After other ground penetrating radar providers failed, US Steel called in the experts. GPR Data LLC responded immediately to Indiana, to resolve a series of concerns in the concrete slab floor of the electrical room in a factory building.

Objective

Evaluate thickness of concrete slab and locate safe coring positions to add drainage for intruding ground water. Provide a safe drilling plan with locations for pressure grouting and waterproofing the underside of slab.

Challenge

Most importantly, this slab is laced with extremely high voltage electrical conduits. Failure is potentially catastrophic. The floor slab in these areas averages seven feet thick but varies by up to a foot. Concrete mix was high in sulfer, which attenuates the radar signal. Visibility is impeded by a great deal of near-surface rebar, and compounded by slag used as random filler during the original pour.

Results

The majority of the substation floor was mapped with high precision and accuracy. Evaluating slab thickness and conduit density in various areas, drainage core locations were selected and drilled. The bottom of slab was hit within one inch of projection with zero conflict. GPR Data provided on-site assistance throughout the drilling and grouting process, and have subsequently completed a second substation remediation project as well.

A sample of target analysis for one area of the floor follows, showing both a top-down plan view and an (X,Y,Z) orthoginal view of target depths.

Montana Rail Link Bridge 209 was constructed in 1908 and is situated 12.2 miles north east of St. Regis, MT. on the Clark Fork River. It is a four span railroad bridge resting on concrete piers. Pier 3 is located in the middle of the Clark Fork River and is the center of this GPR evaluation. Over time the upstream face of the pier has experienced the most dramatic weathering and erosion. A large scour was discovered on the southeast portion of the upstream face towards the base of the pier. During a construction phase of stability upgrades to Pier 3, wooden timber fragments were discovered while installing micro pile along the sides of the pier. The wooden fragments were at a depth of 8.0’ to 10.0’ below river bottom and came up in drill tailings on both sides of the pier. Upon discovering this wooden material, drilling was halted in order to determine if the wooden material are pieces of the original structural piling installed when the pier was constructed or unrelated construction debris. It was assumed that the original wooden piles around the base of the pier had been eroded away and were no longer there.

Objective

Use ground penetrating radar to find location and orientation of wooden pilings.

Findings

GPR Data:

• provided our client with images of the wooden pilings beneath the pier.
• proved that the pilings were at an angle which extended underneath the pier.
• proved that on the upstream side, wooden pilings are still embedded in the pier body.

The Booth Kelly Lumber Mill in Springfield is a historical icon, dating back to the late 1800's. As the years passed, numerous fires engulfed the mill, and each time the remnants were typically plowed under and the structures rebuilt. As utilities were added and replaced, old pipes were sometimes abandoned, sometimes only partially removed. In the end, no cohesive record of utilities was retained, and subsurface relics and debris were anyone's guess.

Objective

Promote future development in a historic and underused site:

• 1) Recreate as-built diagrams of underground utilities.
• 2) Map all significant unnatural subsurface features.
• 3) Conduct a complete GPR survey of a 400' x 200' area.

Findings

A series of as-built information was generated from this 3D Ground Penetrating Radar utility mapping survey. Pipe locations are shown in the four subgrids on the left, while amplitude maps describe subsurface features in the six subgrids to the right. A sampling follows:

Background

Creating a deterioration map of a bridge deck is a relatively straightforward process for any good GPR company. The technology is extremely well suited to the task. However, all turn-key GPR systems and training are designed for rectangular collections. The reality of roadbeds and bridge decks poses a challenge then, as there is often a varying degree of curvature. In many cases, this bend is shallow enough to be safely ignored, but sometimes it is not...

Experience

On a recent project in Oregon, GPR Data LLC was tasked with mapping a horseshoe-shaped bridge deck, specifically the area just offset from the apex of the bend. In linear terms, the collection area was roughly 200' long. A sample of the working plans was provided, as copied below with selective blurring:

After collection, processing, and converting back to the original roadbed shape, we were able to provide our customer with a full deterioration report which included this:

Background

Hydronic radiant heating systems are become increasingly popular in concrete, and with good reason. They are highly efficient for maintaining ambient temperature, concrete's thermal properties are ideal for heat retention, and the cost of installing tubing at time of construction can be reasonably offset. PEX tubing is a popular choice for these hydronic systems, due to its flexibility and durability. That same flexibility carries some drawbacks however.

