Geotechnical Report - AC-830579_Hwy-106.pdf

GEOTECHNICAL REPORT

LANDSLIDE AND ROAD DAMAGE EVALUATION

AND REPAIR RECOMMENDATIONS

PR-124 KM 21.9, LARES, PR

ER-HWY-106

AC-809544

Submitted to:

José A. Batlle Montalvo, PE

José A. Batlle y Asociados, CSP

Prepared by:

Rommel Cintrón Aponte, MSCE, PE

Date:

January 29, 2019

Revision:

September 21, 2021

Job no. 7943

Geotechnical Report: Site ER HWY 106

Landslide and Road Evaluation and Repair Recommendations PR 124 KM 21.9, Lares, PR

J a c a & S i e r r a E n g i n e e r i n g , P S C

P O B o x 3 6 3 1 1 6 , S a n J u a n , P R 0 0 9 3 6 - 3 1 1 6

R o a d 8 5 0 K m 0 . 2 L a s C u e v a s W a r d , T r u j i l l o A l t o , P R 0 0 9 7 6

T . ( 7 8 7 ) 7 6 1 - 2 5 7 0 w w w . j a c a s i e r r a . c o m

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

José A. Battle y Asociados, CSP. 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 one (1) test boring to 6.3 mts (20.5 ft) depth. Boring was completed with CME-45 drill rig at accessible locations along 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 location in Appendix A

Figure A2.

3. Site Geology

Based on the USGS Geology Map (refer to Appendix A Figure A1) Tmb – Milagros

Formation: Breccia member, predominantly brown to gray tuff-breccia with lesser amounts of lapilli tuff.

Site ER HWY 106 PR 124 KM 21.9, Lares, 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: The upper fill stratum has a thickness of 0.6 mts (2 ft) and consists of sandy silt with traces of gravel. The SPT-N value recorded was 10 blows/ft and the moisture content measured was 25 %.

Stratum no. 2: Soft to Stiff Clayey Silt: The above described fill layer overlays clayey silt with some sand extending to the end of boreholes at 6.3 mts (20.5 ft). SPT-N values registered are ranging from 4 to 17 blows/ft for a soft to stiff consistency. Moisture contents obtained are from 35 to 44 %.

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 the storm sewer pipe that crosses underground perpendicular to the road and discharge water over the ground at the side of the road. The relatively high flow during storm event eroded the existing fill and native clayey silt soils.

5.2. Slope Rehabilitation Alternatives

All alternatives shall consider the design of an inlet apron to protect the inlet area of the storm sewer pipe as well as riprap or Reno mattress armoring along the outlet area to control soil erosion from discharge. The remaining slope downhill shall be leveled to uniform inclination and armoring with turf reinforcement the deep-rooted vegetation such as vetiver.

mailto:contact@jacasierra.com

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5.2.1. Concrete Cantilever Retaining Wall:

This option has the advantage that it can be built right on the edge of the road as a

Jersey barrier extension (typical PRHTA section). The closer the retaining wall is to the roadway edge the less the retaining wall height required. The wall shall be embedded at least 1.2 mts (4 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 1.82 mts

(6.0 ft) at the highest location.

5.2.2. Concrete Gravity Wall:

This option has the advantage of minimizing excavation width at the edge of the road.

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. Similar to the cantilever wall, it shall be embedded at least 1.2 mts (4 ft) below slope surface as measured from the lower side. With this requirement it is estimated that the retaining wall height will likewise be in the order of 1.82 mts (6.0 ft) at the highest location.

5.2.3. Gabion Wall:

This option will need a retaining wall to be offset from the edge of the road to allow placement of a guard rail or Jersey barrier. The gabions at the proposed locations shall be embedded at least 1.2 mts (4 ft) below ground surface. It is estimated that the gabion wall height will be in the order of 3.62 mts (11.9 ft) at the highest location. This will result in a higher wall if compared with the concrete cantilever and gravity walls above because of offset distance off the edge of the road and steep gradient of the slope. The advantage of this option is that it can be installed with less excavations and disturbance to the existing road.

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5.2.4. 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.

