Geotechnical Report - AC-916579_HWY-287.pdf

GEOTECHNICAL REPORT

LANDSLIDE AND ROAD DAMAGE EVALUATION

AND REPAIR RECOMMENDATIONS

PR-159 KM 3.5, MOROVIS, PR

ER-HWY-287

AC-822544

Submitted to:

Rafael Fernández, PE

DG3A Design Group, PSC

Prepared by:

Rommel Cintrón Aponte, MSCE, PE

Date:

May 28, 2019

Revision:

November 4, 2022

Job no. 7973

Geotechnical Report: Site ER HWY 287 Road Damage Evaluation and Repair Recommendations PR 159 KM 3.5, Morovis, PR

1. Introduction

The present geotechnical report addresses the geotechnical conditions and recommendations for the road damages at the reference site location. This investigation is prepared based on approved scope of work and economical proposal by DG3A Design Group, PSC. This report is part of a multiple site assessment project for similar landslide rehabilitation cases related to damages by

Hurricane Maria on September 20, 2017. This report is prepared exclusively for design purposes.

2. Scope of Work

The scope of work consisted of two (2) test borings to 6.3 mts (20.5 ft) depth. Borings were completed with CME-55 drill rig and hollow-stem auger method of drilling at accessible locations on the side of the road. Test borings and soil sampling were performed by casing installation in accordance to ASTM D1452 and soil sampling per Standard Penetration Test (SPT) method per

ASTM D1586. Refer to enclosed boring location plan for reference on boring locations (Appendix

A Figure A2). The area of the landslide was not accessible for performing test borings with portable equipment due to existing debris and safety hazards on the slope surface.

3. Site Geology

Based on the USGS Geology Map (Appendix A Figure A1), the site’s predominant geologic formation is San Sebastian Formation (Tssg), described as sand and gravel member of the San

Sebastian formation consisting of weak limestone formation with layers of sand, clays, sandstone and silt containing gravel and cobbles. The findings in the geotechnical investigation are more consistent with a clayey stratum derived from weathering of this formation.

Site ER HWY 287 PR 159 KM 3.5, Morovis, PR

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Jaca & Sierra Engineering, PSC

t. 787-761-2570 e. contact@jacasierra.com / www.jacasierra.com

4. Site Stratigraphy

Stratum no. 1: Fill: A heterogeneous fill layer consisting of clayey silt with some sand, sandy clay and silty sand with some clay was encountered having depths of 14 ft at boring no. 287-A and

7 ft at 287-B. SPT-N values for this layer were recorded to range from 3 to 9 blows/ft and moisture contents in the order of 15 to 20 %. The fill was found on a loose state or of medium consistency for the cohesive strata within the unit. Tests made on the sandy clay unit unveiled PI values ranging from 20 to 30.

Stratum no. 2: Stiff Clayey Silt: Underlying the above described fill, a lateritic clayey silt to sandy silt formation was detected having stiff to very stiff consistency. SPT-N values ranged from 12 to over 15 blows/ft. The moisture contents ranged from 15 to 25 %. The clayey silt was underlain by a stiffer sandy silt. The SPT-N values for this stratum ranged from 30 to 46 blows/ft and moisture contents from 10 to 31 %.

4.1. Groundwater

Groundwater level was not detected within the depth range of the test borings. Temporary localized perched water may occur after prolonged rain events.

5. Geotechnical Recommendations

5.1. Opinion on Probable Causes for Road Damage

It is our opinion that the apparent cause of road edge damage is related to a shallow landslide of fill material and underlying clayey soils occurring by erosion and water infiltration from over the edge of road runoff during storm event. The slope failure mechanism can be described as a shallow landslide or slope erosion. Based on observations, at the time of our site visit, the slope is covered with vegetation and landslide material. The landslide plane depth is estimated to range from 3 to

4 ft.

mailto:contact@jacasierra.com

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5.2. Slope Rehabilitation Alternatives

The landslide stabilization alternatives include: type C concrete barrier and concrete cantilever and gravity walls. The soils at this site consist of high moisture content medium to high plasticity clayey silt which can be easily disturbed by construction process and water ponding inside excavations. Proper internal wall drainage is also of utmost importance. Also, storm runoff shall be managed with swales and curbs, and gutters to prevent zones where water drains over the slope over an unplanned zone with drainage features designed by civil engineer hydrologist.

