summary report of a sinkhole evaluation nw 13th …

SUMMARY REPORT OF A SINKHOLE EVALUATION

NW 13TH PLACE SINKHOLE GAINESVILLE, ALACHUA COUNTY, FLORIDA

GSE PROJECT No. 14866

Prepared For:

CITY OF GAINESVILLE

DECEMBER 2020

Certificate of Authorization No. 27430

December 9, 2020

Mr. Lee R. Feldman, ICMA-CM, City Manager City of Gainesville 200 East University Ave Gainesville, Florida 32601

Subject: Summary Report of a Sinkhole Evaluation NW 13th Place Sinkhole Gainesville, Alachua County, Florida GSE Project No. 14866

Dear Mr. Feldman:

GSE Engineering & Consulting, Inc. (GSE) is pleased to submit this report of a sinkhole evaluation of the rights-of-ways of NW 13th Place and NW 14th Place that are adjacent to a sinkhole that recently developed. This report summarizes an evaluation by GSE of the findings and geologic conditions at the site and whether sinkhole activity is present beneath the road right-of-ways.

GSE appreciates the opportunity to have assisted you on this project. If you have any questions or comments concerning this report, please contact us.

Sincerely,

GSE Engineering & Consulting, Inc.

Jason E. Gowland, P.E. Kenneth L. Hill, P.E. Senior Geotechnical Engineer Principal Geotechnical Engineer Florida Registration Number 66467 Florida Registration Number 40146

JEG/KLH:maj Q:\Projects\14866 NW 13th Pl Sinkhole\14866.docx

Distribution: Addressee (1-Electronic) File (1)

Summary Report of a Sinkhole Evaluation December 9, 2020 NW 13th Place Sinkhole Gainesville, Alachua County, Florida GSE Project No. 14866

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EXECUTIVE SUMMARY

GSE Engineering & Consulting, Inc. (GSE) was retained by City of Gainesville to conduct a sinkhole evaluation of the right-of-ways on NW 13th Place, NW 14th Place and NW 40th Terrace adjacent to a recently developed sinkhole. The purpose of this evaluation was to determine if the sinkhole activity that occurred on the adjacent property extended beneath the roadway right-of-ways.

GSE explored the subsurface conditions beneath the roadway right-of-ways using geophysical screening methods, Standard Penetration Test (SPT) soil borings and cone penetrometer soundings. Our exploration found conditions typical of the regional geology, with a thin sand veneer overlying clay-rich soils to the limestone formation which was encountered at depths of about 77 to 87 feet below land surface. One anomaly was detected by the geophysical screening beneath NW 13th Place at a depth of approximately 100 feet below land surface, and was believed to be within the limestone formation. SPT boring B-1 was located within the anomaly and extended to a depth of 120 feet below land surface, and found slightly weaker limestone at the 100 feet depth, but no indicators of sinkhole activity.

Based upon the results of our sinkhole evaluation, sinkhole activity was not found beneath the right-of-ways of NW 13th Place, NW 14th Place and NW 40th Terrace within the areas explored that are adjacent to the recently developed sinkhole.

The remainder of this report summarizes the services conducted as part of this sinkhole exploration and presents our evaluations and conclusions.


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TABLE OF CONTENTS

LIST OF FIGURES ...................................................................................................... iv APPENDIX ................................................................................................................. iv

1.0 INTRODUCTION ............................................................................................ 1-1 1.1 General .......................................................................................................................... 1-1 1.2 Project Description ........................................................................................................ 1-1 1.3 Purpose .......................................................................................................................... 1-1

2.0 SITE RECONNAISSANCE ............................................................................... 2-1 2.1 General Site Observations ............................................................................................. 2-1

3.0 PUBLISHED DATA REVIEW ........................................................................... 3-1 3.1 Review of Published Topographic Data........................................................................ 3-1 3.2 Review of Published Hydrological Data ....................................................................... 3-1 3.3 Review of Published Soil Information .......................................................................... 3-1 3.4 Review of Published Regional Geology ....................................................................... 3-2

4.0 FIELD AND LABORATORY TESTS ................................................................. 4-1 4.1 General Description....................................................................................................... 4-1 4.2 Seismic Reflection Geophysical Study ......................................................................... 4-1 4.3 Standard Penetration Test Borings ................................................................................ 4-2 4.4 Cone Penetrometer Soundings ...................................................................................... 4-2 4.5 Soil Laboratory Tests .................................................................................................... 4-2

5.0 FINDINGS ...................................................................................................... 5-1 5.1 Seismic Reflection Geophysical Study ......................................................................... 5-1 5.2 SPT Boring Results ....................................................................................................... 5-1 5.3 Cone Penetrometer Sounding Results ........................................................................... 5-2

6.0 EVALUATION ................................................................................................ 6-1 7.0 FIELD DATA .................................................................................................. 7-1

7.1 Standard Penetration Test Boring Logs ........................................................................ 7-2 7.2 Cone Penetrometer Sounding Logs ............................................................................... 7-3 7.3 Key to Soil Classifications ............................................................................................ 7-4

8.0 LIMITATIONS ................................................................................................ 8-1 8.1 Warranty ........................................................................................................................ 8-1 8.2 Standard Penetration Test Borings and Cone Penetrometer Soundings ....................... 8-1 8.3 Site Figures .................................................................................................................... 8-1


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LIST OF FIGURES Figure

1. Project Site Location Map 2. Site Plan Showing Approximate Locations of Field Tests

APPENDIX GeoView Project No. 32347 dated December 8, 2020


1-1

1.0 INTRODUCTION

1.1 General GSE Engineering & Consulting, Inc. (GSE) was retained by City of Gainesville to conduct a sinkhole evaluation of the right-of-ways along NW 13th Place, NW 14th Place and NW 40th Terrace that are adjacent to a recently developed sinkhole (Figure 1).

1.2 Project Description A sinkhole developed at the northeast corner of a residential lot located at 4006 NW 13th Place on approximately October 15, 2020. The sinkhole affected four properties, as the sinkhole was located nearly directly beneath the convergence of the rear property corners. The additional properties affected include 4004 NW 13th Place, 4005 NW 14th Place and 4025 NW 14th Place. You are concerned that the recently developed sinkhole has affected the stability of the subsurface beneath the roadway right-of-ways of the adjacent streets.

1.3 Purpose The purpose of this evaluation was to determine the presence or absence of sinkhole activity beneath the portions of the right-of-ways of NW 13th Place, NW 14th Place and NW 40th Terrace that are adjacent to the sinkhole.


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2.0 SITE RECONNAISSANCE

Mr. Kenneth L. Hill, P.E. and Jason E. Gowland, P.E. with GSE visited the site on multiple occasions in October and November 2020 to observe the site conditions and discuss our exploration with City personnel. This exploration has been coordinated with Mr. Brian M. Singleton, P.E., Acting Public Works Director and personnel from Florida Department of Transportation (FDOT).

2.1 General Site Observations A sinkhole developed at the northeast corner of the residential lot located at 4006 NW 13th Place on approximately October 15, 2020. The sinkhole affected four properties, as the sinkhole was located nearly directly beneath the convergence of the rear property corners. The additional properties affected include 4004 NW 13th Place, 4005 NW 14th Place and 4025 NW 14th Place.

