Load-settlement Behavior Research Articles

Experimental and Numerical Modeling of Connected and Disconnected Piled Raft

Piled raft foundations, wherein a small number of connected piles are utilized as settlement reducers, have been widely used for high-rise buildings. Recently, a new technique has been introduced by disconnecting the piles from the raft and inserting a cushion layer between them. In such cases, the piles are considered as soil reinforcement components rather than structural members. To explore the feasibility of utilizing the disconnected piled raft foundation, a series of experimental model tests were conducted to examine the load–settlement behavior and pile load sharing ratio of the connected piled raft (CPR) and disconnected piled raft (DCPR) foundation systems using cushions of different thicknesses and stiffnesses. In addition, ABAQUS 3D finite element analyses were performed to analyze the axial stress along the piles and the bending moments along the raft. The results indicated that the total settlement of the system was minimized significantly when disconnected piles were used. In addition, the disconnected technique provided a significant reduction in the axial stress along the piles and the bending moment along the raft compared with that of the CPR. These findings may be accompanied by economic and environmental benefits.

Numerical Analysis of a Dual-Layer Geosynthetic-Encased Stone Column Installed in Soft Soil

Stone columns are being used to reduce soft soil settlement and increase load-carrying capacity. Since there is inadequate lateral support from the local native soil, soft soil undergoes excessive settlement under vertical loading. This issue is effectively resolved by suitably encasing stone column material by geosynthetic with significant axial stiffness, which provides the required additional confinement reported in the literature. In the current study, an effort has been made to examine the load settlement behaviour of the dual-layered geosynthetic-encased stone column (DL-GESC) under vertical loading. In order to simulate the behaviour of stone column-reinforced soft soil, a FEM analysis was performed using PLAXIS-3D and three-dimensional (3D) models made utilising the unit cell idealisation technique for a single column. The stone column diameter, spacing to diameter (s/d) ratio, and encasement layers were varied to determine their influence on load-settling behaviour. The vertical load-carrying capacity of the ground was significantly improved when an additional layer of geosynthetic encasement was inserted into the stone column as compared to SL-GESC. Improvement of 15–25% was observed for the analysis of a single column installed in soft clay, according to the result obtained. Improvement ratios have been discussed in detail for various encasement conditions.

Experimental and numerical study of the settlement behavior of soil reinforced by stone columns

Purpose The paper aims to present an experimental and numerical investigation of the load–settlement behavior of soil reinforced by stone column, as well as to evaluate the plane strain unit cell model for the analysis of stone columns. Design/methodology/approach The numerical analysis was done using both axisymmetric and plane strain models. The elastic perfectly plastic behavior of Mohr–Coulomb was adopted for both soil and column material. The numerical results of this study were validated by the comparison with the in-situ measurements of a full-scale loading test on a stone column. This study also evaluated the effect of different parameters involved in the design of a stone column, including Young’s modulus of the column material, column diameter, spacing between the stone columns and Poisson’s ratio of the column material. Findings After the numerical simulation, the results from both axisymmetric and plane strain models are quite comparable. In addition, the numerical results revealed that the stone column with low spacing, a large diameter and a high Young’s modulus indicated better behavior against the settlement. Originality/value The axisymmetric unit cell model was used in many numerical studies on the behavior of stone columns. In the present work, a field load test on stone column was simulated using a plane strain unit cell model. This research adds that the plane strain unit cell model can be used to predict the settlement of reinforced soil with stone columns.

Experimental Study on the Behavior of Square-Skirted Foundation Rested on Gypseous soil Under Inclined Load

This work investigates experimentally the effect of using a skirt with a square foundation of 100 mm width resting on dry gypseous soil (i.e., loose soil with 33% relative density), and subjected to an inclined load. Previous works did not study the use square skirted foundation rested on gypseous soil and subjected to inclined load. The investigated soil was brought from Tikrit city with 59% gypsum content. Standard physical and chemical tests on selected soil were carried out. Model laboratory tests were carried out to determine the effect of using a skirt with a square foundation on the load-settlement behavior of gypseous soil and subjected to inclined load with various Skirt depth (Ds) to foundation width (B) ratio Ds/B (0,0.5,1, and1.5). The results show that using a skirt with a square foundation improves load-carrying capacity and reduces settlement of foundation rested on loose gypseous soil and the amount of improvement increase with increasing skirt depth to foundation width Ds/B. Bearing capacity improved by about (193) %, and Settlement ratio (Sᵣ) reduced from (1) % for square foundation without a skirt to (0.14) at Ds/B, equal to 1.5 at θ =0° with the y-axis (Where θ is the inclination angle of the applied load); and bearing capacity improved by about (162) % for the square skirted foundation with Ds/B, equal to 1.5 and θ =15° with the y-axis.

