Blasting is a cost-effective method of soil compaction that can be utilized for various types of soil, including granular, silt, clay, and loess. It is not only highly effective in loose soil but can also compact granular soil to a depth of 40 meters. To apply the blasting method, one must determine the appropriate amount of explosive materials required, place the explosives at a suitable depth below the water table, and detonate them safely. The technique can be performed using either surface or internal blasting, but the latter is considered to be more efficient and safer.
Blasting is commonly employed in construction projects involving earth rockfill dams, airfields, roads, and harbors. However, there are limitations to this technique, such as the potential risks associated with explosives, unexpected outcomes of blasting, and the requirement to obtain permission to store and use explosive materials.
How to Use blasting for Deep Compaction of Soil?
Assessing the potential for blast-induced vibrations to cause structural damage or trigger landslides around a construction site requires an understanding of the expected impact, which can be challenging. Before using explosives, permission must be obtained, and the appropriate quantity of explosives must be determined. Individual charges typically range from 1-12 kg or 10-30 g/m3 of the soil to be compacted. Explosive materials are placed in drilled or jetted boreholes at a depth of about 50-75% of the intended total soil depth to be compacted, below the water table. The distance between boreholes should range from 5-15 m. For large projects, test blasting can be used to determine the optimal borehole spacing, charge size, interval, and spacing of blasting. However, further compaction cannot be achieved by reducing explosive spacing or increasing the quantity of explosives. The maximum blasting repetition ranges from 2 to 3 times since soil compaction after three rounds of the blast is low.
The first blast is responsible for 50-60% of the total settlement, and the second blast is accountable for an additional 20% of the full settlement. However, the compaction result within the blast-affected area may vary. The soil around the blasting point and hard soils may loosen due to the blasting effect, and the increase in relative density can range from 15 to 30%. A relative density of 75-85% can be achieved at depths of 12 m or shallower, but the relative density would decrease to 65-75% at depths greater than 12 m. The soil surface typically settles between 2-10% of the total depth of the compacted soil layer after the escape of gasses through fissures and dissipation of pore water pressure. Engineers can check the achieved state of compaction by measuring surface settlement or conducting tests such as the cone penetration test, standard penetration test, or weight soundings.
Blasting can compact up to 1.5 times charge depth and 1.2 to 1.3 times charge depth in loose sand and medium dense sand, respectively. A maximum depth of 40 m of granular soil can be compacted by blasting. However, if the relative density of the soil from the surface to a depth of 2 to 3 m is low, additional surface compaction may be necessary. The loosened soil surface thickness may increase as the quantity of explosives used increases. Blasting efficiency is dependent on the blasting-generated pore water pressure and the size of the liquefied zone around the blasting point. However, a small amount of gas in the soil can reduce the blasting effect considerably, thereby decreasing the degree of compaction. Blasting creates high pressure in saturated sand, with 1 kg of explosives generating more than 14 MPa pressure at a distance of 4 m.
FAQs for soil compaction by blasting
What is explosive compaction?
The technique of soil compaction involves the placement of an explosive charge at a suitable depth within the soil. Once in place, the charge is detonated, causing ripples to form within the soil that are akin to those generated by earthquakes. This ripple effect ultimately leads to the compaction of the soil.
How to check the soil that is compacted by blasting?
There are various methods that engineers can use to check the compaction of soil. One way is to measure surface settlement after blasting. This approach involves detonating explosives and then observing the amount of soil settling that occurs as a result. Another option is to utilize tests such as cone penetration test, standard penetration test, or weight soundings. These tests can provide valuable information about the density and strength of the soil, which are critical factors in determining the level of compaction that has been achieved. By using these methods, engineers can ensure that soil compaction meets the necessary standards and that structures built on the soil have a stable foundation.
What is the maximum repetition for blasting compaction?
According to the provided information, the maximum number of times that blasting can be repeated ranges from 2 to 3. This limitation is due to the fact that the compaction of soil after three rounds of blasting is not significant. In other words, the soil becomes too dense to continue the process of blasting after three rounds. Therefore, it is advisable to limit the blasting repetition to a maximum of three times to ensure optimal results without causing damage to the soil. By adhering to this guideline, the likelihood of successfully completing a blasting operation can be increased while minimizing the negative impact on the surrounding environment.
How to set up spacing and size of charges for blasting compaction in large projects?
Engineers often encounter the need to execute large projects that require precise planning and execution. In such situations, they may choose to use a method called test blasting to determine the optimal parameters for blasting. These parameters can include factors such as the spacing of the boreholes, the size of the charge, and the interval and spacing of the blasting itself.
Test blasting involves setting off small charges in a controlled environment and measuring the resulting vibrations and shock waves. This information can then be used to calculate the ideal parameters for the actual blasting. By conducting test blasts, engineers can ensure that the blasting is performed safely and efficiently while minimizing any potential negative effects such as damage to nearby structures or environmental harm.
Overall, test blasting is a crucial tool for engineers working on large-scale projects that involve blasting. It allows them to optimize their methods and ensure that the blasting is performed in a safe and effective manner, ultimately leading to a successful project outcome.
What is the maximum soil surface settlement due to blasting?
The range of surface settlement is stated to be between 2% to 10% of the complete depth of the compacted soil layer. In other words, the amount of sinking or subsiding of the surface is within this specified percentage range relative to the overall depth of the soil layer that has undergone compaction. It is important to note that settlement refers to the reduction in elevation or level of the surface and is often caused by factors such as the weight of structures or materials placed on top of the soil layer. The given range of settlement provides a rough estimate of the amount of sinking that may occur and can help in designing structures or planning activities that take into account the potential for settlement.