Behavior Of Piled Raft Research Articles

Superstructure stiffness effect on the behavior of piled raft under wind and earthquake loadings

Superstructure stiffness effect on the behavior of piled raft under wind and earthquake loadings

Behavior of piled rafts in sand under nonuniform and eccentric loads

Behavior of piled rafts in sand under nonuniform and eccentric loads

Experimental and Numerical Analysis of Piled Raft Foundation with Different Length of Piles Under Static Loads

In order to understand the effect of (length of pile / diameter of pile) ratio on the load carrying capacity and settlement reduction behavior of piled raft resting on loose sand, laboratory model tests were conducted on small-scale models. The parameters studied were the effect of pile length and the number of piles. The load settlement behavior obtained from the tests has been validated by using 3-D finite element in ABAQUS program, was adopted to understand the load carrying response of piled raft and settlement reduction. The results of experimental work show that the increase in (Lp/dp) ratio led to increase in load carrying capacity by piled raft from (19.75 to 29.35%), (14.18 to 28.87%) and (0 to 16.49%) , the maximum load carried by piles decrease from(9.1 to 22.72%), (15.79 to 47.37%) and (44 to 81.05%) and the response of settlement piled raftdecrease from (16.67 to 23.33%), (9.09 to 39.39%) and (30%) with increase the number of piles from 4 to (6 and 9) and (length of pile / diameter of pile) ratio increase to (14.14 and 21.2), respectively. The numerical and model test results are found to be in a good agreement.

The Effect of Jet Grouting on Enhancing the Lateral Behavior of Piled Raft Foundation in Soft Clay (Numerical Investigation)

Soft clay soils cannot usually support large lateral loads, so clay soils must be improved to increase lateral resistance. The jet grouting method is one of the methods used to improve weak soils. In this paper, a series of 3D finite element studies were conducted using Plaxis 3D software to investigate the lateral behavior of piled rafts in improved soft clay utilizing the jet grouting method. Parametric models were analyzed to explore the influence of the width, depth, and location of the grouted clay on the lateral resistance. Additionally, the effect of vertical loads on the lateral behavior of piled rafts in grouted clay was also investigated. The numerical results indicate that the lateral resistance increases by increasing the dimensions of the jet grouting beneath and around the piled raft. Typical increases in lateral resistance are 11.2%, 65%, 177%, and 35% for applying jet grouting beside the raft, below the raft, below and around the raft, and grouted strips parallel to lateral loads, respectively. It was also found that increasing the depth of grouted clay enhances lateral resistance up to a certain depth, about 6 to 10 times the pile diameter (6 to 10D). In contrast, the improvement ratio is limited beyond 10D. Furthermore, the results demonstrate that the presence of vertical loads has a significant impact on sideward resistance.

Parametric Investigations into the Analysis of Piled Raft for Multi-Storeyed Building

This paper presents the analysis of the piled raft for a 50-story building using an approximate method to estimate the settlement and load distribution of the foundation. The pile and soils are considered to be interacting springs, and the raft is represented as a thin plate. The model takes into account both the resistance of the piles and the resistance of the raft foundation. It is calculated how the raft, soil, and pile interact. The suggested technique enables the use of the finite element based program ETABS to quickly address the issues of small, non-uniformly arranged rafts and big, non-uniformly ordered rafts. The effect of different pile length and diameter is evaluated on the behaviour of piled raft. With an increase in pile lengths, the moments in the raft are found to increase while the settlement of the pile decreases. Further, increases in pile diameter are found to increase the moments in the raft while decreasing the settlement of the raft. The parameters such as pile diameter and pile length have a considerable effect on the response of a foundation considered in the present study

Experimental Study on Vibration Velocity of Piled Raft Supported Embankment and Foundation for Ballastless High Speed Railway

In recent years, the high development of high-speed railway lines cross through areas with poor geological conditions, such as soft soil, offshore and low-lying marsh areas, resulting geotechnical problems, such as large settlements and reduction of bearing capacity. As a new soil reinforcement method in high speed railway lines, the piled raft structure has been used to improve soil conditions and control excess settlement. In order to study the dynamic behavior of piled raft supported ballastless track system in soft soil, an experimental study on vibration velocities of piled raft supported embankment and foundations is presented in soft soil with different underground water levels. Vibration velocities at specified positions of the piled raft supported embankment and foundations are obtained and discussed. The vibration velocity curves on various testing locations of piled raft foundations are clearly visible and have sharp impulse and relaxation pattern, corresponding to loading from train wheels, bogies, and passages. Vibration velocity distribution in the horizontal direction at three train speeds clearly follows an exponential curves. Most of the power spectrums of vibration velocity at various locations are mainly concentrated at harmonic frequencies. The change in water level has slight impaction on the peak spectrum of vibration velocity at harmonic frequencies. The vibration power induced by train loads are transmitted, absorbed, and weakened to a certain extent through embankment and piled raft structure. The dynamic response character of embankments are affected by their self-vibration characteristics and the dynamic bearing capacity of the piled raft structure.

