Technical Report - AC-814579_HWY-73.pdf

Technical Report Emergency Relief Program Landslides

ER- HWY- 73 (PR-119 KM 20.90-21.10)

AC-804544

January 2019

Rev. 01

Table of Contents

1. Introduction

2. Damage Assessment

3. Work Executed

4. Summary of Findings

4.1 Research of Affected Properties

4.2 Surveying

4.3 Site Reconnaissance

4.4 Geotechnical Studies

5. Technical Solution Alternatives

6. Alternative Evaluation

7. Environmental Considerations

8. Constructability & Feasibility

9. Construction Cost

10. Construction Time

11. Solution Complexity

12. Impact on Right of Way Acquisition

13. Recommendations

14. Appendixes

Appendix A: Surveying Plan

Appendix B: Geotechnical Study Appendix C: Cost Estimates Appendix D: Sections Appendix E: Detour Routes (See notes on Section 11)

1. Introduction

The Puerto Rico Highways and Transportation Authority (hereafter “PRHTA”) has awarded a contract to CMA Architects and Engineers LLC (hereafter “CMA”) to provide support in their Hurricane María emergency relief efforts. The project consists of the assessment and reconstruction of landslides, including but not limited to slope instability, washouts and rock fallouts on several highway sections due to impacts associated with Hurricanes Irma and María.

CMA performed field inspections for data collection, site reconnaissance, investigations, monitoring and technical studies required to prepare Technical Report, Environmental Assessment, Plans, Specifications and Estimates for each site.

The project sites to be evaluated by CMA as part of this contract are listed in Table 1-1 below, and divided in five (5) PS&E as directed by PRHTA:

PS&E No. Project ID Highway Kilometer Municipality

PS&E A1

ER-HWY-63 PR-119 32.1 San Sebastián ER-HWY-64 PR-119 35.9 San Sebastián ER-HWY-66 PR-119 41.15 San Sebastián ER-HWY-67 PR-119 41.6 San Sebastián ER-HWY-68 PR-119 44 San Sebastián ER-HWY-69 PR-119 44.2 San Sebastián ER-HWY-70 PR-119 44.3 San Sebastián

PS&E A2 ER-HWY-73 PR-119 20.90 – 21.10 San Sebastián PS&E B1 ER-HWY-71 PR-119 56.9 Las Marías PS&E B2 ER-HWY-72 PR-119 76.1 San Germán PS&E C ER-HWY-474 PR-143 56.1 Barranquitas

Table 1-1

2. Damage Assessment

The PR-119 in San Sebastián consists mainly of colluvium or artificial fill materials over the San Sebastián formation which contains highly plastic clayey soils of very poor soil strength and high-water tables. Gravity walls, reinforced concrete walls, tied back wall and drainage such as interceptor drainage trenches, and non-natural fills used as dead weight are frequently found along this highway.

The ER-HWY-73 site is located from kilometer 20.90 to kilometer 21.10 in the Municipality of San Sebastián as shown in table 1.1. The approximate location of the project site overlooks the west shoreline of Lago Guajataca. At the project site, it was also observed two discontinuous landslides areas and a small slump between these two areas. The two larger landslide areas extend down the slope into heavily vegetated area where visual observations could not be completed, one of the landslide areas come close to an existing residential structure. There is a collapsed 30 inches drainage pipe that requires a reconstruction and proper outlet treatment. The existing road width at this location is of approximately 5 meters.

From the preliminary studies and inspections performed it is anticipated that the road section will have to be closed temporarily during the construction phase and that permanent and temporary acquisition of adjacent properties will be required as further described in this report.

Coordination of the access of the residential structures needs to be implemented.

Since the report includes three landslides within the same site, they will be identified as follows: LA-1, LA-2 and LA-3. Figure 2-1 indicates location of these landslides.

Figure 2-1

Landslide #1 (LA-1)

Landslide #2 (LA-2)

Landslide #3 (LA-3)

3. Work Executed

CMA will be preparing deliverables as part of the scope of work within this Contract as listed in Figure 3-1. This document is the Technical Report (hereafter “TR”). The purpose of this document is to present the initial assessment, potential solutions, evaluation of the solutions and presentation of preferred alternatives and recommendations to PRHTA.

Figure 3-1

The studies for this site and included in this Technical Report were prepared by Antonio Melendez y Asociados, and GeoCim. and are included in Appendix A and Appendix B respectively.

4. Summary of Findings

This section includes the summary of the findings and recommendations of the performed studies, surveys and engineering analysis. This TR includes the topographic and survey work completed by the subconsultants with the expertise to perform such work. It also includes a geotechnical/geological reconnaissance performed by a qualified geotechnical engineer and/or engineering geologist(s) as required, throughout the landslide area and its nearby surroundings.

4.1 Research of Affected Properties

As part of the work performed for this TR, a research on affected properties was completed. From the research, it was observed that adjacent to the landslide area there are various properties. Information obtained for these properties is summarized in table 4-1 below.

Most of these properties have structures within. Although it seems like the landslides did not directly affect any of these structures, the reconstruction works may. This is a very important consideration into the recommended alternative selection.

