ABSTRACTStudies in geotechnical engineering have the nonlinear behavior of soils. An experimental study was carried out on models of piled rafts, and four piles with a diameter of 25 mm and a length of (300, 400, and 500) mm were taken, with a raft of (180x180) mm, and compared with the piled-raft system of 180 × 180 raft and nine piles of 19 mm and 500 mm in diameter and length respectively. They were tested for raft resistance, number of piles, length, and diameter while maintaining the spacing between piles. Test results showed the raft performance improved by 76% when adding piles. The increase in the (L/D) ratio for variable (L) length leads to an increase in pile share of 87% for the groups (2×2). Also, pile share was increased by 10% with a decrease in the diameter of piles and an increase in the number of piles in the group. Therefore, the increment in each pile’s skin friction results in an increase in the bearing capacity of each pile.
In this paper, a practical method of analysis of the pile displacements is proposed on the basis of the theory of load-transfer curves widely used in pile design and analysis. The parameters of the load-transfer curves for piles under axial load (called t-z, q-z curves) or lateral load (called P-Y curves) were correlated with the number of blows Nspt measured during the standard penetration test (SPT). Well documented case histories of full-scale axial or lateral loading tests on single piles in sand were collected, and the analysis of the experimental results led to define the parameters of the load-transfer curves. Two practical methods of computation of a single pile under an axial load or a lateral load were proposed to be used within the scope of a pile foundation project. At last, a validation process of the load-transfer curves was undertaken by direct comparison of the predicted pile displacements to those measured during other pile loading tests, which showed a good predictive capability of the two proposed methods
The finite element method is used to simulating the behavior of deep foundations subjected to negative skin friction in Basrah soil. Pile groups are analyzed under dragforces using 3D Plaxis software. Linear elastic and Mohr–Coulomb constitutive relations are adopted for the pile and soil materials. Three sites are selected to perform the study, where the negative skin friction is developed due to fill loads. The dragforces on driven piles, within (3 x 3) square groups with spacing of (3B), are evaluated and compared to their counterparts of single piles. The dragforces are decreased on piles constituting the group, and the reduction depends on pile location within the group. Centeral piles exhibit maximum reductions of (50%). To study the effect of pile spacing, a range of [(3B) to (6B)] was adopted. Apart from pile location, it is concluded that, the dragforce is proportional to pile spacing.
The finite element method capable of simulating the behavior of deep foundations subjected to negative skin friction in Basrah soil is investigated. Single piles under drag forces are analyzed using the PLAXIS program with an axisymmetric model. Linear elastic, Soft Soil and Mohr-Coulomb constitutive relations are adopted, where higher order triangular element is chosen for pile and soil clusters. Both pile and soil are modeled using (15)-node triangular elements. Three sites in Basrah province (Umm Qasr Port, Khor Al-Zubair, and Shatt AlArab Hotel) were selected to perform this study. The soil profile and layer characteristics are obtained from the soil investigation reports. Where the negative skin friction is evaluated due to filling loads. It is Conclusion thatSmall relative displacements are necessary to activate the negative skin friction. The elastic shorting for pile effect negative skin friction, due to increase relative displacement. The elastic shorting of the driven pile is more than that of the bored pile due to the less cross-sectional area of the driven pile. The results revealed proportional relation between the developed drag forces and pile section dimensions, interface friction factor, and fill height, with a maximum effect on the section dimension and minimum effect on the interface factor. The locations of neutral points are not sensitive to the above-mentioned factors.
Abstract:This paper presents exact probabilistic model as a complementary mathematicalbase for the traditional deterministic approach to quantify the selection of a factorof safety for each term of the load equation of friction piles in clay. The procedureof assigning a partial value of factor of safety for each clay layer using a quantifiedprobabilistic model instead of the use of a single global factor of safety for alllayers that based on arbitrarily judgments seems to introduce an enhancement toboth economical and safety consideration in the design procedure of the frictionpiles. it is suggested in this paper to derive probabilistic equation that describe eachlayer of the problem individually, each term of the pile load equation (clay layers) consists on a certain amount of uncertainty and each request assigning a certainvalue of factor of safety to eliminate this variability and to keep the probability offailure (which is more reliable risk index) at certain level. Exact probabilityequation is mathematically derived on the bases of the variability inherited in soilparameters (average un-drained shear strength and thickness of each clay layerinserted). The equation was verified using Monte carol simulation method andresults indicate excellent agreement in both, probability distribution shape andcalculated failure values. The relationship between factor of safety and probabilityof failure produced from the derived equation was inspected in addition to thesensitivity of the equation to the change of the variability of input parametersthrough a reference example.Keywords: Friction Pile, Load, Probability, factor of safety