Geotechnical Report - HWY-221.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-146, KM 19.3 on Cordillera Ward of the Municipality of

Ciales, Puerto Rico.

Reference No. DA/18O3741

PROJECT ID: ER-HWY-221

January 20, 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 20, 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 ER-HWY-221 at State Road PR-146, KM 19.3 on Cordillera Ward of the Municipality of Ciales, Puerto Rico. Reference No. DA/18O3741

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-221, at State Road PR-146, KM 19.3 on Cordillera 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/04-09-18R 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 Cantilever Retaining Structure Foundation Recommendations

5.3 Additional Recommendation for a Reinforced Soil Wall

5.3.1 Steps for Geogrid Reinforcement Selection

5.4 Additional Recommendations for a Sheet Pile Retaining System

5.4.1 Lateral Load Design Considerations

5.5 General Slope Surfaces Recommendations

5.5.1 Summary of General Construction Guidelines for the Slope Improvements

5.6 Earthquake Design

5.7 Excavations

5.8 Earthwork Recommendations for Fill and Cut Sections

5.8.1 Fill Sections

5.8.2 Temporary Cut Sections

5.9 Additional Earthwork Recommendations

5.9.1 Recommended Fill Types and Compaction Specifications

5.10 Proposed Storm Water Run-off Control

5.11 Nearby Structures

5.12 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) - Fill Specifications Appendix (2-A) - Benching 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-221, at State Road

PR-146, KM 19.3 on Cordillera 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/04-09-18R 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 two (2) major slides occurred along the southern edge of State

Road PR-146, these landslides scarps caused the partial rupture of the pavement structure and

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the collapse of an electric pole located on the southern edge of State Road PR-146, near KM

19.3, after the passing of Hurricane Maria.

Based on the US Topographic map a drainage gully running almost perpendicular to State Road

PR-146 (at an approximate elevation of 358 mts.) exists where the landslide occurred. This drainage gully is an affluent, which drains surface flows from the highland sectors toward the

Cialito River found east-southeast of the project site, some 1030 meters southeast of the site.

Water runoff along this drainage gully triggered the instability of the sloping grounds.

Therefore, to cope with the presently disclosed subsoil conditions and to assure no further instability is experienced, the herein recommendation shall be applied along the southern edge of PR-146 to render stable grounds and road safety. The herein recommendation by themselves and/or a combination of them shall be applied to the presently affected area (southern sloping grounds) to render stable grounds. 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 two (2) standard penetration test borings performed to assess the existing subsoil conditions at the project site. The location of

Boring No. 4 was established on the northern sloping grounds, some 4.5 meters north of PR-181 road edge. The location of borings is shown in the accompanying Boring Location Plans, in

Appendix A, Figure No. 2.

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.

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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 Florida Quadrangle

(Map 12221-C), prepared by Mr. A. E. Nelson and W. H. Monroe C (1962-63), the geologic units that lie at or near the site are the following:

1. San Sebastian Formation (Ts) – Described as mostly pale red clay, with abundant pebbles of volcanic rock.

2. Landslide Deposits (Ql) - Described as clay and sand with boulders as large as 5 meters in dimension. Large deposits result chiefly from slow earth and rock flow on moderately to deeply weathered slopes.

3. Lares Limestone (Tl) – Described as Massive hard crystalline pale-orange to neary white locally coralline limestone

4. Pozas Formation (Kp) - Described as mostly grayish volcanic breccia and some conglomerate volcanic sandstone, siltstone, and crystal tuff.

The approximate Unnamed Fault (dashed), was identified at about 482 feet, southwest of the site, having a southeast alignment and downthrown to the east, it starts near State Road PR-146, at

Hacienda Santa Helena. Several additional approximate Unnamed Faults lines are shown in the

Geologic map, with a near east south trend and intersecting the Cialitos River south from the study area.

