Improvement In Bearing Capacity Research Articles

Stone column effectiveness in soils with creep: a numerical study

ABSTRACTWhile it is well established that vibro stone columns reduce primary settlement and improve bearing capacity, their effect on creep compression has largely been overlooked to date. However, with increasing pressure to develop marginal sites underlain by soft organic soils, the effect of ground treatment on creep is an important emerging issue in geotechnical engineering. In this paper, a series of axisymmetric unit cell analyses have been carried out using the PLAXIS 2D finite element program in conjunction with the Soft Soil Creep (SSC) model. Examination of the evolution of settlement improvement factor with time has indicated that the presence of creep leads to a lower ‘total’ improvement factor than would be obtained for primary consolidation settlement alone. Separate ‘primary’ and ‘creep’ improvement factors have also been derived; the latter are much lower than the former, but are nevertheless greater than unity. Creep results in a stress transfer process; as the soil creeps, vertical stress is transferred from the soil to the stone column. The additional load carried by the column induces additional yielding and shear-plane formation in closely-spaced columns. The additional increment of stress transferred to the already yielded column reduces its efficacy.

Tailoring of bonded composite scarf joint interface for impact damage mitigation and stiffness compatibility

A novel composite scarf joint is successfully fabricated with thermoplastic core shell microparticles incorporated into the interlaminar interface regions with a dual objective of mitigating the impact damage and improving the stiffness compatibility of the joint. The impact analysis of the joints revealed that the incorporation of microparticles led to a significant improvement of the impact load bearing capacity of joint and reduced the extent of the damage area. It is also observed from flexural tests that the microparticles reduces the stiffness of the laminate proportional to the weight fraction of the particles and thereby help design a joint adherend with controlled matching stiffness. This engineered scarf joint adherend configuration has the potential to minimise stiffness mismatch between a fatigue worn-out damaged composite part and the new scarf repair patch laminate designed for it. This shall help ensuring an easy restoration of uniform load distribution in the newly bonded composite scarf joints and repairs.

Bearing capacity of strip footing in reinforced granular bed over soft non-homogeneous ground stabilized with granular trench

This paper presents a method to estimate the bearing capacity of a strip footing embedded in a geosynthetic reinforced granular bed over soft non-homogeneous ground, i.e., increase of undrained shear strength with depth, stabilized with granular trench. Madhav and Vitkar’s solution for bearing capacity of granular trench-supported strip footing in soft ground together with Meyerhof’s punching failure mechanism for dense sand overlying soft clay, extended to include the effect of axial tension in the reinforcement, form the basis of the analysis. A parametric study is performed and charts are developed to quantify the contributions of various parameters on the degree of bearing capacity improvement. The results of the present study are compared with experimental results from literature.

Improvement in Bearing Capacity of a Soft Soil by Addition of Fly Ash

Soft soils are not suitable for use in runway and highway construction due to their undesirable characteristics such as poor grading, low strength, and excessive plasticity, tendency to shrink or swell. By stabilizing such soils with appropriate agents, their engineering properties can be improved. One of the stabilizing agents is Class C fly ash. The paper aimed to study the bearing capacity improvement of a soft soil (from Elmadağ area) by using Class C fly ash (from Soma Thermal Power Plant). In the experimental study, index properties of soft soil and fly ash stabilized samples are determined. Then modified Proctor compaction, soaked California Bearing Ratio, and Unconfined Compressive Strength characteristics of the samples are investigated. During the study, the stabilized soil samples are prepared at different fly ash contents, i.e., 0%, 3%, 5%, 7%, and 10%. The samples are subjected to soaked California Bearing Ratio tests after 0, 7, and 28 days of curing. In addition to California Bearing Ratio tests, Unconfined Compressive Strength tests with 0, 7, and 28 days of curing are performed. In order to observe microstructures of samples, Scanning Electron Microscope-Energy Dispersive X-ray analysis are performed. The results of the study show that bearing capacity of Elmadağ soft soil can be improved substantially and swell can be reduced significantly by using Class C fly ash.

