SUBJECT: Blast wall requirements and usage for search areas and other VBIED targets

Transcription

1 DEPARTMENT OF THE ARMY DET 8/412 th ENGINEER COMMAND LSA ANACONDA APO AE REPLY TO ATTENTION OF AFRC-ENMS-DET8 26 JUNE 2006 MEMORANDUM FOR RECORD SUBJECT: Blast wall requirements and usage for search areas and other VBIED targets 1. BLUF: An effective blast wall is needed to protect personnel and equipment in and around areas where VBIEDs are most likely to detonate. T-walls alone will more likely contribute to the casualtyproducing effects of a blast than having no T-wall at all. A composite wall of two rows of T-walls with HESCO bastions or a similar soil barrier would provide the needed blast and fragment protection for the minimum footprint with available materials. 2. References: a. UFC (Volumes 1-4), Security Engineering b. UFC Design and Analysis of Hardened Structures for Conventional Weapons c. USCENTCOM OPORD 05-01, App. 2, Annex V (Force Protection) d. Joint Forward Operations Base (JFOB) Force Protection Handbook (Final Draft, Feb. 2006) e. Blast Effects Estimation Model (BEEM) software, US Army Corps of Engineers (USACE) f. CONWEP software, USACE g. HEXDAM blast modeling software, Trinity Consulting 3. Threat weapons. The minimum standard for the CENTCOM Vehicle Borne Improvised Explosive Devices (VBIED) is 100 kg (220 lbs) of TNT (ref. 2c). This corresponds to a low VBEID threat by Department of Defense (DoD) standards. Based observed VBIED tactics, its is common to stack four to five artillery shells in a vehicle. Based on this, plus the shrapnel generated by the vehicles itself, a set of five 155mm rounds is assumed to be the fragment hazard, which is a standard data set for BEEM. 4. Threat distance. Based on typical seach lanes being 20 feet wide or less, with a typical road lane being 12 feet wide, it can be safely assumed that a VBIED could be detonated at a distance of 10 feet from a wall. Blast effects are closely tied to distance, so a distance closer than 10 feet would have increased effects. Therefore, a 10 foot distance is not worst case but instead is typical of a VBIED trying to blend in with regular traffic instead of pulling up next to a wall for maximum effects. 5. Blast analysis using CONWEP shows that for the following thicknesses are required for 220 lbs of TNT at a distance of 10 feet, blast effects only (no fragments from VBIED): Concrete Strength Prevent Breach Prevent Spall 4500 psi (US typical min. strength) 14.5 inches 20.5 inches 1500 psi (Iraq typical min. strength) 24.0 inches 44.0 inches Given T-walls vary from 6 inches to 12 inches in thickness, a single T-wall will be destroyed by the minimum VBIED blast charge in a typical search lane configuration, regardless of the strength of concrete. The concrete from the destroyed T-walls would become deadly hazards, creating a threat a

2 AFRC-ENMS-DET8 SUBJECT: Blast wall requirements and usage greater distance than the blast effects alone would have had, generally continuing out in the direct line of sight for hundreds of meters or until they hit something large enough to stop the fragments. 6. The threat posed by blast near concrete barriers is well understood. Concrete barriers are typically employed for counter-mobility or explosive blast/fragment mitigation at entry control points (ECPs) and along avenues of approach. Concrete barriers employed in this fashion can be effective in stopping primary debris, if they are sufficiently tall. However, they also may become secondary debris hazards in the immediate vicinity of a large explosion and could cause additional damage. Soil-backed concrete barriers provide better protection against secondary debris hazards. (Ref. 2c, Chapter 6,) 7. Standard security practice is to assume the vehicle search area is where a VBIED is detected. This mitigates the risk to sites within the protected perimeter such that it can be assumed a VBIED attack will not occur within that perimeter. However, this is done by assuming the explosive device will be detected and possibly detonated in the search area. This requires the search area to have proper standoff from all other facilities and personnel areas or to have appropriate structures to mitigate fragment and near term blast. (Ref 2a, Vol. 2, Chapt. 3) 8. A blast analysis of the attached design (Blastwall Type 1 Design) was conducted using HEXDAM. This is a less conservative program than BEEM. However, BEEM does not account for blast wave interaction with structures whereas HEXDAM does. HEXDAM is a commercial program used in industry. The attached design uses materials and techniques currently available in the region. a. Fig. 8a below shows the effects of 220 lbs of TNT detonated 10 feet from a T-wall with 1500 psi compressive strength concrete. The two figures in line with the T-wall are directly in the path of the blast wave. The remaining figures to the right of the wall are behind the wall. The results show the wall failed and the shock wave continued, causing damage to the people. It does not factor any fragments effects from the T-walls. 2 of 3

