Geosynthetics structures subject to blast load

GEOSYNTHETICS REINFORCED STRUCTURES SUBJECT TO BLAST LOAD HE ZHIWEI NATIONAL UNIVERSITY OF SINGAPORE 2008 GEOSYNTHETICS REINFORCED STRUCTURES SUBJECT TO BLAST LOAD HE ZHIWEI (B.Eng, Tsinghua University, China) A THESIS SUBMITTED FOR THE DEGREE OF DOCTORATE OF PHILOSOPHY DEPARTMENT OF CIVIL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2008 ACKNOWLEDGEMENTS First and foremost, I would like to take this opportunity to express my deepest gratitude to my supervisors, Dr. Chew Soon Hoe and Dr. Tan Siew Ann, for their valuable advice, support, suggestions, patience and encouragement. They are always willing to go extra miles to help students. I also like to express my sincere appreciation to my seniors in this project, Chew Chiat, for the extensive information and materials collected, not forgetting the brothers and sisters in Geosynthetics group: Kam Weng, Yeow Teck, Tian Hai, Mei Ling, Hui Kiat, Howard, Andy, Ma Rui, Hung Leong and Desmond. They have given me valuable suggestions and ideas for the research. Most of them have been working with me in Australian desert at Woomera for the field blast trials. It has been a great pleasure to be with them, not only for work, but also for our self-cooking food and fun time in Australia. Also, thanks to other Research Scholars in Geotechnics Group for their numerous help, discussions, chit chats and so on. I am also especially grateful to the staff of the Geotechnical Engineering Laboratory for their assistance during the entire duration of the project. Special thanks are reserved for Mr Loo, Dr. Shen Rui Fu, Mdm Jamilah, Lam Foo, John Choy, Lye Heng, Wong and Shaja. I would also like to extend my appreciation to all those who had helped me either directly or indirectly, especially to those staff from Structural Laboratory, Mr. Koh, Annie and Edgar. i I wish to acknowledge gratefully the support of the Defence Science and Technology Agency, Singapore and Centre for Protective Technology, National University of Singapore in this collaborative research and permission to publish these results. I also wish to acknowledge gratefully the assistance of DSTO Australia, Halliburton KBR and MacMAHON services, for the assistance and cooperation in the construction of the test targets and data capturing during the blast events. Last but not least, I wish to thank my parents, my wife Hongyan, and my children Helen and James. They have always been patient and supportive throughout these years. ii Table of Contents Acknowledgement i Table of Contents iii Summary vi List of Tables viii List of Figures xi List of Symbols Chapter Introduction xxiii 1.1 Geosynthetics Reinforced Soil (RS) structures 1.2 Blast effects and Protective structures 1.3 Geosynthetics RS structures in protective applications 1.4 Numerical investigation of RS structures subject to blast load 1.5 Objectives of this research Chapter Literature review 10 18 2.1 Introduction 18 2.2 Blast loading on RS wall structures 18 2.3 Numerical modelling of blast loading and structure response 24 2.4 Field blast trials and numerical simulation of RS walls 28 2.5 Summary of literature review 31 iii Chapter Development and instrumentation of RS walls in full-scale field blast trials 47 3.1 Introduction 47 3.2 Design of RS walls in field blast trial BT2002 52 3.3 Instrumentation of RS walls in BT2002 65 3.4 Design of RS walls in field blast trial BT2004 76 3.5 Instrumentation of RS walls in BT2004 79 3.6 Design of RS wall in field blast trial BT2006 81 3.7 Instrumentation of the RS wall in BT2006 82 3.8 Summary and concluding remarks 82 Chapter Field test results and discussions 129 4.1 Overview 129 4.2 Results of RS walls subject to 27 ton blast in BT2002 130 4.2.1 Visual records for 27 ton blast event in BT2002 131 4.2.2 Digital signal records for RS1~RS3 during 27 ton blast event 135 4.2.3 Summary of the results for RS walls in 27 ton blast 147 Results of RS walls subject to ton blast in BT2002 148 4.3.1 Visual records for ton blast event in BT2002 148 4.3.2 Digital signal records for RS4~RS6 during ton blast event 149 4.3.3 Summary of the results for RS walls in ton blast 152 Results of RS walls subject to ton blast in BT2004 152 4.4.1 Visual records for ton blast event in BT2004 153 4.4.2 Digital signal records for RS walls during ton blast event 156 4.4.3 Summary of the ton blasts in BT2004 164 4.3 4.4 iv 4.5 Results of the RS wall subject to ton blast in BT2006 165 4.6 Summary