Improvement In Bearing Capacity Research Articles

Bearing capacity improvement of anisotropic sand ground

Bearing capacity of anisotropic sand beds beneath structures subjected to monotonic and cyclic loadings was experimentally elucidated. Using a model ground of Toyoura sand prepared by the air-pluviation method, a series of loading tests on model structures under several foundation conditions was carried out. Firstly, the effect of fabric anisotropy on bearing capacity and its mobilisation mechanism was revealed, and secondly the applicability of countermeasures constructed by side walls and sheet piles on the bearing capacity was investigated on sand deposits with fabric anisotropy. The test results showed that fabric anisotropy of sand deposits affects the bearing capacity remarkably under monotonic and cyclic loading conditions, and that constructions of side wall and sheet piles are advantageous as countermeasures against ground failures, although their prevention effects on bearing capacity vary with the changes in depositional conditions.

Experimental investigations on ultimate bearing capacity of peat stabilized by a group of soil–cement column: a comparative study

The aim of this paper was to determine the ultimate vertical bearing capacity of rectangular rigid footings resting on homogeneous peat stabilized by a group of cement deep mixing (CDM) columns. For this purpose, a series of physical modeling tests involving end-bearing and floating CDM columns were performed. Three length/depth ratios of 0.25, 0.5, and 0.75 and three area improvement ratios of 13.1, 19.6, and 26.2 % were considered. Bearing capacity of the footings was studied using different analytical procedures. The results indicated that compared to unimproved peat, the average ultimate bearing capacity (UBC) improvement of floating and end-bearing CDM columns were 60 and 223 %, respectively. The current study found that simple Brom’s method predicted the UBC of the peat stabilized with floating CDM columns with reasonable accuracy, but underestimated the UBC by up to 25 % in the case of end-bearing CDM columns. Published laboratory experiences of stabilizing soft soils using soil–cement columns were also collated in this paper.

Stabilization of an expansive overconsolidated clay using hydraulic binders

Urban areas of the wilaya of M’sila in Algeria nowadays experience a considerable development because of an unceasingly increasing demography, from where its extension toward virgin zones is often less favorable than those already urbanized. This wilaya is located in a zone classified as semi-arid, whose geology comprises clayey formations characterized by a high variation of volume when the conditions of their equilibrium are modified (natural climatic phenomena due to a prolonged dryness, human activity by modification of the ground water level because of excessive pumping, configuration of constructions in their environment). This paper presents and analyzes the results of a series of laboratory tests (identification, compaction, penetration and direct shear tests) performed on an expansive overconsolidated clay obtained from an urban site situated in Sidi-Hadjrès city (wilaya of M’sila, Algeria), where significant damages frequently appear in the road infrastructures and in the light structures. Test results obtained show that the geotechnical parameteric values deduced from these tests are concordant and confirm the bearing capacity improvement of this natural clay treated with hydraulic binders (composed Portland cement and extinct lime) and compacted under the optimum Proctor conditions, which is translated by a significant increase in soil strength and its durability.

Cement and lime mixture stabilization of an expansive overconsolidated clay

Urban areas of the wilaya of M'sila in Algeria nowadays experience a considerable development because of an unceasingly increasing demography, from where its extension towards virgin zones often less favorable than those already urbanized. This wilaya is located in a zone classified as semi-arid, whose geology comprises clayey formations characterized by a high variation of volume when the conditions of their equilibrium are modified (natural climatic phenomena due to a prolonged dryness, human activity by modification of the ground water level because of excessive pumping, configuration of constructions in their environment). This paper presents and analyzes the results of a series of normal Proctor compaction tests, methylene blue tests, California bearing ratio tests and undrained direct shear tests performed on Sidi-Hadjrès expansive overconsolidated clay treated with mixture of various cement and lime contents and compacted under the optimum Proctor conditions. These test results show that the geotechnical parameters values are concordant and confirm the bearing capacity improvement of this natural clay, which is translated by a significant increase in soil strength and its durability. However, the best performances are obtained for a mixt treatment corresponding to 8% cement and 4% lime contents.

