Settlement Of Raft Research Articles

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.

Numerical Evaluation of Settlement and Stresses of Annular Raft

Numerical Evaluation of Settlement and Stresses of Annular Raft

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.

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.

Parametric Study of Twin Tunneling Effects on Piled Foundations in Stiff Clay: 3D Finite-Element Approach

Due to urbanization, development of society, and growth of population, there are new demands for tunneling technique to facilitate the public transport as well as high-rise buildings to accommodate an increasing population. Piled foundations are commonly preferred for the construction of high-rise buildings. It is, therefore, unavoidable that tunnels must be constructed near extant buildings resting on piled foundations. Inevitable movement of the ground due to stress changes induced by a tunnel can induce additional settlement and reduce the load-carrying capacity of nearby pile foundation systems. This numerical parametric study investigates the responses of two-by-two piled raft to twin side-by-side tunnels either near the mid-depth of the pile shaft or adjacent to or below the pile toe in stiff clay. In addition, it investigates the effects of different group configurations of the piled raft and elevated pile group. The ground in all the finite-element analyses was modeled using the hypoplasticity (clay) model because of its ability to capture degradation of soil stiffness at a small-strain level. Twin tunneling below the pile and near the middepth of the pile shaft caused the largest and smallest settlement of the piled raft, respectively. Unlike induced piled raft settlement, the most significant transverse tilting of the raft is induced after the advancement of the first tunnel. After the twin tunneling near the pile shaft was completed, the raft was separated from the ground, and a portion of the working load carried by the raft was transferred to the piles. The computed results have revealed that the induced settlement of the elevated pile group was significantly larger than that of the piled raft. A significant effect number of piles in the group was found on the piled raft responses to tunneling.

Behavior of Different Configuration of Piled Raft Foundation for a High-Rise Building by using FEM

Abstract In this paper, the numerical simulation is performed on two piled raft configurations having uniform loading on a piled raft foundation. To investigate the interaction between various parameters of pile soil foundation with varying components of its length of pile, diameter and raft thickness. These components are critical for increasing the foundation’s bearing capacity. It’s important aspect to achieve a reliable design to optimize piled raft foundations subjected to uniformed load- settlement behaviors of the curves. These load – settlements are basically depending on the changing of their components piled raft foundation. These component of piled raft foundations to choose an optimal selection of embedded length of pile (L/dP), normalized diameter of pile (L/dP) and normalized raft thickness (tR/dP). The effect of load-settlement on distributions of shear force and bending moments is also investigated. In this study, a finite elements methods based on numerical tools ELPLA software is used for numerical simulation. The study’s findings validate the numerical analysis for the calculation of proper pile configuration arrangement, as a result of settlements. It will be generated as formation of contours patterns as shear stress and bending moments on the rafts, may be minimized with the total pile length. The conclusion drawn from the study validates the numerical analysis for the computation of proper pile arrangement can results in total and differential settlements, as well as generated shear stress and bending moments on the rafts, are all being reduced, with identical total pile length. Moreover, it captures the contours patterns of different behaviors of piled raft settlements, maximum shear force and maximum moments.

Estimation of Raft Settlement Based on Linear Elastic Finite Element Analysis

Estimation of Raft Settlement Based on Linear Elastic Finite Element Analysis

Improved Performance of Raft Foundation Using Detached Pile Columns in Loose Subsoil Conditions

Piles act as settlement reducers in case of connected piled‐raft foundation and hence decrease the settlements of the raft. The design concept of the connected piled‐raft foundations is to lessen the number of piles and utilize the bearing capacity of the system piled raft. Due to significant straining actions at the pile head‐raft connection, an alternative technique is proposed to disconnect the piles from the raft. A granular layer (cushion) beneath the raft is incorporated. The disconnection has a beneficial effect on reducing axial load compared to connected piles. For small piled rafts, nonconnected piled rafts show less stiffness than connected piled rafts, and the soil is highly stressed and shows greater raft settlement. In the case of the large piled raft, nonconnected piled rafts show greater settlement efficiency. Cushion stiffness was realized to be more substantial for a nonconnected piled raft with shorter piles than one with longer piles. The results show that the load transfer mechanism in a nonconnected piled raft is mainly governed by the thickness and stiffness of the cushion layer and by the stiffness of the subsoil.

