Report - Geotechnical_HWY_5 and 6_AC-826579.pdf

Suelos, Inc.

Soil & Construction Materials Laboratory and Environmental Drilling Services

REPORT ON LANDSLIDE AT PR-10, KM. 41.6 AND 41.9

AC 826579, ER-HWY-5 AND ER-HWY-6 (Project Site 2)

UTUADO, PUERTO RICO

(Revised March 22, 2021)

1.0 INTRODUCTION

This report presents the results of the geotechnical investigation performed for the anomalies that affect state road PR#10, at Km. 41.6 and 41.9, in Utuado, Puerto Rico. The work was performed at the request of Eng. Ray Morales, on behalf of the PRHTA, following the scope of work presented in our November 17, 2017's technical proposal to JOV & Associates.

The object of the exploration was to investigate the soil instability phenomena affecting the shoulder and fill embankment of PR#10, specifically at Km. 41.6 and 41.9. These two areas were severely affected by hurricane Maria landfall back in September 22, 2017. Possible stabilization alternatives are evaluated and presented as remedial measures.

2.0 PROBLEM DESCRIPTION

The subject areas are located at Km. 41.6 and 41.9. Figure 1 is a recent aerial photo showing the general location of the affected areas.

According to information provided to this office, various site visits performed by our personnel and assessment of the USGS topographic map, the areas under study correspond to natural drainage channels (creeks) that traverse PR-10 at Km. 41.6 and 41.9. These creeks were piped in a general west-to-east direction, below PR-10 fill embankment. Refer to Figure 2.

For the case of Km. 41.6, the creek banks and the fill slope of the PR-10 embankment suffered severe erosion and instability due to hurricane Maria. At this particular site, the southbound lane partly collapsed due to scouring (see Figure 3).

For the case of Km. 41.9, the effects of Maria were significantly higher. The entire segment of the road (southbound and northbound lanes) collapsed during the hurricane. Refer to Figure 4.

REPORT ON LANDSLIDE AT PR-10, KM. 41.6 AND 41.9

AC 826579, ER-HWY-5 AND ER-HWY-6 (Project Site 2)

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 1

Figure 2

For both cases, it was evident that high water velocities and extraordinary flow produced by the hurricane, combined with inadequate drainage systems, provoked the erosion and collapse of the roadway.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com mailto:suelosinc@gmail.com mailto:jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 3. PR-10 segment at Km. 41.6 partly eroded due to inadequate drainage system.

Figure 4. PR-10 segment at Km. 41.9 collapsed due to inadequate.

drainage

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 5. Boring locations at Km 41.6

3.0 WORK PERFORMED

As part of our scope of work delineated in our November 17, 2017's proposal, four (4) borings were performed at Km. 41.6 and two (2) borings at Km. 41.9. Boring locations are presented in Figure 5 and 6.

Numerous laboratory tests were performed to obtain (using well known empirical correlations) the best estimates of the in-situ governing soil strength parameters. The laboratory test program consisted of soil classifications, Atterberg Limits and Grain Size Analyses.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 6. Boring locations at Km 41.9

4.0 GENERAL GEOLOGY

The area under study should spars entirely within geologic Unit QTd, as shown on the

Geologic Map of the Utuado Quadrangle by Arthur Nelson (1967) in Figure 7.

The Qtd unit consists mostly of alluvium, terrace and blanket sand deposits. These are chiefly gravel, sand and sandy clay. These should be followed with the geologic unit Tku, rocks of the

Utuado Pluton. The later consists of massive granodiorite.

The subsoil investigation also disclosed a thick fill layer, making up the roadway embankment.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 7. Geologic setting

5.0 SUBSOIL CONDITIONS

As expected, the typical subsurface strata in the affected areas consists of artificial fill down to approximately 8 ft to 28 ft deep (boring dependant) measured from roadway elevation. This fill is the result of filling the natural drainage gullies or creeks that existed originally at both sites.