We understand the sinkhole originally developed as an approximate 20 feet diameter ground subsidence that was 10 to 12 feet deep. On approximately October 22, 2020 the sinkhole abruptly enlarged to approximately 60 feet in diameter and 30+ feet deep. Since that time, the sinkhole has slowly enlarged to approximately 100 feet in diameter and 40+ feet deep. Currently the sinkhole is holding water that has been seeping in from the side slopes, and the bottom cannot be observed. Based upon our last site observation, the water level within the sinkhole is approximately 12 feet below land surface.

During the first few weeks of development of the sinkhole, the sinkhole filled with groundwater several times, and then the groundwater “flushed” down the throat of the sinkhole exposing the sinkhole throat. With each flush, the sinkhole enlarged. The sinkhole has now been holding water for approximately 3 to 4 weeks. The southern edge of the sinkhole is estimated to be approximately 80 feet from the NW 13th Place right-of-way. The northern edge of the sinkhole is estimated to be approximately 90 feet from the NW 14th Place right-of-way. The NW 40th Terrace right-of-way is more than 170 feet from the edge of the sinkhole.


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3.0 PUBLISHED DATA REVIEW

This section presents a review of readily available published information related to topography, hydrological data, soil survey information and regional geology.

3.1 Review of Published Topographic Data The Alachua County Map Genius indicates the ground surface elevations in the area of the site are near 146 to 148 feet1. The site is gently sloping down toward the south from the north. Regional topography is gently to moderately sloping. A closed depression was identified on the topographic map approximately 400 feet west of the site. A second closed depression was identified approximately 500 feet northeast of the site. Closed depressions are not necessarily an indicator of sinkholes, and could represent other landforms. However, the closed depressions appear to be relic (ancient) sinkholes.

3.2 Review of Published Hydrological Data The Floridan Aquifer in the vicinity of the site has an elevation on the order of 45 to 55 feet2. This elevation is below land surface, indicating a downward hydraulic gradient occurs at the site.

3.3 Review of Published Soil Information The Alachua County Soil Survey3 maps one soil type in the vicinity of the site. The following soil description is from the County soil survey.

Millhopper-Urban land complex, 0 to 5 percent slopes – This complex consists of moderately well drained, nearly level to gently sloping Millhopper soils and Urban land. The areas are irregular in shape and range from about 15 to 250 acres. This complex is within most urbanized areas of the county.

About 50 to 85 percent of each delineation is open areas of Millhopper soils. These open areas are vacant lots or are used for gardens, lawns, parks, or playgrounds. They are either too small or so intermingled with areas of Urban land that it is impractical to map them separately. About 20 to 30 percent of the soils in these open areas have been modified by cutting, grading, and spreading of soil material during urban related construction and development.

About 15 to 50 percent of each delineation is Urban land. Urban land consists of areas covered with buildings, streets, parking lots, sidewalks, and other structures. The Urban land of this map unit is generally developed on Millhopper sand or fine sand.

Typically, the surface layer of Millhopper soils is dark grayish brown sand about 9 inches thick. The subsurface layer is yellowish brown to pale brown sand about 49 inches thick. The subsoil extends to a depth of 80 inches or more. The upper 6 inches is yellowish brown, mottled loamy sand, and the lower 16 inches is gray, mottled sandy clay loam.

1 Alachua County Map Genius, https://mapgenius.alachuacounty.us/ 2 Potentiometric Surface of the Upper Floridan Aquifer in the St. Johns River Water Management District and Vicinity, Florida, May 2009, U.S. Geological Survey. 3 United States Department of Agriculture, Natural Resources Conservation Service, Alachua County Soil Survey.

https://mapgenius.alachuacounty.us/


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The Millhopper soils have a water table that is 40 to 60 inches below the surface for 1 to 4 months and is at a depth of 60 to 72 inches or 2 to 4 months during most years. The available water capacity is low in the surface and subsurface layers and low to medium in the subsoil. Permeability is rapid in the surface and subsurface layers, and it is slow to moderate in the subsoil. Natural fertility is low. Organic matter content is low to moderately low.

3.4 Review of Published Regional Geology Alachua County straddles two physiographic provinces: Northern Highlands and Coastal Lowlands4. A broad karst escarpment known as the Cody Scarp separates these two provinces. The NW 13th Place Sinkhole is in the central portion of Alachua County and is located at the southern edge of the Northern Highlands.

The Northern Highlands, which lie north and east of the Cody Scarp, are underlain by a thick sequence of relatively impermeable Miocene to Pleistocene sediments. Because of this thick sequence of sediments, the Northern Highlands Province contains few karst features. This upland plateau is nearly level, sloping gently to the west, north and east. Elevation ranges from about 150 to 200 feet above sea level. The plateau, which originally extended completely across the county, has many swamps. Sinkholes are not common within the plateau, but a few are found near its margin.

Thin Plio-Pleistocene sediments overlying thin and discontinuous, residual Miocene strata and Eocene limestone characterize the Lowlands. Karst features are numerous in the Lowlands. The western plains region has low relief. Elevation ranges from about 50 to 80 feet above sea level. The plain is devoid of stream channels, but it is dotted with sinks and limestone mines. While the Ocala Limestone is essentially near the surface in this region, many of the old sinks have become filled (some to a depth of 250 feet) with sand, clayey sand, and sandy clay. These soil materials come from marine submergence, soil creep and slumping, and stream transport from the Northern Highlands. This sinkhole fill tends to mask many of the karst irregularities of the Ocala surface.

The Cody Scarp, which separates the Northern Highlands from the Coastal Lowlands, contains large sinkholes, sinking streams, and other karst features. The bottoms of the karst features often penetrate to the Ocala Limestone and the depressions are usually filled with organic soils, fluvial and lacustrine sediments, and clay-rich soils. The hills within the scarp contain Miocene sediments similar to the Northern Highlands Province. Many of the large, flat-bottomed lakes and wet prairies are associated with the scarp and represent coalescent sinkholes known as poljes and uvalas. Many of these level prairies and lakes, most of which are near or below 60 feet NGVD, are associated with ground water levels.

Three major geologic formations occur at or near the surface within the county. These formations have influenced soil development. They are, in order of decreasing age, the Ocala Limestone of Eocene age, the Miocene to Pliocene Hawthorn Group, and the Plio-Pleistocene Terrace Deposits.

4 White, W.A., 1970. The Geomorphology of the Florida Peninsula. Florida Geological Survey, Bulletin 51.


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The Ocala Limestone underlies the entire county; exposures are common in the Coastal Lowlands in the southern and western parts of the county. Here a limestone plain is formed which is covered by a veneer of loose sand in most places. Thin and discontinuous beds of clay-rich soils may also occur in this region of the county. The Ocala Limestone consists of soft, white to cream colored, chalky, limestone that is approximately 98 percent calcium carbonate. Boulders and irregular masses of chert are common near the top. In many areas the Ocala is cavernous and fractured.

The Miocene Hawthorn Group includes at least three formations in Alachua County. These are, from bottom to top, the Penny Farms Formation, Marks Head Formation, and Coosawhatchie Formation5. All three formations consist of varying proportions of interbedded clay, sand, limestone, and dolostone, all of which are phosphatic. The Hawthorn Group crops out in isolated areas around the town of Micanopy and in an irregular pattern along the Cody Scarp from Lochloosa Lake northwestward through Gainesville and into the north-Northern and northwestern part of the county. Much of the outcrop area is hill and valley terrain created by the formation of karst features at the foot of the escarpment. A thin veneer of loose sands of the older Plio-Pleistocene Terrace deposits covers the Hawthorn Group of sediments in the Cody Scarp and Northern Highlands. The Hawthorn Group lies unconformably on the solution-pitted Ocala Limestone surface.

