Sequential Detonation Research Articles

A hybridized continuum-discontinuum modeling for investigating the fracture and energy evolution characteristics of rock mass under sequential explosive detonation using a bilinear cohesive fracture model

Modelling the dynamic mechanical response of rock mass under sequential explosive detonation, especially the fracture and energy evolution characteristics, is the key to optimizing the spatial distribution and initiation time interval of explosives. A hybridized continuum-discontinuum element method and energy statistics algorithm are implemented in this study to accurately investigate the rock dynamic response induced by sequential detonation loading. Based on the rock fracture status and the stress–strain curve of bilinear cohesive fracture model, an energy statistics algorithm considering all energy components is first proposed, and its accuracy and robustness are verified. Then, the continuum-discontinuum element method and energy statistics algorithm are adopted to simulate the dynamic response of rock mass under sequential detonation loading. The results indicate that the area of cracked interfaces generated by each explosive first increases and then decreases, which caused by explosive 2 is the largest, accounting for 38.19%. Due to the damage to rock caused by the previous detonation loading, the rock around explosive 1 mainly undergoes shear fracture, while the rock around explosives 2 and 3 mainly undergoes tensile fracture. The change trends of various energy components are different, and the explosion energy is mainly converted into friction energy and element kinetic energy.

Loading rate effects on the responses of simply supported RC beams subjected to the combination of impact and blast loads

This paper investigates the residual capacities and damage states of simply supported RC beam subjected to the combination of a close-in explosion loading with varied-rate impact loadings using the finite element (FE) simulation through LS-DYNA. Two damage indices on the basis of the residual shear and flexural capacities of the RC beams are proposed. Different loading phases are investigated to assess the sensitivities of the RC beams to the impact loading rate when they are subjected to different combination modes. The combination modes vary in terms of two key loading-related parameters, i.e. the loading sequence and the time interval (i.e., the time lag) between the onsets of impact and explosion loadings. From the FE simulation results, the severity of spallation increases in the beams, when the impact loads are applied prior to the detonations and particularly when the impact loading rate is higher in the combined actions. However, the increase of impact velocity in the combined loadings where the explosion loads are applied prior to the impact loads will lead to direct shear failures near the beam supports. Moreover, the beam experiences more severe damages and greater residual displacements under combined loadings when the sequential detonation is initiated at the time of the peak mid-span displacement is reached. Besides, larger shear forces are produced under combined loadings where the explosion is initiated at the time of the initial peak of impact force. In addition, it is found that the shear and flexural mode based damage indices are more sensitive to the increase of the impact velocity for the combined loading scenarios, where the explosion loads are applied simultaneously with the initial peak of impact force or the peak mid-span displacement, respectively.

Improving Rigidity of Clay by Using Explosives and Proofing by Multichannel Analysis of Surface Waves (MASW)

The construction foundation problem in complex conditions with specific types of soils (peat and organic sediment, sludge, soft clay, etc.) is relevant at the present time. Excessive moisture, low bearing capacity, high compressibility, and other negative qualities of these soils make the process of foundation more expensive and complicated. To improve the properties of granular soil can be applied explosive compaction (EC) technology, which has been used for more than 80 years, but mostly for the compaction of gravels, sands and silts. This paper documents the successful application of EC for the compaction of clay soils. To cause compaction, the sequential detonations were performed using explosives placed in boreholes. To investigate the efficiency of explosive compaction on cohesive clay soil, geophysical testing was performed. Applied geophysical testing methods were a Multichannel analysis of surface waves (MASW) and seismic down-hole, whose test results are shear wave velocities (Vs) in depth. The shear modulus (Go) at small deformation, which is directly related to the Vs, were used to determine the degree of soil improvement. From a comparing of results of pre- and post-blast testing, the positive effects are evident.