of results for RS walls in field blast trial BT2002, BT2004 and BT2006 165 Chapter Numerical modelling 233 5.1 Overview 233 5.2 Overview of the numerical simulation tools 234 5.3 Numerical simulation of incident air blast pressure 236 5.4 Numerical simulation of reflected air blast pressure on RS wall 241 5.5 Modelling of RS wall subject to blast loading using PLAXIS 249 5.6 Concluding remarks 253 Conclusions and developing of design chart 293 6.1 Performance of Reinforced Soil structures in field blast trials 293 6.2 Functions of geotextile in RS wall 296 6.3 Numerical modelling of RS wall subject to blast load 297 6.4 Design charts of RS walls in protective applications 298 6.5 Recommendation for future works 301 Chapter References 304 v Summary To protect human beings and properties from blast effects, three methods can be used: 1) confine the hazard output of the blast; 2) increase the stand-off distance from the blast; and 3) place protective structures (barriers) around or in front of the targets. While protective structures suitably designed and built with structural steel and concrete may be effective, they will produce secondary sharp debris at failure. As an alternative, the geosynthetics Reinforced Soil (RS) structures are innovative, cost effective and efficient type of protective barriers, able to accommodate different site conditions with no secondary debris at failure. To study the performance of RS structures subjected to blast load, a total of 11 fullscale RS walls were tested in Australia with detonations of ton to 27 ton equivalent TNT. Eight RS walls survived the blast events with small deformations, two walls collapsed and one wall reached its ultimate limit state. The measured peak air blast pressure at the front face of RS wall was up to 1250 kPa. The measured peak soil stress was up to 320 kPa. The measured peak dynamic strain of the relatively stronger geotextile was up to 3.5%. Subsequently, the air blast pressure was compared analytically by using programs ConWep and AUTODYN. The stresses within the soil and the displacement of RS walls were also modelled by AUTODYN and PLAXIS. Based on field data analysis and numerical modelling, a design chart was developed to design RS walls as protective structures in defence and civilian environments. The deformation is considered to be the most apparent physical response of the RS wall during a blast event, and thus the overall performance of a RS wall can be identified by its deformation. The height of the RS wall above ground is defined as H; the width of vi the wall as B; the horizontal deformation of the upper corner at the rear facing as DX. The rear facing rotation given by ratio DX/H is used as a criterion to judge the stability of RS walls under blast loading. It was found that the stability (indicated by DX/H) depends mainly on the scaled distance K (R/W1/3) and relative height H/B, and to a lesser extent on the properties of geotextile. The findings of his research should be useful for the organizations and personnel who are responsible for the applications of protective structures. Keywords: Protective structure, reinforced soil, RS wall, scaled distance, field trial, numerical modelling, design chart vii List of Tables Table 2.1 Comparison of field blast trials by other researchers and this PhD work Table 2.2 Comparison of numerical modelling by other researchers and this PhD work Table 3.1 Basic configuration of all RS walls in field blast trials Table 3.2 Predicted air blast pressure for RS walls in BT2002 using ConWep Table 3.3 Technical data of geotextile Table 3.4 Properties of residual soil from Woomera test site Table 3.5 Factor of Safety under static condition for RS1, RS3, RS4 & RS6 (reinforced by PEC200, BT2002) Table 3.6 Factor of Safety under self weight for RS2 & RS5 (reinforced by TS80, BT2002) Table 3.7 External stability of RS walls under air blast loading using pseudostatic analysis Table 3.8 Number of Sensors installed for RS walls in BT2002 Table 3.9 Technical data of air pressure transducer and accelerometer in BT2002 Table 3.10 Technical data of strain gauges in BT2002 Table 3.11 Type and calibration coefficient of total pressure cells in BT2002 Table 3.12 Summary of the impact calibration results for total pressure cells Table 3.13 Predicted air blast pressure for RS walls in BT2004 using ConWep viii Chapter Conclusions and development of design chart Chapter Conclusions and development of design chart To study