Report_Geotechnical_ER-HWY-361.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-440, KM 0.20 on Caimital Bajo Ward in the Municipality of Aguadilla, Puerto Rico.

Reference No. DA/18O3793

PROJECT ID: ER-HWY-361

January 30, 2019

Prepared for:

Roberto Rexach Cintrón & Associates 800 Roberto H. Todd Ave.

San Juan, Puerto Rico 00907

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 30, 2019

Roberto Rexach Cintrón & Associates 800 Roberto H. Todd Ave.

San Juan, Puerto Rico 00907 Ph: 787.525.6956 E-mail: rexach@gmail.com

Attn.: Mr. Roberto L. Rexach Cintrón, PE - President

Subject: Proposed Geotechnical Engineering and Subsurface Exploratory Services for the

Landslide and Road Damage Evaluation and Reconstruction Project at State Road

PR-440, KM 0.20 on Caimital Bajo Ward of the Municipality of Aguadilla, Puerto

Rico. Reference No. DA/18O3793

Dear Eng. Rexach:

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-361, at State Road PR-440, KM 0.20 on Caimital Bajo Ward of the Municipality of Aguadilla, Puerto Rico.

The work was undertaken at the request of Mr. Roberto L. Rexach Cintrón, PE, President of Roberto Rexach Cintrón & Associates The work was made in accordance to Proposal No. DA/04- 30-18R for the subsurface exploration dated May 21, 2018. The work was commenced after order to proceed for the work was received on November 28, 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. roadway structures and 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:rexach@gmail.com

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS i

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

3.4 Groundwater Levels

IV. OBSERVATIONS AND FINDINGS

V. ENGINEERING RECOMMENDATIONS

5.1 General Design Foundation Design Parameters

5.1.1 Additional Design Considerations

5.2 Pavements Design Parameters and Recommendations

5.3 Breakwater Structure Recommendations

5.4 Earthquake Design

5.5 General Earthwork Recommendations

5.5.1 Excavations

5.5.3 Temporary Cut Sections

5.5.4 Backfill Material

5.6 Proposed Storm Water Run-off Control

5.7 Dewatering Considerations and Recommendations

5.8 Nearby Structures

5.8.1 Additional Considerations for control of Vibrations for 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-361, at State Road

PR-440, KM 0.20 on Caimital Bajo Ward of the Municipality of Aguadilla, Puerto Rico.

The work was undertaken at the request of Mr. Roberto L. Rexach Cintrón, PE - President of

Roberto Rexach Cintrón & Associates The work was made in accordance to Proposal No. DA/04-

30-18R for the subsurface exploration dated May 21, 2018. The work was commenced after order to proceed was received on November 28, 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. roadside structures and 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 12 to 12.55 meters. Within this sector, one (1) major sink occurred along the western edge of State Road

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 2

PR-440 near km 0.2. The extent of road damage was found to be some 12.3 meters long, occurred along the western edge of State Road PR-440, causing severe erosional effects and degradation of the undersoil beneath the westernmost pedestrian sidewalk, causing the observed damages and partial rupture of the pavement and sidewalk structure.

Also, an existing retaining structure (5.0 ft. in height approximately), which serves as a shore break during high-tides is located parallel to State Road PR-440 on the west side was observed.

Although no specific structural engineering review was performed by the undersigned, no structural damage was observed nor reported.

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 a rapid raise and drop of the water table, caused the re-arrangement of the sand particles causing the observed settlements and cavity under the pedestrian sidewalk. Once its bearing soil raveled, the structural integrity of the sidewalk structure was compromised and subsequently it broke. After the complete rupture occurred, excessive raveling and wash-out occurred causing the detrimental consequences observed. Thus, the intense or above normal Storm Surge and erosional conditions experienced during Hurricane Maria were the primary factors which caused the prevailing conditions.

Based on the US Topographic map the Aguadilla Bay borders the western edge of State Road

PR-440. Also, to the east of PR-440 several haystack hills with drainage gullies exist. These gully streams drain the surface water from the hill tops through saddles towards State Road PR-

440 finally ending on the Aguadilla Bay. The roadside elevation is at an approximate elevation is approximately 1.5 to 2.00 meters higher than the Aguadilla beach.

