CBC · California Building Code

What must a geotechnical investigation/report include?

The CBC requires a geotechnical investigation and a written report whenever the code or building official calls for one. The report must show where borings were taken, provide full boring/test logs, describe the soil profile and groundwater (including historic highs when relevant), state foundation recommendations and expected settlements, and include condition‑specific analyses (for compacted fill, CLSM, deep foundations and seismic hazards) as spelled out in §§ 1803.6 and 1803.5.

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Last reviewed: July 5, 2026

What the code requires — plain English

Under the CBC a geotechnical investigation must be performed where indicated by the code and the building official, and a written geotechnical report must be submitted with the permit application that documents site-specific subsurface conditions and design recommendations. The core reporting requirements are set out in § 1803.6 (reporting) and the scope of investigations and required topics for specific conditions are listed in § 1803.5 and its subsections (for example, foundations on compacted fill, deep foundations, and controlled low‑strength material) — see § 1803.6 and § 1803.5 (CBC) for the list of required information and § 1803.5.9 for CLSM‑specific items.

Note: I could not find text for § 1803.3.1 in the provided files. If you need the exact language of § 1803.3.1, please upload or point me to that page of the code; I will cite it directly rather than infer its content.

Requirements in detail

Below I summarize the decision‑relevant contents the CBC requires a geotechnical investigation and report to include and tie each required element to the controlling section(s).

A. Mandatory report contents (what must be in the written geotechnical report)

Per § 1803.6 the geotechnical report shall (at minimum) include:

  • A site plan/plot showing the location of all soil investigations. § 1803.6
  • Complete boring/test logs, penetration test records, and soil samples records. § 1803.6
  • A record of the soil profile and groundwater elevations (historic highs if relevant). § 1803.6
  • Recommendations for foundation type and design criteria (bearing values, mitigation for expansive soils, liquefaction and settlement mitigation, effects of adjacent loads). § 1803.6
  • Expected total and differential settlement, and deep‑foundation information where applicable (see § 1803.5.5 for deep foundations). § 1803.6; § 1803.5.5

B. Condition‑specific investigations and report requirements (high‑priority subsections of § 1803.5)

  • Compacted fill bearing foundations: where shallow foundations will bear on compacted fill more than 12 in (305 mm) deep, the geotechnical investigation must include site‑prep specifications, material specifications, lab test methods to determine maximum dry density and optimum moisture, maximum allowable lift thickness, field test method for in‑place dry density, minimum acceptable in‑place dry density (as a percent of max dry density), and number/frequency of field tests. § 1803.5.8
  • Controlled low‑strength material (CLSM): where shallow foundations will bear on CLSM, the investigation and report must include (specifically) site preparation specs, CLSM specifications, laboratory/field test methods to determine compressive strength or bearing capacity, field acceptance test methods, and number/frequency of field tests. § 1803.5.9
  • Deep foundations: where deep foundations will be used, the geotechnical investigation shall include recommended deep foundation types and capacities, spacing, driving/installation criteria, field inspection/reporting procedures (including verification of installed bearing capacity where required), load test requirements, suitability of materials, designation of bearing strata, and group‑action reductions. § 1803.5.5
  • Groundwater: the investigation must determine whether groundwater is above or within 5 feet (1524 mm) of the lowest floor elevation where that floor is below adjacent finished grade, and whether groundwater depth affects design and construction. § 1803.5.4
  • Seismic/geologic hazards: for structures in Seismic Design Categories C–F the investigation must evaluate slope instability, liquefaction, total/differential settlement, and surface displacement due to faulting or seismically induced lateral spreading/flow; for D–F additional seismic‑specific analyses are required (e.g., dynamic seismic lateral earth pressures and liquefaction evaluation for site peak ground acceleration). § 1803.5.11–.12

Decision‑relevant numeric thresholds and values (quick reference table)

Decision / value When it matters Required content or threshold Code reference
Compacted fill depth threshold If shallow foundations bear on compacted fill > 12 in (305 mm) Geotechnical investigation must include site prep, material specs, lab/field test methods, lift thickness, field density method, minimum acceptable in‑place dry density (percent of max) and test frequency. § 1803.5.8
CLSM (Controlled Low‑Strength Material) If shallow foundations will bear on CLSM Report must include site prep specs, CLSM specs, lab/field test methods for compressive strength/bearing capacity, field acceptance tests, test frequency. § 1803.5.9
Groundwater trigger If water table is above or within 5 ft (1524 mm) of lowest floor located below finished grade adjacent to foundation Investigation required to determine effect on design/construction; report must give elevations, historic high water where relevant. § 1803.5.4; § 1803.6
Seismic Design Categories C–F Structures assigned SD C–F Evaluate slope instability, liquefaction, settlements, surface displacement; D–F require additional seismic analyses (e.g., dynamic lateral earth pressures, liquefaction for MCE PGA). § 1803.5.11–.12
Minimum boring/test documentation Always when investigations are required Plot showing location of investigations and complete boring/test logs must be included in the report. § 1803.6

Exceptions & special cases

  • Some small, simple residential projects may not require a geotechnical report: the code allows exceptions for one‑story wood‑frame/light‑steel‑frame buildings of Type II or V construction ≤ 4,000 ft² not located in Earthquake Fault Zones or Seismic Hazard Zones — check the exception language and local ordinances. § 1803.1.1 / § 1803.2 exceptions.
  • Where the code does not require a full geotechnical report but fill compaction verification is needed, a special inspector shall verify in‑place dry density is not less than 90% of maximum dry density per ASTM D1557. (This applies to cases where reporting of fill placement materials/procedures is not required.) See § 1705 and the compaction verification exception.
  • Chapter 18A (state agency/OSHPD/DSA) contains parallel or additional provisions (e.g., Chapter 18A § 1803A.7 geotechnical reporting, and minimum boring frequency language in 1803A.3.1). Where your project is state‑regulated (schools, hospitals, OSHPD), follow the Chapter 18A provisions in addition to the base Chapter 18 requirements. § 1803A.7; § 1803A.3.1.