Limit Analysis Optimization of Design Factors for Mechanically Stabilized Earth Wall-Supported Footings

Increasingly in the past few decades, mechanically stabilized earth (MSE) walls have been a common choice for earth retention solutions due to their ease of construction, cost-effective design, and flexibility. However, limit state capacity of footings atop a MSE structure, such as a bridge abutment, is a complex and non-intuitive stability problem dependent on factors like reinforcement layout and strength, location of footing, and failure mechanism. In order to evaluate the effects of these factors, a parametric study was performed utilizing a robust tool in the framework of limit analysis of plasticity. It demonstrates the effect of the parameters on bearing capacity and optimized reinforcement efficiency, all in context of an existing MSE wall-supported bridge abutment. It is shown that closely spaced reinforcement layouts allow for more efficient reinforcement behavior and improved bearing capacity nearer to the wall facing, while inverse, detrimental trends were observed for wider reinforcement spacing. The implications of this analysis illustrate that an optimized approach involving footing location, reinforcement strength, and reinforcement spacing allow for reduced bridge deck length requirements. This clearly has economic consequences. The optimization of these design factors is especially applicable to MSE wall-supported bridge abutments since the location of the footing affects expensive elements such as length of girders. Fundamentally, this work adds to the limited existing knowledge of bearing capacity of footings on top of MSE walls.

Numerical Simulation Study of Concrete Beam with Bonding Steel Plates Bending Failure

In the sphere of the consolidating technique of the engineering structure the new and developing theory of the steel adhered reinforcement has gradually applied to the practical engineering. Reinforcement steel structural adhesive is a method using steel plate pasting on the component surface to improve bearing capacity of the structure, which is widely used in reinforced concrete bending, eccentric compression and tension reinforcement. In this paper, based on continuum damage theory and statistical strength theory, Starting from each phase of the concrete, medium micro softening plasticity and strain of non-uniform, Numerical simulation of steel bonded reinforcement bending failure of concrete beam was carried out and Analysis of the crack propagation and failure form were put forward. Based on FEM analysis, the size of material and binder were selected reasonably, ensuring the safety and durability of concrete beams, provide technical support for the practical engineering as well.

Bearing capacity of geotextile-reinforced sand with varying fine fraction

Use of geotextile as reinforcement material to improve the weak soil is a popular method these days. Tensile strength of geotextile and the soil-geotextile interaction are the major factors which influence the improvement of the soil. Change in fine content within the sand can change the interface behavior between soil and geotextile. In the present paper, the bearing capacity of unreinforced and geotextile-reinforced sand with different percentages of fines has been studied. A series of model tests have been carried out and the load settlement curves are obtained. The ultimate load carrying capacity of unreinforced and reinforced sand with different percentages of fines is compared. The interface behavior of sand and geotextile with various percentages of fines is also studied. It is observed that sand having around 5% of fine is suitable or permissible for bearing capacity improvement due to the application of geosynthetic reinforcement. The effectiveness of the reinforcement in load carrying capacity improvement decreases due to the addition of excessive amount of fines.

Soil Stabilization Using Waste Shredded Rubber Tyre Chips

Construction of engineering structures on weak or soft soil is considered as unsafe. Improvement of load bearing capacity of the soil may be undertaken by a variety of ground improvement techniques. In the present investigation, shredded rubber from waste has been chosen as the reinforcement material and cement as binding agent which was randomly included into the soil at three different percentages of fibre content, i.e. 5% 10% and 15% by weight of soil. The investigation has been focused on the strength behaviour of soil reinforced with randomly included shredded rubber fibre. The samples were subjected to California bearing ratio and unconfined compression tests. The tests have clearly shown a significant improvement in the shear strength and bearing capacity parameters of the studied soil. The results obtained are compared with unreinforced samples and inferences are drawn towards the usability and effectiveness of fiber reinforcement as a replacement for deep or raft foundation and on pavement subgrade soil as a cost effective approach. The low strength and high compressible soft clay soils were found to improve by addition of shredded rubber and cement. It can be concluded that shredded rubber fibre can be considered as a good earth reinforcement material.

Experimental Investigation for Horizontal Ultimate Bearing Capacity and Target Ductility Factor Improvement Results of the RC Column Reinforced by AFL with Damages

Deem test results from the low reversed cyclic loading quasi-static test with 2 RC columns as the basic information of secant stiffness damage of the reference column and take use of the TMS instrument in the test to artificially make the damage percentage of secant stiffness of the RC column as 33%, 50% and 66%, 6 damaged columns in total; reinforce the 6 damaged columns and 2 undamaged ones under the same conditions with AFL, through quasi-static contrast test. Test results show that it is able to effectively boost horizontal ultimate bearing capacity and ductility deformability of the RC columns with AFL for reinforcement; besides, there is a linear function relationship between horizontal ultimate bearing capacity, target ductility factor, and damage percentage of secant stiffness.