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.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 3

III. FIELD SUBSURFACE AND SAMPLING PROGRAM

3.1 Subsurface Investigations

The subsurface soil conditions at the site were investigated three (3) 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.

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 Aguadilla

Quadrangle (Map I-569), prepared by Mr. Watson H. Monroe (1969), the geologic units that lie at or near the site are the following:

1. Beach Deposits (Qb) – Described as Quartz sand, shell fragments and scattered grains of other minerals resistant to weathering. Cementation to beach-rock is common; deposits inland from present shoreline covered by a thin blanket of sand blown from beaches and dunes. Generally, dips toward the sea.

2. Aguada Limestone (Ta) - Described as thick layers of very plae orange to pink hard calcarenite alternating with chalky and rubbly limestone. At the top, between 1 to 9 meters consists of orange to pink granular thin-bedded and cross-laminated limestone.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 4

3. Aymamón Limestone – Lower member (Tay) – Described as white to very pale orange, locally pale-yellow and grayish-pink very pure fossiliferous limestone, generally indurated into finely crystalline rather dense limestone., locally a recemented solution breccia. The surface has been dissolved into abundant sharp spires. Thin -bedded granular limestone and chalk like underlying Aguada Limestone.

An approximate Unnamed Fault (dashed), was identified at about 570 meters, west the site, having a near northwest-southeast alignment. Several additional approximate Unnamed Faults lines are shown in the Geologic map, parallel to the previously mentioned fault further to the east.

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

3.3 Stratigraphic Units

Following the a four (4”) thick asphalt wearing course [Boring 361-1] was disclosed. Generally, at the road surface, the results of the exploration disclosed a surface layer varying between 3.0 to 8.0 ft. in thickness. The surface fill layer is composed of a brown, pale yellow, yellowish brown silty sand and gravel, with traces of clayey sand. The standard resistance to penetration (N-values) of the surface layers varied from 2 to 26 blows/foot, at a loose to medium State of

Consistency. The natural moisture content values range from 5 to 15 percent. Random samples of this layer disclosed AASHTO class type A-2-4 (0) and A-1-b (0) AASHTO type soils (USSCS type SM and SP-SM, respectively).

Following the surface layer, a loose to medium yellowish-brown silty sand with some gravel fragments was found. This layer extends to about 20 to 23 ft. in depth. The standard resistance to penetration (N-values) of the surface layers varied from 5 to 24 blows/foot and the natural moisture content values range from 9 to 31 percent. At the location of Boring 361-1 higher N-values (62 blow/ft.) were obtained due to a coarse gravel disclosed. Random samples from this horizon disclosed at A-1-b and A-1-a [USCS SP-SM].

At the deeper explored depths, until the borings were bottomed a layer composed of reddish yellowish-brown fat clay and clayey silty sand with traces of limestone fragments was disclosed.

The standard resistance to penetration (N-values) of the surface layers varied from 6 to 64

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 5

blows/foot and the natural moisture content values range from 30 to 36 percent. Random samples of this horizon disclosed at AASHTO class type A-7-5 and A-7-6 soils [USCS type CH and SC] was obtained.

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 ground water level was found at about 8.0 ft. in depth. All depths were measured from the existing ground surface prevailing during the period of exploration.

At the site the ground water level is influenced by the adjacent body of water (Aguadilla Bay).

Therefore, dewatering shall be expected during the foundation excavations due to the high-water table found at the site. Any groundwater flows must be intercepted and carried to adequate drainage facilities outside any structure (i.e. pavement, retaining walls, etc…).

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 edge of State Road PR-440, where severe erosional effects and degradation of the undersoil beneath the westernmost pedestrian sidewalk, causing the observed damages and partial rupture of the pavement structure and sidewalk.

