AGENCY OF TRANSPORTATION OFFICE MEMORANDUM To: Mike Fowler, P.E, Project Manager, Pavement Management From: Matthew Gardner, Geotechnical Engineer via Callie Ewald, P.E., Senior Geotechnical Engineer Date: September 8 th , 2015 Subject: Cavendish-Weathersfield ER STP 0146(14) – Roadway & Culvert Borings 1.0 INTRODUCTION We have completed our additional geological and geotechnical investigation of VT Route 131 beginning in the town of Cavendish and ending in Weathersfield, Vermont. As requested, an investigation was performed on an 8.953 mile section of roadway, starting at approximately the intersection of VT 103 and VT 131 in Cavendish and extending east to MM 1.306 in Weathersfield at the intersection of VT 106 and VT 131. The proposed project consists of full-depth reclamation of the roadway, widening, as well as replacement of a box culvert located at MM 1.667 in Cavendish. Contained herein are the results of field sampling, testing, and laboratory analyses of soil borings performed in the roadway as well as soil parameters and a feasibility analysis for the proposed box culvert and wingwalls. 2.0 FIELD INVESTIGATION The field investigation was conducted between July 7 th and 15 th , 2015. Fifty-seven solid stem auger borings were performed in general accordance with AASHTO test method T 306, Processing Auger Borings for Geotechnical Explorations, to determine the subsurface profile to aid in the design and reconstruction of Route 131. Forty-seven of these borings were performed throughout the roadway cross section at various offsets from centerline. The borings were laid out in the field based on visual observation of the pavement. Ten auger probes, denoted below with a P, were performed in locations adjacent to bedrock outcroppings. The purpose of these probes was to determine the depth of potential bedrock or boulder under the roadway to help define the risk during construction. Additional pavement cores were performed to determine the extents of the concrete pavement under the asphalt pavement that was encountered between MM 0.12 and MM 0.47 in Cavendish. A summary of the location of each boring is provided below in Table 2.1. If refusal was encountered, additional borings were taken typically 25 feet on each side of the boring to aid in defining the horizontal limits and depth of the presumed shallow bedrock. The auger borings were conducted every 0.2 miles, alternating westbound and eastbound lanes. Table 2.1: Boring Locations Town Boring No. Mile Marker Offset (ft) Asphalt Pavement Thickness (ft) Concrete Thickness (ft) Cavendish B-101 0.00 -18.4 0.42 --- Cavendish B-102 0.2 5.1 0.68 0.32 Cavendish B-103 0.4 -11.7 0.56 0.49
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AGENCY OF TRANSPORTATION OFFICE MEMORANDUM To: Mike Fowler, P.E, Project Manager, Pavement Management
From: Matthew Gardner, Geotechnical Engineer via Callie Ewald, P.E., Senior
Geotechnical Engineer Date: September 8th, 2015 Subject: Cavendish-Weathersfield ER STP 0146(14) – Roadway & Culvert Borings 1.0 INTRODUCTION
We have completed our additional geological and geotechnical investigation of VT Route 131 beginning in the town of Cavendish and ending in Weathersfield, Vermont. As requested, an investigation was performed on an 8.953 mile section of roadway, starting at approximately the intersection of VT 103 and VT 131 in Cavendish and extending east to MM 1.306 in Weathersfield at the intersection of VT 106 and VT 131. The proposed project consists of full-depth reclamation of the roadway, widening, as well as replacement of a box culvert located at MM 1.667 in Cavendish. Contained herein are the results of field sampling, testing, and laboratory analyses of soil borings performed in the roadway as well as soil parameters and a feasibility analysis for the proposed box culvert and wingwalls.
2.0 FIELD INVESTIGATION
The field investigation was conducted between July 7th and 15th, 2015. Fifty-seven solid stem auger borings were performed in general accordance with AASHTO test method T 306, Processing Auger Borings for Geotechnical Explorations, to determine the subsurface profile to aid in the design and reconstruction of Route 131. Forty-seven of these borings were performed throughout the roadway cross section at various offsets from centerline. The borings were laid out in the field based on visual observation of the pavement.
