3-450 Scottys Way - MASW Report.pdf

MASW GEOPHYSICAL SURVEY

450 Scottys Way Bowling Green, Kentucky

Prepared for:

Nick Lawhon, P.G., C.F.M.

Geologist Bowling Green Public Works Department (270)537-1377

May 8, 2026

Prepared by:

NSG Innovations, LLC Near Surface Geophysics 741 Greenlawn Ave., Bowling Green KY 42103 859-462-2449

Respectfully submitted:

Thomas B. Brackman Trent Edwards

Bringing the Subsurface into View

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Contents

1.0 Introduction

2.0 Technical Background

2.1 Geological Setting

2.2 Multichannel Analysis of Surface Waves

3.0 Procedures

Table 3 – MASW Lines Conducted

4.0 Summary of Findings

5.0 Recommendations

6.0 Limitations

Figure 1 Vicinity Map Figure 2 Site Map Figure 3 Line Location Map Figure 4 Geological Setting Figure 5 Line 1 Figure 6 Line 2 Figure 7 MASW Overlay Figure 8 Exploration Locations

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1.0 Introduction

The purpose of this project was to perform a geophysical survey near a recent surficial collapse located at 450 Scotty Way in Bowling Green, Kentucky. The study area featured a service road, a drainage ditch, and multiple utilities directly east of the recent collapse. The intent of this geophysical project was to evaluate the subsurface conditions and determine the approximate extent of the recent collapse. A total of two Multichannel Analysis of Surface Waves (MASW) survey lines were conducted across the site, one on the northern side of the collapse and one on the southern side. A vicinity map showing the location of the site is included as Figure 1 and an aerial photograph or map (termed site map) showing the location of the survey area in relation to the project site is illustrated in Figure 2. Figure 3 is a detailed aerial view or map illustrating the approximate locations of the MASW 2-D shear-wave velocity profiles (line location map).

2.0 Technical Background

The challenge for this project was to select the correct non-intrusive tools and techniques to evaluate the subsurface on site and delineate the extent of strip-mining activity. In general, a variety of geophysical techniques can be applied to the mapping of subsurface features; however, certain methods, sensitive to a range of contrasting physical properties, can have attributes that make them more suitable than others, depending on site-specific conditions. Contrasting physical properties that typically are found to be useful for mapping soil and bedrock include electrical conductivity or resistivity, acoustic velocity, density, and magnetic susceptibility. Of these, MASW is commonly found to have a sufficient range of contrast and is most applicable for detailed characterization of sites. Given the desired depth of investigation (approximately 100 feet), two-dimensional (2-D) MASW was selected as the method of choice to document the soil-sediment-rock profile beneath the site. A description of techniques used in this field study is presented in the sections following basic geologic setting discussion.

2.1 Geological Setting

The site possesses terra rossa or red, iron-rich clay soils representing limestone replacement by silica, clay minerals and iron, as well as gravel fill material from a past repair. Overall, the site is located atop soils formed from the weathering of the Mississippian-aged Ste. Genevieve Limestone (Figure 4, Geological Setting). This limestone unit was formed from carbonate sediments deposited on topographic highs associated with a shallow marine shelf or ramp setting. Nodular chert commonly occurs within the Ste. Genevieve Limestone and the dominant lithology is composed of argillaceous, fine grained to grainy or skeletal carbonates (dominantly limestone but some dolostone also is present). Such Ste. Genevieve Limestone units where exposed or nearly exposed, commonly result in the development of karst features at the surface and these can result in geohazards such as subsidence, soil piping or less commonly, collapse. The generalized geologic map of the site is shown in Figure 4 that specifically shows that the Ste. Genevieve Limestone is the first encountered bedrock at the site. The red-hashed areas represent mapped sinkholes in the area. This information is made available by the Kentucky Geological Survey’s interactive web service.

2.2 Multichannel Analysis of Surface Waves

Since its introduction in the late 1990s, use of surface-wave techniques has rapidly increased for two reasons: (1) they provide the shear-wave velocity (Vs) of ground materials, which is one of the most important geotechnical parameters in civil engineering, and (2) they are easier to use than are other common seismic approaches (e.g., refraction, reflection, and surface-wave surveys).

