Technical Report - AC-893579_HWY-264.pdf

Technical Report Emergency Relief Program Landslides

ER- HWY- 264 (PR-155 KM 45.50)

AC-827544 RPE 2799544 ER9999 (353)

MOROVIS, PUERTO RICO

March 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: Alternatives Cost Estimates Appendix D: Sections Appendix E: Detour Routes

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-3 PR-1 111.6-111.8 Juana Díaz

PS&E A2

ER-HWY-479 PR-1 23.0 Guaynabo ER-HWY-480 PR-1 23.70 Guaynabo ER-HWY-481 PR-1 25.40 Guaynabo

PS&E B ER-HWY-264 PR-155 45.5 Morovis PS&E C ER-HWY-200 PR-143 34.1 Orocovis PS&E D ER-HWY-482 PR-143 1.7 Adjuntas

Table 1-1

2. Damage Assessment

Site HWY-264 is located in kilometer 45.5 of PR-155 in the Municipality of Morovis. Within this site there are two adjacent landslide areas. The roadway at this location has a width of approximately 6 meters. There are utilities both underground and overhead along PR- 155.

The first landslide area required a roadway side slope reconstruction of approximately 100 meters north and south of the existing Bridge No. 334. There is an unnamed creek, which is a tributary of the Morovis River crossing at this site. During the site visits, no water flow was observed, and it was substantially clogged upstream. The original project scope submitted to PRHTA, included the debris removal at the channel bed, the evaluation of cut slopes of the roadway and the reconstruction of concrete barriers. From the preliminary site visits it was observed that for this landslide area, the morphology was that of a slide produced by heavy scouring along the toe of the slope probably due to heavy erosional forces of the water along the river. It was expected to find a soil profile of a weak colluvium, weak artificial fill materials or highly plastic residual soils laying over more competent materials and/or on very steep slopes. This, combined with the development of high groundwater tables and extraordinary stream flow velocities was assumed to be the cause for the landslide development along creek banks. Nonetheless, on December 2018, during a site inspection, it was observed that construction work had started on this area. A gabion wall was built adjacent to the bridge to correct the scouring and the slope had been stabilized.

Therefore, as discussed with PRHTA, the scope of work for this landslide area was reduced and limited to reconstruct the concrete parapet of the bridge and concrete waterway along the PR-155.

For the second landslide, hereafter the “area under evaluation”, the local topography within the affected area is mainly characterized by a cut slope that grades downward from east to west with an overall relief of some 14 meters (measured from PR-155 average elevation). According to the surveying completed and field data gathered, a large landslide occurred in the cut slope during hurricane Maria landfall, blocking state route

PR-155. The failure resembles a landslide with an approximate length of 30 meters (in plan view). The most critical section (steepest slopes) occur between Stations 2+05 and 2+38.

These characteristics are typical of a mud flow. The original topography of the cut slope is unknown but considering the very steep slope that remained after the mud flow, it is conceived that the cut slope was originally near vertical.

Landslide Area 1 (Rehabililtated by Others)

June 2018

December 2018

Landslide Area 2 (Area under evaluation)

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

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. 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. The studies for this site, as included in this Technical Report, were prepared by Melendez and Suelos and are included in Appendix A and B respectively. It should be noted that this TR and appendices will focus on Landslide Area 2.

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 the landslide area is surrounded by a large partially developed property that apparently belongs to a single owner. Information obtained for this property is summarized in table below:

Cat. Number Owner Structures 138-085-105-19-000 Carmen L. Marrero Padro Yes

Table 4-1

For the reconstruction work to be performed, partial acquisition of property with Cat. Number 138-085- 105-19-000 is required. Existing accesses to the property will remain as existing and no relocation of families is required. Depending on the alternative selected, the area of acquisition varies as detailed in Section 12 of this Report.

4.2 Surveying

Surveying work was limited to 7,100 square meters approximately. The landslide areas were 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 and structures. The most relevant data obtained for Landslide Area 2 from the As Built Topographic Survey Plan, which is included as Appendix A, is that the approximate landslide height from the head scarp to its toe is 14 meters. Its most obvious manifestation is a relatively vertical scarp in the upper residual soils which forms the uppermost boundary of the landslide (the head scarp). The head scarp is underlaid by a steep slope of exposed saprolitic material that shows several erosion grooves produced by run-off water.

