Senin, 24 November 2014


There are two principal explosive mechanisms namely:
a) Shock pressure
b) Gas pressure

Chapman and Jouguet proposed the first theory of detonation in 1899. This was modified by Zeldovich in 1943 and has gone through many improvements since then. Modern computers have made it easy to apply the theories to explosive compositions and calculate the expected detonation parameters. Calculated energy values based on thermochemical and hydrodynamic theories are commonly quoted by explosive manufacturers.

Different explosives exhibit different degrees of gas and shock pressure. The extent to which an explosive possesses these properties is described by the Aquarium test for bubble energy and shock energy.

On detonation, explosive energy is converted into mechanical energy, heat and incomplete reaction products. The initial detonation pressure Pd is quickly reduced to the explosion pressure Pe and as the gaseous reaction products expands to fill available voids, it reduces to blasthole pressure Pd. This pressure is maintained until venting occurs. The relationship between Pd and the explosion pressure Pe depends on the type of explosive used. In general the relationship between them is [Pd = n x Pe] where n lies between 1 and 2. The blasthole pressure Pd will depend on the extent to which the hole is filled.

The energy transferred from the explosive charge to the rock will depend on the extent to which the blasthole is coupled with the explosive charge. Any air-gap will cushion the blast and will reduce the efficiency of the energy transfer. This effect is called the decoupling effect. Decoupling factor D which is diameter of borehole divided by diameter of charge is always greater than or equal to 1. D is '1' when the explosive charge is fully coupled with the borehole wall. The smaller the decoupling factor, the greater will be the blasthole pressure and efficiency of the energy transfer.

The shock pulse transmitted to the rock creates stressing resulting in radial compressive strains which tend to crush the rock close to the borehole, and also tensile hoop stresses which are concentric to the borehole and cause local radial cracking. If the transmitted shock pulse is strong in relation to the confined strength of rock, then considerable initial crushing and fracturing near the explosive charge is bound to occur (Figure 1).

Figure 1: Process of Rock Breakage

Beyond the fracture zone, the pulse travels as an elastic wave until it reaches the free face, where the wave is reflected as a tensile wave. The amount of energy transferred to a given rock is a linear function of the product of density and the rate of detonation. This term is called the characteristic impedance of explosive.

The explosive must be selected to match with the operational aspects of blasting so that maximum energy could be transferred to the surrounding rock mass. The ideal one being that which breaks the rock in tension. If the compressive strength of the rock is exceeded by the shock pulse then annular rock around the borehole will be crushed to a fine size, and this powder will prohibit the propagation of the strain pulse. In addition, increased amount of dust will be formed.

Out of the energy available in the explosive, it is estimated that only 3 to 20% is transmitted into stress waves. The major portion comes out as heat, which is not wasted but expands the gas products of detonation.


Two basic forms of energy are released when high explosives react. The first type of energy will be called shock energy. The second type will be called gas energy. Although both types of energy are released during the detonation process, the blaster can select explosives with different proportions of shock or gas energy to suit a particular application. If explosives are used in an unconfined manner, such as mud capping boulders (commonly called plaster shooting) or for shearing structural members in demolition, the selection of an explosive with high shock energy would be advantageous. On the other hand, if explosives are being used in boreholes and are confined with stemming materials, an explosive with a high gas energy output would be beneficial.

 Figure 1: Pressure Profiles for Low and High Explosives
(Source: Konya and Walter, 1990)

To understand the difference between the two types of energy, compare the difference in reaction of a low and high explosives. Low explosives are those which deflagrate or burn very rapidly. These explosives may have reaction velocities of two to five thousand feet per second (600 to 200 m/s). Such explosives produce no shock energy. They produce energy only from gas expansion. A very typical example of low explosive would be black powder. On the other hand, high explosives detonate and produce not only gas pressure, but also another energy or pressure which is called shock pressure. Figure 1 shows a diagram of a reacting cartridge of low and high explosive.

High explosives are explosive materials that detonate, meaning that the explosive shock front passes through the material at a supersonic speed ranging from 3 to 9 km/s. A high explosive detonation exhibits shock pressure at the reaction front which travel through the explosive before the gas energy is released. Generally the shock energy is higher pressure than the gas energy. After the shock energy passes, gas energy is released. The gas energy in detonating explosives is much greater than the gas energy released in low explosives. In a high explosives, there are two distinct and separate pressures. The shock is estimated to account for only 10% to 15% of the total available useful work energy in the explosion. The gas pressure accounts for 85% to 90% of the useful work energy and follows thereafter. However, the gas energy produces a force that is constantly maintained until the borehole ruptures.

 Figure 2: Underwater Test Record Sample


The shock energy is commonly believed to result from the detonation pressure of the explosion. The detonation pressure is a function of the explosive density times the explosion detonation velocity squared and is a form of kinetic energy. Determination of the detonation pressure is very complex. There are a number of different computer codes written to approximate this pressure. Unfortunately, the computer codes come up with widely varying answers. Until recently, no method existed to measure the detonation pressure. Until that time occurs, one could use this formula to achieve a number that may approximate the detonation pressure.

The detonation pressure or shock energy can be considered similar to kinetic energy and is maximum in the direction of travel, which would mean that detonation pressure would be maximum in the explosive cartridge at the end opposite that where initiation occurred. It is generally believed that the detonation pressure on the sides of the cartridge are virtually zero, since the detonation wave does not extend to the edges of the cartridge. To get maximum detonation pressure effects from an explosive, it is necessary to place the explosives on the material to be broken and initiate it from the end opposite that in contact with the material. Laying the cartridge over on its side and firing in a manner where detonation is parallel to the surface of the material to be broken reduces the effects of the detonation pressure. To maximize the use of detonation pressure, maximum contact area between material and explosive is required.

Figure 3: Mud Cap Blasting


When the charges confined are detonated in boreholes, then the expanding gas energy cause majority of the rock to break. The gas pressure, often called explosion pressure, is the pressure that is exerted on the borehole walls by the expanding gasses after chemical reaction has been completed. Explosion pressure results from the amount of gases liberated per unit weight of explosive and the amount of heat liberated during the reaction. The higher the temperature produced, the higher the gases pressure. If more gas volume is liberated at the same temperature, the pressure will also increase. For a quick approximation, it is often assumed that explosive pressure is approximately one-half of the detonation pressure. 

It should be pointed out that this is only an approximation and conditions can exist where the explosion pressure exceeds the detonation pressure. This explains the success of ANFO which yields a relatively low detonation pressure, but relatively high explosion pressure. Explosion pressures are calculated from computer codes or measured using underwater tests. Explosion pressures can also be measured directly in boreholes, however, few of the explosive manufacturers use the new technique in rating their explosives. A review of some very basic explosives chemistry helps one to understand how powdered metals and other substances effect explosion pressures.

Please remember that the action of explosion pressure is important in loosening, expanding and throwing material.

Figure 4: Nomograph of Detonation and Explosion Pressure


Chemical explosives are materials which undergo rapid chemical reactions to release gaseous products and energy. These gases under high pressure exert forces against borehole walls which causes rock to fracture.

The elements which comprise explosives, are generally considered either fuel elements or oxidizer elements (Table 1). Explosives use oxygen as the oxidizer element. Nitrogen is also a common element in explosives and is in either a liquid or solid state, but once it reacts it forms gaseous nitrogen. Explosives sometimes contain ingredients other than fuels and oxidizers. Powdered metals such as powdered aluminum are used in explosives. The reason for the use of the powder metals is that, upon reaction, powdered metals give off heat. The heat formed heats up the gases, which result from other ingredients, causing a higher explosion pressure.

Table 1: Explosive Ingredients 

Explosive may contain other elements and ingredients which really add nothing to the explosives energy. The other ingredients are put into explosives to decrease sensitivity or increase surface area. Certain ingredients such as chalk or zinc oxide serve as an antacid to increase the storage life of the explosive. Common table salt actually makes an explosive less efficient because it functions as a flame depressant and cools the reaction. On the other hand, the addition of table salt allows the explosive to be used in explosive methane atmospheres because the cooler flame and shorter flame duration makes it less likely that a gas explosion would occur. This is the reason that permissible explosives are used in coal mines or in tunneling operations in sedimentary rock where methane is encountered.

This basic elements or ingredients which directly produce work in blasting are those elements which forms gases when they react, such as carbon, hydrogen, oxygen, and nitrogen.

When carbon reacts with oxygen, it can either form carbon monoxide or carbon dioxide. In order to extract the maximum heat from the reaction, we want elements to be completely oxidized or in other words for carbon dioxide to form rather than carbon monoxide. Table 2 shows the difference in heat released when one carbon atom forms carbon monoxide versus the case where one carbon atom form carbon dioxide. In order to release the maximum energy from the explosive reaction, the elements should react and form the following products:
1.) Carbon reacts to form carbon dioxide
2.) Hydrogen reacts to form water (Figure 5)
3.) Liquid or solid nitrogen reacts to form gaseous nitrogen (Figure 6)

 Table 2:Heats of Formation for Selected Chemical Compounds

Figure 5: Hydrogen-Oxygen Ideal Reaction

Figure 6: Nitrogen-Nitrogen Ideal Reaction

If only the ideal reactions occur from the carbon, hydrogen, oxygen, and nitrogen, there is no oxygen left over or any additional oxygen needed. The explosive is oxygen balanced and produces the maximum amount of energy.

