geotechnical engineering investigation ... report...geotechnical engineering investigation report...

GEOTECHNICAL ENGINEERING INVESTIGATION REPORT

FAYETTE COUNTY JUSTICE AND REHABILITATION CENTER UNIONTOWN, FAYETTE COUNTY, PENNSYLVANIA

Prepared for:

SLEIGHTER ENGINEERING, INC. LEMONT FURNACE, PENNSYLVANIA

JUNE 2014

Prepared by:

GEO-MECHANICS, INC. ELIZABETH, PENNSYLVANIA

GMI PROJECT NO. 14012

June 30, 2014

Sleighter Engineering, Inc. 1331 Connellsville Road Lemont Furnace, PA 15456 Attention: Mr. Derrick Crane, P.E. Sr. Project Engineer Re: Geotechnical Engineering Report Fayette County Justice and Rehabilitation Center Dunbar Township, Fayette County, PA GMI Project No. 14012 Gentlemen: GeoMechanics, Inc. is pleased to present the report of its subsurface exploration and geotech-nical engineering investigation for the above-referenced project which is located in Dunbar Township, Fayette County, Pennsylvania. This report contains the data obtained during the subsurface exploration and labora-tory testing programs. The interpretation and analysis of these data have formed the basis for our conclusions concerning the geotechnical behavior of the subsurface materials under the anticipated stresses imposed by site grading and proposed building loads. Recommendations are presented for the type and depth of the most economical and constructable foundation to support the structure with associated geotechnical design parame-ters and ground improvement criteria. We wish to extend our appreciation for this opportunity to once again be of service to you. Should you have any questions or require additional information, please contact us. Very truly yours, GEO-MECHANICS, INC. ________________________________ __________________________________ Jahangir J. Kabir, Ph.D., P.E. Pervaiz M. Alvi, M.S.C.E. Sr. Geotechnical Engineer Project Manager __________________________________ Javaid M. Alvi, Ph.D., President PMA:JJK:JMA:lg wpg\2014 Jobs\14012\GER Report(2014-06-30).docx

TABLE OF CONTENTS 1.0 INTRODUCTION 1 1.1 Authority 1 1.2 Objective of Investigation 1 1.3 Scope of Investigation 1 2.0 SUBSURFACE EXPLORATION 3 2.1 Soil Sampling 4 2.2 Rock Sampling 4 2.3 Ground Water Reading 5 3.0 LABORATORY TESTING PROGRAM 6 3.1 Natural Moisture Content Tests 6 3.2 Classification Tests 7 3.3 Modified Proctor Compaction Tests 8 3.4 California Bearing Ratio Tests 8 3.5 Sulfur Form Tests 8 4.0 GENERAL CONDITIONS 10 4.1 Location and Topography 10 4.2 Geology 10 4.3 Mining Conditions 11 5.0 DISCUSSION AND EVALUATION OF SUBSURFACE CONDITIONS 12 5.1 Soils Conditions 12 5.2 Bedrock Conditions 14 5.3 Ground Water Conditions 14 6.0 GEOTECHNICAL DESIGN AND CONSTRUCTION CONSIDERATIONS 16 6.1 Building Pad and Parking Lots 16 6.2 Access Roadway, Treatment Plant and Stormwater Management Basin 17 7.0 RECOMMENDATIONS 19 7.1 Type and Depth of Foundations 19 7.2 Ground Floor Slab 20 7.3 Retaining Walls/Below-Grade Walls 20 7.4 Cut Slope Design 21 7.5 Pavement Design 22 7.6 Concrete Pavement 23 7.7 Seismic Design Parameters 23 7.8 Site Preparation 24 7.9 Ground Improvement at Building Pad 25

Table of Contents (Cont’d) Page 2 7.10 Temporary Excavations 26 7.11 Inspection and Testing 26 7.12 Limitations 27 FIGURES APPENDIX A Test Boring Logs APPENDIX B Laboratory Test Results APPENDIX C Test Boring Location Plan and Geologic Cross-Sections APPENDIX D Infiltration Test Results

Fayette County Justice and Rehabilitation Center GMI Project No. 14012 Uniontown, Fayette County, PA Page 1

1.0 INTRODUCTION 1.1 Authority This investigation has been performed in accordance with our technical and price pro-

posal that was submitted to Sleighter Engineering, Inc. on February 14, 2014. Approval of our pro-

posal by Sleighter Engineering, Inc. and a signed contract was provided to us by Mr. Derrick Crane,

P.E., Sr. Project Engineer through his e-mail of April 4, 2014.

1.2 Objective of Investigation The objective of the geotechnical investigation was to determine and characterize the

subsurface geomaterials across the proposed building, access road and parking lot as well as at the

stormwater management pond areas. Evaluation of their interaction with the building foundations and

site development and presentation of a set of recommendations for the most economical, safe and

practical foundation support system for the building, related geotechnical design parameters, cut and

fill slope design, special subgrade improvement, pavement design as well as general site development

criteria is the additional objective.

