Report_Geotechnical_ER_HWY_110.pdf

ADVANCED SOIL ENGINEERING

GEOTECHNICAL CONSULTING ENGINEERS

P.O. BOX 1286, ISABELA, PUERTO RICO 00662

GEOTECHNICAL CONSULTING ENGINEERING

CONCRETE AND MATERIAL TESTING LABORATORIES

ON THE GEOTECHNICAL EXPLORATION

PERFORMED AT THE SITE OF THE PROPOSED

LANDSLIDE AND ROAD DAMAGE EVALUATION AND REPAIR

RECOMMENDATIONS AT STATE ROAD PR 128,

ALGARROBO WARD, YAUCO, PUERTO RICO

SUBMITTED TO:

GERMÁN TORRES BERRÍOS & ASSOCIATES – PROJECT DESIGNER

C/O: JOSUÉ TORRES ORTIZ, P.E.

BY:

NELSON MUÑOZ, P.E.

JUNE 12, 2019

FILE NO. 1823-1C FINAL REPORT

PROJECT: ER-HWY-110

P.O. BOX 1286, ISABELA, PUERTO RICO 00662

ON THE GEOTECHNICAL EXPLORATION

PERFORMED AT THE SITE OF THE PROPOSED

LANDSLIDE AND ROAD DAMAGE EVALUATION AND REPAIR

RECOMMENDATIONS AT STATE ROAD PR 128,

ALGARROBO WARD, YAUCO, PUERTO RICO

1.0 INTRODUCTION:

This report covers the results of a geotechnical exploration conducted at the site of the existing road slope failure at State Road PR 128 km 9.0 (ER-HWY-110), Algarrobo Ward, Yauco, Puerto Rico.

The investigation was made following instructions from Josué Torres Ortiz, P.E. from German Torres Berríos & Associates – Project Designer. The study was performed in general accordance with the scope of work included in our Proposal

No.19 (Revised), dated June 12, 2018.

This report has been prepared to summarize the data obtained during this study and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of geotechnical engineering considerations related to construction of the proposed structure are included in the report.

This report has been prepared for the exclusive use of the owner, their designers and others involved in the construction and preparation of the plans and specifications of the project.

File No. 1823-1C Page 3

2.0 SITE LOCATION AND PROJECT DESCRIPTION:

The site of the proposed project is located at State Road PR 128 km 9.0 (ER-

HWY-110), Algarrobo Ward, Yauco, Puerto Rico. State road segments are part of our scope of work. Segments of the road were damaged as a result of intense run-off water, erosion, shallow slumping and earth flows triggered by a significant precipitation by the events of Huracan María in September 20, 2018. The roadways generally consist of two-lane roads located on steep slopes with one side of the road cut into the hillside and the other side of the road constructed on embankment fill.

Typical distress caused by the flooding and significant rainfall event generally consisted of erosion, slumping or movement of the roadway embankment along the downslope side of the roadways. Some minor undermining of the roadway pavement or cracking of the pavement near the edge of the roadway occurred along each roadway. Drainage, roadway and embankment improvements including the construction of retaining structures are planned at the subject roadways to stabilize the roadways and repair the damage.

Physical evidence gathered at the site during our field visual inspections make us to believe the slope failure could have been triggered by waters from faulty pipe/swale line connections and damaged catch basin leaking into the fill slope provoking the fill mass saturation with subsequent loss in strength and increase on the corresponding unit weight of the soil. Both eventualities significantly contribute to the weakening of the soil/fill strength properties, thus provoking an instability problem.

File No. 1823-1C Page 4

The following Figure 1 shows portion of US Geological Survey Service

Topographic Map of the Yauco and Punta Verraco Quadrangles with the site location enclosed.

Figure 1: Site Location Map

SITE

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3.0 SCOPE OF INVESTIGATION:

Field Exploration:

A joint visit was conducted with the project designer to confirm boring locations. All boring locations were adjusted based on utilities interference and client’s requests. The field exploration consisted of drilling two (2) test boring along the proposed construction area of site ER-HWY-110. The location of the borings was as close as possible to the staked locations, subject to utilities interference and drilling convenience. Test borings were drilled to depths varying from 20.0 to 30.0 ft.

with a total footage of 50.0 lin. ft.

The borings were performed using the rotary hollow-stem auger technique in accordance with ASTM D 1452. Samples were obtained using the "Standard

Penetration Test (SPT)", as specified in ASTM D 1586. Please refer to Appendix

No. 1 (Boring Location Map), for boring location.

Maintenance of Traffic (MOT) Safety Controls:

Set up basic MOT safety controls prior to and during the performance of the field drilling and testing operations. Please refer to Appendix No. 8 (Maintenance of Traffic Sheet “MOT”).

4.0 SUBSOIL CONDITIONS & GROUNDWATER:

A subsurface exploration program consisting of drilling two test borings to depths varying from 20.0 to 30.0 feet below the ground surface was performed on

December 14, 2018. An approximately 2-inch thick asphalt pavement section was

File No. 1823-1C Page 6 encountered in each boring. Beneath the pavement section in both borings, a man-made fill material composed of brown silty sand with rock fragments at the uppermost

2.0 ft. The above described fill layer is resting over light olive brown clayey, gravelly sand, extending to depths varying from 6.0 to 8.0 ft. Underlying the aforementioned stratum and extending to the end of the test holes, the exploratory work shows gray rock formation decomposed into rock fragments trace silty sand on boring 1B-1, and gray rock formation decomposed into rock fragments trace silty sand underlain by gray rock formation decomposed into rock fragments trace silty sand on boring

No.1B-2.

