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SUMMARYThe hierarchical composite element algorithm is developed for drainage holes in rock masses. The composite elements containing drainage hole segments have definite sets of hydraulic potentials defined at their nodes. By the variational principle the governing equation for the solution of the nodal hydraulic potentials can be formulated. To deal with the complicated seepage pattern in the composite elements containing drainage hole segments, hierarchical shape functions are introduced. The method and algorithm have been implemented in the program. A comparative study using the finite element (FE) method with fine mesh and the composite element method (CEM) with simple mesh for pressure well problem has been carried out. The results show that as the upgrade of the shape function order, the calculation accuracy of the CEM can be improved even with a coarse mesh. The restraints of the drainage holes on the composite element mesh generation are therefore further reduced by the algorithm proposed in this paper.

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