the performance of geosynthetics Reinforced Soil (RS) structures subject to blast loads, a series of field blast trials and numerical modelling were conducted, the results were analyzed and summarized. This chapter reports the development of specific design charts of RS walls in protective applications based on the above results. This design chart will be useful for engineers to design RS walls of appropriate dimensions with respect to the expected blast charge and scaled distance. Sections 6.1 to 6.3 summarize the key findings of the performance of RS walls in field blast trials, and in the numerical modelling. Section 6.4 reports on the development of Design Chart. Section 6.5 discusses recommendations on the future work. 6.1 Performance of Reinforced Soil structures in field blast trials Full-scale field blast trials were conducted to study the dynamic performance of RS walls, with the geotextile as facing and reinforcement when the walls were subjected to blast loading. The main objective was to verify the effectiveness of RS walls in reducing blast pressure and stopping sharp debris. The response and performance of the geotextile facing and reinforcement were also investigated. In the field blast trials BT2002, BT2004 and BT2006, a total of eleven geotextile RS walls were constructed and tested at various distances from the detonation center housing tons and 27 tons TNT in Woomera, Australia. These walls were of typical height of m and the width varied from m to m. During the blast events, RS0 in BT2002 collapsed as it was only m from the 27 ton 293 Chapter Conclusions and development of design chart detonation. The wall RSM in BT2006 also collapsed as it had a relative height H/B=2.0 and was located at very close scaled distance. RS2 in BT2004 had 443 mm horizontal displacement and just reached its serviceability limit state. All other walls survived the blast events with only 50-160 mm horizontal displacements. Some sharp debris was captured by RS walls and was found embedded in the walls; no secondary debris was produced from RS walls. Hence, RS walls are very effective to resist air blast pressure and to stop sharp debris. The air blast loading on the wall face, the acceleration and displacement of the wall, the dynamic stresses of soil and strain of geotextile at some critical points inside the RS wall were recorded and analyzed. The results from field blast trials enable further investigation into the protective mechanism of RS wall against blast effects. Based on the instrumented results, the following conclusions can be drawn: i) Air blast pressure – Air blast pressure was measured for most of the RS walls. It can be seen that the program ConWep over-predicts the air blast pressure at scaled distances below 13. For scaled distance greater than 13, the prediction of ConWep matches quite well with the measured value. However, for air blast impulse, ConWep constantly over-predicts the air blast impulse at all scaled distances, especially at small scaled distances. This is important for the design of protective structures at small scale distances, E.g. from terrorist attacks. ii) Acceleration – Both negative and positive phase of acceleration during the blast were correctly measured. The results show that for stable RS walls, the velocitytime ended at zero velocity with only very small deformation at the point of measurement of acceleration. The observed large face deformation basically came from the thin layer of loose soil near the surface. 294 Chapter Conclusions and development of design chart iii) Geotextile strain – It was observed that the positive phase gave rise to very small compressive strain (0.2-0.7%), while the negative phase resulted in large strain in the order of 2-3.5%. This range of strain indicates that the geotextile is properly utilized and still within its elastic range with sufficient factor-of-safety as the usual breaking strain of geotextile is 11-13%. iv) Soil pressure – The results show that the soil pressure dissipated very rapidly from the front face of the wall towards the rear. However, due to the effect of the reflected air pressure exerting at the rear face of the wall (travelled via air over the RS wall), the soil pressure near the rear face of RS wall was even higher than at the center of wall. The combined effect of soil pressure is shown in Figure 4.31. The effect of relative height H/B and scaled distance K on the soil pressure distribution along the horizontal distance