Most Standard Penetration Tests performed in the fill material obtained N-values in the range of 7 to 19 blows per foot (bpf). Natural Moisture Contents resulted with average values between 14 to 32 percent.

Below the fill layer, the borings typically encountered strong brown alluvial soils followed by residual granodirite and then moderately weathered to massive granodiorite as noted from drilling cuttings. The presence of fresher boulders of granodiorite is common within the weathered granodiorite matrix.

The particular soil conditions for Km 41.6 are described in borings B-22, B-23, B-24 and B-

25. A schematic subsoil profile for this location is presented in Figure 8.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 8. Schematic representation of subsoil conditions at Km. 41.6.

Similarly, the particular soil conditions for Km. 41.9 are noted in borings B-20 and B-21. The schematic subsoil profile for this site is presented in Figure 9.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 9. Schematic representation of subsoil conditions at Km. 41.9.

6.0 DISCUSSION

Both areas have been affected by significant erosion induced by high velocity water flows and flooding mainly at the upstream side of the roadway. At the time being, the road portion that collapsed at the Km. 41.9 site has been temporarily repaired to permit traffic flow.

For the solution at Km. 41.9, the consultant has proposed a permanent solution consisting of a bridge supported on drilled shafts. For the solution at Km. 41.6, the installation of a box culvert has been proposed. The following sections discuss the geotechnical recommendations for the design and construction of the aforementioned remedial measures.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 10. Typical box culvert section for Km. 41.6.

7.0 GEOTECHNICAL RECOMMENDATIONS FOR KM. 41.6

The new box culvert section is described in Figure 10. It will be comprised of a single cell culvert 4 meters wide by 3 meters high (interior dimensions). The thickness of the soil cover on top of the culvert varies between 3.3 to 5.8 meters. Maximum excavation depth will be in the order of

9.5 meters (31 ft). In plan view, the extension of the new culvert section is presented in Figure 10.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Taking into account the information obtained from borings B-23 and B-24, the soil conditions at the planned invert elevation should be comprised by stiff sandy silt and medium density silty sand, both of alluvial nature.

Considering the dimensions, type and depth of the new box culvert, bearing capacity aspects shall not control design, provided proper soil conditioning is performed at the bottom of the excavation. That said, load compensation due to the excavated soils and the relatively low contact pressures beneath the culvert make its construction feasible from the geotechnical standpoint.

However, it is very important to mention that the excavation necessary to reach the proposed bottom of culvert would be performed on alluvial soils and fill material. These materials will lost strength upon disturbance, hence, the bottom of the excavation will need to be conditioned and stabilized prior to culvert construction. The contractor shall be required to control and manage surface waters and run-off entering the excavations. The use of sum pumps will be necessary to maintain the excavation dry. Water flow deviation will be necessary.

The temporary excavation for the box culvert shall consider 1H:1V temporary slopes.

Excavations deeper than 15 ft shall require an intermediate bench or terrace 8 ft wide to improve cut slope stability and better control/manage of run-off water.

Due to the presence of silts at the proposed excavation bottom, it will be necessary to over-excavate approximately 18 inches below proposed excavation bottom. The 18-inch overexcavation shall be backfilled with crushed stone or gabion-type stone of 4-inch minus gradation with not more than 10 percent by weight of non-plastic fines passing the No. 200 sieve.

Since the exposed silt will make the bottom of the excavation unstable, it is very important to install a non-woven geotextile filter/separator between the rockfill and the bottom of the excavation. A non-woven geotextile such as AMOCO 4551 or similar can be considered. This geotextile has a grab tensile strength of 150lb, burst strength of 315 psi and a puncture resistance of

90 lb.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

The 18 inches of crushed stone or gabion type stone shall be placed over the geotextile. Then a smooth drum, non-vibratory roller shall be passed several times over the stone until the stone surface does not yield. The non-vibratory compactor shall have a minimum operating weight (static weight) of 8 tons. After the crushed stone mat is properly compacted, culvert construction can be started.

