NWSE Geotech Report - Part C.pdf

HAGER-RICHTER

GEOSCIENCE, INC.

©2023 Hager-Richter Geoscience, Inc.

GEOPHYSICAL SERVICES

NWS EARLE

SWIMMING RIVER CULVERTS

TINTON FALLS, NEW JERSEY

Prepared for:

Jacobs 412 Mt. Kemble Ave, Suite 100 Morristown, New Jersey 07960

Prepared by:

Hager-Richter Geoscience, Inc.

dba HR Geological Services in NY 846 Main Street Fords, New Jersey 08863

File 23J13 June 2023

HRGS

HAGER-RICHTER GEOSCIENCE

GEOPHYSICS FOR THE ENGINEERING & ENVIRONMENTAL COMMUNITIES

2 Industrial Way S/2, Atkinson, NH / 603.893.9944

846 Main Street, Fords, NJ / 732.661.0555 www.hager-richter.com

ATKINSON, NEW HAMPSHIRE • FORDS, NEW JERSEY

www.hager-richter.com

June 05, 2023 File 23J12

Sam Nauss, P.E.

Jacobs 412 Mt. Kemble Ave, Suite 100 Morristown, New Jersey 07960

Cell: (973) 886-2297 Email: Sam.Nauss@jacobs.com

RE: Geophysical Services NWS Earle Swimming River Culverts Tinton Falls, New Jersey

Dear Mr. Nauss:

In this letter, we report the results of a geophysical survey conducted in May 2023 by Hager-Richter Geoscience, Inc., (HRGS) at the above referenced site for Jacobs. The scope of the current project and area of interest were specified by Jacobs.

INTRODUCTION

According to information provided by Jacobs, areas of subsidence and settlement of the ground surface are occurring along a railroad leading from NWS Earle to its pier facility at Sandy Hook at their crossing of the Swimming River in Tinton Falls, New Jersey. The general location of the Site is shown in Figure 1. A timber trestle was initially present at the river crossing, and as its condition deteriorated, an embankment was constructed, and the trestle was buried within the embankment. To maintain the river flow in the area, two sets of culverts, each consisting of eight culverts, were placed at the river mudline level to allow for the Swimming River to continue to flow through the area. One set of culverts is adjacent to the north bank of the river, while the second set is adjacent to the south bank.

Depressions and voids have been observed along the tracks and roadway at the location of the river crossing. Based on boring information provided by Jacobs, very loose soils are also present in the subsurface at the locations of the crossing. It is believed that the culverts are currently deteriorated and corroded, and possibly the overburden soil is flowing through the culverts and causing this loose soil condition to develop within the embankment. The area of interest was approximately 500 feet by 40 feet centered along the railroad tracks.

Jacobs requested a geophysical survey to determine the extent of the areas of subsidence and sinkholes, and, if possible, the cause of the subsidence in the specified area of interest at the site.

Geophysical Services

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OBJECTIVE

The objective of the geophysical survey was to determine the extent of the subsidence, and, if possible, to determine the cause of the subsidence in the specified area of interest.

THE SURVEY

Amanda Fabian, P.G. and Alexis Martinez of HRGS conducted the field operations on May 11- 12, 2023. The project was coordinated with Mr. Nauss. The geophysical survey was conducted using two geophysical methods, ground penetrating radar (GPR) and muti-channel analysis of surface waves (MASW), to attempt to determine the extent of subsidence in the subsurface, and if possible, the cause of the subsidence.

The GPR survey was conducted within the ballast, along both sides of the tracks and inside the tracks along parallel lines spaced approximately 2 feet apart, as access permitted. The MASW survey was conducted along two transects identified as Lines 1 and 2. Line 1 was located between the two tracks and Line 2 to the west side of the tracks. Data were acquired using 24 4.5- Hz geophones spaced at 5-foot intervals. The energy source was a 12-lb sledgehammer striking the surface.

Figure 2 is a site plan showing the geophysical transects and borings performed by Jacobs. The GPR and MASW methods were conducted in order to try to detect shallow and deep voids or disturbed soils, respectively. The geophysical data was georeferenced using a handheld GPS system Tremble Geox7 and superimposed on a site plan provided by Jacobs.

EQUIPMENT

GPR: The GPR survey was conducted using a GSSI UtilityScan DF subsurface imaging radar system with 300 MHz and 800 MHz antennas recording data simultaneously. Data are recorded digitally, and the GPR data can be reviewed in the field. The system includes a survey wheel that triggers the recording of the data at fixed intervals, thereby increasing the accuracy of the locations of features detected along the survey lines. Data were recorded using an 80 ns1 time window.