is best illustrated in Figure 4.79. In the design, it can be clearly seen that the soil pressure reduces with relative distance to the front face until about X=0.6B where B is the width of wall, beyond which the reflected back pressure dominates and the soil pressure increases. This result also shows that with larger H/B, it is less effective in reducing the soil pressure within the RS wall due to relatively smaller wall width. For the RS walls with the same width and height, the wall at larger scaled distance K will display much smaller soil pressure at the front and rear faces, as well as all the locations inside the RS wall. The soil pressure was also found to be varying along the vertical line. The soil pressure measured at the mid-height of the wall was the highest. This could be due to the combined air pressure travelling directly from the blast source, plus the pressure reflected from the base of the wall. The difference in arrival time at different locations reflects the hemispherical nature of the blast wave, which is more pronounced at smaller K. 295 Chapter Conclusions and development of design chart v) Wall Deformation – For RS walls of H/B=1.0 to 1.5, at scaled distance K=2.0, the resulted wall deformation is in the order of 110-160mm at the top of wall. When K is reduced to 1.28, the relative deformation can be as large as more than 400 mm. These are total surface deformation, which may be dominated by the loose soil mass near the surfaces. The walls are still considered as structurally stable RS wall. However, when H/B increased to 2.0, at K=2.0, the RS wall was observed to have failed which indicates the limit of stability of the RS wall at this range of sizes and blast charge which produce overall global behavior. 6.2 Functions of geotextile in RS wall As described in Chapter for design and construction of RS walls, the geotextile is needed to contain soil during construction phase and to maintain the stability of RS wall under static loading. As discussed in Chapter 4, during the blast events, the geotextiles of different tensile strengths have very little effect on the overall performance of RS walls during the positive phase of air blast loading which is the main driving force on the RS wall. However, the geotextile is still very important to prevent soil from falling down during the negative phase of air blast loading. Hence, the geotextile can maintain the local stability of the RS wall. The function of geotextile inside a RS wall is also proven by the numerical modelling in Chapter 5. For the cases with and without geotextile reinforcement, the deformed mesh of RS wall is very close to each other. The extreme displacement of RS wall is also close (67 and 70 mm). The soil stress distribution and soil stress-time history for the two cases are also close to each other. It can be further proven by the fact that the computed axial force of geotextile is quite small. 296 Chapter Conclusions and development of design chart Hence, the insertion of geotextile reinforcement inside the RS wall has very little effect on the deformation and soil stress of the RS wall during dynamic loading. The geotextile mainly functions as soil containment during construction phase and provides the static equilibrium, as well as prevents local instability. 6.3 Numerical modelling of RS wall subject to blast load The air blast loading, the overall performance and soil stress of RS walls are computed by different numerical tools. The results of numerical modelling are compared with actual field measurements. The air blast pressure can be computed by programs ConWep and AUTODYN. ConWep is an easy-to-use and fast-running numerical tool. Upper bound value of air blast pressure and impulse can be obtained by this program for simple geometry and configuration. AUTODYN is an advanced numerical tool and the air blast loading for complex geometry and configuration can be simulated. But it takes more effort and longer time to setup the model and run the analysis. AUTODYN-2D gives reasonably good results for both peak incident overpressure and peak impulse. It gives better predictions than AUTODYN-3D in most cases tried in Chapter 5. However, for situations involving reflected air blast pressure on targets, air blast pressure leaking through 3-D openings and more complex geometry, AUTODYN-3D has to be used. In the AUTODYN-3D analysis of air blast loadings from to ton TNT, the mesh size has to be as small as 0.5 m to give