If two ingredients are mixed together, such as ammonium nitrate and fuel oil, and an excess amount of fuel oil is put into mixture, the explosive reaction is said to be oxygen negative. Thus means that is not enough oxygen to fully combine with the carbon and hydrogen to form the desired end products. Instead, what occurs is that free carbon (soot) and carbon monoxide will be liberated (Figure 7).

Figure 7: Non-Ideal Carbon-Oxygen Reaction

If too little fuel is added to a mixture of ammonium nitrate and fuel oil, then the mixture has excess oxygen which can't react with carbon or hydrogen. This is called an oxygen positive reaction. What occurs is that the nitrogen which is normally an inert gas will be changed from nitrogen gas to an oxide of nitrogen (Figure 8). If oxides of nitrogen are formed, they will form rust colored fumes and reduce the energy of the reaction.

 Figure 8: Non-Ideal Nitrogen-Oxygen Reaction

The energy is reduced because nitrogen oxides absorb heat in order for them to form. This can be seen in Table 2. Water and carbon dioxide have a negative sign which means they give off heat when they form. On the other hand, the nitrogen oxides have a plus sign meaning that they take in heat when the form.

Please remember that the net result is that the reaction will occur at a lower temperature. The gas pressure is lowered if the reaction temperature is lowered.

Figure 9: Identification of Problem Mixture of ANFO and Fuel Oil

Figure 10: Energy Loss in ANFO


Broadly controlled blasting is done for controlling overbreak (in opencast and tunnel) and ground vibration. It can be catagorised into four types: pre-splitting, trim blasting, line drilling, and smoothing blasting. Muffle blasting is done to restrict fly-rock.

1) Pre-Splitting

This method is not new blasting technique. It became a recognized blasting technique for wall control when it was used in the mid-1950s on the Niagara Power Plant. The purpose of pre-splitting is to form a fracture plane across which the radial cracks from the production blasting can't travel. This method may cause a fracture plane which may be cosmetically appealing and allow the use of steeper slope with less maintenance. Pre-splitting uses lightly loaded, closely spaced drill holes, and is fired before the production holes.

2) Trim (or Cushion) Blasting

Trim blasts are designed to produce a final wall similar to a pre-split blast, but they are fired after the production holes. The idea is to eliminate costly small diameter blasthole and work along with the associated hole loading difficulties. The spacing normally larger than in pre-splitting because there is relief towards which the holes can break. Since the trim row of holes along the a perimeter is the last to fire in a production blast, it does nothing to protect the stability of the final wall. Radial fractures from production blasting can go back into the final wall. Mud seams or other discontinuities can channel gasses from the production blast areas into the final wall. The sole purpose of a trim blast is to create a cosmetically appealing, stable perimeter. It offers no protection to the wall from production blast.

3) Line Drilling

This system involves a single row of closely spaced uncharged holes along the neat excavation line. This provides a plane of weakness. It also causes some of the shock waves generated by the blast to be reflected, which reduces shattering and stressing in the finished wall of the host rock. Thus, preserving, to a great extent, the original strength of the host rock is possible. This technique gives maximum protection to the host rock to preserve its original strength.

It may, under proper circumstances, help to protect the final contour from radial fractures by acting as stress concentrators causing the fracture to form between line drill holes during the production blasting cycle. If, on the other hand, the wall contour was extremely important, one could not depend on line drilling to necessarily protect the final wall. Line drilling is more commonly used in conjunction with either pre-splitting or trim blasting rather than being used alone. Although the use of control blasting is more common for surface excavations, it has been successfully used underground, residual stress conditions permitting.

4) Smooth Blasting (or Contour or Perimeter Blasting)

A technique used (rarely in surface and mostly in underground blasting) in which a row or closely spaced drill holes are loaded with decoupled charges (charges with a smaller diameter that drill hole) and fired simultaneously to produce an excavation contour without fracturing or damaging the rock behind or adjacent to blasted face. In this technique, perimeter or contour holes are drilled along specified final excavation limits and are lightly loaded than that of buffer holes and production holes. The spacing is kept closer than buffer holes and production holes. Unlike production drill hole blast where higher charge concentration is required, contour drill holes require low charge concentration and explosives should be lightly distributed all along the length of the bore hole. Sometimes the use of high grammage Detonating Fuse (about 40 gm/m core wt., to 60 gm/m core wt.) for contour blasting can give effective result in tunneling. This results in an air cushion effect, which prevents over-break and reduces in-situ rock damage for preservation of strength of host rock.

4) Muffle Blast

In case of blasting in congested areas, muffling or covering of blast holes properly before blasting, is the common solution to prevent fly-rock from damaging human habitats and structures.

Figure 1: Blast Doors

Minggu, 23 November 2014


There are several steps for the process of tunnel blasting:

1) Drilling and Preparation for Blasting

2) Priming & Loading Explosives & Steaming

3) Making Bunches With Nonel System and Ready for Fire

Source: Nitro Nobel