Ch. 18E.90 App. A Geological Assessments – Liquefaction or Dynamic Settlement Hazard Areas

18E.90.060 – Appendix A Geological Assessments – Liquefaction or Dynamic Settlement Hazard Areas

A. A geotechnical letter shall, at a minimum, include the following:

1. The letter shall be labeled identifying the submittal as a "Liquefaction or Dynamic Settlement Hazard Geotechnical Letter," and will include all mandatory items listed in PCC 18E.90.030 B.4.

2. The geological assessment must include a determination an evaluation that no portion of the subject property [site] includes a liquefaction and/or dynamic settlement hazard.

3. A paragraph that states the following specific language:

"The services described in this letter were completed under the responsible charge of (Individual's Name). (Individual's Name) meets the qualifications contained in Section 18E.90.030 to prepare this geological assessment. (Individual's Name) understands the requirements of the current Seismic (Earthquake) Hazard Areas Chapter 18E.90 and the definitions of the applicable terms contained within Chapter 18.25 and Title 18E. Individuals under my responsible charge have conducted an investigation in general accordance 18E.90.060 – Appendix A, Geotechnical Letter – Liquefaction or Dynamic Settlement Hazard Areas. In my opinion, the scope of services completed for this project is adequate to meet the requirements of the Department and it does not appear that a liquefaction and/or dynamic settlement hazard area exists within the boundaries of the proposed site.

4. The name, mailing address and telephone number of geotechnical professional(s) who prepared the letter.

5. The name, mailing address, and telephone number of the property owner.

B. The Geotechnical Letter shall be prepared under the responsible charge of an appropriately licensed geotechnical professional(s) and be signed, sealed and dated by the geotechnical professional(s) (as defined in Chapter 18.25 PCC) and the format shall be pre-approved by the Department.

A. A geotechnical evaluation shall, at a minimum, include the following:

1. The first page of the document shall be labeled identifying the submittal as a "Liquefaction or Dynamic Settlement Hazard Geotechnical Evaluation," and will include all mandatory items listed in PCC 18E.90.030 B.4.

2. The geological assessment must include a determination an evaluation that a liquefaction and/or dynamic settlement hazard exists on the site, but is located outside the proposed project area.

3. The Geotechnical Evaluation shall include an accurate site plan drawn at a scale of 1" = 20', 1" = 30', 1" = 50' (or other scale deemed appropriate by the Department) is required. The Department may require that the site plan information be based on a field survey by a licensed surveyor. The site plan shall include:

(a) Property lines for the site, and the location of any existing structures.

(b) The existing site topography presented in 2-foot contours.

(d) The full geographical limits of the proposed project area (i.e., area to be developed) and the location of any proposed structures, on-site septic systems, wells, and stormwater management features or facilities associated with the development.

(e) The limits of any setbacks from the defined locations of the liquefaction and/or dynamic settlement hazard areas determined by the geotechnical professional(s) as necessary to protect any portion of the proposed development activity from damage caused by liquefaction-induced ground displacement.

4. A paragraph that states the following specific language:

"The services described in this evaluation were completed under the responsible charge of (Individual's Name). (Individual's Name) meets the qualifications contained in Section 18E.90.030 to prepare this geological assessment. (Individual's Name) understands the requirements of the current Seismic (Earthquake) Hazard Areas Chapter 18E.90 and the definitions of the applicable terms contained within Chapter 18.25. (Individuals' Name) or someone under his/her responsible charge has conducted an investigation in general accordance 18E.90.060 – Appendix A, Geotechnical Evaluation – Liquefaction or Dynamic Settlement Hazard Areas. In my opinion, the scope of services completed for this project is adequate to meet the requirements of the Department and it does not appear that a liquefaction and/or dynamic settlement hazard area exists within the boundaries of the proposed site."

5. The name, mailing address, and telephone number of geotechnical professional(s) who prepared the letter.

6. The name, mailing address, and telephone number of the property owner.

B. The geotechnical report shall be prepared under the responsible charge of an appropriately licensed geotechnical professional(s) and be signed, sealed and dated by the geotechnical professional(s) and the format shall be pre-approved by the Department.

A. A geotechnical report shall, at a minimum, include the following:

1. The first page of the document shall be labeled identifying the submittal as a "Liquefaction or Dynamic Settlement Hazard Geotechnical Report," and will include all mandatory items listed in Section 18E.90.030 B.4. The report shall be prepared by an engineer and shall be co-written by a geotechnical professional where geological interpretations and conclusions critical to the assessment of liquefaction and/or dynamic settlement hazard and potential effects are necessary or prudent. The introductory Section of the report shall specify the desired performance level of the structures and other development facilities (e.g., safety to building occupants, minimal damage to structure, post-earthquake serviceability for pre-earthquake operations, no damage, etc.).