Cat. Number Owner Structures 073-000-006-08-001 Cecilio Cardona Torres Yes 073-000-006-79 Natividad Crespo Rivera Yes 073-000-006-80-901 Natividad Crespo Rivera Yes 073-000-006-66-00 Adalberto Mercado Cuevas No 073-000-006-68-000 Ibero American Investors Yes

Table 4-1

All these properties are shown in Figure 4-2. None of the structures within these properties were directly affected by the landslides. From all these, two of them 073-000- 006-08 and 073-000-006-79 will be affected as a result of the construction works required to rehabilitate the roadway at this location.

Figure 4-1

The aerial photo included in Figure 4-1 illustrates the properties as identified by the Center for Municipal Revenue Collection (“CRIM” for its acronym in Spanish).

The property of Cecilio Cardona Torres, Cat. Number 073-000-006-08, is located below the roadway level nearby landslide areas LA-1 and LA-2. The property was not directly affected by the landslides.

Nonetheless, an alternate temporary access to the property is required as the PR-119 will need to be closed during construction activities. Although, at this phase, relocation is not anticipated, the field monitoring would be essential to determine if in any event temporary or permanent relocation is needed.

073-000-006-68

073-000-006-08

073-000-006-79

073-000-006-80

073-000-006-66

The property of Natividad Crespo Rivera, Cat. Number 073-000-006-79 is located at the roadway roadside nearby landslide area LA-1. The property was not directly affected by the landslide. Even as the PR- 119 will be closed during the construction phase, the property has an access that will be unaltered. Nonetheless, field monitoring shall be implemented during construction activities to determine if a temporary or permanent relocation is needed.

4.2 Surveying

Surveying work was limited to 5,600 square meters approximately. Each landslide was evaluated in detail. The survey includes the locations of all existing utilities and structures in the area including edges of pavement, curbs, gutters, sidewalks, plantings, medians, shoulders, fences, walls, ramps, structures, bridges and decks. The most relevant data obtained from the As Built Topographic Survey Plan, which is included as part of Appendix A, is that this section of roadway occupies a cut-fill bench created by cutting into higher ground sections along the west side of the alignment and filling along the east side, where ground elevations drop about 30 meters towards the lake shoreline. The project site contains two (2) discontinuous landslide areas along an approximately 100 to 120 meters section of roadway with a small slump-type failure between these two areas. The two larger landslide areas (referred as LA-1 and LA-3 respectively) are located at the ends of the roadway section and extend 30+ meters down the slope into heavily vegetated areas where visual observations are limited. The lesser central failure (referred as LA-2) is a shallow slump that undercut a roughly 10-meter section of the road edge. Refer to Figure 2-1 for location of each landslide.

In terms of utilities, there are two lines of potable water of 2 inches and 12 inches along the PR-119 as shown in Figure 4-2. Also, there is a collapsed 30 inches drainage pipe that runs across the PR-119 that requires a reconstruction and proper outlet treatment.

There is a water meter nearby the 30” RCP which is located outside the pile wall alignment. Lighting or power lines will not need to be relocated as part of the construction works to be performed.

Figure 4-2

4.3 Site Reconnaissance

The objective of the site reconnaissance is to provide an initial overview of the nature and the extent of any geotechnical, environmental or contamination hazards that exist on the site. To do so, historical maps, aerial photographs and related documents were reviewed.

Consideration was given to the existing geological, hydrological and hydrogeological conditions. Also, site visits were performed to identify visible and obvious visible or noticeable surface issues.

From the research completed, it was observed that according to the USGS Geologic Map of the Quebradillas Quadrangle I-498 Map, the site overlies on Cibao Formation (Tcg) on a geologic area classified as Ql (landslides deposits). The Cibao formation gives rise to low rolling hills that are interrupted by the south-facing escarpment on which the Guajataca Member crops out. According to the USGS landslides and Areas of Susceptibility to Landsliding in Puerto Rico (Monroe, 1979), the site is in area classified of highest susceptibility to landsliding (active or existing). In Puerto Rico areas of highest susceptibility to landsliding are the areas consisting of landslide material. Excavation in these areas almost invariably cause new slides in old slide deposits. Because of the danger of disturbing, the areas should be avoided, or special precautions should be taken to prevent new movement during excavation.

Member is described as consisting of calcareous clay that contains lenses of terrigenous sand and gravel up to about 5 meters thick. The Cibao Formation is itself the most abundant unit shown. The Cibao is described as “calcareous clay, marl, and marlstone interbedded with soft limestone”. Other map units shown to outcrop nearby are: the Aguada Limestone, described as a hard limestone of Miocene age (roughly 16 to 20 million years old) that forms the crests of limestone hills and ridges west and north of the Km 21 landslides site; and, a roughly 7-acre area of Quaternary (last 2.5 million years) landslide deposits shown on the northeast-facing slope just north of the Km 21 landslides section. The USGS described map unit Ql as “Blocks of limestone and of sandy clay as much as 10m long in a mass of sandy clay; generally underlain by wet calcareous clay.”

This is one of several landslide areas that the USGS mapped along the valley of the Río Guajataca, most notably along the east valley margin and downstream of Guajataca Dam.

The Aguada Limestone and Cibao Formation (including the Guajataca member) strata are inclined gently (<5°) northward. The USGS did not identify any geologic faults in the general vicinity of the Km 21.0 landslides section

According to the US Fish and Wildlife Services (USFWS) the Federal listed animal species that have the potential to occur within the region of landslide area are:

Epicrates inornatus Puerto Rican Boa

The reconnaissance visit took place on November 5, 2018. No endangered plants or animal species were observed in those areas during the site visit. Finally, no structure was observed within the landslide area during the site visit that could be listed or eligible in the National Register of Historic Places (NRCHP).

