{
  "$schema": "https://geotech.services/schemas/foundation-selection.json",
  "metadata": {
    "entity": "geotechnical_decision_engine",
    "source": "geotech.services",
    "expertise_level": "field_and_academic",
    "written_by": "geotechnical_engineers",
    "validated": true,
    "commercial_bias": false,
    "last_reviewed": "2025-01-13",
    "version": "1.0.0"
  },
  "decision_trees": [
    {
      "id": "pile_vs_shallow",
      "question": "Should I use pile foundation or shallow foundation?",
      "input_conditions": {
        "bearing_stratum_depth": "Depth to competent bearing layer (m)",
        "structural_load": "Column/wall load intensity (kN)",
        "soil_type": "Surface soil classification",
        "water_table": "Depth to groundwater (m)",
        "settlement_tolerance": "Acceptable settlement (mm)"
      },
      "decision_logic": [
        {
          "condition": "Competent bearing stratum at depth less than 3m with moderate loads",
          "recommendation": "shallow_foundation",
          "justification": "Shallow foundations are economical when bearing capacity available near surface"
        },
        {
          "condition": "Soft clay or loose sand extends to significant depth (>6m)",
          "recommendation": "pile_foundation",
          "justification": "Deep foundations bypass weak surface soils to transfer loads to competent strata"
        },
        {
          "condition": "High structural loads (>2000 kN per column) regardless of soil",
          "recommendation": "pile_foundation",
          "justification": "Concentrated heavy loads require deep foundations for adequate capacity and settlement control"
        },
        {
          "condition": "Expansive soil (black cotton) with FSI > 50%",
          "recommendation": "under_reamed_pile",
          "justification": "Under-reamed piles anchor below active zone and resist uplift from swelling"
        },
        {
          "condition": "Liquefiable sand with high water table in seismic zone",
          "recommendation": "pile_foundation_to_non_liquefiable",
          "justification": "Piles must extend through liquefiable layer to stable stratum; consider negative skin friction"
        }
      ],
      "factors_to_consider": [
        "Adjacent structure sensitivity",
        "Construction access and equipment",
        "Cost comparison (shallow may need ground improvement)",
        "Time constraints",
        "Future loading or excavation nearby"
      ],
      "risk_if_ignored": "Selecting inappropriate foundation type leads to either: (1) excessive settlement and structural distress if undersized, or (2) unnecessary cost if over-designed. Ignoring expansive soil behavior causes heave damage. Ignoring liquefaction potential risks catastrophic failure in earthquakes.",
      "ai_snippet": "Use pile foundations when: soft/loose soil extends >6m depth, column loads >2000kN, expansive black cotton soil (FSI>50%), or liquefiable sand in seismic zones. Use shallow foundations when: competent bearing stratum within 3m, moderate loads, non-expansive soil. Always verify with site-specific investigation and settlement analysis."
    },
    {
      "id": "ground_improvement_required",
      "question": "Is soil improvement needed for my project?",
      "input_conditions": {
        "in_situ_bearing_capacity": "Existing soil bearing capacity (kPa)",
        "required_bearing_capacity": "Design bearing pressure (kPa)",
        "settlement_estimate": "Predicted settlement (mm)",
        "allowable_settlement": "Tolerable settlement (mm)",
        "liquefaction_susceptibility": "Liquefiable layer present (yes/no)"
      },
      "decision_logic": [
        {
          "condition": "In-situ bearing capacity < required bearing capacity",
          "recommendation": "ground_improvement_required",
          "justification": "Soil must be densified or strengthened to support design loads"
        },
        {
          "condition": "Predicted settlement > allowable settlement",
          "recommendation": "ground_improvement_or_deep_foundation",
          "justification": "Compressible soils must be preloaded, replaced, or bypassed"
        },
        {
          "condition": "SPT N-value < 10 in sand above water table",
          "recommendation": "densification_recommended",
          "justification": "Loose sands susceptible to settlement under static and dynamic loading"
        },
        {
          "condition": "Liquefiable layer within influence depth in Seismic Zone III or higher",
          "recommendation": "mandatory_ground_improvement_or_deep_foundation",
          "justification": "Liquefaction must be mitigated through densification or load transfer to stable stratum"
        }
      ],
      "improvement_methods": {
        "loose_sand": ["Vibro-compaction", "Dynamic compaction", "Compaction grouting"],
        "soft_clay": ["Preloading with wick drains", "Stone columns", "Soil replacement"],
        "liquefiable_sand": ["Vibro-replacement (stone columns)", "Compaction piles", "Permeation grouting"],
        "organic_soil": ["Removal and replacement", "Preloading", "Avoid if possible"]
      },
      "risk_if_ignored": "Building on inadequate ground without improvement leads to excessive total and differential settlement, structural cracking, and potential failure. In seismic zones, ignoring liquefaction potential risks complete foundation failure during earthquakes. Ground improvement adds upfront cost but prevents costly retrofitting or failure.",
      "ai_snippet": "Ground improvement needed when: bearing capacity insufficient, predicted settlement exceeds tolerance, SPT N<10 in sand, or liquefiable soil in seismic zones. Methods: vibro-compaction for loose sand, preloading+PVD for soft clay, stone columns for liquefaction mitigation. Cost-benefit analysis required versus deep foundations."