2. The results, conclusions, and recommendations resulting from the geological assessment of the liquefaction and/or dynamic settlement hazards on the subject property as prepared by the geotechnical professional(s).

3. The geological assessment-geotechnical report shall include:

(a) A statement that the proposed project area falls within a liquefaction and/or dynamic settlement hazard area.

(b) A detailed engineering evaluation of expected ground displacements or other liquefaction and/or dynamic settlement effects (e.g., bearing failures, floatation of buried tanks, etc.) and proposed mitigation measures to ensure an acceptable level of risk for the proposed structure type or other development facilities, as well as, the proposed land use type (i.e., occupancy category). The minimum level of acceptable risk for any proposed structure or development facility shall ensure be the life safety of any occupant. Designs shall evaluate the range of alternatives for achieving limited structural damage to no structural damage based on the proposed use intended for the structure.

4. The report shall include an accurate site plan drawn at a scale of 1" = 20', 1" = 30', 1" = 50' (or other scale deemed appropriate by the Department) is required. The Department may require that the site plan information be based on a field survey by a licensed surveyor. The site plan shall include:

(a) Property lines for the site and the location of any existing structures.

(b) The existing site topography presented in 2-foot contours.

(d) The full geographical limits of the proposed project area (i.e. area to be developed) and the location of any proposed structures, on-site septic systems, wells, and stormwater management features or facilities associated with the development.

(e) The limits of any set-backs from the defined locations of the liquefaction and/or dynamic settlement hazard areas determined by the geotechnical professional(s) as necessary to protect any portion of the proposed development activity from damage caused by liquefaction-induced ground displacement.

(f) Location and unique identifier of geotechnical borings and/or CPT soundings used to characterize subsurface conditions.

5. The field investigation shall require the following elements:

(a) Subsurface characterization using conventional geotechnical borings and Standard Penetration Testing (SPT) or using Cone Penetration Testing (CPT).

(b) Conventional geotechnical boring data shall be reported as a graphic log utilizing the following standards:

(1) The vertical scale of the graphic log shall be such that 5 feet of drilled depth is scaled to range of 1" to 2" (1:60- or 1:30-scale), and shall include vertical columns that record depth in 1 foot increments, SPT value and incremental blow counts, a graphic pattern representation of the soil type encountered during drilling, and sample descriptions and other comments regarding drilling.

(2) The graphic log shall have a header on the first page that includes a unique identifier for the boring, the times and dates of the start and completion of drilling, the manufacturer and model of the drilling rig, the company name of the drilling contractor, the name(s) of the site geologist(s) or engineer(s) overseeing the drilling activities, the details of the method used to advance the borehole (e.g., 4" i.d. hollow-stem auger), the type of drilling fluid used to stabilize the borehole, verification that the SPT followed all applicable ASTM standards including a description of the sampler, hammer weight, drop height, the type of hammer used to perform the SPT, number of turns of rope if a cathead is used to raise the hammer, condition of rope (i.e., new, used, frayed, oily, etc.), and the depth of static groundwater measured immediately prior to abandonment of the boring and the time and date of this measurement.

(3) All subsequent pages of the graphic log shall have the unique identifier for the boring, the times and dates of the start and completion of drilling, and the number of the page and the total number of pages comprising the log.

(4) Each SPT value will be reported in the appropriate column showing the blow counts recorded at each 6" interval, and the sum of the blow counts between penetration distances of 6" to 18," unless refusal conditions (50 or more blows with less than 6" of sampler penetration) are met anywhere in this interval. At refusal, the blow count shall be recorded as the number of blows with the corresponding sampler penetration, in inches.

(5) SPT tests shall be performed every 5 feet during drilling, at a minimum. Additional undisturbed samples, collected following ASTM standards for undisturbed soil sampling, cannot be substituted for SPT testing.

(6) The soil sample descriptions will include the total length of the recovered sample, the soil color, odor, the density or consistency (loose to very dense, very soft to very stiff), degree of water saturation (dry, moist, wet, saturated), and dilatancy. For granular (sand and gravel) soils, the description shall include a physical description of the soil sample, including size distribution (poorly or well graded), angularity, composition, amount and plasticity of the fines fraction. For fine soils (silt and clay), the description shall include a qualitative estimate of the proportion of the silt and clay size particles (e.g., silty clay, clay with some silt, etc.), plasticity, and amount and type of organic material. The sample description shall include a description of any bedding, laminations, slickensides, or other textural or deposition features, including contact between dissimilar soil types. The sample description shall also include a field classification of the soil sample using the Unified Soil Classification System where the classification is expressed in lower case letters (e.g., sp, ml, etc.). The sample classification shall be expressed in upper case letters (e.g., SP, ML, etc.) where subsequent laboratory testing has been performed. This column of the graphic log will also include any other information relevant to the subsurface investigation, such as loss of drilling fluid, heaving, churning of the drill in gravelly soils, etc.

