(1) Except where constructed in accordance with Section 9.15., walls supporting drained earth shall be designed,
(a) for a pressure equivalent to that exerted by a fluid with a density of not less than 480 kg/m3 and a depth equal to that of the retained earth, or
(b) in accordance with Section 4.2. so as to be able to resist the loads and effects described in Article 4.1.2.1.
(2) Walls supporting other than drained earth shall be designed,
(a) for the pressure described in Clause (1) (a) plus the fluid pressure of the surcharge, or
(b) in accordance with Section 4.2. so as to be able to resist the loads and effects described in Article 4.1.2.1.