Predicting and validating the load-settlement behavior of large-scale geosynthetic-reinforced soil abutments using hybrid intelligent modeling

Settlement prediction of geosynthetic-reinforced soil (GRS) abutments under service loading conditions is an arduous and challenging task for practicing geotechnical/civil engineers. Hence, in this paper, a novel hybrid artificial intelligence (AI)-based model was developed by the combination of artificial neural network (ANN) and Harris hawks’ optimisation (HHO), that is, ANN-HHO, to predict the settlement of the GRS abutments. Five other robust intelligent models such as support vector regression (SVR), Gaussian process regression (GPR), relevance vector machine (RVM), sequential minimal optimisation regression (SMOR), and least-median square regression (LMSR) were constructed and compared to the ANN-HHO model. The predictive strength, relalibility and robustness of the model were evaluated based on rigorous statistical testing, ranking criteria, multi-criteria approach, uncertainity analysis and sensitivity analysis (SA). Moreover, the predictive veracity of the model was also substantiated against several large-scale independent experimental studies on GRS abutments reported in the scientific literature. The acquired findings demonstrated that the ANN-HHO model predicted the settlement of GRS abutments with reasonable accuracy and yielded superior performance in comparison to counterpart models. Therefore, it becomes one of predictive tools employed by geotechnical/civil engineers in preliminary decision-making when investigating the in-service performance of GRS abutments. Finally, the model has been converted into a simple mathematical formulation for easy hand calculations, and it is proved cost-effective and less time-consuming in comparison to experimental tests and numerical simulations.

Suction Influence on Load-Settlement Curves Predicted by DMT in a Collapsible Sandy Soil.

The plate load test (PLT) is the most reliable in situ testing for studying the load-settlement behaviour of footings on unsaturated collapsible soils. In these soils, the suction profile is not constant along the depth, and the scale effect between the prototype and footing leads to different suction averages and, consequently, different data. One method to eliminate the effect of soil suction on the test data is to fully saturate the soil prior to the test, which is also recommended at the design process for footing on collapsible soils. However, the inundation process on PLTs is expensive and time-consuming, which makes this procedure difficult to incorporate into engineering practice. This study presents a device that can be attached to flat dilatometer (DMT) to allow local inundation of the soil as part of the in situ test campaign and obtain the DMT-constrained modulus (MDMT) for both natural and inundated conditions. The MDMT presented an average reduction of 56% from natural to inundated condition. This parameter can be used in a model to predict load-settlement curves by DMT data considering the suction influence on this behaviour. The curves obtained from the prediction model were compared to curves determined by PLT conducted under the same in situ conditions. Good agreement was found between the curves predicted by DMT and those measured by PLT for both conditions. The proposed procedure, which uses a device attached to the DMT blade, provides an investigation method to obtain the load-settlement curve under different suction conditions, which can help in the selection and performance prediction of shallow foundations, taking into account suction and collapse phenomenon-related problems.

Experimental Study for Load-Settlement Behavior of Flat and Shell Footings on Sandy Silt Soil

Shell foundations are often used to raise the carrying capacity of a structure on weak soils. In cases where large superstructure loads must be transferred to poorer soils, shell foundations are more cost-effective than ordinary shallow foundations. Advances in the study and design of shell-type foundations have shown their superiority over traditional footings in poorer soils. The current study aims to investigate shell shape’s influence on ultimate load capacity. Seven footing types’ models were created along with an appropriate testing box. The soil needed for the study was from the region north of Mosul city, classified as silt with low plasticity (sandy silt) soil. A laboratory model experimentally determined the ultimate load capacities for inverted and upright conical, inverted and upright pyramid, and hemispherical shell foundations on silty soil. The achieved results were associated with those for conventional flat squares and circles. According to the findings, the “upright conical” shell footing has a load capacity of 12.7 kN, higher than the other foundations, and its efficiency was 51%. When comparing foundations, the “upright pyramidal” shell footing has better settling characteristics and a settlement factor of 0.017. As the shell factor decreases, the shell foundation begins to behave more like a flat foundation, which reduces the maximum load capacity of the shell foundation.