Ten auger probes, denoted below with a P, were performed in locations adjacent to bedrock outcroppings. The purpose of these probes was to determine the depth of potential bedrock or boulder under the roadway to help define the risk during construction. Additional pavement cores were performed to determine the extents of the concrete pavement under the asphalt pavement that was encountered between MM 0.12 and MM 0.47 in Cavendish. A summary of the location of each boring is provided below in Table 2.1. If refusal was encountered, additional borings were taken typically 25 feet on each side of the boring to aid in defining the horizontal limits and depth of the presumed shallow bedrock. The auger borings were conducted every 0.2 miles, alternating westbound and eastbound lanes.
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 3 of 12
*P-signifies a ledge probe where no samples were taken All roadway auger borings and probes were performed using the CME 45C trailer mounted skid rig. A 4-inch auger flight was rotary drilled to 5 feet below the top of roadway at each location. The auger was then removed so a visual observation of the soil profile could be made. This method has proven to be an efficient and reasonably accurate way to view pavement thickness, changes in strata, and obtain samples off the auger flights. Additional borings were performed when auger refusal was encountered, noted as a letter next to the original boring number (P-7A). Auger refusal was assumed to be either a boulder or bedrock. The typical practice was to move the rig 25 feet in both directions to determine the extents of the large boulders or bedrock.
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 4 of 12
For each auger boring, soil samples were visually identified and taken back to the Construction and Materials Bureau Central Laboratory for testing and classification. Two standard penetration borings were drilled to determine the existing subsurface stratum in order to aid in design and construction of the proposed culvert replacement. Boring locations were collected in the field using our Trimble GPS unit and are based on the Vermont State Plane Grid NAD 83. Elevations were interpolated from the survey file based off of the Northings and Eastings. A summary of the location of each boring can be found in Table 2.2. The locations and elevations of the borings should be considered accurate only to the degree implied by the method used to determine them.
Table 2.2: Boring Locations
Boring Number
Station (ft) Offset (ft) Northing (ft) Easting (ft) Elevation (ft)
B – 149 87+06 16.7 322145.93 1609414.21 926.0
B – 150 86+77 -11.4 322183.84 1609402.19 927.0
Borings B-149 and B-150 were performed in general accordance with AASHTO T206, Standard Method of Test for Penetration Test and Split-Barrel Sampling of Soils. During the boring operations, split spoon samples and standard penetration tests (SPT) were taken continuously for the first 20 feet and then at 5 foot intervals until 35 feet. For each boring, soil samples were visually identified and SPT blow counts were recorded on the boring logs. 3.0 FIELD AND LABORATORY TESTING
3.1 Pavement Auger Borings
Laboratory tests were conducted on samples to evaluate grain size, moisture content, percent finer than No. 200 sieve, and liquid and plastic limits when applicable. This testing, along with field descriptions, was conducted on all of the soil samples and can be found on the attached drilling notes. Concrete pavement was encountered under the asphalt pavement between approximately MM 0.2 and MM 0.4 in Cavendish. The extents of the concrete were verified by taking several pavement cores to get an accuracy of within 25 feet. The concrete pavement was found to begin between 450 feet and 425 feet west of MM 0.2 and ended between 400 feet and 375 feet east of MM 0.4, which results in a total length of concrete of approximately 1800 feet. Three concrete cores were extracted from the concrete pavement, one sampled near each limit of the concrete and one from the center of the concrete roadway section. The concrete cores were brought back to the lab for testing. Uniaxial compressive tests were performed on the 4-inch diameter cores. The testing was performed in general accordance with ASTM C42, Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete. One specimen, C-101 was noted to have horizontal rebar reinforcement in the core. Table 3.1 below shows results of testing for each concrete core.
