Zipper Zeman Associates, Inc. Geotechnical and Environmental Consulting A lrierracan Company

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1 Zipper Zeman Associates, Inc. Geotechnical and Environmental Consulting A lrierracan Company J June 2006 City of Burlington Engineering Department 820 East Washington A venue Burlington, Washington Attention: Subject: Mr. Rod Garrett, P.E. Public Works Director Subsurface Evaluation and Geotechnical Engineering Evaluation Distressed Pavement at Tinas Coma Plat Hillcrest Drive Burlington, Washington Dear Mr. Garrett: Zipper Zeman Associates, Inc. (ZZA) is pleased to present herein our report for the above-referenced project. This report presents the results of our assessments of the areas of distressed asphalt pavement in two areas along Hillcrest Drive in the Tinas Coma plat. This report supplements our draft report dated 21 March Scope of Services Our scope of service was based on our Proposed Scope of Services and Cost Estimate proposal dated June 20, 2005 (P-2930), authorized by the City on June 29, Our services consisted of reviewing documents available to ZZA, a field reconnaissance, subsurface exploration, laboratory testing, analysis of the data, and preparation of this report. Our original scope of services was modified by way of Mr. Rod Garrett, P.E. 's 14 April 2006 request and authorization for ZZA to complete a planning level opinion of cost summary ZZA completed a distressed pavement evaluation of the affected areas of Hillcrest Drive in 2002, the results of which have been incorporated into this report. The 2002 evaluation consisted of reviewing published geologic literature, geotechnical documents and inspection reports prepared by others, as well as interviewing people involved with the original development, construction and inspection of the roadway. The current effort was focused on obtaining and reviewing information regarding stability analyses, permanent sloped fill design and construction recommendations, site preparation, and fill compaction records in order to evaluate potential causes of distress that have developed in the road and stabilization alternatives. Site Description The subject site is located on Burlington Hill in Burlington, Washington. Hillcrest Drive extends approximately 2,200 feet around the north face of Burlington Hill from approximately the northwest portion to the southeast portion of Burlington Hill. The road is relatively steep with maximum grades on the order of 15 percent. Both of the affected areas appear to have been rd Avenue West #117, Lynnwood, WA Fax:

2 ZZA Hillcrest Drive J June 2006 Page 2 constructed in areas where the roadway consists of a combination of cuts and fills. We understand the road existed prior to development as a narrower logging road. The inbound lanes on both ends of Hillcrest Drive are situated above steep fill slopes estimated to be on the order of lh:lv to 1 ¼H:lV. We understand that portions of the former logging road were removed and replaced during construction of the existing roadway. We further understand that the roadway fill material originated from on-site sources. Some of the roadway fill appeared to consist of gravel to boulder sized materials, based on the material exposed at the crest of the slope and immediately behind the curb. The fill material appears to have settled around the guardrail posts and the finer soil fraction of the fill appears to have been washed down into the fill, leaving only clean gravel and cobble sized aggregate at the surface. The asphalt surfacing in the affected areas has developed longitudinal tension cracks that parallel the steep fill slopes approximately 4 feet off of the curb and gutter. The degree of cracking is more significant in the northwestern area, although separation cracks are also evident between the asphalt surfacing and the curb and gutter in the southeastern area. We understand that the cracking was first noticed in November In the northwestern area, there is visual evidence of downset of the fill slope whereas the southeastern slope is covered with significantly thicker brush and small trees and such evidence has not been observed. SITE CONDITIONS The site conditions were evaluated during site visits in July and August 2005 and January and February The surface and subsurface conditions are described below, while the exploration procedures and interpretive logs of the explorations are presented in Appendix A. Laboratory testing procedures are described in Appendix B and the results are presented in Appendix B and on the logs in Appendix A. The northwest and southeast study areas are shown on the Vicinity Map, Figure 1. Approximate exploration locations of Borings B-1 through B-9, advanced at the northwest study area, are shown on the Northwest Site and Exploration Plan, Figure 2. Approximate locations of explorations completed at the southeast study area, Borings B-10 through B-12, are shown on the Southeast Site and Exploration Plan, Figure 3. Regional Geographic Setting Burlington Hill is a bedrock promontory located in the City of Burlington and is surrounding by valley alluvium. Hillcrest Drive traverses the northern end of the hill in a roughly northwest-southeast orientation. Two portions of Hillcrest Drive have experienced displacement and associated pavement distress. These two areas are located near the northwestern and southeastern ends of the road alignment where Hillcrest Drive descends from Burlington Hill down to the valley floor. Regional Geologic Setting Regional geologic conditions were evaluated by reviewing the publication Geologic Map of Washington-Northwest Quadrant (Department of Natural Resources, Map GM-50, 2002). The publication describes Burlington Hill as being composed of two Jurassic Period low grade J-2 I 89,Fina1RPT,June06.doc