The most recent formation is a surface mantle of fine to medium sand, silt, and clay that formed as Pliocene and Pleistocene sea levels fluctuated and periodically inundated portions of the county. Primarily, the terrace deposits overlie the Hawthorn Group. They are exposed in the Northern and eastern parts of the county.

5 Scott, T.M., 1988. The Lithostratigraphy of the Hawthorn Group (Miocene) of Florida. Florida Geological Survey, Bulletin No. 59.


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4.0 FIELD AND LABORATORY TESTS

4.1 General Description The procedures used for field sampling and testing are in general accordance with industry standards of care and established engineering and geological investigation practices for this geographic region. This exploration consisted of performing geophysical services consisting of Seismic Reflection, Standard Penetration Test borings, and cone penetrometer soundings. The following sections describe our field and laboratory testing program in more detail.

4.2 Seismic Reflection Geophysical Study Seismic reflection was performed at the site by GeoView, Inc. (GeoView) as a subconsultant to GSE.

Seismic reflection profiling involves the measurement of the two-way travel time of seismic waves transmitted from surface and reflected back to the surface at the interfaces between contrasting geological layers. Reflection of the transmitted energy will only occur when there is a contrast in the acoustic impedance (product of the seismic velocity and density) between these layers. The strength of the contrast in the acoustic impedance of the two layers determines the amplitude of the reflected signal. The reflected signal is detected on surface using an array of high frequency geophones (typically 24-96). As with seismic refraction, the seismic energy is provided by a 'shot' on surface. For shallow applications this will normally comprise a hammer and plate, weight drop or explosive charge. In most reflection surveys shots are deployed at a number of different positions in relation to the geophone array in order to obtain reflections from the same point on the interface at different geophones in the array. Each common point of reflection is termed a common mid-point (CMP) and the number of times each one is sampled determines the 'fold coverage' for the survey. Traces relating to the same CMP are stacked together to increase the signal-to-noise ratio of the survey before being combined with other CMP's stacked traces to produce a reflection profile. In order to stack related CMP traces a stacking velocity is applied to each trace. This accounts for the difference in two-way travel time between the normal incidence reflection (vertical travel path below the shot) and those at increasing offsets from the shot (known as the normal moveout or NMO). The stacking velocity will vary down the trace to take account of the increase in velocity with depth for each reflection event.

Data acquisition was accomplished using a Geometrics Geode, 48-channel seismograph system. GeoView acquired compression- (P-) wave seismic reflection data using a basic 48-geophone spread. The geophones were placed in a line with 10 foot spacing between each of the geophones. Shot points were performed at 10 feet intervals along the transect. A total of 82 shot points were acquired. The energy source used at each shot point consisted of a polyethylene plate being struck by a 16-pound sledgehammer. Each shot point consisted of multiple hammer blows in an attempt to maximize the desired signal while minimizing background noise.

A more detailed description of the seismic refraction methods is included in the GeoView report in the Appendix (GeoView Project No. 32347).


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4.3 Standard Penetration Test Borings The boring locations were selected considering the findings of the geophysical screening and the location of the sinkhole. The soil borings were performed with a drill rig employing mud rotary drilling techniques and Standard Penetration Testing (SPT) in accordance with ASTM D1586. The SPTs were performed continuously to 10 feet and at 5-foot intervals thereafter. Soil samples were obtained at the depths where the SPTs were performed. The soil samples were classified in the field, placed in sealed containers, and returned to our laboratory for further evaluation.

After drilling to the sampling depth and flushing the borehole, the standard two-inch O.D. split-barrel sampler was seated by driving it 6 inches into the undisturbed soil. Then the sampler was driven an additional 12 inches by blows of a 140-pound hammer falling 30 inches. The number of blows required to produce the 12 inches of penetration were recorded as the penetration resistance (“N” value). These values and the complete SPT boring logs are provided in Section 7.1.

Upon completion of the sampling, the boreholes were abandoned in accordance with Water Management District guidelines. The SPT boring locations are indicated on Figure 2.

4.4 Cone Penetrometer Soundings Cone penetrometer soundings were performed at the site by the Florida Department of Transportation, through an agreement with the City. The approximate locations of the cone penetrometer soundings are indicated on the attached Figure 2.

The cone penetrometer soundings were performed by FDOT in accordance with ASTM D5778. The soundings involve pushing an electronic penetrometer instrument into the soil and recording multiple measurements continuously with depth. The soundings performed at this site measured cone resistance, sleeve friction and friction ratio. This data is used to estimate the soil types penetrated. The soundings were terminated when penetration refusal occurred. Results from the cone penetrometer soundings are provided in Section 7.2.

4.5 Soil Laboratory Tests The soil samples recovered from the soil borings were returned to our laboratory, and examined by an engineer to confirm the field descriptions. No laboratory testing was performed for this evaluation.


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5.0 FINDINGS

This section summarizes the findings of the field and laboratory services.

5.1 Seismic Reflection Geophysical Study A complete discussion of the seismic reflection methods and findings are presented in the GeoView report in the Appendix. The following discussion was taken from the GeoView report.

The final processed high-resolution seismic reflection sections are presented in in Figures 2 and 3 for Lines 1 and 2, respectively (GeoView report in the Appendix). Seismic reflection sections illustrate geologic layers as continuous (“coherent”) horizons that can be traced across the full section. Disturbances such as faults, sinkholes, and cavities are observed as corresponding offsets or loss of continuity in these reflecting horizons. The horizontal scale on these sections is merely distance along the particular transect. The vertical scale is the reflection time. That is, it is the time taken from the moment of the hammer blow for the seismic wave to travel down to the geologic horizon, reflect/echo from it, and travel back up to the ground surface.

On the cross section, we see a strong, mostly consistent reflection (highlighted in green) that occurs near the 60 to 70 millisecond time range. This corresponds to a depth of approximately 80 to 90 feet. It is suspected that this reflection is from the top of limestone layer. A possible disruption of the reflections immediately below the top of the suspected limestone is evident from a horizontal distance of 170 to 240 feet along the Transect 1. The seismic data in this area indicates that the upper surface of the limestone may have a higher degree of weathering than the surrounding material. The anomaly extended to a depth of approximately 100 to 120 feet. This area is indicated in magenta on the figures. A boring performed by GSE in the center of this anomaly did not encounter any voids, very soft material or other indications of significant karst activity. No anomalies were observed on Seismic Transect 2.

5.2 SPT Boring Results Five SPT borings were conducted at the site. The selected boring locations considered the geophysical survey information and the location of the sinkhole. SPT boring B-1 was performed in the anomaly identified by the geophysical screening. The remaining soil borings were located along the right-of-ways adjacent to the sinkhole. Descriptions for the soils encountered are based on visual observations of the recovered soil samples. Stratification boundaries between the soil types should be considered approximate, as the actual transition between soil types may be gradual. The SPT boring locations are indicated on Figure 2. The SPT values and complete boring logs are provided in Section 7.1. The key to soil classifications is provided in Section 7.3.