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 5 of 12
Table 3.1. Concrete Uniaxial Compressive Test Results Core
Number Mile
Marker Thickness of Concrete (ft)
Compressive Strength (psi)
C-101 0.2-425 ft 0.60 7820 C-102 0.4+375 ft 0.54 8370 C-103 0.3 0.54 12290
3.2 Standard Penetration Testing (B-149 & B-150)
The standard penetration resistance of the in-situ soil is determined by the number of blows required to drive a 2 inch OD split barrel sampler into the soil with a 140 pound hammer dropped from a height of 30 inches, in accordance with procedures specified in AASHTO T206. During the standard penetration test, the sampler is driven for a total length of 2 feet, while counting the blows for each 6 inch increment. The SPT N-value, which is defined as the sum of the number of blows required to drive the sampler through the second and third increments, is commonly used with established correlations to estimate a number of soil parameters, particularly the shear strength and density of cohesionless soils. The N-values provided on the boring logs are raw values and have not been corrected for energy, borehole diameter, rod length, or overburden pressure. The VT Agency of Transportation has determined a hammer correction value, CE, to account for the efficiency of the SPT hammer on the drill rig. For this project, a CME 45C track rig was used, with a CE of 1.34. This value, included on the boring logs, should be used in calculations to determine soil parameters. Laboratory tests were conducted on all samples to evaluate grain size, moisture content, percent finer than No. 200 sieve, and liquid and plastic limits (when applicable). This testing was conducted on all of the soil samples and results can be found on the attached boring logs.
4.0 SOIL PROFILE
4.1 Pavement Auger Borings
Review of the lab data, borings, and field testing revealed the following information about soil strata for the roadway auger borings:
The thickness of bituminous pavement varied from 0.28 to 1.09 feet thick across the entire length of roadway investigated. The average thickness of asphalt pavement of both above the concrete and directly above subgrade was 0.69 feet. The thickness of concrete varied from 0.32 to 0.60 feet, with an average of 0.50 feet. The asphalt pavement and concrete overlie a layer of silty gravely sand and silty sand. Groundwater was not encountered during drilling. Refusal was encountered in eight places throughout the project. The least amount of overburden above either bedrock or a large boulder was found to be 1.8 feet at MM 4.28 in Cavendish. Additional borings were performed to gauge the extents of the potential
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 6 of 12
shallow bedrock when refusal was encountered. Table 4.1 below shows the depth of refusal encountered and the corresponding boring or probe ID. It was not confirmed by coring whether this refusal was bedrock or a boulder, however exposed bedrock could be seen in all of the probe locations where refusal was encountered.
Table 4.1. Depth of Refusal and Corresponding hole ID
P-7A 4.28-25 ft 223+26 -7.9 2.3 P-7C 4.28+25 ft 223+76 -8.2 2.2 P-7D 4.28+50 ft 224+01 -8.4 2.2
The attached drilling notes contain specific information regarding particle percentages, depths, and additional tests, if applicable. Also attached are visual representations of the subsurface profile, interpreted by the borings, showing the various stratum. 4.2 Culvert Borings Two Borings were performed at the inlet and outlet of the existing culvert at approximately MM 1.67 in Cavendish. Review of the lab data, borings B-149 and B-150, and field testing revealed the following information about soil strata for the culvert borings:
B-149: The ground surface elevation at B-149 was approximately 926.0 feet. The groundwater was measured after drilling at a depth of 12.8 feet below the ground surface on July 10th, 2015.
Depth (Below Ground Surface
Elevation) Soil Profile
0-10 feet Dense Sandy Gravel
10-37 feet Loose Silty Sand
B-150: The ground surface elevation at B-150 was approximately 927.0 feet. The groundwater was measured after drilling at depth of 13.0 feet below the ground surface on July 9th, 2015. Cobbles or a boulder was encountered at a depth of 5 feet to 7 feet.