The backfill material to be used against the walls of the box culvert shall classify A-2-4 or better, according to the AASHTO Soil Classification System. The granular texture of A-2-4 to A-1-a materials will prove to be beneficial for backfilling in moist conditions. The backfill shall be placed in layers not thicker than 8 inches and compacted to 95 percent its Modified Proctor Test.

Care shall be taken to avoid distressing the concrete wall with large compaction equipment. Only small tampers shall be allowed within 6 feet from the wall. If the wedge between the excavation wall and the concrete wall is too narrow to work in, well graded, tamped gravel can be used as backfill in this area.

For the actual design of the culvert walls, the coefficient of earth pressure at rest (Ko) shall be used. The following soil parameters may be used.

TABLE 1; Parameters for In-situ and Fill Materials

Soil Material à sat c ö

Existing Foundation Soils 115 pcf neglect 26

Select Fill A-2-4 128 pcf neglect 34

Select Fill A-1-a 132 pcf neglect 38

à sat = Natural Unit Weight, pcf ö = Angle of Internal Friction, ö, degrees

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

7.1 Earthwork Recommendations

After the culvert bedding and culvert placement is complete, the embankment construction over the culvert will begin. At this point it will be necessary to backfill around the completed culvert structure. The backfill material provides protection to the culvert during subsequent construction operations, and prevents piping of fines along the outside of the pipe should a headwater develop at the culvert inlet.

7.1.1 Recommendations for Fill Placement

Prior to the performance of any earthwork, the site shall be stripped and prepared to the satisfaction of the observing geotechnical engineer.

The removal of the upper soil crust and generally loose soils or fills shall be performed under the direct supervision of a geotechnical engineer or his representative. The aerial extent and depth of removal shall be established by the soil inspector at the field.

7.1.2 Placement and Preparation of Fill

7.1.2.1 Borrow

Fill will have to be imported to the project. The material to be imported can be used provided it is processed to A-2-4 or better.

7.1.3 Sequence and Operations

Filling shall begin in the lowest section of the area. Fill will be spread in layers as herein specified. The surface of each layer will be approximately horizontal, but it will be provided with sufficient longitudinal and transverse slope to permit run-off of surface water from every point.

Filling shall be conducted so that no obstruction to drainage from other sections of the fill areas is created. Sumps, if any, shall be maintained in effective operating condition for the duration of the works.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

7.1.4 Layer Construction

Fill shall be spread in approximately horizontal layers 8 inches in thickness prior to compaction.

7.1.5 Condition

Each layer of fill shall be inspected prior to compaction. All visible roots, vegetation or debris shall be removed. Stones larger than 8 inches in diameter for fine soil fills shall be removed or broken. Water content tests shall be performed on each layer in order to determine if the layer is suitable for compaction. Material incorporated in the fill which is not satisfactory shall be subject to rejection and removal at the Contractor's expense.

7.1.6 Compaction

The fill shall be compacted so that the dry unit weight of the compacted material is equal to or greater than 95 percent of the maximum dry unit weight as obtained in the laboratory Modified

Proctor Compaction Test.

It shall be the responsibility of the Resident Engineer, to instruct the Soils Engineer retained by the owner on a consultative basis, to determine the maximum dry density and corresponding optimum moisture of every type of fill material to be used by the contractor in order to properly evaluate the compaction of the fill material.

7.1.7 Equipment and Procedure

The contractor shall employ suitable equipment, to obtain the required compaction. The number of passes of the equipment over each section of the work surface shall be determined in the field. However, the soils engineer shall determine the density of the fill material after the compaction of each 8 inch layer, and the contractor shall not place any additional fill until the preceding compacted layer has been found to fulfill the aforementioned requirements. Each successive pass shall overlap the preceding adjacent pass by 10 percent. Roller passes made on material in unsuitable condition will not be considered in judging compliance with these specifications. Should

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021) the contractor fail to obtain the required compacting energy, he must get the appropriate equipment to comply with the compacting criteria.

