Report_GEO_AC-829579_HWY-27.pdf

GEOTECHNICAL REPORT

LANDSLIDE AND ROAD DAMAGE EVALUATION

AND REPAIR RECOMMENDATIONS

PR-109 KM 16.40-16.63, AÑASCO, PR

ER-HWY-27

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. 7935

P

O

B o x

S a n

J u a n

P

R

Geotechnical Report: Site ER HWY 27

Road Damage Evaluation and Repair Recommendations PR 109 KM 16.40-16.63 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 four (4) test borings to 15 to 20 ft (4.6 to 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

Kb – Rio Blanco Formation. The rock formation consists of a massive well indurated tuff breccia with blocks of basalt and andesite. This formation was encountered to be weathered into a silty sand saprolite soil, as described below.

Site ER HWY 25

PR 109 KM 16.40-16.63 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 in all locations having depths of 2 to 4 ft beneath existing ground surface. The fill was heterogeneous, consisting mostly of sandy gravel, sandy silt and clayey silt. SPT-N values ranged from 2 to above 100

(i.e. refusal blow counts) blows/ft and moisture contents from 4 to 27 %. High N values are chiefly related to the presence of gravel and not necessarily represent dense/hard fill soil material.

Stratum no. 2: Saprolite: A saprolite soil was encountered also in all locations extending to the end of test borings at 15 and 20 ft beneath existing ground surface.

The saprolite soils consisted of silty sand with relic joints. SPT N values ranged from

4 to 78 blows/ft and moisture contents from 7 to 28 %. Per soil classification tests, this saprolite material has classifications of AASHTO A-4 and A-2-4. Weathered rock sampled as silty sand with rock fragments was found in boring no. 27-C having refusal blow counts.

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 sandy soil slope displacement occurring by over-steepening of the slope due to erosion from overland runoff and diversion of water in to the edge of the road by small landslides and debris flows occurring from the up-slope to the west of the road.

Seepage was noted from the top cut slope west of the road. It is important that any backfill used consist of granular soil materials per recommendations of this report and that sub-drain systems be incorporated on the backfill behind the wall. The approximate slide dimensions are 12 mts long by 8.5 mts wide by 8 mts deep mailto:contact@jacasierra.com

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(elevations from 62 to 54 mts). The depth of the slide scarp at the edge of the road is about 1 mt.

5.2. Slope Rehabilitation Alternatives

5.2.1. Gabion Wall: This option is preferred due to the inherent ability to drain any seepage occurring on to the backfill of the wall. This option will need to be offset from the edge of the road to allow placement of a guard rail or a jersey barrier, thus resulting in a higher wall compared to concrete cantilever wall combined with a top concrete barrier. The base of the wall shall be embedded at least 1.2 mts (4 ft) into the saprolite and weathered rock formation. Based on profiles provided to us, the wall height will be in the order of 4 to 6 mts (13 to 20 ft).

5.2.2. Anchored Gabion Wall: This concept consists of a gabion wall with single or double basket per row with a tie back anchor supporting the baskets. This has the advantage of minimizing excavations on the slope and reducing overall size of the gabion wall.

Figure 1: Anchored Gabion Schematic Concept (Not to Scale)

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5.2.3. 2:1 Fill Slope or Steeper Reinforced Soil Slope: If deemed feasible, this option will entail restoring the slope with engineered fill. It is important to build benches on transition between cut and fill. The parameters used for engineered fill backfill can be used to verify internal stability. If this option is adopted, the base of the wall shall be embedded at least 0.9 mt (3 ft) into the saprolite and weathered rock formation.

5.2.4. 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. 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 height of the required concrete retaining wall will vary from 3 to 5 mts (10 to 16 ft). This option shall include leveling the slope to uniform inclination and armoring with turf reinforcement and deep-rooted vegetation such as vetiver.

5.2.5. 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 and the slope extending beyond the base of the wall shall be protected against erosion.

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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) 7.2 (150)

Drained angle of internal friction, φ, ˚ 32 32

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

Seismic horizontal coefficient, kh - 0.2

Base shear coefficient, * - 0.4

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

- 191.5 (4,000)

Table 1: Earth pressure parameters for retained soils

*For passive resistance neglect upper 4 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. Since underlying in-situ soil consists of medium dense silty sand, no consolidation settlement is expected, or negligible. Elastic settlement occurring immediately upon gravity wall construction is assumed to be lower than 1 inch due to the existing medium dense or greater relative density based on SPT-N values.