Common mistakes

  • Treating the CBC as prescribing a single fixed compaction percentage for all compacted fills. The code requires the report to state the minimum acceptable in‑place dry density for fills > 12 in (see § 1803.5.8); the universal 90% figure in the code applies only to fills 12 in or less where a report is not required (special‑inspection verification). § 1803.5.8; § 1804 exception and § 1705.6 guidance.
  • Omitting groundwater history. The CBC requires historic high groundwater elevations be addressed when evaluating liquefaction and settlement potential — do not report only a single field measurement. § 1803.6; § 1803.5.4.
  • Assuming that CLSM needs no testing or documentation because it is “weak concrete.” The CBC explicitly requires the geotechnical investigation for CLSM to specify the CLSM mix, lab/field test methods for compressive strength or bearing capacity, field acceptance tests and testing frequency. § 1803.5.9.
  • Forgetting seismic‑category requirements. If the structure falls into SD C–F, the geotechnical investigation must evaluate liquefaction, slope instability and settlements; for D–F additional seismic analysis is required. Do not rely solely on generic prescriptive foundation tables. § 1803.5.11–.12.

Worked example — concrete scenario with numbers

Scenario: You are designing a 3,600 ft² single‑family house to be supported on shallow foundations. A previous site grading plan shows 18 inches (457 mm) of engineered compacted fill under the planned footing pads.

Step‑by‑step CBC requirements (based on the cited sections):

  1. Because shallow foundations will bear on compacted fill more than 12 in (305 mm), the project requires a geotechnical investigation that addresses compacted fill per § 1803.5.8. § 1803.5.8
  2. The geotechnical investigation report must include:
    • Specifications for site preparation prior to placement of compacted fill (e.g., removal of organic soil, scarification). § 1803.5.8
    • Specifications for the fill material (gradation, plasticity limits as applicable). § 1803.5.8
    • Test methods to determine maximum dry density/optimum moisture (lab method such as ASTM D1557 or equivalent). § 1803.5.8
    • Maximum allowable lift thickness for field placement (the geotechnical engineer will state this; e.g., commonly 6–8 inches loose thickness but the code requires the report to state it). § 1803.5.8
    • Field test method for in‑place dry density and the minimum acceptable in‑place dry density expressed as a percent of maximum dry density — the report must state that percent (the CBC does not set a single universal percent here but requires the geotechnical report to specify it). § 1803.5.8; § 1803.6
  3. The report must also include: a plot of borings/test pits, boring logs, soil profile and groundwater information (current and historic high if applicable). § 1803.6
  4. Construction control: testing frequency and the number of field tests required to demonstrate compliance must be specified in the report and implemented under special inspection per § 1705. (If the geotechnical report requires continuous inspection or specified test frequency, the special inspector/geotechnical engineer will verify.) § 1803.5.8; § 1705.6

Practical numeric example supplied by the geotechnical engineer (illustrative, must be in the report): “Maximum dry density (ASTM D1557) = 125 lb/ft³; minimum acceptable in‑place dry density = 95% of max; lift thickness = 6 in; compaction method = vibratory compactor; in‑place density test = nuclear densometer at 1 test per 500 ft² per lift.” The code requires the report to specify these items (the numeric choices above are examples that the geotechnical engineer would set and report). § 1803.5.8; § 1803.6

Related provisions (use these CBC sections when applying/reading the requirements)

  • § 1803.6 — Reporting (list of minimum geotechnical report contents).
  • § 1803.5 — Investigated conditions and condition‑specific requirements (compacted fill, deep foundations, rock, excavation near foundations, CLSM, seismic categories).
  • § 1803.5.9 — Controlled low‑strength material (CLSM) specific investigation/report items.
  • § 1803.5.4 — Groundwater considerations (within 5 feet criterion).
  • § 1705 / § 1705.6 — Special inspections and tests (compaction verification and responsibilities).
  • Chapter 18A (e.g., § 1803A.3.1, § 1803A.7) — state‑agency (DSA/OSHPD) geotechnical scope and reporting variations — consult when project is state‑regulated.

Code references

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

  • CBC § 1803.5.9 High relevance — show source text

    1. Field test method for determining the in-place dry density of the compacted fill.

    2. Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.

    3. Number and frequency of field tests required to determine compliance with Item 6.

    1803.5.9 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), a geotechnical investigation shall be conducted and shall include all of the following:

    1. Specifications for the preparation of the site prior to placement of the CLSM.
    2. Specifications for the CLSM.
    3. Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM .
    4. Test methods for determining the acceptance of the CLSM in the field.
    5. Number and frequency of field tests required to determine compliance with Item 4.

    1803.5.10 Alternate setback and clearance. Where setbacks or clearances other than those required in Section 1808.7 are desired, the building official shall be permitted to require a geotechnical investigation by a registered design professional to demonstrate that the intent of Section 1808.7 would be satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material.

    1803.5.11 Seismic Design Categories C through F. For structures assigned to Seismic Design Category C, D, E or F, a geotechnical investigation shall be conducted, and shall include an evaluation of all of the following potential geologic and seismic hazards:

    1. Slope instability.

    2. Liquefaction.

    3. Total and differential settlement.

    4. Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.

    1803.5.12 Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E or F, the geotechnical investigation required by Section 1803.5.11 shall include all of the following as applicable:

    1. The determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1.83 m) of backfill height due to design earthquake ground motions.
    2. The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude and source characteristics consistent with the maximum considered earthquake ground motions. Peak ground acceleration shall be determined based on one of the following: 2.1. A site-specific study in accordance with Chapter 21 of ASCE 7.

    2.2. In accordance with Section 11.8.3 of ASCE 7.

    1. An assessment of potential consequences of liquefaction and soil strength loss including, but not limited to, the following:

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    3.1. Estimation of total and differential settlement.

    3.2. Lateral soil movement.

    3.3. Lateral soil loads on foundations.

    3.4. Reduction in foundation soil-bearing capacity and lateral soil reaction. 3.5. Soil downdrag and reduction in axial and lateral soil reaction for pile foundations. 3.6. Increases in soil lateral pressures on retaining walls.

