Report - Geotechnical_HWY_8_AC-827579.pdf

Suelos, Inc.

Soil & Construction Materials Laboratory and Environmental Drilling Services

GEOTECHNICAL SUBSOIL EXPLORATION AND

REPORT ON LANDSLIDE AT PR-10, KM. 46.7

PROJECT I.D. ER-HWY-8 (PROJECT SITE 1A)

UTUADO, PUERTO RICO

REVISION No.1

1.0 INTRODUCTION

This report presents the results of the geotechnical investigation performed for the landslide that affects state road PR#10, Km 46.7, 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

May 8, 2018's technical proposal to JOV & Associates.

The object of the exploration was to investigate the slope instability phenomena affecting the shoulder and fill embankment of PR#10, specifically between Km. 46.6 and 46.8. Potential reasons behind the landslide are investigated and possible stabilization alternatives evaluated and presented as remedial measures.

2.0 LANDSLIDE LOCATION AND MORPHOLOGY

The subject areas are located to the east side of the existing PR-10, around Km. 46.7. Figure

1 is portion of a Goggle aerial photo showing the general location of affected area.

According to information provided to this office, various site visits performed by our personnel and assessment of the USGS topographic map, the area under study corresponds to a natural, elongated drainage gully which has suffered severe erosion and instability due to run-off and underground water seepage. The PR-10 alignment lays at the upper reach of the hillside while the

Caguanita river bounds the hillside on the east. Portion of the fill embankment and a large segment of the hillside have suffered from slope instability, mainly due to uncontrolled run-off water and underground water seepage.

GEOTECHNICAL SUBSOIL EXPLORATION AND

REPORT ON LANDSLIDE AT PR-10, KM. 46.7

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 1. Site location

Based on the topographic plan submitted to us by JOV & Associates, the approximate elevation of road PR-10 at the area under study is 209 mts while the lowest portion of the affected hillside is at about elevation 170 meters. This suggests that the affected slope is around 39 meters high (128 ft). The total length of the area under study is 95 mts (311 ft). The most obvious and recent manifestation of the landslide is a steep head scarp and a deep and long erosion gorge (see

Figures 2, 3 and 4). The original geometry of the slope is unknown but it probably varied between

1.5H:1V and 2H:1V.

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 2. Partial view of affected area

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 3. Long and deep erosion gorge (looking downslope)

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 4. Long and deep erosion gorge (looking upslope)

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 5. Several water marks evidencing groundwater seeping out thru the asphalt.

From our site visits, it is evident that heavy scoring has damaged the earth slope (Figures 3 and 4). The erosion has down-cut thru the slope of the hillside and fill embankment, triggering a localized landslide. With time and continued erosion, the erosion gorge has evolved into a large landslide due to rear scarp retrogression (Figure 4).

During heavy weather events, groundwater seepage runs beneath PR-10 from the high land west of PR-10. Some of this groundwater find its way out thru the asphalt, as evidenced by watermarks in the pavement (Figure 5). It is conceived that most of this groundwater also seeps out at the face of the hillside, compromising the slope stability. This domino-effect has left behind a deep erosion gorge with near-vertical upper slopes, which jeopardize the stability of the road.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

3.0 WORK PERFORMED

As part of our scope of work delineated in our March 8, 2018's proposal, the following works were carried-out:

a) The installation of one SPT boring to 55 ft deep at location showed in Figure 6. A second boring was originally scheduled but could not be performed due to access restrictions.

b) Geotechnical models of the landslide were prepared using as built transverse cross section provided by JOV & Associates.

c) 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.

d) Slope stability analyzes were performed to investigate current landslide safety factor and to obtain via back-calculation soil strength parameters. These values were then compared with the ones obtain via empirical correlations.

e) Slope stability analyzes were performed to develop possible corrective and stabilizing alternatives to mitigate the existing instability conditions.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 6. Boring location plan

4.0 GENERAL GEOLOGY

The area under study should spars entirely within Dioritic intrusive rocks (Unit Tki), as shown on the Geologic Map of the Utuado Quadrangle by Arthur Nelson (1967) in Figure 7.

The Tki consists mostly of small bodies of granodiorite and some diorite, locally occurring as dikes. However, the subsoil investigation disclosed a thick fill layer, followed by weathered granodiorite. It appears that the naturally occurring drainage gully was filled during PR-10 construction. It is also evident that slope instability has produced landslide deposits which now lay scattered throughout the hillside surface.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

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 50 ft deep measured from boring elevation. This fill is the result of filling the natural drainage gully that existed originally at the site.

Most Standard Penetration Tests performed in the fill material obtained N-values in the range of 7 to 17 blows per foot (bpf). Natural moisture contents resulted relatively low with average values between 8 to 15 percent.

At 53 feet deep, the SPT obtained refusal count. The SPT gathered no sample recovery but evidence of severely weathered granodiorite was noted from drilling cuttings.

