penetrationpenetration depthpenetration factorpenetration groove weldpenetration indexpenetration macadampenetration methodpenetration probepenetration resistancepenetration resistance testpenetration testpenetrometerpenstockpercentage consolidationpercentage frequencypercentage of reinforcementpercentage reduction in areapercentage saturationperceptionperception modelperception pointperception reaction timeperception timeperched aquiferperched horizonperched waterperched water tablepercolationpercolation forcepercolation headpercolation linepercolation ratepercolation testpercussionpercussion drillpercussion drillingpercussion hammerpercussion sampleperennial artesian flowperennial artesian wellperennial canalperennial streamperfect fluidperfect gasperfect plasticityperfectly elasticperfectly plastic materialsperforated brickperforated cover plateperforated metal basket