CELE Geotechnical Engineering — Foundations (Shallow and Deep)Concept Map

Related concepts

Concept connections

• Shallow Foundations→Bearing Capacity AnalysisShallow foundations are sized and verified using bearing capacity equations and allowable bearing pressure qa
• Deep Foundations→Pile Capacity ComponentsDeep foundation capacity is computed as the sum of end bearing and skin friction; pile capacity is the fundamental design parameter
• Pile Capacity Components→Soil Parameters & MethodsCalculation of Qp and Qs depends critically on soil strength parameters (cu for clay, φ for sand) and design method (α-method or β-method)
• Group Behavior & Interactions→Pile Capacity ComponentsGroup capacity is derived from individual pile capacity multiplied by group efficiency factor η; block failure is an alternative limit state
• Special Conditions & Phenomena→Pile Capacity ComponentsNegative skin friction (downdrag) reduces the effective skin friction contribution, lowering overall capacity
• Footing Sizing Formula→Bearing Capacity AnalysisThe area required is determined by A = P/qa; this connects applied load to allowable bearing pressure
• Settlement Estimation→Shallow FoundationsSettlement must be checked for shallow foundations to verify serviceability; excessive settlement may require a mat or switch to deep foundation
• Bearing Capacity Equations→Soil Parameters & MethodsBearing capacity factors and equations (Nc*, Nq*, fs) are derived from soil mechanics theory and depend on soil type and properties
• End Bearing Capacity→Soil Parameters & MethodsEnd bearing is calculated using soil strength (cu for clay) and bearing capacity factors; it is depth-dependent and controlled by tip conditions
• Skin Friction Resistance→Soil Parameters & MethodsSkin friction is computed using adhesion factor α (clay) or lateral stress coefficient K (sand); it accumulates over the shaft length
• Negative Skin Friction→Consolidation PotentialNegative skin friction occurs when surrounding soil (especially recent fill) consolidates more than the pile, creating downdrag load
• Design Standards & Codes→Bearing Capacity AnalysisNSCP 2015, ACI 318, and RA 544 provide load factors, safety factors, and design requirements for foundation calculations
• Structural Considerations→Shallow FoundationsFooting flexure and shear (per ACI 318) are designed after the area is determined; moment and shear depend on bearing pressure distribution
• Structural Considerations→Deep FoundationsPile head connections and load distribution through pile groups require structural design; capacity governs layout and pile sizing
• Group Efficiency→Overlapping Stress ZonesGroup efficiency η < 1 accounts for the reduction in capacity due to overlapping stress bulbs from adjacent piles in the group
• Block Failure Analysis→Group Behavior & InteractionsBlock failure is an alternative failure mode where the entire pile group and surrounding soil move as one unit; controls capacity when it is lower than individual pile capacity
• Mat/Raft Foundation→Footing Sizing FormulaA mat is used when the total footing area exceeds ~50% of the building footprint; sizing follows the same A = P/qa principle but as a single large footing
• Undrained Shear Strength (cu) — Clay→End Bearing CapacityIn clay, end bearing Qp = 9cu·Ap; cu is the primary soil parameter controlling tip capacity
• Adhesion Factor (α)→Skin Friction ResistanceIn clay, skin friction fs = α·cu; α typically ranges 0.5–1.0 and depends on cu magnitude and stress history
• Angle of Internal Friction (φ) — Sand→Skin Friction ResistanceIn sand, skin friction fs = K·σ'v·tan(δ); φ (and the derived δ) governs frictional resistance
• Safety Factor Application→Allowable CapacityAllowable capacity Qa = Qu/FS (typically FS = 2.5–3.0); safety factor converts ultimate to service-level design value
• Clay Soil Profiles→Soil Parameters & MethodsClay strength profile (cu vs. depth) is obtained from boring, laboratory testing, or field tests (CPT); it drives pile capacity and bearing capacity calculations
• Sand Soil Profiles→Soil Parameters & MethodsSand density and friction angle (from SPT N-value or triaxial) determine K and δ; these control skin friction and end bearing in sand
• Mixed Soils→Pile Capacity CalculationMixed soil profiles (clay + sand layers) require applying the appropriate method (α or β) to each layer and summing contributions; total Qs = Σ(fs·As)
• Effective Stress (σ'v)→Skin Friction ResistanceIn sand, effective stress σ'v is used in fs = K·σ'v·tan(δ); accounts for pore pressure and depth
• Lateral Earth Pressure Coefficient (K)→Skin Friction ResistanceIn sand, K represents lateral stress state; higher K (denser, more confined sand) increases skin friction
• Pile Friction Angle (δ)→Skin Friction ResistanceIn sand, δ is the pile-soil friction angle; typically 0.75φ to φ depending on pile roughness; directly enters fs = K·σ'v·tan(δ)
• Consolidation Settlement→Special Conditions & PhenomenaIn soft clay, consolidation settlement occurs over time after construction; if surrounding soil settles more than the pile, negative skin friction develops
• Recent Fill or Embankments→Negative Skin FrictionRecently placed fill undergoes consolidation; if it settles faster than a new pile, it creates downdrag loading on the pile shaft
• NSCP 2015→Bearing Capacity EquationsNSCP 2015 adopts Philippine-specific load factors and design criteria for bearing capacity; references ACI 318 and AISC 360 for structural design
• ACI 318→Structural ConsiderationsACI 318 provides reinforced concrete design requirements for footing flexure, shear, and detailing; foundation design must comply
• AISC 360→Structural ConsiderationsAISC 360 governs steel pile design and connections; used when piles are steel H-piles or when steel pile caps are employed
• RA 544→Design Standards & CodesRA 544 (Philippine National Building Code) sets the legal framework; foundation design must comply with its minimum standards

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