Geotechnical Engineering Concepts Quiz

Resistance Factor Selection

• Resistance factors depend on the method for determining nominal shaft resistance.
• Local experience with geologic formations and shaft construction is crucial for shafts in clays or easily disturbed formations.
• Resistance factors in Table 10.5.5.2.4-1 should be reduced by 20% when applied to a single shaft supporting a bridge pier.
• Reducing the resistance factor does not allow increasing the R factor to address lack of foundation redundancy, as per Article 1.3.4.
• The number of static load tests needed to justify resistance factors in Table 10.5.5.2.4-1 depends on site variability.
• A site, for variability assessment, is defined as a project site (or a portion) where subsurface conditions are geologically similar (strata sequence, thickness, geologic history, engineering properties, and groundwater).

Exploration Depth and Points

Retaining Walls

• At least one exploration point per retaining wall.
• For walls longer than 100 ft, points every 100-200 ft, alternating locations in front and behind the wall.
• Additional points in anchorage zone (at 100-200ft intervals) for anchored walls; and 1.0 to 1.5 times wall height behind the wall for soil-nailed walls.
• Exploration depth should reach a point where stress increase from estimated foundation load is less than 10% of existing effective overburden stress. And between one and two times the wall height.
• Depth should penetrate soft/compressible soils (e.g., peat, organic silt, soft fine-grained soils) to competent material (e.g., stiff to hard cohesive soil, compact dense cohesionless soil, bedrock).

Shallow Foundations

• One exploration point per substructure (piers or abutments) for widths ≤ 100 ft.
• Two points per substructure for widths > 100 ft.
• Additional points for erratic subsurface conditions.
• Depth should fully penetrate unsuitable foundation soils to suitable bearing resistance materials.
• At least reach a depth where stress increase from estimated foundation load is less than 10% of existing effective overburden stress.
• If bedrock is encountered before this depth, explore at least 10 ft into the bedrock to characterize its compressibility. (Sufficient rock exploration needed, possibly more than 10 ft if highly variable bedrock conditions or large boulders).

Deep Foundations

• One point per substructure (bridge piers or abutments widths ≤ 100 ft).
• Two points for widths > 100 ft.
• Additional points for erratic conditions (especially for shafts socketed into bedrock).
• At least one exploration point per large diameter shaft (> 5 ft), especially when socketed into bedrock.
• Exploration in soil extends at least 20 ft below anticipated pile or shaft tip. (Or twice the minimum pile group dimension, whichever is deeper).
• Borings extend through unsuitable strata (e.g., unconsolidated fill, peat, organic materials, soft fine-grained soils, loose coarse-grained soils) to reach hard or dense materials.
• For rock bearing piles: 10 ft rock core at each point.
• For shafts on or in rock: 10 ft rock core, or a length of rock core equal to 3x shaft diameter (isolated shafts), or 2x minimum shaft group dimension (whichever is larger); to determine rock properties.
• Sufficient rock exploration, possibly exceeding 10ft or rock core, if highly variable bedrock conditions or large boulders likely.

Test your knowledge on key concepts in geotechnical engineering, including resistance factors and site variability assessments. This quiz covers important topics such as nominal shaft resistance and the considerations for retaining walls. Perfect for civil engineering students or professionals looking to refresh their understanding.