Report - Geo-Report_Addendum_2_Sch A_Hwy-386.pdf

Geotechnical engineers providing geotechnical engineering solutions .... Patricia A. Crumley, MECEE Tirso A. Alvarez, PhD Alan R. Crumley, MSCE

P.O. BOX 362040, SAN JUAN, PUERTO RICO 00936-2040 TEL (787) 783-3585 FAX (787) 793-0410 Founded 1981 – Peer Reviewed by ASFE www.geoconsult.us

ADDENDUM NUMBER TWO

TO

GEOTECHNICAL ENGINEERING REPORT

LANDSLIDE REMEDIATION

PR-568 KILOMETER 25.8

Corozal, Puerto Rico

Report dated January 10, 2019

Addendum One was dated March 13, 2019.

Addendum Two is dated May 29, 2020.

In response to comments regarding the previous reports by an unnamed reviewer from an agency named Eastern Federal Lands, we submit this second addendum. Responses are given in the same order as received.

Comment No.

1 Eastern Federal Lands Comment

Analysis is provided in the addendum, but no summary of the soil properties used for the analysis is provided.

GeoConsult Response

The soil properties used in my analysis were included. See Appendix One, on the figures depicting slope stability results, as follows:

Stiff soil, = 35 degrees, c = 10 kPa, = 18.42 kN/m3

Residual soil, = 35 degrees, c = 50 kPa, = 20.02 kN/m3

2 Eastern Federal Lands Comment

Geotechnical report does not show a lab result summary table.

PR-568, kilometer 25.8

Addendum No. 2 to Geotechnical Engineering Report

GeoConsult Response

The actual lab results are referred and identified in the appendix to the report. The two results are repeated in the following list:

Boring QR-1, depth 4-6 feet: LL 33, PI 11, USCS SC, 11% gravel, 76% sand, 13% passing #200 sieve

Boring QR-2, depth 4-6 feet: LL 37, PI 13, USCS SC, 66% sand, 34% passing #200 sieve

3 Eastern Federal Lands Comment

The analysis provided in the addendum shows that a surcharge of 200 psf was used.

(The surcharge used in the analysis seems low, it is recommended to use a surcharge of 240 to 250 psf. Please verify and correct.)

GeoConsult Response

The reviewer is correct in his or her observation that I mistakenly used a 200 psf surcharge load. While 250 psf is normally used, I have redone the analyses using 300 psf. As noted in Appendix One, these analyses can only be considered conceptual since there is too little information for more precise stability analyses. To start, many more borings would be necessary.

4 Eastern Federal Lands Comment

Sheet 1-2, and 6: The seismic global stability analysis results show a factor of safety of

1.0. The addendum states that this result corresponds to "minimal displacement". If a displacement based design is used for the seismic global stability analysis, it is required to provide the actual displacement of the wall structure for a factor of safety

1.0 and a ky of 0.38g. In addition the Addendum report should specify the allowable displacement criteria for the type of structure being evaluated.

GeoConsult Response

The report indicates that approximate soil parameters were obtained by analyzing conditions before failure, first a stable situation without water, and then using a high water table to cause instability, the high water table being produced by the hurricane.

These soil parameters were used for a static stability analysis of the proposed solution, which yielded a high factor of safety (FS-2.3) even with the high water table produced by the hurricane. Then, a seismic load was applied using the same high storm water level, which yielded a safety factor of one. On that basis, given the result (FS=1) the reviewer requests further displacement analyses.

To correct the previous analyses with a lower value, the analysis was redone using a

PR-568, kilometer 25.8

Addendum No. 2 to Geotechnical Engineering Report surcharge of 300 psf, and a seismic acceleration of 0.38g. The result is FS=0.9, Figure 101, which would indicate even higher displacements from the earthquake than the previous analyses. However, the analysis we first did is incorrect because it includes a high water table; the likelihood of a hurricane and an earthquake at the same time is remote and we can repeat the same seismic analyses without water, which is the correct approach. Using a lower water table with 0.38g, the factor of safety is 1.6 (Figure 102).