Depth (Below Ground Surface
Elevation) Soil Profile
0-13 feet Dense Sandy Gravel
13-35 feet Medium Dense Silty Sand
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 7 of 12
5.0 ANALYSIS
5.1 Shallow Foundation Analysis – Culvert at MM 1.67 AASHTO’s LRFD Bridge Design Specifications Manual (2012) was used as the reference for settlement and bearing resistance equations. Section 10.6.3.1.2 contains the equation used for bearing capacity. Neither depth factors nor load inclination factors were used in analysis as they were not considered pertinent. Hough’s Method, used to calculate settlement in normally consolidated cohesionless soils, can be found in section 10.6.2.4.2. We recommend the bottom of footing to be 4 feet below the ground surface based on frost susceptibility and the bearing stratum at the site. An embedment value of 4 feet was used for the strength limit state analysis and an embedment value of 0 ft was used for the service limit state analysis to account for potential scour conditions. A groundwater elevation at the bottom of footing elevation was used in design. As per section 10.5.5.1 of the 2012 AASHTO LRFD Bridge Design Specifications, a resistance factor of 1.0 should be applied to the unfactored bearing resistance for use in service limit state design. Service limit state design includes, but is not limited to, settlement and scour. Section 10.5.5.2.2 specifies that a resistance factor of 0.45 should be applied to the unfactored bearing resistance for use in strength limit state design for spread footings on rock and soil. Strength limit state design includes, but is not limited to, checks for bearing resistance, sliding and constructability. Potential for overturning is limited by controlling the location of the resultant of the reaction forces (eccentricity). Eccentricity, e, shall be limited as follows:
Foundations on soil: |e| < b/3 Foundations on rock: |e| < 0.45b
Eccentricity should be considered for settlement and bearing resistance design of spread footings by using effective footing widths based on AASHTO Section 10.6.1.3. All footing widths presented in this report are effective footing widths.
5.1.1 Bearing Resistance The wingwall length chosen for analysis was assumed to have a length of 7 feet based on the Boring Plan provided dated May 28, 2015. The loose silty sand layer encountered in Boring B-149 was chosen for analyses as the bearing stratum for all wingwalls at this site. It was determined the soil has a friction angle, ϕ = 33º and density, γ = 115 lb/ft3. The embedment was assumed to be 4 feet below the ground surface, at a bearing elevation of 910.00 feet in the loose silty sand layer. Figure 5.1 displays the minimum effective footing width per maximum bearing resistance, factored due to LRFD strength and service limit states. For effective footing widths of 2, 4, 6, and 8 ft the maximum factored bearing resistances for the controlling service limit state are 1.8, 3.1, 4.0, and 4.4 kips/ft2 (ksf), respectively.
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 8 of 12
Figure 5.1 Effective Footing Width vs. Bearing Resistance for Culvert Wingwalls
Soil settlement values were calculated for various footing widths based on the nominal bearing pressure. Found in Figure 5.2 are the settlement values for effective footing widths of 2 to 8 feet for the wingwalls. Due to the granular nature of the foundation soils, settlement is expected to occur during or immediately after construction.
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
1 3 5 7 9
Bea
rin
g R
esis
tan
ce (
ksf
)
Footing Width (ft)
Effective Footing Width vs. Bearing Resistance (Factored)
Service Φ = 1.0
Strength Φ = 0.45
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 9 of 12
Figure 5.2 Settlement vs. Nominal Bearing Pressure
5.2 Global Stability Analysis A global stability analysis was conducted to evaluate the overall stability of the soil slope and proposed wingwalls. Using Slide 6.0, developed by Rocscience, a slope stability analysis was performed which evaluated both compound and deep-seated failures. A wall height of 13.9 feet was used in the analysis based on the existing cross sections provided by the Design Section. The soil slope was modeled using a conservative assumption of a high water table, indicative of a large rain event. According to the FHWA Soils and Foundations Manual Volume I, the Simplified Bishop Method is recommended for slope stability analysis for non-cohesive soils. As a result, this method produced a factor of safety against of greater than 1.3. Therefore, it was determined that no modification of the slope or wall would be required to ensure a minimum factor of safety against failure of 1.3. A factor of safety of 1.3 is equivalent to a resistance factor of ϕ=0.75, which according to AASHTO LRFD Section 11.6.2.3, is the resistance factor for overall stability of a slope that does not support or contain a structural element. Figure 5.3 shows an image of the slide with a minimum factor of safety of 1.394 using the Simplified Bishop method.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0.00 0.20 0.40 0.60 0.80
Bea
rin
g P
ress
ure
(k
sf)
Settlement (in)
Settlement Based Upon Effective Footing With and Bearing Pressure
B'=2
B'=3
B'=4
B'=6
B'=8
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 10 of 12
Figure 3.3 Wingwall modeled in Slide 6.0.