1.3 Scope of Investigation The scope of work performed by GeoMechanics, Inc. to achieve the above objectives

consisted of the following:

reconnaissance of the site to observe the physical setting; review of the available geologic and mining maps and the published liter-

ature related to the general area of the site;

review of the previously performed geotechnical engineering investiga-

tions by others at the overall project site;


drilling of test borings at the building area, access road, parking areas and

stormwater management pond areas;

performance of infiltration tests at the site of the proposed stormwater

management ponds;

performance of laboratory physical and chemical soil tests to characterize

the subsurface soils;

preparation of generalized subsurface profiles (geologic cross-sections)

based on the extrapolation of the borings as well as laboratory test data

illustrating the type, thickness and spatial distribution of soils (and bed-

rock if encountered) as well as ground water conditions;

performance of geotechnical evaluation of the subsurface soils (bedrock

if encountered), mining and ground water conditions pertaining to the site

preparation, foundation design and cut and fill slopes;

performance of bearing capacity and settlement analyses under the shal-

low foundations;

preparation of a geotechnical investigation report documenting the data

collected, analyses performed and conclusions drawn regarding the be-

havior of subsurface materials and presenting a set of recommendations

concerning the following:

-- type and depth of foundations -- geotechnical design parameters and coefficients -- pavement design -- safe cut and fill slope design -- seismic coefficients -- ground improvement methods -- site preparation criteria.


2.0 SUBSURFACE EXPLORATION The subsurface exploration program, which forms the first phase of data collection and

material characterization, consisted of drilling a total of 31 standard test borings. Out of these, nine

borings (GM-11 through GM-19) were drilled in the building area, five (GM-6 through GM-10) at the

parking lot areas, four (GM-20, 21, 30 and 31) at the stormwater management basin sites, one (GM-

22) at the water treatment plant site and twelve (GM-1 through GM-5 and GM-23 through GM-29)

along the access roadway. The locations of the building borings were based on the building layout

and the locations of the three (3) borings (B-1 through B-3) previously drilled by CEC in 2004. The

pertinent data of all the test borings has been summarized on Table No. A-1 in Appendix A of this

report. For boring locations, see the Test Boring Plan, Sheet No. 1 in Appendix C.

The depths of the borings were dictated by the presence of thick mine turnover at the

site as revealed by the data obtained from the three (3) borings drilled by CEC. Visual observation of

the site as well as the review of published mine literature and maps confirmed the past strip mining

activities at the site. Consequently, two (2) of the building borings were advanced to a depth of about

50 feet and one (1) boring to a depth of 74 feet in an effort to determine the thickness of fill. The

remaining six (6) building borings were terminated at an approximate depth of 25 feet, which was

considered the depth of major stress influence induced by the building foundations. The borings

drilled in the parking lot and access road were terminated at relatively shallower depth of 10 feet,

which again is considered the depth of influence of the stresses imposed by vehicular traffic. The

borings in the stormwater basin were advanced to a depth of 2 feet below the anticipated bottom of

the ponds for in-place permeability testing. The results of the infiltration tests are summarized in

Appendix D of this report. Accordingly, the borings were advanced from a minimum depth of 10

feet to a maximum depth of 74 feet resulting in 547.3 lineal feet of soil sampling.

The drilling was performed in the month of April 2014 by GeoMechanics, Inc. using

in-house equipment and personnel. The staking of the borings in the field was performed by Sleighter

Engineering, Inc., who also provided surveyed boring elevations, which were used in the preparation

of subsurface profiles.

The methodology used in the collection of subsurface data is discussed below.


2.1 Soil Sampling The soil sampling program consisted of obtaining split spoon (disturbed) samples

(ASTM Method: D 1586). The split spoon samples were obtained by conducting Standard Penetration

Tests (SPT) while advancing the test boring through the soil zone in accordance with ASTM Desig-

nated Method 1586-84. The samples were collected at 3-foot intervals by a 2-inch O.D. Split Spoon

Sampler that was driven 18 inches into the soil with blows from a 140-pound hammer falling a distance

of 30 inches. The number of blows required to drive the sampler for each 6-inch interval was recorded,

and the cumulative number of blows for the last two 6-inch intervals is designated as “Standard Pen-

etration Resistance” (SPT-N values). This value generally gives an indication of the relative density

of granular soils or consistency of fine-grained soils which, in turn, could be related to shear strength

and compressibility of the in-situ soils. The SPT N-values at various depths, and the description of

the soils based on visual identification and laboratory soil classification tests are recorded on the bor-

ings logs included in Appendix A and the Geologic Cross-Sections presented in Appendix C of this

report. In addition, two (2) bag samples were obtained from representative locations at the site to

conduct appropriate laboratory tests.

2.2 Rock Sampling Due to greater depth of bedrock below the ground surface and the anticipated light to

moderate building and traffic loads, no effort was made to sample bedrock at the building, parking lot

or the access road areas. However, bedrock was sampled in one (1) boring that was drilled in area of

the cut near the entrance of the access roadway. Bedrock was cored using a diamond bit with NQ2

size rigid double-tube core barrel that provides 1.99-inch core. The rock core description, the core

recovery of each interval and the rock quality designation (RQD) values (expressed in percent) for

each run and as well as for each lithologic unit were measured and are recorded on the test boring log.

The RQD values reflect the quality, bedding and fracture spacing of the rock and are calculated as the

summation of all core samples greater than 4 inches divided by the length of each coring interval or

the thickness of the rock layer. Both the core recovery and RQD values provide a quantitative basis

for defining the engineering properties of rock.


2.3 Ground Water Reading Efforts were made to measure the depth to ground water table immediately upon com-

pletion of each boring and, again, after 24 hours provided the bore holes had not caved or filled in for

safety reasons. The ground water readings are included in the test boring logs and are also plotted on

the Geologic Cross-Sections. These readings are used to establish the ground water regime at the site.