Effect of shape on bearing capacity of embedded footings on reinforced foundation beds over soft non-homogeneous ground

The paper presents the effect of shape on bearing capacity of footings on reinforced foundation bed over soft non-homogeneous ground. The model considered for study consists of a two-layered system of granular fill over soft non-homogeneous ground with a single horizontal layer of geosynthetic reinforcement in the granular fill. Meyerhof’s punching mode of failure for footings on dense sand overlying soft homogeneous clay is extended to include the effects of non-homogeneity of soft ground and the axial resistance of the reinforcement to pullout. Shape of footing is an important parameter that influences the ultimate bearing capacity of ground/soil. Solutions are given for strip, square, circular and rectangular footings on both unreinforced as well as reinforced granular beds. A parametric study quantifies the contributions of various parameters on the improved bearing capacity of footings upon consideration of non-homogeneity, embedment and reinforcement. Predictions compare well with experimental results in literature.

Pengaruh Ukuran dan Kedalaman Geotekstil Teranyam Tipe HRX 200 terhadap Daya Dukung Ultimit dan Penurunan Tanah Lempung Lunak

Geotextile as one of improvement material in soft clay soil has been widely used. This study aims to examine the effect of geotextile dimention and placement depth on ultimate bearing capacity, settlement and Bearing Capacity Ratio of soft clay soil. This test was conducted on a series of square plate foundation loading of 10 cm width on clay soil sample and installing one layer of geotextile-improvement inside with several dimention variations and geotextile depth. Clay soil is on soft condition taken into a box model made of steel plate with the dimention of 120 cm x 120 cm x 100 cm. The result of this research shows that dimension and depth of geotextile affected the bearing capacity and settlement of soft clay soil. There were improvement in ultimate bearing capacity of as high as 3 times higher for geotextile 3Bx3B; 4 times higher for geotextile 4Bx4B; 5 times higher for geotextile 5Bx5B and 6 times higher for geotextile 6Bx6B comparing with bearing capacity of non supported-clay soil. Decreasing of settlement on clay soil was observed on the 3Bx3B improvement (twice lower), and 3 times lower, 4 times lower and 5 times lower for 4Bx4B, 5Bx5B, 6Bx6B, respectively. Geotextile which placed at a depth of 0.4 B and 0.8 B resulted in increased ultimate bearing capacity by 3.13 times. Dimension and depth geoxtile also affect the value of BCR. The highest BCR was on the dimention 6Bx6B on the depth of 0.6 B.

Study on stiffness and recoverability of Fiber Reinforced Polymers-Reinforced Concrete (FRP-RC) composite T-beams with prefabricated Basalt fiber-reinforced polymers shell

This paper focuses on the stiffness and recoverability of a new type of composite beam, the Fiber Reinforced Polymers-Reinforced Concrete (FRP-RC) beam, in which steel bars are the main reinforcement. Ten pieces of beams under both static and cyclic bending load were conducted. Fiber-reinforced polymer profile made by the vacuum infusion molding process is used as reinforcement in the composite beams, in which basalt fiber-reinforced polymer sheets were axially laid at the bottom of the beams in order to improve bearing capacity, and hoop-directionally laid at the lateral side of the beams with the advantages of improving the shear resistance. A finite element model is proposed to predict nonlinear deflections and stresses. The flexural stiffness and recoverability index of this new type of composite beam are studied. The results show that the recoverability of the FRP-RC composite beam is better than that of the normal RC beam and it increases along with the fiber-reinforced polymers reinforcement ratio. Stiffness calculation formulas at various stages and residual deformation formulas are proposed. Finally, the calculation results and test results are compared, which shows that the formulas for stiffness and deformation demonstrate good precision.

Piled Raft Design Strategies for High Rise Buildings

Piled rafts have been widely adopted as an effective foundation for designing high-rise buildings because of their efficiency in controlling the total and differential settlements and improving bearing capacity. In many cases the piled rafts settlements are likely to be large, which leads to an increase of the pile length and/or number of piles required to reduce the settlements. However, this increase does not satisfy the design requirements or an economical design. The majority of piled raft foundations has been designed with a uniform pile length and configuration. This paper describes the process of optimizing the design of a piled raft foundation for a high rise building in the Mazandaran province in Iran by considering an economical design methodology in which piles are placed more densely beneath the maximum load positions when the piled raft is subjected to non-uniform loads. By using the ELPLA software in the analysis process, the validity of the software is examined through the results of a report prepared on behalf of Technical Committee TC18 on piled foundations. The study shows that the pile arrangement method can help to considerably reduce the total and differential settlements with similar total pile length as well as the induced bending moments and shear forces of the raft. This study can help practicing engineers to choose pile and raft parameters with the pile arrangement method to produce an economical design.