    3.7. Flotation of buried structures.

    1. Discussion of mitigation measures such as, but not limited to, the following: 4.1. Selection of appropriate foundation type and depths. 4.2. Selection of appropriate structural systems to accommodate anticipated displacements and forces.
  • CBC § 5.5. High relevance — show source text

    The report shall_ contain the results of the analyses of problem areas identified in the geohazard report. The geotechnical report shall incorporate esti- mates of the characteristics of site ground motion provided in the geohazard report. This geotechnical report shall include, but need not be limited to, the following information:

    1. A plot showing the location of the soil investigations.
    2. A complete record of the soil boring and penetration test logs and soil samples.
    3. A record of the soil profile.
    4. Elevation of the water table, if encountered. Historic high ground water elevations shall be addressed in the report to adequately evaluate liquefaction and settlement potential.
    5. Recommendations for foundation type and design criteria, including but not limited to: bearing capacity of natural or compacted soil; provisions to mitigate the effects of expansive soils; mitigation of the effects of liquefaction, differential settlement and varying soil strength; and the effects of adjacent loads.
    6. Expected total and differential settlement.
    7. Deep foundation information in accordance with Section 1803 A .5.5.
    8. Special design and construction provisions for foundations of structures founded on expansive soils, as necessary.
    9. Compacted fill material properties and testing in accordance with Section 1803 A .5.8.
    10. Controlled low-strength material properties and testing in accordance with Section 1803 A .5.9. 11. The report shall consider the effects of stepped footings addressed in Section 1809A.3. 12. The report shall consider the effects of seismic hazards in accordance with Section 1803A.6 and shall incorporate the associ- ated geohazard report.

    1803A.8 Geotechnical peer review. [DSA-SS and DSA-SS/CC] When alternate foundations designs or ground improvements are employed or where slope stabilization is required, a qualified peer review by a California-licensed geotechnical engineer, in accordance with Section 322 of Part 10, Title 24, CCR, may be required by the enforcement agency. In Section 322 of Part 10, Title 24, CCR, where reference is made to structural or seismic-resisting system, it shall be replaced with geotechnical, foundation or ground improvement, as appropriate.

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    SECTION 1804 A —EXCAVATION, GRADING AND FILL

    1804 A .1 Excavation near foundations. Excavation for any purpose shall not reduce vertical or lateral support for any foundation or adjacent foundation without first underpinning or protecting the foundation against detrimental lateral or vertical movement, or both, in accordance with Section 1803 A .5.7.

    1804 A .2 Underpinning. Where underpinning is chosen to provide the protection or support of adjacent structures, the underpinning system shall be designed and installed in accordance with provisions of this chapter and Chapter 33.

    1804 A .2.1 Underpinning sequencing. Underpinning shall be installed in a sequential manner that protects the neighboring structure and the working construction site. The sequence of installation shall be identified in the approved construction documents.

  • CBC § 5.9 High relevance — show source text
    1. Number and frequency of field tests required to determine compliance with Item 6.

    1803 A .5.9 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), a geotechnical investigation shall be conducted and shall include all of the following:

    1. Specifications for the preparation of the site prior to placement of the CLSM.
    2. Specifications for the CLSM.
    3. Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM.
    4. Test methods for determining the acceptance of the CLSM in the field.
    5. Number and frequency of field tests required to determine compliance with Item 4.

    1803 A .5.10 Alternate setback and clearance. Where setbacks or clearances other than those required in Section 1808 A .7 are desired, the building official shall be permitted to require a geotechnical investigation by a registered design professional to demonstrate that the intent of Section 1808 A .7 would be satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material.

    1803 A .5.11 Seismic Design Categories C through F. For structures assigned to Seismic Design Category C, D, E or F, a geotechnical investigation shall be conducted, and shall include an evaluation of all of the following potential geologic and seismic hazards:

    1. Slope instability.

    2. Liquefaction.

    3. Total and differential settlement.

    4. Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.

    1803 A .5.12 Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E or F, the geotechnical investigation required by Section 1803 A .5.11 shall include all of the following as applicable:

    1. The determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1.83 m) of backfill height due to design earthquake ground motions.
    2. The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude and source characteristics consistent with the maximum considered earthquake ground motions. Peak ground acceleration shall be determined based on one of the following: 2.1. A site-specific study in accordance with Chapter 21 of ASCE 7.

    2.2. In accordance with Section 11.8.3 of ASCE 7.

    1. An assessment of potential consequences of liquefaction and soil strength loss including, but not limited to, the following:

    3.1. Estimation of total and differential settlement.

    3.2. Lateral soil movement.

    3.3. Lateral soil loads on foundations.

    3.4. Reduction in foundation soil-bearing capacity and lateral soil reaction. 3.5. Soil downdrag and reduction in axial and lateral soil reaction for pile foundations. 3.6. Increases in soil lateral pressures on retaining walls.

    3.7. Flotation of buried structures.

    1. Discussion of mitigation measures such as, but not limited to, the following: 4.1. Selection of appropriate foundation type and depths. 4.2. Selection of appropriate structural systems to accommodate anticipated displacements and forces.

    4.3. Ground stabilization.

    4.4. Any combination of these measures and how they shall be considered in the design of the structure.

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  • CBC § 1803A.5.11 High relevance — show source text

    In addition, the most recent version of_ CGS Special Publication 42: Earthquake Fault Zones, A Guide for Government Agencies, Property Owners / Developers, and Geoscience Practitioners for Assessing Fault Rupture Hazards in California, shall be considered for project sites proposed within an Alquist-Priolo Earthquake Fault Zone. The most recent version of CGS Special Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California, shall be considered for project sites proposed within a Seismic Hazard Zone. All conclusions shall be fully supported by satisfactory data and analysis.

    In addition to requirements in Sections 1803A.5.11 and 1803A.5.12, the report shall include, but need not be limited to, the following: 1. Site geology. 2. Evaluation of the known active and potentially active faults, both regional and local. 3. Ground-motion parameters, as required by Sections 1613A and 1617A, and ASCE 7.