Comparative Study on Ground Improved by Stone Columns and Ground Improved by Hybrid Concrete Columns

This paper provides a detailed discussion and comparison of two deep ground improvement techniques, stone columns and hybrid concrete columns (HCC’s), in terms of design, construction procedure and performance, through a case history from a recent petrochemical project in Malaysia. Two full-scale group load tests (GLT’s) were conducted on test columns constructed prior to construction of production columns and used to calibrate the analytical models adopted for the design of stone columns and HCC’s. The ground improved by HCC’s shows a stiffer load-settlement behavior compared to the ground improved by stone columns as predicted by analytical models. In addition, the time-dependent settlement is more obvious in the stone column improved ground than in the HCC improved ground. Stone columns may act as a drainage path helping expulsion of pore water as the applied load increases whereas concrete columns transfer the load to the surrounding soils through the load transfer at the interface between a concrete column and the surrounding soil. The results of all four GLT’s on production columns confirm that the settlement predictions with the calibrated analytical models are satisfactory. This paper also summarizes the key calibration techniques adopted at the project site for quality control during construction. These calibration techniques can be considered as a useful guide for other project sites with similar ground improvement methods proposed in similar ground conditions.

Behavioural Assessment on Influence of Adjacently Placed Strip Footings at Different Embedment Level

Abstract The footings laid in close proximity imposes a definite change in the behaviour of the adjacent footing, subsequently changing the behaviour of the nearby footings. The present study emphasises the behaviour of the nearby strip footings embedded at a different level by adopting the commercially available finite element analysis program, ABAQUS. The load-settlement behaviour, ultimate bearing capacity (UBC), and the failure patterns of adjacent strip footings are assessed by considering the Mohr-Coulomb failure criterion. The UBC is of the nearby footings (left and right) are estimated and represented in terms of interference factors (ξL/ξR ) defined as the UBC of a footing in the presence of adjacent footing to that of same considered for equivalent isolated footing. The results reveal that a significant influence of the adjacent footing is experienced when the spacing between the footings (S/B) is lesser, and they behave as the single footing of greater width at S/B = 0.25 irrespective of the level of embedment depth. Furthermore, the influence of interference increases with the increase in the embedment depth of adjacent footing. It is found that the ξL is significantly more for a lower level of embedment depth, and the same increases with an increase in the embedment depth of the right footing but on the contrary ξR decreases. The increase in the peak interference factor, ξL-max for DL/B = 0.5 is 2.1% and 4.2% when DR/B = 0.75 and DR/B = 1.0, respectively.

Load–settlement behaviour of membrane-confined grouted pile: experimental and analytical study

Load–settlement behaviour of membrane-confined grouted pile: experimental and analytical study

A Semi-empirical Method for Studying Load-Settlement Behavior of Geocell-Reinforced Footings

A Semi-empirical Method for Studying Load-Settlement Behavior of Geocell-Reinforced Footings

Utilization of Shredded Waste Tire as a Substitute for Gravel in Stone Column Groups

The present study investigates the load-carrying capacity response of gravel-shredded tire stone column groups as a strategy for strength improvement in loose soils. The experimental study was conducted using large-scale oedometer tests on the stone column groups of gravel and gravel-shredded tire mixtures of different tire content, arrays, and spacings. Also, the efficacy of shredded tire addition on the stone column group bearing behavior was explored using the unit cell concept. To this aim, the entire area of the unit cell was loaded to determine the stiffness of the improved bed soil while applying load directly on single stone columns was done to evaluate the load-carrying capacity of the reinforcing elements. The results demonstrate enhancements in the load-settlement behavior of the stone column groups in mixtures containing 20% of the shredded tire, while further tire addition can adversely affect it. Additionally, adding an optimum shredded tire to the stone column materials leads to an increase in stiffness (Young's Modulus) of the bed soil. This behavior is directly correlated with the created friction angle and area ratio (A/AS) of different arrangements of the stone column groups.