Test boring refusal, presumably bedrock, was met at a depth of 30.0 ft. on boring No. 1B-1, and at a depth of 20.0 ft. on boring No.2B-1 below existing grade.

The ground water level of the explored site was not encountered within the depths drilled during the time of our field exploratory work, thus indicating that it must be present at a greater depth. However, temporary bodies of water or perched water might be or be found entrapped within the fill deposit or between the zone of transition of fill deposit and virgin soil.

Subsurface water observations were limited to the depths explored using dry auger drilling techniques and within these depths, groundwater was not observed.

The borehole was backfilled upon completion of the water level measurements.

The absence of free water at these boring locations should not necessarily be construed that subsurface water is not present at the site or is deeper than the boring depth. The short-term field observations generally do not permit an accurate evaluation of the subsurface water levels at this location and should not be interpreted as a groundwater study. It is not unusual to encounter groundwater in

File No. 1823-1C Page 7 the granular silty and clayey sands during and after periods of rainfall. It should be noted that the observations made during this investigation may not represent conditions at the time of construction and the presence of groundwater may affect certain construction activities and long-term performance of the foundations. The quantity of transient water is variable and is highly dependent on climatic conditions before and during construction. The foundation contractor should check the subsurface water conditions just prior to foundation excavation activities.

The above information corresponds to a general description of the subsoil conditions of the area, however, for detailed description regarding the soil profile, field and laboratory test results, please refer to Appendix No. 2 (Boring Logs). For detailed description of the procedures followed for the drilling of the test borings and laboratory testing, please refer to Appendix No. 3 (Field and Laboratory Testing

Procedures), and Appendix No.5 (Laboratory Test Results).

5.0 U.S. GEOLOGICAL SURVEY MAPS:

The Department of the Interior through its U.S. Geological Survey offices published a Geologic Map No. I-1147 The Yauco and Punta Verraco Quadrangles.

This was surveyed by Richard D. Krushensky and Watson H. Monroe and published on 1979. The proposed project lies in a formation described as:

Kat – AUGITE TRACHYBASALT (UPPER MAESTRICHTIAN THROUGH

CAMPANIAN): Dark green or dark-bluish-green, light-brown weathering, abundantly porphyritic augite trachybasalt. Characteristically contains abundant and conspicuous large (1-3 cm long) deep-green augite and rare to sparse small (<.5

File No. 1823-1C Page 8

cm) tabular and generally dark inconspicuous appearing plagioclase (labradorite-andesine) phenocrysts held in a felted trachytic groundmass composed of abundant microphenocrysts and microlites of plagioclase and some augite in a sparse to common chloritized glass. Granular magnetite in the ground mass in an abundant accessory. Intrusive contacts are chilled and show fewer plagioclase phenocrysts than rock away from contacts. Chilled contacts, smaller stocks, and some widespread areas of the intrusive rocks are widely brecciated. Three generations of brecciation are locally evident in the field. Clasts are mineralogically and texturally alike; they differ only in the degree of crystallization, crystal size, amount of magnetite, and, consequently, color. Locally, contact zones are vesicular and amygdaloidal (calcite and chlorite) and adjacent country rock (chiefly the calcareous siltstone-claystone of the Yauco Formation) is depleted in calcite. Augite is generally fresh, but groundmass glass is invariably chloritized. Areas of alteration show a progressive replacement of groundmass, plagioclase phenocrysts, and augite by chlorite, calcite, and rarely by pistacite. Plagioclase phenocrysts are commonly party saussaritized. Typically, only stubby pseudomorphs of limonite after augite and clay-calcite after plagioclase remain visible in saprolitized augite trachybasalt

Km – MARICAO BASALT (UPPER MAESTRICHTIAN THROUGH

CAMPANIAN): Chiefly thick-bedded (I m+ ) to massive volcaniclastic breccia composed or dark-green, and subordinate dark – to light -gray and dark-red angular to well rounded clasts (predominantly 3-15 cm on a side, rarely to 3m on a side) of generally dense porphyritic augite trachybasalt held in a clay-sandstone or in a coarse sandstone-conglomerate or lithic-crystal tuff matrix. Breccia clasts are composed of conspicuous, abundant, and large (1-3 cm long) augite and smaller.

