Enhance Bearing Capacity Research Articles

Stabilisation of soft clay by deep cement mixing (DCM) method – A case study

Soft ground under the sea often presents challenges for supporting seawall or reclamation without treatment if no dredging is implemented. Ground treatment is often required to improve the engineering properties of weak soils to enhance bearing capacity for supporting the intended structures. Deep soil mixing with addition of binder is one of the ground treatment methods that has been widely used in Asia and worldwide. This method was recently adopted by the authors for a practical ground improvement project in Hong Kong. This paper presents the characteristics of cement-soil mixture in the laboratory environment as well as performance of the field mixed soil using the same binder material. A detailed test programme was developed to evaluate the strength and other properties of the cement-soil mixtures by using various amounts of binder and water to binder ratios. A series of unconfined compressive strength (UCS) of the laboratory mixture were performed. The relationship of strength of the cement-soil mixture with binder dosages is developed. Test results of laboratory mixed soils were compared with those of field mixed soils. The relationship of strength between laboratory mixed soils and field mixed soils was derived. Field installation of deep mixing for the project is discussed.

Interference joint of enhanced bearing capacity

State of the art technology implies the application of increasing power at high speeds, therefore various interference joints strength enhancing is an urgent task. On the basis of the review of the existing interference joints bearing capacity improving research methods, the approach being implemented by the joint internal member mounting surface modification with the help of grooves of shallow depth is proposed. The experimental results of the modification various parameters influence on the fit bearing capacity are presented. It is reasonable to use the given engineering solution for fit strength restoring when performing the repair work.

Enhancement of bearing capacity from consolidation: due to changing strength or failure mechanism?

Bearing capacity of shallow foundations is higher following preload (or self-weight)-induced consolidation because the soil strength changes, and perhaps because the failure mechanism changes. Previous studies have illustrated this effect by plotting or predicting changes in either bearing capacity factor or strength. In this study, the relative contribution of these two effects is explored. This is achieved by formalising a definition of bearing capacity factor, which is described in terms of the average strength mobilised in the deformation mechanism at failure. Using the alternative definition of bearing capacity factor, the gain in foundation capacity is shown to be almost entirely due to changes in soil strength, rather than bearing capacity factor, which remains largely unaffected by the strength gains. This observation should encourage future studies into consolidated bearing capacity to present gains in capacity in terms of changes in mobilised strength rather than changes in bearing capacity factors, and supports the use of prediction methods that focus on defining the change in soil strength.

Behaviour of geocell–geogrid reinforced foundations on clay subgrades of varying strengths

This paper reports a laboratory model investigation performed on circular footing rested on geocell–geogrid reinforced foundations of different configurations. The model foundations comprised of geocell–sand mattresses (with an additional planer geogrid at the bottom) of varying thicknesses (H = 0·63–2·19D; where D is the footing diameter) placed on clay subgrades of different undrained shear strengths, ranged over very soft (cu = 7 kPa) to stiff (cu = 60 kPa). Responses of model tests have indicated significant influences of base-geogrid on the performance of geocell reinforced foundations, in terms of bearing pressure and surface deformation variations. An enhanced bearing capacity and uniform deformations at the foundation surfaces were noticed due to the inclusion of base geogrid. However, the beneficial effects were limited to shorter geocells (h ≤ 1·05D) and softer clay subgrades (cu ≤ 15 kPa); while, adverse effects were noticed for thicker geocells (h ≥ 1·57D) and foundations on comparatively stiff clay (cu ≥ 30 kPa). In general, improvements in bearing pressure were observed with an increase in footing settlement; about 40–70% enhancements in bearing pressures compared with geocell-alone systems, and maximum about 12-fold overall improvement (compared with corresponding homogeneous clay bed) were obtained in the experimental programme.