The SPT borings encountered relatively consistent subsurface conditions. The borings first encountered loose brown, gray and tan sand and sand with silt (SP, SP-SM) to depths of 3 to 6 feet below land surface (bls). Borings B-4 and B-5 were located in the paved roadway due to the presence of buried utilities adjacent to the road, and the pavement section consists of 1 to 1.5 inches of asphalt overlying 8 to 12 inches of limerock base course.

The soil borings next encountered medium dense to very dense light gray, orange and red clayey sand to very clayey sand (SC) to depths of 18 to 23 feet bls. Very stiff pale green clay (CL/CH) was interbedded in this layer in boring B-4 from 13 to 18 feet bls.


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The borings next encountered a phosphate-rich layer consisting of very loose to medium dense light gray and olive green silty sand (SM), clayey sand and very clayey sand (SC) and firm to stiff silty sand clay and clay with sand (CL/CH), all with abundant phosphate and limestone chunks to depths of 38 to 42 feet bls.

Medium dense gray, orange, red and green clayey to very clayey sand (SC) and stiff to very hard sandy clay and clay (CL/CH) was next encountered to depths of 48 to 62 feet bls. A very soft zone was encountered in boring B-5 at the 50 feet sampling interval with no sample recovery, but there was no loss of drilling fluid circulation. The soils became very hard at the 55 feet sampling interval.

The borings next encountered clay-rich soils consisting of firm to hard, gray, orange, brown and green clay and clay with sand (CL/CH) to depths of 62 to 78 feet bls. A loss of drilling fluid circulation occurred in boring B-1 at a depth of 70 feet bls.

The SPT borings next encountered the epikarst zone, which is the zone where the soils transition to the limestone formation. The epikarst consisted of dense to very dense, light brown, light gray and orange silty sand (SM), silty clayey sand (SC), clayey sand (SC), silty clay (CL/CH), with some of these soils containing fragments of limestone. Very hard clayey limestone was encountered in some of the SPT borings. Drilling fluid circulation returned in boring B-1 at a depth of 83 feet bls.

White limestone was next encountered in the borings to the boring termination depths. The limestone was generally very hard. A loss of drilling fluid circulation occurred in the limestone in boring B-4 at 93 feet bls. Boring B-1 was extended to a depth of 120 feet bls to evaluate the anomaly identified by the geophysical screening, and the limestone was found to be soft to hard from 93 to 118 feet bls confirming the higher weathered condition of the limestone by the seismic reflection study. No drilling fluid losses occurred in this weaker zone of limestone.

Groundwater was encountered in boring B-3 at a depth of 4 feet bls. Groundwater was not determined in the remaining SPT borings due to the mud rotary drilling method not allowing the detection of the water table.

5.3 Cone Penetrometer Sounding Results Six cone penetrometer soundings were performed at the site by FDOT. The locations of the cone soundings are indicated on the attached Figure 2.

Cone penetrometer soundings evaluate soil strength properties, and these properties are used to estimate the soil types penetrated. Sandy and silty soils typically have low friction ratios (the correlation between the cone tip stress and sleeve stress) and are noted by the yellow, tan and light gray colors on the cone logs. Clay-rich soils typically have large friction ratios, and are noted on the cone logs as blues and greens.

The cone penetrometer soundings found a relatively consistent subsurface profile. The soundings first encountered about 10 feet of sandy soils. The upper 4 to 6 feet of these soils are loose to medium dense, with cone tip resistance values of 25 to 50 tons per square foot (tsf). These soils become dense to very dense from about 6 to 10 feet, where the tip stresses are typically greater than 100 tsf.


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Stiff to hard clay-rich soils were penetrated from about 10 to 18 feet bls. These soils have sleeve resistance values of 2 to 8 tsf. These soils are underlain by a mixture of medium dense to dense sandy and stiff to very stiff clay-rich soils to a depth of about 30 feet. The variability of this layer is consistent with the phosphate-rich layer encountered by the SPT borings.

Hard clay-rich soils were then penetrated to depths of 58 to 70 feet. These soils have cone sleeve resistance values of 2 to 8 tsf. The cones next encountered very dense sandy materials to the cone termination depths of 65 to 73 feet bls. This zone correlates well with the epikarst zone found by the SPT borings. The cone soundings were terminated due to refusal or from excessive sleeve friction.

The cone penetrometer logs are included in Section 7.3.


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6.0 EVALUATION The material types and depths encountered by the borings are relatively consistent with the County Soil Survey mappings and the regional geology.

The geophysical screening performed along NW 13th Place and NW 14th Place did not detect indicators of sinkhole activity in the soils overlying the limestone formation. The only anomaly detected was along NW 13th Place and consisted of a more porous or weathered zone of limestone below a depth of 100 feet.

The SPT borings and cone penetrometer soundings found relatively consistent subsurface conditions at the site, with a surface veneer of sandy soils overlying clayey sands, silty clayey sands, sandy clays and clays. Limestone was generally encountered at depths of 72 to 87 feet. Groundwater was encountered in only one of the SPT borings at a depth of 4 feet bls. Groundwater was not determined in the other SPT borings due to the mud rotary method of advancing the boreholes, but groundwater is expected to be within 6 feet of land surface.

The relative densities of the soils generally ranged from medium dense to very dense for the sandy soils and stiff to hard for the clay-rich soils. The limestone was generally very hard. The exceptions to this were a very soft zone in the clay in boring B-5 at a depth of 50 feet bls, and soft to medium hard limestone in boring B-1 from 93 to 118 feet bls. This soft zone is consistent with the anomaly detected by the geophysical screening. However, there were no losses of drilling fluid circulation in these zones to suggest these conditions are related to sinkhole activity.

A loss of drilling fluid circulation occurred in boring B-1 at a depth of 70 feet bls in the epikarst. Circulation returned at a depth of 83 feet after penetrating limestone. A loss of drilling fluid circulation occurred in boring B-4 at a depth of 93 feet bls within the limestone formation. Circulation losses are common in the epikarst and limestone, and alone are not indicators of sinkhole activity.

The SPT borings and cone penetrometer soundings in our opinion did not encounter indicators of sinkhole activity. It is GSE’s opinion that sinkhole activity is not occurring beneath the right-of-ways of NW 13th Place, NW 14th Place and NW 40th Terrace within the limits of our exploration.