(.2-5 cm long) plagioclase (labradorite-andesine) phenocrysts in a trachytic groundmass composed of abundant microphenocrysts and microlites of plagioclase

File No. 1823-1C Page 9 and augite in a sparse chloritized glass. Typically, the groundmass is dark colored because of abundant granules of magnetite. Breccia ranges from fresh to deeply weathered and mostly replaced by clay, calcite, and chlorite. Outcrops in the central and dark-brownish-green sandstone and subordinate siltstone. These are composed of rounded to angular lithic and mineral (chiefly augite and plagioclase) clasts and generally unweathered clasts. These rocks are tuffaceous sandstone-siltstone or more probably tuffs. Weathered surfaces of the breccia clasts are studded with conspicuous limonite coated augite phenocrysts weathered into positive relief. Widespread areas of the Maricao are deeply saprolitized; these show little or no breccia texture, but large limonite pseudomorphs after augite are commonly present and diagnostic. Laterally restricted lenses of pale-pink or light-brownish-gray biosparite are composed of angular to rounded fragments of rudists, other pelecypods, plates of calcareous algae, and large foraminifers in a generally sparry matrix. A thick sequence of such calcarenite and interbedded volcaniclastic breccia comprises the summit of Cerro Rodadero. The Maricao locally includes 7-10 m thick fine crystalline sparsely vesicular nonpillowed basalt flows. These lack the coarse augite phenocrysts characteristic of the Maricao Basalt. Volcaniclastic breccia in the sratigraphically upper part of the Maricao includes sparse clasts of angular to subrounded homblende dacite

File No. 1823-1C Page 10

Figure 2: U.S. Geological Survey Map

SITE

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6.0 FOUNDATION RECOMMENDATIONS:

Recommendations for the geotechnical aspects of the project are based on the subsoil study presented in this report. This office warranties that our recommendations are in the line with the generally accepted practice in the field of

Soil Mechanics and Foundation Engineering. This is our only warranty, either expressed or implied.

The use of the subsoil information and recommendations herein detailed for other structures or areas, except when done by specialist, may lead to serious design errors and should not be attempted.

The deposits encountered as disclosed by these test borings, not necessarily represent the most critical conditions of the site and might vary from one boring to another. These recommendations are based on the subsoil conditions as encountered on the test borings rather than the worst conditions of the site.

Three alternatives are considered as a solution to the soil stability problem.

After having evaluated the results of the test borings, we strongly recommend the construction of reinforced soil slope (RSS) retaining structures, Gabion Wall, and the construction of a concrete retaining wall system (Mass Gravity Wall “Ciclópeo” and/or Cantilever). Gabion wall and reinforced soil slope (RSS) retaining structures are being considered in the project as alternatives. Since these walls are proprietary systems, the supplier shall design and warrant them to satisfy their internal and external stability. This design will be done in collaboration with German Torres

Berríos & Associates (project designer representing PRHTA). The specific alignment of the wall and RSS shall be defined by the project designer. This design will be done by an experienced and qualified structural engineer. The options listed

File No. 1823-1C Page 12 below area based on site limitations and soil conditions.

6.1 RSS Retaining Structures Recommendations:

The RSS structures consist of a geogrid-wrapped sloping face with geogrid reinforced zone behind the face and are intended to reconstruct the embankment to or close to its pre-damaged slope. RSS may be used as an alternative to purchasing additional right of way or the construction of a retaining wall. In general, RSS be less expensive when a wall or additional right of way would otherwise be necessary. Please refer to (Figure 5 at Appendix No.6: Reinforced Soil Slopes

(RSS).

Design Criteria: The design approach for the RSS generally followed the U.S.

Department of Transportation Federal Highway Administration (FHWA) design procedure in their publication FHWA-NHI-10-024 and FHWA-NHI-10-025 dated

November 2009.

Design Considerations: A summary of the design considerations including geology, wall geometry, material strengths, segmental blocks, geogrid materials and various design features of the walls and RSS are presented in the following discussions.

• Subsurface information from the exploratory borings and the geologic reconnaissance performed at each site should be used by project designer to interpret the elevation of the competent bed material at the RSS structure. The design of the RSS assumes the wall leveling pads are founded on at least 2.0 ft. selected fill material classified as A-2-4 or better at an elevation of 154.5 meters. Variations in the elevation of competent

File No. 1823-1C Page 13 material will occur and may require modifications to the RSS designs at the time of construction once competent material is exposed in the excavations so that design assumptions are maintained. Foundation improvements below the leveling pad may be required if poor quality material is encountered.

The geotechnical engineer should observe the excavations as competent material is encountered to determine the design assumptions remain applicable or if modifications to the designs or foundation improvements are required. Additional discussion of site grading and excavation considerations are presented later in the “Site Grading” section of this report.

• Geosynthetic reinforcements (geogrid) were selected for use in the reinforced zone of the wall and RSS structures.

• The geogrid in the RSS structures are designed to be surrounded by properly compacted A-2-4 or better Structure Backfill having a drained friction angle of at least 34 degrees. The limits of the geogrid and the Structure Backfill is referred to as the “reinforced zone”. Requirements for the structure backfill and compaction are presented in the “Site Grading” section of this report.

• The “retained fill” placed between the limits of the temporary excavation and the reinforced zone should consist of granular embankment fill. We anticipate that some of the onsite fill and natural soils encountered in the excavations cannot be reused as granular embankment fill, except only when laboratory tested site material providing it is found in suitable conditions for said purposes. Other appropriate deposit for this excess soil may be along green areas, and others, determined in coordination and approval of the standing

Geotechnical Engineer of the site.

File No. 1823-1C Page 14

• The RSSs should be provided with one or more drainage systems, in accordance with the design drawings and the requirements presented in the

“Site Grading” section of this report.

