Geotechnics, foundations, and engineering geology
Geotechnics, foundations, and engineering geology
This domain tests how ground conditions govern foundation choice: soil classification, bearing capacity, settlement, groundwater, frost heave and permafrost. Mongolia’s cold climate makes frost depth and seasonal thaw critical, especially for shallow foundations and buried services.
Core rules
- Distinguish allowable bearing pressure from ultimate bearing capacity; serviceability settlement often governs design.
- Foundation depth must be below frost depth or protected by insulation and drainage; otherwise frost heave can lift and crack structures.
- In permafrost, avoid disturbing the thermal regime; use ventilated piles or insulation as designed.
- Groundwater needs dewatering and, for concrete, sulphate/chloride assessment.
- Piles transfer load through skin friction and end bearing; verify both from site investigation.
Worked example A column load is 800 kN. Allow the footing self-weight at 10%: total 880 kN. The allowable bearing pressure from the geotechnical report is 200 kPa. Required area = 880 ÷ 200 = 4.4 m². For a square pad, B = √4.4 = 2.10 m; adopt 2.2 m × 2.2 m. If frost depth is 2.0 m and groundwater is at 1.5 m, founding at 2.2 m may require dewatering and frost-protection detailing; check settlement and the construction method before accepting the size.
Traps that cost marks
- Using ultimate bearing capacity as if it were allowable pressure.
- Sizing a footing only by bearing pressure and ignoring settlement.
- Founding above frost depth without insulation or drainage.
- Ignoring groundwater effects on excavation stability and concrete durability.