Report_GEO_AC-820579_HWY-312.pdf

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

April 12, 2019

Enrique Ruiz & Associates PO Box 360977 San Juan, Puerto Rico 00936-0977 Ph: 787.783.6717; Fax: 787.782.6760 E-mail: e.ruiz@era-pr.com

Attn.: Mr. Enrique Ruiz, PE, President

Subject: Addendum No.1 Proposed Geotechnical Engineering and Subsurface Exploratory Services for the Landslide and Road Damage Evaluation and Reconstruction Project ER-HWY-312 at State Road PR-181, KM 46.4 on Celada Ward of the Municipality of Gurabo, Puerto Rico.

Reference No. DA/18O3776

Gentlemen:

Following the necessary approval of our revised proposal by the PRTHA’s Soils Engineering office, Despiau

Associates was engaged for the Geotechnical Engineering & Subsurface Exploratory Services on the referenced project. The scope of work and associated terms and conditions of our engagement were detailed in said revised proposal.

However, in order to verify the adequacy of the presented reconstruction alternatives, internal and external stability analyses for slopes within the project’s limits were performed. The degree of stability of a slope is expressed as the factor of safety, which is the ratio of the forces resisting failure to the driving forces causing instability.

The undersigned hereby certifies that the analyses contained in our geotechnical report were performed following the Puerto Rico Transportation and Highway Authority (PRTHA) Design guidelines, including internal and external stability. Moreover, the undersigned confirms that, provided the recommendations contained in the geotechnical report of reference are strictly followed and considered in the design, adequate safety factors for global stability against Static and Pseudo-Static conditions will be obtained. Furthermore, additional slope stability analyses may be performed to assure the global stability of the finally selected alternative.

Should you have any question regarding these matters, please do not hesitate to contact the undersigned.

Respectfully submitted, DESPIAU ASSOCIATES

Jose R. Despiau, P.E.

Geotechnical Engineer http://www.despiau.net/ mailto:e.ruiz@era-pr.com

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

April 29, 2022

PO Box 360977 San Juan, Puerto Rico 00936-0977 Ph: 787.783.6717; Fax: 787.782.6760 E-mail: e.ruiz@era-pr.com

Attn.: Mr. Enrique Ruiz, PE, President

Subject: Addendum No.2 Proposed Geotechnical Engineering and Subsurface

Exploratory Services for the Landslide and Road Damage Evaluation and Reconstruction Project ER-HWY-312 at State Road PR-181, KM 46.4 on Celada Ward of the Municipality of Gurabo, Puerto Rico. Reference No. DA/18O3776

Gentlemen:

Please attached the revised boring logs with the revised soil description based on the classification column. The herein submitted revised Boring Logs shall supersede the previously submitted with the geotechnical report. Therefore, this Addendum No. 2 is an integral part of the already submitted geotechnical report.

Should you have any question regarding these matters, please do not hesitate to contact the undersigned.

Respectfully submitted, Jose R. Despiau, P.E.

Enclosure http://www.despiau.net/ mailto:e.ruiz@era-pr.com

PROJECT: REFERENCE NO.:

BORING NO.:

LOCATION:

NORTHING:

EASTING:

DATE:

GROUND ELEV.:

DEPTH OF HOLE (ft.):

DRILL MACHINE:

DRILLER:

DRILL METHOD:

SHEET: 1 of 2

CASING:

Hammer Weight ( lb.): Drop ( in.):

Type : Size :

SAMPLER:

Hammer Weight (lb.): Drop (in.):

Type: Size:

Soil / Geotechnical Engineering Laboratories D ep th ft

S a m p le r

S a m p le N o

B lo w s

/6 i n

S P

T N

-V a lu e

S y m b o l

Material Description

R e co v er y

R .Q

.D

W a te r

C o n te n t q u

W a te r

L e ve l

L iq u id

L im it

P la st ic it y

I n d ex

S o il

C la ss if ic a ti o n

$ DEPTH OF WATER BEFORE COMPLETION

# DEPTH OF WATER AFTER 24 HOURS

qu (TSF) - UNCONFINED COMPRESSION STRENGTH wh = WEIGHT OF HAMMER TO DRIVE SAMPLE Wn = NATURAL WATER CONTENT IN PERCENT OF DRY WEIGHT

ER-HWY-312 DA/18O3776

312-1

Gurabo

248921.752 249464.289

01/31/19

126.66

CME-45

J. Bruno

5-5/8" Auger

N/A

N/A N/A

N/A N/A

SS

140 30

Split Spoon Sampler 1-3/8" I.D.

SS

SS

UU

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

80-32-11

6-8-11

4-4-4

4-3-3

4-7-8

10-11-8

10-12-30

60/4"

20-50-60/3"

100/3"

100/4"

100/2"

Ground Surface

9"-Inches Asphalt

Well-Graded Sand With Gravel Asphalt, trace light olive gray well-graded sand with gravel, some subangular gravel fragments.