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Elastic moduli are commonly used in geotechnical engineering to describe the behavior of Earth materials under stress, which is ultimately related to such tasks as properly designing earthworks and structural foundations, risk assessment under specific site conditions, and monitoring various types of existing infrastructure for public safety. Among three primary types of moduli: Young’s (E), shear (μ), and bulk (ĸ) moduli—the first two are most commonly used because of what they represent. Young’s modulus simply describes the deformation tendency along the axis of stress, whereas the shear modulus describes the tendency for shape deformation (shearing) that, in turn, is related to the viscosity or rigidity of material.

Young’s and shear moduli are determined from the parameters of density (ρ), Vs, and Poisson’s ratio (ó).

Vs plays the most important role as it is included as squared terms in expressions. In addition, Vs, in reality, changes through a broader range than do density and Poisson’s ratio. Therefore, accurate evaluation of Vs can be extremely valuable in geotechnical engineering. The shear modulus can be determined fairly accurately once Vs is determined. Alternatively, Young’s modulus requires Poisson’s ratio to obtain a comparable accuracy. The Vs information of ground materials is obtained by processing Rayleigh-type surface waves that are dispersive when travelling through a layered media (i.e., different frequencies travel at different speeds). This dispersion property is determined from a material’s Vs (by more than 95%), P-wave velocity (Vp) (≤ 3%), and density (ρ) (≤2%). By analyzing dispersion properties, we can therefore determine Vs accurately by assuming some realistic values for Vp and ρ. The accurate evaluation of the dispersion property is most important with any surface-wave method in this sense.

By using a transformation function, the surface-wave method converts raw field data in a time-offset (t-x) domain into a frequency-slowness velocity (f-p) domain. The remaining procedure extracts a dispersion curve that is to be used in a subsequent process in search for the 1-D Vs profile. An accurate dispersion analysis is obviously an important part of data processing, and this is because shear-wave velocity (Vs) information is a good indicator of a given material’s stiffness. The surface-wave method is commonly applied in civil engineering to address mechanical aspects of ground materials for example, assessment of load-bearing capacity, ground behavior under continuous and prolonged vibration, and ground amplification and liquefaction potential. The surface-wave method outputs are relatable to soil profiles as are observable in Table 1 and can be related to blow counts or N values and CPT (Cone Penetrometer Testing) values (Table 2). Note that both tables 1 and 2 have been inserted for convenience of viewing on all MASW profiles.

MASW is a surface-wave seismic method for measuring in-situ shear-wave (S-wave) velocity profiles. The MASW method is used to determine shear-wave velocity profiles for the subsurface. The Rayleigh wave method has since been used for delineation of landslides and tunnel assessment, soil-compaction

Table 1 Site Class definitions partially reproduced below

Site Class Soil Profile Name

Average Properties in Top 100 feet (as per 2000 IBC section 1615.1.5)

Soil Shear Wave Velocity, Vs

Feet/second Meters/second

A Hard Rock Vs > 5000 Vs > 1524

B Rock 2500 < Vs< 5000 762 <Vs< 1524

C Very dense soil and soft rock 1200 < Vs < 2500 366 < Vs< 762

D Stiff soil profile 600 < Vs< 1200 183 < Vs< 366

E Soft soil profile Vs < 600 Vs < 183

Site Classifications adopted from Table 1615 1.1 Site Class Definitions published in 2000 International Building code, International Code

Council, Inc. on page 350.

Soft Soil Vs<600 ft/s

Standard penetration resistance, N

N < 15 Undrained shear strength (psf) <1,000

Very Dense Soil and Soft Rock

1200 < Vs < 2500 ft/s Standard penetration resistance, N N > 50

Undrained shear strength (psf)

SU > 2,000

Rock 2500 < Vs< 5000 ft/s Standard penetration resistance, N N/A

Undrained shear strength (psf)

N/A

Stiff Soil 600 < Vs< 1200 ft/s Standard penetration resistance, N 15 ≤ N ≤ 50

Undrained shear strength SU (psf)

1,000≤SU≤2,000

Table 2: Scale used in velocity profile with site classification, standard penetration values

(N) and undrained shear strength. Values from IBC 2006 Table 1613.5.2 Site Class Definitions (section 1613.5.50).

