Geotechnical Report - HWY 227.pdf

DESPIAU ASSOCIATES

CONSULTING GEOTECHNICAL ENGINEERS

PO BOX 260370

San Juan, PR 00926-2622 www.despiau.net

Report of Geotechnical Engineering and Subsurface Exploratory Services for the Landslide and Road Damage Evaluation and Reconstruction Project at State Road PR-149, KM 42.8 on Ala de la Piedra Ward of the

Municipality of Ciales, Puerto Rico.

Reference No. DA/18O3743

PROJECT ID: ER-HWY-227

January 23, 2019

Prepared for:

Klein Engineering, PSC.

PO Box 12009 San Juan, Puerto Rico 00922-2009

Jose R. Despiau, P.E., License #17343 Geotechnical Engineer, Despiau Associates – Consulting Geotechnical Engineers.

P.O. Box 260370 San Juan, PR 00926-2622 ● 787.281.0686 ● www.despiau.net

January 23, 2019

Klein Engineering, PSC.

PO Box 12009 San Juan, Puerto Rico 00922-2009 Ph: 787.993.2071 E-mail: franciscoklein@klein-engneering.com

Attn.: Mr. Francisco R. Klein, PE., MECE, PTOE, President

Subject: Proposed Geotechnical Engineering and Subsurface Exploratory Services for the Landslide and Road Damage Evaluation and Reconstruction Project at State Road PR-149, KM 42.8 on Ala de la Piedra Ward of the Municipality of Ciales, Puerto Rico. Reference No. DA/18O3743

Dear Eng. Klein:

As requested, we have completed the Subsoil Exploration and Geotechnical Engineering Assessment for the review of the landslide(s) and/or road, which were affected post Hurricane María as part of the Landslide and Road Damage Evaluation and Reconstruction Project ER- HWY-227, at State Road PR-149, KM 42.8 on Ala de la Piedra Ward of the Municipality of Ciales, Puerto Rico.

The work was undertaken at the request of Mr. Francisco R. Klein, PE., MECE, PTOE, President of Klein Engineering, PSC. The work was made in accordance to Proposal No. DA/04-10-18R for the subsurface exploration dated May 22, 2018. The work was commenced after order to proceed for the work was received on November 5, 2018.

This report presents the results of the field exploratory drilling, laboratory tests performed on secured soil samples, engineering assessments from geotechnical standpoint, soil and foundation design parameters for the proposed improvements (i.e. retaining walls, cut and fill earthwork specifications) as required thereof.

It has been a pleasure to have been of your assistance in this project.

Respectfully Submitted, Jose R. Despiau, PE.

Geotechnical Engineer mailto:franciscoklein@klein-engneering.com

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TABLE OF CONTENTS

Page No.

I. INTRODUCTION

II. SITE AND PROJECT DESCRIPTION

III. FIELD SUBSURFACE AND SAMPLING PROGRAM

3.1 Subsurface Investigations

3.2 Geological Notes

3.3 Stratigraphic Units

IV. OBSERVATIONS AND FINDINGS

V. ENGINEERING RECOMMENDATIONS

5.1 General Design Parameters for Retaining Structures

5.1.1 Additional Considerations for Retaining Structures

5.2 Additional Recommendations for Cantilever Retaining Structures

5.3 Additional Recommendations for a Sheet Pile Retaining System

5.3.1 Lateral Load Design Considerations

5.4. Additional Recommendations for a Drilled Shaft Retaining System

5.4.1 Drilled Shaft Types and Capacities

5.4.2 Additional Drilled Shaft Recommendations

5.4.3 Lateral Load Design Considerations

5.4 Earthquake Design

5.5 Excavations

5.6 General Earthwork Recommendations

5.6.1 Excavations

5.6.3 Temporary Cut Sections

5.6.4 Backfill Material

5.7 Proposed Storm Water Run-off Control

5.8 Nearby Structures

5.9 Additional Recommendations

VI. LIMITATIONS OF THIS REPORT

Appendix (A) – Figures

1. US Geological Survey Service Topographical plan at a scale 1:20,000 1A. Geological Map

2. Boring Location Plan

Appendix (1) - Boring Logs Appendix (2) - Earthwork Specifications Appendix (3) - Special Laboratory Tests

I. INTRODUCTION

This report covers the Subsoil Exploration and Geotechnical Engineering Assessment for the review of the landslide(s) and/or road, which were affected post Hurricane María as part of the

Landslide and Road Damage Evaluation and Reconstruction Project ER-HWY-227, at State Road

PR-149, KM 42.8 on Ala de la Piedra Ward of the Municipality of Ciales, Puerto Rico.

The work was undertaken at the request of Mr. Francisco R. Klein, PE., MECE, PTOE, President of Klein Engineering, PSC. The work was made in accordance to Proposal No. DA/04-10-18R for the subsurface exploration dated May 22, 2018. The work was commenced after order to proceed for the work was received on November 5, 2018.

This report presents the results of the field exploratory drilling, laboratory tests performed on secured soil samples, geotechnical assessments, and summary of findings, and recommendations for required site improvements.