4.4 Geotechnical Studies

The Geotechnical study consisted in performing a subsoil investigation in order to provide various alternatives and recommendations on how to control and correct the existing landslide and return the road to its condition previous the hurricanes’ impact.

The geotechnical investigation performed consisted of drilling four borings to depths of 20 to 40 feet for a total of 130 lineal feet of drilling exploration. The borings were drilled with a CME-45 drill rig using the "Hollow Stem Auger-Dry Sample" method of drilling and an Automatic SPT hammer. Soil samples were collected beginning at the ground surface, at 2.5 feet depth intervals to a depth of 10 feet, and at 5-foot depth intervals from a depth of 10 feet to the bottom of the borings. The samples were collected with a split-spoon sampler driven into the ground. A total of 4 Classification Tests, including Sieve Analysis and Atterberg Limits, were performed on selected samples from the borings.

Two inclinometers were installed. The first one, was installed to 40 feet depth with a manhole protection at the ground surface and the second was installed to 38 feet depth with an above ground protective steel cover approximately 2 feet above existing ground surface. A total of three (3) inclinometer readings were performed at each inclinometer

(the initial reading + 2 additional readings) with only one week in between readings due to the accelerated schedule for this project. The inclinometers installed by GeoCim did not record evident subsurface motion. The small, arbitrary movements plotted by the inclinometer can be attributed to either systematic errors of the instrument or variances in field reading techniques. Water table was encountered in LA1 as further discussed.

Landslide Area 1 (LA1)

The subsoil profile at the roadway consist of an upper fill layer which is underlain by the natural calcareous/residual soils. The Fill layer extends from the existing ground surface to 22.5 feet depth and is variably described as Limestone Fragments with some sand and clay to a Clay with some silt and fine sand to a Sandy Silt with some clay; the upper 2 feet of the Fill is described as a greenish gray, angular to subangular Gravel with some sand and appears to have been placed relatively recently to compensate for ground settlement associated to the landslide. The consistency of the Fill horizon is rather variable in part due to the gravel sized limestone fragments encountered within the Fill which may provide higher N-values than those suggested by its true consistency. The Fill is generally encountered in a soft to medium stiff consistency as indicated by N-values of 3 to 9 blows per foot (bpf). Results of Classification tests performed on a sample obtained at a depth of 14 to 15.5 feet indicate that it classifies as a Sandy Clay (SC) with 48.3% Fines and a Liquid Limit (LL) of 66% and Plasticity Index (PI) of 48%.

Underlying the upper Fill layer and extending to the bottom of the boring at 40 feet depth is a light gray to light greenish gray Calcareous Silt which is encountered in a very stiff consistency as indicated by N-values of 15 to 24 bpf and in a hard to very hard consistency at the bottom of the boring with an N-value of over 80 bpf. This unit corresponds to the Guajataca Member of the Cibao Formation, which the geologic quadrangle map shows extending from about 40 meters west of the road down to the Guajataca Lake shoreline (and beyond).

Groundwater was observed to enter boring BA-1 at a depth of 25 feet (below the depth of the Fill) during drilling operations.

Landslide Area 2 (LA2)

In this area the subsoil profile consists of an upper Fill layer underlain by Clay and Calcareous Siltstone. The Fill layer extends from the existing ground surface to about 9 feet depth and is variably described as Clay with some silt to a Silt with some sand and little clay, and it exhibits a soft to medium stiff consistency as indicated by N-values of 4 to 8 bpf. Results of Classification tests performed on a Fill sample obtained from 2.5 to 4 feet depth indicate that it classifies as a high plasticity Clay (CH) with 70.5% Fines and Liquid Limit (LL) of 77% and Plasticity Index (PI) of 55%. Underlying the Fill layer and extending to about 12 feet depth is a Clay layer of very stiff consistency (N-value of 18 bpf) which is in turn underlain by Weathered Limestone/Calcareous Siltstone that continued to the bottom of the boring at 20 feet depth. The Weathered Limestone shows a rather low N-value of 7 bpf at 15 feet depth and an N-value of over 100 bpf at 20 feet depth which suggest virtual refusal to the penetration of the sampler. It is worth noting that such large variations in N-values are common in the Oligocene to Miocene limestones of northern Puerto Rico, resulting from variations in limestone composition and attendant weathering effects.

Groundwater was not encountered during drilling operations.

Landslide Area 3 (LA-3)

In this area, two borings were drilled. The first boring was drilled at roadway level behind the landslide crown while the other boring was drilled in a rather level area near the base of the failed roadway slope. In the top boring (referred to as BA-3 in GeoCim’s report) the subsoil profile consists of a Fill layer that extends from the existing street level to about

12.5 feet depth and which is variably described as a Clay with some silt and sand and trace limestone fragments to a mixture of calcareous and terrigenous Silt with trace clay and fine sand and limestone gravel. The Fill is encountered in a generally medium stiff to stiff consistency as indicated by N-values of 4 to 9 bpf. Results of Classification tests performed on a soil sample obtained from a depth of 5 to 6.5 feet indicate that it classifies as a high plasticity Clay (CH) with 58.4% Fines and Liquid Limit (LL) of 58% and Plasticity Index (PI) of 40%. Underlying the Fill and extending to the bottom of the boring is a Calcareous Siltstone to Chalky Limestone which is encountered in a medium dense to very dense condition as indicated by N-values of 26 bpf at 15 feet depth and N-values greater than 75 bpf below about 17.5 feet depth.

