1. Stress and Strain Analysis

2. Elasticity and Elastic Boundary-Value Problems

3. Fundamentals of Plasticity Theory

4. Basic Soil Constitutive Models

5. Theoretical Geomechanics and Relation to Practice

Terzaghi's Theoretical Soil Mechanics is still a good read. It is outdated in many respect but the (unchanging) fundamentals are covered well. Scott's Foundation Analysis is not a quick read but has an interesting coverage of various theoretical problems in foundation engineering. My own book, while not a theoretical text, does attempt to establish a firm link between analysis and the use of analysis and design.

6. Numerical Methods

7. Programming with FORTRAN