Traces of a concrete gutter were observed on site. It seems like part of this gutter is buried under the landslide residue and will need to be reconstructed. Also, an overhead power line crosses the landslide area. There is a water line of 2“ of diameter that runs along the PR-155. The exact location of the 2” water line is unknown. A subsurface utility exploration is required. Nonetheless, based on data obtained from GIS, the line location was approximated and it is not likely to be relocated. A cast iron pipe of 16” of diameter is attached to the bridge structure and continues underground along the edge of PR-155.

The cast iron pipe needs to be reattached to the bridge.

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.

The reconnaissance visit was conducted on December 27, 2018. From the research completed, it was observed that the area under evaluation has slid, been eroded and destabilized by the extraordinary rain events during Hurricane María. This area has been affected by slope instability in the form of mudflow landslides triggered by soil saturation and deep erosion. With time and continued erosion, the mudflow has evolved into a landslide that shows a very steep slope and a near-vertical scarp in its upper reach.

According to the USGS Geologic Map of Ciales Quadrangle 1184 Plate 1 Map, the site overlies on plutonic igneous intrusive rock (Tkg) making up the Ciales and Morovis stocks.

According to the USGS landslides and Areas of Susceptibility to Landsliding in Puerto Rico (Monroe, 1979), the area is in area classified of high susceptibility to landsliding. In Puerto Rico areas of high susceptibility to landsliding generally coincide with areas of high incidence of landslides. Areas of high susceptibility include almost all areas having slopes greater than 50 percent.

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

Patagioenas inornata wetmorei Puerto Rican Plain Pigeon Epicrates inornatus Puerto Rican Boa

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.

No endangered plants or animal species were observed in those areas during the site visit. Also, 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 DNER and the USACE must be consulted to evaluate impacts that cannot be avoided during construction activities.

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 project site has been mapped as part of the Ciales Geologic Quadrangle (USGS Miscellaneous Investigations Series). According to the information contained in this source, the reference area should be underlain by Granodiorite (TKg). This formation consists of light to medium gray, medium-grained rock; plagioclase, quartz and orthoclase predominate; hornblende and biotite are common. Locally grades into quartz diorite.

The presence of severely weathered Granodiorite has been confirmed during the site visits performed. At the head scarp of the landslide the presence of residual Granodiorite is evident. The weathering of the geologic unit Tkg decreases with depth along the exposed surface of the land slide. Nucleus of less weathered material can be observed close to the PR-155 elevation, exhibiting some features of the structure of the parent rock and core stones.

According to the information issued by the USGS in the geologic map of the Ciales Quadrangle, the site is underlain by Granodiorite. This native stratigraphy is a typical profile of residual soil consisting of three indistinctly divided zones. The upper zone consists of completely to highly weathered soil. The intermediate zone consists of highly to moderately weathered material exhibiting some features of the structure of the parent rock and may contain core stones. This zone often contains pedogenic material such as nodules of calcium or iron slats which may give it a mottled or spotted appearance.

Landslide Area 1 (By Others)

No geotechnical investigation was performed at this landslide area. No borings were drilled, nor soil testing performed. This area was already stabilized and cleaned when visited last December. Construction for this area will be limited to the reconstruction of the concrete barrier, guardrails and bridge transitions.

Landslide Area 2 (Area under evaluation)

A total of four boreholes were drilled to a depth of 30 feet. In general, the borings show a relatively thin crust of fill below the asphalt wearing surface of PR-155, followed by a 2-layer stratigraphy. Below the fill crust below the asphalt (fill associated with PR-155 construction), the upper layer appears as a competent silty or clayey sand and sandy clay delivered from the Granodiorite formation. Common color in this severely weathered layer is brown and yellowish-brown. Relative densities and consistencies, based on SPT values, varies from dense and very stiff. The thickness of this soil layer averages 6 to 12 feet below PR-155 elevation. The Standard Penetration Tests (SPT) performed within the fill horizon vary from 24 to around 88 blows per foot.