Clayey Sand With Gravel Olive brown, light gray mottled, grayish brown clayey sand with gravel, some asphalt.

Clayey Sand (R)

Grayish brown, light gray mottled, yellow mottled clayey sand, some subangular gravel fragments.

Clayey Sand (WC)

Yellow, red, white and light olive gray clayey sand, trace clay, trace weathered rock fragments.

Silty Clayey Sand With Gravel (WC)

Light olive gray silty clayey sand with gravel, trace weathered rock fragments.

Note: Weathered rock was broken by sampling device into the described constituents.

G ro un d w at er w as n ot fo un d w ith in th e ex te nt d ril le d.

NP

38.3

25.7

36.4

29.5

18.2

18.7

8.6

17.8

9.1

4.7

A-1-a (1)/SW

A-6 (0)/SC

A-2-4 (0)/SC

A-6 (3)/SC

A-4 (1)/SC

A-1-b (0)/SC-SM

LOCATION:

NORTHING:

EASTING:

DATE:

GROUND ELEV.:

DEPTH OF HOLE (ft.):

DRILL MACHINE:

DRILLER:

DRILL METHOD:

SHEET: 2 of 2

CASING:

Hammer Weight ( lb.): Drop ( in.):

Type : Size :

SAMPLER:

Hammer Weight (lb.): Drop (in.):

Type: Size:

Soil / Geotechnical Engineering Laboratories D ep th ft

S a m p le r

S a m p le N o

B lo w s

/6 i n

S P

T N

-V a lu e

S y m b o l

Material Description

R e co v

.D

W a te r

C o n te n t

W a te r

L e ve l

L iq u id

L im it

P la st ic it y

I n ss if ic a ti o n

$ DEPTH OF WATER BEFORE COMPLETION

# DEPTH OF WATER AFTER 24 HOURS

qu (TSF) - UNCONFINED COMPRESSION STRENGTH wh = WEIGHT OF HAMMER TO DRIVE SAMPLE Wn = NATURAL WATER CONTENT IN PERCENT OF DRY WEIGHT

ER-HWY-312 DA/18O3776

312-1

Gurabo

248921.752 249464.289

01/31/19

126.66

CME-45

J. Bruno

5-5/8" Auger

N/A

N/A N/A

N/A N/A

SS

140 30

Split Spoon Sampler 1-3/8" I.D.

SS

SS

SS

100/3"

100/2"

100/1"

Continue - Silty Clayey Sand With Gravel (WC)

Same as above.

LOCATION:

NORTHING:

EASTING:

DATE:

GROUND ELEV.:

DEPTH OF HOLE (ft.):

DRILL MACHINE:

DRILLER:

DRILL METHOD:

SHEET: 1 of 1

CASING:

Hammer Weight ( lb.): Drop ( in.):

Type : Size :

SAMPLER:

Hammer Weight (lb.): Drop (in.):

Type: Size:

Soil / Geotechnical Engineering Laboratories D ep th ft

S a m p le r

S a m p le N o

B lo w s

/6 i n

S P

T N

-V a lu e

S y m b o l

Material Description

R e co v

.D

W a te r

C o n te n t

W a te r

L e ve l

L iq u id

L im it

P la st ic it y

I n ss if ic a ti o n

$ DEPTH OF WATER BEFORE COMPLETION

# DEPTH OF WATER AFTER 24 HOURS

qu (TSF) - UNCONFINED COMPRESSION STRENGTH wh = WEIGHT OF HAMMER TO DRIVE SAMPLE Wn = NATURAL WATER CONTENT IN PERCENT OF DRY WEIGHT

ER-HWY-312 DA/18O3776

312-2

Gurabo

248929.31 249480.071

02/01/19

127.33

CME-45

J. Bruno

5-5/8" Auger

N/A

N/A N/A

N/A N/A

SS

140 30

Split Spoon Sampler 1-3/8" I.D.

SS

SS

UU

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

67-52-71

30-21-27

4-5-4

3-5-4

5-6-8

4-5-7

5-6-11

60/4"

60/6"

90/2"

100/3"

100/3"

100/1"

Ground Surface

8"-Inches Asphalt Asphalt.

Gravel Black gravel, trace clay (possible asphalt binder).

Clayey Sand Light olive gray, yellow mottled clayey sand, some subangular gravel fragments.

Sandy Silt (R)

Light olive brown, yellow mottled sandy silt, some weathered rock fragments.

Clayey Sand With Gravel (WC)

Light olive brown, yellow mottled clayey sand with gravel, completely weathered rock fragments.