    1803A.7 Geotechnical reporting. Where geotechnical investigations are required, a written report of the investigations shall be submitted to the building official by the permit applicant at the time of permit application. The geotechnical report shall provide completed evaluations of the foundation conditions of the site and the potential geologic/seismic hazards affecting the site. The geotechnical report shall include, but shall not be limited to, site-specific evaluations of design criteria related to the nature and extent of foundation materials, groundwater conditions, liquefaction potential, settlement potential and slope stability. The report shall contain the results of the analyses of problem areas identified in the geohazard report. The geotechnical report shall incorporate esti- mates of the characteristics of site ground motion provided in the geohazard report. This geotechnical report shall include, but need not be limited to, the following information:

    1. A plot showing the location of the soil investigations.
    2. A complete record of the soil boring and penetration test logs and soil samples.
    3. A record of the soil profile.
    4. Elevation of the water table, if encountered. Historic high ground water elevations shall be addressed in the report to adequately evaluate liquefaction and settlement potential.
    5. Recommendations for foundation type and design criteria, including but not limited to: bearing capacity of natural or compacted soil; provisions to mitigate the effects of expansive soils; mitigation of the effects of liquefaction, differential settlement and varying soil strength; and the effects of adjacent loads.
    6. Expected total and differential settlement.
    7. Deep foundation information in accordance with Section 1803 A .5.5.
    8. Special design and construction provisions for foundations of structures founded on expansive soils, as necessary.
    9. Compacted fill material properties and testing in accordance with Section 1803 A .5.8.
    10. Controlled low-strength material properties and testing in accordance with Section 1803 A .5.9. 11. The report shall consider the effects of stepped footings addressed in Section 1809A.3. 12. The report shall consider the effects of seismic hazards in accordance with Section 1803A.6 and shall incorporate the associ- ated geohazard report.
  • CBC § 1803.5.12 High relevance — show source text

    1803.5.12 Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E or F, the geotechnical investigation required by Section 1803.5.11 shall include all of the following as applicable:

    1. The determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1.83 m) of backfill height due to design earthquake ground motions.
    2. The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude and source characteristics consistent with the maximum considered earthquake ground motions. Peak ground acceleration shall be determined based on one of the following: 2.1. A site-specific study in accordance with Chapter 21 of ASCE 7.

    2.2. In accordance with Section 11.8.3 of ASCE 7.

    1. An assessment of potential consequences of liquefaction and soil strength loss including, but not limited to, the following:

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    3.1. Estimation of total and differential settlement.

    3.2. Lateral soil movement.

    3.3. Lateral soil loads on foundations.

    3.4. Reduction in foundation soil-bearing capacity and lateral soil reaction. 3.5. Soil downdrag and reduction in axial and lateral soil reaction for pile foundations. 3.6. Increases in soil lateral pressures on retaining walls.

    3.7. Flotation of buried structures.

    1. Discussion of mitigation measures such as, but not limited to, the following: 4.1. Selection of appropriate foundation type and depths. 4.2. Selection of appropriate structural systems to accommodate anticipated displacements and forces.

    4.3. Ground stabilization.

    4.4. Any combination of these measures and how they shall be considered in the design of the structure.

    1803.6 Reporting. Where geotechnical investigations are required, a written report of the investigations shall be submitted to the building official by the permit applicant at the time of permit application. This geotechnical report shall include, but need not be limited to, the following information:

    1. A plot showing the location of the soil investigations.

    2. A complete record of the soil boring and penetration test logs and soil samples.

    3. A record of the soil profile.

    4. Elevation of the water table, if encountered.

    5. Recommendations for foundation type and design criteria, including but not limited to: bearing capacity of natural or compacted soil; provisions to mitigate the effects of expansive soils; mitigation of the effects of liquefaction, differential settlement and varying soil strength; and the effects of adjacent loads.

    6. Expected total and differential settlement.

    7. Deep foundation information in accordance with Section 1803.5.5.

    8. Special design and construction provisions for foundations of structures founded on expansive soils, as necessary.

    9. Compacted fill material properties and testing in accordance with Section 1803.5.8.

    10. Controlled low-strength material properties and testing in accordance with Section 1803.5.9. 11. [OSHPD 1R, 2 & 5] The report shall consider the effects of seismic hazard in accordance with Section 1803.7.

    1803.7 Geohazard reports. [OSHPD 1R, 2 & 5] Geohazard reports shall be required for all proposed construction.

  • CBC § 5.11 High relevance — show source text

    ** For structures assigned to Seismic Design Category D, E or F, the geotechnical investigation required by Section 1803 A .5.11 shall include all of the following as applicable:

    1. The determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1.83 m) of backfill height due to design earthquake ground motions.
    2. The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude and source characteristics consistent with the maximum considered earthquake ground motions. Peak ground acceleration shall be determined based on one of the following: 2.1. A site-specific study in accordance with Chapter 21 of ASCE 7.

    2.2. In accordance with Section 11.8.3 of ASCE 7.

    1. An assessment of potential consequences of liquefaction and soil strength loss including, but not limited to, the following:

    3.1. Estimation of total and differential settlement.

    3.2. Lateral soil movement.

    3.3. Lateral soil loads on foundations.

    3.4. Reduction in foundation soil-bearing capacity and lateral soil reaction. 3.5. Soil downdrag and reduction in axial and lateral soil reaction for pile foundations. 3.6. Increases in soil lateral pressures on retaining walls.

    3.7. Flotation of buried structures.

    1. Discussion of mitigation measures such as, but not limited to, the following: 4.1. Selection of appropriate foundation type and depths. 4.2. Selection of appropriate structural systems to accommodate anticipated displacements and forces.

    4.3. Ground stabilization.

    4.4. Any combination of these measures and how they shall be considered in the design of the structure.

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    1803A.6 Geohazard reports. Geohazard reports shall be required for all proposed construction.

    Exceptions: 1. Reports are not required for one-story, wood-frame and light-steel-frame buildings of Type II or Type V construction and 4,000 square feet (371 m [2] ) or less in floor area, not located within Earthquake Fault Zones or Seismic Hazard Zones as shown in the most recently published maps from the California Geological Survey (CGS) or in seismic hazard zones as defined in the Safety Element of the local General Plan. 2. Reports are not required for the following scopes of work in existing buildings: nonstructural alterations, voluntary struc- tural alterations without foundation work, or structural repairs for damage not caused by an earthquake. [OSHPD 1 & 4] Incidental structural additions or alterations.

    3. A previous report for a specific site may be resubmitted, provided that a reevaluation is made and the report is found to be currently appropriate.

    The purpose of the geohazard report shall be to identify geologic and seismic conditions that may require project mitigations. The reports shall contain data which provide an assessment of the nature of the site and potential for earthquake damage based on appro- priate investigations of the regional and site geology, project foundation conditions and the potential seismic shaking at the site. The report shall be prepared by a California-certified engineering geologist in consultation with a California-registered geotechnical engineer.

