Evaluation of end bearing capacity of drilled shafts in sand by numerical and SPT-based methods

Drilled shafts are a common type of pile foundations which are often used as foundations for buildings, bridges and other structures. The end bearing capacity of drilled shafts, which plays an important role in their design particularly in sandy soils, has traditionally been estimated using empirical or semi-empirical methods. With advances in computing power, it is now possible to conduct more realistic analyses. In this paper, at first, the end bearing capacity of drilled shafts in sandy soils is analyzed numerically and validated with the results of pile load test. Then, the numerical results are compared with the results of Standard Penetration Test (SPT)-based methods. The comparison indicated that there is a satisfactory agreement between the results of numerical method proposed in this paper and the results achieved by SPT-based methods

EVALUATION OF END BEARING CAPACITY OF DRILLED SHAFTS IN SAND BY NUMERICAL AND SPT-BASED METHODS

Drilled shafts are a common type of pile foundations which are often used as foundations for buildings, bridges and other structures. The end bearing capacity of drilled shafts, which plays an important role in their design particularly in sandy soils, has traditionally been estimated using empirical or semi-empirical methods. With advances in computing power, it is now possible to conduct more realistic analyses. In this paper, at first, the end bearing capacity of drilled shafts in sandy soils is analyzed numerically and validated with the results of pile load test. Then, the numerical results are compared with the results of Standard Penetration Test (SPT)-based methods. The comparison indicated that there is a satisfactory agreement between the results of numerical method proposed in this paper and the results achieved by SPT-based methods

An experimental evaluation of size effect and bearing capacity of footing on non-woven geotextile-reinforced sand

Reinforced soil is a composite material in which elements with tensile strength were utilized for reinforcement. Geotextile is the most common material in group of geosynthetics for soil reinforcement. This paper presents the effect of a non-woven geotextile which have a higher failure strain on bearing capacity of rigid footing constructed on sand. A research has been done to investigate the bearing capacity of granular soil with plates which have standard width according to ASTM D 1194. In this study, a total number of 62 model tests were carried out in a laboratory using two square rigid steel plate with the sides of 270 mm and 350 mm. A broad series of conditions was tested by varying parameters such as the location of upper layer of geotextile, number of geotextile layers, width of reinforcement and vertical spacing between layers. In second step a series of tests were additionally carried out by varying of spaces between layers and width of geotextile layers in proportion to increase of depth. The results demonstrated that in all cases non-woven geotextile increases bearing capacity and the maximum bearing capacity was obtained in 4-layer reinforcement system. It is also shown that the optimum value of vertical spaces between layers after the upper one are respectively, 0.30 B, 0.35 B, 0.45 B. In addition, the results indicate that optimum width of the first two layers of reinforcement are 4 B and for the third and fourth one are 3 B and 2.5 B respectively. © Published under licence by IOP Publishing Ltd

EVALUATION OF END BEARING CAPACITY OF DRILLED SHAFTS IN SAND BY NUMERICAL AND SPT-BASED METHODS

Drilled shafts are a common type of pile foundations which are often used as foundations for buildings, bridges and other structures. The end bearing capacity of drilled shafts, which plays an important role in their design particularly in sandy soils, has traditionally been estimated using empirical or semi-empirical methods. With advances in computing power, it is now possible to conduct more realistic analyses. In this paper, at first, the end bearing capacity of drilled shafts in sandy soils is analyzed numerically and validated with the results of pile load test. Then, the numerical results are compared with the results of Standard Penetration Test (SPT)-based methods. The comparison indicated that there is a satisfactory agreement between the results of numerical method proposed in this paper and the results achieved by SPT-based methods

Effect of silica fume on the ultrasonic pulse velocity of cemented sand

One of the geotechnical engineering strategies for dealing with weak soils in a construction site is to modify their mechanical properties with the aid of soil improvement techniques. Chemical stabilization of soil using cement is one of these effective approaches that can considerably enhance workability and shear strength parameters of soil. However, very limited investigations have been carried out to reveal the effect of silica fume on the ultrasonic pulse velocity (UPV) and the ultrasonic stiffness (Eu) of cement-treated sandy soil. For this purpose, in the present research, a series of UPV tests were performed on sand-cement-silica fume specimens. The cement percentages were 3, 5 and 7% and silica fume contents were 0, 0.25, 0.5 and 1% by weight of dry sand. The cylindrical samples were prepared and cured for 3, 7, 14, 28, 42 and 56 days and tested. The results show that inclusion of silica fume to the cemented sand increases UPV and Eu which this enhancement is more pronounced at longer ages. © Published under licence by IOP Publishing Ltd

Factors influencing the critical piles length in reinforced slope

In this research, the performance of a homogeneous slope reinforced with one row of piles is studied using coupled numerical analysis and the method of shear strength reduction as implemented in the finite element analysis software, ABAQUS. Parametric studies are performed by changing geometric and strength parameters such as piles head conditions, piles location and the soil cohesion to assess their influence on the slope stability. For each of these parameters, the safety factor of the slope and the piles critical length was assessed. The results indicates the performance level of piles with different head conditions will not be similar; so that hinged and fixed heads are the most effective and cause the piles critical length to reduce, whilst free heads are less effective. The optimum location of the piles depends on their length, but regardless of the piles head type, the maximum increase of the safety factor is achieved when the piles are located in the mid-section of the slope. In addition to this, various levels of soil cohesion do not affect the piles optimum location, whilst cause significant changes in their critical length and increase rate of safety factor. © Published under licence by IOP Publishing Ltd

The influence of micro silica on the compaction properties of cemented sand

In this experimental research, a series of standard Proctor compaction tests have been performed to explore the effect of micro silica on the compaction properties of cemented sand. The cement contents were 3, 5 and 7% and micro silica contents were 0, 0.25, 0.5 and 1% by weight of dry sand. The results showed that micro silica particles increase maximum dry unit weight of sand-cement mixtures and decrease their optimum moisture content. The results of Scanning Electron Microscope (SEM) images confirmed the results of compaction tests and indicated that micro silica can effectively fill the pores of sand-cement mixtures which can lead to creation of a cement-treated sand mixture with compact microstructure. © Published under licence by IOP Publishing Ltd