Abstract : Beach abrasion is one of the national disasters that concern the Indonesian government. This disaster has resulted in adverse coastline changes in West Sumatra Province. The mainland area has been lost for hundreds meters due to abrasion. A field study has been conducted and found that beach without vegetations is very vulnerable to abrasion than the beach with vegetations. In some place, abrasion protection has been done by using hard structures but this way is not natural and attractive. A field investigation also found that several types of endemic beach vegetation in West Sumatra can live for decades till now. This condition shows that beach vegetations can be used for beach protection purposes against abrasion. This study describes the mechanism of vegetation root in protecting beaches against abrasion using numerical simulation. The data for simulation are obtained from laboratory tests of beach sands, In the numerical simulation, the beach sand is considered as geo-material that follows MohrCoulomb’s constitutive law while the roots are modelled as geo-synthetic elements that can only resist the tension forces. There are three conditions to be considered in the numerical models. The first model: beach without any roots, the second one: roots under the ground surface and The third model: roots reach the ground surface. Those three models are analyzed separately using the same dimensions and parameters. The simulation results show that vegetation roots give the unity effect to the surrounding sand into a large mass. This unified soil mass that come down into the bottom provides mechanical resistance against the pull force. The simulation results explain the root mechanism of vegetation in protecting beach against of abrasion. (Link)