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

6. Numerical Methods

Without a doubt, Chapra and Canale's award-winning would be the starting point for anyone aiming to develop a background in numerical methods in engineering.

For studies in the finite element method, Potts and Zdravkovic's volume 1 (theory) and 2 (practice) are very good references.

7. Programming with FORTRAN