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

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3.3 Stratigraphic Units

Upper Surface Section – Generally at the road surface, the results of the exploration disclosed a surface layer thickness of about 4.0 to 6.0 ft. in depth. Following the six (6”) inch asphalt overlay, the surface layer is composed of a mixture of clay, sand, and silt, with some subangular gravel fragments, with varying colors: brown, brownish yellow, and pink. Also, at the location of Boring

221-2 calcareous limestone rock fragments were disclosed, probably used as the base course of the pavement section, however these were not found on Boring 221-1. The standard resistance to penetration (N-values) of the surface layers varied from 25 to 46 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 221-1- from 0.0’ to 4.0 ft.] disclosed AASHTO class type A-6 (7) AASHTO type soils (USSCS type CL-Sandy lean clay); the results of the Free Swell

Test show a 20 percent.

Following the upper surface layer, a light yellowish brown, light gray silty clay with traces of sand and subangular gravel fragments were encountered. This second layer extends up to 6 ft. in depth. The standard resistance to penetration (N-values) of the surface layers varied from 13 to

30 blows/foot, at a stiff to very stiff State of Consistency. The natural moisture content values range from 13 to 14 percent. Random samples from this horizon disclosed A-7-6 (21) [ML –

USCS] on Borings 221-2. The Standard Free Swell determination tests performed on this samples disclosed value of 30 percent, where a moderately high shrink/swell potential is predicted.

Based on the US Soil Conservation Manual (Sheet 37), south of State PR-146, the surface virgin soils are identified as Alonso clay 40 – 60 percent slope, eroded (AoF2). These were described to be on side slopes and ridgetops on humid uplands. They are deep and well drained and are formed in fine textured residuum weathered from basic volcanic rocks. They are described as friable sandy loam, and strongly acid. They have a moderate permeability and the available water capacity is high. The runoff is very rapid. Most of the its original surface layers has been removed by erosion.

To the north of State PR-146, the surface soils are identified as Rock outcrop- Tanamá Complex, 12 – 60 percent slope (RtF); The complex consists of areas of soils on hills. The complex is about

65 percent exposed rock, 30 percent moderately steep to very steep Tanamá soils and 5 percent

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other soils. Typically, the surface layer of the Tanamá soils is dark reddish-brown firm clay about

5-inches thick. The subsoil is mainly dark reddish brown and yellowish red clay 11-inches thick.

Limestone bedrock is at depth of 16-inches. They have moderate permeability and low available water capacity and runoff is rapid.

Residual Material – Beneath the above described layers, the residual material was found, extending from about 6 ft. to about 20 ft. [Boring 221-1] and to about 23 ft. [Boring 221-2] in depth.

These were described as brown, pale red, brownish yellow, with mottles white silty sand with traces of subangular gravel fragments. The standard resistance to penetration (N-values) of the residual layers varied from 42 to 80 blows/foot, at a dense to very dense State of Compactness.

The natural moisture content values range from 12 to 15 percent. Random sample of the residual material from both boring of exploration, disclosed AASHTO class type A-6 (3) and A-6 (2) soils

(USSCS type SC-Clayey sand, with gravel).

Completely Weathered Rock - At the deeper explored depths, until the borings were bottomed a weathered rock was broken by the sampling device into yellowish brown, light gray and pale red and white mottled sandy silt fines with traces of volcanic sandstone, siltstone, and crystal tuff fragments, product of the weathering of the parent geologic units was found. The standard penetration test attempts varied from 118 blows/foot to practical refusal to penetration with values greater 75 blows for a few inches of penetration. The natural moisture contents range from 10 to

16 percent. Random sample of this horizon disclosed AASHTO class type A-6 soils (USCS type

SC – Clayey sand).

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

(1) to this report.

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.

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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 southern sloping grounds, where landslides scarps have been experienced on the southern edge of State

Road PR-146, which was subjected to extensive degradation, erosional effects, and landslides causing the observed damages and rupture of the road embankment and pavement structure and existing infrastructures.

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 runoff, which caused the oversaturation (reducing the shear strength), and erosion of the lower southern sloping ground subsurface silty sand and sandy silt soils. The oversaturation of the underlaying clayey soils triggered a reduction of the shearing strengths causing unbalance conditions causing slope failure. Also, the intense or above normal erosional conditions experienced during Hurricane Maria was another primary factor which caused the prevailing conditions.