  • CBC § 2.4 High relevance — show source text

    SECTION 1802 A —DESIGN BASIS

    1802 A .1 General. Allowable bearing pressures, allowable stresses and design formulas provided in this chapter shall be used with the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605 A .2. The quality and design of materials used structurally in excavations and foundations shall comply with the requirements specified in Chapters 16, 19, 21, 22 and 23. Excavations and fills shall comply with Chapter 33.

    SECTION 1803 A —GEOTECHNICAL INVESTIGATIONS

    1803 A .1 General. Geotechnical investigations shall be conducted in accordance with Section 1803 A .2 and reported in accordance with Section 1803A.7. The classification and investigation of the soil shall be made under the responsible charge of a California regis- tered geotechnical engineer. All recommendations contained in geotechnical and geohazard reports shall be subject to the approval of the enforcement agency. All reports shall be prepared and signed by a registered geotechnical engineer, a certified engineering geolo- gist and a registered geophysicist, where applicable.

    1803 A .2 Investigations required. Geotechnical investigations shall be conducted in accordance with Sections 1803 A .3 through 1803A.6 .

    Exception s : 1. Geotechnical reports are not required for one-story, wood-frame and light-steel-frame buildings of Type II or Type V construction and 4,000 square feet (371 m [2] ) or less in floor area, not located within Earthquake Fault Zones or Seismic Hazard Zones as shown in the most recently published maps from the California Geological Survey (CGS) or in seismic hazard zones as defined in the Safety Element of the local General Plan. Allowable foundation and lateral soil pressure values may be determined from Table 1806A.2.

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    2. A previous report for a specific site may be resubmitted, provided that a reevaluation is made and the report is found to be currently appropriate.

    1803 A .3 Basis of investigation. Soil classification shall be based on observation and any necessary tests of the materials disclosed by borings, test pits or other subsurface exploration made in appropriate locations. Additional studies shall be made as necessary to evaluate slope stability, soil strength, position and adequacy of load-bearing soils, the effect of moisture variation on soil-bearing capacity, compressibility, liquefaction and expansiveness.

  • CBC § 5.1 High relevance — show source text

    Borings shall be of sufficient size to permit visual examination of the soil in place or, in lieu thereof, cores shall be taken.

    Borings shall be of sufficient depth and size to adequately characterize sub-surface conditions.

    1803 A .4 Qualified representative. The investigation procedure and apparatus shall be in accordance with generally accepted engineering practice. The registered design professional shall have a fully qualified representative on site during all boring or sampling operations.

    1803 A .5 Investigated conditions. Geotechnical investigations shall be conducted as indicated in Sections 1803 A .5.1 through 1803 A .5.12.

    1803 A .5.1 Classification. Soil materials shall be classified in accordance with ASTM D2487. Rock shall be classified in accordance

    with ASTM D5878.

    1803 A .5.2 Questionable soil and rock. Where the classification, strength, moisture sensitivity or compressibility of the soil or rock is in doubt or where a load-bearing value superior to that specified in this code is claimed, the building official shall be permitted to require that a geotechnical investigation be conducted.

    1803 A .5.3 Expansive soil. In areas likely to have expansive soil, the building official shall require soil tests to determine where such soils do exist.

    Soils meeting all four of the following provisions shall be considered to be expansive, except that tests to show compliance with Items 1, 2 and 3 shall not be required if the test prescribed in Item 4 is conducted:

    1. Plasticity index (PI) of 15 or greater, determined in accordance with ASTM D4318.

    2. More than 10 percent of the soil particles pass a No.200 sieve (75 µm), determined in accordance with ASTM D6913.

    3. More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D6913.

    4. Expansion index greater than 20, determined in accordance with ASTM D4829.

    1803 A .5.4 Groundwater. A geotechnical investigation shall be performed to determine if:

    1. Groundwater is above or within 5 feet (1524 mm) below the elevation of the lowest floor level where such floor is located below the finished ground level adjacent to the foundation.
    2. The groundwater depth will affect the design and construction of buildings and structures.

    1803 A .5.5 Deep foundations. Where deep foundations will be used, a geotechnical investigation shall be conducted and shall include all of the following, unless sufficient data on which to base the design and installation is otherwise available:

    1. Recommended deep foundation types and installed capacities.
    2. Recommended center-to-center spacing of deep foundation elements.
    3. Driving criteria.
    4. Installation procedures.
    5. Field inspection and reporting procedures (to include procedures for verification of the installed bearing capacity where required).
    6. Load test requirements.
    7. Suitability of deep foundation materials for the intended environment.
    8. Designation of bearing stratum or strata.
    9. Reductions for group action, where necessary.

    1803 A .5.6 Rock strata. Where foundations are to be constructed on or in rock, the geotechnical investigation shall assess variations in rock strata depth, competency and load-bearing capacity.

  • CBC § 5.4 High relevance — show source text
    1. Expansion index greater than 20, determined in accordance with ASTM D4829.

    1803 A .5.4 Groundwater. A geotechnical investigation shall be performed to determine if:

    1. Groundwater is above or within 5 feet (1524 mm) below the elevation of the lowest floor level where such floor is located below the finished ground level adjacent to the foundation.
    2. The groundwater depth will affect the design and construction of buildings and structures.

    1803 A .5.5 Deep foundations. Where deep foundations will be used, a geotechnical investigation shall be conducted and shall include all of the following, unless sufficient data on which to base the design and installation is otherwise available:

    1. Recommended deep foundation types and installed capacities.
    2. Recommended center-to-center spacing of deep foundation elements.
    3. Driving criteria.
    4. Installation procedures.
    5. Field inspection and reporting procedures (to include procedures for verification of the installed bearing capacity where required).
    6. Load test requirements.
    7. Suitability of deep foundation materials for the intended environment.
    8. Designation of bearing stratum or strata.
    9. Reductions for group action, where necessary.

    1803 A .5.6 Rock strata. Where foundations are to be constructed on or in rock, the geotechnical investigation shall assess variations in rock strata depth, competency and load-bearing capacity.

    1803 A .5.7 Excavation near foundations. Where excavation will reduce support from any foundation, a registered design professional shall prepare an assessment of the structure as determined from examination of the structure, available design documents, available subsurface data, and, if necessary, excavation of test pits. The registered design professional shall determine the requirements for support and protection of any existing foundation and prepare site-specific plans, details and sequence of work

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    for submission. Such support shall be provided by under-pinning, bracing, excavation retention systems or by other means acceptable to the building official.