Attenuation of blast vibration in tunneling using a pre-cut discontinuity

A pre-cut discontinuity, similar to the pre-splitting around a tunnel periphery, is introduced to investigate the attenuation of the wave propagation due to tunnel blasting. For this, two empty holes were drilled to support the sawing jigs and a wire sawing machine with embedded industrial diamond wire was used to cut an artificial discontinuity near the initial blasting holes at the tunnel face. The peak particle velocity with/without pre-cut was measured during tunnel blasting and the effect of the pre-cut method was quantitatively accounted for, although, due to limited time and unfavorable field conditions, the cutting depth was not able to reach the initial design depth. Numerical analysis was also performed in order to model the tunnel geometry and blasting procedure. For this, a commercial package called UDEC was used and the accuracy of UDEC was initially proven by an analytical solution of the reflection and transmission of the incident wave. Various parametric studies including sequential detonations were performed and the reduction factor of attenuation with ideal cut-off discontinuity was shown to be 50%. Future work will concentrate on the improvement of the wire sawing machine to reduce the cutting time and three dimensional modeling of the blasting effect will also be performed.

On vibrational behavior of pulse detonation engine tubes

This paper presents a set of analytic solutions for the transient elastodynamic response of orthotropic cylindrical tubes to sequential moving pressures with specific profiles. The general form of the presented formulations and the solution methods are applicable to a number of theoretical and practical problems. However, the final solutions are tailored for sequential gaseous detonations, with direct application in the stress analysis of pulse detonation engines (PDE). The PDE generates trust by high cycling of gaseous detonations and is regarded as a promising candidate for providing very efficient propulsion systems for aviation and electric power generation. The presented analytic solutions are validated with the available experimental data and complementary finite element simulations. Representative analyses are carried out for an experimental detonation tube subjected to different boundary conditions and loading sequences. It is shown that the proper (or improper) combinations of the relevant parameters can result in substantial attenuation (or amplification) of the tube vibration. It is also demonstrated that the realistic analysis of the overall vibrational behavior, which can be highly affected by the specifications of the loadings and boundary conditions, requires the simulation of hundreds of sequential detonations.

Plane shock compression generators, utilizing convergence of conical shock waves

The results of experimental testing of shock wave generators, based on irregular Mach reflection of shock waves in a conical geometry, along with the results of numerical simulation is presented. The shock in a layered cylindrical central body was produced by an impact of a converging conical flyer plate. Conical flyer plate was originating from initially cylindrical cavity liner in a cylindrical HE charge that was launched by a sliding detonation. This approach led to device simplification, since manufacturing of conical parts from metal and explosive is not required. The sequential detonation of HE charge by a multi- point distributor was employed to vary the geometry of formed conical flyer. The dependence of parameters of shock wave in cylindrical Polymethylmethacrylate (PMMA) core on launch angle was investigated. It was found that launch angles below 10° lead to failure of the Mach reflection mode, while larger angles produced flat Mach disks that can be utilized in various shock experiments.

Seabird and Dolphin Mortality Associated with Underwater Detonation Exercises

AbstractWe report the details of two wildlife mortality events that were associated with underwater detonations. The detonations occurred as part of military training activities at Silver Strand Training Complex in San Diego, California. In March 2006, an underwater detonation resulted in 70 western grebes (Aechmophorus occidentalis) being killed by subsequent sequential detonations in the same training exercise. Ten of the 70 western grebes impacted were necropsied, verifying cause of death as primary blast injury. In March 2011, a time-delayed underwater detonation resulted in the death of three or possibly four long-beaked common dolphins (Delphinus capensis). While these blast events were unlikely to impact these species on a population level, underwater detonations do have the potential for population-level impacts on wildlife. Both events were accidental mortalities and the first ever documented from Navy underwater detonation training in Hawaii, Southern California, and along the U.S. East Coast. The Navy updated its underwater explosive mitigation measures after each of these mortality events to limit the potential of future mortalities by requiring sequential detonations to occur either less than 5 s or more than 30 min apart and by suspending time-delayed detonation training exercises until more robust precautionary measures can be developed.

