Load Test Data Research Articles

New Design Correlations for Piles in Sand

A critical review of the literature clearly shows that existing theories which are used to determine the bearing capacity of piles driven in sand are not satisfactory. Careful examination of the results of experimental studies indicates that existing theories fail to consider all significant parameters. Field load test data are used to determine which of the pile geometry and soil property parameters are significant. Special attention is given to the problem of residual stresses. Bearing capacity factors are calculated from measured unit point and side resistances. The bearing capacity factors are correlated with relative depth (depth of penetration to diameter ratio) and friction angle or relative density of sand. New design correlations are developed for use in predicting the bearing capacity of axially loaded piles in sand.

Duration of load and probability of failure in wood. Part I. Modelling creep rupture

Two models are considered for the study of wood creep rupture behaviour and the associated load duration effects on strength. Both are damage accumulation models. In model I, the damage rate is expressed as the product of a stress-dependent factor and a damage-dependent factor. In model II, the damage rate is given as the sum of a stress-dependent term and a damage-dependent term. Both models consider a stress threshold below which the damage rate vanishes. For each model, stress histories corresponding to two types of tests are considered: a step function load test and a ramp load test. The predictions of the models for these two cases are used to obtain model parameters by fitting constant and ramp load test data. Data used correspond to small, clear specimens of Douglas-fir in bending. As an application, the problem of residual strength in a ramp load test after a time of constant load is discussed.

Analysis of Pavements Designed by CBR Equation

Using the layered computer program, the parameters computed for the pavements included: (1)The elastic stresses, strains, and displacements; and (2)the accumulated permanent deformations in the subgrade in conjunction with laboratory repeated load test data. These results showed that, for pavements designed for the same performance level but for various conditions, the elastic displacements at both pavement and subgrade surfaces and accumulated subgrade permanent deformations vary with the subgrade strength and the wheel load. An exception is the elastic vertical strain at the subgrade surface, which is nearly independent of these factors. The surface permanent deformations measured from field test pavements are also examined. Two factors must be emphasized: (1)Surface rutting is not considered as a primary factor in judging pavement failure in most failure criteria; and (2)the computed results and the measured surface ruts are strongly related to the failure criteria employed in judging the pavement performance.

Behaviour of Isolated Bored Enlarged Base Pile under Sustained Vertical Loads

ABSTRACT Many static methods and dynamic formulae are available in the published literature, for predicting the pile capacities. So also, the procedures for evaluating the ultimate capacities based on the load test data. All these methods and procedures, instead of providing unique answer, give different load values. Thus placing the designer in a dilemma with respect to the method that is to be adopted. Most of experimental suggestions are based on the results of small size piles driven in sandy deposits. But none of these suggestions try to dwell upon their limitations. In the present study an attempt has been made to analyse the behaviour of isolated piles, based on series of field tests, conducted on bored piles with enlarged base in a uniform deposit of silty sand. The performance mechanism of isolated piles have been studied. Also suggestions for estimating their capacities based on load tests and static methods have been provided. The predicted load-settlement behaviour by the elastic theory approach does not agree with the observed one.

A design approach for pile foundations in permafrost

A design philosophy for piles in ice and ice-rich permafrost is proposed, whereby the pile settlements over the design life of the structure are retained within acceptable limits.The secondary creep law for ice is reviewed and the relationships between secondary creep rate, stress, and temperature are obtained using existing creep test data from many different sources. An analysis is performed which relates the steady pile settlement rate to the pile shaft stress and the constant ground temperature.A review of the pile load test data available in the literature is carried out, and the results are compared with the theoretical predictions provided by the pile settlement analysis. Reasonable agreement is obtained between prediction and observation, and it is thought that the analysis presented here provides a conservative (safe) bound on the observed results.The analysis is extended to account for the compression of the pile shaft, varying ground temperature profiles, stress readjustment along the pile shaft, and the end bearing capacity of the pile.The analysis presented here provides a rational basis for pile design in permafrost and, in addition, explains many of the phenomena likely to be observed in the behavior of piles under sustained loading.

Settlement of Building on Pile Foundation in Sand

Displacement type compacted concrete piles (pressure-injected Franki type) were driven into the upper portion of a medium dense sand stratum for the foundation of a 19-story reinforced concrete building. Results of pile load tests and actual building settlements were recorded over a 2 yr. period. The settlement ranged from 1.6 in (4.0 cm) to 3.3 in. (8.4 cm), the average group settlement being approx. 2.5 in. (6.4 cm). These field measurements are compared with settlement predictions computed using: (1) classical elasticity theory which greatly overestimates the actual settlement of a single pile; (2) recent extensions of elasticity theory which provide reasonable results for both single pile and pile group settlement behavior; and (3) empirical curves which require pile load test data to give average group settlement and compare favorably with the field measured values.

