Technical Report - AC-916579_HWY-287.pdf

TECHNICAL REPORT

PR-159 KM 3.5

Morovis, P.R.

ER-HWY-287

PRHTA Design Area

Landslide and Road Damage Evaluation and Repair Recommendations

Government of Puerto Rico

May 6, 2019

EMERGENCY RELIEF PROGRAM

AC-822544

Contents

SUMMARY

1. INTRODUCTION

2. DAMAGE ASSESSMENT

3. WORK EXECUTED

4. INTRODUTION TO TECHNICAL SOLUTION ALTERNATIVES

5. ALTERNATIVE EVALUATION

6. RECOMMENDATIONS

Appendixes

Geotechnical Report

Lead and Asbestos

Environmental Assessment

Survey and Topographic Drawing

Recommended Solution Plan

Probable Construction Cost

Puerto Rico Highway and Transportation Authority Landslide and Road Damage Evaluation and

Repair Recommendations Technical Report-Group B

SUMMARY

The Puerto Rico Highway and Transportation Authority (PRHTA) intends, thru the project Landslide and Road Damage Evaluation and Repair Recommendations, the reconstruction of landslides; i.e., slope instability, erosions, washouts and rock fall, on several highway segments caused by the impacts associated with Hurricanes Irma and

María.

These highway segments are located within the Puerto Rico’s Federal Aid Highway

System, and other highways and roads under the Department of Transportation and

Public Works (DTPW) jurisdiction. DG3A Design Group, PSC performed the site reconnaissance, investigations, and studies, necessary to provide appropriate recommendations to reconstruct the highway to its previous condition. Highway improvements will comply with existing codes, regulations, standards and directives

(Except as specified herein).

DG3A Design Group, PSC will also prepare Plans, Specifications and Estimates

(PS&E) as part of the next phase.

The project’s main goal is to study possible alternatives complying with current state and federal highway policies and regulations to reconstruct the affected roadway to its previous condition.

This study was focused on analyzing alternatives to solve the road damage.

1. INTRODUCTION

The Puerto Rico Highway and Transportation Authority (PRHTA) proposes to reconstruct the landslide at PR-159 km 3.5 (ER-HWY-287) in the Municipality of Morovis. To achieve this goal and to determine the needs, the following areas were evaluated: general roadway condition, drainage system, geotechnical conditions and environmental considerations. Figure 1 shows project location and Figure 2 illustrates the location of the landslide at PR-159.

1. Figure 1

2. Figure 2

PROJECT

LOCATIONS

Based on AASHTO, the segment of road (PR-159) subject to consideration under this project is classified as rural local road.

Based on the Commonwealth Highway System contained in the PRHTA HDM, PR- 159 is classified as a rural local road (R-9).

2. DAMAGE ASSESSMENT

As part of the request of proposal km 3.5 of the roadway PR-159 was visited and visually inspected on April 10, 2018 and revisited on December 26, 2018 as part of site reconnaissance to evaluate the landslide and possible solution alternatives. On the following pictures taken on April (left) and December (right) of 2018; in these 8 months interval it was observed that the magnitude of erosion did not change, and new vegetation is growing.

2.1 Highway PR-159 (ER-HWY-287):

APR-10-2018 DIC-26-2018

3. WORK EXECUTED

The following works were performed as part of the evaluation of the highway PR-159 km 3.5 landslide problem:

1. Reconnaissance visits, one time on April 10, 2018 and a second in December 26, 2018

2. Survey and topographic was performed on December 2018.

3. Geotechnical Evaluation was performed on December 2018.

4. Lead and Asbestos Evaluation was performed on December 2018.

5. Preliminary Environmental Assessment was performed on January 2019.

4. INTRODUTION TO TECHNICAL SOLUTION ALTERNATIVES

Different alternatives were evaluated between the DG3A Design Group, PSC team and are presented as follow:

4.1 Backfilling

Backfill slopes should be constructed with a 2:1 or flatter slope. Over-steep fill slopes, steeper that 2:1 slope, may continue to ravel with time and are difficult to stabilize.