5.2.1. Type C Concrete Barrier:

Considering the relatively shallow landslide conditions, it is our opinion that a type C concrete barrier at the edge of the road is a feasible solution for this site. This option shall include leveling the remaining slope to uniform inclination and armoring with turf reinforcement the deep-rooted vegetation such as vetiver. The base of the type C concrete barrier shall extend to a minimum depth of 1 mt (3.3 ft) below existing ground surface.

Figure 1: Type C concrete barrier on existing slope profile (not to scale)

5.2.2. Concrete Cantilever Retaining Wall:

This option has the advantage that it can be built right on the edge as a concrete barrier extension

(typical PRHTA section) or at offset location to prevent excavation within the recently paved road area. The closer the retaining wall is to the roadway edge the less the retaining wall height required.

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This option shall include leveling the remaining slope to uniform inclination and armoring with turf reinforcement the deep-rooted vegetation such as vetiver. The wall shall be embedded at least

1 mt (3.3 ft) below slope surface as measured from the lower side. With this requirement it is estimated that the retaining wall height will be in the order of 1.5 mts (5 ft).

Figure 2: Concrete cantilever wall on existing slope profile (not to scale)

5.2.3. Concrete Gravity Wall:

The concrete gravity wall option has the same advantage as discussed above, but its design usually results in a reduced excavation size compared to a cantilever wall. Also, the construction process is faster and reduces the exposure time to workers being inside an excavation. The gravity wall can be designed per PRHTA’s standard design section to be verified and adjusted by designer based on the herein provided bearing capacity and earth pressure parameters. In designing gravity walls, the sides of the wall shall be confined within natural soils. If natural soil confinement is not possible, then a wall transition into the natural soils shall be designed to avoid scouring issues. The wall shall be embedded at least 1 mt (3.3 ft) below slope surface as measured from the lower side.

With this requirement, it is estimated that the retaining wall height will be in the order of 1.8 mts

(6 ft), located at a 0.6 mts (2 ft) offset distance of the edge of the road.

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Figure 3: Concrete gravity wall on existing slope profile (not to scale)

5.3. Earth Pressure Parameters for Retaining Wall Design

Strength or Earth Pressure Parameters Engineered Fill / Retaining Wall

Backfill In-Situ Soils

Drained cohesion, c, kPa (psf) 0 (0) 9.6 (200) Drained angle of internal friction, φ, ˚ 32 26

Undrained cohesion, c, kPa (psf) - 35.9 (750) Undrained angle of internal friction, φ, ˚ - 0

Moist unit weight, γ, kN/cu.mt. (pcf) 20.4 (130) 18.9 (120) Seismic horizontal coefficient, kh - 0.2

Base shear coefficient, µ * - 0.3 Net allowable bearing capacity for retaining wall over native soil, qa, kPa (psf) - 120 (2,500)

Table 1: Earth pressure parameters for retained soils *For passive resistance neglect upper 3 ft. Passive side unit weight of backfill shall be assumed as 15.7 kN/cu.mt. (100 pcf).

It is our opinion that the above recommendations will stabilize the slope against global stability concerns. If any other option is wished to be considered, we should be provided with the information on the alternative to provide specific recommendations for that option. Also note that the recommended wall height is based on interpretation of landslide plane depth that need to be confirmed during excavation process. Adjustments to this wall heights may be required.

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5.4. Global Stability Analysis Results

Soil Condition Seismic Coefficient

Minimum Factor of Minimum Factor of Safety Obtained Safety Required

Drained None (Static) 5.175 1.500 Drained Horizontal (Pseudostatic) 3.643 1.125

Undrained None (Static) 13.992 1.500 Undrained Horizontal (Pseudostatic) 10.021 1.125

Table 2: Summary of global stability analysis results

ROCSCIENCE SLIDE2 Version 9.024 software was used for global stability analysis of the preferred type c wall alternative. Results and relevant information are presented in Appendix D.

6. Generalized Recommendations

6.1. Recommended Backfill Material: All engineered fill shall consist of A-2-4 or A-1 AASHTO

Classification fill placed and compacted to 95% of the modified Proctor density. Fines content shall not be greater than 6 %. Engineered fill shall be handled and placed per latest applicable PR

Highway Authority Specifications. Engineered fill shall be monitored by soil technician with guidance from a geotechnical engineer.

6.2. Fill Recommendations: Any fill shall be constructed upslope in horizontal layers and benched terraces shall be cut at the interface of fill and natural soils. The benches shall have a minimum width of 0.9 mts (3 ft) and shall be made at a maximum vertical distance of 0.9 mts (3 ft) as fill progresses upward. Unreinforced engineered fill slopes shall not exceed 2:1 (H:V) inclination.

