Geotechnical Report - AC-916579_HWY-286.pdf

GEOTECHNICAL REPORT

LANDSLIDE AND ROAD DAMAGE EVALUATION

AND REPAIR RECOMMENDATIONS

PR-159 KM 3.2, MOROVIS, PR

ER-HWY-286

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. 7972

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B o x

S a n

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Geotechnical Report: Site ER HWY 286 Road Damage Evaluation and Repair Recommendations PR 159 KM 3.2, Morovis, PR

1. Introduction

The present geotechnical report addresses the subsurface conditions and recommendations for the repair of 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 286 PR 159 KM 3.2, 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 8 ft at boring no. 286-A and

4 ft at 286-B. SPT-N values for this layer was recorded to range from 6 to 7 blows/ft and moisture contents from 9 to 18 %. The fill was found on a loose state or of medium consistency for the cohesive strata within the unit.

Stratum no. 2: Clayey Silt/Sandy Clay: Underlying the above described fill, a lateritic clayey silt to sandy clay soil was found. At boring no. 286-B, a clayey silt was found from 6 to 14 ft depth having medium stiff consistency. The SPT-N values ranged from 4 to 8 blows/ft. The moisture contents ranged from 22 to 25 %. The clayey silt was underlain by a sandy clay with stiffer consistency. The SPT-N values for this stratum ranged from 10 to 30 blows/ft and moisture contents from 21 to 31 %. A test made on the sandy clay unit unveiled a PI value of 21.

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 failure is related to a shallow landslide of fill material and underlying clayey soils occurring by erosion and water infiltration from storm runoff over the edge of the road. The slope failure mechanism can be described as a shallow landslide. 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 1.2 to 2.4 mts (4 to 8 ft).

mailto:contact@jacasierra.com

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5.2. Slope Rehabilitation Alternative

Considering that the existing slope beyond the road edge has fairly shallow angle, it is our opinion that the most feasible solution at this site is to provide drainage improvements along with energy dissipators at discharge area. Storm runoff shall be managed with swales and curbs, and gutters along the entire edge of the road and perhaps a low wall (3 ft height) combined to prevent zones where water drains over the slope over an unplanned zone with drainage features designed by hydraulic civil engineer. The design shall consider a grouted riprap or Reno mattress armoring to control soil erosion from discharge. This solution shall include leveling the remaining slope to uniform inclination and armoring with turf reinforcement the deep-rooted vegetation such as vetiver. The designer shall discuss with our office the design sections to make sure that all details and improvement extent is covered.

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)

- 95.8 (2,000)

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. In the event that a retaining wall becomes necessary, Table 1 above provides soil parameters for design. 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.

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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) 2.549 1.500 Drained Horizontal (Pseudostatic) 1.345 1.125

Undrained None (Static) 2.549 1.500 Undrained Horizontal (Pseudostatic) 1.345 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 new backfill 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 the 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 mailto:contact@jacasierra.com 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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286-B 286 A

Figure A2: Boring Location Map (Topography Drawing provided by DG3A)

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Appendix B: Site Conditions Photographic Images

Figure B1: Damaged road area facing east

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

Figure B3: Road edge slide facing west

Figure B4: Landslide area

Appendix C:

Boring Logs and Laboratory Tests

223.00

221.78

220.56

218.73

FILL: sandy clay some silt, medium stiff, brown, red

FILL: silty sand with gravel, loose, brown, yellow

Do... some clay and asphalt fragments

SANDY CLAY some silt, stiff, brown

SAPROLITE: sandy clay some silt, very stiff, red, purple, brown

S-1

S-2

S-3

S-4

S-5

S-6

S-7

SUBSURFACE EXPLORATION LOG

BORING N0.: 286-A

PROJECT

ER Hwy 286

JOB

OF

SHEET 1

LOCATION PR-159 Km.3.2, Morovis, PR DRILLER/DRILL RIG: Eduardo Santiago / CME-55

COORDINATES 205123.342 E 254455.295 N DATE HOLE STARTED 2-6-19 COMPLETED 2-6-19

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 223 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

223.00

221.78

218.73

FILL: clayey silt some gravel, medium stiff, brown

CLAYEY SILT trace sand, medium stiff, brown, reddish brown

SAPROLITE: sandy clay some silt, very stiff, red, purple, brown

S-1

S-2

S-3

S-4

S-5

S-6

S-7

SUBSURFACE EXPLORATION LOG

BORING N0.: 286-B

PROJECT

ER Hwy 286

JOB

OF

SHEET 1

LOCATION PR-159 Km.3.2, Morovis, PR DRILLER/DRILL RIG: Eduardo Santiago / CME-55

COORDINATES 205130.978 E 254453.452 N DATE HOLE STARTED 2-6-19 COMPLETED 2-6-19

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 223 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

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

Geotechnical Report Site 286 PR 159 KM 3.2 Morovis PR.pdf