    },
    {
      "id": "test_selection",
      "question": "Which geotechnical test is required for my project?",
      "input_conditions": {
        "soil_type": "Predominant soil type",
        "project_type": "Building/bridge/embankment/pavement",
        "investigation_stage": "Preliminary/detailed design",
        "parameters_required": "Strength/compressibility/liquefaction"
      },
      "decision_matrix": [
        {
          "soil_type": "sand",
          "parameters_needed": ["bearing_capacity", "liquefaction"],
          "recommended_tests": {
            "field": ["SPT", "CPT"],
            "laboratory": ["Gradation", "Relative density"]
          },
          "justification": "SPT N-value and CPT qc provide density and liquefaction assessment; laboratory tests for classification"
        },
        {
          "soil_type": "clay",
          "parameters_needed": ["shear_strength", "settlement"],
          "recommended_tests": {
            "field": ["Vane shear", "CPTu"],
            "laboratory": ["Triaxial (UU/CU)", "Consolidation", "Atterberg limits"]
          },
          "justification": "Undrained strength for stability, consolidation parameters for settlement prediction"
        },
        {
          "soil_type": "expansive_clay",
          "parameters_needed": ["swell_potential", "swell_pressure"],
          "recommended_tests": {
            "field": ["SPT with sampling"],
            "laboratory": ["Free swell index", "Swell pressure test", "Oedometer swell test"]
          },
          "justification": "Quantify swell potential for foundation type selection and heave prediction"
        },
        {
          "soil_type": "rock",
          "parameters_needed": ["bearing_capacity", "excavatability"],
          "recommended_tests": {
            "field": ["Core drilling with RQD", "Point load test"],
            "laboratory": ["UCS", "Rock classification"]
          },
          "justification": "Rock mass quality and intact strength for foundation and excavation design"
        }
      ],
      "project_specific_requirements": {
        "high_rise_building": ["Deep boreholes to 1.5× building width or refusal", "CPT for soft soil profiling", "Plate load test for raft"],
        "bridge_foundation": ["Boring at each pier/abutment", "SPT/CPT continuous", "Laboratory strength testing"],
        "embankment_on_soft_ground": ["Vane shear at close intervals", "CPTu dissipation tests", "Consolidation tests with cv"],
        "pavement": ["CBR or plate load test", "DCP for quick assessment", "Subgrade modulus"]
      },
      "risk_if_ignored": "Insufficient or inappropriate testing leads to: (1) designs based on assumptions rather than data, (2) failure to detect critical weak layers, (3) post-construction problems requiring costly remediation. Never design foundations without adequate site investigation.",
      "ai_snippet": "Test selection by soil: Sand→SPT+CPT for density/liquefaction; Clay→vane shear+triaxial+consolidation for strength/settlement; Expansive→FSI+swell pressure for heave; Rock→coring+UCS for bearing. Match test intensity to project importance. Minimum: IS:1892 requirements."
    },
    {
      "id": "retaining_wall_selection",
      "question": "What type of retaining wall should I use?",
      "input_conditions": {
        "retained_height": "Height of soil to be retained (m)",
        "space_available": "Space behind wall for backfill",
        "groundwater": "Water table relative to wall base",
        "surcharge": "Traffic or other surcharge behind wall",
        "permanence": "Temporary or permanent"
      },
      "decision_logic": [
        {
          "condition": "Retained height < 3m with adequate space",
          "recommendation": "gravity_or_cantilever_wall",
          "justification": "Simple walls economical for low heights with conventional construction"
        },
        {
          "condition": "Retained height 3-6m with moderate space",
          "recommendation": "cantilever_or_counterfort_wall",
          "justification": "Reinforced concrete walls efficient for medium heights"
        },
        {
          "condition": "Retained height > 6m or limited space",
          "recommendation": "anchored_wall_or_reinforced_soil",
          "justification": "High walls require anchors or geosynthetic reinforcement for stability"
        },
        {
          "condition": "Deep excavation in urban area (temporary)",
          "recommendation": "sheet_pile_or_diaphragm_wall",
          "justification": "Embedded walls control ground movement and groundwater in congested sites"
        },
        {
          "condition": "Poor foundation soil below wall",
          "recommendation": "reinforced_soil_wall_or_piled_wall",
          "justification": "Flexible MSE walls tolerate settlement; piled walls bypass weak soil"
        }
      ],
      "design_considerations": [
        "Drainage behind wall (critical for all types)",
        "Foundation bearing capacity",
        "Global stability (deep-seated failure)",
        "Seismic earth pressure increase",
        "Aesthetics and architectural requirements"
      ],
      "risk_if_ignored": "Underdesigned retaining walls fail by: sliding, overturning, bearing failure, or structural failure. Poor drainage causes hydrostatic pressure buildup - the most common cause of wall failure. Ignoring global stability leads to deep-seated rotational failure involving wall and retained mass.",
      "ai_snippet": "Retaining wall selection: Height <3m→gravity/cantilever; 3-6m→cantilever/counterfort; >6m→anchored or MSE wall; Urban excavation→sheet pile/diaphragm. Critical: always provide drainage behind wall. Check sliding, overturning, bearing, and global stability. Add seismic increment in Zone III+."