Presently, three (3) reconstruction alternatives to cope with the disclosed conditions at the Site can be considered by the A/E Design Team. However, should the A/E design team consider other(s) and/or additional design reconstruction alternatives these shall be forwarded to this office to evaluate them and provided the required geotechnical recommendation, if deemed necessary.

In the following sections of this report the soil and foundation design parameters for the proposed improvements (i.e. retaining structures, cut and fill earthwork specifications) are being provided.

The selected boring locations were used to establish the profile data at the specific explored locations for the present geotechnical engineering review. This report has been prepared for the exclusive use of the owner and the A/E Consultant Firm involved in the preparation of the site engineering design plans and specifications.

II. SITE AND PROJECT DESCRIPTION

The Site observation revealed the complete study sector extends for an approximately 100 meters. Within this sector, one (1) major slides, some 25 meters long, occurred along the western edge of State Road PR-149, causing a partial rupture of the pavement structure caused by the

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landslides experienced. However, reportedly smaller slide observed do not form part of the present project. Although it is our understanding these shall also be repaired considering similar reconstruction approaches as the presently considered for the major slide being presently considered.

Based on the results of the subsurface exploration performed, evaluations and Site observations, our engineering assessment is that the primary cause for the prevalent conditions were caused by the excessive surface subsurface water runoff, which eroded the western sloping grounds.

The intense or above normal erosional conditions experienced during Hurricane Maria was the primary factor which caused the prevailing conditions.

Based on the US Topographic map a Toro Negro River borders the western edge of State Road

PR-149 (at an approximate elevation of 620 mts.). Two (2) storm water ephemeral gully streams drain the surface water from the hill top and saddle at the highland ridge, about 151.8 mts. east of the site towards State Road PR-149 and thereafter to the Toro Negro river. The roadside elevation is at an approximate elevation is approximate 15 to 20 meters higher than the Rivers stream bed, near the major slide observed. These difference in elevation creates very steep sloping ratios, in the order of 45° to 54° degrees.

Also, field observations revealed the average total width of State Road PR-149 at the project sector is approximately 3.65 to 4.5 mts. (12 to 15ft.). This narrow road section presents limits the reconstruction alternatives to cope allow at least one (1) lane in service during construction.

The following sections of this geotechnical report will provide the required Site improvements and foundation design recommendation for the proposed improvements required at the Site.

III. FIELD SUBSURFACE AND SAMPLING PROGRAM

3.1 Subsurface Investigations

The subsurface soil conditions at the site were investigated four (4) standard penetration test borings performed to assess the existing subsoil conditions at the project site. The location of borings is shown in the accompanying Boring Location Plans, in Appendix A, Figure No. 2.

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Sampling of soils was performed continuously in the upper 10 ft. and thereafter, at approximately five-foot intervals. All soil samples were taken with a 2"-O.D. split barrel sampler following the standard penetration test procedures in ASTM D-1586. Penetration resistance values from the standard penetration tests are recorded in the "N" column of the boring logs.

The procedures used for the laboratory tests, as well as the routine and special laboratory procedures used, for the determination of the index soil properties are contained in the Appendix

(1) to this report.

3.2 Geological Notes

Based on the US Geological Survey of the Geologic Map and Sections of the Jayuya Quadrangle

(Map I-520), prepared by Mr. Peter H. Mattson (1968), the geologic units that lie at or near the site are the following:

1. Cotorra Tuff (Kct) – Described as disconformity, mostly massive dark-green and greenish-black coarse tuff and lapilli tuff interbedded with minor volcanic breccia and basalt lava flows. At the site the geologic plan shows, an inclined 80-degree shear cleavage is found near the site. Also, it was observed south of the site an inclined narrow dike with a 36-degree alignment toward the southeast. Additional planar features were identified on the east bank of the river.

2. Achiote Conglomerate (Upper Cretaceus) (Ka) - Described as massive red volcanic conglomerate interbedded with subordinate green tuffaceous conglomeratic sandstone and red mudstone.

3. Maravillas Formation (Upper Cretaceus) (Km) – Described as medium- to thick-bedded muddy, dark-colored feldspathic sandstone, and siltstone, dark mudstone, green coarse crystal-lithic tuff, and silty brown coarse crystal tuff.

4. Volcanic kikes and sills (Cretaceous or lower Tertiary) (Tkp) - Described as grayish-blue, and bluish-gray porphyritic basalt, andesite, and dacite in resistant steeply dipping

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tabular bodies as much as 50 m. thick, but most commonly 5 to 10 m. in thickness.

Phenocrysts include feldspar, hornblende, some pyroxene, and rare quartz.

Faults are numerous in Jayuya Quadrangle, however only two (2) faults have been named. The

Cerro de Punta Fault crosses the quadrangle from east to west south Cerro de Punta. The fault or fault zone shows left-lateral apparent horizontal displacement of 600 to 900 m. and cuts lower

Tertiary rocks; it also has some apparent vertical movement but, as is typical or strike-slip-faults, with no one side consistently up or down. The San Patricio Fault, crossing the southwest corner of the quadrangle, extends as an important fault in both directions. At this location it shows apparent normal movement forming (with a subsidiary fault) the south side of the Tertiary sequence.

