Synopsis The results of recent research into the immediate and final settlement and rate of settlement of pad foundations on clay are given. The necessity for a three-dimensional approach is discussed and a method of predicting settlements is proposed, based the use of elastic displacement theory in combination with experimental soil parameters determined over a representative range of stress. The results computations of elastic theory suitable for this method are outlined. The limitations of an elastic approach to the calculation of immediate settlements are discussed in relation to local yield within the soil. The results of laboratory tests on model footings and predictions by the proposed method are compared. The agreement is good with respect to the total final settlement, fair with respect to the immediate settle- ment, and good with respect to the rate of settlement. Les resultats des recents travaux de recherche portant sur le tassement immediat et final et de la vitesse de tassement des plaques d...

The Use of Elastic Theory for Settlement Prediction Under Three-Dimensional Conditions

This report provides a design guideline and recommended standard for geofoam applications in the design and construction of highway embankments. The guidelines and standard will assist highway agencies in designing and constructing highway embankments using expandable polystyrene (EPS) blocks. The report will be of immediate interest to engineers in the public and private sectors involved in the design, construction, and material specification of lightweight embankments constructed on soft foundation soils.

Guideline and recommended standard for geofoam applications in highway embankments

One of the 12 instrumented sections of the Virginia Smart Road was used to compare measured vertical compressive stress and measured transverse horizontal strain under the hot-mix asphalt (HMA) layer induced by a 25.8 kN (5.8 kip) single tire and a 39.5 kN (8.9 kip) set of dual tires to those calculated using layered linear elastic theory. The pavement section is composed of 38 mm (1.5 in.) HMA wearing surface, 150 mm (6 in.) of HMA base mix, 75 mm (3 in.) of asphalt stabilized open graded drainage layer, 150 mm (6 in.) of cement stabilized aggregate layer, and 175 mm (7 in.) of unbound aggregate base. The subgrade is a fill material composed mainly of rocks. Measured stresses were obtained using pressure cells embedded in the pavement during construction. Horizontal transverse strain was measured using H-type strain gauges that were also embedded during construction. Temperature in the pavement layers was measured using embedded T-type thermocouples. Theoretically calculated stresses and strains were obtained using software based on the layered-elastic theory (Kenpave, Bisar 3.0, Elsym5, and Everstress 5.0). In addition, two finite-element approaches were used. Results indicated that the layered elastic theory overestimates pavement responses at low and intermediate temperatures, but significantly underestimates the pavement responses to vehicular loading at high temperatures.

Difference between In Situ Flexible Pavement Measured and Calculated Stresses and Strains

An investigation was conducted to characterize and relate in situ soil stress-strain behavior to roller-measured soil stiffness. Continuous assessment of soil stiffness via roller vibration monitoring has the potential to significantly advance performance based quality assurance of earthwork. One vertically homogeneous and two layered test beds were carefully constructed with embedded sensors for the field testing program. Total normal stress and strain measurements at multiple depths reveal complex triaxial soil behavior during vibratory roller loading. Measured cyclic strain amplitudes were 15–25% of those measured during static roller passes due to viscoelasticity and curved drum/soil interaction. Low amplitude vibratory roller loading induces nonlinear in situ modulus behavior. Roller-measured stiffness and its dependence on excitation force is influenced by the stress-dependent modulus function of each soil, the varying drum/soil contact area, and by layer characteristics (modulus ratio, thickness) when layering is present. On vertically homogeneous clayey sand, roller-measured stiffness decreased with increasing excitation force, a behavior attributed to stress-dependent modulus reduction observed in situ. On the crushed rock over silt test bed, roller-measured stiffness increased with increasing excitation force despite the mild stress-dependent modulus reduction observed in the crushed rock. In this case, the stiffer crushed rock takes on a greater portion of the load, resulting in the increase in roller-measured stiffness.