Field observations revealed one (1) major sink occurred along the western edge of State Road

PR-440 near km 0.2, where a void was formed beneath the western pedestrian sidewalk. Also, an existing retaining structure (5.0 ft. in height approximately), which serves as a shore break during high-tides is located parallel to State Road PR-440 on the west side.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 6

The extent of road damage was found to be some 12.3 meters. However, the actual extent of damages may extend even more beneath the existing sidewalk structure. Therefore, during construction, once the actual excavation is performed, the actual extent of damages shall be confirmed.

Our engineering assessment is that the primary cause for the prevalent conditions were caused by a rapid raise and drop of the water table, caused the re-arrangement of the sand particles causing the observed settlements and cavity under the pedestrian sidewalk. Once its bearing soil raveled, the structural integrity of the sidewalk was compromised and subsequently it broke. After the complete rupture occurred, excessive raveling and wash-out occurred causing the detrimental consequences observed.

The rapid raise and drop of the water table, may have caused the same effects experienced when a liquefaction phenomenon occurs. This phenomenon is more apt to have effect on loose silty sands which are found beneath the groundwater level as is the case of the Site [Borings 361-1, 361-2, & 361-3]. Whenever the loose silty sandy soils are subjected to sustained vibrations, like those experienced during an earthquake, these tend to lose their capacity. As the soil grain are separated a “boiling effect”, under the progressive buildup of water pressure, is produced by the seismic ground shaking. Once the “boiling effect” is experience a re-accommodation of the soil particle takes place, causing the settlement of any loose soil above.

In the present project liquefaction did not occurred, however, rapid raise and drop of the water table may have caused similar circumstances with the increase of the water pressure triggering the observed settlements. In addition, the storm surge caused excessive erosion/raveling of the undersoil causing additional detrimental effects experienced during Hurricane Maria was the primary factor which caused the prevailing conditions.

In addition, evaluation of the topographic plan submitted for the present evaluation revealed, all surface runoff from higher elevations drain towards west to the Aguadilla Bay through drainage ramps. Moreover, it was on of these ramps where the rupture by the aforementioned discussion prevailed.

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

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 7

western edge of PR-440, to repair the observed damages assuring the road safety. The herein recommendation by themselves and/or any combination of them shall be applied to the presently affected area (western edge of PR-440). 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 relatively flat affected area extends for an approximately 12.3 meters west of State Road PR-440, at the study sector. As discussed with the A/E Design team, the first alternative to be consider is to reconstruct the affected areas as they were before the hurricane event. This would entail the reconstruction of the affected sidewalk and ramp with a spillway over the existing western retaining structure towards the beach area. This reconstruction alternative will entail the removal of the existing loose surface layer and debris (i.e. cans, plastics bottles, and refuse), to a depth varying between 2.0 and 5.0 ft., prior to the backfilling process. Also, a non-woven high-density filter fabric shall be provided at the bottom and sides of the open excavation. This geotextile will prevent the migration of fine material.

2. As a second alternative which is being considered is the reconstruction of the affected area is to re-construct the sidewalk and ramp by providing a curb inlet to drain surface runoff beneath the proposed sidewalk structure and over or through the existing western retaining structure towards the beach area. This reconstruction alternative will also entail the removal of the existing loose surface layer and debris (i.e. cans, plastics bottles, and refuse), to a depth of 2.0 and 5.0 ft., prior to the backfilling process. Also, a non-woven high-density filter fabric shall be provided at the bottom and sides of the open excavation. This geotextile will prevent the migration of fine material.

3. As a third alternative the western sector of the project may consider the re-construction of the sidewalk and ramp by providing a curb inlet with a catch basin to drain surface runoff beneath the proposed sidewalk structure and through the existing western retaining structure towards the beach area by providing drainage pipe. The actual pipe diameter to be installed

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 8

shall be based on the hydrological analysis of the area. This alternative will also entail the removal of the existing loose surface layer and debris (i.e. cans, plastics bottles, and refuse), to a depth of 2.0 and 5.0 ft., prior to the backfilling process. Also, a non-woven high-density filter fabric shall be provided at the bottom and sides of the open excavation. This geotextile will prevent the migration of fine material.