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7.0 FIELD DATA


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7.1 Standard Penetration Test Boring Logs

3-4-3-3(7)

3-3-6-10(9)

11-14-20-22(34)

3-4-6 (10)

11-13-14 (27)

4-6-7 (13)

7-5-6 (11)

4-5-5 (10)

7-7-11 (18)

9-8-10 (18)

5-6-7 (13)

AP1

AP2

SPT3

SPT4

SPT5

SPT6

SPT7

SPT8

SPT9

SPT10

SPT11

SPT12

SPT13

6

13

18

23

28

32

38

42

47

(SP-SM) Loose brown and tan SAND with silt

(SC/CL) Loose to dense light brown and gray veryclayey SAND

(CL/CH) Stiff light gray CLAY

(SC/CL) Medium dense light gray and orange veryclayey SAND

(SC) Medium dense light gray clayey SAND withphosphate

(SM) Stiff light gray silty sandy CLAY

(SC/CL) Medium dense gray very clayey SAND withphosphate

(SC) Medium dense greenish gray clayey SAND

(SC/CL) Medium dense light gray and orange veryclayey SAND

(CL/CH) Firm to stiff olive green to gray CLAY

GROUND ELEVATION

LOGGED BY SDI

DRILLING METHOD Mud Rotary

HOLE SIZE

DRILLING CONTRACTOR Standard Drilling Services, LLC. GROUND WATER LEVELS:

CHECKED BY KLH

DATE STARTED 11/23/20 COMPLETED 11/23/20

ESTIMATED SEASONAL HIGH NA

NOTES

AT TIME OF DRILLING NE

SPT N VALUE

20 40 60 80

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BORING NUMBER B-1

PROJECT NUMBER 14866 PROJECT LOCATION Gainesville, Alachua County, Florida

CLIENT City of Gainesville PROJECT NAME NW 13th Place Sinkhole

GSE Engineering & Consulting, Inc.5590 SW 64th St.Gainesville, FL 32608Telephone: (352)377-3233Fax: (352)377-0335

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US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

3-4-4 (8)

30-19-14 (33)

14-25-34 (59)

3-3-1 (4)

39-50/4"50/4"

50/5"

50/4"

48-31-28 (59)

21-13-23 (36)

12-12-13 (25)

9-10-17 (27)

SPT14

SPT15

SPT16

SPT17

SPT18

SPT19

SPT20

SPT21

SPT22

SPT23

SPT24

57

62

68

73

77

83

93

Loss of circulation at 70 ft

Return of circulation at 83 ft

(CL/CH) Firm to stiff olive green to gray CLAY(continued)

(SC/CL) Dense light gray very clayey SAND withlimestone

(CL/CH) Very hard light green CLAY with sand

(CL/CH) Soft light gray and orange CLAY with sand

(SM/SC) Very dense light gray and orange silty SANDwith clay

Very hard white clayey LIMESTONE

Very hard white LIMESTONE with shell

Soft to hard white LIMESTONE

SPT N VALUE

20 40 60 80


GR

AP

HIC

LOG

DE

PT

H(f

t)

50

60

70

80

90

100

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-1




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

>>

>>

>>

11-15-20 (35)

29-9-3 (12)

30-36-30 (66)

SPT25

SPT26

SPT27

118

120

Soft to hard white LIMESTONE (continued)

Very hard white LIMESTONE

Bottom of borehole at 120.0 feet.

SPT N VALUE

20 40 60 80

GR

AP

HIC

LOG

DE

PT

H(f

t)

110

120

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-1




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

4-5-2-2(7)

4-7-15-23(22)

13-20-28-31(48)

5-5-5 (10)

4-3-4 (7)

3-3-4 (7)

5-6-4 (10)

4-4-7 (11)

5-11-11 (22)

5-8-9 (17)

5-6-7 (13)

AP1

AP2

SPT3

SPT4

SPT5

SPT6

SPT7

SPT8

SPT9

SPT10

SPT11

SPT12

SPT13

4

6

13

18

32

38

42

47

(SP-SM) Brown and gray SAND with silt

(SC/CL) Loose tan and orange very clayey SAND

(SC) Medium dense to dense light gray and orangeclayey SAND

(CL/CH) Stiff gray and green CLAY with sand

(SC) Loose light gray clayey SAND with phosphate

(CL/CH) Stiff light gray and orange silty CLAY with sand

(SC) Medium dense grayish green clayey SAND withlimestone

(CL/CH) Very stiff gray and orange CLAY with sand

(CL/CH) Stiff gray, green and dark orange CLAY withtrace limestone

GROUND ELEVATION

LOGGED BY SDI


HOLE SIZE


CHECKED BY KLH



NOTES


SPT N VALUE

20 40 60 80


GR

AP

HIC

LOG

DE

PT

H(f

t)

0

10

20

30

40

50

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-2




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

5-6-9 (15)

12-12-15 (27)

14-16-17 (33)

10-18-50/2"68/8"

50/5"

32-50/4"50/4"

23-45-50/4"95/10"

SPT14

SPT15

SPT16

SPT17

SPT18

SPT19

SPT20

57

62

67

82

85

(CL/CH) Stiff gray, green and dark orange CLAY withtrace limestone (continued)

(CL/CH) Very stiff dark gray and green sandy CLAY withphosphate

(SM/SC) Dense dark orange silty clayey SAND

(CL/CH) Very hard tan and orange silty sandy CLAYwith limestone



SPT N VALUE

20 40 60 80

GR

AP

HIC

LOG

DE

PT

H(f

t)

50

60

70

80

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-2




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

>>

>>

>>

>>

2-3-3-4(6)

3-4-8-11(12)

15-17-27-26(44)

20-21-25 (46)

9-10-9 (19)

2-2-2 (4)

1-2-2 (4)

2-3-5 (8)

7-9-10 (19)

10-16-17 (33)

3-5-5 (10)

AP1

AP2

SPT3

SPT4

SPT5

SPT6

SPT7

SPT8

SPT9

SPT10

SPT11

SPT12

SPT13

1

6

13

22

33

38

42

48

(SP-SM) Dark gray SAND with silt(SP) Loose tan to light gray SAND

(SC/CL) Medium dense to dense orange, brown and tanvery clayey SAND

(SC) Medium dense to dense light gray and orangeclayey SAND

(SC) Loose light gray to tan clayey SAND withphosphate

(CL/CH) Firm gray and brown silty sandy CLAY

(SC) Medium dense light gray to olive green clayeySAND with phosphate

(SC/CL) Dense dark orange and green very clayeySAND with cemented clay

(CL/CH) Stiff to very stiff light gray and green CLAY withsand

GROUND ELEVATION

LOGGED BY SDI


HOLE SIZE


CHECKED BY KLH



NOTES

AT TIME OF DRILLING 4.0 ft

SPT N VALUE

20 40 60 80


GR

AP

HIC

LOG

DE

PT

H(f

t)

0

10

20

30

40

50

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-3




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

4-5-6 (11)

8-14-13 (27)

15-21-30 (51)

31-22-18 (40)

17-16-17 (33)

50/4"

36-35-50/3"85/9"

SPT14

SPT15

SPT16

SPT17

SPT18

SPT19

SPT20

63

68

77

85

(CL/CH) Stiff to very stiff light gray and green CLAY withsand (continued)

(SM) Very dense tan, brown and orange silty SAND

(CL/CH) Hard orange and light gray silty CLAY withlimestone



SPT N VALUE

20 40 60 80

GR

AP

HIC

LOG

DE

PT

H(f

t)

50

60

70

80

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-3




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

>>

>>

5-8 (13)10-6-4 (10)3-7-10 (17)

10-10-11 (21)

14-20-19 (39)

16-17-21 (38)

5-11-13 (24)

1-2-5 (7)

4-3-3 (6)

1-1-1 (2)

1-1-2 (3)

5-7-7 (14)

3-5-6 (11)

8-11-12 (23)

SPT1

SPT2

SPT3

SPT4

SPT5

SPT6

SPT7

SPT8

SPT9

SPT10

SPT11

SPT12

SPT13

SPT14

1.125

3

5.5

7

13

18

28

33

38

43

48

1.5" ASPHALT12" LIMESTONE BASE(SP-SM) Medium dense brown and light gray SANDwith silt(SC) Medium dense light gray amd orange clayey SAND