6.3. Drainage: Road drainage shall be controlled by jersey barriers, curbs and gutters or storm runoff management devices designed in such way that it prevents any overland water discharge over the project areas.

6.4. Slope Erosion Control: Protect all slopes disturbed by excavations process with sodding or turf reinforcement. Deep rooted vegetation, such as vetiver and ferns (“helechos”), is recommended within any area impacted by the project. For this particular case, we recommend avoiding disturbance of existing vegetated slopes downslope of the retaining wall, thus limiting the above erosion control measures to areas impacted by excavations and retaining wall construction.

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6.5. Differing Site Conditions: These recommendations are based on test borings performed on locations, which are considered as representative of the subsoil conditions within the site, but not all areas of the site could be explored due to limitations of access. Therefore, differing site conditions could occur. In such instances, we shall be notified to proceed with a field visual inspection directed to formulate the corresponding solution.

6.6. Excavation Safety: The contractor is responsible for adjusting the excavation inclination and providing shoring where necessary, to ensure safety of working personnel per latest applicable

OSHA excavation safety standards. The contractor shall consult with the geotechnical engineer or geologist on excavation inclination and shoring requirements.

6.7. Geotechnical Engineer Confirmation: The excavations shall be coordinated with the undersigned to conduct a site visit by a representative from Jaca & Sierra Engineering, PSC to verify conditions and confirm foundation depth among other geotechnical considerations.

Thanks for the opportunity of providing our field investigation, testing and engineering consulting services. Feel free to contact us for any questions on our report.

Respectfully submitted, JACA & SIERRA ENGINEERING, PSC

Rommel Cintrón Aponte, MSCE, PE

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Appendix A: Geology Map and Boring Location Plan

SITE

Figure A1: Site Geology Map: Berryhill, H.L., Jr., 1965, Geology of the Ciales quadrangle, Puerto Rico: U.S. Geological Survey, Bulletin B-1184

287-A 287-B

Figure A2: Boring Location Map (Topography Drawing provided by DG3A) https://ngmdb.usgs.gov/Prodesc/proddesc_20963.htm https://ngmdb.usgs.gov/Prodesc/proddesc_20963.htm https://ngmdb.usgs.gov/Prodesc/proddesc_20963.htm

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Appendix B: Site Conditions Photographic Images

Figure B1: Damaged road area facing south

Figure B2: Tension crack in road edge east of slide area

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Figure B3: Road edge slide facing northeast

Figure B4: Road edge damaged by erosion

Appendix C:

Boring Logs and Laboratory Tests

213.50

212.59

209.23

FILL: silty sand with asphalt fragments and gravel, brown, black

FILL: clayey silt with sand, soft, brown

Do... roots

Do... some gravel (fill)

SAPROLITE: clayey silt some sand, very stiff, red, brown, purple

S-1

S-2

S-3

S-4

S-5

S-6

S-7

SUBSURFACE EXPLORATION LOG

BORING N0.: 287-A

PROJECT

ER Hwy 287

JOB

OF

SHEET 1

LOCATION PR-159 Km.3.5, Morovis, PR DRILLER/DRILL RIG: Eduardo Santiago / CME-55

COORDINATES 205312.985 E 254621.986 N DATE HOLE STARTED 2-6-19 COMPLETED 2-6-19

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 213.5 GROUNDWATER (FT) Initial: Not Found Final: ENGINEER Carlos R. Sierra Del Llano DRILLING METHOD: Hollow-Stem Auger 2.25 ID TOTAL DEPTH OF HOLE (ft): 20.5

N W Qu PL+LL

"N" - Number of blows required to drive the sampling spoon a distance of 12 in. with a 140 lbs hammer falling 30 in.

"W" - Natural Moisture Content in percentage of dry weight. Initial G.W. Depth "Qu" - Unconfined Compressive Strength in tons per square foot. Final G.W. Depth "Rc" - Core recovery in percent for each successive run. "Rqd" - Rock quality designation.

"WH" - Sample was recovered by advancing the sampler with the weight of the hammer.

"P" - A "P" in the Unconfined Compressive Strength test indicates the use of the pocket Penetrometer.

Elev.

(mts)

0.00

DEPTH

(feet) DESCRIPTION

LE

G

E N

D

S am pl e

N o.

