Analysis of the Shaft Resistance of Nondisplacement Piles in Sand

The paper examines, using numerical modelling, the problem of the limit shaft resistance of non-displacement piles installed in sands. The modelling makes use of an advanced, two-surface-plasticity constitutive model. The constitutive model predicts the soil response in both the small- and the large-strain range, while taking into account the effects of the intermediate principal effective stress and of the inherent anisotropy of the sand. Finite element analyses of shearing along the pile shaft are performed in order to examine the development of limit unit shaft resistance and the changes in stress state around the shaft upon axial loading of the pile. Special focus is placed on the operative value of the lateral earth pressure coefficient when limit shaft resistance is reached. The analyses offer useful insights regarding the factors controlling the value of unit shaft resistance in sands. The simulations predict a significant build-up of horizontal effective stress for dense sands. Based on these simulations, we propose a relationship between the lateral earth pressure coefficient for use in the calculation of the limit shaft resistance of the pile and the initial density and stress state of the sand

Effect of Relative Density and Stress Level on the Bearing Capacity of Footings on Sand

The design of shallow foundations relies on bearing capacity values calculated using empirical procedures that are based in part on solutions obtained using the method of characteristics, which assumes a soil that is perfectly plastic following an associated flow rule. In this paper the problem of strip and circular footings resting on the surface of a sand layer is analysed using the finite-element method. Analyses are performed using a two-surface plasticity constitutive model that realistically captures the aspects of the mechanical response of sands that are relevant to the bearing capacity problem. In particular, the model accounts for non-associated flow, strain-softening, and both stress-induced and inherent anisotropy. Based on the results of the analyses, the paper examines the validity of the bearing capacity factors N γ and shape factors s γ used in practice. A relationship for determining appropriate values of friction angle for use in bearing capacity calculations is also proposed

Stress-dilatancy Relation for Mohr-Coulomb Soils Following a Non-Associated Flow Rule

Rowe\u27s stress–dilatancy relation for frictional (cohesionless) materials has been a cornerstone of soil mechanics. The original derivation of this relationship was based on incorrect energy minimisation considerations, but the relationship was proven later by De Josselin de Jong using friction laws, and has been confirmed by a large body of experimental results. In contrast, the validity of Rowe\u27s stress–dilatancy relation for cohesive-frictional materials, which has also been used, although not as extensively, was never verified. This paper shows that Rowe\u27s stress–dilatancy relation for Mohr–Coulomb soils (cohesive-frictional materials) is in fact incorrect. The paper also provides a correct stress–dilatancy relationship for non-associated Mohr–Coulomb soils that have both cohesive and frictional strength components. The derivation of the relationship for cohesive-frictional soils presented in this paper relies on use of the sawtooth model together with the application of the laws of friction

NEW PHOSPHORUS COMPOUNDS K[PCL3(X)] (X= SCN, CN): PREPARATION AND DFT AND SPECTROSCOPIC STUDIES

Indexación: Web of Science. Scielo.Two new phosphorus complexes, potassium trichlorothiocyanophosphate (III) (PTCTCP; K[PCl3(SCN)]) and potassium trichlorocyanophosphate (III) (PTCCP; K[PCl3(CN)]) were synthesized from the reaction of KSCN and KCN, respectively, with PC^. The chemical formulas and compositions of these compounds were determined by elemental analysis and spectroscopic methods, such as phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy (31P-NMR), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy and mass spectrophotometry. All of the theoretical calculations and determinations of the properties of these compounds were performed as part of the Amsterdam Density Functional (ADF) program. Excitation energies were assessed using time-dependent perturbation density functional theory (TD-DFT). In addition, the molecular geometry was optimized and the frequencies and excitation energies were calculated using standard Slater-type orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all of the atoms. The assignment of the principal transitions and total densities of state (TDOS) for orbital analysis were performed using the GaussSum 2.2 program.http://www.scielo.cl/pdf/jcchems/v61n1/art15.pd

Pile Driving Analysis for Pile Design and Quality Assurance

Driven piles are commonly used in foundation engineering. The most accurate measurement of pile capacity is achieved from measurements made during static load tests. Static load tests, however, may be too expensive for certain projects. In these cases, indirect estimates of the pile capacity can be made through dynamic measurements. These estimates can be performed either through pile driving formulae or through analytical methods, such as the Case method. Pile driving formulae, which relate the pile set per blow to the capacity of the pile, are frequently used to determine whether the pile has achieved its design capacity. However, existing formulae have numerous shortcomings. These formulae are based on empirical observations and lack scientific validation. This report details the development of more accurate and reliable pile driving formulae developed from advanced one-dimensional FE simulations. These formulae are derived for piles installed in five typical soil profiles: a floating pile in sand, an end‐bearing pile in sand, a floating pile in clay, an end‐bearing pile in clay and a pile crossing a normally consolidated clay layer and resting on a dense sand layer. The proposed driving formulae are validated through well-documented case histories of full-scale instrumented driven piles. The proposed formulae are more accurate and reliable on average than other existing methods for the case histories considered in this study. This report also discusses the development of a pile driving control system, a fully integrated system developed by Purdue that can be used to collect, process, and analyze data to estimate the capacities of piles using the Case method and the pile driving formulae developed at Purdue