    1803 A .5.8 Compacted fill material. Where shallow foundations will bear on compacted fill material more than 12 inches (305 mm) in depth, a geotechnical investigation shall be conducted and shall include all of the following:

    1. Specifications for the preparation of the site prior to placement of compacted fill material.

    2. Specifications for material to be used as compacted fill.

    3. Test methods to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill.

    4. Maximum allowable thickness of each lift of compacted fill material.

    5. Field test method for determining the in-place dry density of the compacted fill.

    6. Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.

    7. Number and frequency of field tests required to determine compliance with Item 6.

  • CBC § 1803.5.6 High relevance — show source text

    1803.5.6 Rock strata. Where foundations are to be constructed on or in rock, the geotechnical investigation shall assess variations in rock strata depth, competency and load-bearing capacity.

    1803.5.7 Excavation near foundations. Where excavation will reduce support from any foundation, a registered design professional shall prepare an assessment of the structure as determined from examination of the structure, available design documents, available subsurface data, and, if necessary, excavation of test pits. The registered design professional shall determine the requirements for support and protection of any existing foundation and prepare site-specific plans, details and sequence of work for submission. Such support shall be provided by under-pinning, bracing, excavation retention systems or by other means acceptable to the building official.

    1803.5.8 Compacted fill material. Where shallow foundations will bear on compacted fill material more than 12 inches (305 mm) in depth, a geotechnical investigation shall be conducted and shall include all of the following:

    1. Specifications for the preparation of the site prior to placement of compacted fill material.

    2. Specifications for material to be used as compacted fill.

    3. Test methods to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill.

    4. Maximum allowable thickness of each lift of compacted fill material.

    5. Field test method for determining the in-place dry density of the compacted fill.

    6. Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.

    7. Number and frequency of field tests required to determine compliance with Item 6.

    1803.5.9 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), a geotechnical investigation shall be conducted and shall include all of the following:

    1. Specifications for the preparation of the site prior to placement of the CLSM.
    2. Specifications for the CLSM.
    3. Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM .
    4. Test methods for determining the acceptance of the CLSM in the field.
    5. Number and frequency of field tests required to determine compliance with Item 4.

    1803.5.10 Alternate setback and clearance. Where setbacks or clearances other than those required in Section 1808.7 are desired, the building official shall be permitted to require a geotechnical investigation by a registered design professional to demonstrate that the intent of Section 1808.7 would be satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material.

    1803.5.11 Seismic Design Categories C through F. For structures assigned to Seismic Design Category C, D, E or F, a geotechnical investigation shall be conducted, and shall include an evaluation of all of the following potential geologic and seismic hazards:

    1. Slope instability.

    2. Liquefaction.

    3. Total and differential settlement.

    4. Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.

  • CBC § 1806A.2. High relevance — show source text

    1803 A .2 Investigations required. Geotechnical investigations shall be conducted in accordance with Sections 1803 A .3 through 1803A.6 .

    Exception s : 1. Geotechnical reports are not required for one-story, wood-frame and light-steel-frame buildings of Type II or Type V construction and 4,000 square feet (371 m [2] ) or less in floor area, not located within Earthquake Fault Zones or Seismic Hazard Zones as shown in the most recently published maps from the California Geological Survey (CGS) or in seismic hazard zones as defined in the Safety Element of the local General Plan. Allowable foundation and lateral soil pressure values may be determined from Table 1806A.2.

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    2. A previous report for a specific site may be resubmitted, provided that a reevaluation is made and the report is found to be currently appropriate.

    1803 A .3 Basis of investigation. Soil classification shall be based on observation and any necessary tests of the materials disclosed by borings, test pits or other subsurface exploration made in appropriate locations. Additional studies shall be made as necessary to evaluate slope stability, soil strength, position and adequacy of load-bearing soils, the effect of moisture variation on soil-bearing capacity, compressibility, liquefaction and expansiveness.

    1803 A .3.1 Scope of investigation. The scope of the geotechnical investigation including the number and types of borings or soundings, the equipment used to drill or sample, the in-situ testing equipment and the laboratory testing program shall be determined by a registered design professional. There shall not be less than one boring or exploration shaft for each 5,000 square feet (465 m [2] ) of building area at the foundation level with a minimum of two provided for any one building. A boring may be considered to reflect subsurface conditions relevant to more than one building, subject to the approval of the enforcement agency.

    Borings shall be of sufficient size to permit visual examination of the soil in place or, in lieu thereof, cores shall be taken.

    Borings shall be of sufficient depth and size to adequately characterize sub-surface conditions.

    1803 A .4 Qualified representative. The investigation procedure and apparatus shall be in accordance with generally accepted engineering practice. The registered design professional shall have a fully qualified representative on site during all boring or sampling operations.

    1803 A .5 Investigated conditions. Geotechnical investigations shall be conducted as indicated in Sections 1803 A .5.1 through 1803 A .5.12.

    1803 A .5.1 Classification. Soil materials shall be classified in accordance with ASTM D2487. Rock shall be classified in accordance

    with ASTM D5878.

    1803 A .5.2 Questionable soil and rock. Where the classification, strength, moisture sensitivity or compressibility of the soil or rock is in doubt or where a load-bearing value superior to that specified in this code is claimed, the building official shall be permitted to require that a geotechnical investigation be conducted.

  • CBC § 1803.1 High relevance — show source text

    SECTION 1803—GEOTECHNICAL INVESTIGATIONS

    1803.1 General. Geotechnical investigations shall be conducted in accordance with Section 1803.2 and reported in accordance with Section 1803.6. Where required by the building official or where geotechnical investigations involve in-situ testing, laboratory testing or engineering calculations, such investigations shall be conducted by a registered design professional. [OSHPD 1R, 2 & 5] The classi- fication, testing and investigation of the soil shall be made under the responsible charge of a California registered geotechnical engineer. All recommendations contained in geotechnical and geohazard reports shall be subject to the approval of the enforcement agency. All reports shall be prepared and signed by a registered geotechnical engineer, certified engineering geologist and a registered geophysicist, where applicable.

    1803.1.1 General and where required for applications listed in Section 1.8.2.1.1 regulated by the Department of Housing and Community Development. [HCD 1] Foundation and soils investigations shall be conducted in conformance with Health and Safety Code Sections 17953 through 17957 as summarized below.