The middle layer consists of severely weathered soils, the boring program found saprolitic silt and sand delivered from parent rock. Colors are brown and yellowish-brown in various combinations and shades. Densities based on SPT values are generally dense to very dense, with most N-values greater than 100 blows per foot. The Natural Moisture Content remained relatively low, consistent with the granular nature of the samples. The saprolitic material extends to the end of borings.

At the bottom of the borings, evidence of the lower zone of the residual soil profile was obtained. This layer consists of physically disintegrated and partially to slightly weathered material often having the appearance of a mass of interlocking blocks of soft rock. This lower zone merges into fractured or jointed, almost unweathered Granodiorite rock. All N-values were >100 bpf with very low percent recovery and natural moisture contents below 10 percent. With increasing depth, this layer should merge into fractured or jointed, almost unweathered, calcareous tuffaceous siltstone and sandstone.

The water table was not observed during drilling operations.

Based on all of the above, the report prepared by the subconsultant includes engineering analyses and the following recommendations:

1. Slope regrading

2. Soil nail reinforcement

3. Retaining wall

5. Technical Solution Alternatives

As indicated on section 4.4, three (3) alternatives were provided by Suelos Inc. to stabilize the soil at the landslide area 2. These alternatives are discussed in detail in this section. Cross sections and details for all alternatives are included in Appendix D.

First, it is recommended that a qualified Geotechnical Engineer performs observations and testing during excavation, foundation construction and any other earthwork activity to be performed. The possibility of subsurface conditions differing from those assumed and developed for this Technical Report cannot be discarded.

Also, the control of surface runoff waters in this project is extremely important. Runoff waters shall not be permitted to drain off the face of the exposed fill and cut slopes. An effective surface drainage system shall be provided in this project. Any stabilization alternative in this area will have to extend below the upper Fill layer and into the underlying strata. The project should be provided with adequate surface drainage measures to collect and conduct runoff to the project storm water system. Under no circumstance should water be allowed to accumulate anywhere within the project or to spill over the recommended retaining walls and/or slope embankments.

For each alternative, a clearing zone of the highway shall be performed to remove vegetation and debris at least 200 meters before and after the landslide at both upper and lower side of the road. Also, clearing and grubbing operations are required as the site is mostly covered with vegetation. The site might have sedimented portions or deleterious materials to be removed since the migration of sediments due to runoff, among other conditions may have deposited them within the site. All deleterious materials must be removed satisfactorily, and a geotechnical engineer must be present observing the clearing and grubbing activities. Also, soil conditions at excavation bottom may not be equal to those disclosed in the borehole and additional considerations may be needed.

Based on the geotechnical investigation performed, Suelos Inc. understands that the instability of the slope has evolved as a consequence of steep slopes combined with soil saturation and heavy erosional forces against the slope surface. It is evident that the water flowing out from the top of the cut slope, has added instability to the steep cut slope.

The scenario has been aggravated by rear scarp retrogression. The development of successive landslide slips in the cut slope would worsen the stability of the cut slope. As shown in Figure 5.1 shows the existing slope stability analysis which indicates that the current Safety Factor is 1.04.

Figure 5.1

Considering that the cut slope remains at a steep angle and shows loose to medium density, it is conceived that severe weather conditions and extraordinary precipitation events would tend to decrease the safety factor of the current slope. This could trigger instability problems in the hillside and jeopardize the integrity of PR-155 between Stations 2+05 and 2+38.

The first alternative evaluated consists of slope regrading. This alternative consists of regrading the cut slope to a 1H:1V geometry at the lower portion of the cut slope and 1.5H:1V at the upper half of the cut slope. For 45 ft high cut slope, an intermediate bench at least 2 meters wide shall also be provided about mid-slope. Taking into consideration the location of the existing right-of-way, this alternative is very prone to erosion caused by run-off water. Therefore, once the cut slope is re-graded to the recommended geometry, it will be necessary to provide erosion protection measures like robust rooted grasses or artificial protection using geosynthetics.

Figure 5.2

Run-off water shall be diverted away from the slope face. A shown in Figure 5.3 this alternative has a safety factor of 1.53.