3 AFRC-ENMS-DET8 SUBJECT: Blast wall requirements and usage b. Fig 8b below shows a composite wall consistent with the attached drawing. The results indicate the T- walls nearest the blast still fail, but the HESCOs absorb a great deal of the kinetic energy and the inner T- walls hold. This indicates there are no secondary effects due to fragmentation of the T-walls. The HESCOS would also absorb the fragments from the VBIED that penetrated the first T-walls. It is likely the T-walls on the protected side will crack and may have minor spalling, becoming unusable for continued service. The T-walls on the protected side remain sufficiently intact, preventing the HESCOS from tipping into the protected area and providing additional fragment protection. Results from CONWEP verify these results. The blast wave propagates up and over the blast wall. It should be noted that the blast effects will begin to arch down towards the ground, which is not shown in the plot of the overpressure wave. Regardless, the individuals closest to the wall will still receive optimal protection from fragment and blast effects. Blast effects dissipate at an exponential rate with distance, so while everything on the other side of the blast wall is not as protected as this graphic may appear, targets are protected from fragment and blast is mitigated. Actual performance will depend on the strength and composition of the walls as well as size, composition, and location of the shot. 6. POC for this is MAJ Clarence B. Kemper, Det 8/412 th ENCOM, LSA Anaconda (Balad), Iraq, AKO bart.kemper@us.army.mil, AKO-S bart.kemper@us.army.smil.mil, DSN //signed// Attachment: Blastwall Type 1 Design.pdf CLARENCE B. KEMPER, P.E. MAJ, EN, ARMY RESERVES MECHANICAL ENGINEER DET 8/412 th ENCOM 3 of 3

4 NOTE: FILL TOP 18 INCHES OF TOP HESCO WITH SANDBAGS TO ELIMINATE WIND SCOURING OF FILL AND REDUCE BLAST DEBRIS OUTSIDE WALL (PROTECTED AREA) (2) MIL1 HESCOS 42" WIDE X 54" HIGH X 32FT *COMPACTED FILL, 6" LIFTS *HESCO FLUSH WITH T-WALL FACE INSIDE WALL (SEARCH AREA) (BLAST CONTAINMENT) "TEXAS" T-WALL, 9" THICK 4 IN FRONT 4 IN BACK *1500 PSI MINIMUM COMPRESSIVE STRENGTH THIS DESIGN IS TO REDUCE INJURY OUTSIDE BLAST AREA. ACTUAL PERFORMANCE VARIES WITH CONCRETE STRENTH AND SOIL TYPE IN HESCO. OUTSIDE WALL MAY CRACK BUT SHOULD NOT SPALL. PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF THE US GOVERNMENT. IT IS SUBJECT TO CLASSIFICATION RESTRICTIONS AND IS NOT FOR COMMERCIAL OR PRIVATE USE. UNAUTHORIZED USE IS PROHIBITED AND MAY BE SUBJECT TO PROSECUTION LBS 10' from inside wall POC: MAJ C.B. KEMPER, P.E. bart.kemper@us.army.mil NEXT ASSY APPLICATION 4 USED ON UNLESS OTHERWISE SPECIFIED: DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH BEND TWO PLACE DECIMAL THREE PLACE DECIMAL INTERPRET GEOMETRIC TOLERANCING PER: LOCATION IRAQ CLASSIFICATION: UNCLASS DO NOT SCALE DRAWING 3 DRAWN CHECKED ENG APPR. MFG APPR. Q.A NAME CBK TYJ AJK DATE 2/3/2006 DET 8 412th ENCOM LSAA, IRAQ APPROX 250 SANDBAGS TO FILL GAP BETWEEN T-WALLS CLIENT: TITLE: Blastwall Type 1 Design Blastwall Overview SIZE MISSION NO. A SCALE: 1:60 WEIGHT: 1 REV 0 SHEET 1 OF 2

5 KEY DESIGN FEATURES, MUST BE MET OR EXCEEDED 3 SANDBAG AT LEAST TOP 12" OF HESCO OR 6" PLUS ALL ABOVE TOP OF T-WALL WHICHEVER IS GREATER MIN WIDTH 9" MIN THICKNESS FILL COMPACT 6" LIFTS MIN HT TEXAS T-WALL MIN. STRENGTH 1500 PSI HESCO ON BASE TO ELIMINATE TIPOVER DUE TO BLAST FORCE 1500 PSI MIN CONCRETE COMP. STRENGTH SANDBAG TO FILL GAP BETWEEN T-WALL BASE FLUSH TO TOP OF BASE TO SUPPORT HESCOS T-WALL USED FOR THIS DESIGN. OTHER T-WALL DESIGNS CAN BE USED AS LONG AS THEY HAVE FLAT TOP OF BASE FOR HESCO SEATING AND MEET OTHER DESIGN CRITERIA. PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF THE US GOVERNMENT. IT IS SUBJECT TO CLASSIFICATION RESTRICTIONS AND IS NOT FOR COMMERCIAL OR PRIVATE USE. UNAUTHORIZED USE IS PROHIBITED AND MAY BE SUBJECT TO PROSECUTION. NEXT ASSY APPLICATION USED ON UNLESS OTHERWISE SPECIFIED: DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH BEND TWO PLACE DECIMAL THREE PLACE DECIMAL INTERPRET GEOMETRIC TOLERANCING PER: LOCATION IRAQ CLASSIFICATION: UNCLASS DO NOT SCALE DRAWING DRAWN CHECKED ENG APPR. MFG APPR. Q.A. NAME CBK TYJ AJK DATE 2/3/2006 DET 8 412th ENCOM LSAA, IRAQ CLIENT: TITLE: SIZE A Blastwall Type 1 Design Blastwall Details MISSION NO. SCALE: 1:48 WEIGHT: REV 0 SHEET 2 OF