In addition, evaluation of the topographic plan submitted for the present evaluation revealed, the prevailing sloping grounds have slope rations varying between 39° to 41° degrees. These slope ratios are too steep considering the surface in-situ soils.

Therefore, to cope with the presently disclosed subsoil conditions and to assure not further instability is experienced, the herein recommendation shall be applied along the southern edge of PR-146 to establish stable grounds and road safety. The herein recommendation by themselves and/or a combination of them shall be applied to the presently affected area (southern sloping grounds) to render stable grounds at the study area. The following sections of this report will provide the required Site improvements and the foundation design recommendation for the herein proposed re-construction alternatives.

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Considering the subsoil profile and slope ratio prevailing at the site the southern sloping grounds shall be reconstructed all-throughout the study sector. However, considering the extent of the repair process this alternative may not be cost effective. Therefore, three (3) re-construction approaches or a combination of them may be considered. These are the following:

1. Evaluation of the site conditions and the prevailing subsoil conditions, a cantilever retaining structure (with or without a slope section on top) to retain the south soil embankment mass and any existing structures (i.e. State Road PR-146 pavement structure). The retaining wall shall be provided all-throughout the affected area(s) parallel to the south edge of State Road

PR-149. Evaluation dictate the retaining structure(s) shall be some 40 meters long, approximately to cover the complete distressed area. However, if two (2) retaining structures are contemplated to cover localized areas, solely, then the approximate lengths to cover the two (2) main distressed areas shall be some 22 and 15 meters, respectively. 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 (358.5 mts. approximately on average).

2. As a second alternative which may be considered is the use of Reinforced Soil Wall using biaxial or triaxial geogrids (i.e. Tensar Geogrids or equivalent). However, this alternative requires enough space to place the required geogrids behind the wall, thus prior to its selection definite assurance that enough space is available to place the minimum required lengths of geogrids shall be guaranteed.

The final length of the geogrids is a function of design, however for cost estimate purposes a minimum embedment length of 0.75 to 0.80 times the height of the wall and a minimum anchorage length passing the failure plane of 5.0 ft. shall be considered. The overall length from the face of the wall to the tail of the geogrids is assumed to be constant throughout the height of the wall structure (square-like).

Once the reinforced backfilling operations are completed, surface erosion protection countermeasures shall be provided throughout the rest of the sloping surfaces (i.e. rip rap, or equivalent).

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3. A possible solution to be considered is the installation of a Combined System composed of

Pre-drilled Steel HP-Piles (with the same minimum length varying between 20 and 30 ft.) with precast or cast-in-place concrete lagging panels to retain 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 6.0 ft., the pre-auguering to encase the Steel-HP Piles shall be required.

If the embankment movements are not restrained, additional earth movements may further affect State Road PR-146. It shall be noted that the final length, type and quantity of pre-drilled HP steel-pile sections and lagging panels shall depend on the final location, expected lateral loads and final grading elevations of the project.

Regardless of the final solution to be implemented the installation of adequate drainage facilities to divert the surface runoff away the sloping surfaces shall be MANDATORY. Drainage facilities of enough capacity shall be provided to carry all surface water away from the embankment slope mass all the way to the toe of the northern sloping grounds, or at least 200 ft. past the proposed retaining structures. Also, the surface of the existing gullies shall be provided with coarse gravely materials or even rip rap, reno mattress or similar erosion protection to prevent further erosion.

Also, 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 aforementioned re-construction alternatives can be implemented. Evaluation of the Site conditions revealed, the existing road width is some 16 ft.

wide and the affected area extends for an approximately 40 meters. Evaluations made revealed the prevailing sloping grounds south of State Road PR-146, at the study sector, have slope ratios

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ranging between 39 to 41 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:

TABLE NO. 1 - SUMMARY OF IN-SITU SOIL PARAMETERS FOR DESIGN

Recommended Range of values in layers for Borings 221-1 & 221-2

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

Clayey Soils (0’-6’)

110 23 800

Residual Material (6' -20')

121 25 - 3.5 Ksf. @ 7.0 ft.*

Weathered rock (>20’)

129 32 -

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.