    1803.1.1.1 Preliminary soil report. Each city, county, or city and county shall enact an ordinance which requires a preliminary soil report, prepared by a civil engineer who is registered by the state. The report shall be based upon adequate test borings or excavations, of every subdivision, where a tentative and final map is required pursuant to Section 66426 of the Government Code.

    The preliminary soil report may be waived if the building department of the city, county, or city and county, or other enforce- ment agency charged with the administration and enforcement of the provisions of Section 1803.1.1, shall determine that, due to the knowledge such department has as to the soil qualities of the soil of the subdivision or lot, no preliminary analysis is necessary.

    1803.1.1.2 Soil investigation by lot, necessity, preparation and recommendations. If the preliminary soil report indicates the presence of critically expansive soils or other soil problems which, if not corrected, would lead to structural defects, such ordi- nance shall require a soil investigation of each lot in the subdivision.

    The soil investigation shall be prepared by a civil engineer who is registered in this state. It shall recommend corrective action which is likely to prevent structural damage to each dwelling proposed to be constructed on the expansive soil.

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    1803.1.1.3 Approval, building permit conditions, appeal. The building department of each city, county, or city and county, or other enforcement agency charged with the administration and enforcement of the provisions of Section 1803.1.1, shall approve the soil investigation if it determines that the recommended action is likely to prevent structural damage to each dwelling to be constructed. As a condition to the building permit, the ordinance shall require that the approved recommended action be incorpo- rated in the construction of each dwelling. Appeal from such determination shall be to the local appeals board.

  • CBC § 5.7 High relevance — show source text

    1803 A .5.7 Excavation near foundations. Where excavation will reduce support from any foundation, a registered design professional shall prepare an assessment of the structure as determined from examination of the structure, available design documents, available subsurface data, and, if necessary, excavation of test pits. The registered design professional shall determine the requirements for support and protection of any existing foundation and prepare site-specific plans, details and sequence of work

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    for submission. Such support shall be provided by under-pinning, bracing, excavation retention systems or by other means acceptable to the building official.

    1803 A .5.8 Compacted fill material. Where shallow foundations will bear on compacted fill material more than 12 inches (305 mm) in depth, a geotechnical investigation shall be conducted and shall include all of the following:

    1. Specifications for the preparation of the site prior to placement of compacted fill material.

    2. Specifications for material to be used as compacted fill.

    3. Test methods to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill.

    4. Maximum allowable thickness of each lift of compacted fill material.

    5. Field test method for determining the in-place dry density of the compacted fill.

    6. Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.

    7. Number and frequency of field tests required to determine compliance with Item 6.

    1803 A .5.9 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), a geotechnical investigation shall be conducted and shall include all of the following:

    1. Specifications for the preparation of the site prior to placement of the CLSM.
    2. Specifications for the CLSM.
    3. Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM.
    4. Test methods for determining the acceptance of the CLSM in the field.
    5. Number and frequency of field tests required to determine compliance with Item 4.

    1803 A .5.10 Alternate setback and clearance. Where setbacks or clearances other than those required in Section 1808 A .7 are desired, the building official shall be permitted to require a geotechnical investigation by a registered design professional to demonstrate that the intent of Section 1808 A .7 would be satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material.

    1803 A .5.11 Seismic Design Categories C through F. For structures assigned to Seismic Design Category C, D, E or F, a geotechnical investigation shall be conducted, and shall include an evaluation of all of the following potential geologic and seismic hazards:

    1. Slope instability.

    2. Liquefaction.

    3. Total and differential settlement.

    4. Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.

    1803 A **.5.12 Seismic Design Categories D through F.

  • CBC § 1801A.1.1 High relevance — show source text

    1801A.1.1 Application. The scope of application of Chapter 18A is as follows: 1. Structures regulated by the Division of the State Architect—Structural Safety, which include those applications listed in Section 1.9.2.1 (DSA-SS) and 1.9.2.2 (DSA-SS/CC). These applications include public elementary and secondary schools, community colleges and state-owned or state-leased essential services buildings 2. Applications listed in Section 1.10.1 and 1.10.4 regulated by the Department of Health Care Access and Information/Office of Statewide Hospital Planning and Development (OSHPD).These applications include hospitals and correctional treatment

    centers.

    1801A.1.2 Amendments in this chapter. OSHPD adopt this chapter and all amendments.

    Exception: Amendments adopted by only one agency appear in this chapter preceded with the appropriate acronym of the adopt- ing agency, as follows: 1. Division of the State Architect-Structural Safety:

    [DSA-SS] For applications listed in Section 1.9.2.1.

    [DSA-SS/CC] For applications listed in Section 1.9.2.2. 2. Office of Statewide Hospital Planning and Development:

    [OSHPD 1] - For applications listed in Section 1.10.1.

    [OSHPD 4] - For applications listed in Section 1.10.4.

    1801A.1.3 Reference to other chapters.

    1801A.1.3.1 [DSA-SS/CC] Where reference within this chapter is made to sections in Chapters 16A, 19A, 21A and 22A, the provisions in Chapters 16, 19, 21 and 22, respectively shall apply instead as defined in Section 1.9.2.2. Referenced sections may not directly correlate, but the corresponding DSA-SS/CC sections to such references still apply.

    SECTION 1802 A —DESIGN BASIS

    1802 A .1 General. Allowable bearing pressures, allowable stresses and design formulas provided in this chapter shall be used with the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605 A .2. The quality and design of materials used structurally in excavations and foundations shall comply with the requirements specified in Chapters 16, 19, 21, 22 and 23. Excavations and fills shall comply with Chapter 33.

    SECTION 1803 A —GEOTECHNICAL INVESTIGATIONS

    1803 A .1 General. Geotechnical investigations shall be conducted in accordance with Section 1803 A .2 and reported in accordance with Section 1803A.7. The classification and investigation of the soil shall be made under the responsible charge of a California regis- tered geotechnical engineer. All recommendations contained in geotechnical and geohazard reports shall be subject to the approval of the enforcement agency. All reports shall be prepared and signed by a registered geotechnical engineer, a certified engineering geolo- gist and a registered geophysicist, where applicable.