7.1.8 Moisture Content

The moisture content of the fill material, prior to compaction, shall be within the limits of

4% less than or 2% greater than the optimum, as determined by the Modified Proctor Test. The water content of the fill may be reduced, when necessary by any appropriate procedure. The water content may be increased by addition of water on the fill or in the borrow area. In either case, the addition of water must be made by the contractor and distributed evenly through the material prior to compaction. Tests for density, optimum moisture content, expansive properties, and percentage stone content will be performed, as required by working conditions.

Expansive soils shall be subject to immediate rejection as fill material. The acceptability of the compacted fill will be established by tests (state whether at Contractor's or Owner's expense).

The unit weight of compacted material will be established by in-place density tests conducted by the

Soil Consultant (at the Resident Engineer's request) by nuclear testing procedures, all in accordance to ASTM requirements. Additional tests to establish or confirm maximum Proctor Density, optimum moisture content, and percentage stone content will be performed as required during the progress of the works.

7.1.9 Unretained Earth Slopes

In order to reduce the tendency of the gradual flattening of slopes due to the effects of erosion, the face or surface of all fill slopes exceeding 26.5 degrees shall be protected by planting a suitable type of grass over the face of the slope or by any other appropriate method.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

7.1.10 Compacting of Slopes

Fill slopes shall be compacted by means of sheep-foot rollers or other suitable equipment.

Compacting operations shall be continued until the slopes are stable, but not to dense for planting on its face, and there is no appreciable amount of loose soil on its surface.

After the foundation for the fill has been cleared and plowed or scarified, it shall be disced or bladed until it is uniform and free from large clods, brought to the proper moisture content, and compacted to not less than 95% of maximum density in accordance with ASTM Designation

D-1557.

7.1.11 Finish Slopes

The fill operation shall be continued in 8 inch compacting layers until the fill has been brought to the finished slopes elevation.

7.1.12 Slope Control Planting

Slopes shall be fertilized and planted with soil fixing grasses, vines and shrubs.

Commercially available stabilization products can also be considered provided these are approved by the Engineer (PRHTA).

7.1.13 Pavement Design

The following Table 2 contains approximate CBR values necessary for the design of the asphaltic or concrete pavement over fill.

TABLE 2; CBR Values for Design

Type of Subgrade Approximate CBR Value

Approximate Kv Modulus

Compacted A-2-4 (Fill) 20 150 pci

Compacted A-1-a or b (Fill) 32 175 pci

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UTUADO, PUERTO RICO

(Revised March 22, 2021)

The above values are recommended for actual design based only on experience. For more exact values, it shall be necessary to make CBR Tests or plate bearing tests in-situ. The design values given above should serve the planning and designing engineers in selecting the most appropriate and economical type of pavement for the proposed project.

8.0 GEOTECHNICAL RECOMMENDATIONS FOR KM. 41.9

A new open channel section and bridge are planned for this site: A trapezoidal channel with heights varying from 2.8 to 5.2 meters, and a single span bridge 35.6 meters long. Bridge abutments will be supported on drilled shafts.

8.1 Bridge Foundations

The evaluation and analysis for the proposed bridge structure was performed following the

“Load Resistance and Factor Design Specifications”.

Considering the results of the subsoil exploration, both abutments shall considered deep foundations. Due to the presence of saprolitic material at relatively shallow depth, the use of drilled shafts is strongly recommended over driven piles.