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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.

• 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

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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 geocomposite (Macaferri MacDrain or equivalent), may be used as a substitute for the granular backfill adjacent to the wall.

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 debris shall be allowed prior to the back filling, which

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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.

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

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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 Cantilever Retaining Structure Foundation Recommendations

As previously mentioned, a cantilever type retaining structure to retain the southern soil embankment mass and any existing structures (i.e. State Road PR-181 pavement structure) may be considered. The retaining wall shall be provided all-throughout the affected area parallel to the southern edge of State Road PR-146.

Evaluations dictate the retaining structure shall be some 30 to 40 meters long shall be required.

Estimates made revealed if the Cantilever wall is installed some 13.5 ft from the south edge of

PR-146, then a shorter wall will result (some 18 ft.). The remainder distance to reach the road side elevation may be provided on top with a slope ratio of 2H:1V, maximum. The minimum depth of foundation (Df) shall be placed at 7.0 ft. (minimum) from the existing ground elevation, into the in-situ residual and weathered material, after any loose/soft soil and slope washed material is removed. Preliminary evaluations dictate the base of the foundation shall be at an elevation of approximately 353.0 mts. However, the actual bottom footing elevation, and total height of the wall will depend on the final wall alignment and grading elevations of the project.

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 7.0 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.

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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. 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.

5.3 Additional Recommendation for a Reinforced Soil Wall

Depending on the project’s requirements the improvements of the southern sloping grounds and pavement structure may also consider the use of Reinforced Soil Wall. However, this alternative requires enough space to place the required geogrids behind the wall, thus prior to its selection definite assurance that enough space is available to place the minimum required lengths of geogrids shall be guaranteed. Depending on the final wall alignment it may be necessary the partial closure of State Road PR-146.

Evaluation revealed if the Soil reinforced wall’s base is installed at an elevation of 355.00 meters, some 14.0 ft from the south edge of PR-146, enough space may be available to place the geogrids for a wall of 8.0 ft. to 10.0 ft., then a low wall may be installed with the pavement section on top of its base until reaching the road side elevation (varying between 358.4 to 358.9 mts.). The low retaining wall may also be used as a Jersey barrier.

The final length of the geogrids is a function of design, however for cost estimate purposes a minimum embedment length of 0.75-0.80 times the height of the wall and a minimum anchorage length passing the failure plane of 5.0 ft. shall be considered. The overall length from the face of the wall to the tail of the geogrids is assumed to be constant throughout the height of the wall structure.

Geogrid reinforcements used in conjunction with the soil, enable the soil to perform better than it would in its unreinforced state. Geogrids enable soils to accommodate greater loads and stand at steeper angles. The geogrids are laid horizontally within the compacted soil mass during

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construction, reinforcing it due to their high tensile strength, low strain and good interaction with the inter-layered compacted soil. Soil reinforced slopes and structures can accommodate differential settlement far better than more rigid solutions.

This alternative entails the complete removal and replacement of any slope-wash and debris which may be found. The new reconstructed reinforced sloping grounds shall be constructed with a reinforced engineered backfill using biaxial or triaxial geogrids (i.e. Macaferri, Tensar Geogrids or equivalent).

The herein recommended reinforced soil wall shall be provided with an external facing to restrain the reinforced soil. Maccaferri Terramesh, Green Terramesh, Sierra Scape or equivalent products provide the flexibility of soil reinforcement with the benefit of a modular system. With factory fitted face elements, geogrid reinforcement and with pre-determined dimensions, these systems significantly reduce on-site installation times, which is beneficial on these types of projects were time is of upmost importance. Regardless, of the type of facing to be selected the most important requirements to consider is their ability to resist environmental weathering (i.e.

corrosion, etc..).

The reinforced soil fill and replacement fill shall be placed in lifts not exceeding 8”-inches (when loose) and compacted to a minimum Modified Proctor Density of 98 % and 95%, respectively.

The replacement fill shall be granular A-2-4 or better AASHTO type and compacted to not less than 95 % of its maximum proctor density test. However, the reinforced soil fill shall be A-1-b or better AASHTO type compacted to 98 % of its maximum modified proctor density.