BG Public Works - 450 Scottys Way, Bowling Green, KY 5 control, mapping the subsurface and estimating the strength of subsurface materials. Testing is performed at the surface using the same conventional seismograph and vertical P-wave geophones that are used for refraction studies. The seismic source consists of a weight-drop system such as a sledgehammer or assisted weight drop and/or the use of ambient seismic noise which is constantly being generated via cultural and natural sources. Depending on the material properties of the subsurface, MASW can determine shear-wave velocities down to a maximum of 100 meters (approximately 300 feet) depth. The data acquisition procedure consists of stacking three to five records for two to three seconds using a conventional seismograph and 4.5 or 10 Hertz (Hz), P-wave geophones. The wave-field transformation of the noise record reveals the shear-wave dispersion curve. The shear-wave dispersion curve is then picked from the wave-field transformation and forward modeled to determine the subsurface shear-wave velocity profile.

3.0 Procedures

Standard Operating Procedures (SOPs) for any geophysical project begins with a site safety check. Each site is evaluated for possible safety concerns and the surveys are modified to take these into account.

Evaluation of the MASW data for the site was completed using the method described by Park (1999). A total of two seismic survey lines were conducted across the site. Seismic records were collected for 30 seconds with a two-millisecond sample rate. A sledgehammer, approximately 30 feet from geophone 1, struck a high-density poly-ethylene plate, triggering each record. Two records were collected at each shot station using a Seismic Source DAQ III data recorder and VibraScope Seismic software. Twenty-four, 4.5-hertz geophones, with 3-foot spacing between each geophone on a seismic land streamer were used for data collection. The land streamer was then moved 00 feet after the collection of every two records. The recorded data were exported to the Parkseis™ proprietary software for processing and modeling. Shear-wave velocities obtained from the forward modeling process are compiled into 1-D or 2-D shear-wave profiles and are included as a profile cross sections to aid in interpretation.

Table 3 – MASW Lines Conducted Field Name and

Processed Name * Report Figure

Sledgehammer Offset (feet)

Geophone

Position

Geophone

Position

Line Length (feet)

MASW Line 1 5 30 NE SW 70 MASW Line 2 6 30 NE SW 100

4.0 Summary of Findings

This site is located along the right of way located at 450 Scottys Way in Bowling Green, KY. The site featured a recent surficial collapse and multiple piles of excavated dirt and construction equipment at the time of the survey. Study of the MASW profiles (Figures 5 and 6) suggests a rather thick layer of Class E, soft soil and Class D, stiff soil material directly below the land surface. This layer of lower Vs values is approximately 5 feet thick near northern portions of the surveyed area and appear to lie approximately 10-to-15 thick near central portions of the surveyed area. Below this layer of soils is a thin layer of Class C, very dense soil and soft rock, before transitioning to Class B, rock material, at an elevation of approximately 515 feet and extending to the base of the profiles. Overall, the very southwestern portion of MASW Line 1 (Figure 5) suggests thicker soil material near the recent collapse, beneath Line 1 station

0. Additionally, MASW Line 2 (Figure 6) stations 30 to 50 show a small, broad depression extending approximately 15-to-20-feet below the surface. A boring is recommended near central portions of Line 2 (black checkered rectangle) to confirm the presence of increased karst development at this location.

Figure 7 is an overlay of the MASW lines conducted across the site. The approximate extent of the surficial collapse is marked via red polygon. A black-dashed ellipse has been drawn connecting the areas

BG Public Works - 450 Scottys Way, Bowling Green, KY 6 of thickening soils observed in the MASW profiles and can be used as an interpretation for the approximate extent of the collapse based on MASW data. Increased development is observed south of the surficial collapse on MASW Line 2, indicating the feature may be trending southeast. Additional exploration is recommended to confirm. Figure 9, Exploration Locations, illustrates areas where further investigation is warranted. There is one well-defined MASW anomalies that is likely related to the recent surficial collapse. This location refers to the Line number and the footage along the line. L2-41 refers to Line 2, station/footage 41. Additionally, the black dashed ellipse has been drawn on Figure 8 as well to outline the approximate extent of apparent settlement based on the MASW profiles.

5.0 Recommendations

We recommend at least one test borehole, excavation or similar investigations be conducted at the exploration areas as presented in the report figures (MASW profiles or Figure 7) or alternatively, excavation of the features. Boring locations noted in red in Figure 8 are recommended. A Google Earth KMZ file has been included supplemental to this report which contains each of these locations relative to the rest of the site. It may be advisable to employ an engineered solution to address hazards associated with a given MASW anomaly identified by the series of presented MASW survey profiles. Addressing control of surface water is also advised.

