Anirban De

Centrifuge modeling of surface blast effects on underground structures

The effects of surface blasts on underground structures were studied through centrifuge model tests. Centrifuge scaling relationships make it possible to model the effects of large explosions, using a relatively small quantity of explosives under a high g-level. Centrifuge tests, conducted at 70 g, using 2.6 mg of TNT equivalent of explosives, resulted in explosions equivalent to those using 8.7 kN (0.9 tons) of TNT equivalent under normal (1 g) gravity. Strains induced at different locations of the model structure due to the explosion were measured using strain gages. Results indicated that the strains depend on the thickness and nature of the intervening medium. The presence of a polyurethane geofoam compressible inclusion barrier appeared to mitigate the impact of the explosion. Centrifuge model testing is useful in determining the effectiveness of different design alternatives, in studying the mitigating effects of different barrier systems, and in verifying and calibrating results of numerical models related to explosions and underground structures.

Mitigation of blast effects on underground structure using compressible porous foam barriers

Explosions on the ground surface induce strains on underground structures, such as tunnels and pipelines. Depending on the size of the explosion, distances involved, and the nature of the intervening material, these strains can be relatively high, thus causing severe damage to the structure. Barriers may be used to protect a structure, by reducing the strains created as a result of the explosion. The role of compressible protective barriers (made of polyurethane foam) and rigid barriers (made of concrete) in reducing the impact of a surface explosion, were studied. Results of physical model experiments, conducted on geotechnical centrifuge, are presented and analyzed to evaluate the effectiveness of different types of barriers. Numerical model analyses were also conducted to further understand the behavior of different types of protective covers compare them to a soil cover. Results of such studies can help design barrier systems capable of mitigating effects of explosions, thus protecting essential components of underground infrastructure.

Physical and Numerical Modeling to Study Effects of an Underwater Explosion on a Buried Tunnel

AbstractThe effects of an underwater explosion on a tunnel buried below submerged ground were studied through a combination of physical model tests, utilizing a geotechnical centrifuge, and numeric...

Effects of Surface Explosions on top of Earth Embankment Dams

An explosion on the crest of an earth embankment dam can create a crater causing a dam breach, eventually leading to extensive flooding downstream of the dam. Results are presented from a series of centrifuge model tests and numerical modeling to characterize crater formation and consequent breaching of an earth dam. The results of the centrifuge model tests were utilized to calibrate the numerical model, which can be used to conduct parametric analyses to study the effects of varying the soil characteristics or geometry in the future.

Site Characterization of Landfills Through In Situ Testing

In situ testing methods to obtain geotechnical engineering characterization at landfill sites present considerable opportunities and some challenges. This paper focuses primarily on the use of cone penetration test (CPT) at municipal solid waste and hazardous waste sites. Lessons learned from case histories where CPT has been used, either alone or in combination with other investigation methods, provide useful information for future work in this area.

Installation and Load Capacity of Torpedo Anchors in Offshore Applications

The effectiveness of torpedo anchor as offshore foundation was investigated through numerical modeling. The installation was modeled in an explicit dynamics code, capable of simulating large strain deformation and matched favorably with data from field installations. Anchor tilt during installation was simulated through artificial columns of soil, resulting in movements that closely match those reported from field tests. Results from anchors with and without fins were compared to assess the potential benefits of fins. Excess pore water pressure generated during anchor installation was included in analyses to accurately characterize the shear strength properties of the soil in the immediate vicinity of an anchor. Pullout capacity was significantly reduced due to increase in excess pore water pressure (and consequent reduction in shear strength). The pullout capacity increased, following dissipation of excess pore water pressure. Results of pullout capacity with and without consolidation matched field results for corresponding conditions.

APPLICATION OF GEOTECHNICAL CENTRIFUGE TESTING TO EVALUATE UNCONVENTIONAL HIGHWAY MATERIALS

The principles involved in using a geotechnical centrifuge to study long-term consolidation and seepage characteristics of an unconventional geotechnical material are described. Results are presented from long-term leaching tests that were performed in a 100 g-ton centrifuge to simulate 30 years of water flow through sludge material from a paper mill. The consolidation and permeability characteristics of these samples were tested, and the leachate flowing through the materials was collected and tested for chemical composition. Two sludges were tested and their behaviors were compared with those of a conventional clay material, also tested in a similar manner. The sludge material was found to be highly compressible and showed large reductions in permeability with time. Chemical analyses performed on the leachate collected after seepage through the sludge material indicated that the sludge material was suitable for the intended use. This same method of testing can also be used in testing new highway materials. The approach can provide information about the geotechnical and hydrological properties of the material and help identify the environmental characteristics by providing leachate for chemical analyses.