The difference between the Allowable Stress Design (AASHTO Standard Specification for

Bridges) Axial Capacity in drilled shafts and the Load and Resistance Factor Design Specifications

(LRFD) stems from the Factors of Safety or Reduction factors used to estimate the Allowable Axial

Load for Piles (ASD), or the Nominal Factored Resistance for Piles (LRFD). While ASD applies factors of safety in a global manner with global factors of safety (typically between 2 and 3) applied to the Ultimate Capacity Estimated from Equations, LRFD applies Reduction Factors (typically between 0.41 to 0.71) to individual portions of the equations of a nominal axial capacity (skin friction and tip capacities are reduced by these factors depending on the geologic materials being considered).

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

8.2 Estimation of Nominal and Factored Axial Compression Resistance of Single Drilled Shafts.

Table 3 presents minimum dimension, and recommended range of nominal and factored loads for pile diameter considered adequate for this project. Graphic results and additional data are presented in Figures 10, 11 and 12. The resistance factors used to estimate allowable capacities were selected according to the method used for determining the nominal resistance. For the later, we made use of the â-method for side resistance in sand (O’Neill and Reese, 1999), the á-method for side resistance in clay (O’Neill and Reese, 1999), and tip resistance in IGM’s (O’Neill and Reese, 1999).

TABLE 3; Recommended Load Capacity for 36" Drilled Shafts

Pile Type and Size Estimate

Embedment Length*

Nominal Compression Pile Capacity (kips)

Factored (Allowable)

Compression Capacity (kips)

Factored (Allowable)

Tension Capacity (kips)

36" dia. Drilled Shaft 55 to 60 ft 1500 750 450

*Estimate Embedment Length Measured from Proposed Grade Elevation.

As shown in Figure 13, an approximate shaft movement (settlement) of 0.8 inches should be expected at the factored load of 750 kips.

The nominal pile capacity and pile length range presented in Table 3 shall only be used as our best engineering values for cost estimates. Therefore, we urge the owner to include in his bid documents, additive and deductive pile footage. The project owner should be aware that piles capacity values calculated by various procedures may vary ± 20 to 40 percent from the actual pile capacity. The pile capacity may vary with the method of installation, proximity of other piles (group action) and a number of other factors.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 10. Nominal compression and tension capacity for 36" drilled shaft

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 11. Factored compression and tension capacity for 36" drilled shaft.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 12. Average soil strength parameters used in analyses

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 13. Vertical load vs. total settlement.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

8.3 Shaft Group Resistance

The bearing resistance of drilled shaft groups in sands is less than the sum of the individual shafts due to overlap of shear zones in the soil between adjacent shafts and loosening of the soil during construction. The individual nominal resistance of each shaft in a group should be reduced by applying an adjustment factor ç taken as shown in Table 4.

TABLE 4; Group Reduction Factors for Bearing Resistance of Shafts in Sand

Shaft Group Configuration Shaft Center to Center Spacing Reduction Factor for group Effects (ç)

Single Row 2D 0.90

3D or more 1.0

Multiple Rows 2.5D 0.67

3D 0.80

4D or more 1.0

8.4 Pile Testing Requirements

Because of uncertainties in estimates of pile capacity using different procedures, load tests must be performed to verify the nominal pile capacity estimate. Although, pile load tests are usually expensive and time consuming, in the long run they usually save money by allowing the designer to modify the required number or length of piles required.

One (1) test pile shall be selected at each abutment. These test piles shall be installed to the predicted depth or otherwise to the depth determined by the Geotechnical Engineer to be in charge of the load testing program. Once installed, the test piles must be subjected to either Dynamic Load

Tests (ASTM D-4945) or Bi-Directional Load Tests. The later is a high capacity device (the O-Cell or GRL-Cell) installed within a deep foundation to statically load test the foundation. As the cell is pressurized, it loads the foundation element in two directions. The portion of the foundation element above the cell location is pushed upward against its shaft resistance. At the same time, the foundation element below the cell location is pushed downward against its shaft resistance as well as against the toe bearing or “base resistance”. Shaft and toe movements as well as embedded strain gage instrumentation are monitored for each applied load. An estimated top load movement curve is

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UTUADO, PUERTO RICO

(Revised March 22, 2021) constructed from the measured shaft resistance load-movement and base resistance load-movement responses.