In Situ Soil Response to Vibratory Loading and Its Relationship to Roller-Measured Soil Stiffness

THE TABLES OF VALUES OF STRESSES ARISING IN A THREE-LAYER ELASTIC SYSTEM LOADED OVER A CIRCULAR AREA HAVE BEEN EXTENDED TO COVER A WIDER RANGE OF PARAMETERS. VALUES OF THE VERTICAL STRESSES AT BOTH INTERFACES ARE GIVEN, AND ARE ACCURATE TO WITHIN 1 PERCENT. THE CALCULATIONS WERE PERFORMED ON THE FERRANTI MARK I COMPUTER AT KONINKLIJKE/ SHELL LABORATORIUM, AMSTERDAM. THE WORK FORMS PART OF A PROGRAM FOR THE DEVELOPMENT OF A METHOD FOR THE DESIGN OF FLEXIBLE ROADS. /AUTHOR/

Tables of stresses in three-layer elastic systems

THEORIES OF LAYERED SOIL DEPOSITS ARE REVIEWED. THE THEORY OF STRESSES ARE DISPLACEMENTS IN A TWO-LAYERED SYSTEM WAS DEVELOPED IN ACCORDANCE WITH THE METHODS OF THE MATHEMATICAL THEORY OF ELASTICITY AND IS PRESENTED IN ORDER TO REVEAL SOME OF THE FUNDAMENTAL RELATIONS EXISTING BETWEEN THE PHYSICAL FACTORS, WHICH CONTROL THE LOAD-SETTLEMENT RELATIONS, AND IN ORDER TO PROVIDE A PRACTICAL METHOD OF ANALYSIS FOR THE DESIGN OF AIRPORT RUNWAYS. THE THEORY REVEALS THE CONTROLLING INFLUENCE OF TWO IMPORTANT RATIOS ON THE LOAD-SETTLEMENT CHARACTERISTICS OF THE TWO-LAYER SYSTEM: (1) THE RATIO OF THE RADIUS OF THE BEARING AREA TO THE THICKNESS OF THE REINFORCING OR PAVEMENT LAYER, AND (2) THE RATIO OF THE MODULUS OF THE SUBGRADE TO THAT OF THE PAVEMENT, FOR PRACTICAL DESIGN PURPOSES, THE THEORETICAL RESULTS WERE EVALUATED NUMERICALLY AND EXPRESSED IN BASIC INFLUENCE CURVES, GIVING VALUES OF THE SETTLEMENT COEFFICIENT IN TERMS OF THESE BASIC RATIOS. THE SETTLEMENT COEFFICIENT IS APPLIED AS A SIMPLE MULTIPLYING OR CORRECTION FACTOR TO THE BOUSSINESQ EQUATION FOR SURFACE SETTLEMENT AT THE CENTER OF A CIRCULAR FLEXIBLE BEARING AREA. THE DESIGN FOR AIRPORT RUNWAYS INVOLVES THE SELECTION OF SUITABLE TYPES OF PAVEMENT CONSTRUCTION AND THE DETERMINATION BY THE INFLUENCE CURVES FOR THE TWO-LAYER SYSTEM OF THE THICKNESS REQUIRED TO GIVE ADEQUATE SUPPORT TO AIRPLANE WHEEL LOADS AND REASONABLE LENGTH OF SERVICE. FIELD LOAD TEST CHECKS OF QUALITY AND STRENGTH CAN BE MADE DURING CONSTRUCTION ON: (1) THE NATURAL SUBGRADE TO DETERMINE TENTATIVELY THE THICKNESS OF BASE COURSE AND PAVEMENT REQUIRED, (2) TOP OF THE BASE COURSE TO CHECK THE QUALITY AND STRENGTH AT THIS STAGE OF CONSTRUCTION, AND (3) TOP OF THE FINISHED PAVEMENT TO CHECK THE EFFECTIVE SUPPORTING CAPACITY OF THE WHOLE PAVEMENT CONSTRUCTION.

T A Middlebrooks

Papers

The theory of stress and displacements in layered systems and applications to the design of airport runways