# Numerical Assessment and Repair Method of Runway
###### Abstract  
This paper addresses the protection capability of a runway pavement by executing a field blast test on an airfield pavement subjected to blast loading from a CBU (cluster bomb unit), and by confirming the numerical simulation of warhead penetration and the form of damage. The CBU's blast loading applies the BAP 100 of an air-to-ground munition in a similar scale. Penetration depth is calculated by a formula which incorporates the terminal speed of a free-falling cluster munition dispersed 20 km above the ground. According to the result of the calculation, the penetration depth by a cluster munition is 33 cm from the surface of the pavement. The field blast test was conducted based on this result. Furthermore, LS-DYNA software simulation was used to assess the condition of damage, determined by the depth of penetration and explosive pressure from a free-falling CBU landing on the airfield pavement from 20 km above the ground. The condition was ultimately used to verify the result of field testing and to confirm the scale of damage repair. The depth of explosion was 78 cm, from the surface to the crushed stone and sand layer below the pavement, and the diameter was 30 cm. The size of the crushed concrete that needed to be removed was an average diameter of 156 cm. The simulation result confirms that the diameter and depth of the crater are 67.6 cm and 67 cm, respectively, when the CBU is detonated under the same depth as the field testing, and the height of upheaval is 12 cm. The most appropriate method for repair, after a series of reviews, is to cut and remove a concrete slab \(1.8\) m \(\times\) 1.8 m and cast the crushed stone layer disrupted from the explosion, followed by repairing the removed damaged concrete slab sections using rapid hardening concrete. airfield; pavement; concrete; blast; explosive; cluster bomb unit; runway repair; numerical assessment; M&S 2022 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022019 March 2022020  
study is to verify the depth of penetration and the damage condition by modeling. For the modeling, a formula was used to compute the relationship between the height at which a warhead of CBU disperses and the depth of penetration into concrete pavement. A concrete pavement similar to that of an airfield was used for an actual explosive test on a live site in order to discover the scale and form of a crater. A cluster bomb unit delivered by a ballistic missile is normally dispersed approximately 20 km above the ground, then flies vertically before free falling onto the target. The speed of free fall allows a warhead to penetrate into the pavement surface followed by an explosion creating a crater. The study simulated by detonating the equivalent amount of TNT installed under the airfield pavement at the same level of depth, and ultimately confirmed the damage condition to the pavement. The field test applied the calculated result which assumes the depth with no penetration into the pavement. The test also confirmed that an explosion inside the concrete pavement creates a disruption due to its pressure, from the surface of pavement down to 78 cm deep where a sand layer is located; and the concrete slab deforms to approximately 156 cm due to upheaval, breaking, and other factors, consequentially limiting the overall traffic of aircraft and requiring removal of these objects. For the modeling results, the scale of damage was 67.6 cm in diameter and 67 cm in depth when running a model in the field test. When comparing the field blast test result and the result of numerical simulation, the latter ended up with a longer diameter and, thus, more severe damage. Additional analysis confirmed that the speed of explosion for the explosives used in the field test was 6000 m/s, which is slower than the speed of explosion for a genuine warhead at 7650 m/s. This was due to the shape of the tube.