Effect of Foundation Shape on Settlement by Numerical Method

Five prototypes arranged in three different soil conditions is presented to find out the load-settlement relationship of soil and foundation. For creating three types of condition two types of managed soils are stiff clay and soft clay. The five prototypes used here represent the condition of shallow foundation. Prototypes area being same for cases has the shape of Triangular, Square, Rectangular, Pentagonal and Hexagonal. The load-settlement behavior has been found out plan-wise using Plaxis 3D software. Geotechnical engineering software which uses finite element method and Mohr-Coulomb failure criterion following mathematical differential equational problems. Plaxis 3D software uses the properties of soil cohesion, angle of internal friction, Elasticity modulus and unit weight, elasticity modulus of the foundation to settle a relation for the interaction between soil and foundation. Load-settlement behavior for the five prototypes as tried to be found out by Plaxis 3D has represented the immediate settlement of soil on which the prototypes have been rested. The graphs also help to understand the difference in the bearing capacity and settlement for the five prototypes, each of which acted as foundations. Pressure bulb is an effect of vertical pressure which differs from shape to shape of foundation. It directly affects the intensity of pressure and the intensity of pressure affects the settlement. The bearing capacity also affects the settlement. A triangular foundation has the best bearing capacity as its settlement is the lowest. But as a triangular shaped foundation is not practically used and not ideal it is not used for structural work. This study shows that square or rectangular foundation is best for a structure due to higher bearing capacity and lesser settlement compared to the same of pentagonal and hexagonal shaped foundation. But if comparison is done between square and rectangular shaped foundation, square is the best.

Failure Mechanism Analysis of Reinforced Foundation from Experimental and Numerical Simulations

Geogrid has been extensively used in engineering practice as a horizontal reinforcing material to improve the performance of foundations, embankments, and road base systems. This paper presented the results of laboratory static load tests on transparent soil foundations reinforced with biaxial polylactic acid geogrid and studied the reinforcement mechanism and foundation failure mode of the reinforced foundation. The different load settlement behaviour between reinforced foundations with different reinforcement layer numbers was studied by varying the number of geogrid layers. The deformation of reinforcements and foundation soil was recorded with an industrial camera. The strain of the reinforcements was monitored by Fiber Bragg Grating (FBG) sensors. In addition, a two-dimensional discrete element model was established based on the model tests to analyse the load transfer behaviour and deformation law of the reinforced foundation. The results indicated that geogrid can effectively improve the bearing capacity of the foundation. As the number of reinforcement layers increases, the improving effect is more significant. The reinforced soil can provide a stronger upward resistance than unreinforced soil by activating the tensile force of the geogrid. The simulation results present the load transfer behaviour and reinforcement mechanism of geogrid. With the increase of reinforcement layers, the position of the sliding surface moves downward, and the area of the sliding surface increases. Geogrid can limit soil displacement and delay the development of the sliding surface.

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.

Dissolution load-settlement behaviour of saline soil and compression criterion for the natural foundation of high-speed railways

Dissolution load-settlement behaviour of saline soil and compression criterion for the natural foundation of high-speed railways

Structural analysis of piled raft foundation in soft soil: An experimental simulation and parametric study with numerical method

The high infrastructural demand and the unavailability of proper foundation soil have increased the evolution of combined piled raft foundation (CPRF) in the current generation. The use of CPRF in soft soils has increased immensely in the last few decades. But there is a lack of laboratory experiments to understand the behaviour of CPRF in soft/clayey soil, and hence, this study considers an innovative approach to understand different behaviour of CPRF using clayey soil through laboratory experiments. Two different types of small-scaled CPRF models are prepared with 2 × 2 and 3 × 3 pile groups, and the spacing among the piles as well as the thickness of clayey soil are also altered. Several aspects are studied through the experiments such as load-settlement behaviour, load improvement ratio, behaviour of piles in CPRF, load sharing behaviour, axial forces, raft-soil contact behaviour, bending moment in the raft, etc. Based on the experimental test results, a numerical model is also prepared, and then a parametric study is performed numerically considering a 10-storey residential building. The effect of different pile lengths in CPRF is also checked and the parametric study is conducted with several types of pile arrangements.