The applicability and load-sharing behavior of piled rafts in soft clay: experimental study

The applicability and load-sharing behavior of piled rafts in soft clay: experimental study

The behavior of piled rafts in soft clay: Numerical investigation

Abstract This research aims to investigate the applicability and performance of piled rafts in soft clay. This aim has been achieved by studying how the pile length, pile number, raft-soil relative stiffness, and presence of a sand cushion beneath the raft would affect piled raft settlement, differential settlement, and load sharing. Piled rafts have been numerically simulated using PLAXIS 3D software. Experimental testing results were used to verify the numerical simulation. The portion of the load carried by the piles to the total applied load was represented by the load sharing ratio (GPR). The results indicated that with increasing pile length and number, settlement and differential settlement decreased. It was also noticed that with increasing raft-soil relative stiffness, the differential settlement decreased. The GPR decreased with increasing thickness and relative density of the sand cushion, whereas it increased with increasing pile length and number. This increase in GPR was 13.7, 36, and 58% with an increase in pile length to diameter ratio from 10 to 30 for the number of piles 4, 9, and 16, respectively. Additionally, the raft-soil relative stiffness was observed to have a marginal effect on the GPR.

Numerical analysis of piled rafts with short bored piles

Abstract Numerical analysis of the behavior of piled rafts seated on uniform soil with low bearing capacity has been important to support the project design. The calibration of the numerical model with instrumented load test allows usage of the results, in given conditions, in the foundation design of small and medium-sized buildings built on soils with the same mechanical properties analyzed in this paper. In this context, this paper evaluates numerical models, which allow to consider the influence of short bored piles connected to the raft. The models are also assessed using piled rafts concepts. From the results obtained, the load supported by the total shaft resistance is significant for the case of bored piles, and this load is from 14% to 30% higher in the case more flexible or thinner raft. Inserting piles in the rafts reduces settlement and increases overall stiffness. Such effects are amplified in piles with higher slenderness ratios (L/d).

Assessing the effect of governing parameters of bearing capacity determination of small piled rafts on clay soil

In the present study, a small piled raft foundation has been simulated numerically through PLAXIS 3-D software. The objective of this study was to investigate the effect of governing parameters such as pile length, pile spacing, pile diameter, and number of piles on the settlement and load-bearing behavior of piled raft, so as to achieve the optimum design for small piled raft configurations. An optimized design of a piled raft is defined as a design with allowable center and differential settlements and satisfactory bearing behavior for a given raft geometry and loading. The results indicated that, with increase in pile length, pile spacing, pile diameter, and number of piles, both the center settlement ratio and differential settlement ratio decreased. The load-bearing capacity of piled raft increased with increase in pile length, pile spacing, pile diameter, and number of piles. Furthermore, the percentage load carried by the piles increased as the pile length, pile spacing, pile diameter, and number of piles increased. The bending moment and shear force in corner pile are noted to be more, and they decreased towards the center pile. With increase in pile length, the maximum raft bending moment decreased, whereas the maximum shear force in the raft increased. Further, with increase in pile spacing, pile diameter, and number of piles, the maximum bending moment and maximum shear force in the raft increased. The optimum parameters for the piled raft foundation can be selected efficiently with the consideration of maximum bending moment and maximum shear force while designing the piled raft foundation. Thus, the results of this study can be used as guidelines for achieving optimum design for small piled raft foundation.

Physical 1g modelling of defective small-scale piled-raft systems founded in sand

The need for understanding the interaction between the elements of a piled-raft foundation system becomes relevant when one of the piles collapses, presents a defect related to the installation procedure, or when it is sought to optimise the number of piles to meet the criteria of load capacity and admissible settlement. In the paper, 20 small-scale 1g load tests were performed in model piled-raft foundations placed within a cylindrical container. Pluviated sand under vertical loading was adopted to evaluate the cross-correlated qualitative behaviour of piled rafts with and without the presence of a single defective pile in systems of four, nine and 16 piles. The defects were simulated by the variation of the length of the pile, considering it shorter or absent, at distinct positions on the system – that is, corner, edge and centre of the raft locations. The results indicate that the position of the defective pile may be more detrimental to the foundation stiffness and load capacity than the level of damage of the pile, such as the cases evolving the presence of defective piles in the corner position.

