Wayne A. Charlie

Split-Hopkinson Pressure Bar Testing of Unsaturated Sand

High amplitude, split-Hopkinson pressure bar (SHPB) laboratory tests were conducted on compacted specimens of 50/80 silica sand to evaluate the influence of saturation on compressional-stress wave velocity, stress transmission, and attenuation. Stress wave velocity and transmitted stress increase as the saturation increases from 0 to 30 to 40% for constant input stress and constant dry density. At saturation levels between 40 to 95%, both the wave speed and the transmitted stress decrease with increasing saturation. Quasistatic confined modulus show similar trends. These trends may be explained by capillary pressure.

BLAST-INDUCED LIQUEFACTION OF AN ALLUVIAL SAND DEPOSIT

A series of six different explosive charges ranging from 0.00045 to 9.06 kg were detonated at a depth of 3 m below a sand island in the South Platte River, northeast Colorado. Pore pressure, particle velocity, and residual pore pressure were measured at several locations. Liquefaction was induced in the dense, saturated, coarse sand at a depth of 3.0 m when peak compressive strain exceeded 0.01 percent, peak particle velocity exceeded 0.16 m/s, or at scaled distances less than 3 m/kg (to the 1/3 power). No residual pore pressure was induced at a peak compressive strain less than 0.002 percent, at peak particle velocity less than 0.03 m/s, or at scaled distances greater than 16 m/k (to the 1/3 power).

Canadian liquefaction experiment (CANLEX) : Blast-induced ground motion and pore pressure experiments

As part of the Canadian Liquefaction Experiment (CANLEX), single and multiple explosive charges were detonated in a level deposit of loose, saturated, sand-size mine tailings. Empirical equations were developed from pore pressure and ground motion recorded at several locations. A condition of zero effective stress was induced at a depth of 6 m when peak particle velocity exceeded 0.65 m/s for single detonations and 0.13 m/s for twelve detonations having millisecond delays. Little or no excess pore pressure was induced from single or multiple detonations when peak particle velocity or peak compressive strain was less than 0.01 m/s or 0.001 %, respectively. The blasting experiments were conducted and analyzed to determine blast-induced ground motion and pore pressure response in a level deposit and to determine the possibility of using explosives to trigger flow-liquefaction in tailings located below an embankment, while keeping peak particle velocities within limits set by Syncrude Canada, Ltd.

Porewater pressure increases in soil and rock from underground chemical and nuclear explosions

Abstract A review and analysis of chemical and nuclear explosive-induced porewater pressure increases and induced rise in groundwater table elevations (groundwater mounding) is presented. Our analysis indicates that residual pore pressure increases and groundwater mounding can be induced by underground chemical and nuclear explosions to scaled distances of 879 m/(kt) 1 3 . This relationship is linear over seven orders of magnitude of explosive energy ranging from a 0.01 kg chemical explosion to a 100 kt nuclear explosion and is valid for a wide variety of saturated geological profiles. Underground chemical explosions, and probably underground nuclear explosions have the potential to induce liquefaction of water-saturated soils to scaled distances of about 260 m/(kt) 1 3 .

Explosive Induced Pore Pressure in a Sandfill Dam

This paper reports on the potential performance of earthfill and tailings dams, and other saturated earthen structures, subjected to blast vibrations. Relationships between explosive-induced residual pore pressure increase and crest settlement versus peak particle velocity are presented. Eight explosive tests, conducted on a 2.25-m-high dam constructed of loose dilative sand, showed that significant increases in residual pore pressure (PPR > 0.1) occurred when peak particle velocity exceeded 0.015 m/s at shallow depths to 0.035 m/s at greater depths. Limited crest settlement occurred when the peak particle velocity exceeded 0.025 m/s. Results of this research, previous research, and the field behavior of full-scale earthfill and tailings dams indicate that peak particle velocity below 0.025 m/s and 0.10 m/s are reasonable thresholds to limit pore pressure buildup in full-size earthfill and tailings dams sensitive and not sensitive to vibrations, respectively.

