A STUDY OF COMPACTION AND ENGINEERING BEHAVIOUR OF SOIL DUE TO FOAM PROPELLANT

Abstract

AStudy of Compaction and Engineering Behaviour of Soil Due to Foam Propellant Amethod of compacting surficial layers of sand by detonation of a thin ribbon strip of propellant over a sand bed complies to the military requirements most. An experimental and analytical investigation has been carried out for the degree and the extent of compaction vis-a-vis the quantity of propellant, In the analytical formulation it has been possible to treat the compaction process consequent upon the disturbance of sand bed due to the propellant blast as 2-D plane strain wave propagation problem of dynamic compaction theory. The wave equation has been solved by finite difference method in order to obtain the acceleration versus time. The depth of compaction has been determined using the concept of dynamic compaction due to vertical vibration acceleration. The magnitude of blast pressure due to the propellant were determined experimentally using the dynamic load settlement behaviour of sand (Ranipur sand) and were used in the solution of wave equation. Further more the non linear stress-strain relationships for the sand, determined by the triaxial tests, were accounted for in the equation by an iterative process. The analytical depth of compaction (ii) was compared to the experimental one. The analysis has been extended for studying the parameteric effect also, wherein it is found that the depth of compaction increases both due to increase in the blast pressure peak value as well the initial relative density of soil. The comparisons have also been made with the known elastic solution of the wave equation. Two theoretical models for computing blast pressures have been proposed. The analytical results have been compared with those obtained from field experimental compaction text results. The parametric effect have also been studied theoretically. In an experimental programme model field tests for compaction have been conducted using foamed ammonium perchlorate and hydrazino mixture (i.e., propellant). Urea formaldehyde resin stabilization method has been studied in laboratory for the preparation of hard surface ove r the s end be d . Atotal of 75 tests have been conducted to study the extent of compaction and suitability of foam propellant for this purpose. The parameters used in this study on Ranipur sand are as follows', (a) initial density of the sand-uniform density was obtained in the pit using sand rainfall method,' the sand was deposited in the pit at relative density varying from CP/o to 50%., (b) quantity of propellant in the strip was varied from ,075 gm/cm to (iii) to 0.15 gm/cm2,,(c) width of the strip-the two widths used are 10 cm and 15cm. (d) mode of application- the prop ellant can be applied in number of ways,' three variations were studied (i) full face of the sand surface covered with propellant, (ii) partial face of the surface covered with propellant, i.e., the method of putting strips to compact area in the vicinity and (iii) partiol face multiblasts, i.e., conducting partial face blast at the same place for more than once. The post blast densities, depth of compaction and optimum quantity of propellant can be obtained using the empirical equations suggested. The partial face blast method is more economical as compared to full face blast. Arelative density increase of 20 to 50% has been obtained using a 10 cm wide strip of 17 gm propellant compacting a surface area of 80 cm length x 22.^ cm width to 80 cm depth. Multiple partial face blast (say two to three) are found to be more effective than the single one, producing 75% post blast relative density of same volume of sand and applying the same amount of propellant as used in the single one. Model test have been found to give results in confirmation with the _ theory developed for the ti0% initial relative density. However the trend of variation of the depth of compaction with quantity of propellant is corroborated for initial relative density ranges 0 to 20% and UQ to 50%. Fast stabi lization of sand was achieved by the two formulations of urea formaldehyde developed.