Safe Bearing Capacity Research Articles

Experimental and numerical study of piled raft system

Raft foundations are used when isolated footings cover more than 70% of the building area under a super structure. A combination between the use of piles and raft foundation is known as piled raft foundation. Piled raft foundations proved to be more economical in case of high rise buildings on clay and can provide safe bearing capacity and serviceability requirements. The use of strategically located piles improves the load capacity of raft and reduces the differential settlement. This research sheds some light on the philosophy of using piles as settlement reducers for raft foundations and also the behavior of piled raft embedded into sand. Small scale model tests are performed. The effects of pile length and alignment on the attained ultimate load are experimentally investigated. From the accomplished studies, it has been concluded that as the length of piles and number of piles decrease, the load carried by raft increases. Additionally, it is found that the best and the optimal settlement ratio (S/B%) to design the piled raft as settlement reducer is 0.7%.Finally the percentage of load carried by raft at S/B=0.7% is found to be 39%.

Prediction of Safe Bearing Capacity of Noncohesive Soil in Arid Zone Using Artificial Neural Networks

Estimation of safe bearing capacity (SBC) of noncohesive soil based on Indian Standard Code requires a lot of field work, viz, conducting direct shear tests to determine cohesion and angle of internal friction, performing the standard penetration test to determine the N-value of soil, and finding the relative density and dry density of soil. The present study does away with these soil parameters except for the design value of density and uses the results of sieve analysis to determine the SBC of soil. This research proposes the use of artificial neural network (ANN) to predict the SBC of noncohesive soil as a function of coefficient of curvature, coefficient of uniformity, and design value of soil density along with footing dimensions such as depth, width and diameter (in case of circular footing), and the desired settlement of the footing. The results show that ANN is a useful technique in estimating SBC of noncohesive soil using parameters derived from sieve analysis results and match closely from the results derived from the traditional methods based on Terzaghi’s theories.

Evaluation of safe bearing capacity of soil foundation by using numerical analysis method

The soil mechanic laboratory results help in accurate soil foundation design and enhancement failure mitigation. The mixing soil design has been used in many geotechnical engineering for soil improvement. In this paper, several types of soil foundations have been made from mixed soil. The bearing capacity of soil foundations by using mixed soil parameters and change footing dimensions have been calculated. 180 footings, placed on 15 soil foundation types have been designed. It is assumed the underground water has not effect to bearing capacity of soil foundation. The results of numerical analysis and mixed soils technique have been combined. The numerical analysis has supported mixed soil design, and introduced an appropriate result for soil foundation design. The effects of mixed soil on depth and width of footing have been compared. The mixed soil design influenced numerical analysis result, and economically, soil foundation design helps to select the appropriate dimensions of footings. The result of numerical analysis supports geotechnical and structural engineering codes, predicts structural stability with different age, natural hazard and prevention as well as it is useful in understanding safe bearing capacity of soil foundation behavior.

STRUCTURAL EVALUATION OF LOW VOLUME ROAD PAVEMENTS USING PAVEMENT DYNAMIC CONE PENETROMETER

Static and dynamic cone penetration tests are widel y used in Foundation engineering for measuring the penetration resistance of the ground and for relating it to the degree of compact ion and safe bearing capacity of soils. In Highway Engineering, Pavement Dynamic Cone Penetrometer (DCP) is used for rapid i n-situ strength evaluation of subgrade and other un bound pavement layers. In the present studies, an attempt has been made to id entify the strength and thickness of different pave ment layers of newly constructed low volume roads in the State of Karnataka, India u sing dynamic cone penetration studies and was compa red with actual measurements at the site. The evaluation of pavemen t test stretches was made for a period of two years , and changes in penetration resistance of different pavement layers were measur ed. A Software was used to analyze the DCP data an d to correlate with field observation. The results have favoured the possibil ity of using dynamic cone penetrometer as a quality control and pavement monitoring tool for low volume roads, eliminating t he need for a Benkelman beam or a falling weight de flectometer.

Experimental estimate of Nγ values and corresponding settlements for square footings on finite layer of sand

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size <TEX>$900mm{\times}1200mm{\times}1000mm$</TEX> is used for conducting model tests. Bearing capacity factor <TEX>$N_{\gamma}$</TEX> is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's <TEX>$N_{\gamma}$</TEX> values. From the experimental investigations it is found that, as the depth of sand cushion below the footing (<TEX>$D_{sc}$</TEX>) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.