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

V. ENGINEERING RECOMMENDATIONS

Field observations revealed one (1) major sink occurred along the western edge of State Road

PR-440 near km 0.2. The extent of road damage was found to be some 12.3 meters. However, the actual extent of damages may extend more beneath the existing sidewalk structure.

Therefore, during construction, once the actual excavation is performed, the actual extent of damages shall be confirmed. Nevertheless, the herein recommendation shall be applied to the complete affected area.

As previously mentioned, the affected area shall be repaired with the reconstruction of the western sidewalk and ramp. Different approaches have been considered by the A/E design team to cope with the surface’s runoff. These are:

1. A spillway over the existing western retaining structure towards the beach area.

2. A curb inlet to drain surface runoff beneath the proposed sidewalk structure and over or through the existing western retaining structure towards the beach area.

3. A curb inlet with a catch basin to drain surface runoff beneath the proposed sidewalk structure and through the existing western retaining structure towards the beach area by providing drainage pipe.

Evaluation indicate that provided the complete removal of the existing loose surface layer and debris (i.e. cans, plastics bottles, and refuse), found to a depth varying between 2.0 and 5.0 ft., Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 9

and the required backfill is properly deposited, the proposed improvements may be built following the herein recommendations. The design of the proposed structures shall be design following the herein foundations design parameters and recommendations.

5.1 General Design Foundation Design Parameters

The proposed ramp and sidewalk structures shall consider an allowable soil bearing pressure of

2.0 K/sq.-ft., over new compacted engineered fill section to a minimum 95 % of its maximum dry density test. For a beam on elastic foundation a Modulus of Sub Grade Reaction of 100 lbs./sq.-inch/inch can be considered by design.

SUMMARY OF FOUNDATION RECOMMENDATIONS

Structure Identification

Boring No.

Allowable Soil Bearing

Pressure (ksf.)

Modulus of Sub Grade

Reaction

Concrete Sidewalk and Ramp

361-1 to 361-3 2.0 ksf. 100 lbs./sq.-inch/inch

Additional Foundation Considerations:

*1. The above soil bearing pressures are based on the complete removal and/or replacement of any surface loose surface layer and debris (i.e. cans, plastics bottles, and refuse), found to a depth varying between 2.0 and 8.0 ft. [Boring 361-2]. However, the actual extent of removal shall be determined at the field by the inspecting soils engineer.

*2. The minimum depth of foundation shall be measured from the Existing Ground Surface during field work.

*3. A non-woven high-density filter fabric shall be provided at the bottom and sides of the open excavation. This geotextile will prevent the migration of fine material.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 10

All fill material as required on this project shall be controlled fill material (AASHTO Classification

A-2-4 or better) and shall be compacted to 95 % Modified Proctor Density. For controlled fill, it is meant to place the fill layers in 6-inch lifts, each layer compacted to not less than 95% Modified

Proctor Density. However, if the backfilling process is to be performed under saturated conditions, then crushed stone compacted to a minimum of 83 % of its bulk density shall be used as back fill material.

Also, a uniform fill section is required, for which the expected fill section may increase even more.

This is to assure the differential settlements are maintained within tolerable limits for the structural building unit. Therefore, IN NO CASE shall a cut/fill scenario within the footprint of any structure shall be allowed.

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

SUMMARY OF IN-SITU SOIL PARAMETERS FOR DESIGN

Soil Description Unit

Weight (pcf.)

Angle of Internal Friction

(degrees)

Cohesion (psf.)

New Fill (A-2-4) 125 27 Neglect

New Fill (Crushed-Stone)

133 33 Neglect

Upper Loose Silty Sand (0’-8.’)

100 22 -

Medium Dense Silty Sand (8' -23')

115 24 -

Clayey Silty Sand and Clay (>23’)

124 23 800

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. Thus, 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.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 11

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

Considering the proposed improvements are to be installed next to the existing retaining structure, the following design considerations may be required.

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 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) to be considered shall be 8.0 ft. [Boring 361-2]. 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.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 12

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 and 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.