Experimental technique for generating fast high-density shock waves with phased linear explosive shock tubes

The sequential detonation of a layer of explosive surrounding a pressurized tube can be used to generate fast, high-density shock waves by means of a piston-like implosive pinch travelling at the detonation velocity of the explosive. A novel technique has been developed to extend the regime of operation to piston velocities greater than the detonation velocity of known explosives. This technique consists of cutting a slit in the tamper of a conventional explosive shock tube and introducing a phased detonation wave into the explosive cladding. Preliminary results indicate that quasi-steady shocks can be generated in helium with velocities between 13–17 km/s for initial fill pressures of 6.9 MPa.

Pre-splitting and stress waves: A dynamic photoelastic evaluation : Simha, K R Y; Holloway, D C; Fourney, W L Proc 23rd Symposium on Rock Mechanics, Berkeley, 25–27 August 1982, P523–530. Publ New York: AIME, 1982

An experimental investigation was performed to evaluate the role of stress waves in the pre-splitting operation. 3D birefringent plexiglas models and the dynamic photoelastic technique were used to visualize the stress waves generated by the detonation. Simultaneous as well as sequential detonation of the explosive charges were investigated. The development of the fractures and stress waves were recorded using a high speed multiple spark gap camera of the Cranz-Shardin type. The experimental data were analyzed and displayed on a lagrangian diagram to present an overall picture of the entire dynamic event. It was repeatedly observed in the tests that the time required for the completion of the pre-splitting operation as practiced in the field is of the same order as that for the transit time for the stress waves between the blastholes thereby revealing the highly elastodynamic nature of the event. For the covering abstract of the symposium see TRIS 452576. (Author/TRRL)

Effect of simultaneous and sequential detonation on explosive-induced fracture : Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P235–242. Publ Reno: University of Nevada, 1978

Effect of simultaneous and sequential detonation on explosive-induced fracture : Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P235–242. Publ Reno: University of Nevada, 1978

Geology of Wagon Wheel Nuclear Stimulation Project, Pinedale Field, Wyoming

Wagon Wheel is a project planned to stimulate a well in gas reservoirs of the Pinedale anticline by means of nuclear explosives. The Pinedale field, in the northern part of the Green River basin of southwest Wyoming, is potentially productive from almost 10,000 ft of lower Fort Union, Lance-Lewis, and Mesaverde sandstones. Attempts to produce the field conventionally have proved uneconomic because of low permeability. The first nuclear stimulation experiment, Gasbuggy, in northwest New Mexico, was detonated in 1967 using a 29-kiloton explosive. Technical questions answered by Gasbuggy resulted in the program at Wagon Wheel, which will be an attempt to define the economics of use of nuclear stimulation. Project Rulison was the second test to stimulate natural gas reservoirs and utilized a device of approximately 40 kilotons. The most recent test, Project Rio Blanco, used three 30-kiloton explosives fired simultaneously. Project Rulison and Project Rio Blanco are in the Piceance basin of western Colorado. Wagon Wheel 1 was drilled to 19,000 ft to evaluate the entire Mesaverde section. Gas was detected on mud-logging equipment throughout the basal Fort Union, Lance-Lewis, and Mesaverde, below the top of the gas reservoir at 7,972 ft. The well has been plugged back to 11,700 ft as a possible emplacement hole in which five 100-kiloton explosives will produce a chimney from 9,000 to 11,650 ft. Reserves in this interval are calculated at 207 Bcf of gas in place per square mile. Extensive logging, coring, and testing were carried out in the program, including special logs for rock-mechanics study. Two special wells in addition to the Wagon Wheel 1 were drilled to evaluate the aquifers above the gas reservoir. Potable water extends to a depth of 3,730 ft. Salt water is present from 3,730 to 5,630 ft. Low-quality subpotable water extends from 5,630 to 7,140 ft. The saltwater zone is interpreted to be a tongue of Wasatch extending from the west into Eocene arkose derived from the Wind River Range on the east. Plans call for sequential detonation of five explosives spaced at intervals from 9,220 to 11,570 ft, to produce a continuous chimney from 9,000 to 11,650 ft. There will be a safety margin of 1,600 ft between the top of fractures and the bottom of the known aquifers.

Status of Gas-Stimulation Technology Employing Nuclear Explosions: ABSTRACT

Recent studies conclude that the tight gas sands in the Rocky Mountain region contain a resource potential of nearly 600 Tcf of natural gas. Of this amount, approximately 300 Tcf may be recovered through the use of nuclear explosives, assuming that nuclearly stimulated wells will produce for 50 years. This volume is equivalent to the present proved national gas reserves of 290 Tcf. Significant results have been obtained from full-scale tests conducted to date, namely Gasbuggy and Rulison. Additional progress has been made in further developing this technology, including (1) the successful testing of a small-diameter (less than 8-in.), low-tritium producing explosive designed specifically for gas-stimulation applications; (2) the completion of technical plans for the Rio B anco test which will stimulate a 1,200-ft gas-bearing section; (3) progress on computer-modeling studies comparing simultaneous versus sequential detonations in the same hole; (4) the formulation of the first experiment needed to develop a sequential explosion system. Extensive studies also have been made on the safety of this technique. Detailed investigations show that users of the gas will be exposed to an increment of radioactivity equal to about 1% of the natural radioactivity in our background. Ground motion due to the nuclear detonation is unavoidable. However, by proper choice of yield, and location, and by sequential detonation, it can be controlled to limit inconvenience and damage such as plaster cracking. Public acceptance will depend largely on a clear understanding of the value of the benefits of the program as compared to the inconveniences involved. The benefits include additional local revenues to those near to stimulated fields, royalties to landowners, and, to the nation, an additional supply of natural gas, which is very much in demand. End_of_Article - Last_Page 809------------

Geology of Wagon Wheel Nuclear Stimulation Project: ABSTRACT

Project Wagon Wheel, if executed will be an attempt to stimulate gas reservoirs of the Pinedale anticline by means of nuclear explosives. The Pinedale field, located in the northern Green River basin of southwest Wyoming, is potentially productive from a section totaling nearly 10,000 ft of lower Fort Union, Lance-Lewis, and Mesaverde sandstone equivalents. Attempts to produce the field conventionally have proved uneconomical due to low permeability. Because its requirements exceeded the state of nuclear technological development, Wagon Wheel was not selected for the first gas stimulation experiment. Project Gasbuggy, in northwest New Mexico, was detonated in 1967 using a 26 kiloton device. Data produced in Gasbuggy were utilized in planning Wagon Wheel, which is an actual attempt at economic use of nuclear energy. Wagon Wheel No. 1 was drilled to 19,000 ft to evaluate the entire Mesaverde section. Gas was detected by mud-logging equipment below 7,972 ft depth throughout the basal Fort Union, Lance-Lewis, and Mesaverde. The well has been plugged back to 11,700 ft leaving approximately 3,700 ft of proved gas-bearing section available for stimulation. This interval will accommodate the 5 100-kiloton explosives planned. In-place End_Page 652------------------------------ gas reserves for this section are calculated at 252 billion cu ft/sq mi. Extensive logging, coring, and testing have been carried out in the program, including special logs for rock mechanics study. Cores were compared with those from Gasbuggy as to compressive strength, shear behavior, and potential for fracturing. Petrographic analyses indicate better fracture potential at Wagon Wheel due to a higher degree of grain to grain contacts and lower clay content. Environmental protection studies include examination of surface waters, springs and wells, man-made structures, mines, flora, fauna, and general land use. The most important aspect from a geologic standpoint is protection of the extensive groundwater aquifers above the gas reservoir. Two wells, in addition to the Wagon Wheel No. 1, were drilled for the purpose of evaluating those aquifers. Potable water extends to a depth of approximately 3,600 ft. Salt water occurs from 3,600 to approximately 5,200 ft. Low quality subpotable water extends from 5,200 to about 7,200 ft. The saltwater zone is interpreted to be in a tongue of Wasatch Formation extending from the west into Eocene arkoses derived from the Wind River Range on the east. Plans call for sequential detonation of 5 explosives spaced at intervals from 9,220 to 11,560 ft to produce a more or less continuous chimney from about 8,700 to about 11,600 ft. There will be a safety margin of 1,500 ft between the top of fractures and the bottom of known aquifers. End_of_Article - Last_Page 653------------

Experimental Tests of a Method for Drilling With Explosives

Abstract TEST TEST A proposed method of drilling utilizes sequential detonation of two types of explosive charges delivered to the hole by a conventional drilling fluid through pipe. A shaped charge first produces a long thin hole. A second charge, called a gauging charge, is pumped into the thin hole, explodes, and enlarges it to full gauge. In one suggested configuration, the explosives are contained in cylindrical capsules 4- to 5-ft long. A drilling head is positioned 2- to 3-ft off bottom. When a capsule is pumped to the bottom of the hole and stops, pressure inside the drill pipe increases and differential pressure detonates the explosive. Primacord along the length of the capsule disintegrates the capsule. The debris circulates out of the hole with the drilling fluid. The gauging-charge action was examined using 2-ft cubes of Berea sandstone. The sandstone (18 per cent porosity) was vacuum-saturated with water and surrounded by concrete. To prevent reflected tensile pulses, the acoustical impedance of the concrete matched that of the sandstone. A 750-psig pressure was applied to a drilling fluid within a shaped-charge-formed hole before detonating the gauging charge. In these tests, 190 gm of rock were removed for each gram of explosive detonated. A similar series of experiments on low-porosity (0.40 per cent) metamorphic limestone provided a more rigorous test. Extensive fracturing from the gauging-charge action prevented an estimate of the volume of the expanded hole. The diameter of the hole was irregular, ranging from about 2 to 4 in-, or about fivefold larger than the hole created by the shaped charge. INTRODUCTION In the past, explosives have found a varied but somewhat limited use in the oil field. An early well stimulation technique, still in use today, involves shooting nitroglycerin to enlarge the borehole and to increase matrix permeability near the wellbore. Bullets and jets are now the conventional method of perforating casing and tubing. Detonations are frequently used to "back off" or "shoot off" stuck pipe and, of course, seismographic work has long depended on explosive-generated pulses to find attractive earth structures. Efforts to use explosives in drilling operations have received limited examinations1 which, in one respect, is surprising because explosives offer one way to transmit large amounts of energy directly to the bottom of the hole. Recently, Ostrovskii1 described a Russian method of drilling with explosives that utilizes small capsules containing explosives which are pumped into the mud stream to the bottom of a borehole. As the capsules leave the end of the drill pipe, a detonation mechanism is armed. Impact detonates the explosive- In another configuration, two liquids (an oxidizing agent and fuel) in the capsule are separated by a frangible membrane. Separately, the liquids are nonexplosive. Near the bottom of the drill pipe, the capsule passes through a narrow constriction which ruptures the membrane. The mixing of the liquids produces an explosive. Impact is again used to detonate the explosive. About the time Ostrovskii was developing his method, Humble Oil & Refining Co. was independently doing research on another explosive drilling concept based on the sequential detonation of two types of explosive charges. The proposed technique consisted of alternately pumping a shaped charge and then a "gauging charge" down a well. The shaped charge should drill a long, tapered hole, and the gauging charge should expand it to full gauge. This paper presents the visualized drilling concept and gives results of laboratory work which showed that sequential firing of charges can form hole at an attractive charge-to-rock removal ratio. An important finding was that increased environmental pressure, which is to be expected in wells, increases rock removal efficiency of the gauging charge.