(SC/CL) Medium dense light gray, orange and red veryclayey SAND(SC) Dense light gray and red clayey SAND

(CL/CH) Very stiff pale green CLAY

(SC) Loose light gray clayey SAND with phosphate

(SP-SC) Very loose light gray silty SAND with clay andphosphate

(CL/CH) Soft olive green silty sandy CLAY

(SM/SC) Medium dense light gray silty clayey SANDwith limestone chunks

(CL/CH) Stiff olive green and orange sandy CLAY

(SC) Medium dense light grayish green clayey SAND

GROUND ELEVATION

LOGGED BY WDI


HOLE SIZE

DRILLING CONTRACTOR Whitaker Drilling, Inc. GROUND WATER LEVELS:

CHECKED BY KLH



NOTES


SPT N VALUE

20 40 60 80


GR

AP

HIC

LOG

DE

PT

H(f

t)

0

10

20

30

40

50

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-4




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

5-7-9 (16)

5-6-7 (13)

7-6-8 (14)

10-11-18 (29)

22-50/5"50/5"

40-50/3"50/3"

45-50/2"50/2"

50/1"

50/1"

SPT15

SPT16

SPT17

SPT18

SPT19

SPT20

SPT21

SPT22

SPT23

53

68

73

78

83

88

92

95

(SC) Medium dense light grayish green clayey SAND(continued)

(CL/CH) Stiff olive green CLAY

(CL/CH) Very stiff gray CLAY

(CL/CH) Very hard orange brown CLAY with sand

(SM/SC) Very dense light brown silty clayey SAND

Very hard light gray to white clayey LIMESTONE

NO RECOVERY (Presumed very hard limestone)

Very hard white limestone


SPT N VALUE

20 40 60 80

GR

AP

HIC

LOG

DE

PT

H(f

t)

50

60

70

80

90

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-4




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

>>

>>

>>

>>

>>

7-9-12-15(21)

19-21-27-39(48)

18-25-25-40(50)

17-14-20 (34)

6-4-5 (9)

5-5-4 (9)

1-2-2 (4)

4-5-7 (12)

5-11-18 (29)

3-4-5 (9)

0-0-0 (0)

AP1

AP2

SPT3

SPT4

SPT5

SPT6

SPT7

SPT8

SPT9

SPT10

SPT11

SPT12

SPT13

0.75

3

8

13

18

22

33

38

42

48

1" ASPHALT8" LIMEROCK BASE(SP) Brown SAND(SC/LC) Medium dense to very dense green, orangeand red very clayey SAND

(SC) Very dense gray clayey SAND

(SC/CL) Dense gray and orange very clayey SAND

(SM/SC) Loose light gray silty clayey SAND

(SC/LC) Loose light gray very clayey SAND withphosphate

(SC) Medium dense olive green clayey SAND

(SM/SC) Medium dense light gray silty clayey SANDwith limestone

(CL/CH) Stiff gray, orange and red sandy CLAY

NO RECOVERY, presumed to be very soft sandy CLAY

GROUND ELEVATION

LOGGED BY SDI


HOLE SIZE


CHECKED BY KLH



NOTES


SPT N VALUE

20 40 60 80


GR

AP

HIC

LOG

DE

PT

H(f

t)

0

10

20

30

40

50

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-5




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

6-16-31 (47)

13-16-13 (29)

2-3-5 (8)

11-13-22 (35)

17-15-16 (31)

26-50/5"50/5"

50/5"

50/0"

SPT14

SPT15

SPT16

SPT17

SPT18

SPT19

SPT20

SPT21

52

58

63

68

78

82

87

90

NO RECOVERY, presumed to be very soft sandy CLAY(continued)

(CL/CH) Very stiff gray and olive green silty sandy CLAY

(CL/CH) Very stiff gray and orange CLAY

(CL/CH) Firm gray CLAY

(CL/CH) Hard gray CLAY

(SM/SC) Very dense light gray and orange silty clayeySAND with limestone

(SC) Very dense light gray clayey SAND with limestone



SPT N VALUE

20 40 60 80

GR

AP

HIC

LOG

DE

PT

H(f

t)

50

60

70

80

90

BLO

WC

OU

NT

S(N

VA

LUE

)

SA

MP

LE T

YP

EN

UM

BE

R

CO

NT

AC

TD

EP

TH

(ft)


MO

IST

UR

EC

ON

TE

NT

, %

PE

RC

EN

T P

AS

SN

O. 2

00 S

IEV

E

LIQ

UID

LIM

IT, %

PLA

ST

IC L

IMIT

, %

PLA

ST

ICIT

YIN

DE

X

BORING NUMBER B-5




SP

T B

OR

ING

S -

GIN

T S

TD

US

.GD

T -

12

/14

/20

14

:39

- Q

:\P

RO

JEC

TS

\14

86

6 N

W 1

3T

H P

L S

INK

HO

LE

\14

86

6 B

OR

ING

S\1

48

66.

GP

J

>>

>>

>>


7-3

7.2 Cone Penetrometer Sounding Logs

SOUNDINGSOUNDINGCUSTOMER: State Materials OfficeOPERATOR: tsbCONE ID: DSA1173LOCATION:

JOB NUMBER: GAINESVILLE SinkHOLE NUMBER: cpt# 1TEST DATE: 11/4/2020 9:21:23 AMCOMMENT: Auto Enhance OnCOMMENT: Filter On

COMMENT:GPS (LAT,LON,ALT): 0.00,0.00,0.0LOCATION:LOCATION:LOCATION:

Depth(ft)

Tip COR(tsf)0 300

0

10

20

30

40

50

60

70

Sleeve Stress(tsf)0 12

F.Ratio(%)0 14

SBT FR(RC 1983)

1 sensitive fine grained2 organic material3 clay

4 silty clay to clay5 clayey silt to silty clay6 sandy silt to clayey silt

7 silty sand to sandy silt8 sand to silty sand9 sand

10 gravelly sand to sand11 very stiff fine grained (*)12 sand to clayey sand (*)

*SBT/SPT CORRELATION: UBC-1983

0 12

rt820dj

Highlight

HOLE NUMBER: cpt# 1




Depth(ft)

Tip COR(tsf)0 450

0

10

20

30

40

50

60

70


F.Ratio(%)0 14

SBT FR(RC 1983)






0 12

rt820dj

Highlight

HOLE NUMBER: cpt# 2


JOB NUMBER: GAINESVILLE SinkHOLE NUMBER: cpt# 3TEST DATE: 11/4/2020 12:42:19 PMCOMMENT: Auto Enhance OnCOMMENT: Filter On


Depth(ft)

Tip COR(tsf)0 400

0

10

20

30

40

50

60

70

80


F.Ratio(%)0 14

SBT FR(RC 1983)






0 12

rt820dj

Highlight

HOLE NUMBER: cpt# 3


JOB NUMBER: GAINESVILLE SinkHOLE NUMBER: cpt# 4TEST DATE: 11/4/2020 2:05:56 PMCOMMENT: Auto Enhance OnCOMMENT: Filter On


Depth(ft)

Tip COR(tsf)0 450

0

10

20

30

40

50

60

70

80


F.Ratio(%)0 40

SBT FR(RC 1983)






0 12

rt820dj

Highlight

HOLE NUMBER: cpt# 4




Depth(ft)

Tip COR(tsf)0 400

0

10

20

30

40

50

60

70

80


F.Ratio(%)0 10

SBT FR(RC 1983)






0 12

rt820dj

Highlight

HOLE NUMBER: cpt# 5




Depth(ft)

Tip COR(tsf)0 350

0

10

20

30

40

50

60

70

80


F.Ratio(%)0 12

SBT FR(RC 1983)






0 12

rt820dj

Highlight

HOLE NUMBER: cpt# 6

CPT notes from 43rd Street Sinkhole Project

CPT # Approximate

Termination Depth (from GSE)

Location Notes

1 65ft 17ft from roadway centerline

300+tsf on tip; no more penetration

2 65.29ft 17ft from centerline 15+tsf friction

Soundings were terminated due to excessive sleeve friction

3 71.69 20ft from centerline 300+tsf on tip; no more

penetration.