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. Under standard design criterion, the backfill shall be granular

(AASHTO A-2-4 or better), carefully placed and of good quality, above 1.0 m. mean sea 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 Design Considerations

Considering the proposed improvements are to be installed next to the existing retaining structure.

It shall be noted the new proposed improvements and construction procedures will impart additional stress to the existing retaining wall structure, therefore as part of the site design the project’s Structural engineer shall calculate expected additional stress and determine if these can be tolerated by the existing retaining wall structure.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 13

For such purposes the following figure (Figure 11 from NAVFAC DM-7.02, page 7.2-74) can be used for such evaluation. Figure 11 can be used to compute the lateral pressure on the wall due to point and line loads. It assumes an unyielding rigid wall and the lateral pressure are approximately double the values obtained by elastic equations.

For uniform surcharge loading lateral stress can be computed by treating the surcharge as if it was backfill and multiplying the vertical stress at any depth by the appropriate earth pressure coefficient.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 14

5.2 Pavements Design Parameters and Recommendations

As part of the reconstruction project, it may be required the partial replacement of the pavement structure. However, in the borings of exploration unsuitable subsurface profile was encountered therefore, a replacement and/or re-compaction of the in-situ subgrade shall be allowed.

Thus, the proposed flexible pavements sections may be designed using a CBR value in the order of 15 to 25, assigned to the in-situ loose silty sand exposed as subgrade of the pavement section.

For the proposed compacted fill types, the CBR value shall not exceed 25 to 40 percent, considering an AASHTO classification A-2-4 or better recommended compacted to a minimum

95 % of its maximum dry density. These values are our best estimates for the in-situ and fill types being considered, placed and adequately compacted in accordance to the earthwork specifications in Appendix 2 to this report.

The thickness of the base and surface course material is a function of the design. At cut and fill sectors the exposed grade shall be scarified and compacted to at least 95 % of its maximum

Modified Proctor Density. At cut sectors, if any, whenever moderate to high expansive clay soils are exposed an over excavation of 1.5 m. shall be necessary to assure adequate subgrade materials beneath the pavement section.

The proposed design of either flexible or rigid pavements shall consist of providing the following pavement components:

(1) The selected surface course;

(2) A Crushed–Stone Base Course, consisting of crushed-stone or gravel or natural gravel, as per AASHTO Classification. It shall be placed at a minimum eighty-three (83) percent compaction of its solid volume density, as obtained by the bulk density. This compaction criterion shall be required for the base course. The base coarse section design shall consider Section 304-2 Materials and 703-4 –Aggregate for Base Course of the

Standard Specification for Road and Bridge Construction of the Department of

Transportation and Public Works (Latest Revision), which states “Aggregate for untreated aggregate base course shall consist of hard durable particles or fragments of crushed

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 15

stone or crushed or natural gravel conforming to the grading requirements shown in Table

703-4, as presented in the following table.

Table 703-4 Grading for Aggregates Base Course

SIEVE Grading

Designation A B C D

2-inch 100 - - 100

1-1/2-inch - 100 - -

1-inch 50-80 - 100 50-80

1/2-inch - 40-75 - -

No.4 20-50 30-60 40-75 20-50

No.10 - - 25-60 -

No.200 5-12 5-12 5-12 0-5

(3) The Sub-grade Course shall consist of A-2-4 or better, as per AASHTO Classification, imparted with a minimum 95 percent compaction. Along most of the project site granular non-plastic materials (A-1-b, A-3 AASHTO Type) were found and can be used as backfill material. However, it shall be noted that sometimes, if too little or no fines exist within the matrix, the compaction process can be difficult to obtain the minimum required compaction effort. If this problem is encountered, then it can be substituted with an adequate borrow material.

5.3 Breakwater Structure Recommendations

Regardless, of the final solution to be implemented, drainage facilities of enough capacity shall be provided to carry all surface water away from the pavement structure all the way past the existing retaining wall, which shall be protected against erosion. In addition, to reduce the energy of the tidal wave effect, a breakwater structure may be considered at the bottom of the western side (beach side) of the existing retaining structure as an erosion protection with coarse gravely materials to prevent further erosion.