Field study on axial bearing capacity and load transfer characteristic of waveform micropile

The waveform micropile is an advanced construction method that combines the concept of the conventional micropile with the jet grouting method. This new form of micropile was developed to improve shaft resistance, and has enabled a higher bearing capacity and greater cost efficiency. Two field tests were conducted to examine field applicability and to verify the effects of bearing capacity enhancement. In particular, waveform micropile construction using the jet grouting method was performed to evaluate the viability of waveform micropile installation. After testing, the surrounding ground was excavated to check the shape of the waveform micropile. The result showed that waveform micropiles can be installed by adjusting the grouting time and pressure. In the loading tests, the bearing capacity of the waveform micropile increased by 1.4–2.3 times that of the conventional micropile, depending on the shape of the micropile. The load transfer analysis using the strain gauge data showed that the waveform micropile increases the shaft resistance in the soil layer. This not only decreases pile settlement, but also contributes to the increase of overall bearing capacity. The overall results clearly demonstrate that the waveform micropile is an enhanced construction method that can improve bearing capacity.

Centrifuge Model Study on the Effect of Lattice Leg and Sleeve on the Postconsolidation Bearing Capacity of Spudcan Foundation

Up to now, the postconsolidation bearing capacity enhancement of jack-up spudcan foundation has been explored using centrifuge model tests and numerical analyses, which however ignored the realistic jack-up lattice leg. This paper investigates both typical lattice leg and sleeve effects on the postconsolidation spudcan bearing capacity using centrifuge model tests, by replicating the entire process of spudcan in normally consolidated clay: “penetration–unloading–consolidation–repenetration.” The experimental results show that the lattice leg and sleeve affect the spudcan bearing capacity in two sides compared with spudcan without leg. First, it increases the transient bearing capacity during initial spudcan penetration; second, less postconsolidation bearing capacity improvement is yielded by the presence of the leg. The former effect is of importance on the prediction of jack-up leg penetration, and the latter effect would suggest a lower risk of spudcan punch-through for realistic offshore jack-up rig during preloading and operation period.

Buckling Behavior of Metallic Cylindrical Shell Structures Strengthened with CFRP Composite

The objective of this study is to evaluate the effect of a CFRP composite layer on the buckling behavior of metallic cylindrical shells. To enhance the bearing capacity of steel shells, classical solutions consider internal or external metallic stiffeners (stringers and/or rings) welded or riveted to the shell. Here, an external skin of composite material which wraps the whole metallic skin of the shell is studied. To be valid for metallic shells structures (storage tanks like silos) as well as for metal pipes (gas or oil pipeline), the procedure for setting up and implementing the composite must be simple. The recommended solution is therefore tested through experimental tests to find their limits and the configuration of optimal behavior. A consistent enhancement of bearing capacity is observed. This experimental base serves also to consolidate a numerical model which corroborates the experimental results. The good correlation between experimental and numerical results is confirmed for the whole loading process, for unstiffened and stiffened shells. For metallic unstiffened shell, an adequacy between experiment and simulation is noticed in the mainly membrane precritical behavior, during the buckling initiation characterized by the boundary layer problem corresponding to axisymmetric wavelength appearance near boundaries and in the postcritical domain associated to localization of the buckling mode at one extremity of the shell. For stiffened configuration, the enhancement of the bearing capacity of the shell is correctly gauged; this confirms the possibility to use finite element simulation for the design.

A laboratory and numerical study on the effect of geogrid-box method on bearing capacity of rock-soil slopes

Currently, layered geogrid method (LGM) is the commonly practiced technique for reinforcement of slopes. In this paper the geogrid-box method (GBM) is introduced as a new approach for reinforcement of rock-soil slopes. To achieve the objectives of this study, a laboratory setup was designed and the slopes without reinforcements and reinforced with LGM and GBM were tested under the loading of a circular footing. The effect of vertical spacing between geogrid layers and box thickness on normalized bearing capacity and failure mechanism of slopes was investigated. A series of 3D finite element analysis were also performed using ABAQUS software to supplement the results of the model tests. The results indicated that the load-settlement behavior and the ultimate bearing capacity of footing can be significantly improved by the inclusion of reinforcing geogrid in the soil. It was found that for the slopes reinforced with GBM, the displacement contours are widely distributed in the rock-soil mass underneath the footing in greater width and depth than that in the reinforced slope with LGM, which in turn results in higher bearing capacity. It was also established that by reducing the thickness of geogrid-boxes, the distribution and depth of displacement contours increases and a longer failure surface is developed, which suggests the enhanced bearing capacity of the slope. Based on the studied designs, the ultimate bearing capacity of the GBM-reinforced slope was found to be 11.16% higher than that of the slope reinforced with LGM. The results also indicated that, reinforcement of rock-soil slopes using GBM causes an improvement in the ultimate bearing capacity as high as 24.8 times more than that of the unreinforced slope.