Figure 5.3

The second alternative evaluated is the construction of a soil nail reinforcement. Soil nailing is a practical and proven method of stabilizing steep slopes with passive inclusions. The inclusions, commonly called nails, are installed in the slope face. The nails are placed near horizontal and improve the shearing resistance of the soil by acting in tension. The concept of soil nailing is to reinforce the soil to produce a zone of stable reinforced ground which helps to support the unreinforced ground behind. Grouted nails are the most common type used in Puerto Rico. Typical horizontal and vertical nail spacings of grout nails range between 4 to 6 feet, 5 ft on average, depending upon the soil conditions and geometry restrictions. Immediately after the installation of a row of nails, the soil surface is covered by a facing. The most common type is a 6 to 8 inches thick shotcrete facing reinforced with welded wire mesh. Figure 5.4 below shows the stability analysis for this option which has a safety factor of 1.69.

Figure 5.4

A final design and corresponding shop drawings shall be presented by the specialty contractor. Additional investigations and borings may be necessary at the upper reach of the landslide to this end. For budgeting purposes and conceptual drawings, 1" diameter nail rods (GR60) spaced at 5 ft c-c (V and H) can be considered. The length of the nail should be in the order of 75% the cut height, or about 35 ft. Plastic centralizers are used to center the nail in the drill hole. The "nails are inserted and the drill hole is grouted full of cement grout to "bond" the nail bar to the surrounding soil. For permanent walls, the nail should be epoxy coated. The final facing typically consists of shotcrete or prefabricated concrete panels approximately 6 inches thick. Pre-fabricated mat drains are provided behind the concrete facing to drain any water that accumulates behind the concrete facing. The safety factor is 1.69.

Figure 5.5

The third alternative evaluated was the construction of a retaining wall along the shoulder of PR-155. This alternative was soon discarded due to the limited space available in the shoulder and the significant height of the cut slope. In any case, the construction of a retaining wall at road elevation would not increase the factor of safety of the cut slope.

6. Alternative Evaluation

Prior to commencing construction, the site shall be cleared and grubbed of vegetation cover and topsoil that may exist at the ground surface and any existing asphalt/concrete pavement from the existing roadway shall be demolished and removed from the site. After the clearing, grubbing, and demolition operations of the existing facilities are completed, and after any cut excavations are performed, the exposed surfaces shall then be proof-rolled with several passes of a heavy vibratory roller to detect any soft soil spot that may have to be removed and to densify any surface soil that may have been disturbed during the clearing and grubbing, and/or cut excavation operations.

Materials from required cuts at the site shall not be used as Fill at the site. Fill material to be used at the site shall consist of a non-expansive A-2-4 or A-2-6 soil or better in accordance with the AASHTO Soil Classification system. All fill within the site shall be compacted to a minimum of 95% of the Maximum Dry Density as obtained in the Modified Proctor Test (ASTM D-1557). Compaction equipment, consisting of rollers, compactors, or a combination of the two, must be used.

Based on the results of the geotechnical exploration combined with the geologic assessment, it can be concluded that a mud flow type of landslide occurred at the landslide area 2 site. A mud flow is a geologic phenomenon whereby a wet, viscous fluid mass of fine-to coarse-grained material flows rapidly and turbulently downslope. This results typically from torrential rainfall that initiates rapid erosion and transport of poorly consolidated surficial residual (plastic) materials that have accumulated in the upper surface of the slope. Evidence of a deep rotational landslide was not observed at the site.

Mud flows are typically recurrent events in steep slopes composed of residual to severely weathered soils. The moving mixture of water, soil, rock and vegetation most commonly has the consistency of freshly mixed concrete. As it moves down a slope, a mud flow may incorporate nearly anything in its paths -trees, rocks, and debris left by previous flows, that in turn increase the erosive power and destruction energy of the moving mass.

The resulting debris load was deposited over PR-155 as a mixed mass forming the debris fan.

Based on all of the above, two of the alternatives were compared in terms of advantages and disadvantages as described in Table 6.1.

Alternative PRO’s CON’s

Slope reconstruction

Lowest cost than other alternatives studied.

The site conditions and topography allow for this alternative.

This alternative is very prone to erosion caused by run-off water.

It will be necessary to provide erosion protection measures like robust rooted grasses or artificial protection using geosynthetics.

An intermediate bench at least 2 meters wide shall also be provided about mid-slope.

Soil Nail Reinforcement

Soil nailing is a practical and proven method of stabilizing steep slopes with passive inclusions.

