Technical Report - AC-922579_HWY-80.pdf

PUERTO RICO HIGHWAY AND

TRANSPORTATION AUTHORITY

TECHNICAL REPORT

SITE - 80

Hurricane Maria Efforts for Landslide and Road Damage Evaluation and Repair Recommendations

Contract Number:2019-000141

AC-810544 / ER-9999(319)

MARCH 7, 2019

REVISION 1 SEPTEMBER 25, 2019

REVISION 2 DECEMBER 14, 2023

REVISION 3 MARCH 25, 2024

ER-HWY-80 REVISION 3 – March 25, 2024 | Page 1 kimley-horn.com Millennium Park Plaza, 15 Calle 2, Suite 135, Guaynabo PR 00968 787 782 5050

Table of Contents

1.0 INTRODUCTION

2.0 DAMAGE ASSESSMENT

3.0 WORK EXECUTED

3.1 Site Reconnaissance

3.2 Highway Design Criteria

4.0 TECHNICAL SOLUTION ALTERNATIVES

4.1 Schematic Geometric Alignments

4.2 Plan and Profile of Proposed Structures

4.3 Drainage Considerations

4.4 Principal Structures

4.4.1 GEOTECHNICAL

4.5 Description of Impacted Utilities

4.6 Typical Cross-Sections

4.7 Environmental Considerations

4.8 Right of Way

5.0 ALTERNATIVE EVALUATION

5.1 Alternatives

5.2 Alternatives - Recommendation

5.3 Construction Cost Opinion

Appendices Appendix A – Site Specific Topographic Drawing

Appendix B – Geotechnical Evaluation

Appendix C – Plan and Profile Sheets

Appendix D – Subsurface Utility Survey Report

Appendix E – Cross Sections

Appendix F – Opinion of Probable Cost

ER-HWY-80 REVISION 3 – March 25, 2024 | Page 2

1.0 INTRODUCTION

Kimley-Horn Puerto Rico, LLC (KHPR) presents the Technical Report for the site ER-HWY-80 as part of the Hurricane María Efforts for Landslide and Road Damage Evaluation and Repair Recommendations contract requirements.

Route PR -120 suffered damage due to Hurricane Maria on September 20, 2017. At site ER- HWY-80, there were landslides on both sides of the road. The landslide deposits that once obstructed the roadway were cleaned by the responsible authorities before our visit. The northbound shoulder suffered a collapse causing the responsible authorities to implement a closure.

ER-HWY-80 is located at route PR-120, Km 27.5 in a steep mountainous area of the municipality of Las Marias. The site is about 4.28 km to the south of the township of Las Marias.

The project site is on a rural two-lane route. According to the HPMS 2016, PR-120 (from Km

27.35 intersection with PR-106 to Km 31.00 intersection with Aguadilla Urban Boundary) has a Fusional Classification of Mayor Collector with an AADT of 800 vehicles.

ER-HWY-80 REVISION 3 – March 25, 2024 | Page 3

2.0 DAMAGE ASSESSMENT

Our first visit to the site was on April 16, 2018. Our staff visited the site accompanied by our Geotechnical sub-consultant in a general site recognition. In this visit, we documented among others, the typical characteristics of the landslide, length of affected roadway, visible geologic characteristics of the soil, possible cause for the landslide, and apparent workable solutions.

The site was visited again on November 29, 2018, for a kickoff inspection with a multidisciplinary team. In that visit, we established the scope of the geotechnical and surveying assessments and started the execution of them. The team members performed a detailed inspection of the site to confirm some aspects from the previous visit and determine others like probable MOT strategies, drainage issues, mitigation of adjacent hazards not included in the original scope, constructability, possible environmental issues, traffic protection devices, and utilities.

ER-HWY-80 REVISION 3 – March 25, 2024 | Page 4

3.0 WORK EXECUTED

Once the site was visited and inspected by the multidisciplinary team, all proceeded with their assignments. A topographic study was performed to determine the as build conditions of the roadway, drainage structures, exposed utilities, and the landslide area among others. It was determined the required borings and its location and immediately after that, they started the coordination to for the geotechnical exploration. Other studies like surveying of subsurface utilities, asbestos and lead tests, research of affected properties, cultural resources, habitat categorization, tree inventory and mitigation plan, biological assessment followed through the design process accordingly.

3.1 SITE RECONNAISSANCE

This site presents steep slopes at both sides of the roadway. The geology of the zone presented dark reddish oxidized clays and claystone.

There are visible signs of a landslide on the uphill side of the roadway. The downhill slope landslide provoked damage to the roadway's northbound shoulder. The affected slope has an elevation difference of more than 14.00 M up to the point of the nearest probable support platform for the construction of a retaining system.

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Aerial Photo – Location of ER-HWY-80

Aerial Photo – Location of ER-HWY-80

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Photo – Roadway Damage at ER-HWY-80

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Photo – Roadway Damage at ER-HWY-21

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3.2 HIGHWAY DESIGN CRITERIA

Route PR-120, at Km 27.5 is a rural two-lane roadway having a Fusional Classification of Mayor Collector with an AADT of 800 vehicles. Based on the AADT of 800 vehicles the roadway section shall be an R-7 with two 3.35 M lanes. The existing condition at the point of analysis shows a paved roadway that varies slightly from 4.38 to 5.08 meters. According to the PRHTA Highway Design Manual 1979, the paved section provided corresponds to an R-10 section instead of a R-7 section.

The scope of this project is to correct the landslide caused by the Hurricane Maria event and provide a roadway section with similar geometric characteristics to the existing one. Based on the above information, we will base the geometric design on the requirements of an R-10 section.

