Improvement In Bearing Capacity Research Articles

Behavior of grouped stud shear connectors between precast high-strength concrete slabs and steel beams

This study aims to examine the interface shear behavior between precast high-strength concrete slabs with pockets and steel beam to achieve accelerated bridge construction (ABC). Twenty-six push-out specimens, with different stud height, stud diameter, stud arrangement, deck thickness, the infilling concrete strength in shear pocket (different types of concrete), steel fiber volume of the infilling concrete in shear pocket concrete and casting method, were tested in this investigation. Based on the experimental results, this study suggests that the larger stud diameter and higher strength concrete promoted the shear capacity and stiffness but with the losing of ductility. The addition of steel fiber in pocket concrete would promote the ductility effectively, but without apparent improvement of bearing capacity or even declining the initial stiffness of specimens. It can also be confirmed that the precast steel-concrete composite structure can be adopted in practice engineering, with an acceptable ductility (6.74 mm) and minor decline of stiffness (4.93%) and shear capacity (0.98%). Due to the inapplicability of current design provision, a more accurate model was proposed, which can be used for predicting the interface shear capacity well for specimens with wide ranges of the stud diameters (from13 mm to 30 mm) and the concrete strength (from 26 MPa to 200 MPa).

Bearing Capacity Improvement of Expansive Soil: Stabilization with Cement and Iron Oxide Additive

This research is intended to increase the bearing capacity and durability of expansive clay subgrade with Portsoil Composite Cement (PCC) and Iron Oxide additives. Using two variants of the stabilization material composition; composition-1 is soil with 5% of PCC, and composition-2 is soil with 5% PCC + 0. 04% Iron Oxide). Tests include swelling potential, durability, and CBR (California Bearing Ratio). The test results showed that the performance of stabilization using composition-2 was able to reduce swelling potential on day 3 by 94. 44% (14. 44% greater than using composition-1), reducing the potential for volume increment by 94. 15% (greater 15. 02% compared to using composition-1) and weight to 93. 31% (15. 32% greater than using first). The highest CBR value in the 3 wet-dry cycle periods was nature soil 2. 32%, using composition-1 reached 25. 26%, while using composition-2 reached 36. 93% (11. 67% greater than CBR value using composition-1). That the addition of 0. 04% Iron Oxide to PCC-soil stabilization can significantly improve cement performance for expansive clay stabilization as a road subgrade.

Experimental research on bearing capacity of special anchor

The bearing capacity of anchor can be greatly improved by adding anchor gills on the basis of traditional anchor. Taking the smaller particle pea stone concrete as anchoring cartridge, this paper conducted the bearing capacity pull-out test on special anchor with additional anchor gills and studied the relationship between bearing capacity of special anchor and layers of anchor gills, strength of pea stone concrete, the size of the block. The test results have revealed that adding anchor gills in anchoring section has an obvious effect on improving the bearing capacity of anchor and the bearing capacity of single-layer rod is 1.2 times - 1.7 times that of finishing rod. There is a non-linear relationship between the bearing capacity of special anchor and the strength of pea stone concrete when the strength of anchor gill is constant. However, as the concrete strength increases, the improvement of bearing capacity becomes smaller. Under the condition of single-layer rod, the bearing capacity of anchor increases with the increase of the size of the block, which shows that the bearing capacity of anchor is positively correlated with the thickness of concrete when the strength of anchor is constant.

Field load tests and modelling of soft foundation reinforced by soilbags

A study was performed to investigate the bearing capacity of foundations reinforced by soilbags filled with excavated soft soils by conducting field load tests and numerical analysis. The effect of the number of reinforcement layers on the bearing capacity of the soilbag-reinforced foundation was investigated. Both the experimental and numerical studies indicated that soilbag reinforcement with reused excavated soft soils as the contained soilbag material can substantially improve the bearing capacity of the soft foundation and reduce settlement under vertical loading conditions. The bearing capacity was also found to increase with increasing number of soilbag reinforcement layers. The numerical analysis indicated that stress dispersion occurred through the soilbag reinforcement to reduce the load transferred to the underlying soft soils. High-quality compaction of the soilbag layers during construction is very important to improve bearing capacity. In addition, the excess pore water pressure generated in the soft foundation was less with the soilbag reinforcement and decreased with an increasing number of reinforcement layers due to the relatively high permeability of the soilbag reinforcement.