Comparative Study of CFRP‐Confined CFST Stub Columns under Axial Compression

This paper presented a comparative study of concrete‐filled steel tubular (CFST) stub columns with three different confinement types from carbon fiber reinforced polymer (CFRP): outer circular CFRP, inner circular CFRP, and outer square CFRP. The compressive mechanism and physical properties of the composite column were analyzed firstly aiming at investigating the confinement effect of CFRP. Ultimate axial bearing capacity of these three CFRP‐confined CFST columns was calculated based on Unified Theory of CFST and elastoplastic limit equilibrium theory, respectively. Meanwhile, the corresponding tests are adopted to validate the feasibility of the two calculation models. Through data analysis, the study confirmed the ultimate strength calculation results of the limit equilibrium method were found to be more reliable and approximate to the test results than those of Unified Theory of CFST. Then axial bearing capacity of the pure CFST column was predicted to evaluate the bearing capacity enhancement ratio of the three types of composite columns. It was demonstrated that the averaged enhancement ratio is 16.4 percent, showing that CFRP‐confined CFST columns had a broad engineering applicability. Through a comparative analysis, this study also confirmed that outer circular CFRP had the best confinement effect and outer square CFRP did better than inner circular CFRP. The confinement effect of CFRP increased with the decrease of concrete strength, and it was proportional with relative proportions of CFRP and steel under the same concrete strength.

The Effectiveness of Deep Soil Mixing on Enhanced Bearing Capacity and Reduction of Settlement on Loose Sandy Soils

The Effectiveness of Deep Soil Mixing on Enhanced Bearing Capacity and Reduction of Settlement on Loose Sandy Soils

An Innovative Device to Enhance Conductor Bearing Capacity in Deepwater Drilling Operations

Deepwater environments raise higher demand on the bearing capacity of the drilling conductor below the mudline. To deal with this problem, a conductor bearing capacity enhancement device was designed. The setting capability of this device and its axial bearing capacity were analyzed with soil mechanics and pile theory. Furthermore, a calculation model was developed, and a numerical method was used to solve for the lateral capacity, coupled with drilling platform, riser, conductor, seabed soft soil, and the device. The result shows that proper setting depth of the device is primarily determined by the property of the soil, rather than the conductor jetting operation. Additionally, appropriate determination of the diameter and wall thickness (WT) of this device can greatly improve the lateral bearing capacity of the conductor.

Performance of Shallow Foundations Resting on Coir Geotextile Reinforced Sand Bed

Soil reinforcement by natural fibers is a cost-effective and reliable technique for improving the stiffness and stability of soil. Coir is an eco-friendly, biodegradable organic material that has high tearing strength, stiffness, and durability compared to other natural reinforcement materials. In this study, the potential of coir geotextile as a reinforcement material was studied through a set of laboratory experiments. Remarkable improvement in strength and settlement properties were obtained with the provision of geotextiles. Bearing capacity improvement by a factor of 5 and a reduction of footing settlement by 87% was obtained by the suggested method. The optimum benefit was realized with the provision of three layers of reinforcement for a width of 3B (B is the foundation width), the topmost geotextile layer being positioned at a distance of 0.25B from the base of footing. Bearing capacity enhancement by a factor of 2.57 and settlement reduction of 73% was obtained even with the provision of a single layer of coir geotextile.