Table 1-13

Design Class Code Approximate ADT Range Terrain (2) L R M L R M L R M Min. Design Speed (mph) 40 30 25 35 25 20 30 25 20 Pavement Width Pavement Min. Shoulder Width Min. Row Width (3)

Max. Superelevation Min. Curve Radius 150 70 50 100 50 30 70 50 30 Min. Stop. Sight Desitance 85 60 50 75 50 40 60 50 40 Min. Pass. Sight Distance 460 335 --- 400 --- --- 335 --- --- Max. Grade (%) 7 8 10 8 10 12 8 12 15 Min. Grade (%) Design Vehicle Bridges

(3) Absolute minimum. Desirable minimum is 20 meters.

General Design Standard for Local Rural Roads (1)

See Chapter 6

See Chapter 7

1.25 1.25 1.25

(1) All dimensions in meters unless otherwise specified.

(2) L=Level, R=Rolling, M=Mountainous.

SU SU SU

6% 6% 6%

0.5 0.5 0.5

14.0 13.4 12.5

5.5 4.9 4.0

R-9 R-10 R-11 Over 400 100-400 Under 100

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Survey and Topography (Horizontal Datum PR NAD 83, Puerto Rico Vertical Datum)

Photo – Location and General Topography at ER-HWY-80 (Source: USGS)

Project Site

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ER-HWY 80 Site Specific Topographic Drawing

Please refer to Appendix A for an 11x17 copy of the site-specific topographic drawing.

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4.0 TECHNICAL SOLUTION ALTERNATIVES

Based on our site reconnaissance, survey information, geotechnical data, and constructability evaluation, several retaining options were considered for downslope site repair. The three main alternatives considered were:

1. Gabion Retaining Wall

2. Gravity Concrete Wall

3. Secant Pile Wall (This wall is composed of 2 parts: 1- the secant wall portion below the existing ground and 2- a cast-in-place portion above the existing ground).

Alternative Description:

1. Gabion Retaining Wall This alternative consists of a stepped-face gabion basket wall placed at the downslope edge of the roadway typical section and using embankment to backfill the void created by the landslide.

Advantages:

o Easy and fast construction o Wall face allows drainage o Flexible wall, which tolerates differential ground settlements

Disadvantages:

o Wide base, which may require the full road closure during construction due to the needed excavation

2. Gravity Concrete Wall This alternative consists of a trapezoid shaped concrete wall at the downslope edge of the roadway typical section and uses an embankment to backfill the void created by the landslide.

Advantages:

o Easy construction

Disadvantages:

o Wide base, which may require the full road closure during construction due to the needed excavation o Requires additional construction time when compared to the gabion wall (for concrete curing period) o Rigid structure does not tolerate differential settlements without cracking.

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3. Secant Pile Wall This alternative consists of a “hybrid wall” with secant CFA piles constructed below the existing ground and a cast-in-place concrete wall attached at the top of the secant piles above the existing ground. This wall is constructed at the downslope edge of the roadway typical section and uses an embankment to backfill the void created by the landslide.

Depending on the wall height and soil conditions additional lateral support (such as tiebacks) be required. The anchor will be designed by the contractor’s specialty engineer.

The information provided in these plans is sufficient for construction. This report includes an estimated value based on the site conditions, this estimated value is used to adjust the cost of the retaining wall.

Advantages:

o Less site preparation o Does not require as much construction area as the gabion or gravity walls

Disadvantages:

o Specific equipment required for drilling operations o Requires additional construction time when compared to the gabion and gravity wall (for drilling and concrete curing period) o Rigid structure does not tolerate differential settlements without cracking.

Other retaining options were considered but were dismissed as they were not considered feasible based on several factors:

A. Sheet Pile Wall. This type of wall was dismissed based on concerns associated with the construction procedures (driving process) and the site stability. We considered that the driving process could cause further damage at the site.

o Cantilever Concrete Wall. This type of wall was dismissed based on construction cost, additional construction space needed (when compared to gravity or gabion).

4.1 SCHEMATIC GEOMETRIC ALIGNMENTS

Roadway alignments are included with the plan sheets, please refer to Appendix C (plan and profile sheets).

4.2 PLAN AND PROFILE OF PROPOSED STRUCTURES

Please refer to Appendix C for copies of the plan and profile sheets.

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4.3 DRAINAGE CONSIDERATIONS

Existing Drainage

The project is located within the Rio Aragoncillo Watershed. A roadside ditch/swale system on the west side collected offsite runoff from the uphill mountainous area and a majority portion of the roadway. While in superelevation, the entire road drains to this swale. When not in superelevation, the area where the landslide occurred, the southbound lane drains to the swale and the northbound appears to have drained directly to the downhill slopes. There was a curb system observed on either side of the affected area that may have collected the northbound lane, however, it is no longer functional due to the landslide and no remnants of the curb have been noted in the landslide area. The outlet of an existing crossdrain has been identified, and the condition of the crossdrain has not been confirmed. No other drainage structures or features were observed. All existing drainage structures are to be removed.

Proposed Drainage

In the proposed condition, a proposed ditch system on the west side of the roadway will replace the existing ditch system. A 1.204 M-wide shoulder gutter will be provided to improve roadway conditions and control spread. This shoulder gutter will help control spread on the west side. To combat road overtopping during high-intensity storms, the gutter will be designed to drain into three gutter inlets that will outfall via a 30” crossdrain to the eastern downhill slopes. Curb and gutter will be installed along the east side of the roadway. Rubble riprap, to reduce erosion at the outlet, will also be introduced. As a significant portion of the roadway drains directly to the downhill slopes, a standard shoulder gutter system will also be added to the west side of the road.

