Technical Report Addendum -AC-883579_HWY-347.pdf

TECHNICAL REPORT

ADDENDUM

LANDSLIDE AND ROAD DAMAGE EVALUATION AND

REPAIR RECOMMENDATIONS

AC-824544

FOR THE

RECONSTRUCTION OF HIGHWAY

PR-445 AT KM. 5.2

SAN SEBASTIAN, PUERTO RICO

ER-HWY-367

PUERTO RICO HIGHWAY AND TRANSPORTATION AUTHORITY

PRHTA Design Area

EMERGENCY RELIEF PROGRAM

Prepared by:

ROBERTO REXACH CINTRON & ASSOCIATES

May 7, 2019

Addendum to Technical Report Project: ER-HWY-367 PR-445 Km.5.20 San Sebastian, PR Project Puerto Rico Highway and Transportation Authority Emergency Relief Program Page – 2

Table of Contents

Cover …………………………………………………………………………………………………….. 1

Index ……………………………………………………………………………………………………... 2

Introduction ......……………………………….………………………………...…….………………… 3

Original Recommendation ………………………………………...…………….…………………...… 3

Addendum Justification ..……………………….………………………………….…………………… 4

Revised Recommendation ……….……….……………………………………………….…………... 5

Revised Opinion of Probable Cost ……….……………………………………………….…………... 6

Revised Plans ……………….……………………………….…………………….…….……………… 6

PR-445 Km.5.20 San Sebastian, PR

Emergency Relief Program Page – 3

Introduction

The Technical Report for this project was submitted on February 21, 2019 and on March 18 our recommendations were approved by the Authority. The recommended alternative was the construction of concrete paved waterways on both sides of the roadway with a gabion retaining wall (Alternate 1). Although not considered as an alternative, because it was included in all the alternates, was the replacement of the existing pavement structure in a significant section of the roadway. Now, because of additional considerations, as discussed herein, we submit this addendum to our original report.

Original Recommendation

We stated in our report:

“There are two main drainage systems the first on at the extreme western section of the project at Sta 1+20 collects runoff from the south lanes and some properties on that side of the roadway and through a 30” dia. pipe discharges into an inlet within a private property

(Church parking lot). This inlet also receives runoff from the north side of the sidewalk.

From the inlet and through the Church property crossing beneath one of the two structures

(classrooms) the system discharges into a stream that runs parallel to the roadway on the northern property line of the properties fronting the roadway. We don’t propose making any improvements to this system other than improving the capturing of runoff into the existing headwall. The second starts at Sta 2+30.91 collects runoff from the south lanes and some properties on that side of the roadway and through a 30” dia. pipe (now collapsed) discharged into a earthen channel that runs along the property line of a frontage lot into the stream on the north line of the property.

A concrete paved waterway (swale) will be built along the south edge of the roadway running from Sta 1+00 to Sta 2+30.91. This will discharge at Sta 1+20 and at its terminus.

On the northern side of the roadway another concrete paved waterway will be built from

Sta 1+39.11 to Sta 2+39.13 where it will discharge into an existing earthen channel. In the area of the two discharge points an existing and collapsed 30” dia. pipe will be replaced;

the entrance structure will be improved and a new headwall built at the discharge point where rip rap will be placed to channel the runoff into the existing earthen channel.

It is important to note that the installation of concrete paved waterways will be done up to

Sta 2+35.40 as there is no receptor to these structures downstream from this point within the project footprint.

At Sta 1+88.00 there is a small eroded area which affected the highway. In that area a small gabion wall will be built in order to strengthen and support the roadway and provide the space to build the concrete paved waterway. In this area the existing pavement structure will be replaced from Sta 2+86 to Sta 2+10.

At Sta 2+90 Sta (2+60 to Sta 3+00) there is a failed section of pavement which will be repaired along with the area from Sta 2+25 to Sta 2+60

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Emergency Relief Program Page – 4

The work in this section will require cold milling of the existing pavement, headwalls type

“B”, special headwall, 30” RCP pipe, concrete paved waterways, rip-rap, clearing and grubbing, fill and unclassified excavation for structures, trench excavation, construction of a fill embankment, gabion retaining wall, erosion control blanket, new pavement structure including base, subbase, bituminous base, and surface courses, guardrail, relocation of

PRASA, PREPA and PRTC utilities, thermoplastic paint, raised markers, reinstallation of highway kilometer markers, traffic signs, installation of a barbed wire and or chain-link fences and the adjustment of concrete entrances to various properties.

The affected roadway section is 200.00 meters long.”

