Hello,
I passed the 2008 April Civil Geotech depth to my surprise. I was demoralized and thought for sure I had failed since I ran out of time and had to flat out guess on about 8 problems
If you are still deciding between depth modules, I recommend Water/Enviro. Geotech is full of complicated subjects that don't necessarily relate to one another and are not covered well in breadth prep. Also, while I'm sure all the depth modules require the use of some engineering judgment, it seems like Geotech is riddled with instances where you have to know when to be conservative beyond the acceptable approach outlined.
If you must take Geotech though, I found Das Fundamentals of Geotech engineering to be very very helpful. In addition to that, I became a community borrower and raided the univeristy's engineering library for texts on everything not covered in Das. Here's the list of Geotech references I took in:
DAS Fund of Geotech 2nd
Geotechnical Materials In Construction 1996 (Rollings & Rollings)
Groundwater Lowering In Construction 2001 (Cashman)
Handbook of Temporary Structures In Construction 1984 (Ratay)
Fundamentals of Earthquake Resistant Construction 1993 (Krinitzsky)
Engineering Principles of Ground Modification 1990 (Hausmann)
Geotechnical Engineering of Embankment Dams 1992 (Fell, MacGregor)
Practical Dam Analysis 1999 (Herzog)
Geotechnical earthquake engineering / Steven L. Kramer 1996
Seismic Design of Bldg. & Structures
They all got used during the exam and all yielded helpful information. I'm sure each one was worth a problem that I would have had to guess on otherwise.
The university had even more and more useful Geotech texts available but someone beat me to those. If I didn't read through the book, I at least tabbed the TOC, Index, and pages that contained topics on the NCEES geotech depth module list.
Spend the majority of your time preparing for depth. Breadth is cake, you just have to print out the breadth NCEES list of topics and know where to look in the CERM. Solving all the breadth 6 minute solutions seals the deal. For depth, print out the list of NCEES topics covered for your specialized discipline and delve delve delve into them. Theory, problems, 6 minute solutions, lengthy essay type problems anything you can find. You will not regret OVER-PREPARING for the depth module especially Geotech!!!