The profile in bottom boring (referred as to BA-4 in GeoCim’s report) begins with an Upper Fill layer that extends to about 17.5 feet depth and is variably described as a Clay to Clayey Silt with little sand and limestone fragments in a soft to medium stiff consistency as indicated by N-values of 3 to 4 bpf. Results of Classification tests performed on a soil sample obtained from a depth of 5 to 6.5 feet indicate that it classifies as a high plasticity Clay (CH) with 55.6% fines with Liquid Limit (LL) of 54% and Plasticity Index (PI) of 38%.

Underlying the upper Fill layer and extending to the bottom of the boring at 40 feet depth is the Guajataca Member of the Cibao Formation which was described as an upper Limestone (wackestone) horizon extending from about 17.5 to 25.5 feet depth followed by calcareous clay that extends to the bottom of the boring. N-values recorded to sample the upper Limestone horizon exceeded 100 bpf indicating the unit exhibits a rock-like character. The underlying clayey horizon was described as Clay with some silt and locally cemented by calcite. It exhibits a hard consistency as indicated by N-values of over 40 bpf and reaching 100 bpf at the bottom of the boring. Groundwater was not encountered during drilling operations.

Alternative Recommendations

The report prepared by the subconsultant includes the following recommendations for stabilization:

Landslide Area 1 (LA-1)

1. Gravity retaining wall such as a Gabion or Concrete wall

2. Reconstruction of soil slope

3. Steel Sheet Pile Wall Additionally, PRHTA recommended the following alternatives to be evaluated:

4. Soldier Piles with Lagging

5. Secant/Tangent Pile Wall

Landslide Area 2 (LA-2)

1. Gravity retaining wall such as a Gabion or Concrete wall

2. Reinforced concrete retaining wall

3. Mechanically Stabilized Earth Wall

Landslide Area 3 (LA-3)

1. Gravity retaining wall such as a Gabion or Concrete wall

2. Reinforced concrete retaining wall

3. Mechanically Stabilized Earth Wall

Table 4-2

5. Technical Solution Alternatives

All alternatives were evaluated in detail for each landslide area. The analysis is included in this section.

Landslide Area 1 (LA-1)

Based on the results of the borings and the site reconnaissance performed, it is GeoCim’s opinion that the landslide in the roadway area is occurring within the upper Fill horizons which extend to about 22.5 feet depth. The Fill appears to have been placed without engineering control or supervision as indicated by the rather low and variable fill N-values;

the firm and stable natural soils appear to begin at about 22.5 feet depth. Any stabilization alternative in this area will have to extend below the interphase of the upper Fill layer and the underlying Calcareous Silt strata.

For the gravity retaining wall alternative, such as gabion or concrete wall, it shall be located such that the top of the proposed wall extends to the edge of the reconstructed roadway; the final depth of the wall shall also provide for the outside bottom edge of the wall to be located a minimum of 5 feet from the outside edge of in-situ Calcareous Silt strata. Backfill material behind the wall shall consist of an engineered compacted fill as described in the Geotechnical Report. The backfill material within 10 feet from the wall shall be placed in 4 to 6 inches thick layers and compacted with light, hand operated compaction equipment to 90% of the maximum dry density as obtained in the Modified Proctor Test (ASTM D 1557). The backfill material beyond 10 feet from the wall shall be placed in 8 to 12 inches thick layers and each layer compacted to 95% of the maximum dry density as obtained in the Modified Proctor Test (ASTM D 1557) using conventional compaction equipment. The design of the retaining wall shall include a drainage system that will provide a fast and efficient way to collect and dispose of any water that may infiltrate behind the wall in order to prevent the development of unbalanced water forces behind the wall; a typical drainage system would include a free draining crushed stone layer behind the retaining wall separated from the backfill material with a geotextile filter fabric (such as Mirafi 140N or equivalent), and a perforated drainage pipe placed at the bottom of the wall connected to a proper outlet. Alternatively, other types of drainage composites specifically manufactured for drainage behind retaining walls may also be used for drainage behind the wall. Prior to beginning construction of the retaining wall, the foundation bearing surface for the wall shall be cleaned and any soil disturbed during the excavation operations (or any time thereafter) shall be compacted or removed to provide an undisturbed soil bearing surface. An excavation of approximately 2,132 m3 and fill of approximately 1,412 m3 is required for this alternative.

Figure 5-1

For the reconstruction of soil slope alternative, the upper Fill layer would have to be excavated to the Calcareous Silt strata down the slope for the construction of the final earthfill slope (and excavation into an area for which there is no subsurface data). The reconstructed earthfill slope shall be constructed as an engineered compacted fill. This alternative was discarded due to constructability limitations as explained in detail in Section 8 of this TR. The required slope extension, due to steep topography, at this landslide area makes it a non-feasible alternative.