Evaluation of Suitability of Raidata Pine (Pinus Radiata) For Making Pallets

Investigations were carried out to study the suitability of Pinus radiata (radiate pine) for making pallets and its performance was evaluated. The physical and mechanical properties of radiata pine were evaluated. Suitability indices with respect to mechanical properties of radiate pine were computed. Suitability figure was derived based on suitability indices and the suitability of raidata pine for making of pallets was arrived. Based on the study, the pallets made from raidata pine were classified as ‘GROUP II’, which is suitable for commonly used pallets and also for dunnage pallets which are used in godowns and warehouses. The performance of pallets was evaluated by simulating the actual work conditions and testing the pallets under uniformly distributed load and also by placing loaded pallets one above the other. The ideal span of forks of fork lift and safe load bearing capacity of wooden pallets were worked out and the suitability of radiate pine for making pallets was established.

Strength and F O S Performance of Black Cotton Soil Treated with Calcium Chloride

Black cotton soil is a typical expansive soil which loses its strength in presence of water resultant in swelling of the soil and in absence of water it shows multiple cracks due to shrinkage. Present paper describes the strength behaviour of Black cotton soil treated with calcium chloride (CaCl2). From the immediate compaction and unconfined compressive strength test up to 30 days of curing, it was observed that Black Cotton Soil with 3% CaCl2 (by weight of soil) combination found to be optimum percentage. Direct shear test was conducted under soaked condition with various curing periods, Safe Bearing Capacity determined as per IS codal practice. In this paper an approach is also made to give a comparison of improvement in factor of safety of the black cotton soil treated with calcium chloride with black cotton soil alone. It is found that addition of 3% calcium chloride has shown higher factor of safety with higher curing periods for an embankment slope of 1:2.5. Keywords -Maximum dry density, unconfined compressive strength, Factor of Safety

Physical and Mechanical Properties of Serpentinized Ultrabasic Rocks in NW Turkey

Serpentinized ultrabasic rocks crop out at various places in the northwestern part of Turkey. They are the foundation rocks of some architecture and the ground under road bases in many areas. They are also frequently used for indoor work such as tables, shafts, pilasters, jambs for chimney pieces and ornaments of different kinds. Owing to their economic importance, in situ geophysical and geotechnical studies were conducted to determine their dynamic engineering parameters such as: P- and S-wave velocities, Poisson’s ratio, rigidity modulus, elasticity modulus, bulk modulus, natural period, safe bearing capacity, and bearing coefficient. Geophysical and geotechnical laboratory tests were performed on cylindrical specimens cored across and along the foliation planes: ultrasonic measurements of compressional pulse velocity (UPV), uniaxial compressive strength (UCS), point load index (Is(50)), and static elasticity modulus (Es); effective porosity (n), dry unit weight (DUW), and saturated unit weight (ϒs) sets of the rock specimens were determined. Finally, statistical correlations were performed by regression analysis to evaluate the relationships between UCS and Is(50), UPV, Es; UPV and Is(50), DUW, ϒs, n, and Es.

Numerical analysis of soil bearing capacity by changing soil characteristics

In this research work by changing different parameters of soil foundation like density, cohesion and foundation depth and width of square foundation at angle of friction of 0° to 50° with increment of 5°, numerically safe bearing capacity of soil foundation is calculated and it is attempted to assess economical dimension of foundation as well as understanding variation range of bearing capacity at different degree. It could help of civil engineering in design of foundations at any situation.

Bearing capacity of mixed soil model

The main objective of this research is the improvement of red soil by the addition of construction materials. This method could provide a scientific way to create a soil foundation with sufficient stability against geo-technical problems or instabilities. Laboratory tests have been conducted to characterize the behavior of red soil when amended with different types of gravels, soils and sand under compacted conditions with Optimum Moisture Content (OMC). Safe bearing capacity of all models have been calculated to identify the best and worst soil mixed model.

Significance of bearing capacity of clayey subgrade in flexible pavement design

Clays as subgrades pose serious problems to flexible pavements built over them as they retain moisture for a longer period and possess low strength. Excessive settlements along the wheel tracks on pavement surface and bearing capacity failures in the subgrade soil are often observed in the flexible pavements constructed over such subgrades. So, the present status of flexible pavements in clayey subgrades necessitates investigation into the design procedure. The present paper is intended to assess the adequacy of flexible pavement design thickness based on CBR method against possible risk of shear failure in subgrade soil. A design methodology for flexible pavements based on safe bearing capacity (SBC) of subgrade soil has been presented for evaluating the safety of pavements against shear failure risk. The pavement thickness designs have been carried out in clays of different compressibility from CBR and proposed SBC methods. Two case studies have also been presented wherein shear failure of subgrade has been noticed. Detailed discussion has been made and conclusions have been drawn for efficient design of flexible pavements.