Blast-Induced Stress Wave Propagation and Attenuation: Centrifuge Model Versus Prototype Tests

This paper presents results of centrifuge model studies and full-scale field (prototype) studies designed to provide insights into the influence of water content and the degree of saturation during compaction and testing on high-strain rate loading response of medium dense sand. Objectives of the study were to determine the influence of moisture content at the time of compaction on blast-induced ground shock and stress wave propagation and to compare centrifuge model explosive tests with prototype explosive tests. Model testing was conducted using a geotechnical centrifuge to simulate prototype testing conducted at a field explosives test site. Centrifuge models were constructed at scales of 1/26.3 and 1/18.9 and tested at acceleration levels of 26.3 and 18.9 times earths gravity. Explosives consisting of 3.50 × 10−4 kg (350 mg) and 1.031 × 10−3 kg (1031 mg) of PBX 9407 were buried at depths of 76 mm and 54 mm, respectively. These scaled model tests simulated prototype tests in which 7-kg TNT equivalent explosive charges were detonated at a depth of 1.4 m. Specimens were compacted to a dry density of 1635 kg/m3 at degrees of saturation ranging from 0 to 60 % (water contents from 0 to 14.4 %). Centrifuge model tests and the prototype tests showed similar results. Peak particle velocity, peak stress, and peak scaled acceleration were found to be a function of the degree of saturation with the lowest values at 0 % saturation. Lowest attenuation coefficients occurred in the sand compacted at degrees of saturation of 13 % for the centrifuge tests and 20 % for the prototype tests. Highest attenuation coefficients occurred in the sand compacted dry and at 60 % saturation for all the prototype tests and most of the centrifuge tests. Attenuation coefficients generally decreased with increasing seismic velocities.

Transmission of pressure waves in partially saturated soils

A split-Hopkinson pressure bar (SHPB) was used to experimentally determine stress-transmission coefficients and wave speeds for dry and moist 50/80 silica soil specimens. Results show that for a constant input pressure the transmitted pressure and wave speed increase to a maximum at approximately five- to ten-percent moisture content. Then, both wave speed and transmission ratio decrease with increasing moisture content down to the approximate values of dry soil. Preliminary analysis indicates that these trends can be explained by the effects that saturation and soil capillarity have on effective stress in the soil.

An experimental laboratory facility for studying shock-induced liquefaction

Our paper describes a new experimental laboratory apparatus developed to investigate the transient and long-term porewater pressure response of saturated soils subject to compressional stress wave loading. An overview of the laboratory system, the various components, and the experimental procedure followed are presented. Measurements include porewater pressure-time histories for the specimen and total stress time histories for the applied load. Test results indicate that Monterey No. 0/30 sand can be liquefied even at high initial densities and effective stresses under undrained, one-dimensional, confined compressive shock loadings.

Magnitude Recurrence Relations for Colorado Earthquakes

Colorado has a significant potential for damaging earthquakes. The Colorado Geological Survey has identified 92 potentially active faults. Two faults have documented slip-rates approaching 1 mm per year. Four hundred and seventy-seven Colorado earthquakes have been felt and/or equaled or exceeded magnitude of 2.0 between 1870 and 1996. Eighty-two earthquakes have equaled or exceeded an MMI Scale of V. Colorados largest historical earthquake, which occurred on 7 November 1882 (8 November UCT), had an estimated magnitude of 6.5 and maximum MMI of VII to VIII. Colorados maximum credible earthquake has been estimated at 7.5 ML. In this paper we analyze independent earthquakes (foreshocks, aftershocks, and fluid-injection induced earthquakes removed) to develop magnitude-recurrence relations. Analysis of instrumentally measured earthquakes predicts that a 6.5 ML or larger earthquake occurring somewhere in Colorado has a mean recurrence interval of about 420 years. A magnitude 6.6 ML earthquake has a 10 percent Poissons probability of exceedance in 50 years. A 7.5 ML earthquake has a 2 percent Poissons probability of exceedance in 50 years. Colorados magnitude-recurrence (Gutenberg-Richter) relation is log N=2.58−0.80 ML.

Measurement of the Pore Pressure Parameter C Less Than Unity in Saturated Sands

Two saturated sands, Monterey No. 0/30 and Enewetak coral, tested undrained under one-dimensional strain loading, were found to have values of the pore pressure parameter C, less than unity. The C parameter for Monterey No. 0/30 sand, determined to be unity at an effective consolidation stress of 86 kPa, decreased with increasing effective consolidation stress and increasing relative density. A similar behavior was observed for the Enewetak coral sand. These trends are similar to those reported by other researchers for the pore pressure parameter B. The decrease in C parameter values for saturated specimens appears to be a direct result of increasing skeleton stiffness due to increases in effective stress and density. A theoretical analysis of skeleton stiffness based on porosity and pore pressure response predicts similar trends.