Influence of subgrade strength on the performance of geocell-reinforced foundation systems

ABSTRACT: Physical model tests were performed on geocell-reinforced foundation systems with circular footings to study the influence of the strength of the subgrade layer. Model tests were conducted with a 150 mm diameter circular footing supported on foundation beds with varied configurations. Three different series of tests were conducted using a clay subgrade with undrained cohesion in the range of 7–60 kPa and dense sand at 80% of relative density. The results showed that the performance of the geocell-reinforced foundation systems was highly dependent on the subgrade strength. A maximum improvement factor of about 11.6 was observed for very soft subgrade with cu= 7 kPa, which decreased to about 3 for stiffer subgrade having cu= 30 kPa under similar test conditions and configuration. In addition, the variation of bearing capacity improvement factors was observed to be significantly influenced by footing settlement and geocell height.

Model studies of multi-edge footings on geogrid-reinforced sand

The ultimate bearing capacity of multi-edge shallow footings on loose and dense sand bed with and without geogrid reinforcement has been investigated. The data used have been obtained from extensive series of laboratory model tests. A total of 140 laboratory model tests were carried out using four different model rigid plates with the shapes of +, H, T and square. Parameters of the testing programme include the density of sand soil, depth of first reinforcement, vertical spacing of reinforcement layers, number of reinforcement layers and the covering of the reinforcement layer. Bearing capacity ratio was defined to evaluate improvement performance. The results indicate that the use of geogrid layers in sand bed has considerable effects on the bearing capacity characteristics and the optimum reinforcement parameters are independent from the shape of the footings. The construction of geogrid reinforcement helps in redistributing the applied load to a wider area. It has been observed that the use of geogrid reinforcement in sand layer provides additional improvement of bearing capacity of the multi-edge footings up to four times that of the unreinforced case.

Effect of Plasma Nitriding and Nitrocarburizing on HVOF-Sprayed Stainless Steel Coatings

In this work, the effects of plasma nitriding (PN) and nitrocarburizing on HVOF-sprayed stainless steel nitride layers were investigated. 316 (austenitic), 17-4PH (precipitation hardening), and 410 (martensitic) stainless steels were plasma-nitrided and nitrocarburized using a N2 + H2 gas mixture and the gas mixture containing C2H2, respectively, at 550 °C. The results showed that the PN and nitrocarburizing produced a relatively thick nitrided layer consisting of a compound layer and an adjacent nitrogen diffusion layer depending on the crystal structures of the HVOF-sprayed stainless steel coatings. Also, the diffusion depth of nitrogen increased when a small amount of C2H2 (plasma nitrocarburizing process) was added. The PN and nitrocarburizing resulted in not only an increase of the surface hardness, but also improvement of the load bearing capacity of the HVOF-sprayed stainless steel coatings because of the formation of CrN, Fe3N, and Fe4N phases. Also, the plasma-nitrocarburized HVOF-sprayed 410 stainless steel had a superior surface microhardness and load bearing capacity due to the formation of Cr23C6 on the surface.

Method of Performance-Based Design

In order to overcome some deficiency of design, American earthquake engineering and structural engineering experts have profound conclusion after the previous earthquakes, improved bearing capacity design method, put forward the theory of performance-based design. Methods of performance-based design mainly include displacement coefficient method; direct displacement based design method, capacity spectrum method and improved capacity spectrum method. Through the understanding of the main methods, enable us to better understand performance-based design, so as to improve the design of civil engineering.

Numerical and experimental evaluation of bearing capacity factor N of strip footing on sand slopes

Results of laboratory model tests and numerical studies on the behavior of a strip footing adjacent to a sand slope are investigated and presented in this paper. The investigated parameters include the effects of depth of the first reinforcement layer, vertical spacing, number of reinforcement layers, and distance between the edges of footings on bearing capacity. Results were analyzed to determine the effects of each parameter. Using a strip footing located near a sand slope crest had a significant effect on improving bearing capacity. The improvement increased when relative density decreased. The depth of the first layer decreased with further improvement when the distance of the footing edge from the slope crest increased. Using a strip footing can be considered effective in controlling the horizontal movement of the subgrade and in decreasing slope deformation. Finite element analysis explained and identified the failure pattern of strip footings adjacent to a slope crest. The findings also confirmed the load transfer mechanism and showed how a slope can be protected when geotextile is used. Key words: Strip footing, slope stability, plaxis, bearing capacity, scale effects.

Calculation Method of Bearing Capacity Improvement of Soft Soil Foundation under Vacuum Preloading

The theory of vacuum preloading was mainly focused on calculations of settlement and consolidation degree, but not on the bearing capacity improvement under vacuum preloading. Based on the Mohr-Coulombs failure criterion and elastic-plastic theory, the formula of bearing capacity improvement of vacuum preloading foundation was deduced under undrained condition. The consolidation and vacuum attenuation degree were taken into the consideration, and a calculation formula with fewer parameters by using CU total stress strength index was derived. Meanwhile the relation between bearing capacity and undrained shear strength was presented as well as that of bearing capacity and vertical effective stress increment.