Note: Weathered rock was broken by sampling device into the described constituents.

un d w at er w as n ot fo un d w ith in th e ex te nt d ril le

34.0

24.5

11.3

7.1

A-2-6 (0)/SC

LOCATION:

NORTHING:

EASTING:

DATE:

GROUND ELEV.:

DEPTH OF HOLE (ft.):

DRILL MACHINE:

DRILLER:

DRILL METHOD:

SHEET: 1 of 1

CASING:

Hammer Weight ( lb.): Drop ( in.):

Type : Size :

SAMPLER:

Hammer Weight (lb.): Drop (in.):

Type: Size:

Soil / Geotechnical Engineering Laboratories D ep th ft

S a m p le r

S a m p le N o

B lo w s

/6 i n

S P

T N

-V a lu e

S y m b o l

Material Description

R e co v

.D

W a te r

C o n te n t

W a te r

L e ve l

L iq u id

L im it

P la st ic it y

I n ss if ic a ti o n

$ DEPTH OF WATER BEFORE COMPLETION

# DEPTH OF WATER AFTER 24 HOURS

qu (TSF) - UNCONFINED COMPRESSION STRENGTH wh = WEIGHT OF HAMMER TO DRIVE SAMPLE Wn = NATURAL WATER CONTENT IN PERCENT OF DRY WEIGHT

ER-HWY-312 DA/18O3776

312-3

Gurabo

248921.752 249464.289

01/31/19 - 02/01/19

128.32

CME-45

J. Bruno

5-5/8" Auger

N/A

N/A N/A

N/A N/A

SS

140 30

Split Spoon Sampler 1-3/8" I.D.

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

70-50-64

24-18-18

20-8-7

12-10-9

9-11-7

6-6-30

8-12-20

60/3"

30-60/2"

100/3"

100/2"

100/2"

100/2"

Ground Surface

8"-Inches Asphalt

Poorly Graded Sand With Gravel Light olive gray and dark brown poorly graded sand with gravel, some subangular gravel fragments, some asphalt.

Silty Sand

Light olive gray, yellow mottled silty sand, some clay, some subangular gravel fragments.

Sandy Silt (R)

Light olive gray, yellow mottled sandy silt, some weathered rock fragments.

Clayey Sand With Gravel (WC)

Light olive gray, yellow mottled clayey sand with gravel, completely weathered rock fragments.

Note: Weathered rock was broken by sampling device into the described constituents.

un d w at er w as n ot fo un d w ith in th e ex te nt d ril d.

38.4

26.4

13.1

8.7

A-1-a (0)/SP-SC

A-2-6 (0)/SM

LOCATION:

NORTHING:

EASTING:

DATE:

GROUND ELEV.:

DEPTH OF HOLE (ft.):

DRILL MACHINE:

DRILLER:

DRILL METHOD:

SHEET: 1 of 1

CASING:

Hammer Weight ( lb.): Drop ( in.):

Type : Size :

SAMPLER:

Hammer Weight (lb.): Drop (in.):

Type: Size:

Soil / Geotechnical Engineering Laboratories D ep th ft

S a m p le r

S a m p le N o

B lo w s

/6 i n

S P

T N

-V a lu e

S y m b o l

Material Description

R e co v

.D

W a te r

C o n te n t

W a te r

L e ve l

L iq u id

L im it

P la st ic it y

I n ss if ic a ti o n

$ DEPTH OF WATER BEFORE COMPLETION

# DEPTH OF WATER AFTER 24 HOURS

qu (TSF) - UNCONFINED COMPRESSION STRENGTH wh = WEIGHT OF HAMMER TO DRIVE SAMPLE Wn = NATURAL WATER CONTENT IN PERCENT OF DRY WEIGHT

ER-HWY-312 DA/18O3776

312-4

Gurabo

248913.67 249479.880

01/05/19

119.38

Mot. Cathead

J. Bruno

Wash Boring

2-1/2" O.D.

300 30

30 N/A

SS

140 30

Split Spoon Sampler 1-3/8" I.D.

SS

UU

SS

SS

SS

SS

SS

SS

SS

SS

SS

1-2-2

5-7-9

5-5-7

11-12-8

7-8-21

11-20-13

46-30-50

40-30-50

37-32-27

24-27-32

Ground Surface

Clayey Sand With Gravel Grayish brown clayey sand with gravel, some subangular gravel fragments, few roots.

Silty Sand With Gravel

Grayish brown, olive yellow mottled silty sand with gravel, some subangular gravel fragments.

Clayey Sand (R)

Light olive gray, brownish yellow and brown clayey sand, some clay, trace weathered rock fragments.

