Report_GEO_AC-829579_HWY-23.pdf

GEOTECHNICAL REPORT

LANDSLIDE AND ROAD DAMAGE EVALUATION

AND REPAIR RECOMMENDATIONS

PR-109 KM 7.30-7.05, AÑASCO, PR

ER-HWY-23

AC-809544

Submitted to:

José A. Batlle Montalvo, PE

José A. Batlle y Asociados, CSP

Prepared by:

Carlos R. Sierra Del Llano, MSCE, PE

Rommel Cintrón Aponte, MSCE, PE

Date:

February 8, 2019

Revision:

August 14, 2020

Job no. 7933

P

O

B o x

S a n

J u a n

P

R

Geotechnical Report: Site ER HWY 23

Road Damage Evaluation and Repair Recommendations PR 109 KM 7.30-7.05 Añasco, PR

J a c a & S i e r r a E n g i n e e r i n g , P S C

P O B o x 3 6 3 1 1 6 , S a n J u a n , P R 0 0 9 3 6 - 3 1 1 6

R o a d 8 5 0 K m 0 . 2 L a s C u e v a s W a r d , T r u j i l l o A l t o , P R 0 0 9 7 6

T . 7 8 7 - 7 6 1 - 2 5 7 0 w w w . j a c a s i e r r a . c o m

1. Introduction

The present geotechnical report addresses the geotechnical conditions and recommendations for the road damages at the reference site location. This investigation is prepared based on approved scope of work and economical proposal by Jose A. Batlle y Asociados, CSP. This report is part of a multiple site assessment project for similar landslide rehabilitation cases related to damages by Hurricane

Maria on September 20, 2017. This report is prepared exclusively for design purposes.

2. Scope of Work

The scope of work consisted of one (1) test boring to 20 ft (6.1 mts) depth. The boring was completed with a man portable motorized derrick and aluminum leg tripod assembly at accessible location along the side of the road. Test boring and soil sampling were performed by casing installation in accordance to ASTM D1452 and soil sampling per Standard Penetration Test (SPT) method per ASTM D1586. Refer to enclosed boring location plan for reference on boring location (Appendix A Figure

A2).

3. Site Geology

Based on the USGS Geology Map (refer to Appendix A Figure A1), the site falls within

Ky – Yauco Mudstone Formation. The rock formation consists of a mostly thin bedded dark gray calcareous mudstone, sandstone and chert with some thin beds of tuff. This formation was encountered to be weathered into a clay saprolite soil, as described below.

Site ER HWY 23

PR 109 KM 7.30-7.05 Añasco, PR

P A G E | 2

0 8 / 1 4 / 2 0 Jaca & Sierra Engineering, PSC

t. 787-761-2570 e. contact@jacasierra.com www.jacasierra.com

4. Site Stratigraphy

Stratum no. 1: Fill: A fill deposit was encountered having a depth of 6 ft beneath existing ground surface. The fill consisted of fat clay with some rock fragments in the upper horizon. SPT-N values ranged from 7 to 11 blows/ft and moisture contents from 20 to 35 %. Per soil classification test and visual and manual description, it is our opinion that this fill material has variable classifications of AASHTO A-2-6 or A-

2-7 and A-7-6.

Stratum no. 2: Saprolite: A saprolite soil was encountered extending to the end of test boring at 20 ft beneath existing ground surface. The saprolite soils consisted of lean clay with sand and relic joints. SPT-N values ranged from 17 to 30 blows/ft and moisture contents from 27 to 34 %. Per soil classification test and visual and manual description, it is our opinion that this saprolite material has classifications of AASHTO

A-6 and A-7-6.

5. Geotechnical Recommendations

5.1. Opinion on Probable Causes for Road Damage

It is our opinion that the apparent cause of failure is related to a shallow landslide and clayey soil slope displacement occurring by over-steepening of the slope due to erosion and overland runoff over the slope. It was observed that the area has been filled with debris, tree trunks and organic matter. The slide dimensions could not be measured due to the presence of debris and dense vegetation.

5.2. Slope Rehabilitation Alternatives

5.2.1. Concrete Cantilever Retaining Wall: This option has the advantage that it can be built right on the edge of the road as a jersey barrier extension (typical PRHTA section). The closer the retaining wall is to the roadway edge, the less the retaining mailto:contact@jacasierra.com

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0 8 / 1 4 / 2 0 wall height required. It being the option that can be built as close as possible to edge of road, it is the alternative having the lowest required height. The wall foundation depth shall be at minimum 1.2 mts (4 ft) beneath slope face as measured from the lower side. The slope along the gully can be restored leveling its surface and re-vegetation with fern or vetiver. Temporary turf reinforcement can be used while vegetation populates the slope. Minimize slope disturbance and removal of existing vegetation, as best as possible, by limit work to the slide area.

5.2.2. Gabion Wall: This option will need a retaining wall to be offset from the edge of the road to allow placement of a guard rail or a jersey barrier. Based on profiles provided to us, the wall height will be in the order of 5.5 mts (18 ft).

5.2.3. Reinforced Soil Slope (RSS): This option will entail excavation of the existing slope, which will be to an extent requiring closing the road and then placement of reinforced engineered fill in layers up to final grades. RSS can have a slope inclination of 1:1 to 1:1.5 (H:V). It is our opinion that this option may not be feasible and it is not known if it will extend into lands that are not owned by PRHTA.

5.2.4. Concrete Gravity Wall: This option has the advantage of minimizing excavation width at the edge of the road. The gravity wall can be designed per

PRHTA’s standard design section to be verified and adjusted by designer based on the herein provided bearing capacity and earth pressure parameters. Similar to the cantilever wall, it shall be embedded at least 1.2 mts (4 ft) below slope surface as measured from the lower side.

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5.3. Earth Pressure Parameters for Retaining Wall Design

Strength or Earth Pressure Parameters

Engineered Fill /

Retaining Wall

Backfill

In-Situ Soils

Drained cohesion, c, kPa (psf) 0 (0) 23.9 (500)

Drained angle of internal friction, φ, ˚ 32 25

Undrained cohesion, c, kPa (psf) - 71.8 (1,500)

Undrained angle of internal friction, φ, ˚ - 0

Moist unit weight, γ, kN/cu.mt. (pcf) 20.4 (130) 19.6 (125)

Seismic horizontal coefficient, kh - 0.2

Base shear coefficient, * - 0.3

Net allowable bearing capacity for retaining wall over native soil, qa, kPa (psf) **

- 143.6 (3,000)

Table 1: Earth pressure parameters for retained soils

*For passive resistance neglect upper 3 ft, for passive side unit weight of backfill assume 15.7 kN/cu.mt.

(100 pcf).

Calculations of allowable bearing capacity, base shear coefficient and seismic horizontal coefficient are presented in Appendix D. Settlements are considered below

1 inch due to the presence of underlying very stiff clay. A conservative rough estimate of consolidation settlement is also shown in Appendix D to support the assumption of expected settlement within a tolerable limit.

5.4. Global Stability Analysis Results

Soil

Condition Seismic Coefficient

Minimum Factor of Minimum Factor of

Safety Obtained Safety Required

Drained None (Static) 3.268 1.500

Drained Horizontal (Pseudostatic) 1.988 1.125

Undrained None (Static) 5.058 1.500

Undrained Horizontal (Pseudostatic) 3.137 1.125

Table 2: Summary of global stability analysis results

GEO-SLOPE SLOPE/W Version 5.2 software was used for global stability analysis of the preferred gravity wall alternative. Results and relevant information are presented in Appendix E.

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6. Generalized Recommendations

6.1. Recommended Backfill Material: All engineered fill shall consist of A-2-4 or

A-1 AASHTO Classification fill placed and compacted to 95 % of the modified Proctor density. Engineered fill shall be handled and placed per latest applicable PR Highway

Authority Specifications. Engineered fill shall be monitored by soil technician with guidance from a geotechnical engineer.

6.2. Fill Recommendations: Any fill shall be constructed upslope in horizontal layers and benched terraces shall be cut at the interface of fill and natural soils. The benches shall have a minimum width of 0.9 mts and shall be made at a maximum vertical distance of 0.9 mts as fill progresses upward. Unreinforced engineered fill slopes shall not exceed 2:1 (H:V) inclination.

6.3. Drainage: Road drainage shall be controlled by jersey barriers, curbs and gutters or storm runoff management devices designed in such way that it prevents any overland water discharge over the project areas.

6.4. Slope Erosion Control: Protect all slopes disturbed by excavation process with sodding or turf reinforcement. Deep rooted vegetation, such as vetiver and ferns

(“helechos”) is recommended within any area impacted by the project. For this particular case, we recommend avoiding disturbance of existing vegetated slopes downslope of the retaining wall, thus limiting the above erosion control measures to areas impacted by excavations and retaining wall construction.

6.5. Differing Site Conditions: These recommendations are based on test borings performed on locations, which are considered as representative of the subsoil conditions within the site, but not all areas of the site could be explored due to limitations of access. Therefore, differing site conditions could occur. In such instances, we shall be notified to proceed with a field visual inspection directed to formulate the corresponding solution.

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6.6. Excavation Safety: Contractor is responsible to adjust excavation inclination and provide shoring, where necessary, to ensure safety of working personnel per latest applicable OSHA excavation safety standards. The contractor shall consult with geotechnical engineer or geologist on excavation inclination and shoring requirements.

6.7. Geotechnical Engineer Confirmation: The excavations shall be coordinated with the undersigned to conduct a site visit by a representative from Jaca & Sierra

Engineering, PSC to verify conditions and confirm foundation depth among other geotechnical considerations.

Thanks for the opportunity of providing our field investigation, testing and engineering consulting services. Feel free to contact us for any questions on our report.

Respectfully submitted, JACA & SIERRA ENGINEERING, PSC

Carlos R. Sierra Del Llano, MSCE, PE

Rommel Cintron Aponte, MSCE, PR

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Appendix A: Geology Map and Boring Location Plan

Figure A1: Site Geology Map (McIntyre, D.H., 1971, Geologic map of the Central La Plata quadrangle, Puerto

Rico: U.S. Geological Survey, Miscellaneous Geologic Investigations Map I-660)

SITE

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Figure A2: Boring Location Map (Topography Drawing by Javier E. Bidot & Associates, PSC)

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Appendix B: Site Conditions Photographic Images

Figure B1: Landslide Area

Figure B2: Landslide Area

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Figure B3: Erosion Gully Area Filled with Debris

Figure B4: Adjacent Cut Slope with Erodible Clayey Silt Saprolite

Appendix C:

Boring Logs and Laboratory Tests

52.40

50.57

FILL: clay some rock fragments, reddish brown

SAPROLITE: clay with sand, very stiff, relic joints, reddish brown

End of Boring

S-1

S-2

S-3

S-4

S-5

S-6

S-7

2.5

1.6

SUBSURFACE EXPLORATION LOG

BORING N0.: 23-A

PROJECT

Site ER-HWY-23

JOB

OF

SHEET 1

LOCATION Añasco, PR DRILLER/DRILL RIG: Carlos I. Diaz / Portable Tripod COORDINATES 250217.437 N 128433.034 E DATE HOLE STARTED 10-19-18 COMPLETED 10-19-18

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 52.4 GROUNDWATER (FT) Initial: Not Found Final: ENGINEER Carlos R. Sierra Del Llano DRILLING METHOD: Portable Tripod TOTAL DEPTH OF HOLE (ft): 20.5

N W Qu PL+LL

"N" - Number of blows required to drive the sampling spoon a distance of 12 in. with a 140 lbs hammer falling 30 in.

"W" - Natural Moisture Content in percentage of dry weight. Initial G.W. Depth "Qu" - Unconfined Compressive Strength in tons per square foot. Final G.W. Depth "Rc" - Core recovery in percent for each successive run. "Rqd" - Rock quality designation.

"WH" - Sample was recovered by advancing the sampler with the weight of the hammer.

"P" - A "P" in the Unconfined Compressive Strength test indicates the use of the pocket Penetrometer.

Elev.

(mts)

0.00

DEPTH

(feet) DESCRIPTION

LE

G

E N

D

S am pl e

N o.

TY

P

E

B

LO

W S

SPT

N W Qu RC RQD%

20 40 60 80

1 2 3 4

Qu

N-W

(X=NO)PERCENTFINERSIZE

PASS?SPEC.*PERCENTSIEVE

Project No:

Project:

Client:

Elev./Depth:Location:

Date:Source of Sample:Sample No.:

Remarks

Classification

Coefficients

Atterberg Limits

Material Description

AASHTO=USCS=

Cc=Cu=

D10=D15=D30=

D50=D60=D85=

PI=LL=PL=

Particle Size Distribution Report

P E R C E N T F

IN

E R

100 10 1 0.1 0.01 0.001500

GRAIN SIZE - mm

% +75 MM % GRAVEL % SAND % SILT % CLAY

i n i n i n

-1 /2 i n i n

/4 i n

/2 i n

/8 i n

0.0 0.3 11.7 88.0

Figure7933

Site ER-HWY-23, Anasco, PR

Jose A. Batlle & Associates

4-5.5'Anasco, PR

12/27/18Project Site23-A (S-3)

Tested by: A. Roman

Checked by: Carlos Sierra Del Llano, MSCE, PE

A-7-6(25)CH

255227

Fat clay

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 99.7 98.6 93.5 90.0 88.0

.375 in.

#4

#10 #40

#100 #200

(X=NO)PERCENTFINERSIZE

PASS?SPEC.*PERCENTSIEVE

Project No:

Project:

Client:

Elev./Depth:Location:

Date:Source of Sample:Sample No.:

Remarks

Classification

Coefficients

Atterberg Limits

Material Description

AASHTO=USCS=

Cc=Cu=

D10=D15=D30=

D50=D60=D85=

PI=LL=PL=

Particle Size Distribution Report

P E R C E N T F

IN

E R

100 10 1 0.1 0.01 0.001500

GRAIN SIZE - mm

% +75 MM % GRAVEL % SAND % SILT % CLAY

i n i n i n

-1 /2 i n i n

/4 i n

/2 i n

/8 i n

0.0 0.0 17.3 82.7

Figure7933

Site ER-HWY-23, Anasco, PR

Jose A. Batlle & Associates

9-10.5'Anasco, PR

12/27/18Project Site23-A (S-5)

Tested by: R. De Jesus

Checked by: Carlos Sierra Del Llano, MSCE, PE

A-7-6(18)CL

0.0914

214524

Lean clay with sand

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 99.9 96.5 90.2 82.7

#4 #10 #40

#100 #200

Appendix D:

Geotechnical Calculations

Allowable Bearing Capacity ϕ = angle of internal friction for soil beneath foundation, c = cohesion for soil beneath foundation, su = undrained shear strength for soil beneath foundation, D = depth of foundation below ground surface, Bc = width of continuous foundation, σzD = vertical stress at depth D below ground surface, γ = soil unit weight around foundation, Nc, Nq, Nγ = Terzaghi’s bearing capacity factors in function of ϕ, qult = ultimate bearing capacity, FS = Factor of Safety, qa = allowable bearing capacity, gc, gq, gγ = Vesic’s ground inclination factors, β = ground inclination

(downslope)

Underlying Soil: Very stiff clay

Method: Terzaghi

Data from cross section Sta. 72+40: D = 3 ft, Bc = 9 ft, Gravity wall, β = 26.5˚

Data from Table 1: γ = 125 pcf

FS > 2 => FS = 2.35 considered σzD = γD σzD = 375 psf 𝑔𝑐 = 1 − 𝛽

147° gc = 0.82 𝑔𝑞 = 𝑔𝛾 = (1 − tan𝛽)2 gq = gγ = 0.25

Drained

Data from Table 1: ϕ = 25˚, c = 500 psf

Bearing capacity factors for ϕ = 25˚: Nc = 25.13, Nq = 12.72, Nγ = 8.34

Continuous Foundations qult = cNc𝑔𝑐 + σzDNq𝑔𝑞 + 0.5γBNγ𝑔𝛾 qult = 12,669 psf qa = qult

FS

qa = 5,391 psf

Undrained

Data from Table 1: ϕ = 0˚, su = 1,500 psf

Bearing capacity factors for ϕ = 0˚: Nc = 5.70, Nq = 1.00, Nγ = 0.00

Continuous Foundations qult = suNc𝑔𝑐 + σzDNq𝑔𝑞 qult = 7,105 psf qa = qult

FS

qa = 3,023 psf => qa = 3,000 psf considered

Base Shear Coefficient ϕ = angle of internal friction for soil beneath foundation, μ = base shear coefficient of friction

Underlying Soil: Very stiff clay

Data from Table 1: ϕ = 25˚ μ = tan(0.7φ) μ = 0.32

Seismic Horizontal Coefficient

PGA = peak ground acceleration, kh = quotient of horizontal component of earthquake acceleration and gravity acceleration, kv = quotient of vertical component of earthquake acceleration and gravity acceleration

From ASCE 7-16: PGA = 0.46 g kh =

PGA

kh = 0.23

Consolidation Settlement

This is a rough estimate to support the assumption of consolidation settlement lower than 1 inch.

H = soil layer thickness, z = depth at midpoint of soil layer, σz0 = initial vertical stress at midpoint of soil layer, d = depth of foundation below ground surface, zf = depth below bottom of foundation, bc = width of continuous foundation, Iσc = stress influence factor for continuous foundation, q = bearing pressure along bottom of foundation, γ = soil unit weight around foundation, σzd = vertical stress at depth d below ground surface, Δσz = induced vertical stress due to load from foundation, σzf = final vertical stress at midpoint of soil layer, Cr = recompression index, e0 = initial void ratio, CR = Cr/(1+e0), δc = consolidation settlement

Data from Boring no. 23-A, 10-15 ft depth (5 ft zone below bottom of foundation), Very stiff clay, N = 25-30 bpf

Data from cross section Sta. 72+40: d = 3 ft, bc = 9 ft, Gravity wall

Data from Table 1: γ = 125 pcf, q = 3,000 psf

Assumptions: H = 5 ft, z = 5.5 ft, Overconsolidated soils σz0i = γ1H1 + γ2H2 +⋯+ γnHn σz0 = 125(2.5) = 313 psf zfi = z − d zf = 2.5 ft

Continuous Foundation

Iσci = 1 − (

1 + ( bc 2zf

)1.38 )2.6

Iσc = 0.95 σzd = γd σzd = 375 psf

∆σzi = Iσ(q − σzd) Δσz = 2,503 psf σzfi = σz0 + ∆σz σzf = 2,815 psf

CRi = Cr

1 + e0

CR = 0.001 => Assumed conservative value δci = CRHlog( σzf σz0 δc = 0.06 in δc = δc1 + δc2 +⋯+ δcn δc = 0.06 in < 1 in

Appendix E:

SLOPE/W Software Results

Figure E1

Figure E2

Figure E3

Figure E4