• Though groundwater was not encountered at the time of the subsurface exploration, it is possible that localized perched water or water in localized joints in the weathered rock formation could be encountered during construction. Considerations for dewatering of the excavation are discussed further in the “Site Grading” section of this report. Provisions for drainage behind the RSSs are also discussed in the “Site Grading” section of the report.

• Concentrated stormwater discharge should not be allowed on the face of the

RSS during or after construction. Concentrated stormwater discharge should also not be allowed at the toe of the RSS without provisions for erosion protection.

• The face of the RSS should be protected from erosion prior to the establishment of vegetation by applying a seeded flexible growth medium, and a turf reinforcement mat where indicated on the design drawings.

• We recommend with Maccaferri, Inc and Tensar International, Corp., regarding the suitability of installing Gabion Wall and RSS structures. Please see Figure 5 at (Appendix No.6: Reinforced Soil Slopes (RSS).

Selection of Material Properties: The geogrid reinforcement in the RSS designs shall be specified by system designer.

File No. 1823-1C Page 15

Estimated drained shear strengths for the existing soils and fill, and retained fill were developed using information obtained from field exploration and laboratory testing including unconfined compressive strength testing discussed previously, published our experience with similar materials. The selected unit weights and drained shear strengths for the analyses materials are presented in the Table 1.

Material Unit Weight

(pcf)

Angle of Internal

Friction, ɸ (Degree)

Cohesion

(psf)

In situ soil 120 30 Neglect

Compacted Reinforced Fill 125 32 Neglect

Foundation Soil 135 36 Neglect

Table 1: Material Unit Weights and Soil Strength Design Parameters

SITE GRADING:

Site/Foundation Preparation: The RSS are anticipated to be supported on the existing embankment fill and can tolerate more significant movement as compared to a segmental block faced walls. But we estimate that because the RSSs will be reconstructed to about the same slope and height of the existing embankment that significant new settlement of the remaining fill would probably not be induced by the new construction.

Although we anticipate that some post-construction differential settlement will occur, we believe the amount of settlement should be relatively small and tolerable for the planned structures provided that adequate sub-drainage is provided, as included in the structure designs. To help mitigate differential

File No. 1823-1C Page 16 settlement impacts, we recommend scarifying and recompacting the upper 24 inches of the remaining fill below the bottom of the RSS structures followed with proof rolling by a heavily-loaded pneumatic-tired vehicle or a heavy, smooth-drum roller compactor, and stabilization of any soft or excessively deflecting subgrade.

Temporary Excavation Slopes/Temporary Shoring: We assume that the temporary excavations will be constructed by excavating the slopes to a stable configuration, the use of temporary shoring methods or a combination of both. All excavations should be constructed in accordance with OSHA requirements, as well as state, local and other applicable requirements. OSHA requires excavations or trenching over 20 feet deep be designed by a registered professional engineer.

In our opinion, existing fills and natural granular soils should be classified as OSHA Type B soils. Excavations below groundwater or where perched water exists and seeps into the excavation are possible could require much flatter side slopes than those specified by OSHA. Excavated slopes may soften or loosen due to construction traffic and erode from surface runoff. Measures to keep surface runoff from excavation slopes, including diversion berms, should be considered.

Temporary shoring systems should be the responsibility of the contractor.

Temporary shoring provided in close proximity to existing structure should be sufficiently stiff to prevent significant movement.

The safety of all the project personnel and adjacent properties during execution of the project shall be considered the most important fact of the work to be performed.

Excavation Dewatering: Because water was not encountered in our borings at the time of drilling, we do not anticipated significant dewatering will be required.

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However, we believe that localized perched groundwater from joints in the weathered rock formation, or possible localized perched water could be encountered at those sites. However, any water entering the excavation can be pumped directly from the bottom of them. Selection of a dewatering system should be the responsibility of the contractor.

Excavation Considerations: Conventional excavation equipment can be used to excavate the embankment fill and natural overburden soils and some of decomposed to weathered rock. The overburden materials contain occasional to frequent cobbles and boulders. Heavy excavation equipment, hydraulic chisels, rams or other mechanical methods will be required for excavation of the less weathered rock.

Material Specifications: The following material specifications are presented for fills on the project site. A geotechnical engineer should evaluate the suitability of all proposed fill materials to be used on the site prior to placement.

• Structural Fill/Reinforced Fill: Select granular materials used in the reinforced fill zone should consist of moisture-conditioned imported soil materials meeting the requirements for A-2-4 or better Structure Backfill. The onsite materials generally do not appear to meet the requirements for

Structure Backfill.

• Granular Embankment Fill: Onsite or imported granular fill material having a soil-like consistency, a maximum size of 4 inches, a maximum of 35% passing the No. 200 sieve, a maximum Liquid Limit of 30, and a maximum

Plasticity Index of 12. Based on the results of laboratory testing of samples collected from the borings some of the existing fill and natural soils from

File No. 1823-1C Page 18 each site appear to meet the above requirements for granular embankment fill. Additional testing during construction should be performed to select suitable on-site material for reuse. Processing to remove oversize materials may be needed to develop this material from on-site excavations.

• Leveling Pad/Drainage Aggregate: Angular crushed stone satisfying the requirements for ¾” crushed rock.