4 73.14 9ft from centerline,2ft from edge of pavement

Same notes as CPT #2

5 73ft 18ft from centerline Same notes as CPT #2

6 71.17ft 15.5 from centerline

300+tsf on tip & high sleeve friction.

Terminated test due to both excessive on tip and sleeve


7-4

7.3 Key to Soil Classifications

GRAPHIC LETTER

COARSE-GRAINED SOILS Gravels Clean Gravels Cu ≥ 4 and 1 ≤ Cc ≤ 3 GW Well graded GRAVEL

Less than 5% fines Cu < 4 and/or 1 > Cc > 3 GP Poorly graded GRAVEL

Gravels with fines Fines classify as ML or MH GM Silty GRAVEL

More than 12% fines Fines classify as CL or CH GC Clayey GRAVEL

Sands Clean Sands Cu ≥ 6 and 1 ≤ Cc ≤ 3 SW Well graded SAND

Less than 5% fines Cu < 6 and/or 1 > Cc > 3 SP Poorly graded SAND

Sand with fines Fines classify as ML or MH SP-SM SAND with silt

5% ≤ fines < 12% Fines classify as CL or CH SP-SC SAND with clay

Sand with fines Fines classify as ML or MH SM Silty SAND

12% ≤ fines < 30% Fines classify as CL or CH SC Clayey SAND

Sand with fines Fines classify as ML or MH SM Very silty SAND

30% fines or more Fines classify as CL or CH SC Very clayey SAND

FINE-GRAINED SOILS Clays inorganic 50% ≤ fines < 70% CL/CH Sandy CLAY

70% ≤ fines < 85% CL/CH CLAY with sand

fines ≥ 85% CL/CH CLAY

Silts and Clays inorganic PI > 7 and plots on/above "A" line CL Lean CLAY

Liquid Limit less than 50 PI < 4 or plots below "A" line ML SILT

organic Liquid Limit - oven dried Organic clay

Liquid Limit - not dried Organic silt

Silts and Clays inorganic PI plots on or above "A" line CH Fat CLAY

Liquid Limit 50 or more PI plots below "A" line MH Elastic SILT

organic Liquid Limit - oven dried Organic clay

Liquid Limit - not dried Organic silt

HIGHLY ORGANIC SOILS PT PEAT

No. OF BLOWS, N RELATIVE DENSITY No. OF BLOWS, N CONSISTENCY

0 - 4 Very Loose 0 - 2 Very Soft

5 - 10 Loose SILTS 3 - 4 Soft

SANDS: 11 - 30 Medium dense & 5 - 8 Firm

31 - 50 Dense CLAYS: 9 - 15 Stiff

OVER 50 Very Dense 16 - 30 Very Stiff

31 - 50 Hard

OVER 50 Very Hard

0 - 8 Very Soft

9 - 18 Soft

LIMESTONE: 19 - 32 Moderately Hard

33 - 50 Hard

OVER 50 Very Hard

BOULDERS: Greater than 300 mm

COBBLES: 75 mm to 300 mm LL = Liquid Limit, %

GRAVEL: Coarse - 19.0 mm to 75 mm PL = Plastic Limit, %

Fine - 4.75 mm to 19.0 mm PI = Plasticity Index, %

SANDS: Coarse - 2.00 mm to 4.75 mm % PASS - 200 = Percent Passing the No. 200 Sieve

Medium - 0.425 mm to 2.00 mm MC = Moisture Content, %

Fine - 0.075 mm to 0.425 mm ORG = Organic Content, %

SILTS & CLAYS: Less than 0.075 mm kh = Horizontal Hydraulic Conductivity, ft/day

50% or more passes the

No. 200 sieve

50% or more of coarse

fraction passes No. 4 sieve

< 0.75

< 0.75

KEY TO SOIL CLASSIFICATION CHART

GROUP NAME

More than 50% retained

on No. 200 sieve

More than 50% of coarse

fraction retained on No. 4

sieve

SYMBOLSCriteria for Assigning Group Symbols and Group Names Using Laboratory Tests

OL

OH

Primarily organic matter, dark in color, and organic odor

PARTICLE SIZE IDENTIFICATION

LABORATORY TEST LEGEND

CORRELATION OF PENETRATION RESISTANCE WITH RELATIVE DENSITY AND CONSISTENCY

Location

of Auger

Sample

SAMPLE GRAPHIC TYPE LEGEND

Location

of SPT

Sample

No. OF BLOWS, N RELATIVE DENSITY


8-1

8.0 LIMITATIONS

8.1 Warranty GSE Engineering & Consulting, Inc. has prepared this report for our client for his exclusive use, in accordance with generally accepted soil and foundation engineering and geological investigation practices, and makes no other warranty either expressed or implied as to the professional opinions provided in the report.

8.2 Standard Penetration Test Borings and Cone Penetrometer Soundings The determination of soil type and conditions was performed from the ground surface to the maximum depth of the borings. Any changes in subsurface conditions that occur between or below the borings would not have been detected or reflected in this report.

Soil classifications that were made in the field are based upon identifiable textural changes, color changes, changes in composition or changes in resistance to penetration in the intervals from which the samples were collected. Abrupt changes in soil type, as reflected in boring logs and/or cross sections may not actually occur, but instead, be transitional.

Depth to the water table is based upon observations made during the performance of the borings. This depth is an estimate and does not reflect the annual variations that would be expected in this area due to fluctuations in rainfall and rates of evapotranspiration.

8.3 Site Figures The measurements used for the preparation of the figures in this report were made using measuring devices and/or by estimating distances from existing structures and site features. The illustrated test locations should be considered approximate. Figures in this report were not prepared by a licensed land surveyor and should not be interpreted as such.


FIGURES

PROJECT LOCATION

FIGURE

1

NOT TO SCALE

NORTH

PROJECT SITE LOCATION MAP

DESIGNED BY: KLHCHECKED BY : KLHDRAWN BY : SCL

NW 13th PLACE SINKHOLEGAINESVILLE, ALACHUA COUNTY, FLORIDAGSE PROJECT NO. 14866

0 50'

SCALE: 1" = 50' APPROX.