Radiant tubing loops are designed to allow specific levels of heating to different zones within a building. These loops are specified fairly precisely and may give tube location to within an inch. Unfortunately, field installation is rarely so precise. This means that when you need to add an unplanned penetration to your slab, you need to know that you can drill without compromising this tube system.

Experience

GPR Data LLC is trained and experienced with PEX tube locating. We can provide real-time field results or a full report with referenced datapoints, such that you can drill any location at any future time with full confidence.

For our most recent project with PEX tubes, we collected data in roughly 20' x 20' sections. Each section was processed with a full 3D analysis, creating a top-down plan view of all tube positions. The tubes are located in a rebar reinforced topper slab over precast beams -- had the client desired, our final deliverable could have included rebar layout and structural elements within the precast beams (cables and air chambers). The end result: our client had their design plans and highly accurate as-builts of where things truly were.

Background

GPR DATA LLC was contacted to perform a geophysical ground penetrating radar survey on a rural area in Lane County Oregon, Sweet Creek Road. The site area has been the location of road base failure over a long period of time. Numerous additional asphalt lifts have been added and applied to the road surface to correct the deformations. The specific location of failure borders a vertical up hill embankment with a near 5 to 1 slope. The down slope embankment continues to the creek some 30 feet below. The bed rock or base rock formation is a brown hard sandstone mixture. This information compiled from a well soil log performed by others for Lane County in the survey grid. The soil log will be used as a ground proof point for depth and identifying geologic soil layers as they exist in the strata.
The critical objective of this report is to establish the angle of the bedrock slope formation at depth as it relates to the road surface over the length and width of the GPR survey.

Findings

After processing and analyzing the positive average amplitude GPR response at various depth slices, 0.0 to 7.5 feet, 7.5 to 10.0 feet, 10.0 to 12.5feet, 12.5 to 15.0 feet, 15.0 to 17.5 feet, 17.5 to 20.0 feet, and finally 20.0 to 24.0 feet depth slice interval maps were selected as most representative. This interval series of 2.5 feet was utilized because it closely demonstrated the slope as a function of depth. The color scale on each map indicates the signal amplitude strength at the indicated depth interval. Violet to dark red coloration indicates areas of relatively stronger reflection amplitudes. The quantitative numbers in the scale, 0 to 9000 at 500 point intervals reveal the change in amplitude with depth. The colors graduate with the stronger reflective signal values as the soil geology changes from fill to bedrock, (hard brown sand stone).

Background

Ground penetrating radar was used to image the concrete slab in the press pit. Depth of concrete, amount of steel reinforcement, and diameter of steel reinforcement at the bearing locations was the target information. Field measurements for rebar diameter and concrete thickness were obtained from core drill samples

Findings

The slab was found to have two mats of structural steel 12” on center in both the longitude and transverse directions. A total of seven profiles were collected on the press pit floor. Profile locations are designated on the data collection layout map. Each file was post processed and structural steel was quantified in excel spread sheets that are attached to this report. Each file has a separate spread sheet that delineates the horizontal (x) position and the vertical (z) position within the slab. An example radar profile for each orientation is below.

Background

Ground penetrating radar wave time travel is the only direct measurement taken by our GPR equipment in the field. Depths or distances to embedded dowel bars can only be obtained by a physical measurement from a drill hole or coring. When both time and distance are know from these two direct measurements, average velocity of radar wave propagation with in the concrete medium can be determined accurately. This accurate depth velocity determination can then be applied to all gpr profiles in the survey. This method is termed the “reflected wave method”, and requires that the radar wave energy be reflected from the embedded dowel that has been directly measured.

Sample of Findings

Note that the direct field measurement for the sixth dowel in profile 013 was field measured at 7.5” in depth, and the average velocity calculation derives a depth of 7.424”. The difference in the two depths stated is well with in the ¼” tolerances of the GPR collection system. The physical point on the dowel at which the field measurement is taken, is often scored by the carbide drill bit and may not be exactly in the center of the circular rebar. The averaged velocity depth calculation logarithmically searches for the highest amplitude value of the closest point of the circular rebar to the receiving antenna. It is not uncommon to find that the averaged velocity depth calculations to be more exact than the direct field measurement.