3.2

1.2

1.7 un d w at er w as n ot fo un d w ith in th e ex te nt d ril

36.5

48.6

34.3

14.8

19.4

11.1

A-2-7 (2)/SM

LOCATION:

NORTHING:

EASTING:

DATE:

GROUND ELEV.:

DEPTH OF HOLE (ft.):

DRILL MACHINE:

DRILLER:

DRILL METHOD:

SHEET: 1 of 1

CASING:

Hammer Weight ( lb.): Drop ( in.):

Type : Size :

SAMPLER:

Hammer Weight (lb.): Drop (in.):

Type: Size:

Soil / Geotechnical Engineering Laboratories D ep th ft

S a m p le r

S a m p le N o

B lo w s

/6 i n

S P

T N

-V a lu e

S y m b o l

Material Description

R e co v

.D

W a te r

C o n te n t

W a te r

L e ve l

L iq u id

L im it

P la st ic it y

I n ss if ic a ti o n

$ DEPTH OF WATER BEFORE COMPLETION

# DEPTH OF WATER AFTER 24 HOURS

qu (TSF) - UNCONFINED COMPRESSION STRENGTH wh = WEIGHT OF HAMMER TO DRIVE SAMPLE Wn = NATURAL WATER CONTENT IN PERCENT OF DRY WEIGHT

ER-HWY-312 DA/18O3776

312-5

Gurabo

248914.368 249492.398

02/09/19

119.21

Mot. Cathead

J. Bruno

Wash Boring

2-1/2" O.D.

300 30

30 N/A

SS

140 30

Split Spoon Sampler 1-3/8" I.D.

SS

UU

SS

SS

SS

SS

SS

SS

SS

SS

SS

2-2-3

4-8-6

10-20-15

8-21-20

20-15-20

21-31-22

30-41-39

41-40-39

30-25-28

19-30-27

Ground Surface

Clayey Sand With Gravel Brown, yellow mottled clayey sand with gravel, some subangular gravel fragments, few roots.

Silty Sand

Grayish brown, olive yellow mottled silty sand, some subangular gravel fragments.

Clayey Sand (R)

Light olive gray, pale yellow, reddish yellow and brown clayey sand, trace weathered rock fragments.

Sandy Silt Pale yellow and reddish yellow sandy silt, some clay, trace weathered rock fragments.

1.4

1.6

2.0 un d w at er w as n ot fo un d w ith in th e ex te nt d ril

37.6

47.2

33.5

17.7

18.3

11.2

A-2-7 (2)/SM

A-2-6 (0)/ SC

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-1814, KM 46.4 on Celada Ward of the

Municipality of Gurabo, Puerto Rico.

PROJECT ID: ER-HWY-312

February 1, 2019

Prepared for:

Enrique Ruiz & Associates, PSC

PO Box 360977 San Juan, Puerto Rico 00936-0977

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

February 6, 2019

PO Box 360977 San Juan, Puerto Rico 00936-0977 Ph: 787.783.6717; Fax: 787.782.6760 E-mail: e.ruiz@era-pr.com

Attn.: Mr. Enrique Ruiz, PE, President

Subject: Proposed Geotechnical Engineering and Subsurface Exploratory Services for the Landslide and Road Damage Evaluation and Reconstruction Project at State Road PR-181, KM 46.4 on Celada Ward of the Municipality of Gurabo, Puerto Rico.

Dear Eng. Ruiz:

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-312, at State Road PR-181, KM 46.4 on Celada Ward of the Municipality of Gurabo, Puerto Rico.

The work was undertaken at the request of Mr. Enrique Ruiz, PE, President of Enrique Ruiz & Associates, PSC. The work was made in accordance to Proposal No. DA/04-54-18R for the subsurface exploration dated May 15, 2018. The work was commenced after order to proceed for the work was received on November 11, 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.

Project No.: DA/18O3776 Gurabo, Puerto Rico February 6, 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 Surface Soils and Geological Notes

3.2.1 Surface Soils

3.2.2 Geology

3.3 Stratigraphic Units

IV. OBSERVATIONS AND FINDINGS

V. ENGINEERING RECOMMENDATIONS

5.1 General Design Parameters for Retaining Structures

5.1.1 Additional Considerations for Retaining Structures

5.2 Additional Recommendation for Cantilever Retaining Structure

5.3 Additional Recommendations for Pre-Drilled Hp-Steel Piles with Pre-Cast Panels

5.3.1 Lateral Load Design Considerations

5.4 Additional Recommendations for a Gabion Wall Retaining Wall

5.5 General Slope Surfaces Recommendations

5.5.1 Summary of General Construction Guidelines for the Slope Improvements

5.4 Earthquake Design

5.5 Excavations

5.6 General Earthwork Recommendations

5.6.1 Excavations

5.6.3 Temporary Cut Sections

5.6.4 Backfill Material

5.7 Proposed Storm Water Run-off Control

5.8 Nearby Structures

5.9 Additional Recommendations

VI. LIMITATIONS OF THIS REPORT

Appendix (A) – Figures

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

2. Boring Location Plan

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

I. INTRODUCTION

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

Landslide and Road Damage Evaluation and Reconstruction Project ER-HWY-312, at State Road

PR-181, KM 46.4 on Celada Ward of the Municipality of Gurabo, Puerto Rico.