4.2 Drainage

Water runoff is one of the main factors in landslides. Improving surface and/or subsurface drainage at the site can increase the stability of a landslide. Surface runoff should be diverted away from the landslide area by channeling water in a lined drainage surface to the base of the slope.

The water should be diverted in such a way as to avoid triggering a landslide adjacent to the site. Surface water should not be allowed to pond on the landslide.

4.3 Support Structures

Retaining walls are structures designed to restrain the soil. They are normally used in areas with steep slopes or where the landscape needs to be shaped severely for construction or engineering projects. However, retaining walls have been found to be a very efficient solution against landslides and reducing steep slopes. There are various ways of constructing a retaining wall, the most common types being:

4.3.1 Retaining wall

Gravity walls, they manage to resist pressure from behind due to their own mass and cantilever walls, they have a large structural footing and convert horizontal pressure from behind the wall into vertical pressure on the ground below.

4.3.2 Soil nailing

Soil nailing consists of installing closely spaced bars into a slope or excavation as construction proceeds from top down. It is an effective and economical method of constructing retaining wall for excavation support, support of hill cuts, bridge abutments and high ways. This process is effective in cohesive soil, broken rock, shale or fixed face conditions.

4.3.3 Anchors, tiebacks

They use cables or other stays anchored behind the rock or soil to increase resistance.

4.3.4 Soldier Piles and Lagging Walls

Soldier piles and lagging wall is an earth retention system consisting of piles, steel or concrete, driven or placed in drill holes.

After the soldier pile have been installed, the earth is excavated along one side of the piles to expose a cut face of earth. Then lagging is installed with either timber or shotcrete to hold back the soil.

4.3.5 Gabions

Gabions are wire mesh, boxlike containers filled with cobble-sized rock that are 10 to 20 centimeters (4 to 8 inches) size (fig. C16). A gabion retaining wall can also be constructed from stacked gabions. Gabion walls usually are inexpensive and are simple and quick to construct. Due to their flexibility, they can withstand foundation movement, and they do not require elaborate foundation preparation. Because of their coarse fill, they are very permeable and thus provide excellent drainage.

4.3.6 MSE

Composite structure consisting of alternating layers of compacted backfill and soil reinforcement elements, fixed to a wall facing. The soil reinforcement elements are typically steel or geosynthetic and the facing elements are modular precast panels, precast blocks or wire mesh and shotcrete.

4.4 Vegetative Cover:

Vegetation can minimize the amount of water infiltrating into the soil, slow erosion caused by runoff flow, and remove water from the soil. Although vegetation alone cannot prevent or stop a landslide, removal of vegetation from a landslide may initiate erosion and then landslide.

4.4.1 Vetiver

Type of grass with extraordinary characteristics that is used as a bioengineering technique for steep slope stabilization and other environmental protection purposes. It is used for sediment control, land stabilization and rehabilitation, when planted is single rows will form hedge which are very effective in slowing and spreading runoff water and reducing soil erosion. Also, the extremely deep and fast growing massively thick roots system binds the soil and makes vetiver very drought tolerant and highly suitable for steep slope stabilization.

4.4.2 Trees

Trees block plenty of rain from reaching the soil due to the canopy effect. The roots act like bonding agent, which helps keep soil in place and reduces the amount of soil washed away. The trees used on slope shall have deep roots.

4.5 Erosion Control

4.5.1 Geotextile

There are many varieties of fiber, biodegradable, and compost blankets on the market today, and they have all been designed to minimize the effects of water erosion on slopes and embankments.

Rolled mats are usually made from mulch that is helps together by a fiber mesh and they degrade slowly, allowing vegetation that may have been grown in the area to grow and take over the job of protecting the soil from erosion when the mats have finally degraded completely.

4.6 Safety

4.6.1 Guardrail

Safety barrier that is placed along the edge of the road intended to shield motorist who has left the roadway, made primary of metal.

4.6.2 Concrete Barrier

Rigid barrier that is placed along the edge of the road intended to shield motorist who has left the roadway, made of concrete.