Effective installation of micropiles to enhance bearing capacity of micropiled raft

While micropiles are used in many geotechnical projects, as ground reinforcement rather than as structural elements, field engineers have reported that the bearing capacity of micropiled rafts greatly exceeds the range of common ground reinforcement. This is known to be due to the confining effects of micropiles from the interaction between the ground and the micropiles, which extends the failure area of the ground significantly. Utilizing micropiles as ground reinforcement can excessively underestimate the structural contribution of the footing in a micropiled-raft system to the bearing capacity. This study investigates the support characteristics of a micropiled raft through model tests and a numerical analysis. The support behavior of the micropiled raft is evaluated for various conditions, such as soil type, pile length, and installation angle. It is found that the micropiles modify the failure behavior of the ground considerably, and that the bearing resistance can be enhanced by considering the appropriate failure mode, installation angle, and pile length.

Influence of size of granulated rubber on bearing capacity of fine-grained sand

Nowadays, in most of the advanced and developing countries, waste tires have caused serious environmental problems such as fire and environmental contamination. For reusing them in an appropriate and beneficial way, waste tires have been utilized as a lightweight fill material in geotechnical engineering applications such as highway embankments. In this study, Babolsar fine-grained sand and granulated rubber with sizes in the ranges of 1 to 4, 1 to 9, and 4 to 9 mm were used. A series of model footing tests on reinforced sand with different sizes of granulated rubber were carried out. According to the results, 4- to 9-mm granulated rubber had the highest effect on enhancement of bearing capacity and reduction of fine-grained sand settlement. The results showed that sand-granulated rubber mixtures with granulated rubber in the range of 4 to 9 mm and content of 10% by weight of mixture can increase the bearing capacity of sand up to 50%. In addition, for this mixture, a series of laboratory tests were conducted to determine the optimum width and depth of the reinforcement layer consisting of sand-granulated rubber mixture. The results indicate that the optimum width and the most effective depth of this mixture are 5B and 1B, respectively (where B is the footing width).

Influence of reinforcement stiffness and strength on load-settlement response of geocell-reinforced sand bases

Improvement in the performance of a strip footing supported on geocell-reinforced sand bed is investigated through series of experimental tests on a reduced scale physical model. Geocells with scaled-down mechanical and geometrical properties produced from various material types consisting of woven geotextile, nonwoven geotextile and biaxial geogrid are used as the reinforcement and the influence of geocell strength and stiffness on the enhancement of bearing capacity and settlement of the surface footing is described. The results indicate that stiffness of geocell makes a significant contribution on the performance of geocell-reinforced soil. For the geocells used in the tests with the height equal to footing width, for example at footing settlement ratio of 6%, improvement in the bearing capacity of geocell with the stiffest material is found to be 1.5 times the geocell with the softest material. The failure mechanism of geocell-reinforced foundation system has been shown to depend highly on geocell modulus and height. It is also concluded that ultimate tensile strength of geocell material is generally not influential at load-settlement behaviour of the footing at practical settlement levels. However, if flexural rupture of reinforcement controls the failure mechanism, geocell strength affects the ultimate bearing capacity.

Effective Use of Plant-Derived Urease in the Field of Geoenvironmental/ Geotechnical Engineering

Geotechnical and geo-environmental engineering applications currently being explored through bio mineralization process include cementation of sands to improve mechanical properties and hence, to enhance bearing capacity and liquefaction resistance, sequestration of carbon, soil erosion control via surficial stabilization, groundwater flow control and remediation of soil and groundwater impacted by metals and radionuclides. Bio mediated system broadly refers to a chemical reaction series that are managed and controlled through biological activities and byproducts resulting from those reactions alter the properties of material in the system. Bio mediated methods such as microbial induced calcite precipitation (MICP), biofilm formation, biogas generation and biopolymers have been developed by injecting or stimulating microbes. MICP is the most widely explored method. Microbes having urease activity enhance the hydrolysis of urea and it helps to control the pH and to precipitate carbonate. Although it is a widely explored bio mediated method it has some disadvantages. The plant-derived urease may offer many benefits over microbial urease to induce carbonate cementation. Therefore, it is advantageous to explore the knowledge regarding such a technique as an eco-friendly method for different applications in the fields of geoenvironmental/geotechnical Engineering. The main objective of this paper is to provide an overview of the importance of plant-derived urease for different applications in the fields of geoenvironmental/ geotechnical engineering. The information presented in this paper may be important for biotechnologists/geoengineers to have wide ranging updates on the current situation.