The work was undertaken at the request of Mr. Enrique Ruiz, PE, President of Enrique Ruiz &

Associates, PSC. The work was made in accordance to Proposal No. DA/04-54-18R for the subsurface exploration dated May 15, 2018. The work was commenced after order to proceed for the work was received on November 11, 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 affected area where the landslide was observed is located in Km 46.4 where State Road PR-

181 bends toward the south with another bend toward the north forming a “horse shoe” shape.

Therefore, PR-181 borders the affected area to the north and south with a difference in elevation

Project No.: DA/18O3776 Gurabo, Puerto Rico February 6, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 2

( ELE) some 17.5 mts., approximately. These difference in elevation creates very steep sloping ratios, varying between 31.5° to 52° degrees steeper sloping grounds were assess on the southern slide.

The Site observation revealed one (1) major landslides occurred along the southern edge of State

Road PR-181 near Km. 46.4. The extent of this major slide extends some 11.5 meters [near

Boring 312-3 & 312-2], however additional (minor) slides were observed extending for an approximate length of 45 to 60 meters [Borings 312-1 to 312-3]. The roadside elevation varies between 125.1 to 128.6 meters.

Based on the US Topographic map, the Gurabo River lies about 1204 meters southwest of the

ER-HWY-312 Site. In addition, in the vicinity of the study area, an intermittent gully stream, tributary to the Gurabo River was identified in the US topographical plan some 230 meters southeast of the project site. Also, three (3) tributary gully stream were identified from the US

Topographic map. The first gully stream crosses perpendicularly to the road embankment mass, with a near north-south alignment. The remaining two intermittent gully streams are found further to the west, also nearly perpendicular to PR-181. The surface runoffs drain from highland sector of the north toward the south through this intermediate gully streams toward the Gurabo River to the south. 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 five (5) 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.

Project No.: DA/18O3776 Gurabo, Puerto Rico February 6, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 3

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 Surface Soils and Geological Notes

3.2.1 Surface Soils

The US Soil Conservation Service Manual – Soil Survey of San Juan Area of Puerto Rico, Sheet

#28, prepared by the Soil Conservation Service identifies the surface soils of the area as follows:

Naranjito silty clay loam, 20 to 60 percent slopes, eroded (NaF2) – These consist of very steep, well-drained soils on strongly dissected uplands. It consists of clayey, formed in residuum of volcanic rocks. The permeability is moderate and the available water capacity is low. Runoff is rapid and erosion is a hazard. Slippage is common in roadbanks ditches, and drainageways. This soil is difficult to work because lay out because it is very steep and because of the stickiness and plasticity of the clay. It has lost most of its original surface layer through erosion.

3.2.2 Geology

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

(Map I-657), prepared by Victor M. Seiders (1971), the geologic units that lie at or near the site are the following:

1. Celada Formation (Kcl) – Described as basaltic pillow lava and volcanic breccia, generally rich in clinopyroxene. Includes subordinate volcanic sandstone and mudstone. Rare lavas contain plagioclase as the principal phenocryst. The bedding planes in the site vicinity are at 30-degrees with the horizontal and with a southwestern alignment

2. Hydrothermally Altered Rocks (TKa) – Described as hard, light-gray and grayish-green altered metamorphosed, and sheared volcanic and plutonic rocks. Primary textures largely absent or obscure. Exposed chiefly on north side of Gurabo valley. West of Quebrada

Project No.: DA/18O3776 Gurabo, Puerto Rico February 6, 2019

DESPIAU ASSOCIATES – CONSULTING GEOTECHNICAL ENGINEERS 4

Grande Fault rock is largely light-gray, fine-grained, strongly silicified; possibly altered felsic intrusive rock. Possibly may be altered strata of the Lomas and Celada Formations and subordinate intrusive rocks.

3. Alluvial and Terrace Deposits (Qat) – Described as sand, gravel, silt, and clay in flood plains along minor streams and in terrace deposits in major valleys.

The geologic map shows east of the site, the Quebrada Grande Fault, with a southeast trend, is at approximately 1420 meters, east of the project site. Several approximate (dashed) Unnamed fault lines are shown on the map close to the study area. These Unnamed approximate fault pass near the site and adjacent to the site, at distances of 150 mts. to the north and 200 mts. to the south, with a near southeast trend, all these three fault lines intersect at or close to State Road

PR-944 at about 600 meters, to the southeast of the project site.