Behavior and Soil–Structure Interaction of Pervious Concrete Ground-Improvement Piles under Lateral Loading

AbstractGranular column ground-improvement methods are widely used to improve bearing capacity and provide a drainage path. However, the behavior of granular columns depends on the confinement provided by the surrounding soil, which limits their use in poor soils. A new ground-improvement method is proposed using pervious concrete piles to provide high permeability while also providing higher stiffness and strength, which are independent of surrounding soil confinement. Building on prior research on the behavior of vertically loaded pervious concrete piles and granular columns, this paper investigates the behavior of laterally-loaded pervious concrete piles and the effects of installation on their response. Two fully-instrumented lateral load tests were conducted on a precast and cast-in-place pile using different installation methods. Advanced sensors measured the soil–structure interaction during installation and under lateral loading. Test results confirmed that laterally-loaded pervious concrete groun...

IMPROVEMENT OF BEARING CAPACITY OF SQUARE FOOTING ON COMPACTED POND ASH WITH REINFORCEMENT

Pond ash is waste by product which is producing in huge quantity by thermal power plants. The disposal of pond ash is the major problem to the environment. The way for disposing pond ash would be as a structural fill for low lying areas and used as embankment material. In this paper laboratory investigations are carried out to improve the bearing capacity of pond ash reinforced with geo-grid by conducting load tests in a model tank. The parameters varied during the tests were number of reinforcement layers and overlapping of reinforcement. The improvement of ultimate bearing capacity is observed. The ultimate bearing capacity ratios were evaluated.

The Behaviour of Confined Granular soil loaded by a square footing

This research involves the behaviour of confined granular soil supported by asquare footing. A series of bearing capacity tests were carried out on a small-scalelaboratory model, which filled with sand, placed in a dense state and confined withUPVC cell. The response of an unconfined state was measured in the beginning,and then compared with the confined sand. The studied variables included thecylinder height and diameter, the depth of the footing to the top of the cylinder andthe embedded depth of the footing.The test results indicated that the soil confinement resists lateral displacement ofsand underneath the footing, which is leading to a significant improvement for theresponse of the footing. The curves of load-settlement generally showed the sametrend in all the cases. Failure was considered as a settlement, which was equal to8% of the total footing width. Also, the recommended optimum cell height,diameter, footing depth to the top of the cylinder and the embedded depth offooting that give the maximum bearing capacity improvement were presented anddiscussed. According to the present research results, a conclusion based on the soilconfinement role and found to be notably increased the bearing capacity andstiffness. Furthermore, a modification of load–settlement behaviour of the subgrade sand was also gained.

IMPROVING THE LOAD CARRYING CAPACITY OF SQUARE FOOTING RESTING ON REINFORCED SAND

The rapid growth of the big cities in the vertical direction leads to essentially of strengthening of low bearing capacity areas as the cost of land is very high and also, the disposal of the plastic wastes such as plastic bottles, bags etc. is a big problem and environmental hazards in such areas. The waste plastic bottles as geotechnical material are used to solve both geotechnical and environmental problems. The laboratory investigations are carried out to evaluate the effect of waste plastic bottles as soil reinforcement for improving bearing capacity of soil. The bearing capacity of square footing on sandy soil reinforced with waste plastic water bottles for different L/D ratio, number of layers and for different densities of foundation soil is evaluated through model test. The increase in the bearing capacity with the provision of waste plastic bottle as reinforcement is observed.

Influence of backfill on coal pillar strength and floor bearing capacity in weak floor conditions in the Illinois Basin

This paper discusses the current theoretical design equations associated with foundation design in the Illinois Basin, as well as the benefits of utilizing high density backfill in a numerical model, to improve pillar and floor stability. Based upon the results, Vesic’s bearing capacity solution for a two layered soil tends to underestimate the true bearing capacity of a foundation, especially at higher friction angles and when footings are placed in close proximity. Minimizing the distance between adjacent foundations has shown an improvement in the ultimate bearing capacity of a foundation; however, placing the foundations in too close proximity has shown the foundations may behave as a single foundation and undergo appreciable settlement. A 10–40% increase in pillar strength and ultimate bearing capacity can be expected when a cohesive fill is used between 25 and 75% fill of the mined height, respectively. The non-cohesive nature of the simulated backfill showed little influence on increased pillar strength, even at higher fill ratios. It was determined, that as the shearing resistance, tensile strength and stiffness of the backfill are reduced, increases in coal pillar strength is due more to the confinement aspect of an underground mine rather than the strength properties of the material itself. A methodology for analyzing the plastic flow characteristics of a coal pillar and a footing using FLAC3D has also been presented herein.