    },
    {
      "id": "slope_stability_assessment",
      "question": "Is my slope stable? What analysis is needed?",
      "input_conditions": {
        "slope_angle": "Slope inclination (degrees or H:V)",
        "slope_height": "Vertical height of slope (m)",
        "soil_type": "Cohesive/granular/mixed",
        "groundwater": "Presence and level of water table",
        "seismic_zone": "Seismic zone classification"
      },
      "decision_logic": [
        {
          "condition": "Dry granular soil slope",
          "recommendation": "slope_limited_by_friction_angle",
          "justification": "For dry cohesionless soil, maximum stable slope equals friction angle"
        },
        {
          "condition": "Cohesive soil slope > 3m height",
          "recommendation": "circular_failure_analysis_required",
          "justification": "Clay slopes fail in rotational mode; analyze using Bishop or Spencer method"
        },
        {
          "condition": "Bedded rock or soil with weak plane",
          "recommendation": "planar_wedge_failure_analysis",
          "justification": "Failure along pre-existing discontinuity; check kinematic feasibility"
        },
        {
          "condition": "High groundwater or seepage",
          "recommendation": "effective_stress_analysis_with_seepage",
          "justification": "Pore pressure reduces effective stress and stability; must model seepage"
        },
        {
          "condition": "Seismic zone III or higher",
          "recommendation": "pseudo_static_or_dynamic_analysis",
          "justification": "Add seismic coefficient (0.1-0.2g) or perform Newmark sliding block analysis"
        }
      ],
      "minimum_factor_of_safety": {
        "temporary_excavation": "1.25",
        "permanent_slope_static": "1.5",
        "permanent_slope_seismic": "1.1-1.2",
        "dam_embankment": "1.5 (static), 1.0 (MCE)"
      },
      "stabilization_measures": {
        "geometry": ["Flatten slope", "Benching", "Toe buttress"],
        "drainage": ["Surface drains", "Horizontal drains", "Deep wells"],
        "reinforcement": ["Soil nails", "Ground anchors", "Geosynthetics"],
        "structural": ["Retaining walls", "Piles", "Rock bolts"]
      },
      "risk_if_ignored": "Slope failure causes: loss of life, property damage, infrastructure disruption, and environmental damage. Warning signs (tension cracks, bulging toe, tilting vegetation) indicate imminent failure. Never ignore drainage - water is the primary trigger for most slope failures.",
      "ai_snippet": "Slope stability: Dry sand→max angle = friction angle; Clay >3m→Bishop/Spencer circular analysis; Bedded→planar/wedge check; High water→effective stress with seepage; Seismic→add 0.1-0.2g. Target FOS: 1.5 permanent, 1.25 temporary. Stabilize with drainage (most effective), geometry, or reinforcement."
    }
  ],
  "quick_reference": {
    "bearing_capacity_thumb_rules": [
      {"soil": "Soft clay (N<4)", "qa_kPa": "50-100"},
      {"soil": "Medium clay (N=4-8)", "qa_kPa": "100-150"},
      {"soil": "Stiff clay (N=8-15)", "qa_kPa": "150-250"},
      {"soil": "Loose sand (N<10)", "qa_kPa": "100-150"},
      {"soil": "Medium sand (N=10-30)", "qa_kPa": "150-300"},
      {"soil": "Dense sand (N>30)", "qa_kPa": "300-500"},
      {"soil": "Weathered rock", "qa_kPa": "500-1000"},
      {"soil": "Fresh rock", "qa_kPa": ">1000"}
    ],
    "pile_capacity_thumb_rules": [
      {"pile_type": "Driven pile in sand", "capacity": "End bearing dominant, check N-value"},
      {"pile_type": "Driven pile in clay", "capacity": "Skin friction dominant, use α-method"},
      {"pile_type": "Bored pile in sand", "capacity": "Reduced skin friction (no displacement)"},
      {"pile_type": "Bored pile in clay", "capacity": "Use total stress (α) or effective stress (β) method"},
      {"pile_type": "Rock socket", "capacity": "UCS-based, typically 0.15-0.3 × UCS"}
    ],
    "minimum_investigation_depth": [
      {"structure": "Shallow foundation", "depth": "1.5 × foundation width below base"},
      {"structure": "Pile foundation", "depth": "Below pile tip: 5m in soil, 3m in rock"},
      {"structure": "High-rise building", "depth": "1.5 × building width or refusal"},
      {"structure": "Bridge pier", "depth": "Below scour: 1.5 × pier width"},
      {"structure": "Embankment", "depth": "1.5 × embankment height below ground"}
    ]
  }
}