Soil nail walls are relatively flexible and can accommodate comparatively large total and differential movements.

Soil nail wall requires smaller ROWs.

Easy adjustments to nail inclination and location can be made when obstructions are encountered, such as boulders, piles or underground utilities.

In projects with strict wall movement criteria, additional measures to limit deflections may be required.

Specialty contractor.

Soil nail walls are not well-suited where large amounts of groundwater seep into the excavation

Permanent soil nail walls require permanent underground easements

Sufficient space to operate equipment including ability to have a drill platform

Need for temporary support in exposed soil between excavation lifts, including placement of an intermediate soil berm may be needed.

Table 6-1

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.

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), Siamese cassia (Cassia siamea), Tall Albizia (Albizia procera), Guinea Grass (Megathyrsus maximus), the Railroad-track grass (Dichantium annulatum), Plush grass (Chloris radiata), “Bejuco de Caro” (Cissus trifoliata) and “Kudzú” (Pueraria phaseoloides). Also, one Almond tree (Terminalia catappa) Bamboo (Bambusa vulgaris) and two Royal Palms (Roystonea borinquena) 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. The areas were affected by the landslide.

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. Regarding the plant species, as discussed earlier, the landslide area was disturbed and most of the vegetation within the area was cleared by the landslide itself. 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

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

The remedial measures presented in this TR require to strictly enforce closely-sequenced construction methods, where the excavation for benching and filling in any part of the hillside area occur in a close sequence such that the length of open excavations is always left to a practical minimum during the work day.

All reconstruction and stabilization works must be accompanied by a careful monitoring program, during and after construction, that will help in assessing the effectiveness of the recommended interim remedial measures. Weak fills or incompetent soils are present on the current sloping ground (landslide debris). This debris must be fully removed before starting the new filling operation.

As indicated in Section 5 of this TR, the third alternative evaluated was the construction of a retaining wall along the shoulder of PR-155 but was soon discarded due to the limited space available in the shoulder and the significant height of the cut slope. In any case, the construction of a retaining wall at road elevation would not increase the factor of safety of the cut slope.

Alternative Constructability Considerations Feasibility Considerations

Slope regrading

Benching the ground surface required.

Weak fills or incompetent soils are present on the current sloping ground and must be fully removed before starting the new filling operation.

The equipment and machinery used is easily available and operated.

The existing topography allows for slope reconstruction, but the slope extension affects the drainage area at the slope bottom.

Soil Nail Reinforcement

It is required to strengthen or stabilize the existing steep slopes and excavations as construction proceeds from the top to bottom.

Both the soil nails and the initial and final facing contribute to the stability of the excavation.

Availability of specialty contractors skilled in soil nailing and shotcrete application near the project site

Have long-term, demonstrable corrosion protection to ensure adequate, long-term performance of the system.

Table 8-1

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 Table 9-1. The cost was considered as an evaluation criterion to select the preferred alternative.

Alternative Estimated Construction Cost Slope Regrading $ 224,341.08 Soil Nail Reinforcement $ 515,917.83

Table 9-1

10. Construction Time

The construction time was considered as an evaluation criterion to select the preferred alternative. As observed in Table 10-1 the estimated construction duration is from 7 to 9 months. This duration does not include the acquisition phase of the project.

Alternative Estimated Duration Construction Phase (in Months)

Slope regrading 8 months Soil Nail Reinforcement 9 months

Table 10-1

11. Solution Complexity

The recommended alternative for this site is slope regrading. This alternative presents constructability considerations that are summarized in Section 8 of this TR. Excavation shall be closely monitored at all times as loose material is found as surface material.

The solution needs to minimize impact on daily traffic. Nonetheless, due to the existing road section and the steep slope, the road may need to be closed to traffic during some construction activities for safety reasons. The Contractor shall implement caution and alternate measures to make sure that traffic is uninterrupted the least time possible and that construction work is coordinated in such way that access to adjacent properties is not affected. Appendix E includes alternate detour routes that may be used during construction. These routes need to be traveled by CMA’s personnel to determine which are feasible and safe to use for MOT. The detour routes suggested range from 1.5 to 3.5 kilometers.