Improvement of bearing capacity of footing on soft clay grouted with lime-silica fume mix

In this study, lime (L), silica fume (SF), and lime-silica fume (L-SF) mix have been used for stabilizing and considering their effects on the soft clay soil. The improvement technique adopted in this study includes improving the behaviour of a square footing over soft clay through grouting the clay with a slurry of lime-silica fume before and after installation of the footing. A grey-colored densified silica fume is used. Three percentages are used for lime (2%, 4% and 6%) and three percentages are used for silica fume (2.5%, 5%, 10%) and the optimum percentage of silica fume is mixed with the percentages of lime. Several tests are made to investigate the soil behaviour after adding the lime, and silica fume. For grouting the soft clay underneath and around the footing, a 60 ml needle was used as a liquid tank of the lime-silica fume mix. Slurried silica fume typically contains 40 to 60% silica fume by mass. Four categories were studied to stabilize soft clay before and after footing construction and for each category, the effectiveness of grouting was investigated; the effect of injection hole spacing and depth of grout was investigated too.It was found that when the soft clay underneath or around a footing is injected by a slurry of lime-silica fume, an increase in the bearing capacity in the range of (6.58-88)% is obtained. The footing bearing capacity increases with increase of depth of grouting holes around the footing area due to increase in L-SF grout. The grouting near the footing to a distance of 0.5 B is more effective than grouting at a distance of 1.0 B due to shape of shear failure of soft clay around the footing.

Load Settlement Behaviour of Sandy Soil Blended with Coarse Aggregate

The structures of every kind rest on the soil under laying them. The stability of these structures depends upon the load carrying capacity of the soil. The bearing capacity of soil also depends upon the quantum of coarser particles presents in it. The plate load test is used for the design of footing. Therefore, in the present investigation, the plate load tests were conducted to study the sand blended with coarse aggregate of various sizes and proportions. To strengthen the sub soil strata, coarse aggregates of 10mm and 20mm sizes were mixed in the sand in various proportions. The soil samples were prepared and tested first without mixing coarse aggregates, then by mixing coarse aggregates in varying percentages by weight starting from 5% to 30%. The plate load tests were conducted on 100mm, 150mm and 200mm diameters mild steel plates which indicates that with the increase in the size of the bearing plate, the bearing capacity of soil decreases (for plate settlement of 25 mm )and there is reduction in the footing settlement with the percentage increase of coarse aggregate. The improvement in the bearing capacity is represented by bearing capacity improvement factor (BCIF).The BCIF of 328 & 247; 307 & 293 and 174 & 185 were achieved with the inclusion of 10mm and 20mm coarse aggregates respectively for the said plate sizes.

The Effect of Geonet Reinforcement on Bearing Capacity of Low-Compacted Soft Clay

In this paper, we studied if geonets, when used for drainage purposes, can also contribute to the bearing capacity of clay. For this purpose, extensive laboratory testing and numerical modeling were performed on various configurations to investigate the effect of geonet on the bearing capacity of low-compacted soft clay. Physical models built with four footing shapes (square, rectangular, and two circular) along with several configurations of the reinforcement layout (i.e., number, length, spacing, and depth of reinforcement layers) were tested in the laboratory. Moreover, finite element modeling was performed and the results were compared with those obtained from the laboratory tests. It was found the geonet reinforcement can improve the bearing capacity of low-compacted clay up to six times more than its natural condition. The results showed that the optimum reinforcement length for the single-layer model is 3B (where B is the width of footing) and beyond this length, no significant improvement was observed. However, for the two-layer and three-layer models, the optimum length of reinforcements was found to be 2B. To maximize the benefit of the reinforcement, it was found that the first, second, and third reinforcement layers should be placed at the depths of B/3, B/2, and B, respectively. Among different footing shapes which were tested, the square footing showed the highest bearing capacity improvement with a bearing capacity ratio of 7.6. Very good agreement was observed upon comparison of the results from the numerical modeling with the experimental tests.