  • CBC § 3.3.1.4 Medium relevance — show source text

    1. Davisson Offset Limit.

    2. Brinch-Hansen 90-percent Criterion.

    3. Butler-Hoy Criterion.

    4. Other methods approved by the building official.

    1810 A .3.3.1.4 Allowable shaft resistance. The assumed shaft resistance developed by any uncased cast-in-place deep foundation element shall not exceed one-sixth of the bearing value of the soil material at minimum depth as set forth in Table 1806 A .2, up to 500 psf (24 kPa), unless a greater value is allowed by the building official on the basis of a geotechnical investigation as specified in Section 1803 A or a greater value is substantiated by a load test in accordance with Section 1810 A .3.3.1.2. Shaft resistance and end-bearing resistance shall not be assumed to act simultaneously unless determined by a geotechnical investigation in accordance with Section 1803 A .

    1810 A .3.3.1.5 Uplift capacity of a single deep foundation element. Where required by the design, the uplift capacity of a single deep foundation element shall be determined by an approved method of analysis based on a minimum factor of safety of three or by load tests conducted in accordance with ASTM D3689. The maximum allowable uplift load shall not exceed the ultimate load capacity as determined in Section 1810 A .3.3.1.2, using the results of load tests conducted in accordance with ASTM D3689 divided by a factor of safety of two.

    Exception: Where uplift is due to wind or seismic loading, the minimum factor of safety shall be two where capacity is determined by an analysis and one and one-half where capacity is determined by load tests.

    1810 A .3.3.1.6 Allowable uplift load of grouped deep foundation elements. For grouped deep foundation elements subjected to uplift, the allowable uplift load for the group shall be calculated by a generally accepted method of analysis.

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    Where the deep foundation elements in the group are placed at a center-to-center spacing less than three times the least horizontal dimension of the largest single element, the allowable uplift load for the group is permitted to be calculated as the lesser of:

    1. The proposed individual allowable uplift load times the number of elements in the group.
    2. Two-thirds of the effective weight of the group and the soil contained within a block defined by the perimeter of the group and the length of the element, plus two-thirds of the ultimate shear resistance along the soil block.

    1810 A .3.3.1.7 Load-bearing capacity. Deep foundation elements shall develop ultimate load capacities of not less than twice the design working loads in the designated load-bearing layers. Analysis shall show that soil layers underlying the designated load-bearing layers do not cause the load-bearing capacity safety factor to be less than two.

    1810 A .3.3.1.8 Bent deep foundation elements. The load-bearing capacity of deep foundation elements discovered to have a sharp or sweeping bend shall be determined by an approved method of analysis or by load testing a representative element.

    1810 A .3.3.1.9 Helical piles. The allowable axial design load, P a, of helical piles shall be determined as follows:

  • CBC § 1804.6 Medium relevance — show source text
    1. In coastal high hazard areas, unless such fill is conducted or placed to avoid diversion of water and waves toward any building or structure.
    2. Where design flood elevations are specified but floodways have not been designated, unless it has been demonstrated that the cumulative effect of the proposed flood hazard area encroachment, when combined with all other existing and anticipated flood hazard area encroachment, will not increase the design flood elevation more than 1 foot (305 mm) at any point.

    1804.6 Compacted fill material. Where shallow foundations will bear on compacted fill material, the compacted fill shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803.

    Exception: Compacted fill material 12 inches (305 mm) in depth or less need not comply with an approved report, provided that the in-place dry density is not less than 90 percent of the maximum dry density at optimum moisture content determined in accordance with ASTM D1557. The compaction shall be verified by special inspection in accordance with Section 1705.6.

    1804.7 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), the CLSM shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803.

    SECTION 1805—DAMPPROOFING AND WATERPROOFING

    1805.1 General. Walls or portions thereof that retain earth and enclose interior spaces and floors below grade shall be waterproofed and dampproofed in accordance with this section, with the exception of those spaces containing groups other than residential and institutional where such omission is not detrimental to the building or occupancy.

    Ventilation for crawl spaces shall comply with Section 1202.4.

    1805.1.1 Story above grade plane. Where a basement is considered a story above grade plane and the finished ground level adjacent to the basement wall is below the basement floor elevation for 25 percent or more of the perimeter, the floor and walls shall be dampproofed in accordance with Section 1805.2 and a foundation drain shall be installed in accordance with Section 1805.4.2. The foundation drain shall be installed around the portion of the perimeter where the basement floor is below ground level. The provisions of Sections 1803.5.4, 1805.3 and 1805.4.1 shall not apply in this case.

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    1805.1.2 Under-floor space. The finished ground level of an under-floor space such as a crawl space shall not be located below the bottom of the footings. Where there is evidence that the ground-water table rises to within 6 inches (152 mm) of the ground level at the outside building perimeter, or that the surface water does not readily drain from the building site, the ground level of the under-floor space shall be as high as the outside finished ground level, unless an approved drainage system is provided. The provisions of Sections 1803.5.4, 1805.2, 1805.3 and 1805.4 shall not apply in this case.

Frequently asked questions

Who must prepare and sign the geotechnical report?

A geotechnical report must be prepared and signed by a registered geotechnical engineer (and, where applicable, by a certified engineering geologist and registered geophysicist). § 1803.1 / Chapter 18 (and Chapter 18A when applicable).

If my foundation sits on 8 in of compacted fill, do I need a geotechnical report?

Not necessarily — the code’s compacted‑fill trigger for a required geotechnical investigation is more than 12 inches (305 mm) for shallow foundations; however, other site conditions (expansive soils, groundwater, seismic category, local ordinance) may require an investigation. § 1803.5.8; see exceptions in § 1803.2.

What must a CLSM report show?

For CLSM supporting shallow foundations the geotechnical investigation/report must include site prep specs, mix/specifications for the CLSM, lab or field test methods to determine compressive strength or bearing capacity, field acceptance test methods, and the number/frequency of field tests. § 1803.5.9.

Is there a single percent compaction the CBC requires for all fills?

No. For compacted fills > 12 in the geotechnical report must specify the minimum acceptable in‑place dry density as a percent of the maximum dry density. A 90% figure in the code is used in a limited context where reporting is not required (special‑inspection verification for fills 12 in or less). § 1803.5.8; § 1705.6.

What if my site is in SD C–F?

If the structure is assigned Seismic Design Category C, D, E or F the geotechnical investigation must evaluate slope instability, liquefaction, settlement potential and surface displacement; for D–F further analyses (e.g., seismic lateral earth pressures, liquefaction analyses using MCE PGA or site‑specific study) are required. § 1803.5.11–.12.

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