TY

P

E

B

LO

W S

SPT

N W Qu RC RQD%

20 40 60 80

1 2 3 4

Qu

N-W

213.10

210.97

207.31

FILL: clayey silt with gravel some sand, brown

CLAYEY SILT some sand, stiff, brown, red, purple

SAPROLITE: sandy silt some clay, hard, brownish yellow

S-1

S-2

S-3

S-4

S-5

S-6

S-7

SUBSURFACE EXPLORATION LOG

BORING N0.: 287-B

PROJECT

ER Hwy 287

JOB

OF

SHEET 1

LOCATION PR-159 Km.3.5, Morovis, PR DRILLER/DRILL RIG: Eduardo Santiago / CME-55

COORDINATES 205317.982 E 254603.542 N DATE HOLE STARTED 2-6-19 COMPLETED 2-6-19

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 213.1 GROUNDWATER (FT) Initial: Not Found Final: ENGINEER Carlos R. Sierra Del Llano DRILLING METHOD: Hollow-Stem Auger 2.25 ID TOTAL DEPTH OF HOLE (ft): 20.5

N W Qu PL+LL

"N" - Number of blows required to drive the sampling spoon a distance of 12 in. with a 140 lbs hammer falling 30 in.

"W" - Natural Moisture Content in percentage of dry weight. Initial G.W. Depth "Qu" - Unconfined Compressive Strength in tons per square foot. Final G.W. Depth "Rc" - Core recovery in percent for each successive run. "Rqd" - Rock quality designation.

"WH" - Sample was recovered by advancing the sampler with the weight of the hammer.

"P" - A "P" in the Unconfined Compressive Strength test indicates the use of the pocket Penetrometer.

Elev.

(mts)

0.00

DEPTH

(feet) DESCRIPTION

LE

G

E N

D

S am pl e

N o.

TY

P

E

B

LO

W S

SPT

N W Qu RC RQD%

20 40 60 80

1 2 3 4

Qu

N-W

(X=NO)PERCENTFINERSIZE

PASS?SPEC.*PERCENTSIEVE

Project No:

Project:

Client:

Elev./Depth:Location:

Date:Source of Sample:Sample No.:

Remarks

Classification

Coefficients

Atterberg Limits

Material Description

AASHTO=USCS=

Cc=Cu=

D10=D15=D30=

D50=D60=D85=

PI=LL=PL=

Particle Size Distribution Report

P E R C E N T F

IN

E R

100 10 1 0.1 0.01 0.001500

GRAIN SIZE - mm

% +75 MM % GRAVEL % SAND % SILT % CLAY

i n i n i n

-1 /2 i n i n

/4 i n

/2 i n

/8 i n

0.0 4.0 20.3 75.7

Figure

Road 287, Corozal, PR

DG3A Design Group

6-10.5'Corozal, PR

2/27/19Project SiteBo. 287A

Tested by: A. Roman

Checked by: Carlos Sierra Del Llano, MSCE, PE

A-7-6(24)CH

0.229

315524

Fat clay with sand.

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 98.6 97.9 96.0 93.2 88.4 81.9 75.7

.75 in.

.5 in.

.375 in.

#4

#10 #40

#100 #200

(X=NO)PERCENTFINERSIZE

PASS?SPEC.*PERCENTSIEVE

Project No:

Project:

Client:

Elev./Depth:Location:

Date:Source of Sample:Sample No.:

Remarks

Classification

Coefficients

Atterberg Limits

Material Description

AASHTO=USCS=

Cc=Cu=

D10=D15=D30=

D50=D60=D85=

PI=LL=PL=

Particle Size Distribution Report

P E R C E N T F

IN

E R

100 10 1 0.1 0.01 0.001500

GRAIN SIZE - mm

% +75 MM % GRAVEL % SAND % SILT % CLAY

i n i n i n

-1 /2 i n i n

/4 i n

/2 i n

/8 i n

0.0 12.5 39.6 47.9

Figure

Road 287, Corozal, PR

DG3A Design Group

4-7.5'Corozal, PR

3/1/19Project SiteBo. 287B

Tested by: A. Roman

Checked by: Carlos Sierra Del Llano, MSCE, PE

A-7-6(6)SM

0.1030.3613.74

194728

Silty sand.

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 95.4 93.9 87.5 78.6 61.6 52.6 47.9

.75 in.

.5 in.

.375 in.

#4

#10 #40

#100 #200

Appendix D:

SLIDE2 Software Results

Figure D1: Drained static condition

Figure D2: Drained seismic condition

Figure D3: Undrained static condition

Figure D4: Undrained seismic condition