PURPOSE
The purpose of this procedure is to provide a guideline for identifying the project’s geotechnical restraints and initiate investigations; feasibility studies including methane mitigation plans as applicable for selected areas in Los Angeles. The Bureau’s Geotechnical Engineering Division (GED) often the Engineer of Record for the project, shall provide recommendations to be included into the concept and pre-design phases of a project. GED shall provide design information and criteria. This can affect the project’s budget, schedule, and overall design. Preliminary geotechnical and geological information provided during the pre-design phase may even determine the location of the specific improvements. Input can range from planning studies that provide advice on the geological and environmental issues of a project, to actual subsurface investigations providing preliminary information that could affect the project’s anticipated budget and schedule. Exploring the environmental or geologic aspects of a particular area, determining restraint completion of the investigation during predesign phase is vital to a successful project.
It is highly recommended that Geotechnical investigation and feasibility studies including methane mitigation be completed during pre-design phase and for the selected option geotechnical report be completed and plan checked.
REFERENCES
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RESPONSIBILITIES
Project Manager (PM): The PM should contact GED at the early stages of the pre-design process to initiate geotechnical investigations and to identify potential geotechnical, geologic and/or environmental issues that may be present at or near the proposed project site. GED shall provide a signed Geotechnical Report to the design engineers. This could have a significant impact on the anticipated project cost and schedule. Once a project enters design, it is the PM’s responsibility to assure that the design meets design criteria defined by the geotechnical investigation, and the geotechnical results and recommendations as outlined in the report. By signing selected plans affected by the geotechnical results and recommendations, GED confirms that the design meets design criteria defined by the Geotechnical Report. For the plan check, the Department of Building and Safety requirement consists of an approved Geotechnical Report and selected drawings stamped by GED.
Project Engineer (PE): On all projects, the PM may delegate and share authority with a PE.
Geotechnical Engineering Division: GED is responsible for providing geotechnical investigation and feasibility studies including methane mitigation to be completed during pre-design phase and providing the Department of Building and Safety plan check support for the geotechnical report.
PROCEDURE
Contacting GED for Pre-Design Input
The PM shall initiate geotechnical investigation with a written request signed by the Program Manager/Division Engineer for the pre-design phase of the project as soon as the project concept and location are developed. GED may also be contacted in different ways, depending on the information required. If general information is needed or just a general idea of what may be expected, then an email or informal meeting should be sufficient. An email to a geotechnical engineer or engineering geologist with a cc to GED Division Engineer or a written memo may begin this process.
The initial contact, which often includes a site walkthrough, will provide an opportunity to discuss the project details and specifics, including the estimated budget for geotechnical services and will initiate information and data collection. It may also establish the need for a more detailed investigation, which could involve drilling and testing, if warranted. After the initial contact, it may be necessary to schedule a pre-design meeting with other appropriate Architectural / Engineering (A/E) Services Groups to discuss exactly what is required. This should be done after GED has had adequate time to do proper research, and the collected data can then be brought to the meeting and discussed.
GED may be able to provide significant value to the pre-design process by making available pertinent information that could have a significant impact on the proposed project. Geotechnical, geological and/or environmental information and data may be available by searching existing soil borings and groundwater information generated on past projects constructed in the vicinity of the proposed project. GED can also research available geologic, seismic, liquefaction potential, hazardous materials (HAZMAT) and groundwater maps, as well as rely on experience gained through past projects in the area. A planning study can be provided to assist in locating proposed structures, and to avoid known faults, landslides, contamination, etc.
If warranted, GED can conduct a preliminary geotechnical investigation and prepare a report consisting of limited exploratory borings and in-situ or laboratory testing. Such a preliminary report is usually performed as a feasibility study or environmental investigation, and the information gained during the feasibility study can be used for real estate transactions and will reduce the cost of the geotechnical report for the design phase. If nothing else, GED can provide advice and/or information regarding geotechnical and geological procedures and principals as they relate to the proposed project.