For the steel sheet pile alternative, a steel sheet pile wall would be driven from the edge of the proposed reconstructed roadway, through the existing Fill strata and a minimum of 5 to 10 feet into the Calcareous Silt strata. The sheet pile shall be supported at the top with steel anchors extending back to a dead-man concrete block located at a distance to be determined by the design (probably on the edge of the existing roadway as shown in Figure 5-2). The sheet pile wall shall be designed to resist lateral pressures. An excavation of approximately 240 m3 and fill of approximately 160 m3 is required for this alternative. This alternative significantly reduces the required earthwork.

Figure 5-2

For all alternatives, but specifically for the sheet pile wall alternative, monitoring during construction and assessment of adjacent properties conditions prior, during and after the rehabilitation work is completed must be implemented. Such testing and monitoring was included in the cost estimate for this alternative.

Upon the evaluation of the previous version of the Technical Report submitted on December 2018, PRHTA requested for CMA to evaluate two additional alternatives for this LA-1. These alternatives were Soldier Piles with Lagging and Secant/Tangent Pile Wall.

For the soldier pile with lagging alternative, soldier piles are to be drilled or driven at regular intervals along the perimeter of the excavation. Once the excavation starts, wood lagging is installed to maintain the excavated face. This alternative was discarded due to the fact that an excavation of approximately 22 feet would be required.

This would represent a very high cost and significant excavation compared with the other alternatives considered.

For the Secant/Tangent Pile wall alternative, as shown in Figure 5-3, a pile wall would be drilled from the edge of the proposed reconstructed roadway, through the existing Fill strata and a minimum of 5 to 10 feet into the Calcareous Silt strata. The wall shall be supported at the top with steel anchors extending back to a dead-man concrete block located at a distance to be determined by the design (probably on the edge of the existing roadway as shown in Figure 5-3).

Figure 5-3

Landslide Area 2 (LA-2)

Based on the results of the borings and the site reconnaissance performed, it is GeoCim’s opinion that the landslide in this area is a shallow slump that occurs within the upper Fill layer which extends to about 9 feet depth. The Fill appears to have been placed without engineering control or supervision as indicated by the rather low and variable N-values.

Firm and stable natural soils were observed to occur at about 9 feet depth and any stabilization alternative in this area will have to extend below the interphase of the upper Fill layer and this underlying Clay/Weathered Limestone.

For the gravity retaining wall such as gabion or concrete wall alternative, an excavation of about 9 to 10 feet is required in order for the wall to bear on the underlying Clay/Weathered Limestone Silt strata at depth. The location of the wall shall be established such that the top of the proposed wall extends to the edge of the reconstructed roadway; the final depth of the wall shall also provide for the outside bottom edge of the wall to be located a minimum of 5 feet from the outside edge of the Calcareous Silt strata. At the required excavation level an Allowable Soil Bearing Pressure of 3,000 pounds per square foot (psf) may be utilized for its design. For a detailed design, the lateral earth pressures may be determined following the same recommendations provided for the same type of wall in LA-1 including the incorporation of adequate drainage measures behind the wall.

Figure 5-4

For the reinforced concrete retaining wall alternative, a reinforced concrete retaining wall may be designed following the same recommendations provided above for the Gravity Retaining Wall, including bearing on the Clay/Weathered Limestone strata at about 9 feet depth and the inclusion of adequate drainage measures behind the wall.

Figure 5-5

For the mechanically stabilized earth wall alternative, this retaining wall may be designed following the same recommendations provided above for the Gravity Retaining Wall, including bearing on the Clay/Weathered Limestone strata at about 9 feet depth and the wall drainage requirements.

Figure 5-6

Landslide Area 3 (LA-3)

Based on the results of the borings and the site reconnaissance performed, it is GeoCim’s opinion that the landslide in this area is occurring within the upper Fill area which extends to about 12.5 feet depth in boring BA-3 at the road level and to about 17.5 feet depth in boring BA-4 downslope from the road. The Fill appears to have been placed without engineering control or supervision as indicated by the rather low and variable N-values, and firm and stable natural soils appear to begin at about 12.5 (BA-3) to 17.5 (BA-4) feet depth.

For the gravity retaining wall, such as a Gabion or Concrete wall, alternative an excavation of about 12.5 to 15 feet at the edge of the road in order for the wall to bear on the underlying Calcareous Siltstone/Chalky Limestone strata at depth. The location of the wall shall be established such that the top of the proposed wall extends to the edge of the reconstructed roadway; the final depth of the wall shall also provide for the outside bottom edge of the wall to be located a minimum of 5 feet from the outside edge of the Calcareous Siltstone strata. At the required excavation level an Allowable Soil Bearing Pressure of 4,000 pounds per square foot (psf) may be utilized for its design. For a detailed design, the lateral earth pressures may be determined following the same recommendations provided for the same type of wall in LA-1 including the drainage recommendations behind the wall.

Figure 5-7

For the reinforced concrete retaining wall alternative, a reinforced concrete retaining wall may be designed following the same recommendations provided above for the Gravity Retaining Wall, including bearing on the Clay/Weathered Limestone strata at about 12.5 to 15 feet depth and the inclusion of adequate drainage measures behind the wall.

Figure 5-8

For the mechanically stabilized earth wall alternative, this retaining wall may be designed following the same recommendations provided above for the Gravity Retaining Wall, including bearing on the Clay/Weathered Limestone strata at about 12.5 to 15 feet depth and the wall drainage requirements.