An approximate Unnamed Fault (dashed), was identified at about 1000 feet, northeast of the site, having a near south alignment and intersect a major approximate Unnamed Fault (dashed) having a near northeast alignment to the north from the site. Several additional approximate Unnamed

Faults lines are shown in the Geologic map, intersecting at the same location of the previously identified Unnamed fault crossing, found about 1100 ft. to the northeast. with a near south-east trend running parallel to Quebrada Doña Juana, which intersects the Toro Negro River north from the study area.

Refer to the US Geological Survey – Geologic Map which is included in Appendix A, Figure 1A.

3.3 Stratigraphic Units

Upper Surface Section – Generally at the road surface, the results of the exploration disclosed a surface layer thickness of about 1.5 ft. Following the six 6”-inch to 8”-inch asphalt overlay, the surface layer is composed of a light olive gray and brown sandy silt with some subangular gravel fragments. The standard resistance to penetration (N-values) of the surface layers varied from

53 to 125 blows/foot, at a medium to very dense State of Consistency. The natural moisture content values range from 3 to 11 percent. Random samples of this layer from [Boring 227-1-from 0.0’ to 1.5 ft.] disclosed AASHTO class type A-1-a (0) AASHTO type soils (USSCS type SP-

SC-Poorly graded sand with clay and gravel). The results of the Free Swell Tests performed disclosed values varying between 5 and 10 percent.

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Following the upper surface layer, a fill section about 7.5-thick of olive, brownish yellow, brown, and olive gray sandy silt, trace clay with some silty clay with subangular gravel fragments was encountered. The standard resistance to penetration (N-values) of the surface layers varied from

50 blows/foot to practical refusal to penetration. The natural moisture content values range from

2 to 15 percent.

Random samples of this layer disclosed AASHTO class type A-2-4 (0) and A-1-a (0) AASHTO type soils. The Standard Free Swell determination tests performed on this samples disclosed value of 10 percent, where a low shrink/swell potential is predicted.

Residual Material – Beneath the above described layers, the residual material was found, from about 7.5’ to 10.5 ft.; extending to about 15 ft. [Borings 227-1] in depth. These were described as olive, and brownish yellow sandy silt, trace clay, with some weathered rock fragments. The standard resistance to penetration (N-values) of the residual layers varied from 46 to 91 blows/foot, at a stiff to hard State of Consistency. The natural moisture content values range from

5 to 12 percent.

Completely Weathered Rock - At the deeper explored depths, until the borings were bottomed a highly weathered rock, broken by the sampling device into olive gray completely weathered rock with clay fines, with traces of basalt lava flows and crystal tuff fragments, product of the weathering of the parent geologic units was found. The standard penetration test attempts disclosed 94 blow/ft. to practical refusal to penetration with values greater 100 blows for a few inches of penetration. The natural moisture contents range from 1 to 21 percent.

Random samples of this horizon highly weathered rock with sandy fines disclosed AASHTO class type A-2-4 (0) USSCS type SC-SM -Silty clayey sand with gravel and A-2-6 (0) (USCS type

SC – Clayey sand).

Graphical representation of the soil profiles is illustrated in the boring logs included as Appendix

(1) to this report.

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3.4 Groundwater Levels

In general, the permanent ground water level was not found within the extent of depth drilled, during the period of exploration. All depths were measured from the existing ground surface prevailing during the period of exploration.

All surface ground and underground water should flow through existing drainage gullies, from higher sectors of the north toward the lowland areas to the south west, towards the Cialitos River.

IV. OBSERVATIONS AND FINDINGS

The present exploratory program was conducted to establish the subsurface profile and to allow the presentation engineering assessment, from a geotechnical standpoint, in addition to providing the construction guidelines for the implementation of the proposed improvements to the western sloping grounds, where several landslides scarps have been experienced on the eastern edge of

State Road PR-149, which was subjected to extensive degradation, erosional effects, and landslides causing the observed damages and partial rupture of the road embankment and pavement structure. Field observation revealed one (1) major slides occurred along the western edge of State Road PR-149, some 17.5 meters south of km 42.8. However, reportedly smaller slide observed do not form part of the present project. Although it is our understanding these shall also be repaired considering similar reconstruction approaches as the herein being presented. Evaluations dictate that besides the surface failures caused by the excessive runoff experience during the hurricane event, an additional failure plane exist between the interface of the upper fill section and the residual weathered material. This interface generally occurs at about

9.0 to 11.0 ft. in depth. Therefore, any retaining structure to be install shall be founded deeper than the previously mentioned failure plane.

Based on the results of the subsurface exploration performed, evaluations and Site observations, our engineering assessment is that the primary cause for the prevalent conditions were caused by the excessive surface subsurface water runoff, which eroded the lower western sloping ground subsurface soils. The intense or above normal erosional conditions experienced during Hurricane

Maria was the primary factor which caused the prevailing conditions.

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In addition, evaluation of the topographic plan submitted for the present evaluation revealed, the

Toro Negro River borders the western edge of State Road PR-149 (at an approximate elevation of 610 mts.). The roadside elevation is at an approximate elevation is approximate 15 to 20 meters higher than the Rivers stream bed. These difference in elevation creates very steep sloping ratios, varying between 45° to 54° degrees. These slope ratios are too steep considering the surface in-situ soils, which minimal surface runoff will trigger additional slides.