Prediction of Piled Raft Settlement Using Soil Subgrade Modulus in Consolidating Clays

AbstractTime-dependent settlements of piled raft foundations embedded in consolidating clays were studied using three-dimensional (3D) finite-element analysis and critical state-based soil constitu...

Prediction of Change Rate of Settlement for Piled Raft Due to Adjacent Tunneling Using Machine Learning

For tunneling in urban areas, understanding the interaction and behavior of tunnels and the foundation of adjacent structures is very important, and various studies have been conducted. Superstructures in urban areas are designed and constructed with piled rafts, which are more effective than the conventional piled foundation. However, the settlement of a piled raft induced by tunneling mostly focuses on raft settlement. In this study, therefore, raft and pile settlements were obtained through 3D numerical analysis, and the change rate of settlement along the pile length was calculated by linear assumption. Machine learning was utilized to develop prediction models for raft and pile settlement and change rate of settlement along the pile length due to tunneling. In addition, raft settlement in the laboratory model test was used for the verification of the prediction model of raft settlement, derived through machine learning. As a result, the change rate of settlement along the pile length was between 0.64 and −0.71. In addition, among features, horizontal offset pile tunnel had the greatest influence, and pile diameter and number had relatively little influence.

Centrifuge and theoretical study on tunnel-raft interaction in clay

Tunnelling induced ground movement may affect adjacent raft foundations. A series of centrifuge model tests was performed to investigate the settlement and induced strain profiles of rafts of different rigidities due to tunnelling. The results reveal that the theoretical relationship between raft bending strain and deflection ratio derived from a simply supported centrally loaded Timoshenko beam is not able to predict the bending strain and raft settlement in certain situations. An elastic-continuum-based simplified method considering raft weight and soil-raft separation is then presented and first verified against the results of centrifuge tests. Parametric studies were further conducted to investigate the effect of the raft-soil relative location on the relationship between deflection ratio and bending strain. The results reveal the original deflection ratio cannot fully capture the deflection characteristic of the raft settlement due to tunnelling. A modified deflection ratio is proposed to better characterize different raft settlement profiles.

Investigation of piled behaviour due to an adjacent excavation: 3D numerical modelling

Zameer Ahmed Channaret al.,InternationalJournal of Emerging Trends in Engineering Research, 9(6), June 2021, 683–689683ABSTRACTIn congested cities, excavations are unavoidably constructed adjacent to high rising building supported by piled raft foundations which reduces differential settlements in the buildings. Since the excavations inevitably induce soil movement and stress changes in the ground, it may cause differential settlements to nearby piled raft foundation. In this numerical study, a 3D coupled consolidation numerical analysis (using a hypoplastic model, which considers strain dependent and path-dependent soil stiffness) was conducted to investigate a (2×2) piled raft responses to an adjacent 25-m deep excavation in saturated clay. The computed results have revealedthat the rate of piled raft settlement increased significantly beyond excavation stage h/He=0.5. This is because of the degradation of stiffness of clay with strain due to excavation-induced stress release. Differential settlement (i.e. tilting) was induced in the piled raft due to non-uniform stress release.Owing to separation of the raft from the ground due excavation, some of the working load was transferred to the four piles. The maximum positive bending moment was 200 kNm at Z/Lp=0.67. However, no any bending moment was induced in both the piles at the toes.

Dynamic behaviour of a piled raft resting on saturated Kasai River sand

ABSTRACT The present work intends to calibrate the cyclic triaxial test and validate the 1-g shake table test of piled raft on saturated Kasai River sand. The outcome of the cyclic tests on Kasai river sand is already reported in the literature, but the present paper attempts to identify and explain the failure modes of the cyclic triaxial test as well as to numerically calibrate the experimental data(s) for relative density of 40% and 60%. For numerical validation and calibration, a bounding surface plasticity model is used. The calibrated parameters obtained from the element tests are used for validation of 1-g shake table test of piled raft resting on saturated sand. The numerical predictions are in good agreement with the experimental observations (in terms of acceleration, pore pressure). In addition, the effect of superstructure loading on piled raft is investigated in terms of variation of pore pressure (or effective stress) near and away from the structure and mechanism for vertical settlement of piled raft is identified. The relevant parameters related to seismic design of piled raft are identified and design guidelines in terms of strength and serviceability has been proposed.