Experimental Study on Connected and Non-connected Piled Raft Foundations Subjected to Eccentric Loading

Piled raft foundations are sometimes used when the supporting soil has no adequate bearing capacity and the raft settlements exceed allowable values. This research investigates the bearing capacity of a foundation subjected to eccentric loads in both connected and non-connected piled raft foundations under 1 g. The load-settlement curves of a strip, square and circular raft are compared. The results illustrate that piled raft behavior is influenced by various factors such as pile length, spacing, shape, and eccentricity ratio in connected and non-connected cases. Test results indicate that connected foundations have greater bearing capacities and lesser settlements in larger pile spacing (S/D = 6), while non-connected foundations have higher bearing capacities and lesser settlements in lesser pile spacing (S/D = 3). Moreover, both the pile length in a connected piled raft system and pile spacing in a non-connected system affected the bearing capacity remarkably. The bearing capacity of the square and circular foundations at S/D = 3 was greater for the non-connected pile (19.8 and 15.8 kg/cm2 receptivity) than the connected pile (18 and 14.1 kg/cm2), while at S/D = 6, the bearing capacity of the foundations was greater for the connected pile than the non-connected pile. However, in both cases, the bearing capacity was enhanced and the settlements were reduced. The effect of various parameters is also evaluated and discussed in this study.

Numerical investigation of optimized piled raft foundation for high-rise building in Germany

Piled rafts have been used as a foundation system for high-rise buildings worldwide in different soil conditions, e.g., in soft to stiff clay as well as in medium-to-dense sand. Piled raft is currently used not only to control the foundation settlement but also to minimize the required raft thickness to reach the most optimized foundation design. The purpose of this study is to investigate the behavior of piled raft as a foundation system for Frankfurt over-consolidated clay based on the well-monitored Messeturm building in Germany. The numerical tool used in analysis is Plaxis 3D finite element software with hardening soil material model. The piled raft foundation behavior will be evaluated based on the total settlement, differential settlement and the pile skin friction. Based on this study, it was found that the chosen foundation system “plied raft foundation” for Messeturm was an optimized solution for the proposed building.

Impact of Pile Head Rigidity on the Response of Piled Raft in Sand Under Pseudo-Static Loading

The 3D finite element simulations are carried out to study the impact of different pile head connection conditions, i.e., rigid and hinged connection on the response of piled rafts in sand subjected to pseudo-static horizontal loading. The time-acceleration histories of Assam (2014), Bhuj (2001), Sikkim (2011) and Uttarkashi (1991) earthquakes are considered to calculate the horizontal pseudo-static loads. Analyses results confirm that pile head connection rigidity greatly influences the behavior of piled raft in many aspects. The horizontal stiffness of piled raft is found to decrease as the rigid pile head connection changes to hinged one. Piles in a piled raft foundation is found to carry about 52–75% of the pseudo-static horizontal load for rigid connection and 32–48% for hinged connection. The horizontal deflection of pile is found maximum at the pile head and becomes negligible along the depth of pile for both cases. For rigidly connected piles, the maximum bending moment occurs at the pile head, whereas piles with hinged connection show zero bending moment at top and maximum value at a certain depth from pile head.

Innovative piled raft foundations design using artificial neural network

Studying the piled raft behavior has been the subject of many types of research in the field of geotechnical engineering. Several studies have been conducted to understand the behavior of these types of foundations, which are often used for uniform loading on the raft and piles with the same length, while generally the transition load from the upper structure to the foundation is non-uniform and the choice of uniform length for piles in the above model will not be optimally economic and practical. The most common method in identifying the behavior of piled rafts is the use of theoretical relationships and software analyses. More precise identification of this type of foundation behavior can be very difficult due to several influential parameters and interaction of set behavior, and it will be done by doing time-consuming computer analyses or costly full-scale physical modeling. In the meantime, the technique of artificial neural networks can be used to achieve this goal with minimum time consumption, in which data from physical and numerical modeling can be used for network learning. One of the advantages of this method is the speed and simplicity of using it. In this paper, a model is presented based on multi-layer perceptron artificial neural network. In this model pile diameter, pile length, and pile spacing is considered as an input parameter that can be used to estimate maximum settlement, maximum differential settlement, and maximum raft moment. By this model, we can create an extensive domain of results for optimum system selection in the desired piled raft foundation. Results of neural network indicate its proper ability in identifying the piled raft behavior. The presented procedure provides an interesting solution and economically enhancing the design of the piled raft foundation system. This innovative design method reduces the time spent on software analyses.

