Simplify the following text for a Grade 12 native English-speaking person.
Original: Geotechnical engineering is important in civil engineering , but is also used by military , mining , petroleum , or any other engineering concerned with construction on or in the ground . Geotechnical engineering uses principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials ; determine the relevant physical\/mechanical and chemical properties of these materials ; evaluate stability of natural slopes and man-made soil deposits ; assess risks posed by site conditions ; design earthworks and structure foundations ; and monitor site conditions , earthwork and foundation construction
Simplified: Geotechnical engineering uses principles of soil and rock mechanics to determine :