Also, field observations revealed the average total width of State Road PR-149 at the project sector is approximately 3.65 to 4.50 mts. (14 to 15 ft.) wide. This narrow road section limits the reconstruction alternatives to cope with the prevailing Site conditions.

Therefore, to cope with the presently disclosed subsoil conditions and to assure no further instability is experienced, the herein recommendation to be considered shall be applied along the western edge of PR-149 to render stable grounds and road safety. The herein recommendation by themselves and/or any combination of them shall be applied to the presently affected area

(western sloping grounds) to render stable grounds. The following sections of this report will provide the required Site improvements and foundation design recommendation for the proposed improvements required at the Site.

Considering the subsoil profile and slope ratios prevailing at the site, the improvement project may consider three (3) construction approaches or any combination of them. These are the following:

1. Evaluation of the Site conditions revealed, the existing road width is some 12 to 15 ft. wide and the affected area extends for an approximately 100 meters and the prevailing sloping grounds west of State Road PR-149, at the study sector, have slope ratios ranging between

45 to 54 degrees. These slope ratios are too steep considering the in-situ soil encountered.

Therefore, a cantilever retaining structure (with or without a slope section on top, if space is available) to retain the western soil embankment mass and State Road PR-149 pavement structure. The retaining wall shall be provided all-throughout the affected area parallel to the western edge of State Road PR-149. However, evaluation reveal the major slide presently considered is approximately 25.0 mts. in length. The total height of the wall will depend on the final wall alignment and grading elevations and if they are provided with an adequate

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slope section (2H:1V) on top, to reach the roadside elevation, however, preliminarily no space is available, therefore a cantilever wall by itself shall be considered.

2. As a second alternative, a retaining structure composed pre-drilled HP-steel piles with pre-cast panels to restrain the soil in between the piles may also be considered. The Steel HP-piles shall be spaced at 8.0 ft. on center approximately, installed along the western edge of

PR-149. These shall have a minimum embedment length of 25 ft. (measured from the existing road side elevation) shall be considered. A minimum unsupported length of 10.0 ft.

shall be considered by design, thus the total length of the pile sections shall be approximately

35 to 40 ft. It shall be noted that the final length and type of the HP steel-pile section will depend on the final wall alignment and grading elevations as well as the expected lateral loads, as the structural evaluation will reveal. Also, the pre-cast panels shall be designed to withstand the expected lateral earth pressures considering the in-situ soil parameters.

3. As a third alternative for the reconstruction of the western sloping grounds which may be consider is the use of a drilled shafts to support a prefabricated cantilever beam Segment

(“Dovela” in Spanish) on top to allow the expansion of the westernmost lane. This alternative can also be used all throughout PR-149, on existing narrow segments.

The drilled shafts spacing shall be determined based on the actual loading conditions required to withstand the expected loading conditions (dead and live loads). However, for cost estimate purposes, solely, 36”-inch diameter shafts spaced at 10 ft. on center can be considered until the final design scheme is established. They shall be installed parallel of

PR-149 at the crest of the western sloping grounds. These shall have a minimum embedment length varying between 15 to 25 ft. (measured from the existing road side elevation). A minimum unsupported length of 10.0 ft. to be considered by design have been preliminarily established. It shall be noted that the final length and type of the Drilled Shaft piles will depend on the final wall alignment and grading elevations as well as the expected lateral loads, as the structural evaluation will reveal.

Regardless of the final design alternative selected, new and/or additional drainage facilities of enough capacity shall be provided, based on hydrologic study. All surface water shall drain freely away from the embankment slope mass. Therefore, all surface water shall drain away from the embankment slope mass and/or diverted past the toe of the sloping grounds discharging into the

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Toro Negro River. Also, the bottom of the existing gullies shall be provided with coarse gravely materials to prevent erosion.

It is strongly recommended the installations of monitoring instruments to assess the lateral yielding of the soil embankment mass adjacent to the identified study zone until the complete reconstruction of the retaining wall system is completed.

The following section of this report will further discuss this alternative and will provided the foundation design parameters.

V. ENGINEERING RECOMMENDATIONS

The present geotechnical review revealed the re-construction alternatives can be implemented.

Evaluation of the Site conditions revealed, the existing road width is some 14 to 15 ft. wide and the affected area extends for an approximately 100 meters. Evaluations made revealed the prevailing sloping grounds south of State Road PR-149, at the study sector, have slope ratios ranging between 45 to 54 degrees. These slope ratios are too steep considering the in-situ soil.

Therefore, these steep sloping grounds shall be improved and/or provided with the retaining structures previously mentioned. The following sections of this report shall be used for the design of the herein recommended retaining structures.

5.1 General Design Parameters for Retaining Structures

Evaluation indicate that provided the proposed retention structure unit(s) are adequately embedded, beneath the upper loose, slope-washed and eroded surface layer, into the dense gravelly sandy clayey silt residual and weathered saprolitic material, an adequate global stability of the proposed retaining system can be obtained.

Considering the soil profiles found at the investigated locations the following parameters of in-situ soils may be used for the design of the proposed retaining systems:

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SUMMARY OF IN-SITU SOIL PARAMETERS FOR DESIGN

RECOMMENDED RANGE OF VALUES PER LAYERS

Soil Description Unit

Weight (pcf.)