Bearing Capacity of Strip Footing Built on Geogrid-Reinforced Sand over Soft Clay Slope and Subjected to a Vertical Load

The present work deals with the study of the behavior of a rigid striped footing, resting on a sand slope reinforced by geo-grids and located above a soft clay layer. For this purpose, numerical analysis was conducted using finite element program; Plaxis software package; where the effects of some parameters on the strip footing behavior were studied. The affecting parameters such as the number of layers of geogrids, the vertical spacing, and the slope of the sand, the depth of reinforcement and the angle of friction of the sand were considered in soil reinforcement by geogrids based on multi-series of tests. The analysis results show an improvement in the soil bearing capacity at the level of the reinforcement depth, whatever the slope of the sand and its density (loose, moderately dense and dense). This improvement was related to the important number of reinforcing elements represented by a small vertical spacing of strips. Whereas, a significant dete-rioration of the soil bearing capacity was detected in the case of steep slopes of sand whatever the number of reinforcing strips and their vertical spacing.

Performance of Circular Footing on Expansive Soil Bed Reinforced with Geocells of Chevron Pattern

Results from laboratory model tests performed on circular footing are presented in this paper to understand the performance of geocell reinforced expansive soil. Naturally occurring expansive soil was used in this study as subsoil. Geocells of chevron pattern fabricated from geotextile made up of polypropylene were used to reinforce the soil bed. The parameters studied in this testing program were the placement depth of the geocell mattress, pocket size of geocell and the height of geocell mattress. Contrary to other researchers; the improvement in the performance of reinforced bed is evaluated at a settlement level equal to the failure settlement of unreinforced soil bed. The performance of reinforced bed is evaluated through two non-dimensional factors viz. bearing capacity improvement factor (If) and settlement reduction factor (PRS%). Test results indicated that with the introduction of geocell as reinforcement, a substantial improvement in bearing capacity and decrease in footing settlement can be achieved. Bearing capacity of reinforced bed increases by more than 200% and 81% reduction in footing settlement was achieved by using geocell mattress of optimal dimensions and placing it just below the footing base.

EFFECT OF DEEP SOIL MIXING TO INCREASING BEARING CAPACITY ON PEAT SOIL

The peat soils have high compressibility properties and low bearing capacity; therefore, the settlement in peat soils is very significant. The ground improvement, such as deep stabilization needs to be carried out to increase the bearing capacity of the peat soil. The deep stabilization or deep soil mixing (DSM) is a method of soil improvement by the soil column reagent mixed with cement and other pozzolanic materials. This study used the following ingredients: added clay + 12% calcium carbide residue (CCR) and clay + 8% rice husk ash (RHA), which are expected to increase soil carrying capacity because of the properties of silica and lime possessed by pozolan materials that can bind soil particles. The variations in diameter and the number of DSM column test piece are as follows: 4 and 16 column variations with a diameter of 3.75 cm and 1 column with a diameter of 15 cm. The soil mixing column is compacted in a pipe and the concrete cylinder formwork is then pressed for 4 days. The test results showed the increased soil bearing capacity on peat using the DSM. The DSM column (clay + CCR) with a diameter of 15 cm showed the highest bearing capacity of 32.44 kPa with a bearing capacity improvement (BCI) value of 6.151 or a percentage increase in the bearing capacity by 515.09%. On the other hand, the columns (clay + RHA) with a diameter of 3.75 (4 columns) have the lowest bearing capacity, which is equal to 18.67 kPa.

Response of micropiles in different seismic conditions

In recent years, due to the growth of the world population, suitable lands for construction and building are being reduced, gradually; hence, researchers have continuously sought to increase the bearing capacity and resistance of soil and improve its properties. One of the effective methods for improvement of the soil bearing capacity and reduction in foundation settlement is the implementation of micropiles below them. In this study, the seismic response of micropiles under real seismic loading was performed using finite element software. The stabilized soil behavior was modeled as elastoplastic along with Rayleigh damping, and micropiles were modeled as elastic beam elements by considering the interaction between soil and structure. The parametric study aims to focus on how to connect micropiles with foundation and effect of earthquake intensity. The results of the analysis show that decreased stiffness of the micropiles foundation system against the applied forces affects the values of lateral displacement and bending moment. Also, it is found that the Arias intensity of an earthquake is important parameter in characterizing of an earthquake nature influence on pile performance in soil.

