Raft Thickness Research Articles

Effects of Ta on the high temperature creep behavior and deformation mechanism of a Ni-based single crystal superalloy

The effects of Ta on the high temperature creep behavior and deformation mechanism in a Ni-based single crystal (SX) superalloy were investigated at 1120 °C/137 MPa. Ta was regarded as an essential strengthening element of the γʹ phase in the alloy, and the results indicated that the increase of Ta prolonged the creep rupture life. In this work, the addition of Ta increased the volume fraction of the γʹ phase and narrowed the γ channels, making the dislocation bowing out at the primary stage of creep more difficult. As creep continued, with a lower effective diffusion coefficient of alloying elements and larger γʹ raft thickness, the alloy with 6.5 wt% Ta addition was considered to possess the lower dislocation climbing rate, which reduced the minimum creep rate of the alloys. Subsequently, it was noted that the density of superdislocations in γʹ phase was clearly reduced with the increase of Ta. This was supposed to be the elevated Ta content in the alloy, which increased the lattice misfit and led to the formation of a denser dislocation network, thereby enhancing the interfacial strengthening effect and effectively preventing the cutting of superdislocations. The Ta effect on high-temperature creep was systematically summarized in this study, which was an important guideline for further composition design and optimization of Ni-based SX superalloys.

The Influence of Raft Thickness on Settlement and Bending Moment of Pile Raft Foundation in Clay Soil

Geotechnical engineers often deal with shallow foundation designs to support relatively simple building structures. However, as the demand for construction grows over time, there is a need for larger and more complex building structures. This is closely related to the weight of the building that will be supported by the foundation as a substructure. Therefore, the development of knowledge about other types of foundations to support the structural loads above them is highly necessary. Pile foundations are a fairly good solution for supporting larger structural loads that cause significant settlement. In designing pile foundations as a structure, there will certainly be raft to combine each pile foundation into a unified group. Raft are often designed only for combining each pile, but in reality, It also provides additional influence on the foundation system besides just serving as pile heads and load distributors to the foundation system. The study will investigate the influence of raft thickness on settlement that occurs in piled raft foundations. The raft thickness varies, namely 0.25m; 0.40m; 0.80m; 1.50m; and 3.00m. The piled raft foundation will be modeled and analyzed using finite element program. This study shows that the raft thickness affects the differential settlement that occurs in the piled raft foundation system. The results indicate that the differential settlement can be addressed by designing the raft thickness.

Enhancing microstructural stability and creep properties by Ta addition in Ni-based single crystal superalloys

To investigate influences of Ta content on microstructural stability during thermal exposure at 900 °C (up to 3000 h) and creep properties at 980 °C/163 MPa in Ni-based SX superalloy, alloys with 7Ta, 8Ta and 9Ta (wt.%) were studied utilizing DSC, SEM, TEM, HR-XRD and APT. The results shows that Ta addition enhanced the partitioning behavior of alloying elements. Besides, lattice misfit was controlled by both alloy composition and temperature. Ta addition increased absolute misfit both room temperature and 980 °C. The difference was that the γ/γ′ lattice misfit changed from positive to negative at room temperature. The γ′ coarsening indicated that Ta addition reduced the effective diffusion coefficient and exacerbated W segregation at γ/γ′ interface, which was beneficial to improve the microstructural stability. Merging of several adjacent γ′ precipitates in preferred direction was observed to be delayed with increasing Ta content, which occurred at 500 h for 7Ta alloy, 800 h for 8Ta alloy and 1000 h for 9Ta alloy, respectively. Ta addition affected the diffusion kinetics and greatly prolonged the steady creep duration, and then resulted in longer creep rupture life. It was discussed based on the γ matrix channels, γ′ raft thickness, the perfection degree of γ′ rafts, residual γ′ precipitates, interfacial dislocation networks and solid solution strengthening.

