The Response of Soils to Dynamic Loadings; Report 26, Final Report

Abstract

In 1967, the uriter was very concerned about an apparent trend toward developing ever more complex computer codes while failing to use existing computer codes to understand important cause and effect relations and to ascertain the effect of uncertainties in the input on the nature of the computed results. The emphasis of Chapter 2, and many of the specific comments, reflected this concern. The writer quite frankly felt that the comrn puter code development, as it was apparently being followed, was largely an academic exercise, that quite likely it would be impossible to rely on the codes for design predictions, aid that designs would still have to be based on very simple prediction equations together with a large dose of judgment.The writer has been "out of the business" since 1967, but from various conversations it appears that he may have been wrong in his assessment of the trends in computer code development and utilization. Apparently there has developed a close cooperation between experienced soil engineers and the developers and users of complex computer codes. Apparently there is also now a recognition of the need to make, in connection with specific design projects and field experiments, a series of computer runs so as to bracket the effect of uncertainties in the input and assumptions.If these statements do reflect the current situation, then some of the statements in this report may happily be out-of-date.However, the writer still does bvlieve in the necessity of developing improved but simple and approximate prediction techniques which do not re-

Attenuation of ground vibrations due to different technical sources

“…Similar differences between the attenuation of displacements, velocities and accelerations have been reported for explosions (Whitman, 1970). The absolute attenuation exponents depend on the specifi c amplitude spectrum U 0 (ω) of the vibration.…”

Stress-strain behavior of sand at high strain rates

“…There are three main mechanisms governing response of sand in uniaxial compression: (1) elastic compression of individual sand grains; (2) slippage and rearrangement of grains; (3) grain crushing. The three mechanisms occur at different threshold stress levels, and four distinct regions may be identified in the response based on the governing mechanism [21]: Zone 1: The axial stress level applied in this region is not enough to overcome the kinetic friction between individual sand grains. Stress-strain response in this initial region is elastic, corresponding to the elastic deformation of individual grains.…”

“…In critical state soil mechanics the definition of failure can be given in a number of ways including simple Mohr-Coulomb envelopes, or by defining a critical state failure line [35] [21]). …”

Uniaxial Stress-Strain Behavior of Unsaturated Soils at High Strain Rates

“…The stiffening is usually referred to as a time or loading rate effect. Some researchers (14,30,31) have suggested that, as the time to peak pressure approaches the submillisecond range, a drastic increase (up to tenfold) in the loading constrained modulus occurs for partially saturated granular soils under unconsolidated-undrained conditions. The existence of this effect has been the subject of much debate."…”

“…Whitman (30) indicated that rate effects become very important at submillisecond loading times and theorized that at high saturations, the pore phase of the soil is much stiffer than the soil skeleton (pore fluid compressibility Limited research has also been conducted using the Split-Hopkinson Pressure Bar to study the uniaxial stress-strain behavior of compacted moist soil under one-dimensional confined compression loading at high strain rates (7,8,11). The results of these studies indicated that the uniaxial stress-strain response is primarily governed by the initial gas filled porosity of the soil specimen, and that strain-rate effects did not occur at strains less than the initial gas filled porosity.…”