4.4 PRINCIPAL STRUCTURES

Retaining wall options for this site are concrete gravity, gabion, and secant walls. Concrete gravity walls are large concrete structures with mild reinforcement that use their mass to retain soil.

Gabion walls are wire baskets filled with stone and their mass is used to retain soil, similar to gravity walls. Secant walls are auger cast concrete piles that are drilled in line. Every other pile is reinforced and provides flexural strength to retain the soil.

For the preliminary design of the gravity walls, a slope of 9:12 (H:V) was used for the back wall.

This slope equates to an approximate ratio of 0.8 wall width to wall height. The gravity wall is embedded a minimum of two feet into the soil. Wall location is based on a 6 meter temporary roadway width and a temporary excavation slope of 0.5:1 (H:V).

The preliminary design of the gabion walls is based on the details provided in the Puerto Rico Department of Transportation standard plans for gabion walls that support a surcharge load. The gabion walls are sloped at 6:1 (H:V) and are embedded a minimum of 3 feet into the soil. Wall location is based on maintaining a 6 meter temporary roadway width and a temporary excavation slope of 0.5:1 (H:V).

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The secant wall preliminary design assumes cantilever walls for retained heights of 5 meters or less and anchored walls for retained heights greater than 5 meters. Embedment depths for cantilever secant walls are based on a ratio of 2:1 (embedment: retained height), and embedment depths for the anchored walls are based on a ratio of 1.5:1. This wall option does not require any excavation; therefore, wall location is based on the typical roadway section and is placed approximately 1.5 meters from the shoulder.

4.4.1 GEOTECHNICAL

Analysis regarding the global stability of the selected alternative will be performed during the final design stage when the final geometry and depth of the alternative are established.

Slopes will be protected from the effects of erosion by placing a suitable fixing grass or open mesh fabric.

4.5 DESCRIPTION OF IMPACTED UTILITIES

A site-specific utility exploration was performed on 1/10/2019. The exploration consisted of designating the existing facilities. A copy of the Subsurface Utility Survey Report is included in Appendix D.

Three facilities were identified: - A water line that generally runs along the landslide edge of the road has been relocated to the middle of the road within the landslide affected area, -an unknown utility was found along the center of the road. The depth of cover on these utilities is estimated between 3-5 ft. We anticipate some impacts to the water line due to the road reconstruction. There is a drainage pipe that crosses the road approximately at the center of the site failure.

4.6 TYPICAL CROSS-SECTIONS

Multiple sets of cross sections have been included depicting the landslide repair alternatives.

Please refer to Appendix E.

4.7 ENVIRONMENTAL CONSIDERATIONS

The area surrounding the site consists of steep side slopes with vegetation. Based on a review of existing GIS data, the project site is not located within an area designated as critical habitat or with known threatened or endangered species. No known historical or archaeological sites are present based on a review of data from the Puerto Rico State Historic Preservation Office.

There are residences located nearby but they will not be directly impacted by the proposed repairs. Therefore, the project will not involve any relocations or displacements.

The proposed repairs will occur adjacent to the existing roadside and could potentially affect some plants and trees depending on the construction staging and methods used.

No additional environmental reviews or documentation is scoped for this project site.

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4.8 RIGHT OF WAY

A review of the information contained in the Junta de Planificacion’s website indicates that the existing right-of-way is ~15 meters centered on the road. The Right of Way information included in this report is not an actual Right of Way survey.

Based on this information most of the roadway, drainage, and structural improvements appear to be just inside the existing right of way lines. Some drainage features, such as: pipe outfalls, end walls, and rip rap are located outside the Right of Way lines (these items may require permanent easements).

Based on our evaluation of the possible construction procedures, we have determined that temporary construction easements may be needed to accomplish the proposed improvements.

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5.0 ALTERNATIVE EVALUATION

5.1 ALTERNATIVES

We have evaluated three structural downslope retaining alternatives to address the repair at this site:

1. Gabion Walls

2. Concrete Gravity Walls

3. Secant Pile Walls

These alternatives were evaluated based on:

· Environmental considerations

· Constructability

· Cost

· Construction time

· Complexity

· Right-of-Way Impacts

The table provided below provides a comparison of the retaining wall alternatives evaluated while maintaining the existing road alignment.

Relative ordinal ratings between the alternatives are included for comparison between the 3 alternatives, with 1 meaning the most favorable alternative for the condition evaluated and 3 meaning the least favorable alternative for the condition evaluated.

Gabion Wall Gabion Rating

Concrete Gravity Wall

Gravity Rating

Secant Pile Wall

Secant Rating

Environmental May require a temporary platform and access road, which could have impacts outside of the limits of the roadway and landslide repair area.

3 May require a temporary platform and access road, which could have impacts outside of the limits of the roadway and landslide repair area.

2 Can be constructed without the temporary access road.

Constructability Relatively easy. Does not require special

1 Relatively easy. Does not require special

2 Relatively easy but requires specialized

ER-HWY-80 REVISION 3 – March 25, 2024 | Page 24 equipment.

Due to the size of the gabion wall’s base, a full closure of the road may be needed.

equipment.

Due to the size of the gabion wall’s base, a full closure of the road may be needed.

labor and equipment.

Cost High 3 Medium 2 Low 1 Construction Time

Fast Requires additional time for concrete curing

Slower process due to multiple drillings and concrete curing.