3.0 LABORATORY TESTING PROGRAM

This task formed the second phase of data collection and material characterization and

consisted of performing index properties tests, sulfur form tests and material behavior tests. Index

properties tests included moisture content, sieve and hydrometer, and liquid and plastic limits tests.

The results of these tests were used in conjunction with the penetration resistance (SPT N-values)

obtained from test borings to estimate the shear strength and compressibility of the soils. The expan-

sive potential of the soil were investigated by performing sulfur form tests on samples which appeared

to be rich in carbonaceous material. The results of these tests provided a measure of the percentage

pyritic sulfur content in the sample. Material behavior tests consisted of compaction and California

Bearing Ratio (CBR) tests. These tests were performed on jar as well as bag samples to determine the

density-moisture relationship for controlling the fill placement and preparing test specimens for CBR

testing. The CBR tests provide the strength values, which are used in the pavement design.

The following paragraphs present a brief description of the methods used in testing of

soils along with our interpretation of the test results.

3.1 Natural Moisture Content Tests (ASTM: D 2216-98) The moisture content of the soils was determined by conducting twelve (12) moisture

content tests on representative soil samples. Moisture content, expressed as the ratio of the weight of

water to the weight of dry solids, for each sample tested is recorded on the Grain-Size Distribution

Test Reports, Figures No. B-1 through B-12 and in Table No. B-1 included in Appendix B of this

report.

Moisture content of the soils at the time of drilling varied between 4.9 and 30.4 percent.

This range corresponds to dry to wet conditions, based on a scale of dry, damp, moist and wet. How-

ever, with the exception of two (2) samples which represented the extreme dry and wet conditions,

respectively, most of the soils had 6.7 to 13.8 percent moisture content that corresponds to damp con-

dition. Slight variation of moisture content can be expected depending upon seasonal precipitation

and may affect the conditioning needed during the fill placement and compaction.


3.2 Classification Tests (ASTM: D 2487-00) The gradation tests and the Atterberg Limits tests are used as the basis for classifying

the soils. Together they form what is commonly referred to as a classification test. A brief description

of each test is given below.

3.2.1 Gradation Tests (ASTM: D 422-63) Twelve (12) representative soil samples which were selected for the moisture content

tests were also selected for conducting sieve and hydrometer tests. The data from these tests, in con-

junction with the data obtained from the liquid and plastic limits tests, were used to classify the soils

according to the Unified Soil Classification System (USCS) and the American Association of State

Highway and Transportation officials methods (AASHTO: M1450-82). These soil classifications are

shown on the Grain-Size Distribution Test Reports, Figures No. B-1 through B-12 and on Table No.

B-1. The test results indicated that the samples tested consisted primarily of coarse-grained clayey

gravel (GC) and clayey sand (SC) with silt as minor constituent, exception being the two (2) samples

obtained from the old tailing pond area, which has since been backfilled. Samples obtained from this

area were classified as silty clay (CL) and highly plastic clay (CH).

3.2.2 Liquid and Plastic Limits Tests (ASTM: D 4318-00) Liquid and plastic limits tests were conducted on each sample selected for gradation

testing. The results of these tests are included on the Grain-Size Distribution Test Reports, Figures

No. B-1 through B-12, and have been used in conjunction with the results of the sieve and hydrometer

analysis to classify the soils according to the USCS and AASHTO systems. The liquid limits (LL) of

granular soils tested ranged from 26 to 37 percent with the plasticity of 7 to 17 percent and the clayey

sols, 49 to 51 percent with the corresponding plasticity index of 30 and 24 percent, respectively. These

results indicate that the in-situ granular soils are slightly to moderately plastic but the material present

in the old pond has high plasticity.


3.3 Modified Proctor Compaction Tests (ASTM: D1557-00, Method C) Two (2) compaction tests, one (2) on the composite jar sample and the other on the bag

sample. The data from these tests is plotted as dry density versus moisture content on the Compaction

Test Report, Figures No. B-13 and B-14, and also summarized on Table No. B-1 included in Appendix

B of this report. The purpose of this test was to obtain the maximum dry density-moisture content

relationship of the soils which will be available from the excavation areas and will be utilized as pos-

sible fill or will form the roadway and parking lot pavement subgrade. This relationship forms the

basis for controlling the compaction of fill. The test results indicate that the soils tested have a maxi-

mum dry density of 120.8 PCF for the clayey (CL) soils and 128.2 PCF for the granular (SC/GC) soils

with respective optimum moisture content of 11.5 and 8.1 percent. These values indicate that the

natural moisture content of the in-situ soils is only slightly higher than the optimum moisture content

at the time of drilling. However, during wet season the moisture content of the in-situ soils could

increase and, if these soils are used as fill they may require moisture conditioning to meet the moisture

content requirement.

3.4 California Bearing Ratio (CBR) Test Two (2) CBR tests were conducted on the same samples on which the compaction tests

had been performed. The density-moisture content values obtained from the compaction tests were

used in the preparation of the CBR test specimens. Attempts were made to mold the CBR samples at

about 95 percent of the respective maximum dry density values. The purpose of the CBR tests was to

determine the load-deformation characteristics of the compacted soils that may potentially form the

pavement subgrade. The data is used for the pavement design for the access roads and parking lots.

The CBR test results are presented in the form of a stress-penetration curve in Figures No. B-15 and

B-16 in Appendix B of this report and provided CBR values of 3.9 for SC/GC soils at 1.8 for CL soils.