A pile installation criteria, to be followed during the production pile works, shall be prepared by the Geotechnical Engineer in charge of the deep foundation work, based on the test data gathered.

The pile installation criteria will state the final pile lengths, as opposed to the herein predicted pile lengths or penetration. Similarly, the production pile operations shall be made under the supervision of a Geotechnical Engineer or his representatives, to assure that the monitoring requirements stated on the AASTHO LRFD method are followed.

8.5 Lateral Resistance of Piles

The analysis of a pile under lateral load is a problem in soil-structure interaction; that is, the deflection of the pile is dependent on the soil response and the soil response is a function of pile deflection. Iteration must be employed because the soil response is a non-linear function of pile deflection and of position along the length of the pile. Therefore, lateral analysis uses the finite-difference method to model soil-structure interaction. By integration of lateral pressure, shear, moment, rotation, and deflection, the pile and soil interaction and behavior are analyzed. This method is the base for the well known COM624 program of FHWA, which solves the nonlinear differential equations representing the behavior of the pile-soil system to lateral (shear and moment) loading conditions in a finite difference formulation using Reese’s p-y method of analysis. For details on COM624, please refer to FHWA publications, FHWA-SA-91-048, COM624P-“Laterally

Loaded Pile program for the Microcomputer”, Version 2.0, by Wang and Reese (1993).

Table 5 list load vs. displacement resulting from the p-y analyses for fixed head conditions.

Graphic results are presented in Figure 13, including bending moment and shear diagram.

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

REPORT ON LANDSLIDE AT PR-10, KM. 41.6 AND 41.9

AC 826579, ER-HWY-5 AND ER-HWY-6 (Project Site 2)

UTUADO, PUERTO RICO

(Revised March 22, 2021)

TABLE 5; Summary of P-Y Analysis For Fixed Head Conditions

Pile Type Lateral Load @ Deflection

Max. Bending Moment (kip-ft)

Approximate Nominal Moment Resistance (MN) for ñ=1.5% **

36" drilled shaft 100 kips @ 0.2" 584 kip-ft 1080 kip-ft

** This involves a quick check of the approximate moment resistance, which is then compared to the maximum bending moment from p-y analysis. For ñ=1.5%, the nominal moment resistance (MN) is approximated by 40 D3.

Considering a resistance factor for flexure of 0.75, the drilled shaft diameter presented above should provide sufficient flexural resistance for the max. bending moment resulting from p-y analysis.

The bending moment curves and pile deflection curves as a function of length along the piles, for the case of a fixed-head pile, are included in Figure 14. From these curves a number of interesting observations can be made. Considering the behavior of the piles under lateral loading, the portion of the pile where the bending moment is largest is relatively small compared to the length of the pile. This suggests that the bending strength of drilled shafts can be tailored to agree with the moment curve, perhaps leading to significant savings in steel reinforcement.

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UTUADO, PUERTO RICO

(Revised March 22, 2021)

Figure 14. Lateral capacity results for 36" dia. Drilled shaft

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258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

REPORT ON LANDSLIDE AT PR-10, KM. 41.6 AND 41.9

AC 826579, ER-HWY-5 AND ER-HWY-6 (Project Site 2)

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Plate A

8.6 Adjusting Lateral Resistance for Close Spacing

The pile lateral capacity values presented in this report do not consider the effect of group action. When the P-y method of analysis is used, the values of P shall be multiplied by P-multiplier values (Pm) to account for group effects. The values of Pm provided in Table 6 should be used.

Refer also to Plate A.