Effects of rock-support and inclined-layer conditions on load carrying behavior of piled rafts

In this study, the load carrying behavior of piled rafts installed in inclined bearing rock layer was investigated for rock-mounted and -socketed conditions. It was found that settlements induced for an inclined bearing rock layer are larger than for a horizontal layer condition. The load capacity of piled rafts for the rock-mounted condition decreased as rock-layer inclination angle (theta) increased, while vice versa for the rock-socketed condition. The load capacities of raft and piles both decreased with increasing theta for the rock-mounted condition. When bearing rock layer was inclined, loads carried by uphill-side piles were greater than those by downhill-side piles. The values of differential settlements of rock-mounted and -socketed conditions were not significantly different whereas slightly higher for the rock-socketed condition. The values of load sharing ratio (alpha_p) and its variation with settlement were not markedly changed by the inclination of bedrock. It was shown that alpha_p for piled rafts installed in rock layer was not affected by theta whereas actual loads carried by raft and piles may vary depending on the pile installation and rock-layer inclination conditions.

Analysis of load sharing characteristics for a piled raft foundation

The load sharing ratio (apr) of piles is one of the most common problems in the preliminary design of piled raft foundations. A series of 3D numerical analysis are conducted so that special attentions are given to load sharing characteristics under varying conditions, such as pile configuration, pile diameter, pile length, raft thickness, and settlement level. Based on the 3D FE analysis, influencing factors on load sharing behavior of piled raft are investigated. As a result, it is shown that the load sharing ratio of piled raft decreases with increasing settlement level. The load sharing ratio is not only highly dependent on the system geometries of the foundation but also on the settlement level. Based on the results of parametric studies, the load sharing ratio is proposed as a function of the various influencing factors. In addition, the parametric analyses suggest that the load sharing ratios to minimize the differential settlement of piled raft are ranging from 15 to 48% for friction pile and from 15 to 54% for end-bearing pile. The recommendations can provide a basis for an optimum design that would be applicable to piled rafts taking into account the load sharing characteristics.

Experimental Investigation of Eccentrically Loaded Piled Raft Resting on Soft Cohesive Soil

Piled rafts have been used successfully in a wide variety of geotechnical applications. However, behaviour of piled raft placed in cohesive soil is not extensively studied. The present research paper describes the performance of eccentrically loaded square rafts connected to short piles and resting on soft cohesive soil. The load was applied with varying eccentricity (e) to raft width (B) ratios of 0.05, 0.1 and 0.2. Experiments were conducted with two different raft sizes of 180 mm × 180 mm and 220 mm × 220 mm connected to 0, 2, 3, 4 and 5 numbers of piles in different cases. The results showed that in general as compared to unpiled rafts, the average bearing pressure increased almost two times for piled rafts having 5 piles corresponding to e/B = 0.2. For rafts with 5 numbers of piles the average settlement reduced to almost one-third in most cases as compared to rafts without pile corresponding to identical e/B ratio. The foundations were also proved to be greatly effective in reducing the tilt. For e/B = 0.05, on increasing the number of connected piles from 0 to 5, the tilt reduced from 2.00° to 0.19° in case of 180 mm × 180 mm raft, and from 2.15° to 0.10° corresponding to 220 mm × 220 mm raft respectively.

Model tests on piled raft subjected to lateral soil movement

Passive loadings due to lateral soil movement-induced activities are highly influencing the serviceability and safety of constructions. This research aims to investigate the influence of axial loads, sand density and the depth of moving soil on the lateral behaviour of piled raft under progressively moving sand. In order to achieve this goal taking into account the complex interaction effects of piles, cap and subsoil, a laboratory apparatus and small scale models have been designed and fabricated carefully to ensure a reasonable simulation of this geotechnical problem. It is found that the above parameters play an important role in the response of piled foundations. The value of soil displacement at which the measured moment reaches its ultimate value decreases as axial loads increase. Peak displacement of the raft has been found to be a function of soil density.

Behaviour of model pile foundations under dynamic loads in saturated sand

In Japan and Turkey, predominantly traditional design concept of pile group is still adopted even though most pile foundations are piled raft foundations in reality. This situation may be attributed to the still limited knowledge about behaviour of piled rafts subjected to the combination of static and dynamic loads. Hence, in this study, a series of shaking table tests on 3-pile piled raft and 3-pile pile group models were carried out in saturated sand at 1-g field under the combinations of static vertical and dynamic horizontal loading, where the input motion was sinusoidal wave having a frequency of 20 Hz and 1.50 and 6.00 m/s2 amplitudes. The results showed that, raft-model ground contact in piled raft is very effective to reduce settlement compared to pile group even in liquefied soil. Moreover, even in piled raft, the horizontal resistance reduces if liquefaction of the ground surface occurs, due to the loss of the raft base resistance.