Piled Raft Foundation Research Articles

Analysis of the capability of pile assembly foundations in soft soil in physical modeling of variationsiin laboratory scale distances

<p>The capacity of raft foundations, pile foundations and pile rafts on soft soil with variations in the distance between the piles. Perform analysis of the carrying capacity and settlement of each foundation test and then compare the results of the theoretical carrying capacity research with the analysis of carrying capacity calculations. The implementation of the test prepares the test along with samples of the raft foundation, pile foundation and pile raft foundation. The test were carried out using a gradual load then a dial gauge is placed at both ends of the sample raft and the load reading is taken. The pile foundation was tested with a decrease of 10 cm while the settlement on the raft foundation and the pile raft foundation was 3 cm, the carrying capacity of the raft foundation was 24 kg, the pile foundation varied 4D distances; 6D and 8D, namely 7.5 kg and the foundation of the pile raft with variations in 4D distance; 6D and 8D are 26 ; 32 and 32 kg. In the interpretation method, the pile raft foundation with various distances increased from 4D to 6D but decreased in 8D. Pile raft foundations with various distances between pile have not a significant effect where raft foundations are more dominant in supporting resistance than pile foundations.</p>

Experimental Study of Lateral Loading on Piled Raft Foundations on Sandy Soil

A Shallow foundation on cohesionless soil cannot support greater weights; piled raft foundations are recommended because they combine the load-bearing qualities of piles and raft. Combined Piled Raft Foundations (CRPF) are efficient for tall buildings because they account for both vertical and lateral loads. In a pile raft foundation, the raft’s load-resistance is disregarded due to soil-structure interaction. Simplification may lead to an uneconomical design. While study on raft’s vertical resistance is extensive, its horizontal resistance is limited. In the present study, 160 mm x 160 mm pile-raft model with different pile spacing and pile length was tested. Studies showed that pile length and spacing of pile improve bearing capacity and reduce settlement of raft. The pile raft system rests 65 percentage of the lateral load, depending on pile spacing and its length. Pile spacing and pile length lessen the raft’s lateral load contribution. Furthermore, as increasing in pile spacing reduces raft overturning by 60 percentage. Upgrade pile raft system design may make a cheaper and more efficient option for skyscrapers and make this foundation system more economical design.

Simplified Analytical Model and Shaking Table Test Validation for Seismic Analysis of Piled Raft Foundation

This study adopted development of a shaking table to simulate real earthquake loadings in the laboratory. It is a platform excited with a type of mechanical loading to provide periodic or random motions. Currently, it is the only experimental method to simulate different types of motion such as earthquakes, ground motions, and sine sweeps directly. In order to perform dynamic testing to simulate seismic loading, a large, effective, and practical shaking table was designed and manufactured in this study. The developed shaking table is capable to move in horizontal and vertical direction forward and backward and combination of those. Several researches utilized shaking tables in geotechnical engineering under seismic loads to evaluate miscellaneous parameters. Although these researches that developed excellent shaking tables, there is a high demand to design and manufacturing a shaking table capable to simulate the seismic load and its effects on the buildings. To attain this objective, this study aims to develop a novel shaking table that can simulate the manner of the real earthquake. The shaking table proposed in this study capable to mimic an earthquake that starts from a high energy then the energy decreases gradually until reach the zero. In addition, the proposed shaking table can implement simulated earthquake for time similar to that occurs in the nature. Therefore, this study can fill the research gap in this domain. The proposed shaking table work was verified and validated by testing based on repeated operating.