A Review of the Seismic Performance for FRP Reinforced RC Frame Joints

Reasonably effective methods of FRP strengthening can dramatically improve the ultimate bearing capacity, ductility and seismic performance of reinforced concrete frame joints. This paper, based on domestic and foreign experimental research and finite element numerical simulation which are working at improving bearing capacity and seismic performance of reinforced concrete frame joints, analyzes mechanism and performance factors of RC frame joints reinforced with FRP material, concludes with basic ideas and methods of FRP material RC joints, together with the direction of continuing studies.

Behavior of raft on settlement reducing piles: Experimental model study

An experimental program is conducted on model piled rafts in sand soil. The experimental program is aimed to investigate the behavior of raft on settlement reducing piles. The testing program includes tests on models of single pile, unpiled rafts and rafts on 1, 4, 9, or 16 piles. The model piles beneath the rafts are closed ended displacement piles installed by driving. Three lengths of piles are used in the experiments to represent slenderness ratio, L/D, of 20, 30 and 50, respectively. The dimensions of the model rafts are 30cm×30cm with different thickness of 0.5cm, 1.0cm or 1.5cm. The raft-soil stiffness ratios of the model rafts ranging from 0.39 to 10.56 cover flexible to very stiff rafts. The improvement in the ultimate bearing capacity is represented by the load improvement ratio, LIR, and the reductions in average settlement and differential settlement are represented by the settlement ratio, SR, and the differential settlement ratio, DSR, respectively. The effects of the number of settlement reducing piles, raft relative stiffness, and the slenderness ratio of piles on the load improvement ratio, settlement ratio and differential settlement ratio are presented and discussed. The results of the tests show the effectiveness of using piles as settlement reduction measure with the rafts. As the number of settlement reducing piles increases, the load improvement ratio increases and the differential settlement ratio decreases.

Influence of geosynthetic encasement on the performance of stone columns floating in soft clay

This paper investigates the influence of geosynthetic encasement on the performance of stone columns floating in soft clay. It was found that with unencased columns the bearing capacity improvement is about 3.5 fold, but with geogrid encasement the improvement increases to 5 fold, where 60% of the column length is encased. With full-length encasement (i.e., 100%), the improvement is only about 3 fold. It is therefore evident that partially encased floating columns are superior to the fully encased ones. In contrast, with end-bearing stone columns, full-length encasement is reported to have exhibited better performance improvement than the partially encased ones. In the former case (floating columns), it is the bulge formation at a deeper depth that enhances the bearing capacity, while in the latter case (end-bearing columns), it is the stiffening effect of the encasement that enables the column to transmit the surcharge pressure onto the competent strata below.

Numerical modelling of the improvements to primary and creep settlements offered by granular columns

Analytical vibro-replacement design approaches typically quantify the settlement reduction using a dimensionless settlement improvement factor, defined as the ratio of the settlements without and with treatment. Most approaches do not explicitly consider the improvement to creep settlement. This is unfortunate because the ‘stone column’ technique is being increasingly used to reduce settlement and improve bearing capacity in soft normally consolidated and lightly overconsolidated cohesive soils (in which creep settlement tends to account for a significant proportion of the total settlement). Analytical design approaches typically consider primary settlement only. In this study, two-dimensional axisymmetric analyses have been carried out using PLAXIS 2D to establish the variation of improvement factor with time using different soil models, one of which incorporates creep behaviour. Two different approaches have been used to establish the influence of creep on predicted settlement improvement factors. The first approach is based on a direct comparison of two different soil models (one of which incorporates creep) whereas the second approach is based solely on the model incorporating creep. The settlement improvement factors have been evaluated for different area-replacement ratios, modular ratios and column lengths. The primary settlement improvement factors are in good agreement with some of the more popular analytical design methods while the creep settlement improvement factors are either equivalent or lower (depending on the approach used). The primary settlement improvement factors show a dependence on the modular ratio whereas it appears that the corresponding creep settlement improvement factors are relatively independent of it.

Numerical Analysis of Bearing Capacity to Q690 Tubular Joints Enhanced by Inner Sleeve

Simple joint is a common connection in tubular structures, it refers to one or more components soldered directly on the surface of the other member. Local buckling occurs in panel zone when the joint under heavy load, such local buckling will reduce the bearing capacity and stiffness. In order to improve bearing capacity of tubular joints, the joint needs to be strengthened. In this paper, the bending performance of the joint will be enhanced by welding a sleeve inner the surface of panel zone of chord member. By ANSYS finite element program, the bearing capacity of the joint with different parameters of inner sleeve was analyzed. The results showed that compare to sleeve length variation, bearing capacity of the joint experiences obvious change with variation of sleeve thickness.