SHEAR CAPACITY EVALUATION OF REINFORCED CONCRETE BEAMS: FINITE ELEMENT SIMULATION

The shear performance of reinforced concrete beams with rectangle cross-section and two different continuous rectangular spiral shear reinforcement under monotonous loading is numerically evaluated. Further, the behaviour of two continuous shear reinforcement systems named, “Single Square Spring Shear Resistance System” (SSSSRS) and “Double Square Spring Shear Resistance System” (DSSSRS) as transverse reinforcements are compared with conventional discontinuous system “Stirrups”. The finite element study includes three (3) beams. The results clearly show that the application of continuous shear reinforcement system delivered improved shear behaviour and enhanced bearing capacity in beams. Beams with Single Square Spring Shear Resistance System (SSSSRS) and Double Square Spring Shear Resistance System (DSSSRS) exhibited 14.4% and 19.8% increased shear performance in comparison with conventional control beam. It was concluded that under the same deflection higher forces was achieved for “Single Square Spring Shear Resistance System” (SSSSRS) and “Double Square Spring Shear Resistance System” (DSSSRS) compared to control specimens.

Load Transfer Behavior of Cracking for Cement Concrete Pavement

In order to reduce the temperature and drying shrinkage cracking in cement concrete pavement, setting up cracks which becomes the weakest part of the cement concrete pavement. Load transfer behavior of cracking has a great influence on road performance and used lifetime in cement concrete pavement. The improvement of load transfer behavior of cracking is conducive to maintain effective load transfer between the pavement and to enhanced bearing capacity of pavement structure, also to reduce the damage of the structure, which is an important technical approach to extend the used lifetime of pavement. This paper describes the mechanism of load transfer and research status of crack, and points out the problems existing in the crack load transfer ability of research and development trend.

Parametric design of surface textures on journal bearing

Purpose – The main purpose of this paper is to understand and model the hydrodynamic influence of surface textures on journal bearings. Design/methodology/approach – In the model, a rectangular array of circle dimples is used to modify the film thickness expression. In full film and cavitation regions, classical Reynolds equation and Reynolds boundary condition are used as the governing equations, respectively. By setting high load bearing capacity as the main optimal goal, the influence of textures on tribological characteristics is studied to get the optimal distribution and parameters of textures. Findings – The results suggest that the load bearing capacity of a journal bearing may be improved through appropriate arrangement of textures partially covering its sleeve. The reduction of the cavitation area may also be achieved by arranging the textures in divergent region. With a high density distribution of textures which have step depths varying linearly along the circumferential direction of the bearing, the load bearing capacity enhancement seems to give good performance. Comparing with smooth bearing, the load bearing capacity enhancement of such textures is about 56.1 per cent, although the influence of texture diameters for the same area density seems insignificant. Originality/value – The paper shows how surface textures can be designed on journal bearing to improve its tribological performances.

Bearing capacity of steel fiber reinforced reactive powder concrete confined by spirals

Based on two basic considerations, (1) the enhancement of bearing capacity by the inclusion of confining spirals and (2) the crack-bridging and energy-absorbing improvements gained by adding steel fibers to the mixture, steel fiber-reinforced reactive powder concrete (SFR-RPC) reinforced by steel spirals can be applied to post-tensioned anchorage zones. Twelve SFR-RPC prisms containing steel spirals and a longitudinal duct hole were loaded at high concentration over a limited circular area. The tests indicated that all specimens retained integrity at failure and exhibited no less than four radial cracks, the entire depression occurred on the loading-end surface, and the splitting tendency generally developed below the first turn of the spiral if the wedge cone formed ahead of the bearing plate. Three major factors related to the geometry of the zone directly influence the bearing capacity: (1) the local aspect ratio of the net area of the concrete supporting the plate to the area of the bearing plate, (2) the core aspect ratio of the area of the bearing plate to the area of the core surrounded by the steel spirals, and (3) the steel ratio of the spirals. An expression of the bearing load capacity is proposed on the basis of the testing results.