Numerical Analysis of Piled Raft Foundations in Alluvial soil

In this age of rapid urbanization, population is rapidly increasing in urban area, therefore a new concept of vertical cities has been introduced in form of high-rise building, and there are many conventional methods for design of foundation systems for high rise buildings. In most of the conventional methods pile foundations have been given preference for high rise buildings, all the loads of the building are transferred to the soil by piles. Some of the pressure of the building can also be transfer by raft directly to the soil by contact pressure which is neglected in most of the conventional designs of pile raft foundation system. But from last decades, optimised way of designing of pile raft foundation system have been started by engineers, in which raft foundation is allowed to transfer some of the total load directly to the ground by contact pressure. This optimised way of designing has made the foundation system more economical and sustainable. This type of foundation system in which some part of the load is transfer by raft and some by piles are called as pile raft foundation system. Soil–structure interaction in this pile raft foundation system is very complex in nature and to study this soil–structure interaction we need some numerical techniques or numerical methods. So, in this paper, we are going to use one of the numerical methods for numerical analysis of pile raft foundation system. There are various factors that influence the behaviour of pile raft foundation, some of the important factor that we are going to see in this paper are raft thickness, pile length, pile spacing and number of piles. All these factors are very important for optimize and economical design of pile raft foundation system. In this paper, numerical analysis has been done by using finite element software that is GEOTECH 3D Foundation to find out the influence of above factors on pile raft foundation system in alluvial soil.

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.

Nonlinear optimization design of pile foundation based on settlement control principle

How to take certain measures to minimize the differential settlement of buildings is one of the urgent problems to be solved in the current pile-raft foundation design. In this paper, the nonlinear optimization design of pile foundation based on the principle of settlement control is developed. For the soil around the pile group, considering its nonlinear characteristics, when it yields, the ideal elastic-plastic model is adopted for calculation. Through numerical simulation, combined with the results of model test and field observation, some practical research results are obtained: the smaller the elastic modulus coefficient is, the flatter the load-settlement curve of CPF (Composite pile foundation) is, and the larger the fixed value is, the load-settlement curve is abrupt. Using settlement control to design rigid pile composite foundation has clear settlement. As a supplement to the insufficient bearing capacity of foundation soil, pile foundation makes full use of the bearing capacity of soil between piles. The design scheme is more economical, and it is a good nonlinear optimization method of pile foundation.

Experimental Analysis of the Behaviour of Piled Raft Foundations in Loose Sand

This paper presents the experimental analysis that was conducted on small-scale 1g physical models of piled raft foundation structures with a group of 2 × 2 piles in loose sand. The purpose of the piles was to reduce the settlement of the raft. The test program included twelve experiments, three of which were conducted on a raft alone and nine on piled rafts at pile distances of 3d, 4d, and 5d and pile lengths of 10d, 20d, and 40d, where d is pile diameter. The test results show that the current conventional approach to design of piled raft foundations, at a high safety load factor in piles that assume to take the whole external applied load, is very conservative. Instead, it is more economical to apply a low bearing capacity factor for piles as settlement reducers and maximize use of raft bearing capacity to carry part of the external load.

A new nonlinear spring‐dashpot model of CPRF of NPP structure based on coupled BEM‐FEM approach

AbstractIn this paper, a BEM‐FEM coupled model of combined piled raft foundation (CPRF) is proposed for both the frequency domain and the time domain dynamic analyses of a NPP structure in the linear, equivalent linear and nonlinear soil domain. The piles are modeled using the finite element method as a beam element, while the raft and internal domain of soil are modeled using the eight nodded brick element. It is assumed that the piles are rigidly connected with the raft. The nonlinearity of soil is modeled using the hyperbolic stress–strain relation and Modified Drucker–Prager Model. The boundary of the layered soil domain is modeled using the boundary element method. For simplification, it is assumed that the raft and piles are rigidly connected with the soil that means there are no slip and separation conditions at the interface of pile‐soil and raft‐soil. In order to validate the proposed approach, numerical results, that is, impedances in the horizontal, vertical and rocking directions, are compared with the published literature. Further, dynamic analyses of a lumped structure founded on CPRF is carried out in the time domain and frequency domain using these impedances and results are compared with the FEM. It is found that the spring‐dashpot models give the reasonably good agreement with finite element method for linear, equivalent linear and nonlinear models for both frequency domain and time domain analyses. Moreover, practical application of proposed model is shown for a very large problem of raft‐pile‐soil‐structure interaction such as a NPP structure on the layered soil. It was found that the nonlinearity significantly increases the response of the NPP structure. The proposed model has many advantage over the finite element model, for example, first it is very simple and second it reduced the computation time significantly with the good accuracy.