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

3.3 Stratigraphic Units

Upper Surface Section – Generally at the road surface, the results of the exploration disclosed a surface layer thickness of about 1.5 to 4.0 ft. Following the nine 9”-inch to 8”-inch asphalt overlay [respectively at Borings 312-1 to 312-3], the surface layer is composed of light olive gray, dark brown, with yellow mottled sandy silt, with variable amounts of clay, with some subangular gravel fragments. At the locations of [Borings 312-4 to 312-5], the borings were drilled on the sloping ground surface where few roots were disclosed; this layer extends into the profile varying from 3 to 4 ft. The standard resistance to penetration (N-values) of the surface layers [Borings

312-1 to 312-3] varied from 36 to 114 blows/foot, at a dense to very dense of Compactness for the fill section and 3 to 4 blows/foot at the sloping grounds for a soft to medium State of

Consistency. The natural moisture content values range from 1 to 14 percent. Random samples of this layer [Boring 1- from 0’ to 1.5’] disclosed AASHTO class type A-1-a (1) AASHTO type soils

(USSCS type SW- Well-graded sand with gravel) and at [Boring 3- from 1.5’ to 3.0’] disclosed

AASHTO class type A-1-a (0) AASHTO type soils (USSCS type SP-SC-Poorly-graded sand with clay and gravel). The Free Swell Tests show percent values varying from 0 to 5 percent.

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Fill Section Material - The fill section [Borings 312-1 to 312-5], of varying thickness that extends to about 3.0 ft. The fill is occasionally intercalated with pavement debris [Boring 312-1] at the sample secured from 3.0 ft. deep. Following the upper fill layer, the subsurface profile extending to about 9.0 ft. was described as a mixture of sand, silt and clay, in varying proportions and with some subangular gravel fragments.

The standard resistance to penetration (N-values) of the fill section [Borings 312-1 to 312-5] varied from 6 to 48 blows/foot, at a loose to very dense State of Compactness for the fill section. The natural moisture content values range from 4 to 32 percent.

Residual Material – Beneath the above described layers, the virgin soil material was found, extending from about 9 ft. [Borings 312-1 to 312-5]. They are formed as textured sediments from the residuum of volcanic rock. The samples from this described as grayish brown, brown, light olive brown, pale yellow and reddish yellow, with yellow mottles sandy silt, with some weathered rock fragments. The standard resistance to penetration (N-values) of the residual layers varied from 15 to 80 blows/foot to practical refusal, at a dense to very dense State. The natural moisture content values range from 7 to 35 percent.

Completely and highly Weathered Rock – Deeper into the profile the completely weathered rock, broken by the sampling device into yellow, red, white light olive gray, brownish yellow, reddish yellow completely weathered rock with sandy silt fines, with traces of volcanic rock fragments, product of the weathering of the parent geologic altered metamorphosed, and sheared volcanic and plutonic rocks found. The standard penetration test attempts disclosed penetration

(N-values) of the residual layers varied from 53 to 80 blows/foot, to practical refusal practical refusal to penetration with values greater 100 blows for a few inches of penetration. The natural moisture contents range from 1 to 29 percent.

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

(1) to this report.

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3.4 Groundwater Levels

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

All surface ground and underground water should flow through existing drainage gullies, from higher sectors of the north toward the lowland areas to the south, through intermittent streams which are tributaries to the Gurabo River further to the south.

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 south and eastern sloping grounds, where landslides scarps have been experienced on the southern edge of State Road PR-181, caused by the extensive degradation, erosional effects provoking the observed damages and partial rupture of the road embankment and pavement structure and south slope surfaces.

Field observation revealed one (1) major landslides occurred along the southern edge of State

Road PR-181 near Km. 46.4. The extent of this major slide extends some 11.5 meters [near

Boring 312-3 & 312-2], however additional (minor) slides were observed extending for an approximate length of 45 to 60 meters [Borings 312-1 to 312-3]. The roadside elevation varies between 125.1 to 128.6 meters.

Evaluations dictate that besides the surface failures caused by the excessive runoff experience during the hurricane event, a failure plane exist at an average depth of 6.0 to 9.0 ft. in depth

[Borings 312-1 to 312-3, respectively]. Therefore, any retaining structure to be install shall be founded deeper than the previously mentioned failure plane.

Based on the results of the subsurface exploration performed, evaluations and Site observations, our engineering assessment is that the primary cause for the prevalent conditions were caused

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by the excessive surface subsurface water runoff, which eroded the south and eastern sloping ground of lower elevations and subsurface soils. Also, the extensive surface and subsurface runoff caused the oversaturation of the sandy silty clay soils, hence reducing its shearing strength further enhancing the driving forces which caused the slope failure. Thus, the primary factor which caused the slope failure was the intense or above normal surface and subsurface runoff experienced during Hurricane Maria. This is in addition to the surface erosion which the surface slides (minors) observed.

In addition, evaluation of the topographic plan submitted for the present evaluation revealed, the prevailing sloping grounds have slope ratios varying between 30° to 52° degrees. These slope ratios are considered very steep, which minimal surface runoff will trigger additional slides.