A New Model for the Prediction of Load Sharing in Piled Raft System—An Experimental Investigation

The complex load sharing mechanism between the raft and piles involving various interaction effects makes the piled raft system very popular and economic for the foundations of high-rise buildings around the world. This study highlights the outcomes of an experimental investigation on piled raft foundation under vertical load to establish a new method for estimating the loads shared by the piles and raft using the interaction factors and the stiffness values of unpiled raft and pile group. From the results, the pile-raft interaction factor $$\left( {\lambda_{{{\text{p}} - {\text{r}}}} } \right)$$ is found to decrease initially and then increase as the raft settles further. However, the raft-pile interaction factor $$\left( {\lambda_{{{\text{r}} - {\text{p}}}} } \right)$$ is observed to increase initially and then decrease indicating a positive influence of raft-pile interaction on the load response of piles. The piled raft coefficient (αPR) is found higher, i.e., 0.83 initially and then converges to 0.51 when the raft settlement reaches a value equals to 10% of the raft width. The developed model is validated with the centrifuge test data available in the literature. Simplified expressions to calculate various interaction factors and the piled raft coefficient are also proposed on the basis of the experimental results.

A study of differential foundation settlement of piled raft and its effect on the long‐term vertical shortening of super‐tall buildings

SummaryIn this study, the long‐term differential foundation settlement and vertical shortening of super‐tall buildings are investigated considering the coupling effect. At first, a time‐dependent settlement model is proposed to predict the foundation settlement based on the construction sequence method, in which both soil compression and pile shortening are considered. The pile shortening including the elasticity, shrinkage, and creep contributes to the most settlement of a single pile. The distribution of foundation settlement of piled raft is pot shaped with a large value in the core while small values in the surroundings. A time‐dependent soil‐foundation‐structure system is then developed using a series of equivalent springs to represent the distributed foundation settlements, by which the vertical shortenings of shear wall and mega column are predicted considering the coupling effect and moisture distribution. The pot‐shaped distribution of foundation settlement of piled raft leads to the decrease of vertical shortening for shear wall while the increase of vertical shortening for mega column, especially in the low stories. Finally, some health monitoring records of the Shanghai Tower are applied to validate the proposed time‐dependent settlement model and soil‐foundation‐structure system. The predicted foundation settlements show reasonable agreement with the monitoring records. The predicted vertical shortenings with considering the differential foundation settlement agree better with measurements than those without considering the differential foundation settlement.

Performance of Raft Foundation under Static Vertical Loading in Contaminated Soil

This study focuses on studying the impacts of residues oil on the geotechnical properties of soil and the performance of raft footing rested on oil contaminated soil and subjected to vertical loads. The contaminant used in the present study is residues oil, which is by product disposed of diesel engine oils. The soil samples are contaminated artificially by soaking with two percentage of disposed engine oil of contaminant consist of (disposed engine oil and gasoline) of 20% weight of dried of intact soil samples to obtain different concentrations of contaminant absorbed by soil samples for 30 days to complete the saturation. The mechanical model manufactured to investigate the behavior of raft footing under vertical static loading rested on intact and contaminated soils. The obtained results detected contaminant content have notable impacts on the physical soil characteristics such as the fine particles, specific gravity, plasticity index, and maximum dry unit weight decreased with the increase of contaminant content than that of intact soil. The mechanical soil properties of soil indicated the increase of the compressibility of soil with increase of residues oil percentage, but the soil strength and stiffness are decreased notably. In addition, the total and permanent settlement of raft footing constructed in contaminated soil samples increased by (27-43) % and by (41-58) % than that of an intact soil sample, respectively.