Enhancing the Structural Analysis of Rc Piled - Raft Foundation by Actual Behaviour of Supporting Piles

Abstract This paper presents a numerical analysis of the piled-raft foundation (PRF) based on the actual behavior of supporting piles. The raft was modeled as a thin plate, while the piles were modeled as springs in different ways. This research also aims to propose an analytical model of piles based on actual behavior at fieldwork. The results proved that the structural behavior of raft member can be improved through utilizing the actual behavior of supporting piles. When the piles were modeled as non-linear stiffness springs, settlements and bending stresses of raft foundation were reduce marginally as compared with those obtained from piles with linear stiffness springs.

Analysis and effect of piles on raft foundation for High-Rise framed structure under seismic loading

In recent years, the usage of piled raft foundations has grown in popularity because the collective response of the raft with piles may enhance soil load carrying capacity, minimize the settling of soil, and the piles may be positioned for preventing unequal deformation in the mat. A stacked raft foundation is less expensive than a piled foundation. As piles are not required to reach the whole thickness of the clayey soil, they may be ended at upper altitudes. Raft foundation with piles is a novel idea by which the complete weight of the structure above is carried partially by the mat slab via soil interaction and partially carried through piles via surface friction. The seismic analysis of a stacked raft foundation is performed in this work utilizing CSI Safe software and response spectrum analysis load cases obtained from ETABS. For the analysis, the G + 10 story structure is taken and designed in ETABS and support reactions were transferred from ETABS to safe software. The analysis had been performed for different values of soil bearing capacities and different thicknesses, the diameter of the pile, and the length of the pile. The effect of different parameters had been analyzed on the foundation design. The results demonstrate that changing the diameter of piles from 200 mm to 400 mm and raft thickness from 300 mm to 500 mm, leads to a 68.66 % reduction in the deformation of the raft slab. After performing the study, it had been concluded that piles provided with raft foundation improve the performance and capacity of the raft foundation under seismic loading and this type of foundation can be used where soil bearing capacity is low.

Deviation rectification of a high-rise building with piled raft foundation: a case study

Deviation rectification of a high-rise building with a piled raft foundation was successfully carried out by vertically digging holes. Through site investigation and finite-element analyses of pile foundation settlement, the building tilt was attributed to shortening of the pile length, large post-construction settlement and cancellation of the setting of the post-cast strip of concrete between the main building and the skirt of an underground garage. A comprehensive rectification scheme was conducted, including drilling settlement-resisting micropiles on the side with a greater subsidence, cutting off the raft between the main building and the garage, vertically digging holes and disturbing soil on the side with less subsidence. When the rectified inclination reached the proposed value, the foundation was strengthened by the micropiles for settlement reduction and bearing capacity enhancement. During construction, close monitoring was carried out to guide dynamically the soil extraction operation and monitor building settlement. By analysing the monitoring data over time, the effectiveness of soil extraction for building rectification was verified, and the rectification mechanism of high-rise buildings supported on piled raft foundations was clarified. Finally, the rectification scheme was evaluated and discussed.

Optimum Design of Oil Tank Foundation on Different Soil Conditions

Tank foundation is a base for the tank which is designed to support the weight of oil tank in order to ensure its stability. Failure of tank foundation usually occurred when the foundation system cannot support the weight of the tank or the soil bearing capacity of the area failed to resist the imposed stress from oil tank inclusive of foundation’s self-weight. Failure of tank foundation can lead to pivoting effect and cracking on the foundation slab. Hence, the right choice of foundation system with reference to the bearing capacity of foundation soil is important to ensure the stability of tank foundation. Thus, this study was carried out in order to determine the deformation characteristics of foundation slab of oil tank foundation on different soil conditions with the aim to determine optimum design of oil tank foundation. The dimensions and design of the models were based on a published case study. Series of analyses with finite element models were conducted using STAAD Foundation CONNECT Edition V9. The models were aimed to analyze the stability of foundation structure, and deformation characteristics of the foundation slabs on different soil conditions. Three types of foundation system (raft, pile raft and pile foundation) were modelled in STAAD Foundation CONNECT Edition V9. The findings showed that the most optimum design for foundation structure on stiff residual soil is raft foundation. Whereas pile raft foundation structure is the most appropriate to construct on unconsolidated marine sediment deposit while pile foundation structure is highly recommended on soft peaty soil.