Complexity Simple. 1 Simple. 2 Simple, but requires specialized labor and equipment.

Right-of-Way Impacts

Construction may occur outside of the road Right of Way, but only impacting the damaged downside slope.

3 Construction may occur outside of the road Right of Way, but only impacting the damaged downside slope.

2 Could be constructed within the roadway Right-of-Way.

MOT Requires full road closure.

3 Requires full road closure.

2 Can be constructed while keeping one lane open.

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5.2 ALTERNATIVES - RECOMMENDATION

Our recommended option for this site is a Hybrid Secant Pile Wall.

During the final structural design of the retaining wall, it was determined that modifications to the wall type were required. To accommodate the proposed roadway typical, the location of the wall had to extend downslope to such a distance that the existing ground profile was 3 to 10 meters below the proposed grade. Secant piles are installed in existing ground and cannot be extended above grade. Due to the location of the wall, a hybrid wall design was required. Secant piles are to be installed into the competent existing soil, and in areas where a wall is needed in a “fill” condition, a cast-in-place concrete wall with soil anchors was designed. The structural analysis of this wall and the required soil anchors is for the internal stability of the wall. Coordination between the structural engineer and the geotechnical engineer took place during the final design, and it was determined that the anchors were not needed for global stability. Since the anchors were not needed for global stability, a modified geotechnical report was not produced. Structural calculations designing the anchors were provided with the submitted construction documents.

When all the factors were evaluated, the gabion and gravity walls required full road closure and the secant pile wall allows the road to remain open (with single lane operation), this MOT factor weighted heavily on our recommendation to use a secant pile wall to minimize the disruptions to the traveling public.

5.3 CONSTRUCTION COST OPINION

Please refer to Appendix F for the Opinion of Probable Cost of the alternatives evaluated.

ER-HWY-280 Technical Report | Revision 3 – March 25, 2024

APPENDIX A

Site Specific Topographic Drawing

ER-HWY-80 Technical Report | Revision 3 – March 25, 2024

APPENDIX B

Geotechnical Evaluation

REPORT

GEOTECHNICAL EVALUATION

LANDSLIDE ID# ER-HWY-80

PRHTA DESIGN AREA

EMERGENCY RELIEF PROGRAM

LAS MARÍAS, PUERTO RICO

GEO 925-2018

REPORT

Prepared for

Kimley-Horn Puerto Rico, LLC Guaynabo, PR

PO Box 270328 San Juan

PR, 00927

T. 787.781.6340 F.787.706.0183

Geotechnical engineering

Construction materials testing

GEOTECHNICAL EVALUATION

LANDSLIDE ID# ER-HWY-80

PRHTA DESIGN AREA

EMERGENCY RELIEF PROGRAM

GEO 925-2018

AASHTO AAP

Accredited Laboratory

Validated Laboratory

PR/FL DTOP

Certified Disadvantaged Business Enterprise

DBE

SBA Certified

HUBZone

MBE Certified

LETTER | page 1

PO Box 270328 San Juan

PR, 00927

T. 787.781.6340 F.787.706.0183

Geotechnical engineering

Construction materials testing

January 10, 2019

Eileen M. Vélez-Vega, PE

Kimley-Horn Puerto Rico, LLC

Millennium Park Plaza

Suite 435, Metro Office Park

15 Second Street

Guaynabo, Puerto Rico 00968

Tel. 787-244-5758, e-mail: Eileen.Velez@kimley-horn.com

Re: Geotechnical Evaluation of

Landslide ID # ER-HWY-80

PRHTA Design Area

Emergency Relief Program

Las Marías, PR

Dear engineer Vélez-Vega:

We are submitting our report on the geotechnical evaluation for the referenced landslide. If you have any questions with regards to this evaluation or require additional services, please do not hesitate to contact us. We are available to meet with you or your representative for any explanation concerning this evaluation.

We thank you for providing us with the opportunity to perform this study.

Cordially, GEO-Engineering

Carlos E. Rodríguez Pérez, PhD, PE

Geotechnical Engineer

Enclosures

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Table of Contents

CONTENTS | I

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1. GENERAL PROJECT INFORMATION

1.1 Introduction

1.2 Landslide General Information

2. SUBSOIL EXPLORATION

2.1 Site Geology

2.2 Site Aerial Photointerpretation

2.3 Subsoil Conditions

3. GEOTECHNICAL ASSESSMENT

3.1 Alternatives of Corrective Measures

3.1.1 Gabion Retaining Wall

3.1.2 Gravity Concrete Wall

3.1.3 Secant Pile Wall (Cantilever CFA Pile Wall)

3.1.4 Relocation of Road

3.1.5 Preferred Alternative – Secant (CFA) Pile Wall

3.2 New Fill

3.3 Construction Considerations

4. GENERAL COMMENTS

4.1 General Comments

FIGURES

Figure 1 Landslide Schematic Location – Las Marías, PR

Figure 2 Views of Landslide ER-HWY-80

Figure 3 Landslide Location on USGS Geologic Map (I-918)

Figure 4 Schematic Location of Borings

Figure 5 Generalized Soil Profile

Figure 6 Alternatives of Corrective Measures – Gabion Retaining Wall

Figure 7 Alternatives of Corrective Measures – Gravity Concrete Wall

Figure 8 Alternatives of Corrective Measures – Secant Pile Wall

CONTENTS | II

APPENDICES

Appendix 1 Standard Clause for Unanticipated Subsoil Conditions

Appendix 2 Procedures Summary

Appendix 3 General Earthwork Recommendations

Appendix 4 Boring Logs and Laboratory Test Results

General Project Information

Section ONE | page 1

1. GENERAL PROJECT INFORMATION

1.1 Introduction

The Puerto Rico Highway and Transportation Authority (PRHTA) requested Kimley-Horn Puerto Rico, LLC to provide support for their

Emergency Relief Program (ER). The program includes the reconstruction of highway segments damaged by landslides associated with the pass of hurricanes Irma and María throughout Puerto Rico.