Angle of Internal Friction (degrees)

Cohesion (psf.)

Allowable Soil Bearing Pressure

(psf.)

New Fill (A-2-4) 125 27 Neglect 2.0 Ksf.

New Fill

(Crushed-Stone) 133 33 Neglect

Upper Sandy silt, with gravel Soils

(0’-7.5’) 125 29 1,000

Residual Material sandy silt, trace clay, with rock fragments (7.5' -15')

130 32 - 4.5 Ksf. @ 11.0 ft.*

Weathered rock (>15’) 134 34 -

ADDITIONAL NOTES:

1. Complete removal of unsuitable soil and/or slope washed shall be guaranteed. By no means should the bearing material be soft/loose. However, any unsuitable material can be replaced with a well compacted engineering fill section, for which the allowable bearing capacity shall be not greater than 2.0 Ksf.

2. The minimum depth of foundation shall be measured from the existing grade.

3. Full hydrostatic conditions and surcharge loads imposed by the construction sequence and vehicular loadings, shall be considered by design.

Lateral earth pressure coefficients are given for the active and for the at-rest case, depending on whether the wall can rotate at the top or not. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The "at-rest" condition assumes no wall movement and is commonly used for basement walls, loading dock walls, or other walls restrained at the top.

The coefficient for lateral earth pressure, based on Rankine’s Theory, can be determined using the following formulas, however other methods and/or theories may be used as well, depending on actual retaining wall configuration.

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• Lateral Pressure Coefficient at rest case:

𝐾𝑜 = 1 − 𝑠𝑖𝑛 𝜙

• Coefficient Active Earth Pressure for sloping backfill:

𝐾𝑎 = cos 𝛽 cos 𝛽−√𝑐𝑜𝑠2𝛽−𝑐𝑜𝑠2 𝜙 cos 𝛽+√𝑐𝑜𝑠2𝛽−𝑐𝑜𝑠2 𝜙

• Coefficient Passive Earth Pressure for sloping backfill:

𝐾𝑝 = cos 𝛽 cos 𝛽+√𝑐𝑜𝑠2𝛽−𝑐𝑜𝑠2 𝜙 cos 𝛽−√𝑐𝑜𝑠2𝛽−𝑐𝑜𝑠2 𝜙

• Coefficient Active Earth Pressure for horizontal backfill for vertical face:

𝐾𝑎 = 𝑡𝑎𝑛2 (45𝜊 − 𝜙

1−𝑠𝑖𝑛 𝜙

1+𝑠𝑖𝑛 𝜙

• Coefficient Passive Earth Pressure for horizontal backfill for vertical face:

𝐾𝑝 = 𝑡𝑎𝑛2 (45𝜊 + 𝜙

1+𝑠𝑖𝑛 𝜙

1−𝑠𝑖𝑛 𝜙

The depth of foundation (Df) shall be compatible with the minimum depth requirements previously described. However, a re-compaction of the in-situ soil to a minimum of 95 % of its maximum dry density shall be allowed prior to the foundation construction.

To reduce hydrostatic loading on retaining walls, a subsurface drain system should be placed behind the wall. The drain system should consist of free-draining granular soils containing less than five percent fines (by weight) passing a No. 200 sieve placed adjacent to the wall. The free-draining granular material should be graded to prevent the intrusion of fines or provided with a suitable filter fabric.

A drainage system consisting of either weep holes or perforated drain lines (placed near the base of the wall) should be used to intercept and discharge water which would tend to saturate the backfill. Where used, drain lines should be embedded in a uniformly graded filter material and provided with adequate cleanouts for periodic maintenance. As an alternative, a prefabricated drainage structure, such as geo-composite (Macaferri MacDrain or equivalent), may be used as a substitute for the granular backfill adjacent to the wall.

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In addition, a perimeter drain shall be placed along the wall footings and drained away from the units to proper out falls. Underground water, if any, may flows beneath foundations, which are not adequately drained, creating unsuitable erosional effects on foundations. This aspect of the construction and design should not be overlooked.

Preferably, the backfill soil is to be clean, free draining coarse granular material (AASHTO A-1-a

Classification), placed in 2-inch to 3-inch layers, each compacted to at least 95% of the material's

Modified Proctor maximum density. However, under standard design criterion, the backfill for the wall should be granular (AASHTO A-2-4 or better), carefully placed and of good quality, above

1.0 m. from the maximum flood level; otherwise, crushed stone compacted to a minimum of 83 % of its bulk density shall be used for the reinforced back fill material.

5.1.1 Additional Considerations for Retaining Structures

Prior to the construction of any retention structure, the complete removal of any soft/loose, unsuitable saturated soil, slope-wash and/or debris shall be allowed prior to the back filling, which shall be done in stages, considering the back-filling recommendations contained in this report.

Also, it is of upmost importance to take all precautions during the excavation procedures to assure slope stability during construction, especially during the excavation phase. To prevent further instability of existing slope surfaces the herein construction sequence shall be performed in alternate improvement (two-stage) sections of not more than 15.0 ft. wide.

