Geotechnical Report - AC-831579_Hwy-134.pdf

GEOTECHNICAL REPORT

LANDSLIDE AND ROAD DAMAGE EVALUATION

AND REPAIR RECOMMENDATIONS

PR-128 KM 51.63, LARES, PR

ER-HWY-134

AC-809544

Submitted to:

José A. Batlle Montalvo, PE

José A. Batlle y Asociados, CSP

Prepared by:

Rommel Cintrón Aponte, MSCE, PE

Date:

March 4, 2019

Revision:

December 17, 2021

Job no. 7957

P

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B o x

S a n

J u a n

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Geotechnical Report: Site ER HWY 134

Landslide and Road Evaluation and Repair Recommendations PR 128 KM 51.63, 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. Batlle 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 two (2) test borings to 6.3 mts (20.5 ft) depth. Borings were completed with CME-45 drill rig 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 location in 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 (refer to Appendix A Figure A1) the site’s predominant geologic formation is Ti – Intrusive Rocks. Ti is described as massive gray to light-gray diorite and quartz diorite; mostly fine-grained, textures range from granitic to xenomorphic granular; locally porphyritic. Refer to the enclosed geologic report prepared by Mr. James Joyce, PhD, PG.

Site ER HWY 134

PR 128 KM 51.63, Lares, PR

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1 2 / 1 7 / 2 1 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 thicknesses of 0.6 to 1.2 mts (2 to 4 ft) and consists of sandy silt with gravel and sandy clay with trace to some gravel. SPT-N values recorded are varying from 3 to 45 blows/ft. Moisture contents measured are from 7 to 25

Stratum no. 2: Saprolite: The above described fill layer overlays saprolitic soils composed of sandy silt to silty sand with trace to some weathered rock fragments from the above-mentioned Intrusive Rocks extending to the end of boreholes at 6.3 mts (20.5 ft) depth.

SPT-N values registered are ranging mostly from 7 to 30 blows/ft. Moisture contents obtained are from 9 to 32 %.

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 native saprolitic soils occurring by erosion from overland runoff during storm event. The slide can be described as a soil washout. At the time of our site visit on

December 27, 2018, the landslide was covered with vegetation.

5.2. Slope Rehabilitation Alternatives:

5.2.1. Gabion Wall:

A gabion wall is favorable for this site due to its inherent ability to drain any water or moisture trapped in the backfill. The base width will be wider if compared to a concrete mailto:contact@jacasierra.com

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1 2 / 1 7 / 2 1 cantilever or gravity wall. Also, this type of wall will require an offset from the guard rails or concrete barrier at the edge of road. Therefore, it will project further in to the slope and thus result in more height required if compared to the concrete wall options.

This option shall be evaluated by design verification of different section profiles to be made along the extent of the project to evaluate the wall height variations. The wall shall be embedded at least 1.8 mts (6 ft) below slope surface as measured from the lower side.

This will result in a wall height of 7.2 mts (24 ft) at the highest location. For this option, a realignment of the road is recommended to reduce the wall height in the order of 4.5 mts (15 ft), if possible. When designing this option, it will be important to have measures to prevent water from infiltrating into the wall from the road side. A perforated pipe drain shall be included in the backfill to allow drainage of any water that accumulates on the backside of the wall or that infiltrates thru the wall. These details are well covered in

PRHTA standard drawings.

5.2.2. Concrete Cantilever Retaining Wall:

This option has the advantage that it can be built right on the edge of the road as a concrete barrier extension (typical PRHTA section). The closer the retaining wall is to the roadway edge the less the retaining wall height required. 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 1.8 mts

(6 ft) below slope surface as measured from the lower side. With this requirement it is estimated that the retaining wall height will be 4.3 mts (14 ft) at the highest location.

5.2.3. Concrete Gravity Wall:

The concrete gravity wall 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

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1 2 / 1 7 / 2 1 capacity and earth pressure parameters. The wall shall be embedded at least 1.8 mts (6

ft) below slope surface as measured from the lower side. With this requirement it is estimated that the retaining wall height will be 4.3 mts (14 ft) at the highest location.