Background

GPR Data LLC was contacted in conjunction with Quaker Oats personnel to perform a ground penetrating radar survey and evaluation of subsurface continuity / discontinuity beneath the asphalt parking area, structural columns on the north west side of the building, the levee, and a portion of the concrete silo pad near elevator G. Significant visual surface deformation and undermining in specific areas were the result of high flood water intrusion in recent weeks. The majority of surface deformation occurred in the south west parking lot where the asphalt surface was washed away. The total amount of undermining and void space under the asphalt and concrete was unknown and is the goal of this evaluation.

Sample of Findings

The flow path of water or void space under the concrete/asphalt surface is apparent in GPR data, appearing on the amplitude maps as blobs of increasingly low negative amplitude signatures. There are a substantial number of these anomalies in the amplitude maps of the GPR response. Since the nature of these anomalies seems to be isolated and because void formation could occur by other processes such as settlement after the flood water had retreated, additional investigation with test borings is required. Three basic types of GPR anomalies are found under the asphalt and concrete surfaces:

• 1. Narrow linear anomalies trending parallel to many of the expansion/cold joints.
• 2. Large multi-layered blobs of increasingly negative amplitude directly below the asphalt and at depth.
• 3. Linear anomalies following the backfill trenched areas of existing utility excavations.

The backfilled areas of the utility piping in the parking lot show consistent evidence of subsidence from water following through these trenches to the river. The survey data lines that were collected 90 degrees to these pathways reflect consistent evidence of erosion and undermining.

Amplitude map of one survey area, showing regular areas of extreme low amplitude shift

Objective

Subsurface evaluation of 60'x35' area within the Coliseum basement:

• 1) Dimensions and depth of cover to column footings.
• 2) Anything of concern within and/or beneath the concrete slab on grade to a depth of five feet that would be in conflict with excavations for hydro pools.

Conclusion & Recommendations

The concrete floor slab on grade is uniformly 10” thick and reinforced with steel rebar placed 6” on center in both the longitude and transverse directions. Potential conflicts with excavation plans include a series of utility lines in which most are associated with the existing floor drain, and the column footings extending out from the base of each column. It is recommended that the dimensions and positions of each utility and footing be transposed to the concrete surface in the field to clearly layout saw cutting lines as to avoid conflict. A to scale (1” = 1/8”) overlay of each survey grid on existing drawings is to the right for reference.

Objective

Use nondestructive ground penetrating radar to characterize and evaluate four (4) areas composed of pre-stressed roof and floor planks. The targeted information was spacing, depth, quantity, diameter of pre-stressed tendons, and beam width of plank members. The purpose of this information is to determine load bearing calculations for new equipment installation.

Conclusions

Individual floor and ceiling plank members consist of similar dimensions and structural design. Each plank surveyed has a 24” width, a 10” depth, and is pre-stressed with three 1/2” steel tendons. The number of strands in each ½” tendon is not known. Each tendon is offset the hollow core spaced 8” - 10” apart.

Background

An irrigation district reservoir spillway was built in the early 1900’s and continues in use today. The spillway is approximately 80’ wide by 70’ long and drops 32 feet in elevation. The structure has had some repair and maintenance over the years, including a new reinforced concrete slab placed over the existing slab making the spillway thickness approximate 24” thick. GPR Data LLC was contacted to perform a ground penetrating radar survey to determine the presence or absence of air voids under this concrete spillway. A visual inspection of the spillway noted the existing void of considerable size (7 ft. diameter) along the west side of the lower section of the angled spillway.

Technical Approach

Voids filled by air are readily apparent on a GPR record profile, appearing as extreme negative low amplitude reflections. The objective of this project is to identify and map any such voids using a widespread analysis of low amplitude returns over several grids encompassing the entire spillway. Given the size of the survey area and the level of detail required, an analysis using single GPR profiles alone would have been cumbersome and time consuming. Instead, the individual profiles were integrated into a 3D file creating a series of plan-view amplitude maps of the negative GPR reflections at various time/depth slices. Amplitude slice mapping creates maps of reflected wave amplitude differences both spatially and with depth within each grid. The reflected measurement recorded digitally exemplifies the changing porosity in subsurface material.