5.4. Global Stability Analysis Results

Soil

Condition Seismic Coefficient

Minimum Factor of Minimum Factor of

Safety Obtained Safety Required

Drained None (Static) 1.590 1.500

Drained Horizontal (Pseudostatic) 1.137 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)

ER-27-A

ER-27-B

E-27-C

ER-27-D

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Appendix B: Site Conditions Photographic Images

Figure B1: Landslide Area, Note Excavation for Replacement of Water Line within the Affected

Shoulder of Road and Seepage from the Upper Roadway Cut Slope

Figure B2: Landslide and Damaged Road Area

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Figure B3: Slope Area within Landslide

Appendix C:

Boring Logs and Laboratory Tests

63.50

62.89

62.28

FILL: sandy gravel, gray

FILL: clayey silt some sand, brownish red

SAPROLITE: silty sand, loose, brownish red

Do... medium dense, relic joints

End of Boring

S-1

S-2

S-3

S-4

S-5

S-6

S-7

50/6"

50/6"

1.0

SUBSURFACE EXPLORATION LOG

BORING N0.: 27-A

PROJECT

Site ER-HWY-27

JOB

OF

SHEET 1

LOCATION Añasco, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45 COORDINATES 249520.032 N 134108.064 E DATE HOLE STARTED 12-20-18 COMPLETED 12-20-18

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 63.5 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

62.90

62.29

FILL: sandy silt with gravel, brown

SAPROLITE: silty sand, dense, brown

End of Boring

S-1

S-2

S-3

S-4

S-5

S-6

50/5"

50/5"

SUBSURFACE EXPLORATION LOG

BORING N0.: 27-B

PROJECT

Site ER-HWY-27

JOB

OF

SHEET 1

LOCATION Añasco, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45 COORDINATES 249528.939 N 134094.797 E DATE HOLE STARTED 12-20-18 COMPLETED 12-20-18

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 62.9 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): 15.5

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

63.00

62.39

FILL: sandy silt with gravel, reddish brown

WEATHERED ROCK sampled as silty sand with rock fragments

End of Boring

S-1

S-2

S-3

S-4

S-5

S-6

50/6"

50/5"

50/4"

50/3"

50/2"

50/6"

50/5"

50/4"

50/3"

50/2"

SUBSURFACE EXPLORATION LOG

BORING N0.: 27-C

PROJECT

Site ER-HWY-27

JOB

OF

SHEET 1

LOCATION Añasco, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45 COORDINATES 249530.028 N 134085.585 E DATE HOLE STARTED 12-19-18 COMPLETED 12-19-18

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 63.0 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): 15.5

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

62.20

60.98

FILL: sandy silt with clay, reddish brown

Do... clayey silt

SAPROLITE: silty sand, dense, relic joints, brown

End of Boring

S-1

S-2

S-3

S-4

S-5

S-6

SUBSURFACE EXPLORATION LOG

BORING N0.: 27-D

PROJECT

Site ER-HWY-27

JOB

OF

SHEET 1

LOCATION Añasco, PR DRILLER/DRILL RIG: Carlos I. Diaz / CME-45 COORDINATES 249541.607 N 134086.672 E DATE HOLE STARTED 12-19-18 COMPLETED 12-19-18

DESCRIPTION BY Carlos R. Sierra Del Llano ELEVATION TOP OF HOLE (mts): 62.2 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): 15.5

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

(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 0.7 51.8 47.5

Figure7935

Site ER-HWY-27, Anasco, PR

Jose A. Batlle & Associates

4-7.5'Anasco, PR

1/2/19Project Site27-A (S-3, S-4)

Tested by: N. Rodriguez

Checked by: Carlos Sierra Del Llano, MSCE, PE

A-4(2)SM

0.08680.1490.510

103525

Silty sand

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 99.3 95.9 82.1 60.1 47.5

.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 11.0 60.0 29.0

Figure7935

Site ER-HWY-27, Anasco, PR

Jose A. Batlle & Associates

2-5.5'Anasco, PR

1/2/19Project Site27-B (S-2, S-3)

Tested by: J. Ortiz

Checked by: Carlos Sierra Del Llano, MSCE, PE

A-2-4(0)SM

0.0809 0.2730.4663.15

NPNPNP

Silty sand

(no specification provided)

JACA & SIERRA

TESTING LABORATORIES

San Juan, Puerto Rico

100.0 97.6 95.1 93.6 89.0 79.8 58.4 38.9 29.0

1 in.

.75 in.

.5 in.

.375 in.

#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: Medium silty sand

Method: Terzaghi

Data from cross section Sta. 165+30: D = 3 ft, Bc = 9 ft, Gravity wall, β = 26.5˚

Data from Table 1: γ = 125 pcf

FS > 2 => FS = 2.95 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 = 32˚, c = 150 psf

Bearing capacity factors for ϕ = 32˚: Nc = 44.04, Nq = 28.52, Nγ = 26.87

Continuous Foundations qult = cNc𝑔𝑐 + σzDNq𝑔𝑞 + 0.5γBNγ𝑔𝛾 qult = 11,869 psf qa = qult

FS

qa = 4,023 psf => qa = 4,000 psf considered

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

Underlying Soil: Medium silty sand

Data from Table 1: ϕ = 32˚ μ = tan(0.7φ) μ = 0.41

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 = 0.45 g kh =

PGA

kh = 0.23

Settlement

Since underlying in-situ soil consists of medium dense silty sand, no consolidation settlement is expected, or negligible. Elastic settlement occurring immediately upon gravity wall construction is assumed to be lower than 1 inch due to the existing medium dense or greater relative density based on SPT-N values.

Appendix E:

SLOPE/W Software Results

Figure E1

Figure E2