5.2.4. Anchored Gabion Wall:

Anchored gabion walls are an alternative to reduce the wall width requirements in conventional gabion walls. The anchor can be designed assuming allowable bond strength of 25 psi for non-shrink grout with over 5,000 psi strength. A minimum free length of 10 ft shall be considered. We recommend a minimum of 2 verification tests and proof tests on 5 % of the installed soil nails or anchors. Anchor testing shall be per Soil

Nail Walls Reference Manual FHWA NHI-14-007 February 2015. Similar to the previous explained alternatives, the slopes shall be excavated and leveled to improve their stability to the extent that the toe of the wall remains embedded 1.8 mts (6 ft).

Figure 1: Anchored gabion schematic concept (not to scale)

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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) 12.0 (250)

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, * - 0.3

Net allowable bearing capacity for retaining wall over native soil, qa, kPa (psf)

- 119.7 (2,500)

Table 1: Earth pressure parameters for retained soils (neglect passive resistance)

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 reinforcements 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. Also note that the recommended wall heights are based on interpretation of landslide plane depths that need to be confirmed during excavation process. Adjustments to these wall heights may be required.

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1 2 / 1 7 / 2 1

5.4. Global Stability Analysis Results

Soil

Condition Seismic Coefficient

Minimum Factor of Minimum Factor of

Safety Obtained Safety Required

Drained None (Static) 1.564 1.500

Drained Horizontal (Pseudostatic) 1.159 1.125

Undrained None (Static) 1.991 1.500

Undrained Horizontal (Pseudostatic) 1.781 1.125

Table 3: Summary of global stability analysis results

GEO-SLOPE SLOPE/W Version 5.2 software was used for global stability analysis of the preferred concrete gravity 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. 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.

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1 2 / 1 7 / 2 1

6.4. Slope Erosion Control: Protect all slopes disturbed by excavations process with sodding or turf reinforcement. Deep rooted vegetation such as vetiver and fern

(“helecho”) 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.

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.

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1 2 / 1 7 / 2 1

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

Geotechnical Engineer

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1 2 / 1 7 / 2 1

Appendix A: Geology Map and Boring Location Plan

Figure A1: Site Geology Map – Nelson, A.E., and Tobisch, O.T., 1968, Geologic map of the Bayaney quadrangle, Puerto Rico: U.S. Geological Survey, Miscellaneous Geologic Investigations Map I-525

SITE

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

A B

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1 2 / 1 7 / 2 1

Appendix B: Site Conditions Photographic Images

Figure B1: Existing road conditions

Figure B2: Existing road conditions

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1 2 / 1 7 / 2 1

Figure B3: Damaged road area

Appendix C:

Boring Logs and Laboratory Tests

436.00

435.39

433.26

FILL: sandy silt with gravel, brownish yellow, white, red

SANDY SILT some weathered rock fragments, brownish yellow, white, red

SILTY SAND some weathered rock fragments, brownish yellow, white, red

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-134)

JOB

OF

SHEET 1

LOCATION PR-128 Km. 51.63, Lares, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45

COORDINATES 246384 N 155193 E DATE HOLE STARTED 11-1-19 COMPLETED 11-1-19

DESCRIPTION BY Rommel Cintron ELEVATION TOP OF HOLE (mts): 436 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

435.00

433.78

430.73

FILL: sandy clay some gravel, brown, brownish yellow Do... trace gravel

SANDY SILT trace weathered rock fragments, brownish yellow, white, red

SILTY SAND some weathered rock fragments, brownish yellow, white, red

S-1

S-2

S-3

S-4

S-5

S-6

S-7

SUBSURFACE EXPLORATION LOG

BORING N0.: B

PROJECT

Landslide and Road Evaluation and Repairs (ER-HWY-134)