• Material Suitability: Unless otherwise defined herein, all fill material should be non- expansive, free of vegetation, brush, sod, trash and debris, and other deleterious substances, and should not contain rocks or lumps having a diameter of more than 4 inches. A fill material should be considered non-expansive if the swell potential under a 200 psf surcharge pressure does not exceed ½% when a sample remolded to 95% of the Modified Proctor

(ASTM D 1557) maximum dry density at optimum moisture content is wetted. The geotechnical engineer should evaluate the suitability of proposed fill materials prior to placement.

Compaction Specifications: We recommend the following compaction criteria be used on the project:

• Moisture Content: Fill materials should be compacted at moisture contents within 2 percentage points of the optimum moisture content for predominantly granular materials.

• Placement and Degree of Compaction: Structural fill and granular embankment fill should be placed in maximum 8-inch loose lifts and compacted to at least 95% of the maximum standard Proctor (AASHTO

T99) dry density. Drainage aggregate and leveling pad material should be

File No. 1823-1C Page 19 densified by at least three passes of a vibrating plate compactor. A representative of the geotechnical engineer should observe fill placement operations.

RSS DRAINAGE SYSTEM: The RSS wall systems should be protected by a drainage system consisting of:

• A 4-inch diameter slotted SCH 40 PVC or PE drainage pipe located at the base of the back of the reinforced zone surrounded by drainage aggregate which is in turn surrounded by a filter fabric specified by designer. The drain pipe should slope at a minimum of 1% to a gravity outlet as shown on the design drawings.

• Outlet pipes oriented perpendicular to the drainage pipes should consist of solid SCH 40 PVC or PE should discharge via gravity to the slope face beyond the toe of the MSE walls.

• Vertically-oriented geotextile wrapped geocomposite drain strips spaced to provide 20% (i.e. 1 foot wide strip every 5 feet) coverage behind the reinforced zone, and extending to a height of two-thirds the height of the

MSE wall at the location of installation. Geocomposite drainage strips should be specified by designer.

Erosion Protection/Revegetation: Concentrated stormwater discharge should not be allowed on the face of the RSS. Though we prefer to accomplish this using a curb, we believe it is acceptable to control the concentration of surface flows through improvements to the drainage swale. Concentrated stormwater discharge should also not be allowed at the toe of the RSS without provisions for erosion protection.

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The sloping face of the RSS and disturbed areas surrounding the structures should be protected from erosion by reseeding to promote the growth of grassy vegetation. Prior to the establishment of vegetation, the face of the RSS and the disturbed areas around the RSS will need erosion protection such as through the use of a flexible growth medium, such as a Flexterra type product and/or turf reinforcement mat. The flexible growth medium will help in revegetation when combined with soil amendments/fertilizer and seeding. Soil amendments and/or topsoil should be placed within the outer 4 inches of the reinforced fill zone at the

RSS to facilitate revegetation of the face; however, all materials within the reinforced zone should be compacted as required in the “Site Grading” section of this report, above.

The removal of the heterogeneous fill material shall be performed under the direct supervision of a geotechnical engineer from this office or his representative.

The aerial extent and depth of removal shall be established by the soil inspector at the field, and notify the soils engineer to make the pertinent recommendations if deemed necessary.

The exposed sub-grade shall be proof rolled to detect weak spots before any filling is done. Any weak spot encountered during the initial operation shall be excavated and replaced with selected fill, is a matter that has to be dealt with during the progress of the proof rolling operations. Prior to the placement of compacted fill, the exposed ground surface should be scarified where practical, moisture conditioned as necessary, and compacted.

The fill material shall be placed in layers not exceeding eight (8) inches uncompacted and each lift be compacted to attain a minimum density of 95% of the fill material maximum dry density obtained on typical compaction test made

File No. 1823-1C Page 21 according to ASTM Designation D-1557 and meeting the requirements of an A-2-4 classification or better material.

6.1.2 Gabion Wall Recommendations:

We understand that the intended project shall require the design and construction of a retaining wall structure – Gabion Wall, necessary for the stabilization existing slope. Please refer to Figure 6 at Appendix No.6.

The results of our investigation show favorable subsoil conditions to erect the proposed retaining wall structure over continuous wall footing foundation.

The footing of the proposed retaining wall structure shall be designed for an allowable soil bearing pressure of 4,000 lbs. per sq. ft. The base of the footings shall be located at a minimum depth of 12.0 ft. below the existing pavement elevation near Boring 1B-2, (elevation of 154.41 meters).

Since the ground water level of the site was not encountered within the depth drilled at each test hole, no dewatering problems are anticipated during the phase of over excavation and footing excavation. However, any water entering the excavation can be pumped directly from the bottom of them.

The foundation wall system at rest is to be acted by lateral pressure and the lateral earth pressure to act in the walls depends primarily in the type of earth material to be used as backfill. Accordingly, we wish to furnish the soil parameter for computing the lateral pressure.

File No. 1823-1C Page 22

(pcf)

Angle of Internal

Friction, ɸ (Degree)

Cohesion

(psf)

In situ soil 135 36 Neglect

Table 2: Material Unit Weights and Soil Strength Design Parameters

The material to be used as backfill has to be laboratory tested to verify soil parameters.