The initial stage is to remove any unstable surface material in benches to create a level area on which to rest the proposed retaining structure alignment. Once the initial demucking operation is performed and the over excavation to prepare the foundation base is completed, then the retaining wall foundation can commence.

Also, considering the proposed retaining structure foundation unit may lie on sloping grounds surfaces, the depth of foundation on these circumstances shall be compatible with a minimum depth requirement such that a line drawn from the bottom edge of the foundation at an angle () of 30⁰ and at a horizontal distance (t) of 15 ft. from the sloping surface do not intersect with the face of the slope. Refer to the following Figure A.

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FIGURE A: Footing in Sloping Grounds

NOTE: The footing depth on sloping grounds shall satisfy a minimum separation requirement such that a line drawn from the bottom edge of the foundation at an angle () of 30⁰ and at a horizontal distance (t) of 15 ft. do not intersect with the face of the slope.

Should the proposed foundation do not meet the minimum separation requirement, deepening of the foundation shall be required. Also, a structural key or soil/rock anchors may be provided to the foundation to avoid the translation of the foundation stresses to the sloping grounds and provide an additional sliding retraining measure. However, the prevailing slopes to remain shall be protected against scour and erosional effects during an intensive rainfall and flooding events.

5.2 Additional Recommendations for Cantilever Retaining Structures

As previously mentioned, a cantilever type retaining structure to retain the western soil embankment mass, pavement and any existing structures, if any, may be considered. The retaining wall shall be provided all-throughout the affected area parallel to the western edge of

State Road PR-149.

The retaining wall shall be provided all-throughout the affected area, some 25 meters long, parallel to the northwestern edge of State Road PR-149. Evaluation dictate the retaining structure shall be some 25 meters long, approximately. Preliminary evaluations dictate that if the proposed wall is installed some 2.0 meters from the western edge of PR-149 (at an elevation of 122.5 approx.) an 18.0 ft. (approx.) high wall would result, considering the bottom foundation elevation is placed at an elevation of 119.15 mts. Regardless, the minimum depth of foundation (Df) shall

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be 11.0 ft., into the in-situ residual and weathered material, however the total height of the wall will depend on the final wall alignment and grading elevations and if they are provided with an adequate slope section (2H:1V) on top, to reach the roadside elevation, should space be available.

The initial stage is to remove the unsuitable surface material to create a level area on which to rest the base of the new retaining structure. The base of foundation of the proposed retaining structure shall be located at a depth which complies with the following criteria:

1. Once the cuts are made and the desired foundation pad is prepared, the base of the retention structure shall be located at a minimum depth of 11.0 ft., beneath any loose/soft saturated and slope-wash material.

2. The base backfill material, if any, shall be placed above the level of the pre-worked foundation pad in the firm in-situ dense residual or weathered material. For such purposes an inspection of the exposed material shall be allowed during the construction sequence.

Also, considering the proposed retaining structure foundation unit may lie on sloping grounds surfaces, the depth of foundation on these circumstances shall be compatible with a minimum depth requirement given in Section 5.1 - General Design Parameters for Retaining Structures.

Should the proposed foundation do not meet the minimum separation requirement, deepening of the foundation shall be required. In lieu, a structural key or soil/rock anchors may be provided to the foundation to avoid the translation of the foundation stresses to the sloping grounds and provide an additional sliding retraining measure.

5.3 Additional Recommendations for a Sheet Pile Retaining System

As a second alternative, a retaining structure composed pre-drilled HP-steel piles with pre-cast panels to restrain the soil in between the piles may be considered. The Steel HP-piles shall be spaced at 8.0 ft. on center approximately. They shall be installed along the western edge of PR-

149. These shall have a minimum embedment length varying between 15 to 25 ft. (measured from the existing road These shall have a minimum embedment length of 25 ft. (measured from

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the existing road side elevation) shall be considered. A minimum unsupported length of 10.0 ft.

shall be considered by design, thus the total length of the pile sections shall be approximately 35 to 40 ft. It shall be noted that the final length and type of the HP steel-pile section will depend on the final wall alignment and grading elevations as well as the expected lateral loads, as the structural evaluation will reveal. Also, the pre-cast panels shall be designed to withstand the expected lateral earth pressures considering the in-situ soil parameters.

Another possible solution to be considered is the installation of a combined system composed of

Pre-drilled Steel HP-Piles with precast or cast-in-place concrete lagging panels, at 8.0 ft. on center, can be considered to restrain and restrict the embankment soil, existing structures movement (i.e. Pavement Structure) and the soil in between the piles. Considering the subsurface conditions at the site, where the residual and saprolitic material was found as shallow as 1.5 ft., the pre-augering to encase the Steel-HP Piles shall be required to encase the Steel HP piles section with poured concrete.

The wall shall be located at a distance from the southern edge of PR-149 such that it encases the proposed fill embankments, perpendicular to the slope failure. Evaluation dictate the retaining structure shall be some 20 to 25 meters long, installed at approximately 2 meters (at an elevation

= 122.5 mts. approx.) of the west from the crest of the road embankment. However, the final location, configuration, length and height shall be determined once the final design scheme is selected by the A/E Design Team.