Addendum Justification

The principal reason for this amendment is the recommendation by our geotechnical consultant, Despiau Associates, that requires the replacement and or reinforcement of the existing material under the highway. Mr Despiau states in his recommendations:

“5.3 Reinforced Embankment Stabilization using Geogrids Based on the results of the exploratory program performed, revealed a very soft to soft layer extending between 10 to 15 ft. in depth [Borings 367-2 & 367-3]. However, the complete replacement of these unsuitable soils shall be removed during the existing drainage pipe replacement. Should the invert elevation of the proposed drainage pipe installation excavation be higher than the very soft material elevation, then a stabilization procedure, using geogrids, to maintain the imparted stresses within the upper horizon and to redirect horizontally the expected stresses shall be allowed. The treatment sector shall extend at least 10 meters (minimum) west and east of Borings 367-3 and 367-2, respectively the foundation from the fill slopes at the base of the retaining walls.

Therefore, the following construction sequence shall be allowed prior to the construction of the required mat foundation. These are:

1. An additional demucking operations shall be allowed to allow the installation of the reinforcement elements (geogrids). Therefore, a partial removal of the under soil, 1.2 m. minimum, below the proposed structure (i.e. Drainage Pipe or Pavement Structure). Also, the horizontal extent of the demucking phase shall extend to a minimum of 2.0 times the excavation depth on all sides of the excavation, without encroaching any existing structures.

2. At the bottom of the temporary excavated section a Heavy-Duty Stabilization Fabric (TerraTex WTEC-HD or Similar) shall be provided with geogrids reinforcement Tensar Triax, TX 190 or similar directly on top.

3. Then, a layer of a minimum of 0.45 mts of bluish gray clean crushed stone (with diameter ranging between 4” to 6” inches) shall be deposited until an initial stabilization is attained. Then another layer of the same (Geogrid Tensar Triax, TX 190 or similar) shall be provided on top of the first 0.45 mts. layer. Once the additional geogrid is place, another layer,

0.30 mts., thick of Granular Backfill AASHTO A-2-4 or better, compacted to a minimum 95 % of its Modified Proctor Density Test shall be place and

PR-445 Km.5.20 San Sebastian, PR

Emergency Relief Program Page – 5 compacted on top. This procedure shall be repeated until reaching the proposed bottom footing elevation to allow the construction of the foundations on top.

4. Afterward, the remaining backfill material, if any, may be laid as required by design (Granular Backfill AASHTO A-2-4 or better, compacted to a minimum 95 % of its Modified Proctor Density Test).

All stabilization fabrics and geogrids (i.e. TerraTex, Tensar or similar), shall continue vertically on the sides of the open excavation to a minimum distance of twice (2) the backfill layer thickness. Also, all borrow materials shall be taken to a soils laboratory for testing and approval prior to their use at the project.”

This recommendation surpasses the amount of excavation under the highway we considered and will require the implementation of a more elaborate MOT for the project.

Revised Recommendations

The recommendation by Eng. Jose Despiau will not require changes to our basic recommendations. It does, however, affects the cost of the improvements to be built. We considered recommending a detour but desisted of the idea because of the distances involved and the additional recommendation by Mr. Despiau to limit the sections of excavation to 15’, as stated in his report, section IV. OBSERVATIONS AND FINDINGS page 13:

“Also, although the available space to carry out the demucking operation seems enough, special care not affects existing structure during the excavation process. Upmost importance shall be given to protect existing structures from any lateral yielding of their foundation and/or settlement. Thus, alternate sequence of not more than 15 ft.

(horizontally) during the excavation procedure shall be considered under such circumstances.”

This limit will reduce the working area to multiples of 4.5 mts. corresponding to the layers of soil reinforcement shown in the detail below and permitting workable lane closures.

4.5 mts. under excavation

4.5 mts. at full depth of 1.35 mts

4.5 mts. at a depth of 0.90

4.5 mts. at a depth of 0.60

4.5 mts. at a depth of 0.30

22.5 mts. Total

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Emergency Relief Program Page – 6

Above we present a possible scenario of the length of the lane closures. The reduced work area will limit the length of the prolonged closing of one of the lanes and permit through traffic in the roadway during the construction operations. None the less, temporary addition to the existing lane widths will be required. This, because of the limited time frame may be paved with gravel.

Revised Estimate

The main items that had significant differences are shown in the following table:

1 Mobilization Revision of the cost database as per PRHTA latest bids

3 Field Office and Laboratory Increase of 30 days construction time 4 Flag men Increase of 30 days construction time 8 Construction Signs Increased complexity of MOT 28 Sub Base Stabilization Geotechnical requirement

In the next page we show a comparison, side by side, of the original estimate for alternate 1 and the revised estimate. We marked all the items that had a differing cost or are new items.

Revised Plans

In the plans included after the revised estimate we include the revised schematic drawings (GR/3, PL/1 and CS/1).

Roberto Rexach Cintron & Associates

Roberto L. Rexach Cintrón, PE

Principal