Optimization of molecularly thin lubricant to improve bearing capacity at the head-disk interface

A molecularly thin lubricant layer (of the order of 1---2 nm thick) has been shown to provide bearing forces at the interface between contacting solid surfaces under light loads and high shear rates. This phenomenon is important, for example, in the head-disk contact in magnetic storage hard disk drives to ensure that some of the contact is sustained by the lubricant layer and thus avoiding damage of the solid surfaces. The magnitude of the normal and tangential bearing forces that the lubricant layer can provide depends on temperature, viscosity of the lubricant, sliding velocity and radius of gyration of the lubricant molecules. This study shows that viscosity has the greatest effect on the load bearing capacity of the molecularly thin lubricant. Thus, by controlling the flash temperature and the ratio of molecularly thin lubricant-to-bulk viscosity, the bearing load carrying capacity of the layer can be controlled. This would allow for the contact to be sustained within the mobile lubricant layer, avoiding solid contact so as to protect the diamond-like carbon coating, and thus reduce wear and potential catastrophic failures.

Bearing Capacity of Strip Footing on Reinforced Foundation Bed over Soft Ground with Granular Trench

The paper presents a method for the estimation of bearing capacity of a strip footing resting on a reinforced foundation bed over soft ground stabilized with a granular trench. Meyerhof’s two-layered punching failure mechanism along with Madhav and Vitkar’s solution for bearing capacity of granular trench supported footing resting on soft ground, form the basis of the analysis. The bearing capacity of a strip footing in a two-layered system of reinforced granular fill overlying soft ground stabilized with granular trench is estimated by incorporating the contribution from the axial tension mobilized in the reinforcement to those from the granular fill and the stabilized soft ground. A parametric study quantifies the effect of various parameters on the degree of bearing capacity improvement. The predictions are compared with experimental studies available in literature. The percentage improvement in the bearing capacity of the strip footing due to reinforcement of the soft ground with a granular trench coupled with unreinforced and reinforced granular fill is established through the comparisons.

Microstructural refinement and wear property of Al–Si–Cu composite subjected to extrusion and high-pressure torsion

Abstract The effect of high-pressure torsion (HPT) on the microstructure and the mechanical properties, especially the wear properties, of an Al–Si–Cu alloy (represented by Al–15%Si–2.5%Cu–0.5%Mg) and its composite, which was reinforced by SiC particles (SiCp) at a volume fraction of 5%, was investigated systematically in this study. The Al–Si–Cu/SiCp composite is produced in a powder metallurgy process followed by hot extrusion (EXTR) at 565 °C. The EXTR specimen is also subjected to HPT processing at an anvil rotation speed of 0.5 rpm under a quasi-hydrostatic pressure of 5 GPa. HPT processing leads to a nanostructured microstructure comprised of equiaxed α-Al grains (60–70 nm) and secondary particles and phases; the SiCp with a damaged facet, the phase exhibiting high Mg content and the intermetallic CuAl2 phase, for the Al–Si–Cu/SiCp composite. The values of the tensile strengths and hardness of the HPT specimens are nearly twice higher than those of the EXTR specimens for the Al–Si–Cu alloy and the Al–Si–Cu/SiCp composite. Ball-on-disc tests were used to examine the wear resistance of the processed materials. The wear test results indicated that HPT processing significantly reduces the wear loss, thereby leading to improvement in the load bearing capacity and the wear resistance of the Al–Si–Cu alloy and the Al–Si–Cu/SiCp composite. This behavior is linked to HPT processing, based on the refined and homogenous microstructure that results in an increase in the hardness.

Parametric Analysis of Seismic Performance of RC Columns Strengthened with Steel Wire Mesh

By establishing a finite element (FE) model of reinforced concrete (RC) columns strengthened with steel wire mesh, the mechanical properties under low-cyclic loading are analyzed, and the correctness of the FE model is verified. Hysteretic curves, skeleton curves, strain curves, and changes in stiffness and ductility of the strengthened RC columns under various strengthening conditions are calculated in this study by using the FE model to examine the effects of axial compression ratio, longitudinal reinforcement ratio, concrete strength, steel wire quantity, and eccentric compression on the seismic behavior of the strengthened columns. The results show that an increase in axial compression ratio results in an improvement in the ultimate bearing capacity of the strengthened columns by 9%-17% and a reduction in ductility by 9%-15%. In addition, increases in the stirrup ratio, longitudinal reinforcement ratio, concrete strength, and steel wire quantity result in improvement in ultimate bearing capacity, and ductility of the strengthened columns can be improved by 2%-28%. Moreover, an increase in vertical pressure results in rapid development of eccentric, stirrup, and steel wire strains in the strengthened columns, which causes reductions in ultimate bearing capacity in the columns by 2%-13%, energy consumption by 35%, and additional reductions in stiffness and ductility.