But, the acceleration coefficient first used (0.38) is for a recurrence interval of approximately 2,475 years, whereas the acceleration for a recurrence interval of 1,000 years, as used by FHWA, is 0.28g. Therefore, the previous analyses were repeated except that the acceleration coefficient is 0.28g, with FS=1.9 (Figure 103). Since the factor of safety with the assumed parameters is greater than one, displacements are not expected and a displacement analysis is not conducted. For the static condition, with low and high water tables, the factors of safety are 3.3 and 2.0, respectively. See Figures 104 and 105.

Alan R. Crumley, PE May 29, 2020 License 5828 San Juan, Puerto Rico File No. 3008-18

0.871

Assumed water surface

Surcharge ~15 kPa = 300 psf

H = 4.9 m

Pile reinforcement, L=9m Length depends on structural design

PR-568, kilometer 25.8 Corozal

Stiff soil

18.42 kN/m³ 10 kPa 35 °

SEISMIC ACCELERATION = 0.38g

Residual soil, maybe weathered rock below

20.02 kN/m³ 50 kPa 35 °

FS = 0.9

Distance (m)

0 5 10 15 20 25 30 35 40

E le va tio n (m

Geoconsult Line

Geoconsult Text Box High water table

Geoconsult Text Box Figure 101. High water table, a = 0.38g

Geoconsult Oval

1.602

Surcharge ~15 kPa = 300 psf

H = 4.9 m

Pile reinforcement, L=9m Length depends on structural design

PR-568, kilometer 25.8 Corozal

Stiff soil

18.42 kN/m³ 10 kPa 35 °

SEISMIC ACCELERATION = 0.38g

Residual soil, maybe weathered rock below

20.02 kN/m³ 50 kPa 35 °

FS = 1.6

Distance (m)

0 5 10 15 20 25 30 35 40

E le va tio n (m

Geoconsult Line

Geoconsult Text Box Low water table

Geoconsult Text Box Figure 102. Low water table, a = 0.38g

1.873

Surcharge ~15 kPa = 300 psf

H = 4.9 m

Pile reinforcement, L=9m Length depends on structural design

PR-568, kilometer 25.8 Corozal

Stiff soil

18.42 kN/m³ 10 kPa 35 °

SEISMIC ACCELERATION = 0.28g

Residual soil, maybe weathered rock below

20.02 kN/m³ 50 kPa 35 °

FS = 1.9

Distance (m)

0 5 10 15 20 25 30 35 40

E le va tio n m

Geoconsult Text Box Figure 103. Low water table, a = 0.38g

Geoconsult Line

Geoconsult Text Box Low water table

3.331

Surcharge ~15 kPa = 300 psf

H = 4.9 m

Pile reinforcement, L=9m Length depends on structural design

PR-568, kilometer 25.8 Corozal

Stiff soil

18.42 kN/m³ 10 kPa 35 °

STATIC CONDITION

Residual soil, maybe weathered rock below

20.02 kN/m³ 50 kPa 35 °

FS = 3.3

Distance (m)

0 5 10 15 20 25 30 35 40

E le va tio n m

Geoconsult Text Box Figure 104. Low water table, static

Geoconsult Line

Geoconsult Text Box Low water table

2.019

Surcharge ~15 kPa = 300 psf

H = 4.9 m

Pile reinforcement, L=9m Length depends on structural design

PR-568, kilometer 25.8 Corozal

Stiff soil

18.42 kN/m³ 10 kPa 35 °

Residual soil, maybe weathered rock below

20.02 kN/m³ 50 kPa 35 °

FS = 2.0

Distance (m)

0 5 10 15 20 25 30 35 40

E le va tio n (m

Geoconsult Text Box High water table

Geoconsult Line

Geoconsult Text Box Figure 105. High water table, static

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