Geotechnical Investigations

Summary of Expertise

  • Foundation Investigations
  • Settlement Evaluations
  • Slope-Stability Investigations

Some architects for a tower in the town of Pisa, Italy are rumored to have decided that detailed geotechnical investigations were superfluous. Although their structure became famous, yours may not be so lucky. Our engineers can assist in your foundation investigations, as evidenced by the following experience:

BRIDGE CAPACITY EVALUATION AND RECOMMENDATIONS.  Structural and geotechnical evaluations were conducted by EarthFax and one of its subcontractors on a private single-lane bridge spanning the South Fork of the Provo River.  The evaluations were performed to determine the weight capacity of the bridge in response to concerns about heavy vehicle traffic crossing the bridge during construction activities performed within a utility easement located west of the bridge.  EarthFax performed the geotechnical evaluation to assess the support structures of the bridge and their associated bearing areas, footing geometry, bearing depth, and soil types.  This information was used to calculate an allowable bearing capacity and geotechnical capacity.  Structural components of the bridge were evaluated by a subcontractor to determine the actual load limits of the bridge and determine whether these were adequate for federal highway loading requirements.  Although the bridge appeared structurally sound and load limits were similar to maximum federal highway loading requirements, recommendations included specifications for repairing some minor erosion between two of the bridge footings as a preventative measure.

GEOLOGIC HAZARDS EVALUATION FOR A PIPELINE REPLACEMENT PROJECT. EarthFax performed geologic hazards analyses for replacement of a natural-gas pipeline in Weber Canyon, Utah. The analyses were performed at several locations including creek crossings, wetlands, fault lines, landslides, and steep embankments. Work included researching published geological data, reviewing aerial photographs, and performing a field reconnaissance. These activities resulted in identification of geologic hazards that included areas of active faulting, areas of significant liquefaction potential, areas of weakened structural strength of soils due to stream bank erosion, areas with a significant potential for landslide activity, and areas of potential erosion due to steep embankments. Recommendations were provided to mitigate these risks and, in many instances, EarthFax assisted the client by providing mitigation designs and having personnel on site to inspect mitigation construction activities. In at least two locations, the pipeline crossed a major irrigation canal located along the south slope of the canyon. At these locations, EarthFax provided recommendations to properly backfill the pipeline trench so that the pipeline would be well anchored beneath the canal and settlement of backfilled soils beneath the canal would be minimized.

EVALUATION OF GEOLOGIC HAZARDS FOR REPLACEMENT OF A PIPELINE IN THE VICINITY OF UNDERGROUND MINES. EarthFax performed a geologic hazards assessment to identify fault locations, evaluate current and historic underground mining activities, and quantify potential mine-related subsidence along a 5-mile segment of a proposed natural-gas pipeline replacement project. Recommendations provided to the client included mitigation design standards and methods for protecting the pipeline from failure due to subsidence, seismic activity, and other geologic hazards.

GEOTECHNICAL INVESTIGATION FOR A PROPOSED STORAGE TANK. EarthFax performed a geotechnical investigation for a proposed 840,000-gallon crude oil storage tank located in northwestern Colorado. The proposed tank is 60 feet in diameter with a 40-foot high internal floating roof tank to be placed on a foundation of compacted structural fill and a concrete ring-wall. The tank is to be located at the site of a former 420,000-gallon crude oil storage tank that was previously demolished. Because the new tank will have a slightly larger diameter than the previous tank, the geotechnical investigation took into account the potential for differential settlement within the footprint of the new tank due to more densely compacted soil beneath the former tank. EarthFax supervised the installation of two borings within the footprint of the proposed tank to evaluate the continuity of soil types and the soil?s engineering properties. One boring was advanced near the center of the previous tank and the other boring was advanced in a location outside the footprint of the previous tank where soil had not been affected by the tank?s previous loading. During drilling activities, EarthFax logged the borings, performed Standard Penetration Tests, collected soil samples and described the soils using the Unified Soil Classifications. Laboratory testing of soil samples collected at the site included Atterberg Limits, Standard Consolidation, Unconsolidated Undrained Shear Strength, Swell Potential, pH, Soluble Sulfates, Soluble Chloride, and Resistivity. These analyses were made to determine subsurface conditions, soil engineering properties, settlement potential, allowable bearing capacity, seismic conditions, soil expansion and shrinkage potential, and soil corrosion potential. Using these determinations, observations made in the field, and literature reviews, EarthFax modeled the soil response to various conditions (full of water during hydrotesting, multiple levels of crude storage, etc.) and made recommendations for construction of the tank foundation. We also provided construction inspection and quality assurance guidelines to ensure that the foundation would not settle excessively following construction of the tank. Recommendations included requirements for excavation, subgrade preparation, backfill, lateral loads and friction, seismic design, and surface drainage controls.