Evaluation of the Structural Health Monitoring Results of the Applied Fiber Optics in the Pile-Raft Foundations of a High-Rise Building

Fiber optics are increasingly being used in structural health monitoring applications. In addition to the well-known advantages, they most reliably transmit the stress–strain condition of the structure in the long term. This article presents the results of structural health monitoring on the embedding of fiber optics in the upper layer of the raft over the entire area of a high-rise building in Astana city (Kazakhstan), including the 75-storey 320 m block R. Temperature and strain data were collected constantly via a distributed fiber optic strain sensing system (DFOSS). The analysis of strains in fiber optic chainage indicated that the compression strains were observed over the entire area of the building, with values from −20 to −40 µε and with progression of the compression loaded up to −80 µε along the core wall closer to the eastern facade of the building. Tension strains were concentrated along the extreme axes of the building, with a predominance in the southern part of the R block, as well as in the immediate vicinity of the columns, in a range of −20 to −40 µε, with separate spots from −40 to −60 µε. Individual patches of tension strains near the columns have been explained by the increased deflection of the raft under the application of a concentrated load (columns). Fiber optic monitoring results at the time of testing did not exceed the permitted values for high-rise building operation; however, they characterized the general picture of the strain in the raft plane and made it possible to determine the initiation of cracks in concrete at an early stage.

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.

Seismic Analysis of RC High-Rise Buildings Rested on Cellular Raft

This paper includes the investigation of the soil–structure interaction (SSI) effect on the seismic response of 20 and 30-story reinforced concrete moment resisting frames (MRFs) rested on a piled raft foundation using the direct approach. After that, a study is conducted to show the impact of using a cellular raft instead of the designed solid raft on the dynamic response of the building. A study is introduced to select the best gap size for the cellular raft. The soil model is assumed as a single layer of sandy clay. Time history analysis by the direct integration method is performed under seven earthquake records (El-Centro, Northridge, Kobe, Chichi, Friuli, Kocaeli, and Loma), which are scaled to the Egyptian Code for Loads (ECP-201) response spectrum using a full 3D model by a finite element software named (Midas GTS NX). It is concluded that considering SSI significantly affects the dynamic response of high-rise buildings, and using cellular rafts generally leads to a decrease in their dynamic response.

Improving the Performance of Piled Raft Foundations Using Deformation Adjustors: A Case Study

Complicated soil conditions are direct difficulties for high-rise building projects. A new device called a deformation adjustor, which is used to optimize the stiffness distribution in the piled raft system, has achieved good results for this challenge. This paper presents a case study on the application of deformation adjustors to improve the performance of a piled raft foundation. This case study describes the preliminary design of pile-raft foundations with deformation adjustors, followed by numerical analysis. Based on the numerical study, the potential savings are demonstrated due to the good performance of soil bearing capacity. Comparing the numerical results with the monitoring results in raft settlements, earth pressures, deformation amount of deformation adjustors, pile top reactions, and load-sharing ratios between soils and piles, the accuracy of the design schemes with an aided numerical analysis is verified. Through a long-term monitoring, soils below the raft carried 63% of the total applied loads, while the piles bear 37% of the loads. This case study proved that a piled raft foundation with deformation adjustors was an effective and economical design scheme, which can make full use of the soil bearing capacity. It is of great significance to facilitate the design and construction of piled raft foundations in complicated soil conditions.