Three-dimensional centrifuge modeling of the influence of side-by-side twin tunneling on a piled raft

Although the effects of tunnel excavation on nearby existing pile foundations have been extensively studied, previous studies mainly focused on response of single piles and elevated pile groups. In this study, three-dimensional centrifuge model tests were carried out to investigate the effects of side by side twin tunneling on an existing two by two piled raft in dry sand. Upon completion of twin tunnel excavation, the measured cumulative settlement of piled raft due to tunneling near the pile toe is 2.7 times of that due to tunneling near the mid-depth of the pile shaft. For twin tunneling near the pile toe, differences of piled raft settlements due to each tunnel excavation are negligible. In contrast, settlement of piled raft due to the second tunneling is about 55% of that due to the first tunneling when twin tunnels are excavated near the mid-depth of the pile shaft. As an advancement of tunnel excavation near the pile toe, the axial loads carried by the front piles are decreased, and the decreased loads are transferred to the rear piles and the raft. On the contrary, twin tunneling at the mid-depth of the pile shaft causes a reduction in the front piles and raft, and the decreased loads are transferred to the rear piles. After completing tunnel excavation, the axial load carried by the raft is increased by 22.0% for tunneling near the pile toe, while it is decreased by 21.7% for tunneling near the pile shaft.

Settlement Profile and Pile Load Distribution Under Vertical Load of Piled Raft Foundation in Clay

In the rigorous analysis using FEM, the load sharing of the piles between the shaft and base resistance increased with increase in limited number of piles i.e. limited to decrease in pile spacing. The load sharing depends upon their location and spacing. The load carried by the center pile reduces with the increase in the number of piles and piled area. For the edge piles, it increased with the increase in the number of piles, whereas decreased for the corner piles. The total load carrying capacity of the piles increased with the pile sizes and spacing. The piled raft settlement decreases with the increase in the number of piles. By rearranging the same number of piles, more settlement of piled raft is observed for less pile spacing, which concentrated at the center, and the settlement is decreased with increase in pile spacing, which scattered outwards. Increased in number of piles is not always advisable and expensive. Based on limitation in settlement as specified by the code, limited number of piles and pile spacing are recommended. The settlement profile along the centre line of the piled raft decreased with the increase in the number of piles and more flexible at larger pile spacing.

Analysis of rigid raft overlying the granular pile with the effect of stiffness of bearing stratum

ABSTRACT With the use of piled raft, the load carrying capacity of the raft is enhanced and its differential settlement is reduced. As an economical alternative to conventional pile i.e. steel or concrete pile, granular pile (GP) is a reasonable option. The numerical solutions are available for floating granular pile overlaying with rigid raft. Present study deals with a method to analyse the end bearing granular pile overlying with rigid raft. A new pile settlement matrix is formulated to predict response of granular piled raft based on the elastic continuum approach. To account for the influence of bearing stratum, the mirror image approximation is used both for granular pile and raft. The results are evaluated in terms of normalised parameters such as settlement ratio, i.e. settlement of piled raft in comparison to rigid raft alone, displacement factor, percentage load transferred to tip of granular pile, percentage load shared by raft, normalised shear stress distribution along the length of granular pile and normalised contact pressure distribution beneath the raft with the variations of relative size of raft, relative length of granular pile, stiffness factor of granular pile and bearing stratum. Abbreviations: GP = Granular pile; L = Length of pile; n = number of elements of granular pile; d = Diameter of pile; L/d = Relative length of granular pile; P = Load on granular piled Raft; D = Diameter of Raft; Eb = Deformation constant of bearing stratum; Es = Deformation constant of soil; Egp = Deformation constant of granular pile; D/d=relative size of raft; νb = Poisson’s Ratio of bearing stratum; νs = Poisson’s Ratio of soil; Kgp = (Egp/Es)Stiffness factor of GP to soil; Kb = (Eb/Es) Stiffness factor of bearing stratum to soil; pr = Raft stresses; pb = Base Pressure; τ =Shear stress; z1(=z/L) Normalised depth of GP; Ip = displacement factor; τ* = τ(πdL)/P Normalised shear stresses of a GP; γ = settlement ratio; Pb = load on base of GP; Pp = load on pile; Pr = load on raft; (Pb/P) × 100 = percentage base load; (Pp/P) × 100 = percentage pile load; (Pr/P) × 100 = percentage raft load.

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.