If the PM needs to request a subsurface investigation to obtain specific and more detailed information concerning the project, then a formal written request should be sent to GED (Attachment 7.3-1). This will initiate GED’s investigation. The written request should contain, at a minimum, the following information:
Project work order
Project type and scope, this should include the method of construction on infrastructure projects, i.e. tunneling vs. open cut
Project location and limits
Estimated budget for geotechnical services
Identification of any known existing, adjacent and nearby improvements, including any known topography
Development concept, if available
In any case, it would be to the PM’s advantage to discuss the proposed project with a geotechnical engineer or geologist to get an idea of what may be expected before a formal written request is sent.
Geotechnical, Geological, and Environmental Issues
Soil and Groundwater Conditions: Based on existing information available in the Division, GED may be able to indicate general soil types and conditions and identify potential problems. Un-engineered or engineered fill may also be identified.
If a project involves trenching or excavations, then issues of soil retention and groundwater immediately arise. It must be made clear to bidders the types of soil retention systems that will be required. For example, if the project requires trenching for a new sewer line, it should be determined whether trench shields will be adequate or if the project will require solid sheeting. Too often in the past, the PE remained silent on such issues, not wanting to accept responsibility, instead waiting until the contractor was on-board and then rejecting submittals because they didn’t meet the requirements. This approach is unacceptable if the PE knows what is required. If the PE doesn’t know and leaves it up to the Contractor’s judgment, then the PE should not be rejecting submittals unnecessarily.
If groundwater will be encountered during any excavation, it is important to conduct sufficient field tests to estimate the rate of groundwater production and the quality of the groundwater. Discharge of groundwater to storm drain or waterway systems must meet increasingly stringent requirements imposed by the California Regional Water Quality Control Board for the Los Angeles Region. It is important to understand both the quantity and quality of any groundwater before bidding the project. In some cases, knowledge of characteristics encountered in similar projects may be sufficient. In other cases, field investigations may be necessary to develop the required engineering data for bidding the project.
Environmental: Known areas of large-scale contamination such as oil fields, superfund sites, published soil and/or groundwater remediation projects, etc. need to be identified immediately. If a project is located on or near such an area, it may increase the project’s budget, put the project on hold, or cause a relocation of the project. GED may also be able to identify existing or potential soil or groundwater contamination through previously drilled borings in the area, or by conducting research with the appropriate regulatory agencies.
Seismic: GED can conduct a fault study and research available seismic related maps to determine if the proposed project will be located on or near a known fault, within a Special Studies Zone, or within a mapped liquefaction zone.
Geologic: If the proposed project is located in a hillside area, existing or potential landslides or unstable slopes may be identified through review of old air photos, existing field investigations and past boring logs.
Potential Problems Due to the Lack of GED Involvement
Sewers and Storm Drains: Buried pipes constructed on hillsides, steep slopes, near bluffs or landslides, through wetlands, oil fields or other environmentally sensitive areas will require special design and construction considerations that could have significant impact to the proposed budget and schedule. These special considerations may also affect worker safety or the stability of adjacent properties.
Roadways and Street Improvements: Roadways built in hillside areas or adjacent to steep cuts may require lateral support by bulkheads or other retaining structures or may require protection by slough walls or debris fencing. Roadways constructed on wetlands or on expansive clays will require special sub-grade modifications, and if there are buried railroad or streetcar tracks beneath the proposed street improvement, it is likely that contaminated materials will be encountered and must be handled during construction.
Bridges and Grade Separations: It is important to involve GED in the pre-design of these types of structures as soon as possible. GED can help to identify potential problems such as liquefaction potential, existing contaminated soil or groundwater, known fault locations, existing or potential landslides, or slope instability, etc. It may be possible to identify the type of foundation required at this stage, as well.
Buildings and Facilities: Again, it is important to involve GED in the pre-design of these types of projects as soon as possible. Not only can GED help to identify similar issues as those listed above, but GED may also assist in locating the structure on the most economically feasible part of a property (before the community or the City Council approves the project footprint). GED may also be able to identify a property as being undesirable for purchase due to environmental or geologic reasons.
Retaining Structures: It is important to identify the type of material that the retaining system may be supporting. For example, if a wall is to support an existing landslide, this may increase the initial cost estimate by three to six times or may even render the project economically unfeasible. GED may also be able to identify the proposed foundation type by researching available records or by conducting a field investigation.
RELATED PROCEDURES
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