JOB

OF

SHEET 1

LOCATION PR-128 Km. 51.63, Lares, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45

COORDINATES 246369 N 155184 E DATE HOLE STARTED 10-1-19 COMPLETED 10-1-19

DESCRIPTION BY Rommel Cintron ELEVATION TOP OF HOLE (mts): 435 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 50.9 34.9 14.2

Figure7957

Landslide and Road Evaluation and Repairs (ER-HWY-134)

Jose A. Batlle y Associados

2-5.5'Lares, PR

2/12/19Project SiteER-134A

Tested by: A. Roman

Checked by: Rommel Cintron Aponte, MSCE, PE

A-2-4(0)GC

0.09290.932 5.048.8722.9

93122

Clayey gravel with sand

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 89.7 76.8 67.6 61.5 49.1 37.9 23.4 17.0 14.2

1.5 in.

1 in.

.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 31.9 30.9 37.2

Figure7957

Landslide and Road Evaluation and Repairs (ER-HWY-134)

Jose A. Batlle y Associados

0-3.5'Lares, PR

2/12/19Project SiteER-134B

Tested by: A. Roman

Checked by: Rommel Cintron Aponte, MSCE, PE

A-6(1)GC

0.6412.0717.0

133623

Clayey gravel with sand

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 88.9 77.7 75.8 68.1 59.7 46.8 40.3 37.2

1 in.

.75 in.

.5 in.

.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

Appendix E:

Geologic Report

Geologic Report - PR 128 Milagros, Barrio Miraflores, Lares PR

James Joyce, Ph.D, PG submitted to

Geologic Report Jaca & Sierra Engineering, PSC PO Box 363116 | San Juan, PR 00936

GEOLOGIC REPORT-PR 128 !1

Geologic Report - PR 128 Geologic Structural Analysis

Geologic Setting The stretch of PR-128 between Milagros and Cerro La Torre under investigation cuts across hydrothermally altered volcanic rock (Tvu) that surrounds the Cerro La Torre igneous intrusion (Ti). Seven slope failure sites were investigated along the highway from North to South from ER-HWY-139(1) to ER-HWY-133(7) at the base of Cerro El Torre (Figure 1). ER-HWY-133 and 134 lie within the Cerro La Torre pluton (Ti) which is described on the Geologic Map of the Bayaney Quadrangle (Figure 2) as:

“Intrusive rocks: Massive gray to light-gray diorite and quartz diorite. Mostly fine grained, textures ranging from granitic to xenomorphic granular; locally porphyritic”.

Rock cuts on the highway below Cerro el Torre expose moderately to highly weathered fine to medium grained feldspar porphyry quartz diorite. ER-HWY-135 to 139 lie within the zone of hydrothermally altered undifferentiated volcanic rock (Tuv) that surrounds the Cerro La Torre pluton. These rocks are described on the geologic map as: “Volcanic rocks, undivided: Light gray to yellowish- to reddish-brown volcanic breccia, lapilli tuff, lava and volcanic sandstone and siltstone. Most of these rocks have been hydrothermally altered (sericitized and silicified). Commonly rock

GEOLOGIC REPORT-PR 128 !2

ER-HWY-134

ER-HWY-133

ER-HWY-136

ER-HWY-139

ER-HWY-138

ER-HWY-137 ER-HWY-135

Figure 1 Nov. 11, 2017 Image of PR-128 between Milagros and Cerro La Torre

Cerro La Torre types cannot be satisfactorily divided, and locally only a soft sericite or hard silicious material is all that remains. Contains some small intrusive bodies”. The Volcanic rocks, undivided (Tuv) in the area of investigation are shown with black stipples on the geologic map (Figure 2). The black stipples designate: “Area of hydrothermal alteration: Very light gray to deep-reddish-brown highly sericitized and silicified rocks. In places contains deep-yellow-brown iron oxide stain and deep red hematite stain. Commonly contains pyrite and locally traces of chalcopyrite. Weathered sericite zones are soft, whereas siliceous zones are hard”. Highly altered Volcanic rocks (Tvu) fitting these descriptions characterize the road cuts and slope failures at sites ER-HWY-139 and 138 and the cascade face of the quebrada between sites ER-HWY-134 and 135. Less altered, weathered tuff is exposed at site ER-HWY-136.