This report presents the results of the geotechnical evaluation performed for Landslide ID# ER-HWY-80, which occurred in Las Marías, PR. Eileen Vélez-Vega, PE, Assistant Vice-President, Kimley-Horn

Puerto Rico, LLC (KHPR), requested this evaluation to GEO-

Engineering, LLC (GEO) on behalf of PRHTA. The purpose of this evaluation is to draw possible corrective measures for the affected road segment. Ramón F. Bretón, PE, from Kimley-Horn’s Orlando, FL office, is the Project Manager.

The evaluation is based upon soil information from borings drilled at the landslide site, a detailed site reconnaissance, a site aerial photointerpretation, topographic and geologic information from the area, and laboratory test results. Information in conjunction with data submitted to this office by Eng. Bretón were also utilized.

General Project Information

Section ONE | page 2

1.2 Landslide General Information

Figure 2 shows views of the landslide area. Given below is general information on the landslide and damaged road segment:

Landslide General Information

ID# Highway Latitude Longitude Municipality

ER-HWY-80 PR-120, Km 27.50 18.213796° -66.996786° Las Marías

Landslide Morphology

Approximate Landslide Geometry: Width: ≈200 ft Length: ≈100 ft Height: ≈65 ft

Landslide Location: Downslope of road pavement

Landslide Type: Earthflow

Landslide Development Stage: Total collapse

Main Scarp Height:

Type:

≈13 ft

Semi-curved and steep

Sliding Surface:

Inclination:

Partially exposed

Near-vertical

Affected Ground:

Partial failure of road embankment

Collapse of downslope gabion retaining wall supporting the road embankment

Moving Ground:

Mainly fill from road embankment and backfill from collapsed gabion wall washed down and deposited downslope. Thickness varied (there were sectors 3 to 6 ft thick).

Loose soil from adjacent cut washed down over the road and descending slope.

Associated structures:

Broken buried storm sewer concrete pipe crossing the landslide site from west to east. Probably the pipe went through the gabion retaining wall.

Cut located on the other side of the road. Exposed ground at cut face: loose reddish saprolitic soil and highly fractured rock

Subsoil Exploration

Section TWO | page 1

2. SUBSOIL EXPLORATION

2.1 Site Geology

The following table summarizes information on the geology of the landslide area, based on published information by the US Geological

Survey (USGS). Figure 3 schematically shows the landslide site within the corresponding USGS geologic map.

USGS Geological Map Information

Quadrangle: Maricao Map ID: I-918 Published Date:

Type of Deposits

Landslide area: Yauco Mudstone (Ky) (Upper Cretaceous)

USGS Description:

Chiefly black to dark-gray thin-bedded calcareous mudstone. The unit also contains greenish-gray thin-bedded volcanic sandstone and thick-bedded pumice and vitric tuff.

Site Observed Ground Conditions:

Fill from the road construction, washed-down soil from adjacent cut, and in-situ highly weathered and fractured rock

Debris from previous gabion wall

Comments:

Exposed highly fractured rock along adjacent cut and landslide main scarp

Faults

N/A

Present

Approx.

location:

325 ft east of the landslide site

Prob. Active

Prob. Inactive

Ky Mudstone and sandstone underlie the landslide area

Section TWO | page 2

2.2 Site Aerial Photointerpretation

The evaluation of the landslide site was performed utilizing aerial photographs that covered a period of several years. According to the aerial photographs, the site showed the following physical features:

Summary of Aerial Photointerpretation

Site original topography: Part of steep shallow gully crossed by the road

Road PR-120: Already existed by 1968

Road construction at site:

Cut along the site western portion

Fill along the site eastern portion

By 2012:

Road sector had undergone previous instability Construction of gabion retaining wall, approximately 6 meters high, on the downslope side, probably to stabilize the road embankment

Deep cut required in the descending slope for the construction of the gabion wall

Widening of road towards the descending slope

Repaving of widened road

Landslide occurred at:

Road sector where gabion retaining wall was constructed

The landslide occurred at a road sector where a previous gabion retaining wall had been constructed

Section TWO | page 3

2.3 Subsoil Conditions

A soil exploration program consisting of five (5) borings (80-01 to 80-05) accompanied by field and laboratory testing, was performed to obtain information on the subsoil conditions along the project sites. The following table summarizes the fieldwork performed at the site for the subsoil exploration:

Summary of Fieldwork

Type of Test Quantity

SPT Borings 5

Figure 4 schematically shows the location of the borings. The borings were distributed along the road pavement adjacent to the landslide. No borings could be performed downslope of the site because the area was not accessible to the drilling equipment (a bulldozer and permit into a private land would have been required to open trails, which would have required more time than available for this investigation). However, the subsoil information obtained with the borings, the laboratory test results, the area’s geology, and the information gathered with the site reconnaissance helped to estimate the subsoil conditions downslope of the site.