The image below shows an amplitude map of the ground penetrating radar data. The image on the right shows how GPR Data LLC integrated this amplitude map into a 3D model we constructed of the spillway, to present the information in a more accessible manner.

Additional Results

With our amplitude maps as a guide, the client measured a sample of depths throughout the survey area. At each point a hole was augered through the concrete, and the depth of both concrete and any void area were recorded. We took their information and superimposed it back over our amplitude map. Click on the small image to view the full-size copy (it will take a while to load) and you can directly see the results.

Background

South Fork Mountain Spring is a naturally occurring fresh water spring located on a 326 acre parcel in the foot hills of the Mad River Mountain Range, in Trinity County, California. It is situated between the boundaries of the Six Rivers National Forest and the Trinity Wilderness. This spring is the source of water for the South Fork Mountain Spring Water Company. There is no existing information that characterizes the collection system or catchment area that supplies the spring.

Objectives

• 1) Collect 2D and 3D images of the collection/catchment area using non-destructive ground penetrating radar.
• 2) Evaluate and process theses images to resolve isolate then report the characteristics of the collection/catchment area.

Findings

Profile 033 is a linear file running down slope directly in line with and stopping at the hatch outlet. The linear orientation of the catchment trench is out lined in red. The catchment area is 25’ + in length. The horizontal red line depicts the water level interface.

The collection system for this spring consists of a linear trench described above that has been backfilled with small round cobble and a coiled perforated pipe. This coiled perforated pipe carries the spring water in a zigzag fashion down slope to a smaller galvanized pipe that is controlled by a valve at the hatch. As shown below, the pipe is concentrated in a spring well up slope from the hatch.

This localized area has a large cavity filled with rock or other porous material bedded with coiled perforated pipe overlapping each other vertically much like the shape of a bee hive. The black white black banding is indicative of the dielectric interface of energy changing from negative to positive to negative. The 3D image below depicts a large circular cone shape built by successive layers of air/water filled cavities.

Objective

Use non-destructive ground penetrating radar to create a high resolution three dimensional image of the embedded structural steel. By imaging specific sections of the concrete columns, our goal was to determine the feasibility of drilling horizontal dowel holes into the columns free of conflict with structural steel.

Methodology

A 24’’ X 48’’ data collection grid was oriented with the point of origin in the lower left corner, and then centered on the column 2’ up from the floor.

Findings

The image to the right is a scaled representation of the 2’ X 4’ grid. The rebar (blue) are 1” square which measure 1.45” on the diagonal cross section. The rebar are presented to scale with this dimension of 1.45”. The only potential areas for dowels are X=9.5 and X=11.25, labeled with 1” green dot.

After careful analysis and evaluation, it is determined that there is not uniformly adequate spacing between the 1” square rebar that is oriented perpendicular to the column face to drill 1” dowel holes free of conflict with structural steel. Each vertical rebar is within 7” of the column face, and oriented in a staggered offset.

Objective

• 1) Locate terminal ends and attached “add-on cables” for several 3rd floor cables. Note areas of probable cable failure.
• 2) Evaluate northern segment of two cable bundles on 4th floor, each of which are accompanied by excessive cracking in the concrete slab.

Methodology

Ground penetrating radar was used to locate, follow, and evaluate cable continuity. Two system configurations were used. Two dimensional line scans were produced with a SIR-3000 interface radar surveyor coupled with a high resolution 2.6 GHz antenna. Three dimensional data grids were collected with a SIR-20 surveyor coupled with a 1.5 GHz antenna. Line scans were collected and analyzed real-time in the field, to rapidly trace and follow cables out from a known point. Data grids provided 3D depth-slice information about problem areas, suspected failure points, and add-on cable sources.

Findings

Analysis of grid 004 is suggestive of cable failure. Directly beneath the patched section, the target reflection becomes very weak for a span of roughly 10”. However, the reflection of a deeper E/W target remains strong and contiguous, which indicates that the weak reflection is not due to attenuation by the material of the patch itself. In the image below, the N/S cable is less than 1.5” deep, while the E/W target is roughly 3”.