5. ALTERNATIVE EVALUATION

The final chosen alternative will comply with the PRHTA Design Manual (HDM), the most recent AASHTO’s manuals, including the Roadside Design Guide, Highway Safety manual, AASHTO Green Book, the PRHTA’s Standard Specifications for Road and Bridge Construction (2005 and amendments), Supplementary Specifications, and Standard Models and Design Directives; and the Federal Highway Administration (FHWA) standards and regulations.

The selection of stabilization measures depends on bedrock characteristics, hillside hydrology, slope gradient, length and curvature, and soil depth and type.

5.1 Backfilling:

Filling the eroded area was the first alternative evaluated, but was discarded because will change the geometry, slope and may also require the acquisition of additional land.

5.2 Drainage:

The erosion problem of the project was triggered by runoff, curbs or swales will be added to avoid future erosions on the area.

5.3 Support Structure:

The project will require a support structure to contain the existing roadway in place and avoid future erosion problems. Different systems were evaluated (see previous section for details). The two systems that we think will adapt better to this project are:

5.3.1 Concrete Barrier Type C

Considering the relatively shallow landslide conditions, it is our opinion that a type C concrete barrier at the edge of the road is a feasible solution for this site. This option shall include leveling the remaining slope to uniform inclination and armoring with turf reinforcement the deep-rooted vegetation such as vetiver. The base of the type C concrete barrier shall extend to a minimum depth of 1 mt (3.3 ft) below existing ground surface.

5.3.2 Gravity Wall:

The concrete gravity wall alternative shall be embedded at least 1 m below slope surface and is estimated that the retaining wall height will be in order of 1.50 mts. Also, guardrails or concrete barrier shall be installed or constructed.

5.3.3 Retaining Wall:

A concrete cantilever retaining wall with an integrated concrete barrier. The cantilever will be projected about 2 meters under the road and 1.0 meters deep, area that will be required to excavate to build the wall.

5.4 Vegetative Cover:

The remaining slope shall be leveled to uniform inclination and armoring with turf reinforcement the deep-rooted vegetation such as vetiver.

5.5 Erosion Control System:

No erosion control system will be required on this project, the area is already vegetated.

5.6 Safety:

A safety device will be required on this project to prevent motorist from falling into the slope, the final system to be use will be related to the system to control the erosion problem. The system will extend about 30 meters.

Concrete Barrier Type C

Gravity Wall Retaining Wall

Environmental Considerations

No environmental impact is expected.

For details see 7.3.

No environmental impact is expected.

For details see 7.3.

No environmental impact is expected.

For details see 7.3.

Constructability No specialized personnel required.

No specialized personnel required.

No specialized personnel required.

Construction Cost (See Appendix for detailed estimate)

$127,768.62 $147,634.59 $155,417.21

Construction Time 4-6 weeks 4-8 weeks 6-10 weeks

Solution Complexity (Pros and Cons)

Pros: Construction method. Material and workmen easy to find on the area Cons: Construction time.

The system will require excavation, installation of formworks for concrete, pavement and painting.

Low Complexity.

Pros: Construction method. Material and workmen easy to find on the area Cons: Construction time.

The system will require excavation, installation of formworks for concrete, pavement and painting.

Low Complexity.

Pros: Construction method. Material and workmen easy to find on the area Cons: Construction time.

The system will require excavation, installation of formworks for concrete, pavement and painting.

Low Complexity.

Impact of Right of Way Acquisition

No right of way acquisition will be required.

No right of way acquisition will be required.

No right of way acquisition will be required.

Others None. None. None.

6. RECOMMENDATIONS

After analyzing all the information, evaluations and reports, specially the impact on users the construction of a Concrete Barrier Type C is our recommendation to assure the mitigation of the landslide with the less impact on the existing road, avoiding a long-term closure.

Appendixes

Geotechnical Report

Lead and Asbestos

Environmental Assessment

Survey and Topographic Drawing

Recommended Solution Plan

Probable Construction Cost