0013 CFT Geotechnical Report SIGNED.pdf

PRELIMINARY GEOTECHNICAL ENGINEERING REPORT

UNITED STATES FOREST SERVICE

CATAWBA FALLS WALKING TRAIL SLOPE STABILIZATION

OLD FORT, NORTH CAROLINA

PREPARED FOR:

TGS ENGINEERS, INC.

201 WEST MARION STREET, SUITE 200

SHELBY, NORTH CAROLINA 28150

MAY 3, 2021

CG2 PROJECT NUMBER: 240021096

2400 Crownpoint Executive Drive

Suite 800

Charlotte, NC 28227

(980) 339-8684 contact@carolinasgeotech.com www.carolinasgeotech.com

041986

May 3, 2021

Mr. Matthew Cornwell, PLS, P.E.

TGS Engineers, Inc.

201 West Marion Street, Suite 200 Shelby, North Carolina 28150

SUBJECT: Preliminary Geotechnical Engineering Report Catawba Falls Walking Trail Slope Stabilization Old Fort, North Carolina CG2 Project No.: 240021096

Dear Mr. Cornwell:

Carolinas Geotechnical Group, PLLC (CG2) has completed the subsurface exploration for the proposed slope stabilization project in Old Fort, North Carolina. Our services were performed in general accordance with the agreement between CG2 and TGS Engineers, Inc. (TGS). This preliminary report contains the results of our subsurface exploration, site characterization, engineering analyses, and recommendations for the design and construction of several slope stabilization options. Our Boring Location Plan, Soil Test Boring Records, and Rock Core Photographs are attached to this report.

We have enjoyed assisting you and look forward to working with you again on future projects. If you have any questions concerning this report, please contact us.

Sincerely, Carolinas Geotechnical Group, PLLC

Robert E. Kral, P.E. D. Matthew Brewer, P.E.

Senior Project Engineer Senior Project Engineer

NC Registration No. 041986

May 3, 2021

PPreliminary Geotechnical Engineering Report

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096

TABLE OF CONTENTS

SCOPE OF WORK

PROJECT AND SITE INFORMATION

EXPLORATION SUMMARY AND PROCEDURES

LABORATORY SERVICES

SUBSURFACE CONDITIONS

Local Physiographic Conditions and Geology

Groundwater

Interpreted Subsurface Profile

LABORATORY TEST RESULTS

GENERAL COMMENTS

Site 1

Site 2

PRELMINARY RECOMMENDATIONS

Potential Wall Options

Additional Considerations

LIMITATIONS OF REPORT

Attachments:

Figure No. 1 – Site Location Map Figure No. 2 - Boring Location Map Key to Symbols Soil Test Boring Records Rock Core Photographs GBA Important Information about This Geotechnical Engineering Report Brochure

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096

SCOPE OF WORK

CG2 was requested to perform a total of four (4) soil test borings at two sites that have historically had slope issues along the walking trail to view Catawba Falls. This preliminary report presents our exploration and testing procedures, findings and recommendations, and includes the following:

A brief description of the project site and proposed construction;

Information regarding the site conditions encountered during the exploration and geologic information relevant to the project area;

A description of the field exploration methodology and findings; and Our preliminary recommendations for the slope stabilization options.

The scope of this geotechnical exploration did not include an environmental site assessment (ESA), wetlands delineation, or pavement design. Consequently, this report does not include any information regarding the presence or absence of toxic or hazardous waste or information regarding wetland issues.

PROJECT AND SITE INFORMATION

We understand that there have been two areas along the walking trail between the first and second pedestrian bridges where the existing slopes have eroded and narrowed the access path to the Catawba Falls viewing area. We understand that the US Forest Service (USFS) wishes to maintain at least a 10-foot-wide access path from the parking area to the second pedestrian bridge location along the main trail. There are several slope stabilization options presented in this report, and we understand that final wall locations, wall type, and wall envelopes have not yet been prepared. CG2 has been provided survey files with the existing topography at each of the slope stabilization areas.

