| 摘要 |
An earth drain which comprises a filter encased core having, on at least one base or web surface, a first array of discrete projections or studs of uniform height and a second array of discrete projections or studs of lesser height than the projections or studs of the first array. The projections or studs of the second array are so disposed between the projections or studs of the first array that, under relatively low pressures, the filter encasing the core is maintained in spaced relationship with the base or web of the core by the free ends of the first array of projections or studs and, at relatively high soil pressures, the filter material forced inwardly toward the base of the core is supported by the free ends of the studs of the second array and is thus maintained in spaced relationship with the base of the core, the spacing corresponding to the height of the second array of projections or studs. |