Assessment of Site Variability from Analysis of Cone Penetration Test Data

Soil property values for use in geotechnical design are often estimated from a limited number of in situ or laboratory tests. The uncertainty involved in estimating soil properties from a limited number of tests can be addressed by quantifying the variability within individual soundings and of the collection of soundings at a site. It has been proposed that factors of safety or resistance factors used in design be linked to site variability. Site variability can be assessed by studying the correlation structure of in situ test data. The cone penetration test (CPT), which is a reliable and widely-accepted in situ test, can be used for this purpose. Soil behavior type (SBT) charts are often used to obtain the subsurface soil profile from CPT parameters such as the cone resistance and the sleeve friction. A soil profile generation algorithm was developed in this research to generate a soil profile from an individual CPT sounding using two modified SBT charts. Soils are variable in both the vertical and horizontal directions. A vertical variability index (VVI) was defined to quantify variability in a CPT sounding. The average of the VVIs for all CPT soundings performed at a site is the site VVI. A site horizontal variability index (site HVI) was also developed, based on cross-correlation between cone resistances, the cone resistance trend differences and the spacing between every pair of CPTs considered, to quantify the soil variability of a site in the horizontal direction. A site variability rating (SVR) system, integrating the vertical and horizontal site variability, was developed to assess the overall site variability. Depending on the SBT chart selected, the soil profile generated using the soil profile generation algorithm may be slightly different; however, the SBT chart effect on the variability indices that compose the SVR index is small. Close agreement was found between the SVRs obtained using the two SBT charts selected for this research. In order to illustrate the use of the algorithms for VVI and HVI calculations and SVR of sites, CPTs from across the state of Indiana were analyzed. CPT data were obtained from Purdue\u27s own database, INDOT’s data repository and the U.S. Geological Survey (USGS) website. Site variability is calculated for specific depths of interest. For example, that depth of interest will be shallower for shallow foundations than for deep foundations. Site variability rating maps (SVR maps) for various depths of interest were constructed for the state of Indiana, illustrating the potential use of the site variability assessment methodology. An optimal sounding spacing calculation methodology was also developed to make the site investigation process more efficient, cost-effective and reliable

Settlement Analysis of Axially Loaded Piles

In pile design, settlement controls the design in most cases because, by the time a pile has failed in terms of bearing capacity, it is very likely that serviceability will have already been compromised. This notwithstanding, pile foundations are often designed based on the calculations of ultimate resistances reduced by factors of safety. This is in part due to the lack of accessible realistic analyses for estimation of settlement, especially for piles installed in layered soil. This paper presents a new settlement analysis method for axially loaded piles in multilayered soil and analyzes two case histories for which load tests were performed on nondisplacement piles. The analysis follows from the solution of the differential equations governing the displacements of the pile-soil system obtained using variational principles. The input parameters needed for the analysis are only the pile geometry and the elastic constants of the soil and pile. A user-friendly spreadsheet program (ALPAXL) was developed to facilitate the use of the analysis

Seismic Design of Pile Foundations in Southern Indiana

In this paper, we present an evaluation of the potential risk of earthquake-induced damage to pile foundations in Indiana. Piles are commonly used in foundations of bridge piers in the southern part of Indiana; the potential seismic sources in this region are the Wabash Valley Fault system and the New Madrid Seismic Zone. Based on in-situ test data for specific sites in southern Indiana, one-dimensional wave propagation analyses are performed. Additionally, the liquefaction potential is estimated based on the calculated acceleration profile. Data on real cases of pile damage due to seismic events are collected after an extensive literature survey. Using this information, the main causes and characteristics of earthquake-induced pile failure are identified, and the conclusions obtained are applied to southern Indiana to make a preliminary assessment of pile damage potential. Simple 3-D numerical analyses for the pile foundations of an existing bridge structure are performed using the finite element method. The results show that, for typical pile foundations and soil profiles in southern Indiana, a credibly large earthquake is capable of producing significant damage to the piles

A Continuum-Based Model for Analysis of Laterally Loaded Piles in Layered Soils

An analysis is developed to calculate the response of laterally loaded piles in multilayered elastic media. The displacement fields in the analysis are taken to be the products of independent functions that vary in the vertical, radial and circumferential directions. The governing differential equations for the pile deflections in different soil layers are obtained using the principle of minimum potential energy. Solutions for pile deflection are obtained analytically, whereas those for soil displacements are obtained using the one-dimensional finite difference method. The input parameters needed for the analysis are the pile geometry, the soil profile, and the elastic constants of the soil and pile. The method produces results with accuracy comparable with that of a three-dimensional finite element analysis but requires much less computation time. The analysis can be extended to account for soil non-linearity

Analysis of Laterally Loaded Piles in Multilayered Soil Deposits

This report focuses on the development of a new method of analysis of laterally loaded piles embedded in a multi-layered soil deposit treated as a three-dimensional continuum. Assuming that soil behaves as a linear elastic material, the governing differential equations for the deflection of laterally loaded piles were obtained using energy principles and calculus of variations. The differential equations were solved using both the method of initial parameters and numerical techniques. Soil resistance, pile deflection, slope of the deflected pile, bending moment and shear force can be easily obtained at any depth along the entire pile length. The results of the analysis were in very good agreement with three-dimensional finite element analysis results. The analysis was further extended to account for soil nonlinearity. A few simple constitutive relationships that allow for modulus degradation with increasing strain were incorporated into the analysis. The interaction of piles in groups was also studied