EXPLORATION SUMMARY AND PROCEDURES

CG2 performed a subsurface exploration that included a total of four (4) Standard Penetration Test (SPT) borings. Borings B-1 and B-2 were performed at the first slope area designated in this report as Site 1. These SPT rock core borings were advanced to depths ranging from 25 to 33.2 feet below existing grades. Borings B-3 and B-4 were performed at the second slope area designated in this report as Site 2. These borings were advanced to depths ranging from 15 to 16 feet below the existing ground surface. The drilling was performed by CG2’s drilling subcontractor from April 1 to April 5, 2021. A track mounted Geoprobe 7822 equipped with an automatic hammer, utilized hollow-stem augers and rock coring techniques to advance to the proposed boring termination depths. Rock coring was performed at each boring to attempt to locate the approximate bedrock boundary and determine the quality of the bedrock. The SPT core boring locations (see Boring Location Plan) were marked in the field using the provided plan, a hand-held GPS, existing topography, and aerial maps included in the attachments for reference. The boring locations and elevations should be

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096 considered approximate as no survey to obtain location and elevation data was conducted by CG2. Utilities were located by NC 811 One-Call prior to our drill crew’s mobilization to the project site. Logging and collection of samples for each boring was performed by a CG2 representative.

The SPT borings were performed in general accordance with ASTM D-1586, "Penetration Test and Split-Barrel Sampling of Soils." At regular intervals, the drilling tools were removed, and soil samples were obtained with a standard 1.4-inch I.D., 2.0-inch O.D., split-spoon sampler. The sampler was first seated six inches and then driven an additional twelve inches with blows of a 140-pound hammer falling approximately 30 inches. The number of hammer blows required to drive the sampler the final twelve inches is designated the "Penetration Resistance" or N-value. The penetration resistance, when properly interpreted, is an index to the soil strength and density.

Upon encountering refusal to the drilling equipment at each of the boring locations, NQ wireline rock coring was performed to obtain samples of the refusal material. Recovered samples of the materials obtained by rock coring were boxed and are presented on photographic logs included in the attachments.

Soil test boring records, included in the attachments to this report, graphically show the penetration resistances, groundwater levels, and present the soil and rock descriptions for the collected samples. The stratification lines and depth designations on the boring records represent the approximate boundaries between different soil types, which may not be representative of the actual boundaries.

LABORATORY SERVICES

Representative portions of the soil samples, obtained from the sampler, were placed in plastic bags and transported to our office. The samples were then examined by CG2 staff under the direction of a North Carolina Professional Engineer and presented on the soil test boring records. The soil classification was performed in general accordance with the Unified Soil Classification System (USCS) and ASTM D-2488. A summary of the soil classifications is included on the respective soil test boring records as attachments to this report. Four rock core samples were selected for unconfined compressive strength testing. The results of the unconfined compressive strength testing for each specimen is included on each of the respective soil test boring records.

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096

SUBSURFACE CONDITIONS

Local Physiographic Conditions and Geology

Available geologic information from the US Geological Survey indicates the geology of the project area consists of the Alligator Back Formation which is typically characterized by massive gneiss but also includes shists, phyllite, and amphibolite. Based on the recovered rock core, much of the materials were classified as Biotite Gneiss and Granitic Gneiss of the Alligator Back Formation. Quartz veins and trace amounts of biotite, muscovite, and phyllite are present. Available literature also indicates the project area is located on a post-metamorphic thrust fault between the Blue Ridge Belt and Chauga Belt. This has been associated as one of the boundaries between the Blue Ridge Belt and the inner piedmont.

Much of the topography found throughout the Blue Ridge Physiographic Province has developed from differential weathering of predominantly igneous and metamorphic rock formations. Due to the continued chemical and physical weathering, the parent rocks in the Blue Ridge Physiographic Province are generally covered with a mantle of soil that has weathered in-place from the parent rocks below. These soils have variable thicknesses and are commonly referred to as residual soils. Residual soils in this area typically contain higher fines content near the ground surface because of the advanced weathering. It is also typical that residual soils contain larger particle sizes with increasing depth becoming more coarse-grained as the amount of weathering decreases. As weathering decreases with depth, residual soils generally retain the overall appearance, texture, gradation, and foliations of the parent rock.