Improvement of bearing capacity of soil by using natural geotextile

An experimental study has been carried out to improve the bearing capacity of soils by using geotextile. In the present study geojute (gunny bags) is used as geotextile, whereas sand is used as soil media. This research presents the results of laboratory load tests on model square footings supported on reinforced sand beds. A total of 32 load tests are conducted to evaluate the effects of single layer reinforcement placed below square model footings. Parameters of testing programme of the research are the depth of reinforcement, the plan area of reinforcement and the footing size. The test results indicated that the maximum gain in ultimate bearing capacity (UBC) of footings on reinforced soil (by using geojute) is found to be increased by a factor of 3.37 as compared to soil without geojute. Also, the optimum size of reinforcement is found to be 3.5B × 3.5B irrespective of the type of reinforcing materials used. The optimum placement position of geotextile is found to be 0.5B from the base of the footing. At low settlement rates, the study on the values of BCR reveals almost the same results with regard to optimum depth and size of reinforcement mentioned above. It is found that with increase in the settlement rate, BCR increases. Also, the improvement in bearing capacity is found to increase with increase in footing size.

Shakedown loading capacity prediction of metal-based nanocomposites

Nano reinforcement of metals cannot escape the attention of designers who seek to improve overall performance of engineering structures from automotive components to biomedical devices. Since many engineering structures are susceptible to variable cyclic load, presenting shakedown design of them is of the present research interest. So that, in the present research the shakedown loading capacity of metal based nanocomposite is estimated through finite element discretization and interior point optimization method. Finally, the results are obtained for plate structures subjected to two independent biaxial loads. A maximum improvement of 71.2% is achieved for shakedown load factor of the structure, which means a remarkable improvement in load bearing capacity of the structure.

Axial and Lateral Loading Behaviour of Pervious Concrete Pile

Ground improvement is the process by which soil behaviour is altered mainly by physical means. Typical examples range from inclusion of structural elements such as piles or soil nails, to use of any compaction technique in which the bearing capacity of soil is enhanced. The use of stone columns in conjunction with soft or weak soils represents a very cost-effective way of improving bearing capacity. In addition, stone columns being highly permeable provide natural drainage, thereby accelerating consolidation. However, the physical behaviour of stone columns is affected by nature of the soil in which they are embedded. In particular, they offer little resistance to lateral loading generated by soil movement. This paper advocates the use of an innovative ground improvement technique, which involves partial cementation of granular columns resulting in Pervious Concrete Piles. This study includes formulation of mix design (1:1:4) for pervious concrete and detailed analysis of pile behaviour under axial and lateral loading. It was found that under same axial loading conditions, the load-carrying capacity of pervious concrete model pile exceeded four times that of a granular column with same dimensions. A series of lateral loading tests were conducted on 5-cm-diameter pervious concrete model piles with length/diameter ratios of 6, 10 and 14. The bending moment profile shows that pervious concrete pile behaves in the same way as flexible piles subjected to lateral loading. This type of behaviour has potential to transfer the load below failure surface without compromising on permeability criteria, thereby improving stability.

Feasibility study on triangular perfobond rib shear connectors in composite slab

This paper attempts to emphasize the experimental study on feasibility of Triangular perfobond rib shear connector in composite slab with cold formed steel beam. This rib shear connector is a feasible alternate to the existing type of connectors like shear studs etc., this perfoplate has triangular hole of size (30 × 50 mm) in the CFS plate of (500 × 40 mm) with two different positioning of triangular hole, one facing the flange (TR1) and the other facing opposite to flange (TR2). Vertical compressive force applied in Universal Testing Machine to find the shear capacity of the new connector in a composite slab. There is an increase in composite interaction which results in both the triangular perfobond have approximately equal load carrying capacity, but the slip behaviour is comparatively higher in the triangle head facing opposite to the flange (TR2). According to the failure phenomenon in ultimate loading state, the failure mechanism of perfobond rib shear connectors was analysed and the results indicates that brittle failure always occurs in perfobond rib connectors. The influence of the perfoplate connector configuration on the load bearing capacity and structural improvement was discussed.