6.0 GROUNDWATER LEVELS

A stabilized groundwater table was not found during the exploration, however, water marks observed at PR-10 asphalt surface tend to indicate that groundwater flows thru the fill embankment beneath the road. Being an old drainage gully artificially filled during PR-10 construction, we believe groundwater flows across the fill embankment during 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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

7.0 DISCUSSION

The affected area can be characterized as a debris flow type of landslide triggered by soil saturation, groundwater flow and deep erosion. With time and continued erosion, the debris flow of unconsolidated rock and soil has evolved into a large landslide which now has a near-vertical scarp in its upper reach, near PR-10.

Using the subsoil information, landslide characteristics and scarp/cracks features in the ground, it can be concluded that the landslide surface lays along the bottom of the erosion gorge.

So far, a deeper surface of rupture, such as a rotational slip surface has not been detected, but its development can not be discarded on account of the deep head scarp present in the upper reach of the slope.

We are of the opinion that the instability of the slope has evolved as a consequence of steep slopes combined with heavy erosional forces against the slope surface and groundwater. It is evident that the water flow has down-cut the slope surface, leading to instability along the gorge flanks. The scenario has been aggravated by rear scarp retrogression. The development of successive landslide slips in the fill mass has worsen the stability of the fill embankment.

The following sections discuss the modeling of stability analyses and remedial measures to improve the stability of the slope around km. 46.7.

8.0 SHEAR STRENGTH PARAMETERS AND LABORATORIES TEST RESULTS

The main input for a stability analysis of a landslide are slope geometry, location of the failure surface, magnitude of pore-water pressures, unit weight of materials involved, and shear strength of the materials that intersect the failure surface. For the latter, a drained or undrained shear strength may be applicable for the materials that intersect the failure surface depending on the hydraulic conductivity of the materials and rate of loading involved. For instance, if the loading (or failure rate) is slow enough that pore-water pressures do not develop, drained or effective shear strength parameters shall be employed.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

8.1 Strength Parameters Based on Empirical Correlations

For the case of drained (effective) shear strength parameters, two conditions can be considered; Residual and Fully Softened. The residual shear strength of cohesive soils is applicable to new and existing slopes that contain a pre-existing shear surface. Typical cases are old landslides, bedding shears in folded strata, in sheared joints of faults, and after an embankment failure

(Skempton, 1985). An effective stress analysis is usually applicable in these cases and thus drained shear strength parameters should be used (ör, C=0).

On the other hand, the fully softened condition corresponds to the condition after which the over-consolidated clay has absorbed as much water as it desires and has reached equilibrium at a particular site. The softening of an oveconsolidated clay reduces the effective stress cohesion component of the Mohr-Coulomb shear stress parameters but does not cause orientation of clay particles or a reduction in the friction angle (Skempton 1970). This condition is numerically equal to the drained peak strength of a normally consolidated specimen (öp, C=0). Skempton (1977), concludes that slopes that have not undergone previous sliding can be analyzed using a fully softened shear strength.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 8. Secant fully softened friction angle

The following Figures 8 and 9 present empirical relationships between the drained, fully softened, peak and residual friction angle (öp and ör respectively) and liquid limit, clay-size fraction and effective normal stresses of 1, 2 and 8.3 ksf (50, 100 and 400 kPa).

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 9. Secant residual friction angle

These relationships, presented by Stark, Choi and McCone (2005), have the benefit of considering the effect of clay-size fraction and effective stresses, contrary to previous correlations presented by Bjerrum and Simons (1960), NAVFAC (1982), and Mesri and Abdel-Ghaffar (1993).

As part of the geotechnical study, various soil samples were subjected to laboratories that included Atterberg Limits and Grain Size Distribution analyses. Appendix “Laboratory Test

Results” contains all laboratory results.

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

From the data presented by Stark et al., and considering a clay fraction <20 percent, the following strength parameters were estimated:

TABLE 1. Soil Strength Parameters (deduced from Stark et al., 2005)

Soil Type LL öp ör

Fill A-1-b to A-2-4 NP 34-36 --

Residual Soil (A-2-4/A-2-6) 30-35 32-34 28-32

Weathered Diorite NP 38 --

As shown in Table 1, the empirical values for the drained, fully softened, peak friction angle are in the range of 32 to 34 degrees for the silty sand material (residual diorite) and about 38 degrees for the weathered diorite). The peak friction angle for the A-1-b/A-2-4 fill is estimated in 34 to 36 degrees.

9.0 SLOPE STABILITY ANALYSIS AND REMEDIAL MEASURES

The stability analyses were performed by using Bishop’s and Janbu’s slope stability methods of slices for circular, non-circular and combined sliding surfaces.

The theoretical mode of failure of the actual landslide profile seems to follow a combined planar/arc slip surface. However, this slip surface has been the result of rear scarp retrogression induced by successive (smaller) landslides thru time and continued erosion forces.

The stability analyses were originally used as back-calculation tools to establish the shear strength governing the failure (slip) surface. With the approximate slip surface defined, subsurface models were prepared using the topographic data and transverse sections provided to us. Then, analyses were performed to model possible remedial measures.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 10. Typical cross section showing remedial measures

9.1 Selected Alternative: Reinforced Slope + Trench Drain

We estimate that the original geometry of the pre-failure slope was 1.5H:1V. Considering that the landslide was triggered (chiefly) by a combination of erosional forces and a steep geometry, the alternative of reconstructing the slope using 1.5H:1V and 1.75H:1V geometries and incorporating reinforcement elements would be a feasible alternative. Clearly, the design and construction of better and more effective drainage structures shall also be integral part of the remedial measures.