Performance Optimization of Piled Raft Foundations in Layered Soil under Uniform Vertical Loading Using Plaxis 3D

Piled raft foundations are composite foundations that combine piles and raft to support civil engineering structure and to reduce the settlement. The data were obtained from Addis Ababa, Ethiopia. In this study, the effects of raft thickness, number of piles, pile length, spacing of piles, and pile diameter on the response of piled-raft foundations were investigated using the finite element-based program Plaxis 3D for layered soils (medium to very stiff high plastic silty clay and medium to very dense silty sand soil) subjected to uniform vertical loading. The results showed that increasing the thickness of the raft from 0.7 m to 1.7 m reduced the differential settlement by 78.21% when there were 16 piles. However, the maximum settlement also increased by 2.81%. Increasing the number of piles from 4 to 16 reduced the maximum settlement by 22.09% for a pile spacing of 4D. Moreover, increasing the pile length from 9 m to 15 m contributed to a 19.49% reduction in the total settlement for a pile spacing of 5D. Therefore, the current study provides a useful framework for analyzing and designing large piled-raft foundations.

Closed‐form solution for natural frequency of flexible combined pile‐raft foundation

AbstractDynamic attributes of flexible combined pile‐raft foundation (CPRF) hold paramount importance in assessing the behavior of it, especially in an earthquake prone area. The present study proposes a closed‐form solution for obtaining the natural frequency of flexible CPRF, where the piles and raft are represented as beam and thin plate respectively, lying on a two‐parameter Pasternak medium. Two simultaneous governing differential equations for the components are formulated and closed form solutions are obtained for finding the natural frequency and transient horizontal displacement of the foundation system. The complex soil‐structure interactions associated with the load‐bearing mechanism of CPRF is incorporated in the analysis scheme. The proposed method is validated with available centrifuge test result. Further parametric studies showcase that with decrease in raft thickness, the spectral acceleration response of the raft decreases. Also, for CPRF with high raft flexibility, the natural frequency of the foundation in dense sand is 34% and 53% higher compared to medium dense and loose sands, respectively. Thus, the present method can be reckoned as a notable contribution in comprehending the dynamic behavior of flexible CPRF.

Displacement-based finite element approach on analysing flexible combined pile–raft foundation in layered soil

The present study proposes a new finite element methodology to analyse the behaviour of flexible combined pile–raft foundation (CPRF) situated in layered soil, in a displacement-based framework. The soil medium is idealised as an advanced elastic Pasternak medium and the piles and raft are modelled as bar and plate element, respectively. The two components of CPRF are analysed simultaneously and displacement compatibility is satisfied at the pile–raft junctions. A number of soil–structure interaction factors, which govern the behaviour of CPRF, are suitably subsumed in the analysis scheme. The proposed method is validated with available analytical and experimental studies. Further parametric studies, investigating the effects of soil layering and raft flexibility on the behaviour of CPRF, are explored. It is observed that the load sharing proportion between the components and the raft deformation pattern depend upon the thickness and position of the soft soil layer in a multilayered soil system. The thickness of the flexible raft plays a pivotal role in determining the behaviour of CPRF, founded in a multilayered soil profile. Thus, this research manifests notable advancement in understanding the behaviour of flexible CPRF in layered soil.

A Parametric Study on Raft Foundation in Loose Sand Considering Soil Structure Interaction

Abstract. An extensive study is performed on the behavior of raft foundation considering soil structure interaction. The foundation is modelled using SAFE2016 software considering thick plate. A parametric study is carried out on raft foundation using finite element method considering static load condition. Several parameters, such as thickness of raft, modulus of subgrade reaction, load pattern, soil condition affect the soil-raft-structure response. The study revealed the analysis of the structure on raft foundation system considering the raft and soil properties. Displacement of raft foundation is decreased as increased in raft thickness. However, displacement of raft foundation is increased as decreased in subgrade modulus. Maximum soil pressure is decreased with increase in raft thickness. Soil pressure is increased with the increase of subgrade modulus. Punching shear ratio for raft foundation is decreased as increased in raft thickness. Punching shear ratio for raft foundation is decreased slightly as increase in subgrade modulus. Thickness of raft is important for designing raft foundation. The soil conditions are affecting the raft characteristics like deflection, soil pressure, punching shear. Increase of edge distances from the center of column decreases the upward soil pressure intensity.