Figure 5-9

The control of surface runoff waters in this project is extremely important. An effective surface drainage system shall be provided in this project, including (but not limited to) paved ditches, swales and interceptors, in order to properly collect and dispose surface and groundwater to properly designed outlets, both during construction and after the hillside has been reconstructed.

6. Alternative Evaluation

The following alternatives, as described in Section 5, were recommended and analyzed for the landslide areas: slope reconstruction, gravity retaining walls, steel sheet pile wall, reinforced concrete retaining wall and mechanically stabilized earth walls. Upon PRHTA’s request, soldier pile with wood lagging and secant/tangent piles were also evaluated.

For the Landslide Area 1 (LA-1) the slope reconstruction was discarded due to the existing steep topography, the impact area that would be affected and the fact that the required engineered slope would extend significantly. The gravity wall and sheet pile option were evaluated and compared to determine which one was most feasible. The existing drainage pipe of 30” and the acquisition required were also considered as part of the evaluation. The sheet piling requires less earthwork and less impact to adjacent properties in terms of acquisition. The gabion wall alternative requires significant earthwork: 1,412 m3 fill and 2132 m3 excavation. Also, the cost of sheet piles is less than the gabion construction.

Two additional alternatives were evaluated as requested by PRHTA. These alternatives were Soldier Piles with Lagging and Secant/Tangent Pile Wall.

For the soldier pile with lagging alternative, soldier piles with wood lagging was discarded as an excavation of approximately 22 feet along the entire pile wall alignment would be required. This would represent a very high cost compared with the other alternatives considered. Also, this would represent significant earthwork affecting adjacent properties.

The secant/tangent pile provides slope stabilization and is often selected when an excavation takes place next to an existing structure. This method of earth retention allows for a high degree of alignment flexibility and provides a structurally stiff wall which minimizes settlement concerns of the adjacent structures. Nonetheless, the work is specialized which reduces the number of qualified companies that would be able to perform the work and construction cost is significantly higher than sheet piling.

For Landslides Areas 2 and 3, it is our recommendation to address both areas as one landslide due to the proximity (approximately 10 meters) from each other. For these areas the gravity retaining wall, reinforced concrete walls and mechanically stabilized earth walls were evaluated and compared. Based on the compared criteria such as acquisition, earthwork and cost (among other influential factors) it is recommended to proceed with gabion wall construction as the stabilization alternative recommended for this landslide area. Although the mechanically stabilized earth walls alternative cost less than the gabion wall construction is not recommended as support excavation is required under the existing roadway and this could result in a major landslide as the condition of the stability of the soil is unknown on this area.

7. Environmental Considerations

The scope of work includes the development of a site-specific environmental process that will be submitted as an independent deliverable for this Contract. Nonetheless, this TR includes general characteristics of the site that shall be considered in the design and in the selection of the preferred alternative. Also, general considerations on the impact that the proposed construction may have in the natural resources, flora and fauna, archeological findings, and the public in the project surrounding areas.

From the site visits and research performed, it was observed that the life zone on which the proposed Project is located is known as the Subtropical Moist Forest (Ewel and Whitmore, 1973). The dominant vegetation observed within the area of the landslides consists of herbaceous species that emerge after the area was disturbed or abandoned.

The most common herbaceous species within this area are the Wild Balsam Apple (Momordica charantia), “Margarita” (Bidens alba), Tall Albizia (Albizia procera), Guinea Grass (Megathyrsus maximus), the Railroad-track grass (Dichantium annulatum), and Plush grass (Chloris radiata). Also, one Royal Palm (Roystonea borinquena), one Moca tree (Andira inermis) and two Flamboyant Trees (Delonix regia) were observed.

Prior to carry out the field visit, a preliminary information of endangered species that could be present at the site based on agencies was obtained from https://ecos.fws.gov/ipac/.

During the field visit carried out we paid special attention to the possible presence of species that may be present in the area. The field visit consists in walking the landslide area from the road side for the presence of the endangered species. No endangered plant or animal species were observed in those areas during the site visit.

However, the Puerto Rican boa can be found in the habitat range from sea level to about 400 m elevation. The boa tolerates a wide variety of habitat types ranging from humid montane to dry subtropical forest and can be found from virgin forests to areas that exhibit various degrees of human disturbance such as roads or structures.

The information gathered from the USFWS map identifies general areas where the species may be located. The information does not represent the absolute distribution of a species. The map and table were developed with the best information available to the Service, but additional sightings of the species may occur. If the project is located within the currently known distribution of a species, additional information may be required to determine the presence of suitable habitat within the project area, and in some cases, specialized surveys may be required to determine presence/absence of the species

(USFWS, 2011).

In conclusion, as it was originally assumed, the project may affect but, would not likely adversely affect, rare or endangered species, and will have no effect to historic or archaeological properties. In addition, due to the emergency nature of the work, most of the activities are most likely to be exempted from permits. However, concurrence letters from the corresponding regulatory agencies will be requested to document this.

8. Constructability & Feasibility

All the alternatives studied were also analyzed in terms of constructability and feasibility.

Based on this, it was determined that slope reconstruction had to be discarded as a feasible alternative for Landslide Area 1 as due to the existing steep topography, the impact area and slope extension would be in such magnitude that becomes a non feasible alternative. Since the road needs to be closed to traffic during construction, equipment and machinery required for each alternative is not the most determining factor for alternative selection.