6.0 Limitations

This study included a limited set of geophysical readings across limited portions of the site. The results and interpretations of the geophysical survey performed are considered generally reliable and were conducted in a manner generally consistent with practitioners in the field of geophysical engineering. The methods used in this investigation are considered reliable; however, localized subsurface variations may exist that have not been completely defined. The seismic results are not unique to geological features and more than one geologic feature or model may yield similar results. Therefore, properly conducted soil test borings and other exploratory techniques are necessary to more completely determine the subsurface conditions at the site.

The site features presented on the site base map are for informational purposes only and no representation is made as to the accuracy or completeness of this information. It is recommended that a practicing geosciences or geotechnical engineering professional be contacted prior to conducting verification drilling or excavating activities.

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Site Location

Figure 1 Vicinity Map

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Figure 2 Site Map

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Figure 3 Line Location Map

L2

L1

Sinkhole extent

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Figure 4 Geological Setting

(as per 2000 IBC section 1615.1.5)

Soil Shear Wave Velocity, Vs

Feet/second Meters/second

A Hard Rock Vs > 5000 Vs > 1524

B Rock 2500 < Vs< 5000 762 <Vs< 1524

C Very dense soil and soft rock 1200 < Vs < 2500 366 < Vs< 762

Standard penetration resistance, N

N < 15 Undrained shear strength (psf) <1,000

Very Dense Soil and Soft Rock

1200 < Vs < 2500 ft/s Standard penetration resistance, N N > 50

Undrained shear strength (psf)

SU > 2,000

Rock 2500 < Vs< 5000 ft/s Standard penetration resistance, N N/A

Undrained shear strength (psf)

N/A

Stiff Soil 600 < Vs< 1200 ft/s Standard penetration resistance, N 15 ≤ N ≤ 50

Undrained shear strength SU (psf)

1,000≤SU≤2,000

Table 2: Scale used in velocity profile with site classification, standard penetration values

(N) and undrained shear strength. Values from IBC 2006 Table 1613.5.2 Site Class

Figure 5 Line 1

Southwest

MASW Profile L1 Figure 5

MASW Survey BG City

Bowling Green, KY

NSG Innovations, LLC Near Surface Geophysics 741 Greenlawn Ave., Figure 5, MASW Profile Line 1 Drawn By: Trent Edwards Thomas Brackman

Horizontal Scale (feet): as shown

Vertical Scale (feet): as shown

B E D C A

Multiple Utilities ~10’ S

Hard Rock

Center of dug out sinkhole

Very dense soil and soft rock

Northeast

Stiff soil

Gravel drainage ditch

Small depression ~5’ S

Rock

Soft soil

10 20 30 40 50 60 0 70

(as per 2000 IBC section 1615.1.5)

Soil Shear Wave Velocity, Vs

Feet/second Meters/second

A Hard Rock Vs > 5000 Vs > 1524

B Rock 2500 < Vs< 5000 762 <Vs< 1524

C Very dense soil and soft rock 1200 < Vs < 2500 366 < Vs< 762

Standard penetration resistance, N

N < 15 Undrained shear strength (psf) <1,000

Very Dense Soil and Soft Rock

1200 < Vs < 2500 ft/s Standard penetration resistance, N N > 50

Undrained shear strength (psf)

SU > 2,000

Rock 2500 < Vs< 5000 ft/s Standard penetration resistance, N N/A

Undrained shear strength (psf)

N/A

Stiff Soil 600 < Vs< 1200 ft/s Standard penetration resistance, N 15 ≤ N ≤ 50

Undrained shear strength SU (psf)

1,000≤SU≤2,000

Table 2: Scale used in velocity profile with site classification, standard penetration values

(N) and undrained shear strength. Values from IBC 2006 Table 1613.5.2 Site Class

Figure 6 Line 2

Southwest

MASW Profile L2 Figure 6

Figure 6, MASW Profile Line 2

Thomas Brackman

Center of dug out sinkhole ~15’ N

Rock

Very dense soil and soft rock

Northeast Fence corner ~15’ N

Stiff soil

0 20 10 30

B E D C A

40 50 60 70 80 90 100

Service road north of L2 with significant traffic

Figure 7, MASW Overlay

MASW Overlay Figure 7

Figure 7 MASW Overlay

Extent of surficial collapse

Possible extent based on MASW Data

MASW Line 1 Figure 5

MASW Line 2

Figure 8, Exploration Locations

Exploration Locations Figure 8

Figure 8 Exploration Locations

Extent of surficial collapse

Possible extent based on MASW Data

MASW Line 1 Figure 5

MASW Line 2