GPR uses a high-frequency electromagnetic pulse (referred to herein as “radar signal”) transmitted from a radar antenna to probe the subsurface. The transmitted radar signals are

1 ns, abbreviation for nanosecond, 1/1,000,000,000 second. Light and the GPR signal require about 1 ns to travel 1 ft in air. The GPR signal requires about 3.5 ns to travel 1 ft in unsaturated sandy soil.

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reflected from subsurface interfaces of materials with contrasting electrical properties. Travel times of the radar signal can be converted to approximate depth below the surface by correlation with targets of known depths and by a curve matching routine. We monitor the acquisition of GPR data in the field and record the GPR data digitally for subsequent processing.

Data from the GPR survey were processed using RADAN 7.6, commercially licensed GPR processing software from GSSI, and the profile images were interpreted. The GPR data were examined in profile format.

The GPR signature for voids and areas of subsidence is site specific and non-unique. Other structures or subsurface conditions, such as debris or changes in construction details may produce GPR reflections that are like the GPR reflections caused by voids and subsidence.

Whether such features are present can only be determined by ground truth.

MASW: The multichannel analysis of surface waves (MASW) method is a seismic method that determines a shear-wave velocity (Vs) profile (i.e., Vs versus depth and horizontal distance) by analyzing a particular type of seismic wave on a multichannel record. The MASW method uses Rayleigh waves, which are elastic waves that travel in the subsurface near the earth’s surface.

The amplitude of such waves decreases with depth and the phase velocity of the waves is a function of frequency. The method uses multichannel recording and processing concepts widely used in reflection surveying by the oil and gas industry.

The MASW method requires multichannel records with at least 12 traces to produce reliable results. We use 48 channels (two 24-channel Geometrics Geode digital seismographs), coupled to 48 geophones to acquire 24-trace records. The data acquired for geophones numbered 1 - 24 are processed as discussed below to determine the shear wave velocity as a function of depth for discrete layers, and the velocity of each layer Vs(x,n) is assigned to the midpoint of the line between Stations 1 and 24, i.e. x = 55 ft if the geophone spacing is 5 feet as shown in Figure 3.

The data acquired for geophones numbered 2 through 25 yield the vertical velocity profile at the midpoint of the line between stations 2 and 25, i.e., x = 55 ft if the geophone spacing is 5 feet. By processing the data for geophones m through m+24 and assigning the vertical profiles to the midpoints, the velocity of each layer is generated as a function of horizontal distance.

The end point for the velocity determined with a 48-geophone spread using data acquired with 24 geophones is located at x = 175 ft from the start of the line if a 5-foot geophone spacing is used. Due to the MASW array configuration, the first and last approximately 55 ft section of each MASW line does not provide results, as shown in the MASW plots in Figure 2.

The MASW survey is conducted using an active source, and the method using an active source is sometimes called an active MASW survey to distinguish it from a passive MASW survey in

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which ambient noise is used as the source. Levels of ambient noise are monitored in real time during data acquisition. Ambient noise is not utilized by the survey but is avoided by waiting for times when nearby traffic (the main source of ambient noise) is not adversely affecting the quality of the data. Only active source data were used for the subject survey and no passive source data were acquired. It is also important to use a low natural frequency geophone for most MASW surveys. For this project, we used our 48-channel seismograph (two 24-channel Geometrics Geodes) coupled to 24 4.5-Hz geophones spaced 5 feet apart mounted along a land streamer towed with a small hand cart. The seismograph is connected to, and controlled by, a notebook PC computer. The software provides for the acquisition, display, plotting, filtering, and storage of seismic data.

The surface waves used in MASW, considered noise in refraction and reflection surveys, are enhanced during data acquisition and processing for the MASW method. The seismic data are analyzed using Surfseis 6.0, a commercially licensed software package developed by the Kansas Geological Survey. Briefly, SurfSeis provides a dispersion curve from which the interpreter selects the fundamental mode in detail, and the software then inverts the dispersion curve in terms of a model of shear wave velocity (Vs) as a function depth at the midpoint of the geophone spread. Results can be presented as 2-D graphical plots of the shear wave velocity as a function of depth and distance along the line using contouring software such as Surfer or in tabular form showing shear wave velocity as a function of depth at a given station.