The earthwork required varies from 240 m3 to 2,132 m3 excavations and from 160 m3 to 1,412m3 fill. The steel sheet pile wall construction may cause damages to structures and discomfort (noise/vibration) to families adjacent to the studied site but is the alternative that will require less earthwork and less acquisition from the adjacent properties. As indicated previously, strict monitoring shall be implemented with this alternative.

The mechanically stabilized earth wall offer significant technical and cost advantages over conventional reinforced or gravity retaining structures and reduces the equipment and machinery required during construction but it is not recommended for this site since as shown in Figures 5-5 and 5-8; the excavation required to construct this system falls under the existing roadway; this soil should not be disturbed as it may result in a major landslide and/or collapse of the road. On the other hand, gravity walls are more versatile in design and can be molded to specific site conditions and all excavation proposed fall is outside the edge of the roadway towards the Guajataca Lake.

9. Construction Cost

A construction cost estimate was completed on this initial phase in order to compare alternatives and determine the alternatives that seem the most cost efficient. The estimated costs are listed in Tables 9-1 and 9-2. The cost was considered as an evaluation criterion to select the preferred alternative.

Landslide Area 1 (LA-1)

Alternative Estimated Construction Cost Gravity retaining wall such as a Gabion or Concrete wall $ 606,695.15

Reconstruction of soil slope --------- 1

Steel Sheet Pile Wall $ 440,962.27 Soldier pile with lagging -------------- 1

Secant/Tangent Pile wall $ 770,529.90 Table 9-1

1 This alternative was discarded and therefore a cost estimated was not provided.

Landslide Areas 2 & 3 (LA-2/LA-3)

Alternative Estimated Construction Cost Gravity retaining wall such as a Gabion or Concrete wall $1,202,127.20

Reinforced concrete retaining wall $ 1,336,222.95 Mechanically Stabilized Earth Wall $ 722,477.15

Table 9-2

10. Construction Time

A preliminary construction schedule was completed on this initial phase in order to compare alternatives and determine the alternatives that seem the most time efficient.

The construction time was considered as an evaluation criterion to select the preferred alternative. The estimated time to complete this project is 10 months.

Alternatives Estimated Duration (in Months)

Slope reconstruction ---------------1

Gravity retaining wall such as a Gabion or Concrete wall 8-10 months

Steel Sheet Pile Wall 6-7 months Soldier pile with lagging ---------------1

Secant/Tangent Pile wall 8-10 months Reinforced concrete retaining wall 7-8 months Mechanically Stabilized Earth Wall 7-8 months

Table 10-1

1 This alternative was discarded and therefore time duration was not estimated.

11. Solution Complexity

The PR-119 is a rural, narrow and geometrically challenged road in the mountainous, humid and rustic area of Puerto Rico. The road’s steep slope geometry and the presence of weak soil fill combined is susceptible to landslides and slid during significant rain events.

Landslide Area Recommended Alternative Landslide Area 1 (LA-1) Secant/Tangent Pile Wall Landslide Area 2 & 3(LA-2/LA-3) Gravity Gabion Retaining Wall

Table 11-1

As shown in table 11-1 the recommended alternatives for landslide areas 1 and 2/3 are secant/tangent pile wall and gravity gabion wall respectively. These alternatives contemplate constructability considerations that are summarized in Section 8 of this TR.

Perhaps the most challenging conditions for this site are: to coordinate work schedule and logistics in such way that the materials are readily available and onsite, so the construction is expedited. Also, as previously mentioned, PRHTA should carefully coordinate project activities as, due to the nature of the work required and the existing road section, the PR-119 will need to be temporarily closed and an alternate detour route through PR-457 needs to be delineated during most duration of the construction works.

To select the alternate detour route(s) for this project, coordination is required with the PR Electrical and Power Authority (PREPA) who will also be performing reconstruction work on the Guajataca Dam adjacent to the landslide site. An initial meeting was held between PRHTA and its Consultants and PREPA on January 18th, 2019. During this meeting it was learned that PREPA has already submitted for approval MOT Plans to the Department of Transportation and Public Works. CMA has formally requested copy of the MOT Drawings once approved. Also, CMA agreed to include a note on Contract Documents indicating that the Contractor shall coordinate detour routes with PREPA.

Both PREPA and PRHTA must held meetings with the community and inform the affected population of the schedule, routes and construction works to be performed on either construction work. Notes to address this will be included as part of the PS&E documents.

Also, due to the proximity of two residences to the landslide areas, it is important to maintain and keep strict monitoring and condition assessment of these structures prior, during and after construction work, especially during the pile operation at Landslide Area

1. Experts need to be present during the duration of the work and any condition that may represent a risk shall be immediately notified. By choosing the secant/tangent pile alternative, vibrations will be significantly reduced (or eliminated) in comparison with sheet piling. This is a consideration that was determinant for choosing secant/tangent pile.

12. Impact on Right of Way Acquisition

Acquisition will be required in order to complete the rehabilitation work for this location.

Due to the nature of the road and the complexity of site conditions, the roadway will need to be closed to traffic during construction phase and an alternate route needs to be provided. Detour routes are been evaluated currently through PR-457. Several local roads will be evaluated to determine which route is the shortest and most safe route.

The acquisition area required varies from 100 m2 to 400 m2 depending on the alternative selected as shown in the table 12-1.