Fracture and joint patterns were measured in rock exposures at the sites to asses their impact on slope stability and drainage system development. Cut slope, failure slope and drainage slopes were also measured at the sites. Data from all of the sites were compiled on a stereonet for analysis and are presented in Figure 3 and plotted on Figure 4. Joint planes are plotted as black lines and curves (great circles) and slope estimates are plotted as blue curves. Joint planes are also plotted as poles (blue dot), which are contoured to accentuate their concentrations. The dominant joint sets are moderately (30°-60°) inclined Northwest and Southeast. The slope estimates clearly parallel these 2 joint sets. Slope drainage channels trend to the

GEOLOGIC REPORT-PR 128 !3

ER-HWY-134

ER-HWY-133

ER-HWY-136

ER-HWY-139

ER-HWY-138

ER-HWY-137 ER-HWY-135

Figure 2 Portion of the Geologic Map of the Bayaney Quadrangle Arthur E. Nelson and Othmar Tobisch - 1968

West parallel to the intersection of these sets. Cut slope failures observed at Sites ER-HWY-139,-138,-136,-134 were controlled by outward inclined joints. Other cut slope failures were largely in clayey (sericitized) altered volcanic rock and soils.

Slope failures below the highway at Sites ER-HWY-137,-136,-135-134-133 appear to be washout debris flows and slides on joint parallel slopes. The natural and cut slope failures above the road diverted road drainage on to the lower slopes. The high intensity rainfall during Hurricane Maria was the primary cause of the excess slope runoff that caused debris flows in the upper tributary channels and the adjacent natural and cut slope failures that diverted the road drainage on to the lower slopes.

GEOLOGIC REPORT-PR 128 !4

1 % Area Contours

C.I. = 2.0 % / 1 % area

Equal Area

Lower Hemisphere

N = 125

North

South

EW 30°45°60°

Figure 3 Stereonet compilation of joint planes and slope estimates - all sites.

Figure 4 Strike and dips of joints and slope estimates measured at sites.

ER-HWY-139

ER-HWY-138

ER-HWY-136

ER-HWY-134

ER-HWY-133

ER-HWY-137

ER-HWY-135

Site 1 ER-HWY-139 This site is characterized by sericitized and silicified hydrothermally altered volcanic rock. The hard siliceous rock on Norhwest facing cut slope south of the tributary spring comprises a joint and slope parallel rockslide. The cut slope estimate was about 50° and is shown as a blue great circle on the adjacent stereonet. The cut slope and failure slope are essentially parallel to joints measured in the silicified rock shown as black great circles. Veins of chalcopyrite and iron oxides riddle the silicified rock. Sericitized (clayey-silty texture) volcanic rock characterizes the cut slope South of the slide block. Debris flows in the upper portions of the tributary spring and excessive slope runoff during Hurricane Maria contributed to the formation of a major debris flow within the spring channel and failure of the section of the highway. The rockslide appears to have formed subsequent to the reconstruction of this section.

GEOLOGIC REPORT-PR 128 !5

Equal Area Lower Hemisphere

N = 15S

EW

Photo 1 Site ER-HWY-139

Spring

Slide Block

Site 2 ER-HWY-138 This site is characterized by sericitized (clayey-silty texture) hydrothermally altered volcanic rock. Two small springs occupy the tributary channel and are coincident with a blue colored porphyry cooper depos i t . The depos i t cons i s t s o f chalcopyrite disseminated in plagioclase porphyry andesite. The cut slope estimates of 40°-50° to the Southwest are shown as blue great circles on the adjacent stereonet. The slope estimates are similar to joint planes measured on the cuts slope that are shown as black great circles on the stereonet. Saturation of the soft and weak hydrothermally altered volcanic rock led to destabilization of the cut slopes and the formation of a debris in the tributary spring channel.