Once the reinforced backfilling operations are completed, surface erosion protection countermeasures shall be provided throughout the rest of the sloping surfaces (i.e. rip rap, or equivalent), if any.

The design parameters given in the previous section of this report can also be used for the

Reinforced Soil Wall.

5.3.1 Steps for Geogrid Reinforcement Selection

The following steps can be used for the wall design as follows:

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1. Determine the total external force required to be applied to the face of the wall, to achieve the target Factor of Safety (FOS) for the wall;

2. Distribute the total force from crest to the toe of the slope;

3. Determine the required geogrid strength, based on the force near the slope toe;

4. Select a suitable geogrid type from available products, based on the geogrid tensile strength and applicable reduction factors;

i. The following reduction factors can be applied to the tensile strength

1. Reduction factor for installation damage in gravel and sand (RFID)

2. Reduction factor for creep in design life (i.e. 120 years) (RFCR)

3. Reduction factor for durability (RFD)

4. The total reduction factor is calculated as:

R = RFCR × RFID × RFD

5. Detail the geogrid dimensions, including vertical spacing and length; and

6. Check the wall slope stability at static and seismic conditions to finalize the design.

The design steps described above, a Tensar, Macaferri or equivalent high-density polyethylene product, can be selected for soil reinforcement. Equivalent geogrid products by other manufacturers can be used; however, any substitutions shall be approved by projects Structural Engineer of record.

Under standard design criterion, the replacement fill shall be granular A-2-4 or better ASHTO type and compacted to not less than 95 % of its maximum proctor density test carefully placed (in 6-to 8-inch lifts). However, in areas where oversaturation is expected, if any, the backfill material is to be clean, free draining coarse crushed-stone material, compacted to at least 83% of the material's Maximum Bulk Density.

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Once the complete replacement of the reinforced soil embankment is completed, surface erosion protection countermeasures shall be provided up to the crest of the new embankment slope, until meeting the northern edge of State Road PR-181. Thus, the exposed upper slope surface, if any, shall be protected using surface MacMat R, BioMAc, MacGrid T or similar.

Also, drainage facilities of enough capacity shall be provided, on every elevation contour to carry all surface water away from the embankment slope mass all the way to the toe of the proposed reinforced soil embankment mass, at least 200 ft. past the proposed retaining structures. Also, the surface of the existing gullies shall be provided with coarse gravely materials or even rip rap, reno mattress or similar erosion protection to prevent further erosion. Neglecting to provide these drainage facilities it is possible future slides will develop due to the oversaturation and surface erosion.

5.4 Additional Recommendations for a Sheet Pile Retaining System

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 6.0 ft., the pre-auguering 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-146 such that it encases the proposed northern fill embankment, perpendicular to the slope failure. Evaluation dictate the retaining structure shall be some 30 to 40 meters long, installed at approximately 2 meters (ELE

= 356.41, approx..) of the south from the crest of the prevailing slide scarp. 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 20 to

30 ft. (measured from the existing road side elevation, ELE = 358.50 mts. approximately) into the residual and completely weathered rock found in the borings of exploration. A minimum

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unsupported length of 10.0 ft. shall be considered by design. 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.

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.

5.4.1 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

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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.

TABLE 2 - SUMMARY OF SOIL PARAMETERS FOR LATERAL PILE DESIGN

Sector Covered By

Boring

Extend of Depth Below Existing

Ground Surface (ft.)

Shear Strength

Value (psf.)

Coefficient of Variation of Lateral Subgrade Reaction (f)

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

310-4 0’ to 10’ neglect Disregard (Consider unsupported) 10’ to 20’ neglect 30 Deeper than 20’ - 45

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.

5.5 General Slope Surfaces Recommendations

As part of the require Site’s improvements it may be necessary to improve adjacent slope surfaces. Thus, the initial stage is to remove any unstable surface material in benches, to create a level area on which to rest an adequate bearing platform for the new backfill material up to the desired grade until meeting the existing crest of the proposed slope.