There are different types of breakwaters (i.e. natural rock, concrete, sand bags, etc…). The height of wave incident on a breakwater generally determines the size and behavior of the breakwater.

It is hence of the utmost importance to obtain realistic values of the waves expected at the project site. Also, a high-density geotextile filter mat (TerraTex HD or equivalent) shall be placed beneath the breakwater structure to prevent it from sinking and disappearing into the undersoil.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 16

Breakwaters can be located offshore or at the shoreline and to protect shoreline infrastructure from wave and current action. The breakwater dissipates offshore wave energy, generating calm water basins where shoreline structures can be successfully and safely developed. Sometimes submerged structures are often used for the containment of the seaward-facing foot of artificial nourishments, operating together to provide beach protection.

Considering the subsoil profile, a rubble breakwater is recommended. However, other types may be considered such as Sand Bags (i.e. Maccaferri MAcTubes, Mac-Bag or equivalent).

MacTubes and MacBags are usually used, where there is sand readily available. On the other hands, gabions and Reno or Marine mattresses may also be considered.

MacTubes can be used to build the groin (breakwater/low wall), meanwhile gabions and Reno or marine mattresses can be used to protect the core from wave and current action. A well-designed filter layer separating the new structure from the existing sea bed shall be provided to assure the performance of the groin, however the traditional geotextile filter fabric is buoyant in sea-water, complicating its installation. Available products in the construction industry such as Macaferri’s

Ballasted Filter Mattress (BFM) have been developed to solve this problem by enabling the placement of a protection, separation or filtration textile on the sea-bed.

Although a rubble breakwater is recommended, replacing rubble mound core material with

MacTubes filled with dredged material (sand or silt) can be an effective. Therefore, if other type of breakwater system/structure, such as sand bags systems are selected by the A/E design Team, detailed plans and specifications shall be forwarded to this office to review their adequacy in this project.

Prior to any fill placement, the complete demucking of any loose material shall be allowed. Once the removal of any unsuitable soil is completed a re-compaction of the daylighted soil shall be allowed to a minimum 95 % of its maximum dry density. Then, the backfilling operations can commence.

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 https://www.maccaferri.com/products/macbag/ https://www.maccaferri.com/products/gabions/ https://www.maccaferri.com/products/reno-mattresses/ https://www.maccaferri.com/products/mactube/

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 17

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 123% of g. (probability of exceedance of 2% in 50 years) is identified for the Municipality of Aguadilla. Considering the soil improvements, a site class “D” can be used for design.

5.5 General Earthwork Recommendations

Any back-fill material shall be compacted to not less than 95% of the material maximum Modified

Proctor Density. For controlled fill, it is meant to place the fill in 6-inch layers of compacted thickness, each layer compacted to not less than 95% Modified Proctor Density. The verification of the compaction being imparted shall be made under the direct supervision of a representative from this office.

The fill shall be of an inorganic and non-swelling nature and shall be A-2-4 or better AASHTO

Classification. However, backfill material below the ground water level shall consist of bluish gray crushed stone. All borrow materials shall be taken to a soil’s laboratory for testing and approval prior to their use at the project. Periodic review of soils classifications as the different material types are brought to the site shall be done, to assure an adequate quality control of the material to be placed for the different sectors of the project.

Should underground structure be considered for the project, it is recommended to provide a crushed-stone base material consisting of a clean (washed) well-graded crushed-stone (1-inch maximum size), to be used to replace the material beneath foundation base. The material shall be provided with impermeable filter fabrics which shall be placed below the foundation base of the mat. In addition, adequate slope shall be provided to drain the design volume of flow to the permanent sump pumps and drainage sub trenches provided for long term storm water control.

The enclosed fill specifications (Appendix 2) detail our recommended Earthwork Specifications.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 18

5.5.1 Excavations

For most parts of the project, shallow excavations to remove the loose surface material can be performed using backhoe equipped with a short tip radius and narrow bucket. However, frequent occurrence of consolidated materials, shells and rock gravel fragments within the profiles, above the foundation elevations, will increase both the time and cost of the operations. High resistance to penetration values were not found at shallow levels, beneath existing grade at the presently investigated locations. At depths where the Standard Resistance to Penetration (N-values) exceeds 40 blows/foot is where difficulty in the trench excavations is predicted. It shall be pointed out that excavations into the on-site soils will encounter possible caving conditions.