predictions that are close and yet slightly higher than the measured values and hence is considered to be adequate for design purposes. At the front and rear faces of RS wall, the region near ground experienced higher air blast pressure than those at higher elevations because of stronger confinement near ground. The reflective 297 Chapter Conclusions and development of design chart air blast pressure on relatively flexible RS walls and rigid walls are very close to each other. An “effective mitigation region” is defined as a region behind a RS wall with a much lower peak air blast pressure as compared to free field pressure. This region is a function of the wall height and the distance from the detonation center. At scaled distance of 1.28, when the wall is m high, the “effective mitigation region” is about - m behind the RS wall. For a higher wall such as m in height, the “effective mitigation region” increases to - m. At a larger scaled distance of 2.0, the “effective mitigation region” is about m and m for wall height of m and m respectively. This implies that at larger scaled distance, the wall with the same dimension will produce smaller “effective mitigation region”. This could be due to both geometrical damping and the relative dimension of the wall height and distance. The soil stresses inside RS wall and the displacement of RS wall are analyzed by AUTODYN and PLAXIS. PLAXIS generates better results, especially for the pattern of the soil stress reduction inside RS wall, which is quite similar to that of the measured values. It was also observed that the displacement is directly related to the Young’s modulus of the backfill soil. The higher the Young’s modulus is, the lower the displacements. The geotextile reinforcement inside the RS wall has very little effects on the performance of the RS wall during the dynamic blast event. 6.4 Design charts of RS walls in protective applications This section seeks to put the lessons learnt and conclusions drawn from both the field blast trials and numerical modelling into practical use. A design chart was developed based on the above study. This design chart enables the engineers to select appropriate dimensions of RS walls to provide sufficient protection against air blast effects arising from charges of various magnitudes placed at various scaled distances. 298 Chapter Conclusions and development of design chart In the development of this design chart, the deformation is considered as the most apparent response of the RS wall during a blast event, and thus the overall performance of a RS wall can be indicated by its deformation. Here, the displacement of the upper corner at the rear facing of the RS wall is a good indication of the degrees of damage of RS walls; hence it is used as an index of the stability of RS walls under blast loading. The displacement of all the RS walls in Woomera blast trials BT2002, BT2004 and BT2006 were surveyed and summarized into a design chart for RS wall as shown in Figure 6.1. This chart is further supported by numerical modelling. During the blast trials, some walls had less than 100mm of horizontal surface deformation and the overall stability was not affected at all. While some walls had very large deformation, the wall RS2 in BT2004 had more than 400 mm horizontal surface displacement and is considered to have reached its serviceability limit state. The wall RSM in BT2006 collapsed which had the maximum H/B=2.0 among all other walls. As shown in Figure 6.1, the horizontal deformation of the upper corner at the rear facing is defined as DX; the height of the wall above ground is defined as H. The ratio of DX/H is used as a benchmark to judge the stability of RS walls under blast loading. Based on the results from the blast trials, the serviceability limit is set as DX/H=10% for permanent structures. While for temporary structures, it is set as DX/H=20%. As shown in this figure, the stability (indicated by DX/H) is a function of scaled distance K and relative height H/B. It should be noted that most of the RS walls in Figure 6.1 were reinforced with geotextile of tensile strength 200 kN/m, only the wall RS5 was reinforced with geotextile of tensile strength 30 kN/m. It was concluded that the tensile strength of geotextile has very minimum effects on the performance of RS walls. 