The borings were performed with a drill rig. The depth of the borings was defined in the field taking into consideration the soil/rock conditions obtained while drilling, the area’s geology, and the observed ground

Section TWO | page 4 conditions during the site reconnaissance. The borings were stopped when hard (probably massive) rock was detected. The following table shows the depths reached by the borings:

Summary of Boring Depths

Boring Depth (ft)

80-01 60

80-02 50

80-03 60

80-04 60

80-05 55

Soil samples from the borings were recovered, identified in the field and laboratory, and subjected to laboratory testing. Appendix 2 provides a brief description of the drilling and sampling procedures utilized.

Appendix 4 presents the boring logs as well as field and laboratory test results.

Three types of materials were found with the borings performed at the project site:

Summary of Materials

Type of Material

Existing Fill

Saprolite

Highly weathered and fractured volcanic rock

Section TWO | page 5

Figure 5 shows a schematic soil profile obtained with the borings. The soil profile is a simplified representation of the subsoil and the layer boundaries found at the borings during the drilling operations. Detailed soil descriptions and engineering properties can be found in the attached boring logs. The following table summarizes the type and approximate depths of the soil/rock layers found with the borings:

Summary of Soil Information from the Borings

Soil Type Description Approx. Depth

Range

Existing fill

Recovered as a mixture of whitish and tannish brown silty sand and clayey sandy silt with angular gray gravel

N-value: 11 to 85 bpf (most from 11 to 18 bpf)

0 to 4 ft (2 to 4 ft thick)

Saprolite

Reddish, tannish, and greenish brown sandy and clayey silt with oxidized planes

Consistency: stiff to hard

Found underlying the existing fill and interlayered with the highly weathered and fractured volcanic rock

Weathered and fractured volcanic rock

Recovered as grayish and brownish rock fragments with brownish and grayish silty sand

Beneath and interlayered with the saprolite to the completion depth of the borings

Comments

The depth range and consistency of the existing fill may vary at other road locations.

Loose failed fill, exposed highly weathered and fractured volcanic rock, and debris from previous gabion wall were observed along the descending slope.

Based upon the results from the borings, the fill required for the construction of the original road was relatively thin (2 to 4 ft thick).

However, the construction of the gabion retaining wall required deep backfill, approximately 20 ft thick. This finding confirmed that a great deal of the failed ground consisted of the soil conforming the wall backfill.

Section TWO | page 6

A great deal of the failed ground consisted of soil conforming the backfill of the collapsed gabion wall

Several soil samples from those recovered with the borings were selected as representative of the soil layers identified with the borings.

These samples were subjected to laboratory testing to obtain the soil grain-size distribution, the liquid (LL) and plastic (PL) limits, and the plasticity index (PI). The following table shows the test results and the soil classification (according to the Unified Soil Classification System, USCS):

Summary of Laboratory Test Results from Selected Soil Samples

Soil Borings Depth (ft)

USCS

Class.

Gravel

Sand

Fines

PL

LL

PI

Existing fill 80-05 0-4 SM 28 45 27 - - NP

Saprolite (from volcanic rock)

80-01 80-01 80-02 80-03 80-04 80-04 80-05

4-10 35-50 2-8 2-8 2-10 13-25 4-15

CL

ML

SM

ML

ML

ML

ML

NP

NP

NP

NP

Highly weathered and fractured volcanic rock

80-03 80-04 80-04 80-05

13-25 38-50 53-60 23-30

SM

SC

SM

SM

NP

NP

NP

Although some of the tested soil samples from the highly weathered and fractured volcanic rock classified as silty sand (SM), a great deal of the

Section TWO | page 7 recovered material consisted of small rock fragments classifying as coarse sand.

Several attempts were performed to recover undisturbed samples from the existing fill and weathered and fractured volcanic rock for laboratory testing. However, due to the material mainly granular nature, it was not possible to retrieve undisturbed samples from these soils. Additional laboratory testing had to be performed on retrieved soil samples to obtain further information on the engineering characteristics of the material involved in the landslide.

No groundwater was found when drilling the borings. Taking into consideration the topographic conditions of the general area, the permanent groundwater level should be at deeper depths than the depth reached by the borings. Temporary groundwater may emanate along the existing slope due to percolation of rainwater.

The specific conditions encountered at the borings are indicated on the enclosed boring logs (see Appendix 4). The stratification or change lines shown in the logs and in the soil profile of Fig. 5 are based upon visual-manual descriptions of the samples and information recorded on the field logs. For this reason, these lines are approximate and thus schematic. The in-situ transition between various soil/rock types may be gradual. The depths mentioned in the report refer to the existing ground surface at the time of opening the borings.

Groundwater

Not found during drilling

Geotechnical Assessment

Section THREE | page 1

3. GEOTECHNICAL ASSESSMENT

3.1 Alternatives of Corrective Measures

Taking into consideration the landslide morphology depicted in Section

1.2, the site existing topography, and the soil information obtained from the site reconnaissance and borings, several alternatives of corrective measures for this landslide were evaluated and discussed with the project designers. Figures 6, 7, and 8 schematically show three feasible alternatives from a geotechnical point of view. The purpose of these alternatives is to reconstruct the road pavement to its previous conditions. Another alternative of corrective measures is to relocate the road towards the west. The road pavement reconstruction will be achieved by providing lateral support to the ground underlying the road pavement.