For piles to be effective they should have a minimum embedment length varying between 25 to

35 ft. into the residual and completely weathered rock found in the borings of exploration. A minimum unsupported length of 10.0 ft. shall be considered by design, thus the total length of the pile sections shall be approximately 35 to 45 ft. It shall be noted that the final length and type of the HP steel-pile section will depend on the final wall alignment and grading elevations as well as the expected lateral loads, as the structural evaluation will reveal. The pile units shall develop the necessary lateral resistance to sustain the earth and structure loads, assuming full mobility of the soil shear strength. Therefore, the final length and type of the pre-drilled HP steel-pile sections shall depend on the expected lateral loads and final grading elevations of the project.

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Also, the precast or cast-in-place lagging panels shall withstand the expected lateral earth pressures, assuming full hydrostatic conditions and surcharge forces imposed by the construction sequence and vehicular loadings.

Once the combined retaining system is installed, then the re-construction of the pavement structure components can commence.

5.3.1 Lateral Load Design Considerations

The following design model shall be used in the foundation design for lateral load evaluations of the proposed Steel HP Piles. For lateral calculations, an unsupported length of the upper 10 ft.

shall be considered in the evaluation. Should the structural evaluation reveal the expected deflection at the top of the pile is too excessive, the larger pile sections, smaller spacing in between piles and/or providing Deadman, beneath the PR-146 Pavement Structure, may be considered to cope with the expected lateral loads.

Lateral load evaluations depend on the specific requirements of the structure. Often, a 1/4-inch allowable lateral deflection is used as a limit. In no case, the lateral load shall exceed 0.33 the ultimate load capacity. The normally consolidated to slightly over consolidated cohesive as well as for granular soils, the pile deformation can be estimated assuming that the coefficient of sub grade reaction Kh, increases linearly with depth in accordance with the expression:

Kh = f * z / D

Where, Kh = coefficient of lateral subgrade reaction (tons/ft.3) f = coefficient of variation of lateral subgrade reaction (tons/ft.3) z = depth (ft.)

D = width/diameter of loaded area

Profile Design Model - Considering the field and laboratory test data, we can establish the soil parameter for lateral load design. The following table presents a summary of the soil parameters to be used in the lateral design evaluations.

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SUMMARY OF SOIL PARAMETERS FOR LATERAL PILE DESIGN

Sector Covered By

Borings

Extend of Depth Below Existing

Ground Surface (ft.)

Shear Strength

Value (psf.)

Coefficient of Variation of Lateral Subgrade Reaction (f)

(tons/sq.-ft./ft.)

227-1 through 227-4 0’ to 10’ neglect Disregard (Consider unsupported)

10’ to 15’ neglect 40 Deeper than 15’ - 50

Compacted Engineered Fill

(A-2-4) - 500 25

Consideration of the loading conditions using the above design models is required to calculate the allowable deflection of the pile top or the pile stresses. The determination of the lateral capacity and deflection shall be based on actual finite element analyses of the rod element embedded in the above soil design model.

All estimated depths are measured from the existing ground surface, prevailing during the period of the field work. A minimum penetration of 20 ft. into the residual and completely weathered material is been required.

5.4. Additional Recommendations for a Drilled Shaft Retaining System

Another reconstruction alternative for the northern sloping grounds which may be consider is the road expansion by using drilled shafts to support a prefabricated cantilever beam Segment

(“Dovela” in Spanish) on top. The cantilever beam would allow the expansion of the westernmost lane. This alternative can also be used all throughout PR-149, on existing narrow segments.

However, the actual length of road improvement using this alternative shall be determined by the

A/E design team.

The drilled shafts spacing shall be determined based on the actual loading conditions required to withstand the expected loading conditions (dead and live loads) in addition to the moments generated by the eccentricity of the cantilever beam segment (“Dovel”).

Preliminarily, 36”-inch diameter shafts spaced at 10 ft. on center can be considered until the final design scheme is established. They shall be installed parallel of PR-149 at the crest of the western sloping grounds. These shall have a minimum embedment length varying between 20

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to 30 ft. (measured from the existing road side elevation) into the residual and completely weathered rock found in the borings of exploration. A minimum unsupported length of 10.0 ft. to be considered by design have been preliminarily established. It shall be noted that the final length and type of the Drilled Shaft piles will depend on the final wall alignment and grading elevations as well as the expected lateral loads, as the structural evaluation will reveal.

Considering the subsurface conditions at the site, where the dense residual and saprolitic material was found as shallow as 3.0 ft., special drilling equipment to obtain the minimum embedment length shall be required.

The pile units shall develop the necessary lateral resistance to sustain the earth and structure loads, assuming full mobility of the soil shear strength. Therefore, the final length and type of the

Drilled Shafts shall depend on the expected lateral loads and final grading elevations of the project.

It shall be noted that the final length, diameter and quantity of the Drilled Shaft piles will depend on the final wall alignment and grading elevations as well as the expected lateral loads and final grading elevations of the project. In the case the expected loading conditions surpass the herein provided, then the project’s structural engineer shall contact the undersigned and request additional recommendations for larger diameter shafts.

5.4.1 Drilled Shaft Types and Capacities

The following Table presents a summary of foundation types and allowable capacities which may be considered.