Based on the present exploratory program, the depth of removal shall involve a minimum thickness of about 3.0 to 6.0 ft., measured from the existing surface. However, special care not affects existing structure during the excavation process shall be guarantee. Upmost importance shall be given to protect existing structures from any lateral yielding and/or settlement of their foundation.

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The criterion contained for benching on existing grounds contained in Appendix 2-A of this report shall be strictly followed. Each bench after surface loose soil removal shall be provided with a surface stabilization fabric to assure that subsequent erosion during the construction sequence does not alter the working surface on which the remaining backfill material shall be constructed.

A Heavy-Duty Stabilization Fabric (i.e. TerraTex HD or similar), to prevent soil intrusion into the under soil shall be provided between the backfill material and the exposed dense silty sand soil at each bench.

Any slope reconstruction shall consider slope ratios not steeper than 2H:1V. However, the complete removal and replacement of the upper 3.0 to 6.0 ft. of unsuitable loose and slope-washed material shall be allowed and provided with surface slope ratios not greater than 2H:1V.

The removal operation of the surface material shall be done under the direct supervision of a Soil

Engineer or approved representative, who would establish the vertical extension of removal.

Under standard design criterion, the replacement fill shall be granular A-2-4 or better ASHTO type and compacted to not less than 95 % of its maximum proctor density test carefully placed (in 6-to 8-inch lifts).

Once the complete replacement of the soil embankment is completed, surface erosion protection countermeasures shall be provided up to the crest of the new embankment slope. Thus, the exposed upper slope surface using surface MacMat R, BioMAc, MacGrid Tor similar shall be provided.

Also, drainage facilities of enough capacity shall be provided, to carry all surface water away from the embankment slope mass. As a minimum French Drain, along same elevation benches shall be provided to drain subsurface runoff away from the soil embankment mass. Neglecting to provide these drainage facilities it is possible additional slides will continue to be experienced due to the oversaturation and surface erosion.

5.5.1 Summary of General Construction Guidelines for the Slope Improvements

Some of the engineering guideless for the project, which shall be considered during the re-construction of the roadway soil embankment mass, are the following:

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1. The initial stage is to remove the unstable surface loose material from scarp surfaces and from the toe of the slope, in addition to any loose slope washed material in benches, so as to create a level area on which to rest the new improved backfill material up to the desired grade, until meeting the crest of proposed slope surfaces. However, the complete removal and replacement of the upper loose and slope-washed material found varying between 3.0 to 6.0 ft. shall be allowed. The removal operation of the surface material shall be done under the direct supervision of a Soil Engineer or approved representative, who would establish the vertical extension of removal at intermediate areas between borings

2. In some areas, an over-excavation may be required to assure that a uniform fill section is

3. After the surface loose soil (slope-washed) removal, benches shall be provided with a surface stabilization fabric. The minimum width of the benches shall be 1.0 meter.

4. A Heavy-Duty Stabilization Fabric (i.e. TerraTex HD or similar), to prevent soil intrusion into the under soil shall be provided between the backfill material and the exposed dense silty sand soil at each bench.

5. Once the benches are constructed and the Stabilization Fabric is placed, then the backfilling operation can commence. The final grading elevations shall consider surface slope ratios not greater than 2.H:1V. The replacement fill shall be granular A-2-4 or better

ASHTO type and compacted to not less than 95 % of its maximum proctor density test.

6. Once the complete replacement of the soil embankment is completed, surface erosion protection countermeasures shall be provided up to the crest of the new embankment slope. Thus, the exposed upper slope surface shall be provided with erosion countermeasures, such as MacMat R, BioMAc, MacGrid T or similar.

5.6 Earthquake Design

Spectral Response Acceleration of 96% of g. (probability of exceedance of 2% in 50 years) is identified for the Municipality of Ciales. Depending on soil conditions and final grading, a site

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class “D” can be used for planning purposes. However, for structures where foundations bearing into the residual and weathered rock material a Site Class “C” as described in International

Building Code 2009 Edition and the Puerto Rico Building Code 2011.

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

TABLE 2 - Soil Profile Types

Sector Covered Range of…