Groundwater

Since water was introduced into the boreholes during rock coring, groundwater level measurements were not attempted in the borings at the completion of drilling operations. For safety reasons, the borings were backfilled immediately upon completion of drilling activities. We do not expect groundwater to impact construction.

The moisture descriptions of the soil samples encountered in the borings were noted as dry to moist.

Sometimes, the presence of wet soils can indicate the proximity to the natural groundwater elevation. Also, soils that are observed to be moist or wet sometimes require additional manipulation of the soil moisture during construction in order to obtain the specified level of compaction. Most of the borings caved in the bedrock portion of the boring.

Please note that water levels tend to fluctuate with seasonal and climatic variations, as well as with some types of construction operations. Therefore, groundwater may be encountered during construction at depths not indicated by the borings.

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096

Interpreted Subsurface Profile

Details of the subsurface conditions encountered by the borings are shown on the soil test boring records in the attachments. These records represent our interpretation of the subsurface conditions based upon field data. Stratification lines on the soil test boring records represent approximate boundaries between soil behavior types; however, the actual transition may be gradual. The general subsurface conditions and their pertinent characteristics are discussed in the following paragraphs.

Residual soils were encountered at Borings B-1 and B-2 at Site 1 and consisted of loose to very dense silty sand (SM) and medium stiff sandy silt (ML). The residual soils extended to depths ranging from approximately 6 to 10.1 feet below existing grades. The SPT N-values in the residual soils ranged from 6 to 62 blows per foot (bpf).

When SPT sampling is performed in residual soils resulting in blow counts that exceed 50 blows with less than six inches of penetration, that material is considered Partially Weathered Rock (PWR). PWR was encountered in Borings B-1 and B-2 at Site 1. The PWR layer is typically a transition layer between the residual soil and the parent bedrock and can be somewhat inconsistent with location, elevation, and relative density/stiffness. The majority of the PWR encountered was sampled as silty sand.

When SPT sampling was performed resulting in blow counts that exceed 50 blows with less than 1 inch of penetration, the material is considered part of the parent rock. The borelogs describe the rock as Crystalline based on the rock type and structure. Some of the project material encountered could not be penetrated with the drill rig equipment and traditional drilling techniques used on the project such as augers. In some instances, these impenetrable materials can consist of large boulders, rock ledges, lenses, seams, or the top of parent bedrock. Rock core drilling techniques were utilized to evaluate the character and continuity of the refusal materials. Rock coring was performed by CG2 at Borings B-1, B-2, B-3, and B-4. As previously discussed, the recovered rock observed at the project site included Biotite Gneiss and Granitic Gneiss of the Alligator Back Formation.

Table No. 1 presents the existing ground surface elevations based on available topographic survey, the estimated depth to crystalline rock, the total rock core obtained, rock core Recovery, and Rock Quality Designation at each of the four (4) test locations. The Recovery (REC) percentage included in the table is defined as the length of the recovered core divided by the length of the core run. The Rock Quality Designation (RQD) is defined as the total length of recovered pieces longer than 4 inches divided by the length of the core run. The RQD gives a relative indication of the degree of fracturing, soundness, and continuity of the rock.

Bore logs and rock core photos for each of the borings discussed below are attached to this preliminary report.

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096

Table No. 1: Rock Core Summary

Boring

ID

Ground Surface

Elevation (feet)

Depth to Crystalline Rock

(feet)

Rock Core Depth (feet)

Cumulative Rock Core

Recovery (REC)

Cumulative Rock Quality Designation (RQD)

B-1 1,682 19.2 14.0 71.7% 24.8% B-2 1,684 13.5 10.0 100.0% 46.2% B-3 1,807 0.0 15.0 91.0% 73.2% B-4 1,808 1.0 15.0 98.0% 91.2%

LABORATORY TEST RESULTS

Table No. 2 presents a summary of the lab testing performed on the recovered rock core specimens. The summary includes the boring number, test specimen sample number, unconfined compressive strength, and unit weight for each specimen tested.