Grid series A consisted of six 4’x2’ data grids for 3D analysis. Each grid’s origin to the SE, and overlapping endpoints were used to allow seamless integration. The first grid, as expected, shows two cables merging into a bundle. This bundle proceeds through the second and third grids without significant issue. Between the third and fifth grids, a small diagonal target is visible, slightly offsetting the cable bundle. In the fourth grid, at an area where the cable is rising in elevation and is most shallow in the slab, the reflection changes abruptly. This area is noted with the yellow rectangle to the left. The abrupt and significant change in the size, sharpness, and strength of the signal return suggests an area of potential cable failure.

Grid series B consisted of seven 4’x2’ data grids for 3D analysis. Grid orientation and layout as in series A. The tendon layout for this section shows four terminal cables, of which three are full length and one is added roughly 20’ from the north wall. In grid 001, a single linear target is traveling due south almost directly beneath the surface crack. However, this target ends in grid 005 at roughly 4” deep, where a new target is picked up at 2”. In grid 001, several other targets of note are observed. Two targets can clearly be seen traveling S-by-SW and merging by the third grid. A third target joins them as well, located just west of the grid edge, barely visible in the top-left corner of 001 and the left edge of 002. The expected source of the add-on cable is roughly 26’, which should put it within grid 007. However, no cable head is visible. It is our estimation that the diagonal target circled in 007 is the add-on cable, terminating at the circled location in 001, and sourced within a few feet of the survey area. Beyond the dominant surface cracking, no suggestions of cable failure were located via GPR in this section.

Tucked away in a high valley in the Wallowa Mountains, Enterprise and Joseph celebrate their rich history and amazing landscape. This valley is the homeland of Chief Joseph. The townspeople are friendly and helpful, and they preserve the region's history. When a pioneer-era cemetery was ravaged by wildfire, they enlisted GPR Data LLC to help with recovery.

The Problem

The Alder Slope Cemetery was founded by 1870 at the latest, and most gravesites were marked out with wooden crosses and other fixtures of remembrance. Only a small portion had been demarked with headstones when fire ripped through the cemetery. The historical society retained records of most internments, but had no way to place them at precise physical locations.

The Results

GPR Data LLC used 270 MHz and 400 MHz antennas to first create a 3d map of the cemetery, then identify dominant rows of graves, and finally mark out all cooresponding locations. Each identified target was marked with a flag at the presumptive head, and paint along the trench, for semi-permanent but easily removed reference. Finally, a reference map was built upon satellite imagery to give an overview perspective (right)

With significant site upgrades coming soon, it was crucial for the El Dorado Hills Irrigation District to have accurate maps of all buried utilities and potential risks. With site hazards such as chlorine gas piping, blind excavation was simply not an option. GPR Data LLC was chosen to create these highly accurate as-builts.

Equipment and Profiles

To meet the range of terrain within the site, both the SIR-20 and SIR-3000 systems were used for various surveys. All survey grids were collected with a 400 MHz antenna, with survey wheels calibrated on-site directly to each individual grid. Each data profile was then processed with the RADAN 6.5 for Windows software, looped into a 3d model, and analyzed via 3d depth/z slices. Velocity migration and a full gambit of post-processing filters were utilized to convert the raw data into highly accurate and usable 3d models of the target grid areas.

Preliminary GPR Evaluation Methodology

Thirteen collection grids of varying dimensions were established to encompass all requested survey regions, as shown in the diagram to the right. Each grid was set on one-foot centers, such that unique line scan profiles were collected at each one foot interval. All grids were demarked on-site with semi-permanent fixtures -- pins, stakes, and survey flags -- to provide easy reference later.

GPR Collection Methodology

Each survey grid was collected independently, with the SIR systems and survey wheel recalibrated to match the local conditions at that time. As the surveys were collected over a period of two weeks, there were a wide variety of weather and soil conditions present. Additionally, there were a wide range of surface and subsurface conditions within the facility itself. This ensured that any lack of attention to system configurations could compromise our ability to later convert the raw data into practical information.

Results

At the conclusion of this project, our client was provided with detailed reports showing the as-built layout of pipes and subterrainean features with the desired areas. Examples of this information is shown to the right and below.

