High-pressure compressibility and shear strength data for soils

Soil behaviour is often an important consideration in the design of protective systems for blast and impact threats, as the properties of a soil can greatly affect the impulse generated from buried explosive devices, or the ability of a soil-filled structure to resist ballistic threats. Numerical modelling of these events often relies on extrapolation from low-pressure experiments. To develop soil models that remain accurate at very high pressures there is a need for data on soil behaviour under these extreme conditions. This paper demonstrates the use of a high-pressure multi-axial test apparatus to provide compressibility and shear strength data for four dry sandy soils. One-dimensional compression experiments were performed to axial stresses of 800 MPa, where the effects of particle-size distribution were observed with respect to compressibility and bulk unloading modulus. Each soil followed a bilinear normal compression line (NCL): more uniform soils initially had higher compression indices, but all four NCLs began to converge at void ratios below e ≈ 0.3. The failure surface of a sand was characterized to mean effective stress [Formula: see text] > 400 MPa using reduced triaxial compression experiments, removing the need to rely on extrapolation from low-pressure data.

A Portable Biosensor for 2,4-Dinitrotoluene Vapors

Buried explosive material, e.g., landmines, represent a severe issue for human safety all over the world. Most explosives consist of environmentally hazardous chemicals like 2,4,6-trinitrotoluene (TNT), carcinogenic 2,4-dinitrotoluene (2,4-DNT) and related compounds. Vapors leaking from buried landmines offer a detection marker for landmines, presenting an option to detect landmines without relying on metal detection. 2,4-Dinitrotoluene (DNT), an impurity and byproduct of common TNT synthesis, is a feasible detection marker since it is extremely volatile. We report on the construction of a wireless, handy and cost effective 2,4-dinitrotoluene biosensor combining recombinant bioluminescent bacterial cells and a compact, portable optical detection device. This biosensor could serve as a potential alternative to the current detection technique. The influence of temperature, oxygen and different immobilization procedures on bioluminescence were tested. Oxygen penetration depth in agarose gels was investigated, and showed that aeration with molecular oxygen is necessary to maintain bioluminescence activity at higher cell densities. Bioluminescence was low even at high cell densities and 2,4-DNT concentrations, hence optimization of different prototypes was carried out regarding radiation surface of the gels used for immobilization. These findings were applied to sensor construction, and 50 ppb gaseous 2,4-DNT was successfully detected.

Direct-SV radiation produced by land-based P-sources — Part 2: Buried explosives

A common view of buried-explosive seismic sources is that a buried explosion is a pure-P source because it is an expanding volume of high-pressure gas. This assumption leads to a popular conclusion that if shear-mode reflections are observed in explosive-source data, those reflections have to be produced by a downgoing SV wavefield that is generated by P-to-SV conversion at an interface above the depth of the buried explosive. This paper challenges this traditional view that a buried chemical explosive is a pure-P source. In our finite-difference modeling, a buried explosion is a pure-P volume of expanding gas for only that fraction of a microsecond that it takes for its expanding gas to reach the wall of the tube that contains the explosive material. As soon as this accelerating high-pressure gas contacts any surrounding elastic media, a chemical explosion ceases to be a pure-P-source, and shearing is initiated. We chose a finite-difference style of numerical modeling so that we could introduce realistic conditions, such as a physical container for explosive material, a shot hole, small zones of Taylor instabilities in the expanding gases, and local sedimentary interfaces, into numerical calculations. This finite-difference modeling verified that buried explosives not only generate direct-P wavefields, but that they also produce direct-SV wavefields. We believe that our work provides important information that seismic interpreters should consider. Namely, our research indicates that seismic reflection data acquired with buried explosives can be processed to generate direct-SV images in addition to traditional direct-P images. This direct-SV imaging option applies not only to new seismic data acquired with buried-explosives, but also to legacy P data that were acquired with buried-explosive sources many years in the past and now sit dormant in digital seismic-data libraries.