Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/17242
Title: Reinforced soil (RS) walls for Mitigation of close range blast loading
Authors: TAN HONG WEI, ANDY
Keywords: close-range blasts, geosynthetics, reinforced soil wall, localized behaviour, blast mitigation, wall stiffness
Issue Date: 27-Oct-2009
Source: TAN HONG WEI, ANDY (2009-10-27). Reinforced soil (RS) walls for Mitigation of close range blast loading. ScholarBank@NUS Repository.
Abstract: Reinforced Soil (RS) walls are good blast energy-absorbing structures due to inherent properties of the backfill soil materials. With the prevalence of terrorist attacks in recent years, there has been a greater need to look into different types of RS walls which can be rapidly constructed as blast mitigation barriers against blast loading damages. Previous research by NUS has shown the effectiveness of RS walls in shielding blast waves and emphasize the differences between close range medium scale blasts and far range large scale blasts. Three field blast trials were conducted from 2004 to 2006 in Singapore and Woomera, Australia with a total of 5 walls and 6 blast events. The main objectives were to study the different response of RS walls when subjected to close range blasts (scaled distance, Z<1) and far range blasts (Z >2) and to study the rapid constructability of new types of RS walls whose responses might be significantly different from conventional geotextile walls. One of the key findings of this study is that the responses of the walls showed a localized failure mechanism occurred in close range blasts in contrast to global behavior in far field blasts. One characteristic of close range blast is the formation of a crater at the bottom of the front face of the wall. Field results and numerical modelling (thru AUTODYN and PLAXIS) verified that this localized behavior occurred due to the non-uniform blast pressure acting on the front face of the wall. This is significantly different from large scale blasts where the front face of the wall is subjected to uniform soil pressure and the RS wall deform as a whole. The governing effect in close range blast was the arching effect (where the soil is compressed by the blast wave) which becomes more pronounced when the RS wall is stiffer. This also leads to better blast pressure absorption in close range. In far range blasts, the stiffer the wall, the less the shock absorption. A design chart was thus derived for the wall when subjected to close range medium scale blast loading, using the crater volume as the key indicator. For more rapidly constructable RS walls, a Geocell and GeoBlock wall were investigated. Geocell walls were also found to behave differently than geotextile walls when subjected to both close range (ETSC2004) and far field blasts (Woomera 2004). Due to their higher rigidity, at close range, they absorb the blast pressure better than geotextile walls. Geocell walls can also be constructed much faster compared to geotextile walls (less than a day compared to 3 to 4 days for RS walls of similar sizes) and does not require specialized labor and formwork. However Geocell walls produce slightly more debris compared to geotextile walls due to their lower melting point and higher rigidity. A Geoblock wall was constructed and tested in Woomera 2006 with even faster construction time of 8 hours only. The construction process was simplified and rapid constructability was achieved with the Geoblock wall. Moreover no significant debris was found on site despite the severe damage suffered by the wall after the large scale blast. Two numerical programs were used to model the three field blast trials conducted, namely AUTODYN and PLAXIS. They serve to compliment the field blast trial results obtained. Sensitivity studies of the key parameters were conducted. Appropriate soil parameters, model space size, boundary conditions as well as mesh size were studied. The air pressure around the faces of the RS walls and the soil pressure within the RS walls were modeled and compared with the actual field data.
URI: http://scholarbank.nus.edu.sg/handle/10635/17242
Appears in Collections:Ph.D Theses (Open)

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