design of different height drain

hello guys

i have considered to design a DIFFERENT HEIGHT DRAIN  for retaining soil by its side and fulfill the requirement of drain at site, as space available is also less.It would be very helpful if any one have design details or staad models on such type of drain.

Should i go for plate or line modelling in staad to calculate maximum moments in drain walls?

what if my active pressure is less that passive pressure, what pressure should i consider for evaluating moment?

should i need to do sliding check?

regards

veeresh