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 25

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. Other options such as soil nailing with shotcrete were discarded due to cost concerns and the fact that the edge of road was lost and a retaining wall is required to allow re-building the road to its original alignment. MSE walls or slopes will not work on this site due to limitations of space and steepness of the slope which will not allow for creating of suitable base and placement of soil reinforcement into the cut without having to excavate almost the entire road width. 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

6. Soil Condition Seismic Coefficient

Minimum Factor of Minimum Factor of Safety Obtained Safety Required

Drained None (Static) 2.098 1.500 Drained Horizontal (Pseudostatic) 1.479 1.125

Undrained None (Static) 3.847 1.500 Undrained Horizontal (Pseudostatic) 2.731 1.125

Table 2: Summary of global stability analysis results

GEO-SLOPE SLOPE/W Version 5.2 software was used for global stability analysis of the preferred type C concrete barrier 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. 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 (3.0 ft) and shall be made at a maximum vertical distance of 0.9 mts (3.0 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. Erosion control measures at discharge locations shall be in accordance to the hydraulic specialist design.

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6.4. Slope Erosion Control: Protect all slopes with sodding or turf reinforcement. Deep rooted vegetation such as vetiver and fern (“helecho”) is recommended within any area impacted by the project and particularly the slope extending downslope from the toe of the retaining wall. Bare soils exposed upslope should also be protected with deep rooted vegetation.

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: Contractor is responsible to adjust excavation inclination and provide shoring, where necessary, to ensure safety of working personnel per latest applicable OSHA excavation safety standards. The contractor shall consult with 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 Cintron Aponte, MSCE, PE Geotechnical Engineer

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Appendix A: Geology Map and Boring Location Plan

Figure A1: Site Geology Map – Tobisch, O.T., and Turner, M.D., 1971. Geologic Map of the San Sebastián Quadrangle, Puerto Rico, Map I-661, Miscellaneous Geologic Investigations, U.S.

Geological Survey, Department of the Interior, Washington D.C.

SITE

https://ngmdb.usgs.gov/Prodesc/proddesc_1369.htm https://ngmdb.usgs.gov/Prodesc/proddesc_1369.htm

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Figure A2: Boring Location Plan – Site plan provided by Javier E. Bidot & Associates, PSC

A

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Appendix B: Site Conditions Photographic Images

Figure B1: Existing road conditions

Figure B2: Damaged outlet area

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Figure B3: Downslope at outlet area

Figure B4: Inlet area at side of the road

Appendix C:

Boring Logs and Laboratory Tests

350.00

349.39

348.17

FILL: sandy silt trace gravel, brown, strong brown

CLAYEY SILT some sand, soft, brown, yellowish red, light gray

CLAYEY SILT some sand, stiff, brown, yellowish red, light gray

Do... relic joints

S-1

S-2

S-3

S-4

S-5

S-6

S-7

SUBSURFACE EXPLORATION LOG

BORING N0.: A

PROJECT

Landslide and Road Evaluation and Repairs (ER-HWY-106)

JOB

OF

SHEET 1

LOCATION PR-124 Km. 21.9, Lares, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45

COORDINATES 248152 N 150379 E DATE HOLE STARTED 1-9-19 COMPLETED 1-9-19

DESCRIPTION BY Rommel Cintron ELEVATION TOP OF HOLE (mts): 350 GROUNDWATER (FT) Initial: Not Found Final: ENGINEER Rommel Cintron 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 0.1 22.8 77.1

Figure7943

Landslide and Road Evaluation and Repairs, Lares, PR (ER-HWY-

106)

Jose A. Batlle y Asociados

2-7.5'Lares, PR

1/23/19Project SiteA

Tested by: J. Ortiz

Checked by: Rommel Cintron Aponte, MSCE, PE

A-7-5(15)MH

0.196

175235

Elastic silt with sand

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 99.9 99.4 91.9 82.6 77.1

.375 in.

#4 #10 #40 #100 #200

Appendix D:

SLOPE/W Software Results

Figure D1: Drained static condition

Figure D2: Drained seismic condition

Figure D3: Undrained static condition

Figure D4: Undrained seismic condition