Table No. 2: Laboratory Test Results

Boring

ID

Sample Reference Number

Sample Depth (feet)

Unconfined Compressive Strength (psi (ksf))

Sample Unit Weight (pcf)

B-1 RS-1 27.9 - 28.8 3,700 (533) 159.6

B-2 RS-2 15.6 - 16.2 10,280 (1,480) 166.6

B-3 RS-3 1.9 - 2.8 18,080 (2,604) 166.2

B-4 RS-4 2.3 - 2.7 13,250 (1,908) 165.5

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096

GENERAL COMMENTS

Site 1

The subsurface investigation revealed approximately 6 to 10 feet of residual soils overlying PWR and bedrock in this area. Boring B-1 and B-2 revealed highly weathered PWR to depths ranging from 13.5 to 19.2 feet below existing grades. Rock core recovery and rock quality in Boring B-1 between 19.2 feet and 24.2 feet was also very poor, indicating the presence of decomposed rock. Based on the provided topographic survey, a 10-foot-wide path could be established with a wall having an exposed height on the order of 5 feet or less.

Additionally, a 4-foot-wide bench should be constructed in front of the wall to provide additional stability and the face of the wall should be embedded below grade at least 1 to 2 feet depending on wall type selected. A potential wall alignment for this site has been included on the provided Boring Location Plan.

Site 2

The subsurface investigation revealed the presence of competent bedrock at the ground surface or very close to the ground surface at Borings B-3 and B-3. Based on the provided topographic survey, a 10-foot-wide path could be established with a wall with an exposed height on the order of 8 to 10 feet. Additionally, a 4-foot-wide bench constructed in front of the wall does not appear feasible at this site due to the subsurface conditions encountered in the borings. A potential wall alignment for this site has been included on the provided Boring Location Plan.

PRELIMINARY RECOMMENDATIONS

Our preliminary recommendation options presented in the following sections are based upon the conditions observed in the borings at each site and our visual observations at each area. We have provided general recommendations for various options that could be utilized to provide a widened path at each site.

Once the specific options are selected and additional information is available, we request the opportunity to provide final recommendations for construction, estimated construction quantities, and construction notes for each site. In addition, if a wall option is selected, we request that a wall envelope be prepared to aid us in preparation of final recommendations and quantities.

Potential Wall Options

Site 1: Gabion Wall Option It is our opinion a gravity wall, such as a gabion basket type wall, could be utilized at this site. Construction of the gravity wall in this location would require excavation of some of the soils along the slope and constructing an access path to the proposed bottom of wall location in order to construct the wall. Gabion walls are composed of rows and tiers of orthogonal wire cages or baskets filled with crushed rock and tied together. They are widely used for earth retaining structures on land, particularly in rugged terrain. Gabion walls are free-draining and with time the stones tend to collect soil and promote vegetation, which improves the wall aesthetics (FHWA 1999). Additionally, driven anchors can be installed

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096 through gabion walls to provide additional resistance to sliding and/or overturning, if needed. As previously discussed, we recommend a 4-foot-wide bench be constructed along the toe of the wall and that the wall foundation be embedded at least 2 feet below existing grade. We also recommend installing a fence or handrail at the top along the top of the wall.