ENGINEERING AND CONSTRUCTION INSPECTION FOR A SOLDIER PILE WALL. EarthFax provided geotechnical and geologic investigation, engineering design, and inspection services during construction of a series of soldier pile walls along the south side of Weber Canyon in northern Utah. The project was undertaken to protect a newly installed 16-inch diameter crude oil pipeline by increasing slope stability along a 1700-foot stretch of the canyon wall that was unstable and had experienced several recent and historic landslides. Design efforts also took into consideration the need to protect existing utilities, railroad tracks, roadways, and the Weber River that are located in close proximity to the project. The soldier pile wall included installation of 30-foot H-piles, pre-cast concrete panels that were constructed on site and placed between the H-piles, cable tie-backs installed at 5 degrees off of horizontal to a maximum distance of 90 feet, and walers installed intermittently along the wall to provide structural support for the cable tie backs. Following re-grading of soils above and below the soldier pile wall, a 6-12-inch layer of topsoil and pre-seeded vegetative mats were installed to facilitate rapid re-vegetation of disturbed soils, thus enhancing soil stability and visual aesthetics in the area of the wall. To assist in monitoring the stability of the slope after construction activities were completed, EarthFax installed four cable inclinometers at strategic locations above and below the wall with coaxial cable from each inclinometer attached to a solar powered consol that is linked via radio signal to the pipeline Simultaneous Computer Assisted Data Acquisition System. Information gathered from the cable inclinometers is used to alert pipeline personnel when soil movement rates at the site would be considered a concern to the stability and integrity of the slope. The scope of work completed by EarthFax includes geologic mapping in the area of the proposed soldier pile wall, interpretation of causative factors at existing landslides in the area, geomorphic mapping of areas at risk of experiencing future landslides, supervision of earthwork and reclamation activities, installation of cable inclinometers, and interim monitoring of slope movement during construction of the project.

GEOTECHNICAL INVESTIGATION FOR A PIPELINE UPGRADE. EarthFax conducted a geotechnical investigation to support the installation of a new section of pipe to upgrade an existing crude-oil pipeline in the Wasatch Mountains east of Salt Lake City, Utah. The goal of the project was to evaluate the feasibility of horizontal drilling to install the 2,500-foot section of pipeline beneath Interstate Highway 80 near the summit of Parley’s Canyon in Summit County. We installed five borings in soil and weathered rock, at depths of up to 64 feet in terrain with slopes exceeding 20%. We took special care during drilling to minimize damage to the high elevation protected watershed in which the pipeline had been installed. Based on data we obtained from the drilling project, we were able to shorten the extent of required horizontal drilling. EarthFax also assisted the client with the preparation of discharge permits and the disposal of the drilling mud to ensure protection of the sensitive watershed.

SETTLEMENT MITIGATION RECOMMENDATIONS FOR A PETROLEUM PIPELINE. EarthFax provided settlement mitigation recommendations for a petroleum pipeline company located in the U.S. and Canada. This work was completed for a section of crude oil pipeline in Missouri that had experienced differential settling related to previous construction of a pump station facility. Although footings for the pump station and associated inbound/outbound pipeline supports were constructed on bedrock, the remainder of the pipeline was supported by native clay overlying bedrock. The weight of the backfill material overlying the pipeline caused differential settling near the pipe supports, thus causing deformation of the pipeline. Recommendations were made for mitigating differential settlement caused by compression of native soils beyond the pipe supports that are adjacent to the pump station. These included alternative measures to allow for flexibility in addressing concerns about site safety, effectiveness of remedial measures implemented, and construction costs.

GEOTECHNICAL INVESTIGATION FOR CONSTRUCTION OF A UTILITIES TUNNEL. EarthFax conducted a geotechnical investigation to assist in the design of a new 500-foot long utilities tunnel at the College of Eastern Utah. The investigation provided the design engineers and construction contractors with sufficient information to select the most cost-effective tunnel system, to design the anchorage system for the tunnel, and to identify any slope stability or groundwater problems that might be associated with design and construction activities. Our scope of work included using a direct-push drill rig to advance soil borings and collect continuous core samples for evaluation of soil engineering properties, logging soils according to the Unified Soil Classification System, installing piezometers in the bore holes, performing slug tests in the piezometers to establish the hydraulic characteristics of the subsurface soils, reviewing previous geotechnical reports adjacent to the site to determine soil strength parameters, and conducting slope stability analyses of the excavation to determine excavation slope and setback requirements. Using this information, we recommended anchor depths and capacities to resist buoyant forces that may exist at the site, and developed excavation and sloping requirements.

FOUNDATION INVESTIGATION OF A PROPOSED HAZARDOUS WASTE INCINERATOR. Cursory foundation investigations were performed at three potential sites for locating a proposed hazardous waste incinerator in western Utah. Each site was drilled and subsurface samples were collected to determine the engineering properties of the local soils. Field tests were performed and the sites were ranked according to the geotechnical properties of the soils. Based on this ranking, one of the sites was selected for future development by the client. Detailed foundation investigations were then performed at the selected site. These investigations involved the installation and sampling of test pits as well as the performance of field and laboratory tests on the local soils. Recommendations were made for use of soil materials beneath structure foundations to minimize settlement potentials, including delineation of potential borrow sources. Footings types were recommended for each structure. The base, subgrade, and pavement for an access road were also designed. Construction inspection services were provided during rough grading and foundation construction at the site. Soil materials to be used at the site were inspected for compliance with the specifications. Design changes were recommended to the client where required. Liaison was provided between the owner and the contractor to ensure that specifications and plans were followed. Field testing was coordinated and interpreted.