FIG

UR

E

2

NORTHLEGEND :

SITE

PLA

N S

HO

WIN

G A

PPR

OX

IMA

TE L

OC

ATI

ON

S O

F FI

ELD

TES

TS

DES

IGN

ED B

Y:

KLH

CH

ECK

ED B

Y:

KLH

DR

AW

N B

Y:

SCL

NW

13t

h PL

AC

E SI

NK

HO

LEG

AIN

ESV

ILLE

, ALA

CH

UA

CO

UN

TY, F

LOR

IDA

GSE

PR

OJE

CT

NO

. 148

66

SPT BORING

B-1 B-2

B-3

B-5B-4

CONE SOUNDINGS PERFORMED BY FDOT

C-1 C-2 C-3

C-6 C-5C-4

ESTIMATEDPERIMETER OF

SINKHOLE

ANOMALY CENTER(2638841, N = 248051)


APPENDIX

FINAL REPORT

GEOPHYSICAL INVESTIGATION

NW 13TH PLACE SITE

GAINESVILLE, FLORIDA

Prepared for GSE Engineering & Consulting, Inc.

Gainesville, FL

Prepared by GeoView, Inc.

St. Petersburg, FL

A Geophysical Services Company

4610 Central Avenue Tel.: (727) 209-2334

St. Petersburg, FL 33711 Fax: (727) 328-2477

December 8, 2020

Mr. Ken Hill, P.E.

GSE Engineering & Consulting, Inc.

5590 SW 64th Street

Gainesville, FL 32608

Subject: Transmittal of Final Report for Geophysical Investigation

NW 13th Place Site - Gainesville, Florida

GeoView Project Number 32347

Dear Mr. Hill,

GeoView, Inc. (GeoView) is pleased to submit the final report that

summarizes and presents the results of the geophysical investigation conducted at

the NW 13th Place site. Seismic Reflection was used to evaluate near-surface

geological conditions. GeoView appreciates the opportunity to have assisted you

on this project. If you have any questions or comments about the report, please

contact us.

GEOVIEW, INC.

Chris Taylor, P.G.

Vice President

Florida Professional Geologist Number 2256

1.0 Introduction

A geophysical investigation was conducted along NW 13th Place and NW

14th Place west of NW 40th Terrace in Gainesville, Florida. Prior to the

investigation, a large sinkhole formed in the property between NW 13th Place and

NW 14th Place. This investigation was conducted using seismic reflection on

November 16, 2020. The purpose of the investigation was to help characterize

geological conditions at depth to identify subsurface features that may be

associated with sinkhole activity along the right of way of the roads.

Several borings were performed by GSE at the site subsequent this

investigation. In general, results from these borings indicate the presence of

alternating layers of sand and clay underlain by limestone. The top of the limestone

ranged from depths of 77 to 87 feet.

2.0 Description of Geophysical Investigation

Data acquisition was accomplished using a Geometrics Geode, 48-channel

seismograph system. GeoView acquired compression- (P-) wave seismic reflection

data using a basic 48-geophone spread. The geophones were placed in a line with

10 foot spacing between each of the geophones. Shot points were performed at 10

feet intervals along the transect. A total of 82 shot points were acquired. The

energy source used at each shot point consisted of a polyethylene plate being

struck by a 16-pound sledgehammer. Each shot point consisted of multiple

hammer blows in an attempt to maximize the desired signal while minimizing

background noise.

The positions of the geophysical transect lines were recorded using a

Trimble Geo7x Global Positioning System.

3.0 Survey Results

The final processed high-resolution seismic reflection sections are presented

in in Figures 2 and 3 for Lines 1 and 2, respectively. Seismic reflection sections

illustrate geologic layers as continuous (“coherent”) horizons that can be traced

across the full section. Disturbances such as faults, sinkholes, and cavities are

observed as corresponding offsets or loss of continuity in these reflecting horizons.

The horizontal scale on these sections is merely distance along the particular

transect. The vertical scale is the reflection time. That is, it is the time taken from

the moment of the hammer blow for the seismic wave to travel down to the

geologic horizon, reflect/echo from it, and travel back up to the ground surface. To

convert these times to actual depth, we need to know or approximate wave speed in

the subsurface or have a deep borehole for calibration. The approximate velocities

used at this site to calculate depth were 1,000 feet per second for unsaturated soils,

3,000 to 5,000 feet per second for saturated soils, and 5,000 to 8,000 feet per

second for weathered limestone.

On the cross section, we see a strong, mostly consistent reflection

(highlighted in green) that occurs near the 60 to 70 millisecond time range. This

corresponds to a depth of approximately 80 to 90 feet. It is suspected that this

reflection is from the top of limestone layer. A possible disruption of the

reflections immediately below the top of the suspected limestone is evident from a

horizontal distance of 170 to 240 feet along the Transect 1. The seismic data in this

area indicates that the upper surface of the limestone may have a higher degree of

weathering than the surrounding material. The anomaly extended to a depth of

approximately 100 to 120 feet. This area is indicated in magenta on the figures. A

boring performed by GSE in the center of this anomaly did not encounter any

voids, very soft material or other indications of significant karst activity. No

anomalies were observed on Seismic Transect 2.

A discussion of the limitations of the techniques in geological

characterization studies is provided in Appendix 2.

APPENDIX 1

FIGURES AND SEISMIC TRANSECTS

AND SITE PHOTOGRAPH

SITE PHOTOGRAPH – SEISMIC LINE ALONG NW 14TH PLACE

A2-1

APPENDIX 2

DESCRIPTION OF GEOPHYSICAL METHODS, SURVEY

METHODOLOGIES AND LIMITATIONS

A2. Seismic Reflection

Seismic reflection profiling involves the measurement of the two-way travel

time of seismic waves transmitted from surface and reflected back to the surface at

the interfaces between contrasting geological layers. Reflection of the transmitted

energy will only occur when there is a contrast in the acoustic impedance (product

of the seismic velocity and density) between these layers. The strength of the

contrast in the acoustic impedance of the two layers determines the amplitude of

the reflected signal. The reflected signal is detected on surface using an array of

high frequency geophones (typically 24-96). As with seismic refraction, the

seismic energy is provided by a 'shot' on surface. For shallow applications this will

normally comprise a hammer and plate, weight drop or explosive charge. In most

reflection surveys shots are deployed at a number of different positions in relation

to the geophone array in order to obtain reflections from the same point on the

interface at different geophones in the array. Each common point of reflection is

termed a common mid-point (CMP) and the number of times each one is sampled

determines the 'fold coverage' for the survey. Traces relating to the same CMP are

stacked together to increase the signal-to-noise ratio of the survey before being

combined with other CMP's stacked traces to produce a reflection profile. In order

to stack related CMP traces a stacking velocity is applied to each trace. This

accounts for the difference in two-way travel time between the normal incidence

reflection (vertical travel path below the shot) and those at increasing offsets from

the shot (known as the normal moveout or NMO). The stacking velocity will vary

down the trace to take account of the increase in velocity with depth for each

reflection event.

The analysis and collection of seismic data is both a technical and

interpretative skill. The technical aspects of the work are learned from both

training and experience. Interpretative skills for geologic studies are developed by

having the opportunity to compare seismic data collected in numerous settings to

the results from confirmatory studies performed at the same locations.

GeoView can make no warranties or representations of geological conditions

that may be present beyond the depth of investigation or resolving capability of the

survey equipment or in areas that were not accessible to the geophysical

investigation.

summary report of a sinkhole evaluation nw 13th …

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