299 Chapter Conclusions and development of design chart To design a RS wall for protection against blast loads, the scaled distance K can be calculated from the distance R of the structure to the detonation center and the charge weight W. The acceptable displacement over height ratio DX/H at serviceability limit state can also be decided according to the importance of the RS wall. With these two parameters, the relative height H/B can then be selected from Figure 6.1. On the other hand, for a given charge weight W, scaled distance K can be calculated for a particular RS wall of interest. Starting from the known relative height H/B, the expected displacement ratio DX/H can then be predicted by using this figure. Using this chart, the factor of safety (FoS) of RS walls can also be obtained. At the serviceability limit state (DX/H=10%), the wall is at critical state thus FoS = 1.0. A factor-of-safety with respect to the relative maximum wall deformation can be defined as F .S DX  DX    H  FoS =1.0  =  DX     H  Actual For a given configuration of detonation (i.e., scaled distance) and RS wall designed as permanent structures, the displacement ratio DX/H can be read from the chart for that H/B, say, 5%. Thus F .S DX = 10% =3 5% It should be noted that certain minimum tensile strength of geotextile is needed for the reinforcement function to be mobilized. It was found in the field trials that the tensile strength of reinforcing geotextile has very minimum affects on the deformation of RS walls. However, in the practical construction of RS walls, it was found that the reinforcing geotextile with lower stiffness give more difficulties during the construction stage. For this reason, it is recommended that the tensile strength of reinforcing geotextile should be higher than 50 kN/m. 300 Chapter Conclusions and development of design chart It should also be noted that development of this design chart was only based on the results of field blast trials on RS walls conducted in Woomera, Australia. When this chart is used in actual protective applications, different soil properties and weather conditions should be considered in the design. 6.5 Recommendation for future works 1) Field blast trial on practical configuration of RS walls Based on the performance of the RS walls in the field blast tests, it is suggested that RS walls have great potentials in protective applications for civilian and military targets. Examples of their usage in military applications include barrier walls in explosive depots, protective barriers for ammunition plants and retaining walls for supporting earth mounds covering buried, reinforced concrete bunkers used for manufacturing or assembling explosives. RS walls or slopes can be built in front of such important buildings to protect them from terrorists' attacks. By constructing an RS slope in between the car drop-off point and the building, extensive damage from car bombs may be prevented as the RS slope will reduce the blast effects which would act on the building. In addition, a garden can actually be built on top of the slope for camouflaging and for decorative purposes. The above mentioned protective applications provided by RS walls need to be tested in actual field trials. The approach applied in this research should be replicated in future blast tests of RS walls for various specific protective designs. This would enable safe and economically viable RS walls be designed to protect personnel and property from blast damage. 301 Chapter Conclusions and development of design chart 2) Dynamic material testing for further numerical modelling For the numerical modelling as shown in last chapter, the computed soil stress value inside RS wall modelled by PLAXIS is much lower than the measured value while the computed soil stress by AUTODYN is much higher than the measured value. The computed wall displacement is also much lower than the measured value. These problems may be due to the lack of actual detailed dynamic soil properties. Hence, the dynamic soil parameters need to be further investigated in future research to enable better detailed modelling of the performance of the RS wall subject to blast load. The dynamic material property of the geotextile should also be tested in the future. 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(1992) “Dynamic Response Analysis of Reinforced Soil Retaining Wall”, Journal of Geotechnical Engineering, Vol. 118, No. 8, August 1992, pp. 1158-1167. 308 [...]... 