3.5 Sulfur Form Tests (ASTM: D 2492) Since the project site is covered with strip mine turnover, the existing soils contain coal

and carbonaceous shale fragments which typically show expansive characteristics. Therefore, it was


decided to perform sulfur form tests in the laboratory on twenty (20) representative soil samples re-

trieved from the test borings located in the building and parking lot areas in order to determine the

concentration of expansive pyritic minerals in the existing fill which may form the subgrade for the

building floor slabs, footings and pavement. As presented on Table B-2, the test results indicated that

the soils tested exhibited pyritic sulfur contents varying from 0.02 to 2.09 percent with 0.41 average

value. A value of 0.10 percent or higher for pyritic sulfur indicate the material to be expansive and

warrants consideration for treatment. Seventeen (17) samples that were tested for pyritic sulfur ex-

hibited contents higher than 0.10 percent, indicating a concern for potential use of existing material as

fill or subgrade at the building and pavement areas.


4.0 GENERAL CONDITIONS 4.1 Location and Topography The proposed Fayette County Justice and Rehabilitation Center project site is located

at the intersection of Mt. Braddock Road (Industrial Park Drive) and Braddock View Drive, approxi-

mately 2,000 feet east of University Drive (S.R. 119) in Dunbar Township, Fayette County, Pennsyl-

vania (see Figure 1).

The site is characterized by a south-southeastward mildly sloping hillside. The site and

its immediate surrounding area has been strip mined and regraded in the past changing the original

site topography as well as the composition of the soil mantle. At present, the ground surface elevations

within the proposed center area vary from approximately 1175 feet along the north end to about

1155 feet along the south end; thus providing about 20 feet of relief across the site. In order to

develop a level building pad and parking areas, the proposed site grading plan will require about 10 to

15 feet of cut along the north and west sides and about 5 to 10 feet of fill along the south and east

sides of the site with first floor elevation set at 1166.25 feet.

The site is presently accessible via an unpaved earth road, an extension of Braddock

View Drive that goes to the now abandoned equipment maintenance and storage area for mining ac-

tivities (see Figures 1 and 2). The road will be improved and realigned as a new asphalt paved roadway

(Development Road). In addition, a treatment plant and an elongated storm water management basin

will be constructed along the south side of the Development Road. The new roadway alignment to-

wards its eastern end will traverse over the now backfilled ponds created by the mining activities. The

site runoff drains toward the southeast resulting in several wetlands along the railroad tracks that skirts

the project site and eventually flows into local Gist Run stream.

4.2 Geology Geologically, the site is underlain by the bedrocks belonging to the Pittsburgh for-

mation of the Monongahela group of the Pennsylvanian age (see Figures 2 and 6). Pittsburgh for-

mation is the basal member of the Monongahela group and is lined at the bottom by the distinct eco-

nomically important Pittsburgh coal seam. The rock overburden at the Pittsburgh coal seam is formed


by the Pittsburgh sandstone, shale and siltstone and would have been present at the site had it not been

strip mined. As a result of the mining activity, the bedrock most likely to be encountered at the site

would be the Pittsburgh limestone member belonging to the underlying Casselman formation of the

Conemaugh group of rocks. The upper section of the Casselman formation consist of underclay, lime-

stone interbedded with sandstone, shale, siltstone and claystone. Structurally, the site is located east

of northeast-southwest trending axis of the Uniontown syncline (see Figure 4). Therefore, the bedrock

at the site is expected to slope in the northwest direction at a rate of 16 percent.

4.3 Mining Conditions The site for the proposed development lies within a region extensively deep mined at

the Pittsburgh coal seam (see Figure 5). Based upon the structural mapping (see Figure 4), the base

of the Pittsburgh coal seam is at approximate elevation of 1100 feet. The present ground surface

elevations at the site range between 1175 and 1155 feet, meaning prior to the mining operation, the

entire site was underlain by a thick rock overburden normally encountered above the Pittsburgh coal

seam which, along with its rider coal and shale layers, is generally about 10 feet thick. Most likely

the site and its surrounding area was initially mined by using deep mining methods such as room-and-

pillar coal extraction. However, since the site is located near the edge of the coal bearing area with

relatively thin overburden, a secondary mining activity took place at the site to recover residual coal

by total strip mining method. Reportedly the strip mining was done in the year 1972 under a permit

issued to Christopher Resources, Inc. and the site was regraded afterwards to its present configuration.

In addition as part of the mining activities, towards the far end of the local dirt road, a number of

shallow tailing or retention ponds were created that were later backfilled using on-site available ma-

terials. Part of the roadway realignment will traverse over some of the pond backfilled areas. No

mining related leaching is observed at the site, even though further east of the site closer to the Penn

Central and Baltimore and Ohio railroad tracks some wetlands were observed. The area ultimately

drains into the local Gist Run stream. The next mineable coal seam is the upper Freeport coal seam

which is expected to be about 500 to 600 feet below the site.


5.0 DISCUSSION AND EVALUATION OF SUBSURFACE CONDITIONS In this section, the data collected from the subsurface explorations and laboratory test-

ing program have been utilized to discuss the engineering characteristics of the subsurface geomateri-

als across the project site and evaluate their impact on the selection of foundation support system for

the building and site development. To facilitate the discussion, a series of generalized cross-sections

depicting the distribution of subsurface geomaterials at the building pad, parking lot areas and also

along the access road alignment have been prepared and included in Appendix C of this report. For

the sake of clarity, the three (3) basic components namely soil, bedrock and ground water have been

discussed separately both at the building pad and the parking lot areas as well as at the access roadway

as follows.