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 south and eastern edge of PR-181, near Km 46.4 to render stable grounds and road safety. As previously mentioned, the major slide observed extends some 11.5 meters [near Boring 312-3 & 312-2], however additional (minor) slides were observed extending for an approximate length of 45 to 60 meters [Borings 312-1 to 312-3]. Thus, the herein reconstruction alternatives can also be considered for the minor slides observed.

The herein recommendation by themselves and/or any combination of them shall be applied to the presently affected area to render stable grounds. The following sections of this report will provide the required Site improvements and foundation design recommendation for the proposed improvements required at the Site.

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

1. The improvements of the southern sloping grounds may also consider the use of a cantilever retaining structure (with or without a slope section on top, if space is available) to retain the southern sloping embankment mass and State Road PR-181 pavement structure.

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Also, considering the Site’s difference in elevation ( ELE) some 17.5 mts., approximately, a double wall system may be considered. This combined system entails the construction of two (2) retaining structures, one along the southern edge of PR-3 and the other on the intermediate sloping grounds, near borings 312-4 and 312-5 elevations. However, these shall be installed within the PRTHA Right of Way.

2. As an alternate solution retaining structure composed pre-drilled HP-steel piles with pre-cast panels to restrain the soil in between the piles may be considered to intersect the failure plane and restrain the road embankment. Evaluations dictate the retaining structure of approximately 10 to 15 meters shall be required for the major slide observed [Borings 312-3

& 312-2]. However, the additional (minor) slides can also be provided with this reconstruction solution. The pre-drill piles shall have a minimum embedment length of 20 to 25 ft. shall be considered. A minimum unsupported length of 9.0 ft. shall be considered by design. It shall be noted that the final length and type of the HP steel-pile section will depend on the final wall alignment and grading elevations as well as the expected lateral loads, as the structural evaluation will reveal. Also, the pre-cast panels shall be designed to withstand the expected lateral earth pressures (with full hydrostatic conditions) considering the in-situ soil parameters.

3. As a third alternative which may be considered is the use of a Gabion Retaining Wall (with or without a slope section on top) to retain the soil embankment mass and any existing structures (i.e. pavement structure). The retaining wall shall be provided all-throughout the affected area following the PR-181 alignment.

Regardless of the final design alternative selected, new and/or additional drainage facilities of enough capacity shall be provided, based on hydrologic study. All surface water shall drain freely away from the embankment slope mass all the way to the southern sector of PR-181 (ELE ≈

111.0 m). Therefore, all surface water shall drain away from the embankment slope mass and/or diverted past the toe of the sloping grounds discharging into adequate outfalls further to the south.

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

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V. ENGINEERING RECOMMENDATIONS

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 proposed improvements to the southern sloping grounds, where several landslides scarps have been experienced on the western edge of State Road PR-

181, which was subjected to extensive degradation, erosional effects, and landslides causing the observed damages and partial rupture of the road embankment and pavement structure.

The herein foundation recommendation shall be used for the foundation design of the retaining structures to be considered by the A/E Design team.

5.1 General Design Parameters for Retaining Structures

Evaluation indicate that provided the proposed retention structure unit(s) are adequately embedded, into the dense gravelly sandy silt residual, 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:

SUMMARY OF IN-SITU SOIL PARAMETERS FOR DESIGN

RECOMMENDED RANGE OF VALUES PER LAYERS – BORINGS 312-1 through 312-3

Soil Description Unit

Weight (pcf.)

Angle of Internal Friction (degrees)

Cohesion (psf.)

Allowable Soil Bearing Pressure

(psf.)

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

New Fill (Crushed-Stone) 133 33 Neglect

Upper Fill Sandy Silt, and gravel

(3.0’-11.0’) 120 23 500

Residual Material (11.0' -20') 126 26 1000 3.0 Ksf. @ 9.0 ft.

Weathered rock (>20’) 131 34 -

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RECOMMENDED RANGE OF VALUES PER LAYERS – BORINGS 312-4 & 312-5

Soil Description Unit

Weight (pcf.)

Angle of Internal Friction (degrees)

Cohesion (psf.)

Allowable Soil Bearing Pressure

(psf.)

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

New Fill (Crushed-Stone) 133 33 Neglect

Upper Fill Layer (0’-3.0’) 95 21 350

Silty Clay, Sand and Silt (3’-9’) 118 25 1200 3.0 Ksf. @ 7.0 ft.*

Residual Material (9' -15') 128 28 -

Weathered rock (>15’) 131 34 -

ADDITIONAL NOTES:

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

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

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

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

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

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Lateral Pressure Coefficient at rest case:

Coefficient Active Earth Pressure for sloping backfill:

Coefficient Passive Earth Pressure for sloping backfill:

Coefficient Active Earth Pressure for horizontal backfill for vertical face:

Coefficient Passive Earth Pressure for horizontal backfill for vertical face:

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

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

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

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

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

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

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

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

5.1.1 Additional Considerations for Retaining Structures

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

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

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

Also, considering the subsoil conditions found a sand cushion shall be provided beneath the proposed retaining units to avoid any punching shear to the base of the wall, provoke by any pinnacles of the rock once the excavation (working platform) is made.

