Hello ,
i found the solution here Cast shadow through alpha masked mesh & customDepthMaterial
the solution is to use MeshDistanceMaterial instead of MeshDepthMaterial cause i use PointLight so the code is
var aa=scene.getObjectByName('serre36') ;
var bb = aa.children[3] ;
var cc= bb.material;
bb.customDistanceMaterial = new THREE.MeshDistanceMaterial( {
map: cc.map, // use map provide by blender
alphaTest: 0.5
} );
work very well see result