5.1 Soils Conditions 5.1.1 Building Pad and Parking Lot Areas A review of the geologic cross-sections B, C, D and F indicates that the building area

is covered with a relatively thick soil zone. Its thickness varies from about 52 feet near the south-

western corner of the building where old test boring TB-1 is located to greater than 50 feet at test

boring GM-17 and greater than 74 feet at test boring GM-18, which is located at the northeastern

corner of the building. The soil zone, with the exception of a thin residual soil layer that may be

present at its bottom, is entirely comprised of strip mine turnover and surface cover used for site res-

toration. The fill is very heterogeneous in composition as well as density. Typical of the strip mine

backfill, the existing fill has been placed with minimum compaction and quality control. This is ap-

parent from the results of the classification tests as well as the intervals within the soil mass of low

penetration resistance (SPT N-values). According to the USCS, the fill consists of mostly coarse-

grained clayey sand with gravel (SC) and clayey gravel (GC) with sand. However, occasional pockets

or layers of silty or sandy clay soils are also encountered. The clayey soils have soft to very stiff

consistency but typically medium stiff. The granular fill has loose to medium dense relative density.

The exceptionally high blow counts encountered are due to the presence of boulders in the soil mass

and do not represent its overall density. Based upon the above description, it is apparent that the fill

in its present condition is unsuitable to support the proposed building and provides poor subgrade for


the parking lots and roadway. The available bearing capacity to design shallow foundation is relatively

low and more importantly the potential for differential settlement of footings and pavement is too high.

In addition, there is a considerable risk of heaving of footings and especially floor slabs and utility

lines if the present fill is used as subgrade. It is, therefore, apparent from the above discussion that

some form of ground improvement/modification will be needed if shallow foundation is to be utilized

for the building and floor slab support as well as the parking lot and roadway subgrade.

An alternative to shallow foundation will be to use deep foundation such as drilled

concrete shafts bearing in bedrock which will be relatively expensive, especially when considering the

greater depth to bedrock and the possibility of encountering obstructions caused by boulders as well

as the requirement for temporary casing so that the hole does not cave in. Besides, the use of deep

foundation would not eliminate the excessive settlement or heaving of the floor slab and grade beams

and would require structural slab with crawl space to support the floor slabs. Although the existing

fill has been in place for a considerable period of time and the majority of consolidation of the fill

under its own weight has been completed, it will still likely to experience considerable future consol-

idation resulting from the continuous deterioration of rock fragments and loss of fines caused by

ground water migration that will result in further readjustment of particles and collapse of voids.

Therefore, to prepare the site for its intended use, it will be necessary to improve the compressibility

aspect and eliminate the expansion aspect of the existing fill. This would require removal of existing

fill to a suitable depth and replacement with properly compacted suitable inert soil as well as in-situ

densification of the underlying fill by such methods as deep dynamic compaction, deep cement mixing

or jet grouting. This will allow use of shallow foundation to support the proposed building.

5.1.2 Access Roadway and Treatment Plant Site All borings drilled along the access roadway alignment were terminated at 10 feet

depth. Similar to the building pad and parking lot sites, the in-situ soils along the roadway alignment

consist of the random uncontrolled fill generated by the mining related activities. Exception may be

in the areas near the entrance and the far end of the access road. Along the first 600 feet of the

roadway residual soils were encountered below a thin layer of the fill. The residual soils have rela-

tively higher consistency, when fine-grained, and higher relative density when coarse-grained in com-

position. Near the eastern (far) terminus of the roadway where old ponds were located, the backfill


material in the ponds tends to be relatively clayey in nature. To ensure a competent roadway subgrade,

it will be necessary to overexcavate a few feet of the in-situ soils and replace them with adequately

compacted inert granular material. The roadway grades require a small cut near its western terminus.

The material at the cut is expected to consist of residual soils that are fairly competent and can safely

support the proposed 2H:1V cut slope. Subsurface profile at boring GM-22 drilled at the proposed

treatment plant site consists of about 6 feet of fill underlain by residuum consisting of dense to very

dense decomposed shale including a thin layer of decomposed carbonaceous shale between the depth

of 9 and 12 feet. Depending upon the floor elevation, the plant building can also be supported using

shallow foundation after some improvement of the in-situ fill similar to the main building pad site has

been performed.

5.2 Bedrock Conditions Although no rock sampling was performed at the building pad and parking lots, based

on the data obtained from the deep borings, it is apparent that at the building pad and parking lots, the

bedrock is considerably deep, as much as 74 feet below existing ground surface. Based on our ex-

perience and published literature, the bedrock below the Pittsburgh coal seam consists of alternative

layers of limestone and claystone. While limestone has high load-carrying capacity, the claystone

layers are soft with low allowable bearing capacity. However, the strength of these rocks is of only

academic importance because they are highly unlikely to be used for foundation support due to their

great depth. Bedrock was sampled in one (1) boring drilled at the proposed cut area near the entrance

of the access road. The bedrock at this location was encountered at a depth of 16 feet. The proposed

cut at this location will be confined to the soil zone, therefore, the competence of bedrock have little

impact on the design or construction of the roadway.

5.3 Ground Water Conditions No static ground water was encountered in the test borings drilled in the building pad

and parking lot and most of the roadway areas. In shallow borings through fill, no ground water was

encountered at all to a depth of as much as 25± feet. However, in a few borings along the roadway

alignment where residual soils were encountered at shallower depths, ground water was encountered

at the fill/residuum interface, which existed as perched water table. The ground water will have no


adverse impact on the design of shallow foundation placed in the improved fill. Absence of shallow

water conditions will also be helpful to implement any ground improvement methods as deemed nec-

essary.