Excavations should be performed with equipment capable of providing a relatively clean bearing area. Excavating equipment should not disturb the soil beneath the design excavation bottom and should not leave large amounts of loose soil in the excavation.

As a safety measure, no equipment should be operated within 5 feet of the edge of the excavation and no materials should be stockpiled within 10 feet of the excavation. Excavations should not approach closer than 10 feet from existing structures/facilities without some form of protection for the facilities. Also, proper beaming or ditching should be performed to divert any surface runoff away from the excavation.

It shall be noted, the soils to be excavated can vary significantly across the site as their classifications are based solely on the materials encountered in widely-spaced exploratory test borings. The contractor should verify that similar conditions exist throughout the proposed area of excavation. If different subsurface conditions are encountered at the time of construction, the actual conditions should be evaluated to determine any excavation modifications necessary to maintain safe conditions.

The subgrade soil conditions should be evaluated during the excavation process and the stability of the soils determined at that time by the contractors’ Competent Person. Slope inclinations flatter than the OSHA maximum values may have to be used. The individual contractor(s) should be made responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local, and federal regulations, including current OSHA

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 19

excavation and trench safety standards. The exposed slope face should be protected against the elements.

5.5.3 Temporary Cut Sections

Temporary cut slopes shall through the upper loose material shall be constructed with a 2.0H:

1.0V (Horizontal: Vertical) slope ratio. However, caving is predicted, and limited space constraints will govern the excavation process. Therefore, special excavation procedures and precautions shall be taken during the excavation process.

Should existing structures (i.e. roadways, retaining wall) exist within the construction area, special construction processes to prevent further instability of the existing slope surfaces shall be put into effect. The construction sequence shall be performed in alternating sections of not more than

15.0 ft. wide. This criterion shall be considered as the general case through the project, except where an existing structure, if any, lie at horizontal distances closer than 15.0 ft., which is the case of this project. Under such circumstance a geotechnical review shall be allowed to establish the impact the proposed temporary slope may have on the existing structure and its foundations.

To assure adequate construction of steeper cut sections, it is mandatory the verification of the site and topographic conditions at the proposed cut sector, to review stability analysis and the specific conditions of the proposed cut slope.

The contractor should use a trench box or shoring and bracing as necessary to maintain a safe and clean excavation which meets with the Occupational Safety and Health Administration

(OSHA) requirements. Excavations must be performed and inspected under the supervision of a contractor designated Competent Person. The Competent Person, as defined by the OSHA

Standard, 29 CFR Part 1926.650 to .652, Subpart P – Excavations, must evaluate the excavations at the time of construction activity to safeguard workers.

The following construction criteria shall also be considered to render stable slope grounds:

A. Any exposed virgin soil slope shall be cut with the maximum slope ratio for temporary slopes.

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 20

B. Any exposed embankment slope face shall be protected against erosion.

5.5.4 Backfill Material

All fill material shall comply with AASHTO A-2-4 or better classification and shall be compacted in layers 6-8 inches in thickness (when compacted) and imparted with a minimum compaction density of 95 % of the Laboratory Modified Proctor (Appendix 2 - Earthwork Specifications).

Also, any backfill material to be deposited beneath the ground water table shall consist of clean crushed-stone (3/4”-inches maximum diameter). All borrow materials shall be taken to a soil’s laboratory for testing and approval prior to their use at the project.

The engineering control of the fill section shall be placed in accordance to the fill specifications of this report and shall also comply with Section 304-3 of the Standard Specification for Road and

Bridge Construction, 1989 Edition.