Profiles of floating ice in Arctic regions using GPR

Geophysical crews have been collecting seismic data on the Arctic Coastal Plain for over 40 years. Most work is performed during the winter months to avoid environmental damage to the tundra. Seismic crews routinely operate over frozen lakes as well as on first year sea ice, and data collection may begin as soon as the ice is strong enough to support the equipment. Traditionally, the safe-bearing capacity of ice has been related to a minimum thickness and a subjective determination of the condition of the ice. This criterion has been established through years of experience and, for the most part, it has been quite successful. Ice conditions are monitored throughout the winter by drilling at designated intervals. This results in accurate thickness data at the collection points but does not provide any information between the points. Ice thickness by itself is not a good indication of ice strength. It is possible to have an ice sheet that is several feet thick and have near zero strength. However, flexural strength may be estimated when ice profiles are used in conjunction with other data. In an effort to obtain continuous profiles of the ice-water interface, a series of ground-penetrating radar (GPR) tests were performed. A GPR system was tested on lake ice as well as sea ice. In both cases, the bottom of the ice could be imaged. Radar profiles are normally displayed on a time scale. To convert the time scale to ice thickness, it is necessary to calculate the relative permittivity of the ice sheet. This is easily accomplished in the field. First year sea ice is a very complex mixture of ice, brine, and air. As the surface temperature of sea ice drops below freezing, small disks and needles of pure ice, termed frazil ice, form on the surface …

Concentrated Loads on a Floating Ice Sheet

Abstract The safe bearing capacity of a floating ice sheet is usually determined by limiting the maximum tensile stress which occurs under the load at the bottom of the ice sheet. If the size of the load distribution is large compared to the ice thickness, the thin plate theory predicts these stresses correctly. However, if the size of the load distribution becomes small compared to the ice thickness, the plate theory overestimates the stresses. In this case the ice sheet should he treated as a three-dimensional elastic layer. Previous investigators have solved the elastic-layer problem for loads distributed over a circular area, and have limited the results to the stress at the bottom of the ice sheet directly under the center of the load. In the present paper the stresses are evaluated at any radial position, and it is shown how these stresses approach those for the plate theory as the radial position becomes large. The solutions for the stresses are presented in integral form, as well as graphs from the numerical integration. These new results are significant for the superposition of stresses when two concentrated loads act near each other. Similarly for loads distributed over a rectangular area, the plate theory will overestimate the stresses if the dimensions of the load becomes small compared to the ice thickness. For this case integral solutions are presented for the stresses, and are evaluated directly under the center of the load.

Concentrated Loads on a Floating Ice Sheet

AbstractThe safe bearing capacity of a floating ice sheet is usually determined by limiting the maximum tensile stress which occurs under the load at the bottom of the ice sheet. If the size of the load distribution is large compared to the ice thickness, the thin plate theory predicts these stresses correctly. However, if the size of the load distribution becomes small compared to the ice thickness, the plate theory overestimates the stresses. In this case the ice sheet should he treated as a three-dimensional elastic layer.Previous investigators have solved the elastic-layer problem for loads distributed over a circular area, and have limited the results to the stress at the bottom of the ice sheet directly under the center of the load. In the present paper the stresses are evaluated at any radial position, and it is shown how these stresses approach those for the plate theory as the radial position becomes large. The solutions for the stresses are presented in integral form, as well as graphs from the numerical integration. These new results are significant for the superposition of stresses when two concentrated loads act near each other.Similarly for loads distributed over a rectangular area, the plate theory will overestimate the stresses if the dimensions of the load becomes small compared to the ice thickness. For this case integral solutions are presented for the stresses, and are evaluated directly under the center of the load.

Safe bearing capacity evaluation of the bridge site along Syafrubesi-Rasuwagadhi road, Central Nepal

The research work was carried out at the proposed bridge site along Syafrubesi-Rasuwagadhi Road, Central Nepal. The study was based on field SPT/DCPT and laboratory tests. N values were determined from SPT/DCPT test. The index and mechanical properties of granular soils were computed in laboratory. Then, ultimate and allowable bearing capacities with safety factor 3 for maximum tolerable limit of 40 mm settlement was estimated by empirical equations provided by Teng (1988) and Terzaghi and Peck (1978). It is recommended that safe bearing capacity for 6 m size open square foundation at left and right abutments are suitable within 4.5 to 6 m depth. doi: 10.3126/bdg.v12i0.2254 Bulletin of the Department of Geology, Vol. 12, 2009, pp. 95-100