Dynamic impedances of CPRF using coupled BEM-FEM approach: A parametric study and application

In this study, dynamic impedances of the Combined Piled Raft Foundation (CPRF) are calculated based on the coupled BEM-FEM approach. The piles, raft, and internal soil domain (near filed) are modelled with the finite element method (FEM). In contrast, truncated soil (far field) is modelled with the boundary element method (BEM). The piles and raft are perfectly bonded with the soil where rigorous pile-soil and raft-soil interaction conditions are imposed. The dynamic impedances are calculated under the horizontal, vertical, and rocking modes of vibration for the CPRF with 2 × 2 pile group. The parametric study is carried out for the CPRF to portray the influence of pile-soil stiffness, pile length, pile spacing, and raft thickness. In addition to the parametric study, the dynamic response of a Nuclear Power Plant (NPP) structure is carried out using the proposed spring-dashpot model. Results are compared with those obtained using FEM model. It can be concluded that the present model can simulate the seismic behavior of NPP under varying earthquake frequency and PGA with good accuracy.

Bearing Capacity of Footing on Soft Clay Strengthened by Lightweight Expanded Clay Aggregate Raft

This research represents an investigation into the effectiveness of replacement methods to increase the bearing capacity of soft clays under footing load, where Light Expanded Clay aggregates (LECA) were used as a substitute for common aggregate fillers. The soil replacement technique is the easiest and cheapest way to improve soft soil compared to installing a raft footing or using a deep foundation such as piles. LECA is known to be light, strong and environmentally sustainable and is widely used in Geotechnical applications where weight is an issue. The bearing capacity of the footing on soft soil reinforced by LECA was analysed through finite element analysis using commercial software PLAXIS 3D (2020). The soft ground is represented by Hardening Soil (HS) constitutive model, while LECA has been modelled as Mohr-Coulomb (MC). Parametric studies were conducted to assess the effect of LECA raft thickness to bearing capacity improvement for various friction angles of LECA. The research found that the bearing capacity is directly proportional to the internal friction angle of LECA and the LECA raft thickness. Nevertheless, the bearing capacity appears to be almost linear when 2.5 m and 3.5 m thick LECA rafts are used, indicating that the depth of replacement ratio more than 25% give insignificant effect towards improvement ratio.

The behavior of micropiled raft foundations subjected to combined vertical and lateral loading: numerical study

The micropiled raft offers a foundation system that combines the advantages of the conventional piled raft and the efficient installation of micropiles. In this paper, a comprehensive numerical analysis was conducted on the behavior of micropiled rafts under combined vertical and lateral loading using finite element modeling. A numerical model calibrated against full-scale axial and lateral field tests is used to conduct the analysis. The soil profile was soft clay soil underlain by a layer of dense sand. Numerous cases were analyzed to assess the lateral performance of micropiled rafts while considering several factors that may affect the performance, such as micropiles spacing, raft thickness, the magnitude of vertical loading, micropiles length, and their arrangement. The difference between the lateral performance of a primary micropiled raft and that of an existing raft enhanced by underpinning micropiles was also investigated. The lateral load capacity of the micropiled raft, the bending moment, and the shear force along the micropiles depth were estimated. Moreover, the load-sharing ratio between the micropiles and the raft was assessed. Based on the parametric study results, significant guidelines for choosing suitable micropiled raft configurations for initial design purposes were provided.

Comparative evaluation of Polygel Dual and commonly used alginate-antacid formulations (ACIDUAL Study)

Purpose: To compare Polygel Dual (PD) and four marketed alginate-antacid combination products, with respect to raft formation and antacid properties.
 Methods: The pharmacopeial tests used were selected based on demonstrable performance of raft-forming potential, including speed and thickness, for all selected products. Evidence-based methods were used to determine the antacid effects in terms of acid-neutralizing capacity and increase in pH.
 Results: Raft-forming ability was demonstrated by three products, with AF-4 and PD outperforming in speed and thickness. PD, AF-1 and AF-2 exhibited superior antacid properties. However, PD was the only product that demonstrated superior performance with respect to raft-formation and antacid potential. Raft-forming capacity was exhibited by 3 out of 5 products, viz, PD, AF-1 and AF-4. Raft formation was faster in AF-4 (15 s), followed by in PD (25 s). Similarly, raft thickness (14.79 mm) was highest in AF-4, followed by (4.39 mm) in PD. Preliminary antacid test results showed that AF-4 failed to raise pH above 3.5, but PD raised pH to 5.86, while AF-1 raised pH to 5.88. Similarly, periodic test analysis revealed that PD maintained pH above 7 for the entire test duration of 210 min, whereas AF-4 failed to raise pH to 7 during the test period.
 Conclusion: Polygel dual (PD) demonstrates desirable raft-forming potential and antacid properties. Moreover, it effectively raises pH and maintains it for longer duration than any of the other antacid products. Thus, PD may be considered a potentially effective treatment for acid-reflux problems. However, this claim should be validated in suitable clinical trials.