GEOLOGIC REPORT-PR 128 !6

Photo 2 Site ER-HWY-138

Springs

Equal Area Lower Hemisphere

N = 10

N

S

EW

GEOLOGIC REPORT-PR 128 !7

Photo 3 Site ER-HWY-137 Slope washout on Northwest facing slope

Spring

Slope Washout

Photo 4 Site ER-HWY-136 Washout debris flow on Southwest facing slope

Washout Debris Flow

Rock Fall Scar

Site 3 ER-HWY-136 The site is located in a heavily vegetated area on the Northwest facing slopes South of the tributary spring channel.

The slope failure below the highway appears to have been restricted to the colluvial cover as no rocks were observed at the site. Storm water overflow from the highway caused the slope washout.

Site 4 ER-HWY-135 This site is characterized by moderately to highly weathered volcanic rock. A debris flow channel scar floored by rock is on the Southwest facing slopes just beyond a curve in the highway. A rock fall scar on the opposite side rock cut exposes fractured weathered rock. Joints measured in the exposure are shown black great circles and debris flow channel and cut slope estimates as blue. Diversion of roadway drainage around the corner and the rock fall debris caused the washout debris flow. The exposure of gabions at both sites indicates that similar washouts have previously occurred there.

GEOLOGIC REPORT-PR 128 !8

Equal Area Lower Hemisphere

N = 15

N

S

Photo 5 Washout debris flow channel

GEOLOGIC REPORT-PR 128 !9

Photo 6 ER-HWY-135 Washout debris flow channel on Southwest facing slope

Photo 7 ER-HWY-134 Slope washout on Northwest facing slope

Site 5 ER-HWY-135 This site is characterized by highly weathered and hydrothermally altered volcanic rock. A washout debris flow scar in the weathered volcanic rock occurs on the Southwest facing slope below the highway, North of a tributary channel. The washout was caused by diversion of road drainage around the corner and the cut slope failures in highly weathered rock.

Site 6 ER-HWY-134 This site is characterized by highly weathered quartz diorite. A slope washout scar occurs on the Northwest facing slope beyond a curve and opposite a rock and soil fall scar in the road cut. Diversion of road drainage around the corner and the rock fall likely caused the washout slope failure. Joint planes measured in the rock exposed in the rock fall scar are shown as black great circles. Slope estimates of the debris flow channel and the washout are shown in blue great circles.

GEOLOGIC REPORT-PR 128 !10

Photo 8 ER-HWY-134 Cut slope failure scar on southwest facing slope.

Equal Area Lower Hemisphere

N = 20S

N

Site 7 ER-HWY-133 This site lies just North of where a major debris flow off the side of Cerro La Torre eroded out a large portion of PR 128 during Hurricane Maria. The site is characterized by moderately to highly weathered quartz diorite. Rock and debris fall scars occur over most of the road cuts. Diversion of roadway drainage around the adjacent curve in the highway and the rock and debris falls over the side of the highway produced the slope washout. The washout appears to have been restricted to the colluvial cover on the slope. Joints measured in rock cuts and failure scars adjacent to the washout and further South along the highway are plotted as black great circles. The washout slope estimates are plotted as blue great circles. As with the other sites failure slope orientation estimations generally parallel the joint patterns in the adjacent exposed bedrock.

It can be clearly seen that joints sets that are moderately inclined to the Northwest and Southeast control the formation of the natural slopes and the stability

GEOLOGIC REPORT-PR 128 !11

Equal Area Lower Hemisphere

N = 11S

EW

Photo 9 ER-HWY-133 Slope washout on Northwest facing slope

N of road cuts at all of the inspected sites. Successful reparation designs must consider the effect of joint orientation and angle on slope stability.

GEOLOGIC REPORT-PR 128 !12