It is imperative that all reconstruction and stabilization works must be accompanied by a careful monitoring program, during and after construction, that will help in assessing the effectiveness of the recommended interim remedial measures. Although, long term remedial measures given herein should be effective in minimizing future landslides at the hillside, variations in the site soil conditions, may require some changes in the stabilization program that can be promptly implemented with the help of the field instrumentation measurements in the hands of a well experienced geotechnical engineer. Therefore, it is recommended to adopt the field monitoring program as a component of the remedial measures suggested for this project.

The exact amount of this instrumentation will be determined by the Soil Engineer in charge of the geotechnical inspection during construction, as the site conditions dictate the requirement of the instrumentation. A typical monitoring station shall consist of control bench marks and inclinometers. Hence, the installation of two (2) inclinometers is recommended and its cost has been included in the Estimates included as Appendix C.

The control of surface run-off waters in this project is of paramount importance. An effective surface drainage system will have to be provided in this project in order to properly collect and dispose surface and groundwater to properly designed outlets, both during construction and after the hillside has been repaired. As indicated on Section 4, concrete gutters along the road edge need to be reconstructed and repaired.

Weak fills or incompetent soils are present on the current sloping ground (landslide debris). This debris must be fully removed before starting the remedial alternatives presented herein. The contractor shall follow all cleaning, stripping and benching recommendations presented by Suelos, PSC., full time soil technician and geotechnical engineer field supervisor. The actual depth and extension of removal shall be identified at the field during actual earthworks. The Contractor shall notify the Geotechnical Engineer at least three (3) days prior completion of excavations. No foundation fill or concrete shall be deposited until the soil bearing capacity is validated by the Geotechnical Engineer.

12. Impact on Right of Way Acquisition

The project will require permanent acquisition from adjacent properties. Table 12-1 shows the estimated permanent acquisition areas that would be required depending on the alternative selected.

Alternative Area required for

Permanent Acquisition (m2)

Cost of Acquisition

Slope regrading 700 $ 9,800.00 Soil Nail Reinforcement 1,000 $ 14,000.00

Table 12-1

13. Recommendations

Site HWY-264 is located in kilometer 45.5 of PR-155 in the Municipality of Morovis. Within this site there are two adjacent landslide areas. The roadway at this location has a width of approximately 6 meters. This Technical Report only focuses on the second landslide area which is referred to as “area under evaluation”.

The first landslide area required a roadway side slope reconstruction of approximately 100 meters north and south of the existing Bridge No. 334. There is an unnamed creek, which is a tributary of the Morovis River crossing at this site. During the site visits, no water flow was observed, and it was substantially clogged upstream. The original project scope presented to PRHTA, included the debris removal at the channel bed, the evaluation of cut slopes of the roadway and the reconstruction of all concrete barriers.

From the preliminary site visits it was observed that for this landslide area, the morphology was that of a slide produced by heavy scouring along the toe of the slope probably due to heavy erosional forces of the water along the river. Nonetheless, on December 2018, during a site inspection, it was observed that construction work had started on this area.

A gabion wall was built adjacent to the bridge to correct the scouring and earthwork along the slope was taking place. Therefore, as discussed with PRHTA, the scope of work for this landslide area was reduced and limited to reconstruct the concrete parapet of the bridge, concrete barriers and concrete waterway along the PR-155.

For the second landslide, hereafter the “area under evaluation”, the local topography within the affected area is mainly characterized by a cut slope that grades downward from east to west with an overall relief of some 14 meters (measured from PR-155 average elevation). According to the surveying work completed and field data gathered, a large landslide occurred in the cut slope during hurricane Maria landfall, blocking state route PR-155. The failure resembles a landslide with an approximate length of 30 meters (in plan view). The most critical section (steepest slopes) occur between Stations 2+05 and 2+38. These characteristics are typical of a mud flow. The original topography of the cut slope is unknown but considering the very steep slope that remained after the mud flow, it is conceived that the cut slope was originally near vertical.

From the research, it was observed that the landslide area is surrounded by a large partially developed property that apparently belongs to a single owner. For the reconstruction work to be performed, partial acquisition of property with Cat. Number 138- 085-105-19-000 is required Existing access to the property will remain as existing and no relocation of families is required.