FOUNDATION INVESTIGATIONS FOR A PETROLEUM REFINERY. Foundation investigations were performed to accommodate facility expansion at a petroleum refinery in northern Utah. Several hollow-stem auger holes were drilled, representative and undisturbed soil samples were collected, and field and laboratory data were interpreted. Recommendations were provided for foundation design to minimize settlement of facilities to be constructed on soft, saturated soils. These recommendations included strip footings, mat foundations, and piles. Pile-load testing was then supervised and the data were interpreted to assist in structural design of the process facilities.

FOUNDATION INVESTIGATIONS OF COMMERCIAL AND RESIDENTIAL PROPERTIES. Several existing and proposed commercial and residential properties have been examined to determine foundation conditions and potential problems due to development. Both surface and subsurface conditions have been evaluated. Problems addressed have included potential faulting, liquefaction, bearing capacities, high water tables, and collapsible soils. Recommendations have been made for correcting foundation problems where they existed.

SETTLEMENT EVALUATIONS OF WASTE-DISPOSAL FACILITIES. Detailed subsurface investigations have been performed at the sites of existing and proposed facilities used for the disposal of radioactive and hazardous wastes. The purpose of these investigations was to evaluate the sites for potential settlement following facility construction and/or attainment of final design conditions. Samples were collected and submitted for laboratory analyses. The resulting data were interpreted and calculations were performed to determine the magnitude of probable settlement to be experienced by the facilities. Modifications in cap designs were made as necessary to ensure that settlement would not compromise the integrity of the cap materials.

SLOPE STABILITY INVESTIGATIONS. Embankment stabilities have been examined for several proposed and existing sedimentation ponds at existing and proposed underground coal and mineral mines. Investigations have also been performed to assess the stability of road embankments, cut and fill slopes associated with a variety of mining and industrial facilities, and embankments associated with holding ponds and waste-disposal cells. Samples of the local soils were collected, cross sections were surveyed, depth to bedrock was determined, and design conditions (high water elevations, earthquake conditions, rapid drawdown conditions, etc.) were selected. The embankments were then modeled to determine slope stability under the various design conditions.

GEOTECHNICAL INVESTIGATION IN SUPPORT OF PIPELINE INTEGRITY MODELING.  EarthFax performed a geotechnical investigation to support a soil-pipe interaction model being developed by a pipeline company’s integrity management consultant. The project was focused on three pipelines located in potentially unstable geologic conditions where underground mining was being performed.  Mining methods in the area of concern include mine-and-pillar and longwall methods.  Each of these methods creates potential for ground subsidence that could negatively impact the pipelines.  To better understand the soil dynamics at work in this area and the potential effects of historic and future subsidence on the pipelines, strain gauges were installed on the pipelines.  As excavations were advanced to install the strain gauges, EarthFax logged and sampled the soils.  We also collected soil samples from among the highest-strength soils so that worst-case conditions for a seismic event could be modeled.  Samples were analyzed for Atterberg limits, grain size distribution, moisture content and soil density, direct shear strength, and unconfined compression strength.  EarthFax made detailed soil observations as the strain gauge excavations were advanced and verified that placement of the strain gauges accurately represented the variability of soils throughout the project area. Site mapping, analytical results, and field observations were presented in the geotechnical investigation.  This information was used to support the soil-pipe interaction model.

PROBABLE MAXIMUM SUBSIDENCE DETERMINATIONS FOR A PROPOSED PIPELINE ALIGNMENT.  EarthFax determined the probable maximum subsidence that could occur above active underground mine works in the event of a mining-induced subsidence event.  The project was performed for a pipeline company and included evaluating a six-mile segment of the proposed pipeline alignment where it crosses above the underground mine works.  An accurate set of mine plans was not available to EarthFax for this project, requiring us to develop inferred mine plans from available information sources based on plans for other areas of the mine, a year-by-year history of areas mined, and projections of future areas to be mined.  Using information from the inferred mine plans and applying technical parameters from the mine into conventional subsidence calculations for longwall coal mining, we calculated a theoretical predicted subsidence from longwall mining beneath the proposed pipeline alignment.  By adjusting the calculated theoretical predicted subsidence with actual field measured subsidence values, we predicted the probable maximum subsidence from the mine site.  Successful completion of this project helped the client evaluate the feasibility of the proposed pipeline alignment.

FAULT INVESTIGATIONS FOR A PROPOSED PIPELINE ALIGNMENT.  EarthFax performed investigations to identify Quaternary and ancient geologic faults along the proposed alignment route for a new pipeline.  The investigation included conducting research and performing field surveys to identify faults and determine whether any of the identified faults were considered active.  Where active faults were identified, they were evaluated to determine whether they had recently been reactivated and may have induced noticeable surface deformations in nearby ancient faults.  EarthFax provided the client with a determination of risk associated with faults in the vicinity of the proposed alignment route.

 

 

 


 

 

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7324 South Union Park Ave., Midvale, Utah 84047 | Phone: 801-561-1555

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