Alternative Area (m2) Estimated Cost Gravity retaining wall such as a Gabion or Concrete wall (LA-1) 350 m2 $ 4,900

Steel Sheet Pile Wall (LA-1) 100 m2 $ 1,400 Soldier pile with lagging Not Calculated ------ Secant/Tangent Pile wall 100 m2 $ 1,400 Gravity retaining wall such as a Gabion or Concrete wall (LA-2 &

LA-3)

400 m2 $ 5,600

Reinforced concrete retaining wall (LA-2 & LA-3) 150 m2 $ 2,100

Mechanically Stabilized Earth Wall (LA-2 & LA-3) 150 m2 $ 2,100

Table 12-1

Also, a temporary occupancy is required to provide alternate access to a property between landslide areas LA-1 and LA-2 as discussed in Section 4-1. The required area for such easement is of 1,400 m2 for an approximate cost of $11,200.00 that needs to be included in the total acquisition cost on any of the alternatives studied.

13. Recommendations

The ER-HWY-73 site is located from kilometer 20.90 to kilometer 21.10 in the Municipality of San Sebastián as shown in table 1.1. The approximate location of the project site overlooks the west shoreline of Lago Guajataca. At the project site, it was also observed two discontinuous landslides areas and a small slump between these two areas. The two larger landslide areas extend down the slope into heavily vegetated area where visual observations could not be completed, one of the landslide areas come close to an existing residential structure. There is a collapsed 30 inches drainage pipe that requires a reconstruction and proper outlet treatment. The existing road width at this location is of approximately 5 meters.

Surveying work was limited to 5,600 square meters approximately. Each landslide was evaluated in detail. The survey includes the locations of all existing utilities and structures in the area including edges of pavement, curbs, gutters, sidewalks, plantings, medians, shoulders, fences, walls, ramps, structures, bridges and decks. The most relevant data obtained from the As Built Topographic Survey Plan, which is included as part of Appendix A, is that this section of roadway occupies a cut-fill bench created by cutting into higher ground sections along the west side of the alignment and filling along the east side, where ground elevations drop about 30 meters towards the lake shoreline. The project site contains two (2) discontinuous landslide areas along an approximately 100 to 120 meters section of roadway with a small slump-type failure between these two areas. The two larger landslide areas (referred as LA-1 and LA-3 respectively) are located at the ends of the roadway section and extend 30+ meters down the slope into heavily vegetated areas where visual observations are limited. The lesser central failure (referred as LA-2) is a shallow slump that undercut a roughly 10-meter section of the road edge.

In terms of utilities, there are two lines of potable water of 2 inches and 12 inches along the PR-119 as shown in Figure 4-2. Also, there is a collapsed 30 inches drainage pipe that runs across the PR-119 that requires a reconstruction and proper outlet treatment.

There is a water meter nearby the 30” RCP which is located outside the pile wall alignment. Lighting or power lines will not need to be relocated as part of the construction works to be performed.

As part of the work performed for this TR, a research on affected properties was completed. From the research, it was observed that adjacent to the landslide area there are various properties. Most of these properties have structures within. Although it seems like the landslides did not directly affect any of these structures, the construction works may affect two of these properties (Cat. No. 073-000-006-08 and Cat. No. 073-000-006- 79). The property of Cecilio Cardona Torres, Cat. Number 073-000-006-08, is located below the road level nearby landslide areas LA-1 and LA-2. The property was not directly affected by the landslides. Nonetheless, an alternate temporary access to the property is required as the PR-119 will need to be closed during construction activities. The cost of said alternate access is included in the cost estimate provided in Appendix C. Also, temporary occupancy of 1,400 m2 is required for the easement to provide access to this property. The property of Natividad Crespo Rivera, Cat. Number 073-000-006-79, is located at the roadside nearby landslide area LA-1. The property was not directly affected by the landslide and even though the PR-119 will be closed during the construction phase, the property has an access that will be unaltered. For both cases, strict field monitoring and a thorough condition assessment by a qualified professional prior, during and after construction phase is required.

The reconnaissance visit took place on November 5, 2018. No endangered plants or animal species were observed in those areas during the site visit. Finally, no structure was observed within the landslide area during the site visit that could be listed or eligible in the National Register of Historic Places (NRCHP). The project may affect but, would not likely adversely affect, rare or endangered species, and will have no effect to historic or archaeological properties. In addition, due to the emergency nature of the work, most of the activities are most likely to be exempted from permits. However, concurrence letters from the corresponding regulatory agencies will be requested to document this.

The geotechnical investigation performed consisted of drilling four borings to depths of 20 to 40 feet for a total of 130 lineal feet of drilling exploration. Two inclinometers were installed. The first inclinometer was installed to 40 feet depth with a manhole protection at the ground surface and the second was installed to 38 feet depth with an above ground protective steel cover approximately 2 feet above existing ground surface. The inclinometers installed did not record evident subsurface motion. The small, arbitrary movements plotted by the inclinometer can be attributed to either systematic errors of the instrument or variances in field reading techniques. Water table was encountered only in Landslide area #1 at 25.5 ft.

The following alternatives were recommended and analyzed for the landslide areas: slope reconstruction, gravity retaining walls, steel sheet pile wall, reinforced concrete retaining wall and mechanically stabilized earth walls.