For increasing the factor of safety against a rotational landslide (for static and seismic conditions), it was reasoned that the slope shall be internally reinforced with geogrids. The alternative of slope regrading combined with internal reinforcing geogrids is presented in Figure

10. Static and seismic stability models (global stability) are presented in Figures 11 and 12. These models resulted with global stability factor of safety of 1.9 and 1.2, respectively. The seismic model considered a horizontal acceleration of 0.2g.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 11

Figure 12

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

The analyzed remedial measure consists of benching of the existing surface, slope regrading to geometries of 1.5H:1V and 1.75H:1V, the inclusion of an intermediate berms (terraces) 20 ft wide, the reinforcement of the new fill slope with geogrids and the construction of a trench drain along the upper reach of the landslide (at PR-10 elevation). The primary reinforcing geogrids shall have minimum length (L) of 20, 24 and 29 meters as shown in Figure 10. We have considered a minimum geogrid long term design strength (LTDS) of 4500lb/ft in the upper region of the RSS and

5500 lb/ft in the lower half of the RSS. The final design (internal design) of the reinforced slope segment shall be performed by others, which shall specify geogrid type, lifts, finishing, internal drainage and installation specs.

When performing the slope reconstruction, filling shall begin in the lowest section of the area. A-1 fill material can be used for slope reconstruction, spreaded in layers 12 inches in thickness prior to compaction. 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. The A-1 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. Proper clearing works followed by an effective benching process shall be provided prior and/or during reconstruction.

The reinforced slope portion shall be erected following designer specs and/or manufacturer recommendations.

9.2 Trench Drain Requirement

As previously mentioned, the remedial measure shall be accompanied by an effective slope drainage system. This can be accomplished by installing one interceptor trench drain along PR-10.

The trench drains shall be 3 feet wide and 18 feet deep, with a 8-inch diameter flexible drainpipe at the base. The drainpipe shall be wrapped around with geotextile fabric before being put into the trench (Figure 13).

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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

Suelos, Inc.

Soil & Construction Materials Laboratory and Environmental Drilling Services

GEOTECHNICAL SUBSOIL EXPLORATION AND

REPORT ON LANDSLIDE AT PR-10, KM. 46.7

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

Figure 13. Typical drainage trench details

Personnel shall not be allowed to enter the trench during construction. The backfill shall be crushed stone of 3-inch minus gradation with not more than 5 percent by weight of non-plastic fines passing the No. 200 sieve. The upper 18 inches shall be constructed using compacted impervious fill.

The remedial process shall start with the installation of the drainage trench. The trench shall be provided with connected to a proper outlet, designed to prevent local erosion during outflow.

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

The trench shall include a geotextile filter fabric that separates the drain rock from the native soils. The characteristics of the non-woven fabric are listed in Table 2.

Table 2. Geotextile Properties

Geotextile Property Test Method Minimum Values

Grab tensile strength ASTM D 4632 180 lb

Burst strength ASTM 3786 290 psi

Puncture strength ASTM D 4833 OR 3787 80 lb

Apparent opening size ASTM D 4751 600 ìm sieve or smaller opening

Permittivity ASTM D 4491 0.01 s-1

The base of the trench should be sloped so that water does not pond in the trench. A minimum slope is 2%, but steeper slopes are better.

Trench excavation should be performed by a large-tracked backhoe. After a length of 30 linear feet of trench has been exposed a width of filter fabric shall be laid across the trench, overlapping the upslope edge of the already built section of the drain. The ends of the fabric on opposite sides of the trench shall be staked to the ground. Any fabric damaged by backfilling or side sloughing should be replaced immediately.

Granular backfill shall then be placed in the drain using any method that provides reasonable care to avoid tearing or disrupting the fabric and sides of the trench. Contractors may use a second backhoe or front-end loader to pour the granular backfill into the trench. Backfilling shall be done from the downstream end of the drain rather than from the side, where the weight of the equipment might destabilize the trench. The backfill shall be tamped by the back of the backhoe bucket to ensure that no large voids have been left in the trench due to arching.

When the backfill has reached to within 18 inches of the trench top, the geotextile fabric shall be wrapped over the backfill with an overlap. Completion of the drain by impervious fill to the ground surface should be shortly thereafter.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

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.

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.

11.0 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 landslide mass 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.

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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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

12.0 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.

13.0 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 15, 2019.

The conceptual remedial measures recommended herein will minimize the sliding problem.

However, these measures are not non-yielding solutions and there always exist the possibility that further small movements may develop during and after construction.

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.

Suelos, PSC.

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

PROJECT I.D. ER-HWY-8 (Project Site 1A)

UTUADO, PUERTO RICO

Rev.1 September 22, 2020

14.0 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, 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.

Respectfully submitted, IVAN JACKSON MADURO, P.E., MSCE

Chief Geotechnical Engineer & Partner mgn

Reference No. 4834-P2.rep

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