Effect of Seismic Analysis Approach and Provision of Shear Walls on Parameters for Raft Foundation Design

The present work attempts to understand the effect of different methods of seismic analysis on the design of building raft foundation. The study also evaluates the role of shear wall on the foundation response. A ten storey building with raft foundation has been analyzed in STAAD Pro using three different seismic analysis methods, viz., Linear static analysis, Linear dynamic analysis and Non-linear dynamic analysis. Furthermore, building with two different arrangements of shear walls (peripheral and core region) are studied by Non-linear dynamic analysis and compared with the model without shear wall. The raft is modeled with plate elements supported by soil springs using Winkler's approach. To consider the effect of different soil and raft stiffness, three different soil spring values and two raft thickness values have been considered. It has been concluded from the study that linear static analysis yields lower values of all foundation design parameters (viz., base pressure, settlement, foundation bending moment and shear stress) as compared to dynamic analysis. Dynamic analysis yields higher variation in base pressure and settlement distribution, which suggests adopting dynamic analysis approach for obtaining more realistic response, especially for settlement sensitive structures. Further the provision of shear wall has negligible influence on base pressure and settlement of foundation, while maximum bending moment and shear stress in foundation increases. Hence, provision of shear wall may increase cost of foundation, however, considering its role in improving structural integrity, shear walls are deemed important. Further, the increase in soil stiffness and reduction in raft thickness yields higher maximum base pressure and variation in base pressure, which confirms the importance of considering the effect of soil-foundation interaction for design of foundation. It is opined that the findings of the study would help in more realistic foundation design to achieve better performance during its life cycle.

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.

A parametric study of large piled raft foundations on clay soil

In the present study, three-dimensional numerical analyses have been conducted to understand the behavior of large piled rafts on stiff clay. The effects of pile number, pile spacing, pile length and loading intensity have been examined. For the same soil, the raft thickness is varied such that the its stiffness changes from flexible to intermediate flexible and to rigid. The load-settlement behavior, load-sharing ratio, raft bending moment and pile axial load distribution are presented and discussed in detail. For a higher pile number, locating piles over a larger central raft area is necessary for the effective reduction of differential settlement. For the intermediate flexible raft, addition of piles covering the maximum raft area is not beneficial in decreasing the differential settlement or the raft bending moment. With the intermediate flexible raft, decreasing the pile length can prove to be advantageous in removing hogging differential settlement. Based on the loading intensity and serviceability limit considerations, the appropriate pile configuration can be determined from the results of the parametric study in the cyclical sequence of firstly the selection of pile number, secondly the adjustment of pile spacing, and finally the reduction of pile length.

Long-term effect of vertical and lateral loads on piled raft foundations: a case study

In this study, numerical analyses of connected and disconnected piled-raft foundations (PRFs) comprising a single pile, 2 × 1, 3 × 1, 2 × 2, 3 × 2, 3 × 3 and 5 × 5 pile groups subjected to different lateral loads, with a constant vertical load, have been carried out by three-dimensional finite-element analysis. Results from the analysis have been validated with reported field studies considering vertical load and reported experimental studies considering lateral load. The reported multilayered sub-soil profile has been considered for the analysis. Parametric studies in terms of the effect of variation in pile length (L/d = 20, 30, 39), spacing of piles in the pile group (S/d = 3, 5, 6), number of piles, thickness of raft (0.5, 1.2 and 2 m), variation of axial force, excess pore water pressure, bending moment and shear force along the depth of the piles for connected and disconnected PRFs have been discussed for a time period of 20 years. The horizontal connected piled-raft coefficients have been determined corresponding to the lateral deflections. A generalised equation has been predicted for the horizontal connected PRF coefficient.