As discussed above, data are acquired for 24 channels at a time and the resulting 1-D shear wave distribution as a function of depth is assigned the horizontal position at the center of the 24-channel spread. The 1-D distributions are then combined to provide shear wave velocity distribution across the survey line and are presented as 2-D color plots. The variations in color correspond to apparent variations in subsurface shear wave velocity. Low shear wave velocities correlate with softer soils and higher shear wave velocities correlate with harder, more dense soil or bedrock.

LIMITATIONS OF THE METHOD

HRGS MAKES NO GUARANTEE THAT ALL TARGETS WERE DETECTED IN THIS

SURVEY. HAGER-RICHTER GEOSCIENCE, INC. IS NOT RESPONSIBLE FOR

DETECTING TARGETS THAT NORMALLY CANNOT BE DETECTED BY THE METHODS

EMPLOYED OR THAT COULD NOT BE DETECTED BECAUSE OF SITE CONDITIONS.

GPR: GPR detects and maps interfaces of contrasting electrical properties, and air- or waterfilled voids have electrical properties very different from soil and concrete. The GPR

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method is useful for detecting voids and determining their footprint, but in general, GPR data cannot be used to determine the thickness of voids.

There are other limitations of the GPR technique: (1) surface conditions, (2) electrical conductivity and thickness of the subsurface layers, (3) electrical properties of the target(s), and

(4) spacing of the traverses. Of these restrictions, only the last is controllable by us in most cases.

The condition of the survey surface can affect the quality of the GPR data and the depth of penetration of the GPR signal. For exterior sites, a surface covered with obstacles such as automobiles, dumpsters, thick leaf debris, materials piles, etc. limit the survey access. Similarly, for interior sites, a surface covered with obstacles such as desks, benches, laboratory equipment, etc. also limit access. Some floor coverings may limit the coupling of the GPR antenna with the subsurface.

The electrical conductivity of the subsurface determines the attenuation of the GPR signals, and thereby limits the maximum depth of exploration. The GPR signal does not penetrate clay-rich soils or soils contaminated with road salt. In some cases, the GPR signal may not penetrate below concrete pavement, and some asphalt is electrically conductive.

A strong contrast in the electrical conductivities of the ground and the target (for example, UST, pipe, void, dry well, drum, contaminant plume) is required to obtain a reflection of the GPR signal. If the contrast is too small, then the reflection may be too weak to recognize, and the target can be missed.

Spacing of the traverses is limited by access at many sites, but where flexibility of traverse spacing is possible, the spacing is adjusted based on the size of the target.

MASW: The MASW method, although theoretically sound, may not be applicable at all sites for the determination of shear wave velocity because of site limitations. Such limitations include adequate space, attenuation of the soils (especially for frequencies in the range 5 Hz to about 15 Hz), and the presence of structures with high velocity materials that extend to appreciable depth (such as thick concrete or asphalt slabs or basement walls of several below-grade stories).

For sites where a high velocity layer overlies a significantly lower velocity layer, Lamb Waves may be generated rather than Rayleigh Waves. Because of their dispersive and multi-modal nature, Lamb waves can be easily misidentified as Rayleigh-type surface waves during a MASW

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survey. The inversion algorithms used to interpret MASW data cannot be utilized to determine shear wave velocity structure when Lamb Waves dominate the data.

The depth of investigation for an MASW survey depends on the frequency spectrum of the seismic signal, and low frequency (long wavelength) signals are required to obtain data at large depths—the lower the frequency, the greater the depth of investigation. For sites where the soils or bedrock are highly attenuating for low frequencies, the depth of determination of the velocity of shear waves with the MASW method may be less than 100 feet. As with all physical measurements, there is experimental error in the velocities that are determined using the MASW method. The uncertainty in velocity of shear waves is estimated to be approximately 10- 15%.

RESULTS

General: The geophysical survey consisted of GPR and MASW surveys. Figure 2 shows the locations of the GPR and MASW traverses, Figure 4 shows the GPR data interpretation and Figure 5 shows the results of the MASW survey and our interpretation of the results. Several borings performed by Jacobs along Line 1 are included in Figure 5 as reference.

GPR: Apparent GPR signal penetration for the areas of interest was good, with two-way travel time reflections received from approximately 40-50 ns. Based on velocity matching calibrations made for the site, the GPR signal penetration is estimated to have been about 6-7 feet.

The typical radar signature of an air-filled void is a distinctive high-amplitude GPR reflection.