(1) The vertical scale of the graphic log shall be such that 5 feet of penetrated depth is scaled to range of 1" to 2" (1:60- or 1:30-scale), and shall include vertical columns that record depth in 1 foot increments.

(2) The graphic log shall have a header on the first page that includes a unique identifier for the boring, the times and dates of the start and completion of the CPT sounding, the manufacturer and model of the CPT system, the company name of the CPT service contractor, the name(s) of the site geologist(s) or engineer(s) overseeing the CPT sounding, and any comments regarding the conduct of the testing, reaction of the CPT system during sounding, etc.

(4) The graphic log shall display, at a minimum, a continuous depth plot of the uncorrected tip resistance, the friction (sleeve) resistance, the friction ratio, and the measured pore pressure with an overlay of the calculated hydrostatic pore pressure. These curves shall be plotted so as to show the full variation of the measured quantities within the depth range of the sounding, and each curve shall have a visible scale with the minimum and maximum ranges labeled.

(5) All of the CPT data recorded for each sounding shall also be provided in either electronic or hardcopy format. Electronic data will be presented in an ASCII text file format.

(d) All SPT or CPT testing will be conducted to a minimum depth of 50 feet below the existing ground surface or lowest proposed finished grade, except where a minimum thickness of 10 feet of consolidated soils are encountered where the (N1)60 is greater than 30, or CPT corrected tip resistance (qc1N) is greater than 175. In addition, SPT or CPT testing should extend a minimum of 20 feet below the lowest expected foundation level, including the lowest elevation of piling support.

6. The three-dimensional subsurface conditions at the site shall be presented using one or more cross-sections showing location and depth penetration of borings or CPT soundings, interpretation of the geometry of major soil units, and projected location of the static groundwater surface determined from the subsurface exploration. The cross-sections shall be presented at a scale of 1" = 20', 1" = 30', 1" = 50' (or other scale deemed appropriate by the Department). Each cross-section shall have a legend with a description of the various major soil units.

7. All assessments of liquefaction and/or dynamic settlement hazards and effects will be based on a design earthquake using ground motion parameters consistent and equivalent to those specified in the Pierce County Building Code. The choice of moment magnitude used in the determination of the magnitude-scaling factor, as well as the scaling relations used in the analysis, shall be justified in the report narrative. These assessments shall use the shallowest groundwater table observed during or inferred from subsurface exploration and characterization (e.g., the measured depth of static groundwater immediately prior to abandonment of borings, observation of iron-oxide mottling of soils samples, etc.)

8. Results of laboratory testing of samples retrieved during drilling and sampling shall be presented in order to support the values of fines contents used in subsequent analysis of liquefaction and/or dynamic settlement hazard. Where only CPT methods are used in site assessment, the correlation between fines content and CPT measurements will be discussed and documented. This documentation will require rigorous correlation of CPT and fines content measurements from similar geological deposits within the Puget Sound region.

9. The geotechnical report shall include a detailed assessment of the liquefaction and/or dynamic settlement hazard based on analysis of all available SPT or CPT data using state-of-the-practice methodologies, such as provided in Youd and Idriss (1997) or subsequent technical publications. The methodology used in the analysis shall be documented, and all results of intermediate and final calculations and results, including factors of safety, shall be included.

10. The geotechnical report shall contain an assessment of the potential for large lateral spreads or flow failures, bearing failures, settlement, limited lateral displacement, and floatation of buried facilities. The methodologies used must be, at a minimum, state-of-the-practice, and where applicable should employ more than one method of analysis. All results of intermediate and final calculations and conclusions regarding the potential and severity of the possible liquefaction- and/or dynamic settlement- induced failure modes shall be presented.

11. Alternative mitigative measures including structural and foundation design options and/or soil improvement techniques shall be evaluated and compared for their effectiveness in reaching the level of performance specified in the report introduction. Final designs and specifications and plans for structural and/or foundation design shall be included if applicable. Effectiveness of soil improvement techniques shall be specified in terms of post-treatment densification or strength improvement as measured by appropriate subsurface investigation and testing. The extent of the post-treatment verification testing shall be provided on a site map at the same scale as the map presented in subsection 4. above.

12. The name, mailing address, and telephone number of geotechnical professional(s) who prepared the letter.

13. The name, mailing address, and telephone number of the property owner.

B. The geotechnical report shall be prepared under the responsible charge of an appropriately licensed geotechnical professional(s) and be signed, sealed and dated by the geotechnical professional(s) (as defined in PCC 18E.10.060 and established in this Chapter) and the format shall be pre-approved by the Department.