Effect of Soil Nonlinearity on Analysis of Raft Foundation

Abstract Soil supporting foundations behave in a nonlinear manner at loading close to its bearing capacity. This behavior affects soil pressure distribution and the corresponding stresses in the raft foundation, which differs significantly from considering the soil as elastic linear material. The present research uses the finite element method to study the effect of soil nonlinearity on the behavior of raft foundations subjected to concentrated loads. The analysis is based on the Winkler type of foundation. The analysis considered different values of the average soil pressure to its bearing capacity. The supporting soil was modeled as elastic perfectly plastic material. The effects of soil nonlinearity on the intensity and distribution of soil pressure, punching shear force, and bending moments in the raft are investigated. The effects of the foundation stiffness evaluation factor L·λ on the behavior of rectangular raft foundations were studied. This parameter combines the effects of the modulus of subgrade reaction, raft thickness, modulus of elasticity of concrete, and column spacing, as these parameters are interrelated. The results indicated that considering the subgrade soil as a linear elastic material underestimates punching shear and bending moments compared to modeling the soil as an elastoplastic material.

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.

Experimental Investigation of piled raft foundation on Cohesionless Soil

The combination of piles and raft foundation is known as piled raft foundation. Piled raft foundations have proven to be more cost-effective and capable of meeting safe bearing capacity and serviceability norms in the case of high-rise buildings on cohesionless soil. The behavior of a stacked raft foundation is influenced by the piles, raft, and soil. The stacked raft system’s bearing capacity is improved and settlement is minimized when the ground beneath the raft foundation bears the burden of supporting the applied loads. The piled raft foundation minimizes total settlement and improves bearing capacity more than the raft foundation. When isolated footings cover more than 70% of the building area under a superstructure, raft foundations are used, and the present study focuses on the vertical load bearing capability of piled raft foundation systems on cohesionless soil for concentric loading. The use of strategically positioned piles increases the load capacity of the raft while reducing differential settlement. The present study sheds some light on the use of piles as raft foundation settlement reducers, as well as the behavior of a piled raft in sand. A series of small-scale model experiments were carried out. The present investigation studies by varying pile length and alignment on the ultimate load of piled raft foundation. The results indicate that for a 10mm raft thickness, installing 4 piles, 6 piles, and 9 piles by varying L/D ratios of 5,10,15,20 carries significant load. In this present work for a 50mm length of pile, and the value of load improvement ratio increases by 36 percent, 60 percent, and 68 percent, respectively, when compared to plain raft.

Behavior of Raft Foundation Built on Layered Soil under Different Earthquake Excitation

Achieving the stability of buildings and facilities against any external influence, such as winds, storms, or earthquakes, depends primarily on the foundations supporting them, which are responsible for transferring those loads to the soil layers beneath them. Accordingly, the design of the foundations to be safe withstand these static and dynamic loads without causing dangers or failures on these structures has recently become the focus of the attention of many researchers. The task of this paper is to predict the behavior of shallow raft foundations supporting loads of structures under the influence of earthquakes in Baquba city and what results from them from downfall and displacement risks. To simulate the soil-foundation model for the study, numerical modeling was used depending finite element approach. Different thickness of raft foundation under different earthquake acceleration-time records that simulate with a Linear Elastic model (LE) built on layered soil represented by Mohr-Coulomb model (MC). The results from this analysis showed properties of soil are used for this study play a vital role in the ground response to the propagation waves. Also observed from the results that an increase in both lateral and vertical displacement as the duration of earthquake increases and raft thickness decreases, but these displacements decreased when the thickness of raft foundation increased from 0.8m to 1.6m are about 9% and 68%, respectively.

A Parametric Study of Piled Raft Foundation in Clay Subjected to Concentrated Loading

The use of piled raft foundation in building and infrastructure constructions is increasingly popular because of its effectiveness in reducing overall and differential settlements. Parameters influencing the performance of the piled raft foundation need to be comprehended in order to optimize the design of the piled raft system. Most of the current available literature focused on the piled raft foundation subjected to a uniform distributed load in sandy material. This parametric study aims to provide insights into the performance of the piled raft foundations subjected to concentrated loading in clay. A series of 2D finite element analyses were performed to investigate the influencing parameters affecting the load distribution and settlement behaviour of the piled raft. The results suggested that increases in both pile length and raft thickness, as well as a decrease in pile spacing would reduce the differential settlement of the piled raft. Comparatively, raft thickness was the most significant controlling parameter affecting the differential settlement. The study also revealed the importance of placing the pile nearer to the location of concentrated load as it would yield a more uniform load distribution, and hence a lower differential settlement.