High-amplitude GPR reflections are due to the large contrast in dielectric properties between the pavement and air gaps. Moderate amplitude GPR reflections are interpreted to be caused typically by disturbed soils with thin air-filled voids.

Strong reflections typical for large voids were not identified in the GPR records. Some areas that exhibit subtle GPR reflections were identified and are possibly associated with the presence of disturbed fill materials. Such GPR anomalies are depicted in Figure 4 as red crossed rectangular areas.

Periodic reflections spaced 12 feet apart throughout the area investigated are evident in the GPR records and may be related to the presence of the former trestle structure supporting the tracks, or the culverts below the ballast.

MASW: MASW. From a practical perspective, the MASW method determines the spatial variation of shear wave velocity (Vs), and interfaces or anomalies are interpreted by relative

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changes in Vs. In general, higher shear wave velocities indicate more dense materials, and lower shear wave velocities indicate less dense materials.

The quality of the MASW was considered to be poor to fair due mainly to the presence of a 35– 40-foot fill layer characterized by heterogeneous materials with very low shear wave velocity.

The color contour MASW profiles shown in Figure 5 exhibit an upper layer of low shear wave velocity that may correspond to the ballast, with shear wave velocity of 500 ft/s approx. A greater velocity layer is present below with shear wave velocity of approximately 700 ft/s, over a lower velocity layer of 400-500 ft/s. This layer distribution corresponds mainly to the fill (green-blue). Several areas with more prominent low velocity values are observed in both profiles and noted in Figure 5 with circles. Those areas correspond to possible zones of collapsed fill/soils that may have caused the observed sinkholes at the surface.

In general, the fill layer appears to be thicker along MASW Line 2. The southern quarter of the MASW lines shows thinner fill over denser soils with shear wave velocities greater than 1,000 ft/s.

Several borings in the vicinity of the MASW profiles are superimposed in Figure 5. The top layer corresponding to fill exhibits good correlation between the boring logs and the results of the MASW profiles. Although the boring logs suggest the presence of voids, it is not possible to detect individual voids on the basis of low shear wave velocity due to the overall low velocity values of the soils in the fill, i.e. there is not enough contrast between shear wave velocity of the voids and surrounding soils.

CONCLUSIONS

Based on the geophysical survey performed by HRGS along a railroad leading from NWS Earle to its pier facility at Sandy Hook at their crossing of the Swimming River in Tinton Falls, New Jersey in May 2023, we conclude:

Possible areas of disturbed soils were detected near the surface.

Large areas characterized by lower shear wave velocity were detected at depth.

Features present below the effective GPR signal penetration, estimated to have been about 6-7, cannot be detected with GPR. Voids, characterized by low shear wave velocity, cannot be detected with the MASW method in areas with generally low shear wave velocity.

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LIMITATIONS ON USE OF THIS REPORT

This letter report was prepared for the exclusive use of Jacobs (Client). No other party shall be entitled to rely on this Report, or any information, documents, records, data, interpretations, advice, or opinions given to Client by HRGS in the performance of its work. The Report relates solely to the specific project for which HRGS has been retained and shall not be used or relied upon by Client or any third party for any variation or extension of this project, any other project, or any other purpose without the express written permission of HRGS. Any unpermitted use by Client or any third party shall be at Client's or such third party's own risk and without any liability to HRGS.

HRGS has used reasonable care, skill, competence and judgment in the performance of' its services for this project consistent with professional standards for those providing similar services at the same time, in the same locale, and under like circumstances. Unless otherwise stated, the work performed by HRGS should be understood to be exploratory and interpretational in character and any results, findings or recommendations contained in this Report or resulting from the work proposed may include decisions which are judgmental in nature and not necessarily based solely on pure science or engineering. It should be noted that our conclusions might be modified if subsurface conditions were better delineated with additional subsurface exploration including, but not limited to, test pits, soil borings with collection of soil and water samples, and laboratory testing.

Except as expressly provided in this limitations section, HRGS makes no other representation or warranty of any kind whatsoever, oral or written, expressed or implied; and all implied warranties of merchantability and fitness for a particular purpose, are hereby disclaimed.

If you have any questions or comments on this letter report, please contact us at your convenience. It has been a pleasure to work with you on this project. We look forward to working with you again in the future.

Sincerely yours, HAGER-RICHTER GEOSCIENCE, INC.

dba HR Geological Services in NY

José Carlos Cambero Calzada, P.G. (NY 000899) Senior Geophysicist

Attachments: Figures 1 - 5

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