SUMMARY OF DRILLED SHAFT FOUNDATION PARAMETERS

Compression Capacity:

Drilled Shaft Diameter (inches) & Type

Length in ft., from existing surface

Allowable Carrying Capacity Per Unit in tons

36” Drilled Shaft 25 ft. 180 tons

Uplift Capacity:

Drilled Shaft Diameter (inches) & Type

Predicted Length in ft., from existing surface

Allowable Tension Capacity Per Unit in tons

36” Drilled Shaft 25 ft. 100 tons

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The herein predicted lengths of the foundation units have been given from existing surface elevation, prevailing during the period of the field work. The actual lengths of the foundation units shall be considered the grade variations prevalent at the time of the pile installation. Regardless, these shall be embedded into the residual silty clay material found.

5.4.2 Additional Drilled Shaft Recommendations

The following recommendation shall also be considered.

1. Any groundwater should be removed from each pier hole prior to concrete placement.

A dewatering system shall be installed which will permit proper excavation, inspection and concreting of each pier unit.

2. Pier concrete should be placed immediately after completion of drilling and cleaning. A tremie should be used for concrete placement. Free-fall concrete placement in piers will only be acceptable if the concrete is placed in a dry hole and provisions are taken to avoid striking the concrete on the sides of the hole or reinforcing steel. The use of a bottom-dump hopper, or an elephant's trunk discharging near the bottom of the hole where concrete segregation will be minimized, is recommended. Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. The free unobstructed fall of concrete with a minimum slump of 2.5

in. produces adequate compaction up to the top 5 ft. of depth. Additional details are presented in ACI 336.3R-72.

3. Casing should be withdrawn in a slow continuous manner maintaining a sufficient head of concrete to prevent infiltration of water or caving soils or the creation of voids in pier concrete. Pier concrete should have a relatively high fluidity when placed in cased pier holes or through a tremie. Pier concrete with slump in the range of 5 to 7 inches is recommended.

4. If the center-to-center spacing of drilled shafts is less than 4 diameters, the interaction effects between adjacent shafts shall be evaluated. Adjacent shafts should bear at the same elevation. The capacity of individual piers must be reduced when considering

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the effects of group action. Capacity reduction is a function of pier spacing and the number of piers within a group.

5. If the center-to-center spacing of drilled shafts is less than 6 diameters, the sequence of construction should be specified in the contract documents. Larger spacing may be required to preserve shaft excavation stability or to prevent communication between shafts during excavation and concrete placement.

6. The project’s geotechnical engineer or approved representative shall observe the bearing surface and shaft configuration during construction.

7. If caving is predicted steel casing shall be required to properly drill the piers prior to concrete placement.

5.4.3 Lateral Load Design Considerations

For lateral load evaluations of the proposed Drilled Shafts Piles the parameters for lateral pile design given above can be considered.

5.4 Earthquake Design

Based on our experience with the geology of the area, it is our opinion that the subsurface characteristics reflect those of Site Class E as described in International Building Code 2018 and the Puerto Rico Building Code 2016. The “Site Class” is a designation used by the 2018

International Building Code (IBC) (ICC 2018) to quantify ground motion amplification.

Spectral Response Acceleration of 96% of g. (probability of exceedance of 2% in 50 years) is identified for the Municipality of Ciales. Considering the soil conditions and final grading, a site class “C” can be used for planning purposes. However, for structures where foundations bearing into the residual and weathered rock material a Site Class “C” shall be used.

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The Soil Profile Types shall be used for the determination of the base shear of the structure units’ and shall be as follows:

Soil Profile Types

Sector Covered Range of Depths (ft.) Soil Type

227-1 through 227-4 0’ to 9’ SD 9’ to 15’ SC Deeper than 15’ SC

5.5 Excavations

For most parts of the project, shallow excavations to remove the soft slope-wash material can be performed using backhoe equipped with a short tip radius and narrow bucket. However, high resistance to penetration values were found as shallow as 3.0 ft., beneath existing grade within the upper horizon at the presently investigated locations. The extent of depth where the Standard

Resistance to Penetration (N-values) exceeds 40 blows/foot is where difficulty in the trench excavations is predicted.

A careful review of the geological plans with the herein enclosed profile information would assist the planners in the selection of the adequate cutting equipment of the project.

Although difficult to excavate materials were encountered in all Borings of exploration. Therefore, they will be encountered as shallow as 6.0 ft. Very dense soil and weathered rock typically require loosening by ripping with large dozers pulling single tooth rippers in mass excavation or possibly blasting in confined (trench) excavation. Ripped weathered rock fragments can be re-used and mixed into engineered fill, provided that it is pulverized to less than 4”-inches in diameter and mixed with soil to create a well graded fill material.

It should be noted that frequent occurrence of consolidated materials, cobbles and rock fragments within the profiles above the foundation excavation will increase both the time and cost of the operations. Boulders, if any, will likely need to be reduced in size prior to be reused as backfill material or hauled off site. Some additional effort may be necessary to extract boulder sized materials, particularly in deep narrow excavations.

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Excavation techniques will vary based on the degree of weathering of the materials, fracturing and jointing in the rock, and the overall stratigraphy of the feature. Excavation of auger refusal material (i.e.