Site 1 & Site 2: Soldier Pile Wall Option A soldier pile wall with timber lagging could also be utilized at either site. The constructed wall would require excavated holes at regular spacing along the length of the wall, typically 4 to 8 feet on center. The holes are typically 18 to 24 inches in diameter. Once the holes are drilled, steel H-piles are installed into the excavations and concrete is used to backfill the boreholes to the bottom of wall elevation after the pile has been placed. The remainder of the borehole can typically be backfilled to existing grade with either excavatable flowable fill or concrete. Once piles are installed, timber lagging is installed between the piles forming the face of the wall. This type of wall installation method is useful when site conditions require top-down construction methods, such as Site 2. Pile installation will require special attention during construction to assure that newly placed concrete is not damaged by adjacent pile installation. Additionally, construction of this type of wall in these two remote locations could require specialized equipment and specialized geotechnical contractors. We also recommend installing a fence at the top along the top of the wall.

If the soldier pile option is selected at either site, we recommend utilizing timber lagging between pile locations. Timber lagging has an approximate design life of 20 to 25 years, depending on site conditions, and will require periodic observation and monitoring for potential damage or deterioration. If this wall option is selected, we recommend that a drainage system be designed to prevent the building up hydrostatic pressures against the back of the wall. Timber lagging should be used in relatively dry environments due to the deteriorating effects of water. The timber lagging utilized should be pressure treated and additional care should be taken to maintain the facing of the wood lagging throughout the life of the structure. Areas showing signs of degradation will need to be repaired. Timber lagging selection and maintenance should be performed in accordance with FHWA guidelines. Concrete panels could also be utilized for an increased life span.

Additional Considerations

At Site 1, there is an existing cut slope just north of the slide area that appears to be composed mostly of soil.

It may be more economical to cut into the existing slope and shift the walking trail away from the slide area at this site. This option could also be used in conjunction with a short wall with a fence or handrail for fall protection at the slide area in order to shift the traveling public further away from the area of concern.

At Site 2, available width along the existing path is limited, and construction of the recommended type of wall will be costly. An additional option for consideration at Site 2 is to construct a raised boardwalk with the

Catawba Falls Walking Trail Slope Stabilization, Old Fort, North Carolina

CG2 Project No. 240021096 desired width to create a walking path through this area. A portion of the boardwalk could potentially be cantilevered over the existing slide area to provide the desired walking path width while providing a safe walking path for the public. A boardwalk of this nature could likely be supported on concrete footings anchored/embedded into rock or drilled-in foundations such as micro-piles. This could be a more economical alternative and longer-term solution to the wall option previously presented for this site.

LIMITATIONS OF REPORT

This report does not reflect variations that may occur between borings, across the site, or due to the modifying effects of weather or construction. If conditions at the site vary during construction, we should be immediately notified so further evaluation or supplemental recommendations can be provided.

This preliminary report has been prepared in accordance with generally accepted geotechnical engineering practice for specific application to this project. The information contained in this preliminary report were based on the applicable standards of our profession in this geographic area at the time this report was prepared. No other warranty, expressed or implied, is made.

ATTACHMENTS

NTS

DMB

REK

4/30/2021

240021096

SITE LOCATION PLAN

Catawba Falls Walking Trail Slope Stabilization

Old Fort, North Carolina

FIGURE NO.SCALE:

DRAWN BY:

CHECKED BY:

DATE:PROJECT NO.:

Approximate Site Location

NTS

DMB

REK

4/30/2021

240021096

BORING LOCATION PLAN

Catawba Falls Walking Trail Slope Stabilization

Old Fort, North Carolina

FIGURE NO.SCALE:

DRAWN BY:

CHECKED BY:

DATE:PROJECT NO.:

LEGEND

APPROXIMATE BORING LOCATION

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SITE 2

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Geotechnical-Engineering Report Important Information about This

Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.

While you cannot eliminate all such risks, you can manage them. The following information is provided to help.

The Geoprofessional Business Association (GBA) has prepared this advisory to help you – assumedly a client representative – interpret and apply this geotechnical-engineering report as effectively as exposure to problems associated with subsurface conditions at project sites and development of them that, for decades, have been a principal cause of construction delays, cost overruns, claims, and disputes. If you have questions or want more information about any of the issues discussed herein, contact your GBA-member geotechnical engineer.