5 ton blast in BT2002 Figure 4.57 Surface deformation of RS5 after 5 ton blast in BT2002 Figure 4.58 Surface deformation of RS6 after 5 ton blast in BT2002 Figure 4.59 RS1 and RS2 after 5 ton blast in BT2004 Figure 4.60a RS1 after 5 ton blast in BT2004 Figure 4.60b Geotextile base melted in 5 ton blast in BT2004 Figure 4.61 RS2 after 5 ton blast in BT2004 Figure 4.62 Side view of RS2 after 5 ton blast. .. deformation of RS3 Figure 4.35 The 5 ton detonation container Figure 4.36 View of the donor container with relation to RS walls Figure 4.37 RS4&RS5 and other targets after 5 ton blast Figure 4.38 Overview of RS4, RS5 and RS6 after 5 ton blast Figure 4.39 RS4 after 5 ton blast Figure 4.40 RS5 after 5 ton blast Figure 4.41 RS6 after 5 ton blast Figure 4.42 The bomb shell cut into the wall facing Figure 4.43... Figure 4.16b Extra piece of geotextile to protect soil at the corner (during construction) Figure 4.17 Air blast pressure for RS walls in 27 ton blast Figure 4.18 Impulse for air blast pressure in 27 ton blast Figure 4.19 Acceleration for RS1 during 27 ton blast Figure 4.20 Acceleration for RS2 during 27 ton blast Figure 4.21 Acceleration for RS3 during 27 ton blast Figure 4.22a Static strain distribution... will give a deeper insight into the performance of RS walls subject to blast loading Finally, the design chart for RS walls in protective applications will be produced 1.4 Numerical investigation of RS structures subject to blast load In the area of civil engineering, physical models are always costly to build and also take very long time to collect the data Furthermore, field blast tests are destructive... Figure 4.10a Crater of 27 ton blast: deeper at the RS0 side xv Figure 4.10b Outline of 27 ton crater Figure 4.11 RS1, RS2 and RS3 after 27 ton blast event Figure 4.12 RS1 after 27 ton blast event Figure 4.13 RS2 after 27 ton blast event Figure 4.14 RS3 after 27 ton blast event Figure 4.15 Small cuts on the geotextile surface Figure 4.16a Soil fell out from the corner during blast event Figure 4.16b... measured value in the 5 ton blast of BT2002 Table 4.5 Comparison of RS walls in 27 ton and 5 ton blasts Table 4.6 Comparison of ConWep prediction and measured air blast loading in the 5 ton blast of BT2004 Table 4.7 Settlement for RS walls after blast (BT2004) ix Table 5.1 Properties of air in numerical modeling by AUTODYN Table 5.2 Properties of TNT in numerical modeling by AUTODYN Table 5.3 Material... Strains for RS1 during 27 ton blast (15 kHz) Figure 4.24 Dynamic Strain for RS2 during 27 ton blast (15 kHz) Figure 4.25 Dynamic Strain for RS3 during 27 ton blast (15 kHz) Figure 4.26 Geotextile dynamic strains in RS walls during 27 ton blast (2 kHz) Figure 4.27 Dynamic soil pressure inside RS1 during 27 ton blast xvi Figure 4.28 Dynamic soil pressure inside RS2 during 27 ton blast Figure 4.29 Dynamic... 3.36 Cable trench from the RS wall to the base station Figure 3.37a The base station with data acquisition system inside Figure 3.37b The firing point for both 27ton and 5ton test Figure 3.38a Connection of sensor to data logger system in 27 ton blast Figure 3.38b Connection of sensor to data logger system in 5 ton blast Figure 3.39 Layout of test targets for first 5 ton blast in BT2004 Figure 3.40 Layout... mitigation of blast pressure Also the model size of previous tests is much smaller than those used in the practical protective 8 Chapter 1 Introduction environments The field blast tests reported by Ng (2000) were on a full-scale RS wall subject to multiple blasts However, the wall configuration was too ideal and its relationship to blast load were different from the practical protective structures Furthermore,... (right side) Figure 4.63 RS3 after 5 ton blast in BT2004 Figure 4.64 RS3 after 5 ton blast (back side) in BT2004 Figure 4.65a Air blast pressure on RS1 in BT2004 Figure 4.65b Air blast impulse on RS1 in BT2004 Figure 4.66a Air blast pressure on RS2 in BT2004 Figure 4.66b Air blast impulse on RS2 in BT2004 Figure 4.67a Air blast pressure on RS3 in BT2004 Figure 4.67b Air blast impulse on RS3 in BT2004 xviii . debris at failure. To study the performance of RS structures subjected to blast load, a total of 11 full- scale RS walls were tested in Australia with detonations of 5 ton to 27 ton equivalent TNT during 5 ton blast event 149 4.3.3 Summary of the results for RS walls in 5 ton blast 152 4.4 Results of RS walls subject to 5 ton blast in BT2004 152 4.4.1 Visual records for 5 ton blast. GEOSYNTHETICS REINFORCED STRUCTURES SUBJECT TO BLAST LOAD HE ZHIWEI NATIONAL UNIVERSITY OF SINGAPORE 2008 GEOSYNTHETICS REINFORCED STRUCTURES SUBJECT TO