GPR Data LLC was contacted by Dave Cotner Senior from Lakeside, Oregon in April of 2007 with regard to gpr services for mapping a buried Chinese Junk that was deposited on the Oregon coast in the early 1400’s by a tsunami originating off the coast of New Zealand. Site conditions, terrain, depth of investigation, subsurface composition, and accessibility were discussed. GPR Data LLC proposed a preliminary site evaluation, as standard practice, to determine the feasibility of GPR, test survey the proposed location, and acquire exact site and subsurface conditions to foreword model the data acquisition plan for this site. This preliminary evaluation was conducted on May 2, 2007 by GPR Data LLC personnel Mike Edwards, Matthew Edwards, and Thomas Royer. Following the preliminary study, a date was set to procure data acquisition on May 22, 2007. This survey was witnessed and observed by Dave Cotner Jr., Dave Cotner Sen., and Gavin Menzies, author of the book, 1421 The Year The Chinese Discovered America.

GPR Data LLC extends a great thanks to 1421, Gavin Menzies, Dave Cotner Sen., and Dave Cotner Jr. for allowing us to provide geophysical evidence to help aid the foreword progress of the project. We are honored to be a part of something with such great magnitude and discovery.

Equipment and Profiles

A SIR-3000 (Subsurface Interface Radar) system was used with a 200 MHz and 400 MHz antenna. The system, antenna, and survey wheel used, were calibrated on site according to local conditions. A 200 MHz and 400 MHz deep penetration profile was used with the target window at 150 nanoseconds; and target depth approximately 40-60 ft. deep were achieved. A relative dielectric was set at 3.09. Using velocity analysis, a standard post-processing procedure, we were able to calculate accurate depths and dimensions for features of interest after the survey was completed.

Each data profile was processed using Radan NT. 6.5007 for Windows software. Each data profile was looped into a 3D model. These models were analyzed using 3D depth slices. The identity of any areas of interest, or subsurface features was noted and analyzed further. A terminal depth, and slope bottom was set at 60 ft. Markers were placed on any targets above this terminal depth within each 3D data model.

Preliminary GPR Evaluation Methodology

A rectangular grid 60 ft. wide and 160 ft. long was positioned off a gps coordinate obtained from Dave Cotner Sen. Profiles were positioned to encompass a 30 linear ft. radius around this gps coordinate, this ensured all potentially useful information in the gpr survey was captured. The subsurface soils were consistent fine grained beach sand. A fresh water interface was noted at 9 ft. deep. The topography was flat, rising in elevation slightly to the north east. The weather was overcast and slightly rainy; the site had been well saturated with rain on the previous night.

GPR Evaluation Methodology

The survey area was positioned directly over the wreck site using Dave Cotner Sen., his MAS system, and preliminary gpr survey models provided by GPR Data LLC. The dimensions were divided into two grids, one grid with dimensions 80 ft. by 100 ft., labeled area A, and the other grid with dimensions 80 ft. by 50 ft., labeled area B. Data profiles were collected using a standard Cartesian coordinate system, on two ft. intervals. GPR Data LLC used a 400 MHz antenna on the larger grid, labeled area A, and a 200 MHz antenna on area B. The 400 MHz antenna provides greater resolution in areas where the distance from surface to the target was not greater than 35 ft.

Findings

After completing the analysis and interpretation of data profiles that were obtained on May 22, 2007 in Winchester Bay, Oregon, we have summarized the following findings; the main portion of the junk is contained in area A, and a broken chunk of the junks bow and masts along with various other items are contained in area B. We base our findings on information provided by Dave Cotner Sen., Gavin Menzies, and the following gpr data.

1. Using the drawing of the Junk produced by Dave Cotner Sen. as a known reference for the dimensions, physical characteristics, orientation, and location, of this junk, 3D data models and amplitude maps, obtained from gpr profiles confirms the presence of a large high amplitude zone between 25 ft. and 55 ft. deep.
2. A 3D depth slice hows the debris field surrounding the high amplitude zone, as described in area A. An outline of the junk is obtained by point reflection markers.
3. A data slice at 19 ft. deep confirms a linear target. The dimensions are consistent with the mast the junk, and the approximate location provided by Dave Cotner Sen. This feature is positioned in sand at a slight angle and can be seen in a line scan mode as a linear round target.
4. A 2D amplitude map of area A shows amplitude values at 26 ft. deep with 4 ft. target window, it appears that the main body of the junk is contained in area A, and a broken off chunk of the ships bow is contained in area B.