Active engagement in GBA exposes geotechnical engineers to a wide array of risk-confrontation everyone involved with a construction project.

Understand the Geotechnical-Engineering Services Provided for this Report Geotechnical-engineering services typically include the planning, collection, interpretation, and analysis of exploratory data from widely spaced borings and/or test pits. Field data are combined with results from laboratory tests of soil and rock samples obtained from field exploration (if applicable), observations made during site reconnaissance, and historical information to form one or more models of the expected subsurface conditions beneath the site. Local geology and alterations of the site surface and subsurface by previous and proposed construction are also important considerations. Geotechnical engineers apply their engineering training, experience, and judgment to adapt the requirements of the prospective project to the subsurface model(s). Estimates are made of the subsurface conditions that will likely be exposed during construction as well as the expected performance of foundations and other structures being planned and/or affected by construction activities.

The culmination of these geotechnical-engineering services is typically a geotechnical-engineering report providing the data obtained, a discussion of the subsurface model(s), the engineering and geologic engineering assessments and analyses made, and the recommendations developed to satisfy the given requirements of the project. These reports may be titled investigations, explorations, studies, assessments, or evaluations.

Regardless of the title used, the geotechnical-engineering report is an engineering interpretation of the subsurface conditions within the context of the project and does not represent a close examination, systematic inquiry, or thorough investigation of all site and subsurface conditions.

Geotechnical-Engineering Services are Performed

Geotechnical engineers structure their services to meet the specific needs, goals, and risk management preferences of their clients. A geotechnical-engineering study conducted for a given civil engineer will not likely meet the needs of a civil-works constructor or even a different civil engineer. Because each geotechnical-engineering study is unique, each geotechnical-engineering report is unique, prepared solely for the client.

Likewise, geotechnical-engineering services are performed for a specific project and purpose. For example, it is unlikely that a geotechnical-engineering study for a refrigerated warehouse will be the same as one prepared for a parking garage; and a few borings drilled during a preliminary study to evaluate site feasibility will not be adequate to develop geotechnical design recommendations for the project.

Do not rely on this report if your geotechnical engineer prepared it:

• for a different client;

• for a different project or purpose;

• for a different site (that may or may not include all or a portion of the original site); or

• before important events occurred at the site or adjacent to it;

e.g., man-made events like construction or environmental remediation, or natural events like floods, droughts, earthquakes, or groundwater fluctuations.

Note, too, the reliability of a geotechnical-engineering report can be affected by the passage of time, because of factors like changed subsurface conditions; new or modified codes, standards, or regulations; or new techniques or tools. If you are the least bit uncertain about the continued reliability of this report, contact your geotechnical engineer before applying the recommendations in it. A minor amount of additional testing or analysis after the passage of time – if any is required at all – could prevent major problems.

Read this Report in Full Costly problems have occurred because those relying on a geotechnical-engineering report did not read the report in its entirety. Do not rely on an executive summary. Do not read selective elements only. Read and refer to the report in full.

You Need to Inform Your Geotechnical Engineer About Change Your geotechnical engineer considered unique, project-specific factors when developing the scope of study behind this report and developing the confirmation-dependent recommendations the report conveys.

Typical changes that could erode the reliability of this report include those that affect:

• the site’s size or shape;

• the elevation, configuration, location, orientation, function or weight of the proposed structure and the desired performance criteria;

• the composition of the design team; or

• project ownership.

As a general rule, always inform your geotechnical engineer of project or site changes – even minor ones – and request an assessment of their impact. The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical engineer was not informed about developments the engineer otherwise would have considered.

Most of the “Findings” Related in This Report Are Professional Opinions Before construction begins, geotechnical engineers explore a site’s subsurface using various sampling and testing procedures. Geotechnical engineers can observe actual subsurface conditions only at those specific locations where sampling and testing is performed. The data derived from that sampling and testing were reviewed by your geotechnical engineer, who then applied professional judgement to form opinions about subsurface conditions throughout the site. Actual sitewide-subsurface conditions may differ – maybe significantly – from those indicated in this report. Confront that risk by retaining your geotechnical engineer to serve on the design team through project completion to obtain informed guidance quickly, whenever needed.

