PURPOSE
The Geotechnical Report is to be used by the Project Engineer (PE)/Architect and support groups for providing geotechnical design parameters and construction guidelines and aiding in project scheduling and cost estimates.
REFERENCES
N/A
RESPONSIBILITIES
Project Manager (PM): The PM is responsible for ensuring that the Geotechnical Report is requested as early in the design process as possible, and that the report is considered while developing the project design, schedule, and cost estimate.
Project Engineer (PE): The PE requests the Geotechnical Report as early in the design process as possible. It is the responsibility of the PE to work closely with the Geotechnical Engineer throughout the design process, both during and after the Geotechnical Report is prepared. The Geotechnical Engineer should be informed of any and all changes or additions to the design that are affected by the geotechnical parameters. The PE is responsible for incorporating the Geotechnical Report into the project design, design documents, and cost estimate.
Geotechnical Engineering Group (GEO): The Geotechnical Engineer in the GEO is responsible for developing and updating the Geotechnical Report.
PROCEDURE
The Geotechnical Report can be vital in getting the project off to the proper start. The Geotechnical Report provides parameters needed at the beginning of design such as site earthwork and grading, foundation type, allowable load capacities, earth pressures, settlement estimates, shoring requirements, R-value/overlay thickness, etc. Therefore, the sooner the subsurface investigation can start, the less likely there will be delays due to geotechnical, geological or environmental conditions. Applicable portions of the report should be extracted and included in the Structural and Civil Design Notes on the plans and in the specifications or included as part of the contract documents.
The Geotechnical Report includes the anticipated subsurface conditions, geotechnical design parameters, construction guidelines, and any geologic and environmental conditions and considerations. During the preparation of the Geotechnical Report, the PE should work closely with GEO and provide any and all updates and changes to the design that occur. Working closely with GEO also keeps the communication flowing and ensures that the Geotechnical Engineer maintains a clearer understanding of the project concepts and requirements. As the Geotechnical Report is being generated, geotechnical design parameters and recommendations can be provided verbally or in draft form, as they are available, in order to keep the design process moving. Geotechnical design parameters and recommendations will then be formalized when the final report is submitted.
As the design process continues, and after the initial Geotechnical Report has been completed, the PE needs to maintain contact with the Geotechnical Engineer throughout the design process. Design changes, such as increasing or decreasing loading conditions and scope changes, such as realignments and changes in pipe inverts, can have a significant impact on the assumptions made in the initial report and can even make the initial Geotechnical Report invalid. This can also significantly delay the project during the Building and Safety review process and can create a dangerous situation during and after the project’s construction. As long as the PE keeps the Geotechnical Engineer informed of any design or scope changes, the appropriate geotechnical changes or modifications can be made to the initial Geotechnical Report, and such delays or dangerous conditions can be avoided.
GEO should also be included in any constructability meetings and/or value engineering meetings, and should review and comment on the 50% and 90% completed plans to ensure that the geotechnical recommendations are being properly implemented. This will also give the Geotechnical Engineer an opportunity to look for design or scope changes. During design, the following typical information can be provided to the PE in the Geotechnical Report:
Anticipated Subsurface Conditions.
Geotechnical Design Parameters and Construction Guidelines.
Shoring Requirements.
Geological Conditions.
Seismic Design Parameters, such as fault locations, liquefaction potential, ground accelerations, ground surface rupture, etc.
Existing and Potential Landslides or Slope Instability.
Adverse Bedding Conditions.
Presence and Depth of Uncertified Fill.
Identification of Problematic and Adverse Soil or Bedrock Conditions, such as expansive or collapsible material, etc.
Location of Groundwater.
Types of Geotechnical Reports
The type of geotechnical report required is based on the jurisdiction of the project. If you have a building project in which the Department of Building and Safety is the permitting agency, geotechnical reporting must satisfy Building and Safety requirements and the terminology is different than with a Public Works infrastructure project. There are several types of geotechnical reports that support each project, regardless of its type.
Public Works Infrastructure Projects: For sewers, storm drains and other types of infrastructure projects, the geotechnical reporting is typically done as follows:
Geotechnical Data Report (GDR) – The GDR is pure data and presents the findings of the field data collection without any interpretation or recommendations. The GDR is a contract document.
