-scale data currently available in the literature. The implications of settlement for the design of piled foundations to serviceability conditions in both level and sloping ground are discussed, with settlement becoming an increasingly important consideration for laterally stiffer piles. Finally, empirical relationships have been derived from the test data to relate suitable static safety factors to given increases in excess pore pressure in the bearing layer within a performance-based design framework (i.e., based on limiting displacements).