Sections 3.1.1 to 3.1.4 include a description of each alternative. The alternatives are as follows:

Alternatives of Corrective Measures

Alternative Figures

1) Gabion retaining wall 6

2) Gravity concrete wall 7

3) Secant pile wall (CFA pile wall)

4) Relocation of road -

Section THREE | page 2

Alternatives 1 and 2 will require the following:

Removal of the existing failed groundmass

An overexcavation within the underlying in-situ ground to found the wall bases (the actual size and depth of the overexcavation will have to be determined in the field during construction)

A layer of gabion revetment to protect against erosion the descending slope located in front of the future wall base

Temporary support of excavation walls during construction

Wall construction be performed in short alternating sections to reduce the risk of additional failures

Installation of a surficial and underground drainage system

Alternatives 3 and 4 will require the following:

A layer of gabion revetment to protect the descending slope against erosion

Installation of a surficial and underground drainage system

All alternatives will require the following:

Improvement of the stability conditions of the adjacent cut to prevent local failures from reaching the road pavement. This improvement can be attained by reducing the cut inclination to approximately 1.5:1 (Horizontal:Vertical, H:V) and leaving a buffer zone with a minimum width of 6 ft between the edge of the pavement and the resulting cut toe.

The resulting cut face will have to be protected against erosion.

Steel wire mesh (protection netting) may be required to be installed in those sectors with exposed highly fractured rock to

Section THREE | page 3 prevent rocky debris and loose boulders from reaching the road pavement. Rolls of straw wattles may also be required in sectors with exposed saprolite.

3.1.1 Gabion Retaining Wall

The alternative of the gabion wall will consist of a stepped-face gabion wall with a backfill having a maximum inclination of 2:1 (H:V). The wall shall be constructed with a 1:6 (H:V) batter (Fig. 6) towards the road.

Given below are the pros and cons of this alternative:

Pros and Cons – Gabion Retaining Wall

Pros

Relatively easy and fast to construct Probably only partial closure of road required during construction Permeable wall face allows drainage Flexible enough to tolerate differential ground settlements

Cons will require:

Compacted select backfill Probably 6 to 8 courses of gabion elements A wide base (probably an area larger than the road right-of-way) Construction in short sections

The gabion retaining wall design shall follow the specifications provided in the Model Plans for Retaining Walls published by the PRHTA. The following parameters shall be used for the gabion retaining wall design:

Section THREE | page 4

Summary of Design Parameters for the Gabion Retaining Wall

Df-min (ft) qall (ksf)

Ka γ

(pcf) µ

(o) δ

3 7.5 0.40 115 0.60 32 29 where

Df-min = minimum depth of embedment of wall base within the underlying saprolite and/or highly weathered/fractured volcanic rock qall = allowable soil bearing capacity

Ka = coefficient of active earth pressure γ = backfill unit weight µ = coefficient of friction along the wall base

= backfill angle of internal friction δ = friction angle along wall/backfill contact

No passive resistance against sliding shall be included in the wall design due to the short distance between the wall base and the face of the descending slope below the base.

The recommended qall-value will probably exceed the contact pressures to be applied by the wall base. A site class D can be used for the wall seismic design.

Section THREE | page 5

3.1.2 Gravity Concrete Wall

The alternative of the gravity concrete wall will consist of a near trapezoid wall probably with toe and heel projections at the base. The wall shall be constructed with a batter back face and a backfill having a maximum inclination of 2:1 (H:V) (Fig. 7). Given below are the pros and cons of this alternative:

Pros and Cons – Gravity Concrete Wall

Relatively easy to construct Probably partial closure of road required during construction Can be probably built within the road right-of-way

Compacted select backfill A wide base More time for construction (due to concrete required curing time) Construction in short sections

Rigid structure that does not tolerate differential settlements or ground movements without undergoing cracking

The gravity concrete wall design shall follow the specifications provided in the Model Plans for Retaining Walls published by the PRHTA. The following parameters shall be used for the gravity concrete wall design:

Summary of Design Parameters for the Gravity Concrete Wall

Df-min (ft) qall (ksf)

Ka γ µ

3 7.5 0.60 115 0.45 32 21

Section THREE | page 6

Df-min = minimum depth of embedment of wall base within the underlying saprolite and/or highly weathered/fractured volcanic rock qall = allowable soil bearing capacity

Ka = coefficient of active earth pressure (assuming ω=10 degrees, Fig. 7, it will change for other ω-values) γ = backfill unit weight µ = coefficient of friction along the wall base

= backfill angle of internal friction δ = friction angle along wall/backfill contact

No passive resistance against sliding shall be included in the wall design due to the short distance between the wall base and the face of the descending slope below the base.

The recommended qall-value will probably exceed the contact pressures to be applied by the wall base. A site class D can be used for the wall seismic design.

3.1.3 Secant Pile Wall (Cantilever CFA Pile Wall)

A third alternative of corrective measures is installing a wall made of secant CFA piles along the affected ground (Fig. 8). Given below are the pros and cons of this alternative:

Section THREE | page 7

Pros and Cons –Secant Pile Wall (CFA Piles)

Pros

Relatively easy to construct Less site preparation Probably only partial closure of road required during construction Can be probably built within the road right-of-way

Specific equipment for installation Special workmanship for installation Use of casing at the upper portion More time for construction (due to concrete required curing time) Rigid structure that does not tolerate differential settlements or ground movements without undergoing cracking

The following parameters shall be used for the secant pile wall design:

Summary of Design Parameters for the Secant Pile Wall (CFA Piles)

Depth Range Ka Kp γ

(o)

0-30 ft 0.28 0.70 115 30 20

30-60 ft 0.22 0.80 125 36 24

Ka = coefficient of active earth pressure

Kp = Coefficient of passive earth pressure (it takes into account the inclination of the descending slope) γ = soil unit weight

= soil angle of internal friction δ = friction angle along wall/soil contact

Section THREE | page 8

The CFA pile installation shall follow the specifications provided by the

PRHTA for these piles.