According to the pressures and resisting shearing forces, the external stability of retaining walls must be checked by the structural designer, i.e., sliding, and overturning.

Our experience shows that during local rainy periods a temporary perched water level develops within the backfill of the wall surface which in some instances may rise close to the ground surface. This temporary perched water level introduces a lateral pressure to the wall.

A filter fabric should be placed between the gabion baskets and the native soil to prevent the migration of the fine-grained soils into the gabion basket zone.

Placement of the fabric should begin at the top of the slope and extend down the full slope face.

Rock material placed in gabion baskets should consist of hard, angular to sub-rounded, durable stone that is of such quality that it will not disintegrate on exposure to water or weathering during life of the structure. Gabion stone should be

File No. 1823-1C Page 23 between 4 inches and 8 inches in nominal diameter. The range in size should allow for a variation of 5 percent oversize and/or 5 percent undersized rock. The size should be such that a minimum of three layers of rock be achieved when filling the gabion baskets. Gabion baskets should be constructed and placed in accordance with manufacturer guidelines and specifications.

6.1.3 Concrete Retaining Wall Recommendations:

Mass Gravity Wall “Ciclópeo” and/ or Cantilever Retaining Wall:

We understand that the intended project shall require the design and construction of a concrete retaining wall structure. Please refer to Figure 7 at

Appendix No.6.

The footing of the proposed mass gravity and/or cantilever wall structure shall be designed for an allowable soil bearing pressure of 4,000 lbs. per sq. ft. The base of the footings shall be located at a minimum depth of 12.0 ft. below the existing pavement elevation near boring 1B-2, (elevation of 154.41 meters) on cantilever retaining wall; and at a depth of 13.4 ft. below existing pavement elevation near boring 1B-2 (elevation of 154.00 meters) on mass gravity wall “Ciclópeo”.

The existing talus is a natural one with some minor intervention by man.

Several stability analyses were ran with the assistance of a computer program

(MACSTARS W, Maccaferri Stability Analysis of Soils). We have performed stability analyses to address the factor of safety of global stability. Ground water was not incorporated on the analysis since none was found at the test borings drilled at the area. As presented in Appendix 7 “Wall Stability Analysis Results”, the analyses show a factor of safety equal to 2.02 for static conditions. The analyses show a

File No. 1823-1C Page 24 factor of safety of 1.47 for pseudostatic condition with ground acceleration equal to

0.15g (as per PRHTA Design Guideline 1002). These safety factors comply with those required by the client in a written statement: FS≥1.5, for static condition, and

FS≥1.1, for pseudostatic condition. Residual strength parameters were assigned accordingly to both the fill material and natural material (please verify Appendix

No.7 Wall Stability Analysis Results).

Our results indicate that the actual condition of the talus is stable if the construction of the retaining wall is made.

The foundations of a retaining wall systems are placed a specified distance below finished grade to provide adequate erosion protection, foundation bearing capacity, and overall global stability when slopes are involved. Please refer to

Figure 3: Typical Wall Embedment Section for specific embedment depth and setback distance.

Figure 3: Typical Wall Embedment Section

File No. 1823-1C Page 25

• Subsurface information from the exploratory borings and the geologic reconnaissance performed at each site should be used by project designer to interpret the elevation of the weathered rock formation at the wall structure. The design of the mass gravity wall assumes the footing base are founded on weathered rock formation. Variations in the elevation of weathered rock formation will occur and may require modifications to the wall designs at the time of construction once weathered rock formation is exposed in the excavations so that design assumptions are maintained.

Foundation improvements below the footing may be required if poor quality or downslope sloping discontinuities at the rock face are encountered. The geotechnical engineer should observe the excavations as weathered rock formation is encountered to determine the design assumptions remain applicable or if modifications to the designs or foundation improvements are required.

• Our observations and measurements of the joints and fractures in the weathered rock formation exposed in the adjacent road cuts suggest that occasional portions of the temporary excavation within weathered rock formation may require support to maintain stability during construction.

Since the ground water level of the site was not encountered within the depth drilled at each test hole, no dewatering problems are anticipated during the phase of over excavation and footing excavation. However, any water entering the excavation can be pumped directly from the bottom of them.

File No. 1823-1C Page 26

(pcf)

Angle of Internal

Friction, ɸ (Degree)

Cohesion

(psf)

In situ soil 135 36 Neglect

Table 3: Material Unit Weights and Soil Strength Design Parameters

The material to be used as backfill has to be laboratory tested to verify soil parameters.

According to the pressures and resisting shearing forces, the external stability of retaining walls must be checked by the structural designer, i.e., sliding, and overturning.

Our experience shows that during local rainy periods a temporary perched water level develops within the backfill of the wall surface which in some instances may rise close to the ground surface. This temporary perched water level introduces a lateral pressure to the wall.

To control the excessive lateral pressure, the wall shall be provided with a foundation wall drain system located over the interior and exterior top surface of foundation wall footings.

The foundation drain system shall be topped with a crushed stone backfill with a grain size of 1/4 to 3/4 in. of at least 1.5 ft. in thickness and 1.0 ft. wide above the wall footings to serve as the vertical drainage media toward the foundation drain.

