DYNAMIC RESPONSE ANALYSIS OF GEOGRID REINFORCED EMBANKMENT SUPPORTED BY CFG PILE STRUCTURE DURING A HIGH-SPEED TRAIN OPERATION

Abstract

THE PERFORMANCE OF RAILROAD STRUCTURE HAS A TREMENDOUS INFLUENCE ON THE SAFETY AND STABLE OPERATION OF HIGH SPEED TRAINS. STRONG VIBRATIONS AND THE DEGRADATION RATE OF THE TRACK ARE THE MAIN FACTORS AFFECTING THE TRANSPORT SAFETY OF A RAILROAD BUILT OVER A WEAK SOIL. GEOGRID REINFORCED EMBANKMENT SUPPORTED BY PILE STRUCTURE IS A NEW EFFICIENT CONSTRUCTION TECHNIQUE USED TO ENSURE THE STABILITY AND ENHANCE THE PERFORMANCE OF THE RAILROAD SYSTEM; BUT ONLY A FEW STUDIES ARE ORIENTED TO ITS BEHAVIOR UNDER TRAIN OPERATION. THIS PAPER INVESTIGATES THE DYNAMIC RESPONSE OF GEOGRID REINFORCED EMBANKMENT SUPPORTED BY CEMENT FLY-ASH GRAVEL PILE STRUCTURE DURING A HIGH-SPEED TRAIN OPERATION. THE ESTABLISHMENT OF A REALISTIC SIMULATION MODEL FOR RAILROAD SUBJECTED TO A MOVING TRAIN LOAD, IS AN IMPORTANT FIRST STEP TOWARDS THE RELIABLE DESIGN OF GEOGRID REINFORCED EMBANKMENT SUPPORTED BY PILE STRUCTURE. THUS, A 3D NONLINEAR FEM HAS BEEN ESTABLISHED TO SIMULATE THE INSTRUMENTED HARBIN-DALIAN RAILWAY TEST SECTION. EACH TRAIN CARRIAGE WAS MODELED AS A TRANSIENT DYNAMIC LOAD THROUGH A USER-DEFINED DLOAD SUBROUTINE. THE DEVELOPED MODEL WAS SUCCESSFULLY VALIDATED BY THE DYNAMIC RESPONSE RECORDED FROM THE FIELD TEST SECTION. THE IMPROVEMENT OF THE RAILROAD STRUCTURE BY THE CFG PILES AND GEOGRIDS CONTRIBUTED SIGNIFICANTLY TO THE REDUCTION OF THE VIBRATION IN THE STRUCTURE, WHICH ATTENUATES 1.2 TIMES FASTER WITH THE STRUCTURE DEPTH, EVEN UNDER OVERLOAD CONDITIONS. MOREOVER, THE PHENOMENON OF RESONANCE OBSERVED WHEN THE TRAIN REACHES SPEEDS OF 100 AND 260 KM/H WERE ANNIHILATED. THE ANALYSIS OF THE STRESS DISTRIBUTION WITHIN THE EMBANKMENT REVEALED THAT A DYNAMIC ARCH IS FORMED IN THE EMBANKMENT AT 2 M FROM THE GROUND. THE STRESS ONTO THE PILE WAS 16 TIMES GREATER THAN THAT ACTED ON THE SOIL AND THE TENSILE STRESS DEVELOPED IN THE GEOGRID WAS HIGH AT THE PILES EDGE BELOW. IN ADDITION, THE COUPLING EFFECT OF GEOGRID WITH VARIOUS TENSILE STRENGTHS AND THE PILES WITH DIFFERENT STRENGTH GRADES INDICATED THAT THE COMBINATION OF A HIGH-STRENGTH PILE AND GEOGRID SIGNIFICANTLY REDUCES THE DISPLACEMENT GAP DUE TO THE VARIATION OF TRAIN SPEED. AS A RESULT, THE VIBRATIONS OF THE TRACK WERE ALMOST CONSTANT DURING THE TRAIN OPERATION; THUS, ENSURING COMFORT TO PASSENGERS AND REDUCING THE RISK OF DERAILMENT.

KEYWORDS

DYNAMIC RESPONSE; 3D-FEM; TRANSIENT DYNAMIC TRAIN LOAD; PILE; GEOGRID, VIBRATION.