3.1.4 Relocation of Road

Given below are the pros and cons of this alternative:

Pros and Cons – Relocation of Road

Relatively easy and fast to construct Probably only partial closure of road required during construction

Construction on private land Geometric redesign of road sector Reduce the inclination of the existing main scarp to an inclination of 1.5:1 (H:V) Protection of descending slope against erosion Protection of resulting cut face against erosion

3.1.5 Preferred Alternative – Secant (CFA) Pile Wall

The preferred alternative of corrective measures for this landslide, from a geotechnical point of view, is the secant pile wall because, when compared with the other proposed alternatives, the secant pile wall is relatively easy and fast to construct and will require less site preparation and probably only a partial closure of the road during construction.

Section THREE | page 9

3.2 New Fill

Unless otherwise stated in this report, any fill or backfill required for the project shall consist of the soil specified as fill in Appendix 3. The soil shall be placed and compacted following the recommendations provided for fill in this appendix.

3.3 Construction Considerations

The following considerations shall be taken into account for the construction of this project. Appendix 3 includes additional recommendations.

1. All earthwork operations in the project shall be conducted under our supervision.

2. One of our Geotechnical Engineers (or his representative) shall examine the bottom of any excavation to verify its conditions with respect to those obtained with the soil exploration program.

Proof-rolling of the excavation bottom may be required depending on the exposed ground conditions (this shall be determined in the field during construction). As the project area was previously subjected to construction, debris and buried abandoned utilities may appear beneath the site as earthwork operations progress.

Any detected soft soil spot, debris, remnants of buried previous structures, doubtful fill, or deleterious material within any

Section THREE | page 10 excavation shall be removed and replaced with compacted fill, as specified in Section 3.2.

3. The project excavations shall be expedited to prevent disturbance of the foundation soils. All excavations shall be performed under dry conditions. The contractor shall take the required provisions to prevent seepage into and accumulation of water (runoff, percolating water, or temporary groundwater) in all excavations.

4. Any water collected from the road pavement shall be properly disposed of into the storm drainage system of the project. No accumulation of water shall be allowed adjacent to the road pavement.

5. No trees with a large, thick, superficial tabular root system shall be planted or exist close to the new retaining wall. Any tree of this type shall be placed at a minimum distance of 50 feet away from the wall.

6. This report is submitted for the project design and it includes construction considerations that shall be reviewed by any bidding contractor. However, the bidding contractors shall not use this report as the only information to base their bid for the project.

GEO-Engineering shall not be held responsible if the contractors use without limitations the information contained herein. Any bidding contractor should conduct a careful review of the

Section THREE | page 11 geotechnical data and comments presented in this report. In addition, GEO-Engineering will not be responsible for the contractor’s interpretation and conclusions made from these data. The bidding contractor shall visit the project site prior to submitting a bid to become acquainted with the site actual conditions.

7. The contractor shall take care to prevent damaging surrounding structures and utilities due to the construction operations. Claims are frequently presented commonly based on vibration effects derived from the construction operations (especially those due to earthwork equipment). A notarization of an overall evaluation of the conditions of nearby structures is recommended prior to starting the project construction.

8. The contractor will be solely and completely responsible for his method of construction, his method of excavation, the working conditions at the job site, and the project safety measures. This requirement applies continuously, and it is not limited to normal working hours.

According to existing regulations, any excavation exceeding a depth of 5 ft must be shored, braced, or be cut with adequate slopes to provide safety to workers. The adequacy of the required shoring or bracing system or the inclination of the excavation walls and the stability of the complete excavation is a responsibility of the contractor.

Section THREE | page 12

9. The contractors and/or subcontractors bidding for this project shall be pre-qualified, since the earthwork, the construction of retaining structures, and their associated activities are all specialized operations.

General Comments

Section FOUR | page 1

4. GENERAL COMMENTS

4.1 General Comments

1. This report has been prepared to evaluate the project site from a geotechnical point of view and provide recommendations for the project design and construction.

2. The scope of this report is limited to the specific project and locations described herein.

3. Our description and analysis of the project represent our understanding of the significant aspects relevant to soil/rock characteristics.

4. In the event that any changes in the project are made, we should be informed so that the changes can be reviewed, and the conclusions of this report be modified as necessary in writing by us.

5. Geotechnical aspects of design and construction are specialized activities. As a result, we should be consulted and should participate in the preparation of the final design plans and specifications for the project. In addition, we recommend that we be authorized to review the project construction plans and specifications to confirm that the findings and conclusions contained in this report have been interpreted in accordance with our intent. Without this review, we will not be held responsible for

General Comments

Section FOUR | page 2 the misinterpretation of our data and/or our analysis, nor how these are or have been incorporated into the final design.

6. The analysis and recommendations submitted in this report are based upon data obtained from borings performed at the locations indicated and from any other information discussed in the report. The report does not reflect any soil/rock variations, which may occur between the borings and other project locations.

If variations appear evident, it will be necessary to re-evaluate the conclusions and recommendations after performing on-site observations during construction and noting the characteristics of the variations.

Submitted by, GEO-Engineering

Carlos E. Rodríguez Pérez, PhD, PE Geotechnical Engineer

January 10, 2019

GEO-925-2018

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FIGURES

Landslide Schematic Location – Las Marías, PR

FIGURE 1 GEOTHECNICAL EVALUATION

LANDSLIDE ID# ER-HWY-80

PRHTA DESIGN AREA

Views of Landslide ER-HWY-80

FIGU…