This Report’s Recommendations Are

The recommendations included in this report – including any options or alternatives – are confirmation-dependent. In other words, they are not final, because the geotechnical engineer who developed them relied heavily on judgement and opinion to do so. Your geotechnical engineer can finalize the recommendations only after observing actual subsurface conditions exposed during construction. If through observation your geotechnical engineer confirms that the conditions assumed to exist actually do exist, the recommendations can be relied upon, assuming no other changes have occurred. The geotechnical engineer who prepared this report cannot assume responsibility or liability for confirmation-dependent recommendations if you fail to retain that engineer to perform construction observation.

This Report Could Be Misinterpreted Other design professionals’ misinterpretation of geotechnical-engineering reports has resulted in costly problems. Confront that risk by having your geotechnical engineer serve as a continuing member of the design team, to:

• confer with other design-team members;

• help develop specifications;

• review pertinent elements of other design professionals’ plans and specifications; and

• be available whenever geotechnical-engineering guidance is needed.

You should also confront the risk of constructors misinterpreting this report. Do so by retaining your geotechnical engineer to participate in prebid and preconstruction conferences and to perform construction-phase observations.

Give Constructors a Complete Report and Guidance Some owners and design professionals mistakenly believe they can shift unanticipated-subsurface-conditions liability to constructors by limiting the information they provide for bid preparation. To help prevent the costly, contentious problems this practice has caused, include the complete geotechnical-engineering report, along with any attachments or appendices, with your contract documents, but be certain to note conspicuously that you’ve included the material for information purposes only. To avoid misunderstanding, you may also want to note that “informational purposes” means constructors have no right to rely on the interpretations, opinions, conclusions, or recommendations in the report. Be certain that constructors know they may learn about specific project requirements, including options selected from the report, only from the design drawings and specifications. Remind constructors that they may perform their own studies if they want to, and be sure to allow enough time to permit them to do so. Only then might you be in a position to give constructors the information available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions. Conducting prebid and preconstruction conferences can also be valuable in this respect.

Read Responsibility Provisions Closely Some client representatives, design professionals, and constructors do not realize that geotechnical engineering is far less exact than other engineering disciplines. This happens in part because soil and rock on project sites are typically heterogeneous and not manufactured materials with well-defined engineering properties like steel and concrete. That lack of understanding has nurtured unrealistic expectations that have resulted in disappointments, delays, cost overruns, claims, and disputes.

To confront that risk, geotechnical engineers commonly include explanatory provisions in their reports. Sometimes labeled “limitations,” many of these provisions indicate where geotechnical engineers’ responsibilities begin and end, to help others recognize their own responsibilities and risks. Read these provisions closely. Ask questions.

Your geotechnical engineer should respond fully and frankly.

Geoenvironmental Concerns Are Not Covered The personnel, equipment, and techniques used to perform an environmental study – e.g., a “phase-one” or “phase-two” environmental site assessment – differ significantly from those used to perform a geotechnical-engineering study. For that reason, a geotechnical-engineering report does not usually provide environmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated subsurface environmental problems have led to project failures. If you have not obtained your own environmental information about the project site, ask your geotechnical consultant for a recommendation on how to find environmental risk-management guidance.

While your geotechnical engineer may have addressed groundwater, water infiltration, or similar issues in this report, the engineer’s services were not designed, conducted, or intended to prevent migration of moisture – including water vapor – from the soil through building slabs and walls and into the building interior, where it can cause mold growth and material-performance deficiencies.

Accordingly, proper implementation of the geotechnical engineer’s recommendations will not of itself be sufficient to prevent moisture infiltration. Confront the risk of moisture infiltration by including building-envelope or mold specialists on the design team.

Geotechnical engineers are not building-envelope or mold specialists.

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Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation.

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