Also, place a 1.0 ft. thick of crushed stone between the wall and the backfill material

File No. 1823-1C Page 27 to be placed against the wall. The wall shall be provided with a series of properly designed weep holes to avoid the accumulation of water behind the concrete wall during heavy rainy period. The last 2.0 ft. of the backfill material at the top of the wall shall consist of clayey material to reduce the superficial water infiltration.

A geotextile liner should be placed between the crushed stoned and the backfill to prevent mixing of the surrounding soil into the gravel. This will keep the porous spaces in the gravel open for the water to flow through.

The crushed stone layer shall be continuous since the top of the wall to the foundation wall footing and drained to the sides of the proposed wall by means of a minimum 2.0 in. perforated PVC pipe.

The retaining wall interior surface in contact with the backfill has to be placed with a plastic membrane with an asphaltic coating or similar substitute material to prevent water migration toward the lower level area, that is shall be design water tight.

Similarly, the construction joints of the walls are also properly sealed to prevent migration to any infiltrated water lower level.

An alternative to the standard gravel column used to provide vertical drainage path behind the wall is by substituting the classic column gravel by Geocomposites, such as Terra Drain or equivalent. Due to the high flow transmissibility characteristic found in the Geocomposites, they can be used behind the wall instead of the column of granular material. In addition, we recommend that an appropriate waterproofing sealant, be applied at the interior surface in contact with the Geocomposite to reduce the likelihood of seepage and vapor transmission into the living spaces.

File No. 1823-1C Page 28

It should be brought to the consideration of all parties involved, the fact that no matter how well-designed the project is, it shall be necessary to provide full time supervision for the foundation works with special interest in the construction of embankments, cuts, and retaining structures.

It is in the execution of these aspects of the suggested work that most of the problems of development construction can be minimized.

7.0 EARTHQUAKE CONSIDERATIONS:

Analysis of the relative density and consistency of the ground based on the

SPT N values; it is our opinion that for seismic design this site corresponds to a soil profile type SC according to the American Association of State Highway and

Transportation Officials (AASHTO) LRFD Design Specifications. Shear wave testing of the soils can be used to provide a more thorough evaluation of the seismic classification of site. A 100-foot deep boring was not required by the structural engineer due to size and height of the proposed structure.

8.0 SITE DRAINAGE AND MOISTURE PROTECTION:

Adequate site drainage is critical to reduce the potential for differential soil movement, erosion and subsurface seepage. Under no circumstances should water be allowed to pond adjacent to footings. The site should be graded and maintained such that surface drainage is directed away from structures. In additions, surface drainage should be directed away from the top of slopes into swales or other controlled drainage devices. Roof and pavement drainage should be directed into

File No. 1823-1C Page 29 conduits that carry runoff away from the proposed structure.

In case of basement walls or building walls retaining landscaping areas, a water proofing system should be used on the wall and joints, and a Miradrain drainage panel (or similar) should be placed over the waterproofing. The project architect or civil engineer should provide detailed specifications on the plans for all waterproofing and drainage.

Underground utilities should be leak free. Utility and irrigation lines should be checked periodically for leaks, and detected leaks should be repaired promptly.

Detrimental soil movement could occur if water is allowed to infiltrate the soil for prolonged periods of time.

9.0 ROAD PAVEMENT SECTION RECOMMENDATIONS:

All areas to be used as street shall be constructed over 1.5 ft. thick of selected fill material classified as A-2-4 or better material. Please note that whenever the fill thickness is greater than 1.5 ft. thick, the over excavation of the existing material is not required (except any existing vegetation, shrubs, grasses, and unstable material. One (1) feet depth of topsoil removal can be considered, excepted where any other foreign matter exists that could require deeper removal. Once the over excavation is made recompact the exposed grade to detect any surficial weak spots and place at least 1.5 ft. of a fill material classified as A-2-4 or better material properly placed and compacted until final sub base elevation is reached. A minimum 1.5 ft. thick of selected fill material is necessary at all areas below final sub-base elevation. Following the procedures of FILLING OPERATIONS

AND COMPACTION SECTION. If modification to grading is incorporated, we shall

File No. 1823-1C Page 30 be consulted to re-evaluate the submitted recommendations.

The use of an A-2-4 type of material properly placed and compacted at the road area of this project sub-base construction would permits the design of a flexible type of pavement based on a subgrade CBR value of about 25 to 30. This CBR values are based on experience with this type of material. However, the material to be used at the project must be tested to obtain its parameters by means of laboratory tests.

A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the physical properties of the subgrade soils and traffic loadings. Soils are represented for pavement design purposes by means of a soil support value for flexible pavements and a modulus of subgrade reaction for rigid pavements. Both are empirical related to strength. The pavement design thickness shall be properly calculated by the project designer.

The purpose of using the A-2-4 material as sub-base is to increase the overall stiffness of the structure of asphalt pavements. The increase in the overall stiffness of the asphalt pavement reduce deflections thereof, thereby reducing efforts and unit deformations which increases the fatigue life of the asphalt layers. Being the sub-base, a friction material is less susceptible to moisture and significant deformation when cracks in the pavement eventually occur. Once established the sub-base, it is practically permanent and will not only be beneficial to the performance of the initial pavement layers but also for future paving asphalt layers when are eventually rehabilitated. Once established in the initial construction, it is practically impossible, if not difficult, replacing it.