TABLE 6; Pile P-Multipliers (averaged from Hannigan et al., 2006)

Pile c-c Spacing (in the direction of loading)

P-Multipliers, Pm

Row 1 Row 2 Row 3 or higher

3B 0.8 0.4 0.3

5B 1.0 0.85 0.7

9.0 SEISMIC GROUND MOTION VALUES

9.1 Mapped Acceleration Parameters

According to the Puerto Rico Building Code 2018, the 0.2 sec spectral response acceleration

(Ss) for the municipality of Utuado corresponds to 1.01g. The 1.0 sec spectral response acceleration

(S1) corresponds to 0.33g.

Suelos, PSC.

258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

TABLE 7

9.2 Site Class Definition

The underlying soils are classified as a “Site Class D” in the following Table 7.

10.0 FIELD MONITORING AND HYDRAULIC ISSUES

As it is always the case for this type of geotechnical problems, field monitoring must be conducted during and after construction of the remedial measure to carefully evaluate the effectiveness of the measure and detect any problem that may occur during the measure construction.

The field monitoring will consist of a periodical measurements from a control bench marks, and inclinometers installed. During construction the instrumentation must be read on a daily basis.

The results of this monitoring program will provide any need to have to incorporate additional control measures. These monitoring program needs to be evaluated daily during construction and monthly thereafter. At the end of construction frequent inspections will also be necessary to check that the system is working properly, especially after storms or heavy rain events.

Suelos, PSC.

258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Several hydraulic issues must also be addressed. Inlet grates are essential to prevent the entrance to the drainage pipe being blocked by logs, branches, and other debris. If the drainage system is subjected to extraordinary storm, there is a possibility that its capacity will be exceeded, creating a temporary pond on the upstream side. Another concern is that pipes speed up the flow of water compared to a natural stream. Higher velocities will increase erosion along the fill slope, especially if the outflow is concentrated at the pipe opening. It is recommended to design and build concrete chutes and energy dissipators to reduce water velocities. Slope erosion protection systems shall also be standard requirement for the reconstruction project.

10.1 Erosion Protection of Embankments

Slopes facing streams or gullies shall be protected against erosion by providing adequate revetments and filters, as necessary. These streams and gullies have been observed to have minimum water levels during the period this exploration was made. However, their maximum flow regimen under intense rainfall has not been evaluated by us and it is not within the scope of this exploration.

It is for this reason that a hydrological study of the area is highly recommended to establish the streams maximum flow regimen and its erosion potential along the most affected embankments.

Table 8 is given below only as a guideline on the water flow velocities that can be supported by some revetment materials depending on their thickness. For gabion and concrete revetments, more specific number should be obtained from the manufacturers.

TABLE 8; Revetment Materials Minimum Diameter in Inches of the Rip-Rap Fragment

Flow Velocity (ft/s)

Rip-Rap Unit Weight (pcf)

100 112 125 137 150

Diameter (inches)

3 3 3 3 3 3

5 6 5 5 4 4

7 7 6 6 5 5

8 11 9 8 7 7

10 15 13 12 11 10

Suelos, PSC.

258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Flow Velocity (ft/s)

Rip-Rap Unit Weight (pcf)

100 112 125 137 150

Diameter (inches)

11 21 18 17 15 14

13 27 24 21 20 18

15 34 30 27 25 23

Gabion Wall 12-inches wide (more or less) 10 ft/s.

Gabion Wall 18-inches wide (more or less) 15 ft/s.

Concrete Facing (more or less) 50-60 ft/s.

11.0 MAINTENANCE

In the past, lack of routine maintenance and inspection of PR-10 roadway drainage systems has caused considerable damage to many elements of the roadway and their surrounding areas including the fill embankment.

Each component of the drainage system has a specific purpose, and the continuous-unrestricted operations of these components is regarded as an integral part of the road cuts and embankments. A routine and periodic maintenance program should be developed to include at least the following:

a) Cleaning and removal of all debris in and around all ditches.

b) Inspection of the ditches and surrounding areas for damage, subsidence and continuity of grade.

c) Inspection of the energy dissipation system including the replacement of rip rap and/or stone revetment.