5.6 Proposed Storm Water Run-off Control

Regardless, of the final solution to be implemented, drainage facilities of enough capacity shall be provided to carry all surface water away from the pavement structure all the way past the existing retaining wall, which shall be protected against erosion. In addition, to reduce the energy of the tidal wave effect, a breakwater structure may be considered at the bottom of the western side (beach side) of the existing retaining structure as an erosion protection with coarse gravely materials to prevent further erosion. Neglecting to provide these drainage facilities it is possible surface slides may develop.

Considering the subsoil profile, a rubble breakwater is recommended. However, other types may be considered such as Sand Bags (i.e. Maccaferri MAcTubes, Mac-Bag or equivalent).

MacTubes and MacBags are usually used, where there is sand readily available. On the other hands, gabions and Reno or Marine mattresses may also be considered.

https://www.maccaferri.com/products/macbag/ https://www.maccaferri.com/products/gabions/ https://www.maccaferri.com/products/reno-mattresses/

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 21

All drainage ways shall be paved or French Drains with rip rap facings constructed at sectors where extreme erosion, is predicted.

Any interception type drains shall consist of French under drains which consist of fabric wrapped, coarse porous backfill in a trenched installation. No pipe is used except for a short length of pipe as an outlet. Pipe-aggregate under drains consist of a geotextile lined trench, perforated plastic or metal pipe, and porous backfill. Functionally, these may be installed either as interception drains to capture localized sources of water.

As temporary mitigation measure, until the complete stabilization procedure is designed and completed, all surface runoff shall be diverted away from slopes to minimize the erosional effects which will yield further saturation causing additional slope failure at the site.

5.7 Dewatering Considerations and Recommendations

Although the ground water was found at 8.0 ft. in depth, measured from the existing ground surface, considering the closeness to the Aguadilla Bay dewatering should be expected during any excavation procedure during construction, due to moderate to high permeability of surface soils.

Therefore, special dewatering techniques (i.e. well points) may be required, if the proposed invert elevation of the proposed excavation is greater (deeper) than the ground water levels.

Dewatering can be accomplished by pumping through a system of well points installed adjacent to the excavation to sump pits near the excavations. The adequacy of the control of the dewatering process should be maintained during the excavation process to prevent the bottom of the excavation to heave or boil.

Also, special care shall be taken not to affect adjacent structures, if any, while dewatering procedures are implemented (i.e. Draw Down). Thus, any dewatering techniques shall be properly designed to cope with these circumstances.

Also, in the case underground structures are considered, an effective drain blanket shall be provided to allow drainage of water continuously throughout the structure that will dispose of the

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 22

relatively large flows through the upper loose sands which are highly permeable. Small volumes of upward seepage through the silty sand material of variable permeability are found below foundation level. The basis of this solution is to account for the groundwater levels found close or above the foundation level. Thus, the final solution requires an estimate to be made of the quantity of water that will be collected for which the pumps (permanent) must be designed. A final design volume determination will require additional evaluations and possibly a pumping test. Such evaluations are beyond the scope of the present work. Furthermore, during the period of the foundation and construction sequence a temporary dewatering system to maintain the excavation dry shall also be required in this project.

5.8 Nearby Structures

Due to the proximity of existing adjacent buildings, the earthwork process requires special consideration regarding vibrations during the earthwork process. Excavation procedures near existing structures me induce a readjustment of the loose sand causing detrimental effects to adjacent buildings.

At this stage, it is difficult to predict the extent of vibrations to be produced by the equipment to be used during the construction sequence. Thus, this aspect of construction shall be evaluated with care.

5.8.1 Additional Considerations for control of Vibrations for Nearby Structures

As a minimum, a vibration survey using the excavation and compaction equipment actually used at the project shall be considered. In order to minimize vibrations during the earthwork process the construction of interception trenches to reduce the horizontal component of the peak particle velocity can be considered.

Regardless of the vibration restrain process provided, the use of photographs prior to the construction sequence is very valuable to establish preexisting conditions of nearby structures.

These are very valuable in court. A monitoring process of vibrations shall be in place during the construction sequence, as considered necessary by the contractor. Thus, where deep excavation

Project No.: DA/18O3793 Aguadilla, Puerto Rico January 30, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL…