Report_GEO_AC-829579_HWY-26.pdf

GEOTECHNICAL REPORT

LANDSLIDE AND ROAD DAMAGE EVALUATION

AND REPAIR RECOMMENDATIONS

PR-109 KM 10.30, AÑASCO, PR

ER-HWY-26

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 7, 2019

Revision:

August 14, 2020

Job no. 7936

P

O

B o x

S a n

J u a n

P

R

Geotechnical Report: Site ER HWY 26

Road Damage Evaluation and Repair Recommendations PR 109 KM 10.30 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 two (2) test borings to 20 ft (6.1 mts) depth. Borings were completed with a trailer-mounted CME-45 drill rig at accessible locations along the side of the road. Test borings and soil sampling were performed by auger drilling 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

Tmp – Mal Paso Formation. The rock formation consists of reddish gray and purple basalt pillow lavas, basalt breccias and tuff. This formation was encountered to be weathered into a clayey silt saprolite soil, as described below.

Site ER HWY 26

PR 109 KM 10.30 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 at both locations having a depth of

4 ft beneath existing ground surface. The fill consisted of clayey silt and sandy silt.

SPT-N values ranged from 6 to 19 blows/ft and moisture contents from 13 to 30 %.

Per soil classification test, this fill material has classification of AASHTO A-7-5.

Stratum no. 2: Saprolite: A saprolite soil was encountered at both locations extending to the end of test borings at 20 ft beneath existing ground surface. The saprolite soils consisted of clayey silt with relic joints. SPT-N values ranged from 9 to 15 blows/ft and moisture contents from 31 to 40 %. Per visual and manual description, it is our opinion that this saprolite material has classification of AASHTO A-6 to 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 silty soil slope displacement occurring by over-steepening of the slope due to erosion from overland runoff during storm event. The cracks in the pavement are likely to be related to the silty fill materials under the road near the slide area which have poor subgrade resistance and become affected by seasonal moisture variations and wetting.

The slide dimensions could not be measured due to the presence of dense vegetation and debris.

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 wall height required. The height of the required concrete retaining wall will be in the mailto:contact@jacasierra.com

P A G E | 3

0 8 / 1 4 / 2 0 order of 1.5 to 2 mts (5 to 7 ft). This option shall include leveling the remaining slope to uniform inclination and armoring with turf reinforcement and deep-rooted vegetation such as vetiver.

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 1.8 mts (6 ft) or two levels of gabion baskets (0.9 mt each) per PRHTA standard designs.

5.2.3. Slope Reconstruction by Excavation and Engineered Fill: This option will entail removing debris from the slope and reconstruct the slope with engineered fill to a slope of 2:1 (H:V). Benching will be required at the contact between fill and in-situ soils as explained below. The slope shall be protected with turf reinforcement and re-vegetation.

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) 16.8 (350)

Drained angle of internal friction, φ, ˚ 32 25

Undrained cohesion, c, kPa (psf) - 47.9 (1,000)

Undrained angle of internal friction, φ, ˚ - 0

Moist unit weight, γ, kN/cu.mt. (pcf) 20.4 (130) 18.9 (120)

Seismic horizontal coefficient, kh - 0.2

Base shear coefficient, * - 0.3

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

- 95.8 (2,000)

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).

P A G E | 4

0 8 / 1 4 / 2 0

Although the preferred alternative is slope reconstruction, calculations of allowable bearing capacity, base shear coefficient and seismic horizontal coefficient are presented in Appendix D for reference purposes. Settlements are considered below 1 inch due to the presence of underlying stiff clayey silt. 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) 1.603 1.500

Drained Horizontal (Pseudostatic) 1.143 1.125

Undrained None (Static) 2.180 1.500

Undrained Horizontal (Pseudostatic) 1.553 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 slope reconstruction alternative. Results and relevant information are presented in Appendix E.

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

P A G E | 5

0 8 / 1 4 / 2 0 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.

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.

P A G E | 6

0 8 / 1 4 / 2 0

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

P A G E | 7

0 8 / 1 4 / 2 0

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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0 8 / 1 4 / 2 0

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

ER-26-A

ER-26-B

P A G E | 9

0 8 / 1 4 / 2 0

Appendix B: Site Conditions Photographic Images

Figure B1: Damaged Road Area and Cracked Pavement

Figure B2: Damaged Area

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0 8 / 1 4 / 2 0

Figure B3: Slope Area Covered with Vegetation and Some Debris Covering an Erosion Gully and

Shallow Slide

Figure B4: Damaged Area

Appendix C:

Boring Logs and Laboratory Tests

28.10

27.49

26.88

FILL: sandy silt with gravel, brown

FILL: clayey silt, brownish red, light gray mottled

SAPROLITE: clayey silt, stiff, oxidized red, light gray mottled

Do... relic joints, light gray, purple, red mottled

End of Boring

S-1

S-2

S-3

S-4

S-5

S-6

S-7

2.9

SUBSURFACE EXPLORATION LOG

BORING N0.: 26-A

PROJECT

Site ER-HWY-26

JOB

OF

SHEET 1

LOCATION Añasco, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45 COORDINATES 249498.222 N 130402.476 E DATE HOLE STARTED 12-17-18 COMPLETED 12-17-18

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 28.1 GROUNDWATER (FT) Initial: Not Found Final: ENGINEER Carlos R. Sierra Del Llano DRILLING METHOD: Hollow-Stem Auger 2.25" ID 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

27.40

26.18

FILL: clayey silt, brownish red, gray

SAPROLITE: clayey silt, stiff, relic joints, light gray, red, white mottled

Do... dark brown, white mottled

End of Boring

S-1

S-2

S-3

S-4

S-5

S-6

S-7

0.9

1.8

SUBSURFACE EXPLORATION LOG

BORING N0.: 26-B

PROJECT

Site ER-HWY-26

JOB

OF

SHEET 1

LOCATION Añasco, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45 COORDINATES 249488.702 N 130408.732 E DATE HOLE STARTED 12-17-18 COMPLETED 12-17-18

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 27.4 GROUNDWATER (FT) Initial: Not Found Final: ENGINEER Carlos R. Sierra Del Llano DRILLING METHOD: Hollow-Stem Auger 2.25" ID 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 0.1 4.4 95.5

Figure7936

Site ER-HWY-26, Anasco, PR

Jose A. Batlle & Associates

2-3.5'Anasco, PR

2/4/19Project Site26-B (S-2)

Tested by: A. Roman

Checked by: Carlos Sierra Del Llano, MSCE, PE

A-7-5(24)MH

185739

Elastic silt

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 99.9 99.8 98.7 96.5 95.5

.375 in.

#4

#10 #40

#100 #200

Appendix D:

Geotechnical Calculations

The preferred solution in this report is Slope Reconstruction. However, geotechnical calculations are presented for reference assuming a Gravity Wall.

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: Stiff clayey silt

Method: Terzaghi

Data from Table 1: γ = 120 pcf

Assumptions: D = 3 ft, Bc = 9 ft, β = 26.5˚

FS > 2 => FS = 2.35 considered σzD = γD σzD = 360 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 = 350 psf

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

Continuous Foundations qult = cNc𝑔𝑐 + σzDNq𝑔𝑞 + 0.5γBNγ𝑔𝛾 qult = 9,483 psf qa = qult

FS

qa = 4,035 psf

Undrained

Data from Table 1: ϕ = 0˚, su = 1,000 psf

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

Continuous Foundations qult = suNc𝑔𝑐 + σzDNq𝑔𝑞 qult = 4,764 psf qa = qult

FS

qa = 2,027 psf => qa = 2,000 psf considered

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

Underlying Soil: Stiff clayey silt

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 Borings no. 26-A & 26-B, 10-15 ft depth (5 ft zone below bottom of foundation), Stiff clayey silt, N = 13-14 bpf

Data from Table 1: γ = 120 pcf, q = 2,000 psf

Assumptions: d = 3 ft, bc = 9 ft, H = 5 ft, z = 5.5 ft, Overconsolidated soils σz0i = γ1H1 + γ2H2 +⋯+ γnHn σz0 = 120(2.5) = 300 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 = 360 psf

∆σzi = Iσ(q − σzd) Δσz = 1,563 psf σzfi = σz0 + ∆σz σzf = 1,863 psf

CRi = Cr

1 + e0

CR = 0.01 => Assumed conservative value δci = CRHlog( σzf σz0 δc = 0.48 in δc = δc1 + δc2 +⋯+ δcn δc = 0.48 in < 1 in

Appendix E:

SLOPE/W Software Results

Figure E1

Figure E2

Figure E3

Figure E4