Modified Interaction Method for Response of Group Piles Considering Pile–Soil Slip

The existing model for calculating the settlements of group piles is based on the principle of superposition, which fails to calculate the interaction between piles more comprehensively and to take into consideration the influence of slip between pile and soil. In this paper, the interaction between group piles is analyzed from a novel perspective. It is assumed that the interaction between piles is a dynamic equilibrium process, i.e., additional shear forces and additional displacements are continuously transferred between piles until a state of equilibrium is reached. On this basis, we propose a new model for calculating the settlements of group piles considering pile–soil slip. First, a calculation method for pile–side resistance is developed considering the influence of slip. Based on experience with the pile–soil interface, pile–side soils can be categorized as near–pile soil and far–pile soil, and different load–transfer models are applied to describe their mechanical states. By equating pile–side soils into a nonlinear spring and connecting them in series to determine the overall equivalent stiffness considering the effect of pile–soil slip, the pile–side resistance under different loading conditions can be accurately determined. Secondly, equilibrium analysis of the pile unit is carried out when the equilibrium condition is reached, and the stiffness matrix for load transfer is derived. Therefore, in this paper, the interaction between piles is concentrated in this matrix, which makes the proposed model for pile settlement calculation clearer and more concise. Compared with measured data, the proposed method can capture the main features of the load–settlement behavior of group piles.

Impact of eccentricity and depth-to-breadth ratio on the behavior of skirt foundation rested on dry gypseous soil

AbstractGypseous soils are considered one of the most problematic soils. The skirted foundation is an alternative technology that works to improve the bearing capacity and reduce settlement. This paper investigates the use of square skirted foundations resting on gypseous soil subjected to concentric and eccentric vertical load with eccentricity values of 4, 8, and 17 mm in 16 experimental model tests. To obtain the results by using this type of foundation, a small-scale physical model was designed to obtain the load–settlement behavior of the square skirted foundation; the dimension of the square footing is 100 mm × 100 mm with 1 mm thickness, the skirt depth (Ds) was 0.5, 1, and 1.5B(whereBis the footing width). The footing rests on dry gypseous soil with a relative density of 33%. The tests show that the gypsum content of the soil is 59%. The result shows that the highest bearing capacity for the square shape footing withDs/B= 1.5 subjected to concentric load results in an improvement ratio of 190%. For the eccentric load, withDs/B = 1.5, the increase in bearing capacity is about 120% ate= 8 mm when compared with using a foundation without a skirt.

Analysis on Response of a Single Pile Subjected to Tension Load Considering Excavation Effects

With the development of urbanization, numerous excavations are carried out to facilitate the development of underground space. As a support for tunnel structures, uplift piles are often installed prior to tunnel excavation. The excavation inevitably causes disturbance to the soil below the excavation surface, changing the soil’s mechanical behavior and stress state significantly. However, there is still a lack of a method to evaluate the change in pile capacity due to excavation. This paper proposes a semi-analytical approach for estimating the change in load-settlement behavior of an uplift pile considering the effects of excavation. A hyperbolic model was adopted to simulate the nonlinear interaction of the pile–soil interface. The nonlinear shear-induced soil displacement outside the pile–soil interface is introduced to obtain a more realistic load-displacement behavior of the uplift pile. An effective iterative program was implemented based on the proposed semi-analytical approach. The comparisons between the results from the proposed methods, well-documented field tests, centrifuge tests, and other analytical methods showed that the proposed approach is suitable for analyzing an uplift pile considering excavation effects. A parametric study was conducted to investigate the effects of main soil properties on the pile capacity loss caused by excavation. The results showed that the soil friction angle and the ratio of the excavation depth to the pile effective length have a great influence on the loss in pile uplift capacity caused by excavation. However, the loss of pile uplift capacity caused by excavation is not affected by the soil’s shear modulus or Poisson’s ratio.