6.0 GEOTECHNICAL DESIGN AND CONSTRUCTION CONSIDERATIONS 6.1 Building Pad and Parking Lots The major geotechnical considerations at the proposed project site are primarily related

to the presence of thick fill with low and non-uniform bearing capacity and excessive long-term com-

pressibility. Typically, low strength foundation soils can be densified to improve their load carrying

capacity and to decrease settlement. Alternatively, deep foundations can be used by-passing the softer

incompetent zone and bearing in more competent materials. At the present site, the random fill is

relatively thick; and deep foundations such as drilled shafts or piles are not economically feasible.

Therefore, to develop the present site for its intended usage, the random fill will have to be improved

to an extent that will allow employment of shallow foundations. Normally, undercutting of unsuitable

material to a suitable depth (typically 2 times the footing width) and backfilling with properly com-

pacted inert material can provide sufficiently high bearing capacity that can safely support light to

moderately loaded buildings such as the proposed center. However, as pointed out earlier, long term

consolidation of the underlying fill will continue and must be minimized to acceptable limits.

A variety of in-situ methods of ground improvements are feasible. These include vibro

compaction, vibro replacement, compaction grouting, jet grouting, deep cement mixing and deep dy-

namic compaction. The selection of the optimum method is dictated by cost, composition of material,

depth to ground water table, environmental impact (including vibration impact on the nearby build-

ings) and scheduling. Based on all the above factors, it is our opinion that deep dynamic compaction

(DDC) is the preferred method of ground improvement. This opinion is based on the following factors:

coarse-grained nature of fill; deep ground water table and relatively dry material; high permeability; easy accessibility to the equipment; and sufficient distance between the site and surrounding structures.

DDC is basically a ground modification technique of densifying the soil at depth by repeatedly drop-

ping heavy weights on the ground surface. The effective depth of densification is a function of the


weight of the drop, height of drop, number of drops per location, number of passes and type of mate-

rial. Based on our experience in similar materials and published case histories, DDC can effectively

densify the fill to a depth of 25 to 30± feet using a drop weight of 15 to 30 tons and a drop height of

40 feet. The number of drops per location may vary from 5 to 10, and the spacing of drop locations is

typically 20 to 30 feet on a grid pattern. The maximum improvement generally occurs within a zone

between one third and one half of the effective depth with lesser improvement below this level due to

diminishing effect of the impact energy. The upper one third of effective depth exhibits lesser densi-

fication due to surface disturbances during impacting and is generally improved by an “ironing pass”

which covers the entire site with lesser energy or by surface densification equipment. The site is

expected to depress by 5 to 10 percent of the effective depth of densification depending upon the

existing density and soil type and the compensating fill that has to be placed to raise the ground surface.

The densified soils typically improve by a factor of 2 to 4.

The objective of this method of ground improvement is to create a raft of densified

material about 30 thick that should bridge or float over weaker (more compressible) areas. Quality

assurance is generally based on SPT-N values obtained through test borings spread across the treated

area. The anticipated range of blow counts should be between 30 and 40.

Based on above discussion, it is proposed that the building site should be excavated to

a suitable depth and after performing DDC backfill the site with fill under quality control. The site

thus prepared can provide an allowable bearing capacity of 3000 PSF and limit the settlement to less

than 1 inch. Based on the case history it is estimated that cost of ground modification using DDC will

be in the range of $4.00 PSF. The cost of undercutting and backfilling will be in addition to the DDC

cost.

6.2 Access Roadway, Treatment Plant Site and Stormwater Management Basin Along a major portion of the access roadway alignment, the subgrade is formed by the

same fill material that was encountered at the rest of the site and will require densification to a suffi-

cient depth in order to provide a competent pavement subgrade. This can most economically be


achieved by “undercutting and backfilling”, typically to a depth of 3 feet. The backfill material must

be free of expansive pyritic soils.

The site for the treatment plant also contains few feet of fill followed by residual soils.

Therefore, the anticipated treatment plant building can be supported using shallow foundations placed

on compacted fill. The stormwater management basin will be constructed by making only minor ex-

cavation and backfill. No geotechnical related concerns are anticipated at the site for the proposed

basin. Results of the infiltration testing and the soil conditions at the pond sites are presented in Ap-

pendix D of this report.


7.0 RECOMMENDATIONS Based on the discussion and evaluation of subsurface conditions presented in the pre-

vious sections, GeoMechanics, Inc. presents the following recommendations.

7.1 Type and Depth of Foundations

Prepare the building pad as described in Section 7.8 by excavating and back-

filling a minimum 10 feet of engineered fill under the floor slab. Extend

the limit of undercutting about 15 feet beyond the building footprint. The

last 5 feet of backfill under the footings and floor slabs must be inert gran-

ular material.

Use strip and spread footings bearing in properly compacted inert engi-

neered fill to support the columns and load bearing walls of the building,

respectively. Use a net allowable bearing pressure of 3,000 PSF and a max-

imum toe pressure of 4,200 PSF to design the foundation.

Use a minimum width of 24 inches for strip footings and 36 inches for

spread footings regardless of bearing capacity to properly distribute the load

and avoid the potential for local or “punching” shear in the foundation sub-

grade. The total and differential settlements of foundations bearing in en-

gineered fill under the structural load of the building are expected to be less

than 1 inch and ¾ inch, respectively.

Place exterior footings exposed to outside weather at least 42 inches below

the adjacent outside finished grade to protect from the frost damage. The

interior footings, which will not be exposed to outside temperatures, can be

placed at shallower depths, typically 18 inches below floor slab.


7.2 Ground Floor Slab

Place the ground floor slab on engineered fill. Immediately prior to floor

construction, the entire subgrade should be proof-rolled and compacted as

described in Section 7.8 in order to re-densify any previously placed fill

which has been disturbed by exposure to weather or construction activities.

Provide expansion joints between the floor slabs on grade and the foundation

walls and/or columns in order to allow independent settlement of the two

structural elements.

Place a 4-inch thick granular base (equivalent to AASHTO No. 57), and sur-

face choke it with fine sand (AASHTO No. 10 rock or equivalent) to provide

a smooth base. For a slab with heavier design loads, the thickness of the base

course should be increased to 6 inches of AASHTO No. 57. This will pro-

vide both structural strength and a “capillary break”.

Place a minimum of 15-mil polyethylene or equivalent vapor barrier between

the base course and the concrete slab to preclude the floor dampness and

minimize loss of concrete water to porous base.

Use subgrade modulus of 150 PCI in designing the concrete floor slab.

7.3 Retaining Walls/Below-Grade Walls

Two (2) types of retaining walls may be needed. The building and loading

dock walls that are restrained at the top will be rigid (restrained) walls; and

the walls that are unrestrained at the top leading up to loading docks will be

flexible structures. The lateral earth pressure for the rigid and flexible walls

are based on “at rest” ko and “active” ka coefficient of earth pressure, respec-

tively.


Add applicable floor slab loads or any other concentrated load as surcharge

loads for building walls. If any retaining walls are subjected to vehicular

traffic load, use a 360 PSF surcharge load.

Use the following soil parameters for the design of both rigid and cantile-

vered walls:

Materials Unit

Weight (PCF)

Coefficient of Lateral Earth Pressure Coefficient

of Friction

Equivalent Hydro-static

Pressure (PCF) ko ka kp Rigid Flexible

Soils 130 0.50 0.33 2.0* 0.35** 65 43 *Kp is reduced by 2/3 to limit lateral movement.

Provide granular filter material, minimum 12 inches thick, behind the re-

taining walls. Provide a 6-inch diameter perforated PVC pipe with positive

outlet at the bottom to collect and remove ground water.

7.4 Cut Slope Design

Use 2H:1V slope ratio to construct cut in the soil zone.

Provide a diversion ditch approximately 5 feet beyond the top of cut to col-

lect and channel out surface run before it reaches the cut face.

Provide a swale near the toe of the cut to collect any runoff from the face of

the cut and ground water seepage. Connect the swale to the nearest storm-

water inlet.

Provide vegetative cover on the cut to minimize the surface erosion.

Follow all erosion and sedimentation (E&S) plans in strict accordance with

the applicable standards and codes.


7.5 Pavement Design

The pavement subgrade available at the parking lots and the access roadway

will consist of either new engineered fill or existing random fill that will be

undercut and backfilled to provide a minimum 3 feet of new engineered fill.

Depending upon the quality of the fill placed below the pavement subgrade

elevation, the CBR value may vary between 2 and 4; the lower value repre-

sents the clayey subgrade and the higher value corresponds to fill consisting

of granular soils.

At this time the traffic data is not available, however, based upon our expe-

rience for similar type of project and using a CBR value of 4, the following

asphalt pavement thickness for the standard duty (parking area) and heavy

duty (access roads) pavement, overlying a layer of Mirafi 600X fabric or

equivalent, are recommended in the table below.

Course (PennDOT 408 Specification

Section)

Standard Duty Pavement

Heavy Duty Pavement

Wearing Course ID-2, 420

1.5” 1.5”

Binder Course ID-2, 421

2.5” 3.0”

Base Course AASHTO #1

8.0” 9.0”

Total Thickness 12.0” 13.5” Use compacted coarse aggregate, equivalent to AASHTO No. 57/ PENN-

DOT OGS crushed stone. The open graded stone should be “surface

choked” with relatively finer coarse aggregate such as PENNDOT No. 2A.

The surface material should be compacted with at least four (4) passes of

smooth-drum steel wheeled roller with a minimum weight of 10 tons.


Proof-roll thoroughly the existing soil/fill surface before the base course is

placed. If a soft and yielding spot is encountered, excavate the soft material

and backfill with properly compacted dry material as outlined in Section 7.8

of this report.

Perform a continuous visual monitoring for the presence of any expansive

pyritic material within the pavement subgrades, specifically in the cut areas.

Tie the base course into side drainage ditches as well as storm water inlets

to provide positive outlet for the trapped water.

7.6 Concrete Pavement

Use a subgrade modulus of 150 PCI in designing the concrete pavement if

needed.

Place a 6-inch thick granular base (AASHTO #57), and choke it with fine

sand (AASHTO #10 or equivalent) to provide a smooth base.

7.7 Seismic Design Parameters

The foundation bearing material will be a compacted and engineered fill.

However, the total thickness of the soil zone will be about 50 to 75 feet.