Design Memorandum – The Design Memorandum is a report based on the GDR to support design criteria and provides the basic geotechnical parameters to the Design Team. The Design Memorandum is not a contract document.
Geotechnical Baseline Report (GBR) – The GBR is an industry standard report which supports the design recommendations, provides a baseline of anticipated subsurface conditions, is a contract document, and serves to level the playing field through formalizing the interpretations of the GDR.
Building Projects: Building projects require a “Foundation Report” which combines the findings of field data collection with geotechnical conclusions and recommendations for the design team. The Geotechnical Report should be sent to Building and Safety’s Grading Division as soon as it is completed. This will allow Building and Safety approval conditions and/or necessary modifications to be incorporated into the final design plans before the Department of Building and Safety’s Plan Check Division reviews them. GEO is required to review the design plans for adherence to the recommendations of the geotechnical report, then sign and stamp those plans before they are submitted to plan check.
Contamination Assessments: Another type of geotechnical report that can apply to any project type is a contamination assessment. Contamination assessments are conducted in three phases. Phase I assessments are typically paper studies and will be provided by the Environmental Management Group. Phase II assessments will be done by GEO and involve field investigations and testing. Phase III assessments address remediation activities.
The procedures for contamination assessment are set in motion when unexpected contamination of soil and/or groundwater is encountered. Many times a contamination assessment may proceed in parallel with the geotechnical work although it may involve data collection significantly beyond that needed for the geotechnical work. Once contamination is encountered, the PE is to work closely with GEO in establishing additional project milestones.
Involving GEO in the Design Process
A Geotechnical Report should be requested as soon as there is a work order number, project scope, and a location. To request a Geotechnical Report, a written memo including the following information should be provided to GEO:
Project Title and Work Order Number.
Project Description and Scope, including pertinent design criteria if available.
Project Location Map.
Substructure and Sewer Y-Maps.
Existing Facility and Building Plans, if applicable.
Project Engineer’s Name and Phone Number
Copy of a Phase I Site Assessment, if applicable
If required, GEO can provide a subsurface investigation and a report preparation budget and schedule to the PE before beginning the subsurface investigation. The PE should work closely with GEO in establishing the milestones leading to the completion of the geotechnical investigation and report.
Geotechnical Report Data Collection Milestones: Typical tasks and attendant milestones to be tracked by the Project Engineer for preliminary data collection include the following:
PE submits a request to GEO.
PE submits the Right of Entry to GEO.
GEO requests a Task Order from Consultants or the Department of General Services (GSD).
GEO selects a Consultant.
PE submits funding information to GEO.
GEO issues a Notice to Proceed to the Consultant.
GEO fieldwork is completed.
GEO Data Report is completed.
Geotechnical Report Milestones: Typical tasks and attendant milestones to be tracked by the PE for preparation of the Geotechnical Report include the following:
GEO drafts its recommendations.
GEO prepares the final Geotechnical Report.
For certain tunnel or microtunnel projects, a Geotechnical Baseline Report (GBR) is prepared at or near the completion of design. The need for a GBR should be agreed on by the PE and GEO early in the project.
Because GEO maintains a staff of registered geotechnical engineers, engineering geologists and groundwater hydrologists, the vast majority of geotechnical related issues may be addressed by GEO staff. However, since GEO also maintains contracts with on-call geotechnical and environmental consultants, if specialized expertise is needed for any project, experts in any particular field can become involved in the project, as required.
Besides geotechnical and environmental reports, GEO can also provide full design, project plans and construction management services for projects that are primarily geotechnical in nature, such as retaining structures, landslide mitigation, and slope stabilization.
Developing a Geotechnical Test Plan
There are two aspects to the geotechnical discipline that apply to all projects. These can be termed data collection and engineering analysis. Geotechnical engineering analysis for Bureau projects is typically done by GEO staff as the scope and conditions of the project require. Data collection is typically outsourced by the GEO to either the Department of General Services or a Consultant; therefore, it is important that the PE and the GEO establish a Geotechnical Test Plan as a project control tool.