Foundation characteristics of the Upper Carboniferous rocks

Summary The paper is primarily concerned with the bearing capacity and settlement characteristics. Mining subsidence is not considered. The location of 'exposed' Upper Carboniferous rocks is briefly outlined in relation to urban and industrial areas, and depths to rockhead are discussed. The characteristic cyclic pattern of deposition of the Coal Measure rocks is described, and descriptions of the principal rock types, and some overlying soils are given. In the Coal Measure rocks the upper surface is usually weathered. Over mudstones there is typically 10 ft or so of material weathered to a clay, followed by less weathered rock. Over sandstones the fully weathered zone is thinner and usually consists of clayey sand containing weathered sandstone fragments. Depth of weathering may be locally increased near faults and where dips are steep. Exploration is often by soft ground boring methods in the overlying soils followed by diamond drilling in rock. NX-size core barrels are the minimum size which can be expected to give 100 per cent core recovery, and on important jobs it is recommended that a larger size should be used. Drill core required for laboratory testing must be protected against drying-out and against frost action. The value of trial pits is emphasized. Some laboratory test values of compression strength and deformation modulus are given in the paper and the limitations of laboratory testing are discussed. Standard Penetration Tests have been used in the Coal Measure shales and mudstones to give a rough guide to rock strength. A tentative correlation between S.P.T. values and rock description is given. Other in situ testing techniques are the Menard Pressuremeter Test, the Plate Loading Test and loading tests on piles. For plate loading tests in pits and at the base of piles it is essential that the material below test level is undisturbed. Seepage forces from ground water must be avoided since they can cause rapid deterioration. The usual pile loading test involves load application at the head of the pile, but valuable information can be obtained from tests in which end bearing resistance is measured separately from side shear within the 'rock socket'. Data is given for three sites where plate loading tests were carried out, together with laboratory testing. From this data and from laboratory test data presented elsewhere in the paper, characteristic values of compression strength and deformation modulus have been chosen. It has been customary to assign allowable bearing capacities to Upper Carboniferous rocks on the basis of visual inspection; typical values are quoted. For a calculation of allowable bearing pressure recent practice is to use the results of in situ loading tests. Unfortunately there do not appear to be any published data concerning the behaviour of full-scale foundations. It is suggested that for the Upper Carboniferous rocks, bored cast– in situ piles are generally preferable to driven piles. Ranges of working loads, and corresponding penetrations, are discussed and comments are made on pile spacings. Pile loading test data presented for three sites appear to support these empirical criteria. A more rational estimation of pile bearing capacity would involve considerations of end bearing capacity and of side shear within the rock socket. This is difficult since side shear between concrete and rock depends not only on rock strength and deformation characteristics, but also on the response of the rock to the pile boring processes. Further development must depend on correlation of performance data with careful and detailed description of the rocks involved.

Pile-Driving Formulas for Friction Piles in Sand

Seven different pile-driving formulas are used to calculate the capacities of 93 timber, precast concrete, and steel piles, for which field load test data are available. The relationship between the computed and the measured capacities is analyzed using the reduced major-axis form of linear regression analysis. The accuracy of the formulas varies with the type of pile. The Gates, Janbu, and Danish formulas yield the highest correlation coefficients, followed closely by the Pacific Coast Uniform Building Code and Hiley formulas. The capacities calculated using the Gow and Engineering News formulas correlate poorly with measured capacities. A statistical adjustment is applied to the formulas to bring them into conformance with the field measurements. The adjusted forms of the Gates, Janbu, and Danish formulas are equally accurate and appear satisfactory for general use. The Gates formula is the simplest to use.

Induction Motor Performance Calculations

By means of solutions of the induction motor exact equivalent circuit in the form of infinite power series, approximate formulas for the important motor characteristics are derived. These formulas enable the effects of magnetizing current, core loss, and primary resistance on maximum torque, starting current, and so forth, to be readily taken into account with engineering accuracy. A new form of power factor chart is presented, which enables the power factor-load curve of any motor to be conveniently determined from no load test data. Exact values of power factor can be obtained from the chart by applying differential corrections, formulas for which are given. The methods outlined were developed to secure an optimum combination of speed, accuracy, and consistency in design calculations, and have been in regular use for the past seven years.