Suelos, PSC.

258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

d) Inspection of the entire drainage system prior to storm conditions to assure satisfactory operation.

12.0 ADDITIONAL CONSIDERATIONS

Remedial works shall be scheduled in the low rainy season (November to May). This shall be considered part of the design. A low groundwater level provides a moderate safety margin to the landslide and allows working with the drainage system and hydraulic structures.

A third important consideration is to require and strictly enforce closely-sequenced construction methods, where the excavation benching and filling in any part of the affected area occur in a close sequence such that the length of open excavations is left to a practical minimum at all times during the work day.

13.0 SPECIAL COMMENTS

It is imperative that all reconstruction and stabilization works must be accompanied by a careful monitoring program, during and after construction, that will help in assessing the effectiveness of the recommended remedial measures. Although the remedial measures given herein should be effective in minimizing the sliding problem, variations in the site soil conditions, specially in the areas between the boreholes, may require some changes in the stabilization program that can be promptly implemented with the help of the field instrumentation measurements in the hands of a well experienced geotechnical engineer. Therefore, it is recommended to adopt the field monitoring program as a component of the remedial measures suggested for this project.

The exact amount of this instrumentation will be determined by the Soil Engineer in charge of the geotechnical inspection during construction, as the site conditions dictate the requirement of the instrumentation. A typical monitoring station shall consist of control bench marks and inclinometers.

Suelos, PSC.

258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

UTUADO, PUERTO RICO

(Revised March 22, 2021)

14.0 LIMITATIONS OF REPORT

The landslides and landslide related features within the study area comprehended by this exploration have been recorded in several different ways, such as site maps, and subsurface cross-sections. These instability features, among others, consist of scarps, toes, tension cracks, slip surface, debris flow and any other relevant feature. These features are those recorded during the course of this exploration and up to March 25, 2019.

This contractor shall receive a copy of this report, carefully visit the area and continuously monitor his operations in order to safeguard life and property.

15.0 GENERAL COMMENTS

The nature of the landslides observed and the objective of the mitigation measures recommended in this report requires that a meeting between PRHTA consultants, the prospective contractor and these consultants be held to discuss the findings and recommendation presented in this report.

The observance or supervision of the earthmoving, excavation operations and excavation monitoring process, in general, is a very delicate matter. In some cases this service is not rendered by the Soils Engineer who made the subsoil investigation and recommended the specific foundation alternatives for a given project. In a large number of projects these operations are successfully completed due to the prevalence of ideal and uniform conditions and to the fact that they are being performed by a competent and responsible contractor. But there are cases, where the lack of proper construction techniques and the lack of adequate supervision has given rise to the occurrence of excavation problems and failures. Conscious of the above exposed problem, we wish to state that the validity of our recommendations is subordinated to the observance of the earthwork operations by us.

If the contract is awarded to another experienced Soils Engineer, he shall receive a copy of this report, evaluate the same and adopt it as his own, or request additional soil data to verify our foundation recommendations or modify them in accordance to his personal knowledge and judgement, thus assuming full responsibility for his recommendations and the report itself.

Suelos, PSC.

258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com

REPORT ON LANDSLIDE AT PR-10, KM. 41.6 AND 41.9

AC 826579, ER-HWY-5 AND ER-HWY-6 (Project Site 2)

UTUADO, PUERTO RICO

(Revised March 22, 2021)

Respectfully submitted, IVAN JACKSON MADURO, P.E., M.S.C.E., CWI

Partner mgn/Reference No. 4834-PS2 Revised

Suelos, PSC.

258 Chile St., San Juan, P.R. 00917-2103 Phone (787) 753-0147. Emails: suelosinc@gmail.com / jackson.suelos@gmail.com mailto:suelosinc@gmail.com mailto:jackson.suelos@gmail.com

7.1.13 Pavement Design