Surveying work was limited to 7,100 square meters approximately. The most relevant data obtained for Landslide Area 2 is that the head scarp to its toe is 14 meters. Its most obvious manifestation is a relatively vertical scarp in the upper residual soils which forms the uppermost boundary of the landslide (the head scarp). The head scarp is underlaid by a steep slope of exposed saprolitic material that shows several erosion grooves produced by run-off water. In terms of utilities, traces of a concrete gutter were observed on site. It seems like part of this gutter is buried under the landslide residue and will need to be reconstructed. Also, an overhead power line crosses the landslide area. There is a water line of 2“ of diameter that runs along the PR-155. The exact location of the 2” water line is unknown. A subsurface utility exploration is required. Nonetheless, based on data obtained from GIS, the line location was approximated and it is not likely to be relocated.

A cast iron pipe of 16” of diameter is attached to the bridge structure and continues underground along the edge of PR-155. The cast iron pipe needs to be reattached to the bridge.

According to the information issued by the USGS in the geologic map of the Ciales Quadrangle, the site is underlain by Granodiorite. This native stratigraphy is a typical profile of residual soil consisting of three indistinctly divided zones. The upper zone consists of completely to highly weathered soil. The intermediate zone consists of highly to moderately weathered material exhibiting some features of the structure of the parent rock and may contain core stones. This zone often contains pedogenic material such as nodules of calcium or iron slats which may give it a mottled or spotted appearance.

No endangered plants or animal species were observed in those areas during the site visit. Also, 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 DNER and the USACE must be consulted to evaluate impacts that cannot be avoided during construction activities.

For the area under evaluation, a total of four (4) boreholes were drilled to a depth of 30 feet. In general, the borings show a relatively thin crust of fill below the asphalt wearing surface of PR-155, followed by a 2-layer stratigraphy. Below the fill crust below the asphalt (fill associated with PR-155 construction), the upper layer appears as a competent silty or clayey sand and sandy clay delivered from the Granodiorite formation. Common color in this severely weathered layer is brown and yellowish-brown. Relative densities and consistencies, based on SPT values, varies from dense and very stiff. The thickness of this soil layer averages 6 to 12 feet below PR-155 elevation. The middle layer consists of severely weathered soils, the boring program found saprolitic silt and sand delivered from parent rock. Densities based on SPT values are generally dense to very dense, with most N-values greater than 100 blows per foot. The saprolitic material extends to the end of borings. At the bottom of the borings, evidence of the lower zone of the residual soil profile was obtained. This layer consists of physically disintegrated and partially to slightly weathered material often having the appearance of a mass of interlocking blocks of soft rock. This lower zone merges into fractured or jointed, almost unweathered Granodiorite rock. With increasing depth, this layer should merge into fractured or jointed, almost unweathered, calcareous tuffaceous siltstone and sandstone. The water table was not observed during drilling operations.

Based on the results of the geotechnical exploration combined with the geologic assessment, it can be concluded that a mud flow type of landslide occurred at the landslide area 2 site. A mud flow is a geologic phenomenon whereby a wet, viscous fluid mass of fine-to coarse-grained material flows rapidly and turbulently downslope. This results typically from torrential rainfall that initiates rapid erosion and transport of poorly consolidated surficial residual (plastic) materials that have accumulated in the upper surface of the slope. Evidence of a deep rotational landslide was not observed at the site.

Mud flows are typically recurrent events in steep slopes composed of residual to severely weathered soils. The moving mixture of water, soil, rock and vegetation most commonly has the consistency of freshly mixed concrete. As it moves down a slope, a mud flow may incorporate nearly anything in its paths -trees, rocks, and debris left by previous flows, that in turn increase the erosive power and destruction energy of the moving mass.

The resulting debris load was deposited over PR-155 as a mixed mass forming the debris fan.

Based on all of the above, the following alternatives were evaluated: slope regrading, soil nail reinforcement and retaining wall construction along the shoulder of PR-155. The retaining wall alternative was soon discarded due to the limited space available in the shoulder and the significant height of the cut slope. In any case, the construction of a retaining wall at road elevation would not increase the factor of safety of the cut slope.

