The subject of this research mainly focuses on the gravel formation along the western foothill of Taiwan. Numerical simulations are performed using discrete element method (DEM) based the software Particle Flow Code (PFC). Physical properties and internal friction angle of gravels are obtained from the three dimensional modeling of in-situ direct shear tests. The numerical experiments using PFC2D are used to model single-vertical anchor installed at shallow depths. The numerical results indicate that the failure range for the tension-type anchor is smaller than the range for compression-type anchor at the same bonded length and friction angle. The pullout resistance for the compression anchor is also greater than the tension anchor. Similar results have been obtained from the field pullout tests. The transmission of forces along the anchor is significantly affected by way of particle permutation with the anchor. If bigger size particles are piled around the anchor, the transmission of forces along the anchor will be faster and the affecting range of particles is also larger.