Geotechnical data collection is usually the most time consuming and costly aspect of the geotechnical work on a project. It includes site investigations, exploratory drilling, laboratory testing, and all of the attendant logistical support tasks and reports. A Geotechnical Test Plan is a cost-loaded working schedule of the geotechnical data collection tasks for the project. The plan should be assembled by the GEO and reviewed by the PE as soon as the project scope is sufficiently developed to detail the plan. The plan should also be flexible enough to allow for unpredictable findings in the course of exploration work.
For budgeting purposes, the following scope of exploratory drilling should be assumed until the site specific plan is assembled. A site specific plan may increase or decrease the exploration scope presented below.
For Stormwater or Wastewater Conveyance Cut and Cover type projects, borings should be spaced every 660 feet or every two blocks. No point on the alignment should be more than 330 feet from a boring. If there are reaches to be jacked at intersection or utility crossings, there should be one boring within 100 feet of each jacking pit. Borings should be to a minimum depth of 5 feet below invert elevation of the storm drain or sewer. If groundwater is present, the depth of borings should be 10 feet below the invert elevation.
For Stormwater or Wastewater Conveyance Tunneling projects, borings should be spaced every 500 feet with one boring at each access shaft. No point on the alignment should be more than 250 feet from a boring. Borings should be to a minimum depth of the tunnel invert, plus 2 tunnel diameters.
For Buildings, Bridges, Stormwater or Wastewater Treatment/Pumping Facilities, assume one boring for each “substructure unit” less than 100 feet in width and a minimum of two borings for each “substructure unit” greater than 100 feet in width. A “Substructure Unit” is either a single building or a bridge support. Borings should be to a minimum depth of 30 feet below the base of shallow foundations or to a depth of 50 feet below the base of pile caps, with at least one 50-foot boring to characterize liquefaction for Buildings in LADBS jurisdiction.
For Pavement Reconstruction projects, borings should be spaced every 660 feet or every two city blocks, with no improvement more than 330 feet from a boring. Borings should be to a minimum depth of 5 feet below the finished pavement surface.
For Earth Retaining Structures, assume a minimum of one boring for each retaining wall; a minimum of two borings for walls greater than 100 feet in length with no point on the wall alignment greater than 200 feet from a boring. Borings should be to a minimum depth of 30 feet below the base of shallow foundations or to a depth of 50 feet below the base of pile caps.
For Mass Grading type projects, assume a minimum of one boring per cut slope or embankment, with a maximum spacing of 300 feet and a minimum of three borings transverse to the most critical slope. Borings should be to a minimum depth of 15 feet below the lowest cut elevation or 50 feet below the base of the embankment.
Utilizing Consultant Resources
There are three primary ways in which GEO can produce the investigation and report:
GEO can utilize the City’s Department of General Services (GSD) to conduct the drilling and laboratory testing under the direction of GEO staff but GEO is responsible for preparing the Geotechnical Report.
GEO can utilize one of their on-call geotechnical consultants to conduct the drilling and laboratory testing services under the direction of GEO staff; however, GEO staff prepares the Geotechnical Report.
GEO can use one of their on-call geotechnical consultants to provide drilling, laboratory testing and all or a portion of the report preparation services under the direct supervision of GEO.
Pre-Qualified on-call consultants are sometimes needed to provide specialized drilling or testing methods, specialized expertise (such as tunneling, ground modification, earthquake time histories, etc.), or to supplement GEO staff during times of heavy work loads. If a pre-qualified on-call consultant’s services are required, a Task Order Solicitation Approval Form signed by the PM, the GEO Group Manager, Administrative Services, the responsible Deputy, and the City Engineer must be completed and GEO must encumber the appropriate funding through the PE before a Notice to Proceed (NTP) can be issued to the consultant. Where the estimated cost of the Task Order exceeds $100,000, a Board Report is required before an NTP can be issued.
Where GSD is used to conduct drilling or laboratory testing, their services are requested by GEO in accordance with the Memorandum of Understanding between the Geotechnical Engineering Group and the Standards Division.
RELATED PROCEDURES
Links / AttachmentS
Links
N/A
Comments