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Considering the proposed retaining structures 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. In lieu, a structural key or soil/rock anchors may be provided to the foundation to avoid the translation of the foundation stresses to the sloping grounds and provide an additional sliding retraining measure. However, the prevailing slopes to remain shall be protected against scour and/or erosional effects during an intensive rainfall.

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 9.0 ft. [Borings 312-2 & 312-

3], beneath any loose/soft fill section and slope-wash material into the residual soil.

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

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

Should the proposed foundation do not meet the minimum separation requirement, deepening of the foundation shall be required. Also, a structural key 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.

5.2 Additional Recommendation for Cantilever Retaining Structure

The improvements of the southern sloping grounds may also consider the use of a cantilever retaining structure (with or without a slope section on top, if space is available) to retain the southern soil embankment mass and State Road PR-181 pavement structure.

Also, considering the Site’s difference in elevation ( ELE) some 17.5 mts., approximately, a double wall system may be considered. This combined system entails the construction of two (2) retaining structures, one along the southern edge of PR-3 and the other on the intermediate sloping grounds, near borings 312-4 and 312-5 elevations. However, these shall be installed within the PRTHA Right of Way.

Therefore, evaluations dictate the retaining structure of approximately 10 to 15 meters shall be required for the major slide observed [Borings 312-3 & 312-2]. However, the additional (minor) slides can also be provided with this cantilever type retaining structure (s).

The minimum depth of foundation (Df) where the base of the retaining structure shall be installed is 9.0 ft into the in-situ residual and weathered material [Boring 312-2 & 312-3]. Thus, the bottom foundation elevation shall be at approximately 125.5 meters. However, a shorter wall may result, Project No.: DA/18O3776 Gurabo, Puerto Rico February 6, 2019

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if it is provided with an adequate slope section (2H:1V) on top, to reach the roadside elevation.

On the other hand, should a retaining wall be installed at mid height of the southern sloping grounds [Borings 312-4 & 312-5], then the minimum depth of foundation shall be 7.0 ft. Thus, the total height of the wall will depend on the final wall alignment, location and grading elevations and if they are provided with an adequate slope section on top, to reach the roadside elevation.

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 9.0 ft., beneath any loose/soft saturated and any slope-wash material.

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

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

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

5.3 Additional Recommendations for Pre-Drilled Hp-Steel Piles with Pre-Cast Panels

Evaluations dictate the retaining structure of approximately 10 to 15 meters shall be required for the major slide observed [Borings 312-3 & 312-2] and the prevailing sloping grounds west of State

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Road PR-3, at the study sector, have slope ratios ranging between 30° to 52° degrees. However, the additional (minor) slides can also be provided with this reconstruction solution

The pre-drilled HP-steel piles with pre-cast panels to restrain the soil in between the piles may be considered to intersect the failure plane and restrain the road embankment. The herein proposed wall shall be located at a distance from the southern edge of PR-181 such that it encases the proposed fill embankments, perpendicular to the slope failure.

The Steel HP-piles shall be spaced at 5.0 to 8.0 ft. on center approximately (depending on actual expected loading conditions), can be considered to restrain and restrict the embankment soil, existing structures movement (i.e. Pavement Structure) and the soil in between the piles.

For piles to be effective they should have a minimum embedment length of 20 to 25 ft. into the residual and weathered rock found in the borings of exploration, shall be considered. However, the final location, configuration, length and height shall be determined once the final design scheme is selected by the A/E Design Team.

A minimum unsupported length of 9.0 ft. plus the height required to reach the roadside elevation

(failure plane depth + H of grading) shall be considered by design. Thus, the total length of the pile sections shall be approximately 25 to 30 ft. (pile bottom tip elevation at approximately 120.5 mts.). Considering the subsurface conditions at the site, where the residual and saprolitic material was found as shallow as 15.0 ft., the pre-augering to encase (with poured concrete) the Steel-HP

Piles shall be required.

It shall be noted that the final length and type of the HP steel-pile section will depend on the final wall alignment and grading elevations as well as the expected lateral loads, as the structural evaluation will reveal.

The pile units and pre-cast panels shall be designed to withstand the expected lateral earth pressures (with full hydrostatic conditions), surcharge loads and structure load. 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 total height of the pre-cast panel sections shall be determined based on the final grading elevations of the project. Preliminary estimates revealed a total height of 8.0 to 10.0 ft.