The soil zone will be comprised of new engineered fill, existing treated and

untreated fill and possibly underlying residual soils. The composition of

the soils would vary from fine to coarse-grained, generally silty clay (CL

type) to clayey sand (SC type) with variable amounts of gravel, or clayey

gravel (GM). These soils will typically be moderately plastic, stiff to very

stiff if clayey, or slightly plastic medium dense if granular, with SPT-N val-

ues between 15 and 50. Therefore, the site should be classified as D (IBC

Code, Table 1615.1.1). The corresponding values of site coefficients can

be determined from Tables 1613.5.3(1) and 1613.5.3(2) of IBC Code.


7.8 Site Preparation Strip and stockpile the topsoil for later use and perform the desired cuts and

fills. All cut and fill slopes should be 2H:1V or flatter.

Undercut the existing random fill to a depth of 10 feet below the finished

floor slab subgrade in the building area and 3 feet in the parking lot and

access road constructed on fill. Backfill the excavation with properly com-

pacted suitable inert granular (conforming to GC-GS, SC-SM) material. Ex-

tend the depth of undercut 15 feet beyond the building footprint and 2 feet

beyond the pavement edge.

Prior to placing any new fill, proof-roll and compact the undercut exposed

base of excavation using heavy earthmoving equipment (such as 20-ton

loaded triaxial dump truck, or a 20-ton smooth drum vibratory roller) until

no perceptible movement is observed or to the satisfaction of the engineer.

If any soft or yielding soil is detected by proof-rolling, which cannot be sta-

bilized with additional compaction, should be undercut to stable material.

The maximum depth of undercut is typically limited to 2 feet, but it has to

be adjusted based on the field condition. Perform backfilling with dry and

granular material under proper compaction control. Proof-rolling should

not be performed when the subgrade is wet or frozen.

Samples of the proposed fill material should be collected and tested prior to

the site work to determine the maximum dry density, optimum moisture

content, gradation and plasticity characteristics. These tests are necessary

to control the quality of the fill material and determine the controlling pa-

rameters for field compaction. The excavated material with the exception

of coal and large-size boulders can be used as new fill up to a depth of 5 feet

below the floor slab and footings provided it is properly blended and dried.

Any coal, organic material, excessive clayey material, wood pieces or any

other deleterious material as determined by the Engineer must not be used

as fill.


Any fill material used within the upper 5 feet of the floor slab and footings

must be granular in composition and free from expansive pyrite rich carbo-

naceous shale and should be granular in composition in order to provide

bearing capacity of 3,000 PSF.

Place and compact fill in 9-inch thick loose layers; compact each layer to 95

percent of the maximum dry density at ±2 percent of the optimum moisture

content as determined by the Modified Proctor Compaction test (ASTM: D

1557). Particles larger than 4 inches in maximum dimension should not be

included in the engineered fill placed within the upper 10 feet of the building

area and 3 feet of the pavement area. Larger rock pieces, mixed with other

soil and rock debris, can be placed within the deeper part of the fill outside

the building pads. In confined areas, use a smaller compactor and reduce

the lift thickness to 6 inches.

7.9 Ground Improvement at Building Pad Use Deep Dynamic Compaction (DDC) as outlined below:

-- After the undercutting and prior to the backfilling operation, perform

DDC over an area of the building pad extending at least 20 feet beyond

the proposed building footprint. Refer to Figure 7 for the limit of DDC

work.

-- Engage a specialty contractor experienced in deep dynamic compac-

tion to design and perform a soil densification program capable of im-

proving the in-situ random mine turnover materials to an effective

depth of 25 feet. The program should be designed to achieve improve-

ment of the uppermost 25 feet of the random fill so that the total set-

tlement within the “improved” zone due to the loads of the new fill (to

reach the finished grade) and the building does not exceed ¾ inch.


-- Perform a testing program, such as Standard Penetration tests (SPT)

after deep dynamic compaction to verify the increase in the degree of

compaction.

7.10 Temporary Excavations

Design all temporary excavations greater than 4 feet but less than 20 feet in

depth, in accordance with current OSHA requirements (Ref. Construction

Standards for Excavations, Occupational Safety and Health Administration,

29 CFR Part 1926 .650- .652, Subpart P). Consider the soils at this site as

“Type C” soils in designing safe cut slope steepness.

For slope heights greater than 20 feet, perform slope stability analyses to

determine acceptable cut slope steepness.

Contractor is responsible for maintaining the stability of all temporary cut

and fill slopes.

7.11 Inspection and Testing

Have a qualified Soils Technician/Resident Geotechnical Engineer under

the direct supervision of a senior geotechnical engineer present at the site to

monitor the gradation, placement and compaction of soil and rock materials

to achieve the desired building pad, parking lot and roadway subgrade. It

will be his responsibility to confirm that he specified density requirements

are being achieved, thus minimizing residual (post-construction) settle-

ments in the fill materials.

Provide a full-time geotechnical engineer to monitor the ground improve-

ment using DDC method including the post-operation verification.


7.12 Limitations The subsurface evaluation of the site is based on a limited number of bor-

ings across the site. Extrapolation among borings was needed to prepare

the generalized geologic cross-sections. The recommendations presented

in this report should be modified, if necessary, based on the actual field data.

During the site preparation and construction, if subsurface conditions en-

countered differ significantly from those reported herein, this office should

be notified immediately so that the analyses and recommendations can be

reviewed and/or revised accordingly.

This report has been prepared in accordance with the generally accepted

geologic and engineering principles and practices. This warranty is in lieu

of all other warranties either expressed or implied. We assume no respon-

sibility for interpretations made by others based upon work or evaluation

made by GeoMechanics, Inc.

geotechnical engineering investigation ... report...geotechnical engineering investigation report...

Documents