6.0 RECOMMENDATIONS
Shallow foundations appear to be feasible for the bottom of box elevation as well as for the wingwalls at the inlet and outlet locations for the culvert. Factored bearing resistances were calculated for various footing widths of the wingwalls and can be found in Figure 5.1. Any settlement is expected to occur during or immediately after construction. These calculations are based on the geometric and geotechnical assumptions outlined in Section 5.0. Sections 10.5.2 and 10.5.3 of AASHTO outline all design states relevant to spread footing design and their respective resistance factors. Eccentricity should be considered for settlement and bearing resistance design of spread footings by using effective footing widths based on AASHTO Section 10.6.1.3. Table 6.1 shows the appropriate resistance factors for various design states.
Table 6.1. Summary of resistance factors
Design State Resistance Factor, φ Settlement 1.0
Scour 1.0 Bearing Resistance 0.45
Sliding 0.80
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6.1 Construction Considerations
6.1.1 Cofferdams/Temporary Earthwork Support: The Contractor should be reminded that Section 208.07 of VTrans’ 2011 Standard Specifications for Construction indicates that “The Contractor shall prepare detailed plans and a schedule of its operation for each cofferdam specified in the Contract. The design and structural details of the cofferdam shall be signed, stamped, and dated by a Professional Engineer (Structural or Civil).” 6.1.2 Construction Dewatering: The bottom of footing elevation for the culvert is estimated to be below the expected water table based on the elevation of the stream. Therefore, temporary construction dewatering may be required to construct the foundation. Temporary dewatering will also be necessary to limit disturbance to and maintain the integrity of the bearing surface. Temporary dewatering can likely be accomplished by open pumping from shallow sumps, temporary ditches, and trenches within and around the excavation limits. Sumps should be provided with filters suitable to prevent pumping of fine-grained soil particles. The water trapped by the temporary dewatering controls should be discharged to settling basins or an approved filter “sock” so that the fine particles suspended in the discharge have adequate time to “settle out” prior to discharge. All effluent, or discharge, should comply with all applicable permits and regulations.
6.1.3 Placement and Compaction of Soils: Fills should be placed systematically in horizontal layers not more than 12 inches in thickness, prior to compaction. Cobbles larger than 8 inches should be removed from the fill prior to placement. Compaction equipment should preferably consist of large, self-propelled vibratory rollers. Where hand-guided equipment (such as a small vibratory plate compactor) is used, the loose lift thickness shall not exceed 6 inches. Cobbles larger than 4 inches should be removed from the fill prior to placement. General embankment fills should be compacted to a dry density of at least 90% of the maximum dry density determined in accordance with AASHTO T-99. Granular Backfill for Structures, or other select materials placed within the roadway base section shall be compacted to a dry density equal to 95% of the maximum dry density as determined in accordance with AASHTO T-99.
6.2 Design Parameters: Table 6.2 highlights the geotechnical design parameters of the foundation bearing soil as well as regularly specified aggregates. These values should be used when designing the substructure units. It is recommended that values of Ko be used for calculating earth pressures where the structure is not allowed to deflect longitudinally, away from or into the retained soil mass. Values for Ka should be utilized for an active earth pressure condition where the structure is moving away from the soil mass and Kp where the structure is moving toward the soil mass. The design earth pressure coefficients are based on horizontal surfaces (non-sloping and backfill) and a vertical wall face.