The slope regrading alternative consists of regrading the cut slope to a 1H:1V geometry at the lower portion of the cut slope and 1.5H:1V at the upper half of the cut slope. For 45 ft high cut slope, an intermediate bench at least 2 meters wide shall also be provided about mid-slope. This alternative will require to provide erosion protection measures like robust rooted grasses or artificial protection using geosynthetics. Run-off water shall be diverted away from the slope face. A safety factor is of 1.53 for this alternative.

For the soil nail reinforcement alternative, grouted nails are the most common type used in Puerto Rico, and therefore preliminarily recommended. Typical horizontal and vertical nail spacings of grout nails range between 4 to 6 feet, 5 ft on average and the soil surface is covered by a facing, which most likely be 6 to 8 inches thick shotcrete facing reinforced with welded wire mesh. The safety factor is 1.69 for this alternative.

The alternatives were analyzed in terms of construction cost, construction time, constructability and feasibility. Permanent acquisition area required ranges from 700 m2 to 1,000 m2. The difference between the acquisition areas is not substantial. The slope regrading’s construction cost is half of the soil nail reinforcement alternative and the safety factor is 1.53 which is comparable when to soil nail reinforcement’s safety factor of 1.69.

Both alternatives satisfy the minimum safety factor required for both static and pseudo static conditions. Also, there are several considerations to be taken for nail reinforcing such as the need of specialty subcontractor to perform the work and the clearance needed for the specialized equipment. Based on the above, the alternative recommended is slope regrading. For slope regrading, even though is expected to minimize the impact on daily traffic when compared with soil nailing, due to the existing road section and the steep slope, the road may need to be closed to traffic during some construction activities for safety reasons. The Contractor shall implement caution and alternate measures to make sure that traffic is uninterrupted the least time possible and that construction work is coordinated in such way that access to adjacent properties is not affected. Appendix E includes alternate detour routes that may be used during construction. These routes need to be traveled by CMA’s personnel to determine which are feasible and safe to use for

MOT.

The recommended alternative has a construction cost of $224,341.08 and should be completed within 8 months. Permanent acquisition of 700 m2 is required at an estimated cost of $9,800.00. The total cost to implement this alternative is of $ 234,141.08.

The contractor shall keep all construction within project limits. These limits will be physically marked on the field before the construction period to minimize any impact to natural systems outside the proposed construction site. The temporary storage areas for materials and contractor parking areas ("staging areas") shall be located within established project right of way. If selected "staging areas" off limits or project access are established for the project, they must be evaluated and placed in areas that do not affect endangered species or within ecological sensitive habitat.

14. Appendixes

Appendix A: Surveying Plan Appendix B: Geotechnical Study Appendix C: Alternatives Cost Estimates Appendix D: Sections Appendix E: Detour Routes

Appendix A

ER- HWY- 264 (PR-155 KM 45.5)

AC-827544 RPE 2799544 ER9999 (353)

MOROVIS, PUERTO RICO

B-17 Marginal Ext. Forest Hills, Bayamon, P.R., 00959 Tel. (787) 505-3190 email-info@antoniomelendezpr.com

SURVEY PLANSCALE 1:100 1

AUTORIDAD

Y TRANSPORTACION

DE CARRETERAS

LANDSLIDE SITE 264

www.antoniomelendezpr.com antonio melendez & asociados, psc Surveying and Mapping Consultants

STATE ROAD NO. 155, KM. 45.5

MOROVIS, PUERTO RICO

NOTES:

LOCATION PLAN

SITE

HORIZONTAL & VERTICAL CONTROL

STATE ROAD NO. 155

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KM 45.5

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TOW=246.82

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TOW=246.83

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TOW=246.94

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TOW=246.96

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CEILING EL=245.07

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CEILING EL=245.09

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CEILING EL=245.04

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TRACES OF CONCRETE FOUND

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(APPEARS TO BE A CONCRETE

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GUTTER UNDER GROUND & MUD)

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BAMBOO

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AREA

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FLOW

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CAST IRON PIPE

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AutoCAD SHX Text 237.69

AutoCAD SHX Text 248.84

AutoCAD SHX Text 251.27

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AutoCAD SHX Text 248.57

AutoCAD SHX Text 248.41

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AutoCAD SHX Text 248.73

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AutoCAD SHX Text 247.52

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FLOW

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