File No. 1823-1C Page 31

The proposed road area shall be design with its appropriate drainage and slopes to avoid accumulation of runoff water at the surface. A well-designed drainage system shall constitute an important part of the pavement design itself. A drainage system should be developed to control storm water run-off that may enter from outside or fall within the road curses. Concrete ditches along the roadways may prove to be efficient for collecting storm water run-off that develops on slopes.

However, the hydraulic capacity of these will govern their shape and size; therefore, hydrologic and hydraulic analyses shall be performed by the designer before sizing the necessary drainage structures.

10.0 PROTECTION OF EXCAVATIONS:

All Excavations at the site should be performed in accordance with 29 CFR

Part 1926, “Occupational Safety and Health Standards – Excavations; Final

Rule,” published by the U.S. Department of Labor, Occupational Safety and Health

Administration. Based on the information obtained from the soil borings drilled at the site, we classify the surficial soils as Type A soils. Stockpiles of excavated material should be setback from the edge of the excavation by distance at least equal to the excavation depth.

THE CONTRACTOR SHALL BE RESPONSIBLE FOR ALL TEMPORARY

EXCAVATIONS AT THE SITE. This includes the design of any required temporary slopes, dewatering, and shoring and bracing, as necessary.

Positive surface gradients should be provided to divert surface runoff water away from excavations for foundations and constructions areas. Ponding of water should be avoided to reduce damage of properly graded areas.

File No. 1823-1C Page 32

11.0 CONSTRUCTION CONSIDERATIONS:

The following considerations shall be taken into account in the construction of this project.

1. The earthwork shall be conducted under the observation and inspection of a

Geotechnical Engineer or his representative working for the project owner.

2. All relocation of existing underground utilities should be completed before grading begins. The ends of abandoned underground utilities should be permanently sealed to prevent the inadvertent introduction of fluids into the construction area. Any underground utility not removed will be subjected to new pressures that can damage it and affect the new structure. Any septic tanks and drain fields within proposed construction areas and 20 feet outside the construction limits should be excavated and removed.

We recommend any / all utility lines be located outside of planned construction areas, the trenches cleaned of backfill soils, and, after utility emplacement, the trench backfilled with compacted fill. Past experience indicates utility trench backfill is often poorly compacted. Also, cracked or deteriorated pipes can collapse, leak or serve as conduits for subsurface erosion. Any of these conditions can result in excessive settlement of foundations and pavements.

3. A Geotechnical Engineer from this office (Advanced Soil Engineering) shall observe the bottom of any excavation to verify its conditions with respect to those obtained with borings. Proof-rolling of the excavation bottom may be required, depending on the exposed ground conditions. Any old deleterious

File No. 1823-1C Page 33 fill, organic matter, or soft spot of soil detected at the bottom of any excavation shall be removed and backfilled as specified in Appendix 3.

4. The project excavations shall proceed in an expedite manner to prevent such disturbance of the foundation soil, and they shall be performed under dry conditions. The contractor shall take the required provisions to prevent the seepage and accumulation of water (runoff or temporary groundwater) into the excavations.

5. This report is submitted for the planning and design of the project and it provides some construction considerations that shall be reviewed by the contractor. However, the contractor shall not use this report as the only information to base his bid for the project. This office shall not be held responsible if the contractor uses this information without limitations. The contractor bidding for this project should conduct a careful review of the geotechnical data and documents given in this report. However, we will not be responsible for his interpretation and conclusions made from these data.

The contractor shall visit the project area prior to bidding to become acquainted with the actual conditions of the site.

6. The contractor shall take care to prevent damage onto surrounding structures and utilities due to the construction operations.

7. The contractor will be solely and completely responsible for his construction method, his method of excavation and support system, the working conditions at the job site, and the project safety measures. This requirement applies continuously, and it is not limited to normal working hours.

File No. 1823-1C Page 34

12.0 EXCAVATION PROCEDURES:

On the basis of the drilling effort rendered in advancing the test holes and the

“N” values recorded whenever sampling was attempted, all excavations should be performed by excavators, ripper and bulldozer to down grade the area to the required footing foundation base elevation. However, and given that the probability of uncovering isolated boulders or rock formations exists, the use of additional equipment like backhoes, heavy excavators, and / or hydraulic powered tools is likely to be required.

The geotechnical engineer for the project must be fully aware of the following utmost facts during the whole excavation process: first, though no ground water level has been recorded at any of the test borings along the site higher grounds nor any seepage or spring were noticed during our field inspections along said area, sometimes the like could show-up during the excavation process and/or at the long run. If this condition arises, further evaluation of the site development shall be considered at once to revise or modify the recommendations given. Some migrating bodies of infiltrated water may be encountered on excavations after prolonged rain events.

13.0 SLOPE CONSTRUCTION:

All cut or fill slopes shall be constructed for a geometry not steeper than 2:1

(H:V) regardless of its height and shall be also protected against gully and laminar erosion by providing proper drainage facilities. Fill slope shall be design with a positive drainage to avoid water running over sloping ground. Immediately upon construction of the slopes (either on fill or cut), these shall be protected from the

File No. 1823-1C Page 35 effects of erosion by adequate seeding…