Prediction of Grouting Penetration Height Along the Shaft of Base Grouted Pile

Post-pressure grouting is an effective method to improve bearing capacity of ordinary bored cast-in-situ piles. The migration of the grout along the pile side is regarded as an important mechanism responsible for the improvement of the pile capacity. Research into the penetration height of the grout is of great important in evaluating the behavior of base grouted piles. In this paper, a prediction method of grouting penetration height along the shaft of the base grouted pile was proposed. Considering the balance and losses of the grout pressure during grouting, an iterative procedure was given to determine the penetration height of the grout in layered soils. Field test results were also provided to indicate the validity of the proposed method.

Potential use of structural skirts towards improving the bearing capacity of shallow footings exposed to inclined loadings

ABSTRACT Though variety of remedial methods for soil stabilization is available and are well developed; however, they are prohibitively expensive and are restricted by some problems related to the site condition. Structural skirts hold promise as an alternative method of improving the bearing capacity of shallow footings subjected to inclined loads. In this study, a series of experimental model tests were carried out to measure the impact of structural skirts on the bearing of footings exposed to inclined loads. On the basis of these tests, modified inclination factors are proposed for footings with and without structural skirts subjected to inclined loads. The results presented the improvement of bearing capacity in the range of 1.2–3.5, depending on the particular geometry of both footings and skirts, the magnitude of the load and the inclination angle. This study provide good insights towards the need of more investigations of the impact of structural skirts on the bearing capacity of sub-structures exposed to different loads.

Experimental Investigation on Strength and Bearing Capacity Improvement of a High Plasticity Clayey Subgrade Soil Using Lime

Limited connectivity and poor infrastructure of roads acts as a roadblocks hampering the socio-economic development of one region. In order to overall development of these regions an effort should be given to cultivate well established road network. But due to scarcity of good quality soil PWD engineers are often forced to build roads over the weak soil which directly affects the strength and durability of the road. It is therefore essential to improve the engineering properties of such problematic soil with suitable stabilization technique as and when encountered. Lime stabilization is one such well known chemical stabilization technique extensively used to improve the poor subgrade condition and it is recommended by several codes in INDIA. This paper attempts to study the effect of lime on strength and bearing capacity improvement of soft clayey soil. A series of UCS and CBR tests are conducted with different percentages of lime (i.e. 3, 5, 7 and 9%) and at different curing period to assess the potential of lime in strength improvement. Test results indicate that strength, stiffness and bearing capacity of the soil is considerably improved after lime amendment. Both unconfined compressive strength (UCS) and California bearing ration (CBR) improved up to 7% of lime beyond that it decreases. The improvement of UCS and CBR is found approx three and five fold as compared to original soil. Underlying mechanisms of this improvement is further scrutinized by microstructural analysis such as X-ray diffraction (XRD), Field Emission scanning electron microscope (FESEM) with Energy dispersive X-Ray Analysis (EDAX). Apparent formation of some new peaks in XRD analysis and change of textural and structural morphology of clayey soils obtained from FESEM confirms the formation of cementitious compounds in the lime stabilized soil.

Организационно-технические мероприятия по использованию криогелей для повышения несущей способности грунтов при строительстве и эксплуатации объектов трубопроводного транспорта

Организационно-технические мероприятия по использованию криогелей для повышения несущей способности грунтов при строительстве и эксплуатации объектов трубопроводного транспорта

Mechanical behavior of welded hollow spherical joints with diameter exceeding 1.0 m

The welded hollow spherical joint (WHSJ) with diameter greater than 1.0 m is commonly employed in long-span tubular transmission towers. It has a relatively higher ratio of diameter to thickness compared to traditional spherical joints, since the larger thickness leads to difficulties in fabricating a spherical joint with a diameter of more than 1.0 meter, and will also lead to deterioration of mechanical properties of materials. Therefore, longitudinal and transverse stiffeners are usually set inside to avoid local buckling and improve bearing capacity. In this study, experimental tests and finite element (FE) analyses of full-scale WHSJs with a diameter of 1400 mm under the multi-axial load are conducted. The results indicate that all specimens have similar failure modes, namely the indentation of the hollow sphere near the main tube, and the failure of the longitudinal stiffeners at the same position. In addition, the setup of longitudinal stiffeners would obviously improve the ultimate bearing capacity (UBC) of WHSJ. After the validity of the FE model is verified, the parametric study is carried out. The results indicate that the UBC of stiffened WHSJ can be approximated by the sum of the resistances of the corresponding unstiffened WHSJ and the stiffeners. Accordingly, design equations are proposed for stiffened WHSJs with diameter greater than 1.0 m. The results obtained by proposed equations are compared with that obtained by tests and FE analyses. They are basically in good agreement, which shows the validity of the equations.