Studying the damping characteristics of the system of building and infrastructure considering the Soil-Structure Interaction

This paper studies the damping characteristics of the soil foundation under a building concerning the Soil-Structure Interaction (SSI). By considering a multi-story building resting on a piled raft foundation as a typical SSI system, subjected to an earthquake (i.e., Chi Chi earthquake, Taiwan 1999), the time-dependent responses of specified locations in the foundation are recorded and analyzed, both in-time domain and frequency domain. Referring to prior knowledge about system identification and damping, this study suggests an overwhelming approach to determining the damping ratio for analyzing more thoroughly a system of SSI systems. Results are a general procedure to establish the damping matrix, namely the Caughey damping matrix which takes several frequencies into account. A different viewpoint that the connection of superstructure and infrastructure in series could help to estimate the damping, and contribute to a wide range of system identification. All these procedures are used to predict more properly the damping characteristics of a system of structures. Suggestions over the findings would be expected to contribute a more rigorous component to the analysis of high-rise buildings in the future.

Interaction analysis of two floating granular piled raft units

ABSTRACT The pile–soil–raft interactions remain a daunting problem in the study of piled-raft foundations. A simple analytical continuum approach is implemented in the present research to analyse the interaction between two granular floating piled-rafts. The formulation uses the equations of Mindlin and Boussinesq for the estimation of the displacements for forces in the interior and on the surface of the continuum. Settlement influence factor, interaction factor, the normalised shear stresses along the granular pile (GP)-soil interface, the percentage load shared by GP, the percentage load transferred to the GP base, and the normalised contact pressure distribution underneath the raft are evaluated and presented for design.

STUDY INTO THE SIGNIFICANCE OF INDIVIDUAL ELEMENTS IN A PILED-RAFT FOUNDATION

Introduction . The prospects of using piled-raft foundations to support the columns of frame buildings and civil engineering works are examined. Aim . To determine the significance and role of individual elements in a piled-raft foundation and its underlying soil to achieve the maximum load capacity. Materials and methods . In order to achieve the stated aim, a series of theoretical numerical studies into horizontally loaded piled-raft foundations was conducted. Here, three-level numerical studies were used to determine the effect of various factors on the load capacity of piled-raft foundations under horizontal and moment loading. The following factors were considered in this work: coefficient of soil reaction around the column pedestal k u ; coefficient of near-pile soil reaction k p ; transverse dimension of the column pedestal d u ; pedestal height l u ; inclination angle of the pile to the vertical α P . The significance of each factor was assessed in terms of the column pedestal displacement at the soil surface level, which is described by a quadratic polynomial in five variables. Results . The impact on foundation resistance to horizontal loading can be determined by analyzing the absolute values of polynomial coefficients and the extent to which the considered factors affect the horizontal pedestal displacement in piled-raft foundations under horizontal and moment loading at the soil surface level. It is established that the most significant factors contributing to the foundation resistance to horizontal loading include the coefficient of soil reaction around the column pedestal k u and the transverse dimension of the column pedestal d u (increasing the foundation resistance to horizontal loading by 60% and 35%, respectively). The other factors have a significantly lower impact. Conclusions . It is shown that numerical theoretical studies into horizontally loaded piled-raft foundations reveal the significance and role of its individual elements and underlying soil, as well as justifying the values of factors affecting the load capacity of foundations.

Seismic response of nuclear power station with disconnected pile-raft foundation using dynamic centrifuge tests

The typical foundation type for a nuclear power station is the raft foundation in rock areas. With the power demand, it is possible that a nuclear power station located in soft soil areas. Traditional connected pile raft foundation (CPRF) has been successfully used in soft soil areas. However, under earthquake loads, high horizontal shear stresses and bending moments are generated in the pile head. Accordingly, researchers have sought to develop an innovative disconnected pile raft foundation (DPRF), and the benefits of DPRF have simulated increasing researches on it in the last two decades. In this study, a series of dynamic centrifuge tests were carried out to identify the effect of cushion and its thickness on the dynamic characteristics of the nuclear power station with DPRF. A withe noise excitation and three earthquake waves with different seismic intensities were adopted as ground motion. The seismic responses of soil, structure, and bending moment of piles were analysed. A cushion thickness equal to the diameter of piles is recommended. Comparing with the CPRF, the cushion layer of DPRF has an isolation benefit. With the gravel cushion, attention must be paid to the horizontal displacement, inclination and rocking of the superstructure.