1.1-If Ground Improvement is necessary, What methods are available ?
Many methods for ground densification and improvement are available, including dewatering, compaction preloading with and without vertical drains, admixture stabilization, grouting of several types, deep mixing, deep densification and soil reinforcement.
Many of these techniques, such as dewatering, compaction pre-compression and some types of grouting, have been used for many years. However, there have been rapid advances in the areas of deep densification (vibrocompaction, deep dynamic compaction, compaction piles and explosive densification), jet and compaction grouting, deep mixing, and stone column systems in recent years.
These methods have become practical and economical alternatives for many ground improvement applications.
1.1.1- Abstract:
Explosive compaction has been a method used in past decades for the compaction of loose granular soil. The method uses energy from confined detonations of explosive charges placed within the soil mass to densify loose, saturated sand or gravel. Various theoretical and case studies have been published in the past. However, most of the studies are limited to applications in granular soils.
1.1.2- Why Blast?
| Compare to remove or replace dynamic compaction, grouting, etc | Inexpensive |
| 1- Maximum depth implemented: 40m 2-EC readily gives volume changes 2-3 times larger than volume that might occur under large earthquake motions, 3-final average relative densities often greater than 70% | Improves soil |
| Controlled blasts leave nearby structures unaffected | Low impact to surroundings |
| Only small-scale equipment is needed (e.g. geotechnical drill or wash boring rigs), | Simple method |
1.2- Over view of the paper:
Here we deal with two methods of Ground Improvement by Explosives (G.I.E).
A) Explosive replacement method.
B) Explosive Compaction for Tailings Volume Reduction.
1.2.1-ENVIRONMENTAL ISSUES (Disadvantages):
Below-ground explosive detonations result in large amounts of gas being released into the soil-water system, in the form of nitrogen oxide carbon monoxide and carbon dioxide. Nitrogen oxide is inert in terms of environmental effects on groundwater.
Release of carbon dioxide may lower the "PH" of the groundwater temporarily, while ammonia levels may also be temporarily elevated. But both nitrogen oxide and carbon monoxide are poisonous in air and venting, it is necessary if blasting is carried out within conned spaces.
1.2.2- Explosive replacement method:
This method uses the energy of the explosion to remove the soft clay and replace it with crushed stones. Explosive charges are placed in the soil to be improved according to a specific pattern. Crushed stones are piled up next to the area where the charges are installed. The explosion creates cavities in the soil and causes the pile of crushed stones to slide into the exploded area. The detail of the method and its application to the highway project are described. The effectiveness of the method is evaluated using borehole exploration, plate load tests and ground probing , radar(GPR) tests.
1.2.3- Explosive Compaction for Tailings Volume Reduction:
Applications of the sequential detonation of explosives to cause tailings volume reduction in tailings ponds are discussed. The method is expected to be effective where the dominant tailings components comprise granular, low to non-plastic silt/sand mixtures. The sequential detonation of below ground explosives placed in cased boreholes has been widely used in civil and mining engineering for over 70 years. Previous applications have included foundation compaction of predominantly granular soils for earth dams, bridges, buildings and offshore oil structures (Goal et al, 2000). This has been largely driven by the need to increase seismic or static liquefaction resistance in granular soils. A potential new applications of explosive compaction (EC) is discussed in the present paper with respect to volume reduction of previously impounded mine tailings in tailings ponds.