The strength and microstructural behavior of lime stabilized subgrade soil in road construction

ABSTRACT This paper attempts to study the potential of lime on strength and bearing capacity improvement of subgrade soil. The effect of soil type, different lime percentages (3, 5, 7 and 9%) and curing duration (0, 7, 14 and 28 days) on the engineering properties of soil is evaluated by conducting series of laboratory tests such as linear shrinkage, unconfined compressive strength (UCS), split-tensile strength (STS) and California bearing ratio (CBR) test. The result indicates that soil with large clay fractions needs a relatively higher percentage of lime to alter their physicochemical characteristics. Addition of lime reduced the linear shrinkage strains and increased the UCS, STS and CBR value of soil. But beyond an optimum lime content opposite trend is observed. The strength improvement of lime stabilized soil is further enhanced with curing time. Moreover, the micro-structural analyses are performed to understand the mechanisms involved in the lime stabilization process. Change in soil morphology from FESEM (Field emission scanning electron microscope) and apparent formation of some new peaks in XRD (X-ray diffraction) and FTIR (Fourier transform infrared spectroscopy) analysis confirms the formation of cementitious compounds in lime stabilized soil. For particular lime content and curing duration, soil with high plasticity index gives lower strength value. Further, soil treated with 3% lime achieves 7 days target compressive strength value (i.e. 345 kPa). CBR values of soil treated with the optimum lime meet the requirement of subbase materials for low traffic rural roads thus reduce the overall pavement thickness and the construction cost.

Improvement of Soft Soil Using Linear Distributed Floating Stone Columns under Foundation Subjected to Static and Cyclic Loading

A stone column is one of the soil improvement methods that are mainly used for improving the geotechnical behavior of soft soils. For deep improvement of soft soil, the floating stone columns are considered the best and effective economically which provide lateral confinement and drainage and longitudinal skin friction. In this study, six tests were carried out on the natural soft soil of undrained shear strength of 5.5 kPa improved by single and two linear distributed floating stone columns. The stone column dimensions are 30 mm in diameter and 180 mm in length and the stone column material is sand of high internal friction angle of 48°. The natural and improved soil samples are tested under isolated raft foundation of dimensions 120×120 mm subjected to vertical static and cyclic loading of frequency 2Hz and continued for 50 seconds. The results showed a significant improvement in soil bearing capacity when reinforced with stone columns despite the small area replacement ratio, where the bearing capacity of improved soil increased by 120 to 145%. The compressibility of improved soil decreased by 57 to 86% in comparison with that of natural soft soil. Also, the floating stone columns reduced the porewater pressure, where the stone columns considered efficient in providing short drainage pathways. This can be one of the reasons why soil reinforced with floating stone columns hold higher cyclic and static stresses regardless the end bearing of stone columns.

Bearing Capacity of Square Footing Resting on Fibre-Reinforced Pond Ash Overlying Soft Clay

This paper presents the results of an experimental and numerical investigation carried out on a two layered soil system which contains unreinforced/randomly distributed fibre-reinforced pond ash (RDFP) layer overlying a soft clay layer. Model tests have been performed on square footing resting on unreinforced/RDFP layer overlying soft clay. The effect of pond ash layer (unreinforced/reinforced) has been studied by varying its thickness as 0.5B, 1.0B and 1.5B where B is the width of the footing. The effect of polypropylene fibres of lengths 6 mm, 12 mm and 18 mm have also been studied with varying in their percentage as 0.5%, 0.75% and 1%. Results have shown that there is significant amount of improvement in ultimate bearing capacity as well as in the settlement of the soil system due to the provision of pond ash layer over soft clay. Finite element analysis of the model footing has also been done with PLAXIS 3D software. The experimental results have been validated by the results obtained numerically.