CAVENDISH-WEATHERSFIELD ER STP 0146(14) Page 12 of 12
Table 6.2. Geotechnical Design Parameters
Design Parameter 703.01A - Granular Borrow
704.08 - Granular
Backfill for Structures
In-Situ Loose Silty
Sand (Bearing Stratum)
Density (lb/ft3): 130 140 115
Internal Friction Angle, φ (degrees) 32 35 33
Coefficient of Friction, f
- mass concrete cast against soil: 0.50 0.55 0.45
- soil against precast/formed concrete 0.40 0.45 0.30
Active Earth Pressure Coefficient, Ka: 0.31 0.27 0.29
7.0 CONCLUSION We have also provided the boring locations and important information in a spreadsheet at the request of the pavement management section. If any further analysis is needed or you would like to discuss this report, please contact us at (802) 828-2561. Attachments: Drilling Notes (7 pages)
1. Stratification lines represent approximate boundary between material types. Transition may be gradual.2. N Values have not been corrected for hammer energy. CE is the hammer energy correction factor.3. Water level readings have been made at times and under conditions stated. Fluctuations may occur due to other factors than those present at the time measurements were made.
STATE OF VERMONTAGENCY OF TRANSPORTATION
CONSTRUCTION ANDMATERIALS BUREAU
CENTRAL LABORATORY
BO
RIN
G L
OG
2 C
AV
EN
DIS
H-W
EA
TH
ER
SF
IELD
ER
ST
P0
146(
14).
GP
J V
ER
MO
NT
AO
T.G
DT
8/3
/15
5-5-5-5(10)
4-15-13-3
(28)31-R@1"
(R)
14-4-23-8
(27)6-6-12-
12(18)
6-12-8-13
(20)4-5-5-5
(10)
6-5-7-6(12)
4-2-5-3(7)
4-2-7-8(9)
4-4-7-6(11)
3-3-7-7(10)
2-4-4-5(8)
10.3
0.6
7.8
14.7
9.3
27.9
29.9
25.3
26.3
29.2
33.7
30.7
45.9
77.7
45.8
2.0
1.2
0.6
9.1
0.7
0.2
55.8
44.6
18.7
41.1
67.9
71.2
63.6
54.3
44.0
53.3
13.5
9.5
3.6
13.1
30.1
27.6
35.8
36.6
55.3
46.5
Asphalt Pavement, 0.0 ft - 0.5 ft
A-1-b, GrSa, Dk/brn, Moist, Rec. = 1.5 ft
A-1-b, SaGr, brn, Moist, Rec. = 0.6 ft, Lab Note: Broken Rock was within sample.
Field Note:, No Recovery
Field Note:, Possible Cobbles or Boulder. NXDC, cleaned out casing.
A-1-a, Gr, blk, Moist, Rec. = 0.4 ft, Lab Note: Broken Rock was within sample. NXDC, cleanedout casing.
1. Stratification lines represent approximate boundary between material types. Transition may be gradual.2. N Values have not been corrected for hammer energy. CE is the hammer energy correction factor.3. Water level readings have been made at times and under conditions stated. Fluctuations may occur due to other factors than those present at the time measurements were made.
STATE OF VERMONTAGENCY OF TRANSPORTATION
CONSTRUCTION ANDMATERIALS BUREAU
CENTRAL LABORATORY
BO
RIN
G L
OG
2 C
AV
EN
DIS
H-W
EA
TH
ER
SF
IELD
ER
ST
P0
146(
14).
GP
J V
ER
MO
NT
AO
T.G
DT
8/3
/15
mgardner
Oval
mgardner
Oval
mgardner
Line
mgardner
Line
mgardner
Text Box
B-150
mgardner
Text Box
B-149
mgardner
Text Box
B-149
mgardner
Text Box
87+06
mgardner
Text Box
16.7' RT
mgardner
Text Box
B-150
mgardner
Text Box
86+77
mgardner
Text Box
11.4' LT
mgardner
Text Box
Revised by the Geotechnical Engineering Section on 9/8/15