3 ZZA Hillcrest Drive J June 2006 Page 3 (greenschist to blueschist facies) metamorphic rock types separated by a roughly north-south trending fault zone that roughly bisects the hill. The western half of Burlington Hill consists of weakly to moderately foliated metavolcanic rocks consisting primarily of greenstone melange with lesser amounts of quartz diorite, micaceous quartz-feldspar schist, and serpentinite. The terms greenstone and greenschist apply to rock material of igneous origin that has been altered through metamorphic processes to produce an abundance of the minerals chlorite, epidote, and hornblende. The affected rock mass frequently exhibits an overall greenish coloration. Observation of road cuts on the northwest portion of Burlington Hill along Hillcrest Drive disclosed the referenced greenstone rock materials. The rock masses are characterized by both massive sections that have widely-spaced structural discontinuities (fractures, joints, bedding planes) to intervals that exhibit very closely-spaced fracture and jointing patterns. Accumulations of fallen rock material were common along the more intensely fractured and jointed exposures, such as those along the east side of Hillcrest Drive at the northwest project site. The eastern half of Burlington Hill consists of weakly to moderately foliated marine metasedimentary rocks consisting of a melange of slate, meta-argillite, phyllitic argillite, volcano-lithic meta-sandstone, and schistic sandstone. During the Vashon Stade of the Fraser Glaciation, approximately 10 to 15 thousand years ago, a relatively thin, laterally discontinuous veneer of glacial deposits consisting primarily of glacial till, outwash, and lacustrine sediments were deposited above the metamorphic bedrock melange. Observation of the road cut along the east side of Hillcrest Drive at the southeast study area disclosed extensive exposures of slaty metamorphic rock (argillite) with relatively widelyspaced structural discontinuities. The exposures of more sound rock were flanked by exposures of greenschist that exhibited more closely-spaced joints and fractures. Field Reconnaissance A visual reconnaissance of surface conditions near the two distressed portions of Hillcrest Drive was made during our 2002 and 2005 site visits. We also completed a visual reconnaissance of a drainage basin located to the south of the northwestern distressed area based on anecdotal information suggesting the possible presence of a "wetland area" that drains towards the failing area. We reference road stationing along Hillcrest Drive relative to design drawings, dated August 1999, prepared by Leonard, Boudinot, & Skodje, Inc. Northwestern Distressed Portion of Hillcrest Drive The northwestern distressed area is located within a portion of Hillcrest Drive that traverses and descends a steep slope from the western side of Burlington Hill down to the valley floor. The eastern side of the road alignment consisted of rock cut slopes up to approximately 45 feet high with inclinations on the order of lh:lv to 3/4H:1V. Several near vertical cuts on the order of 3 to 5 feet high were observed near the base of the cut slope. In general, rocks exposed in the road cut consisted of moderately weathered, medium hard, highly fractured, weakly to J-2189,Fina!RPT,June06.doc

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10 ZZA Hillcrest Drive J June 2006 Page 10 Precipitation, as well as possible runoff from the wetland above the pumpstation, infiltrating into the road embankment fill material would increase its weight and decrease its internal strength. This combination would reduce the ability of the fill embankments to resist the gravitational forces that tend to drive the fill mass downslope. Document Review We reviewed a limited set of design drawings, photographs, aerial photographs and construction observation information provided to us by the City of Burlington and Leonard Boudinot and Skodje. The following drawings were reviewed: 1. Sheet 6 of 13 for LB&S Job Number 96039, dated November 6, 1996, Sheets 1 and 3 of7 for LB&S Job Number A, dated December 24, 1996, and Sheets 14, 19, and 24 of 34 for LB&S Job Number D, dated August 6 or 12, Construction inspection and laboratory testing results prepared by Advanced Soil Mechanics and Materials Testing & Consulting, Inc. (MTC) were also reviewed. We understand that Advanced Soil Mechanics provided inspection an'd testing services to C&C Construction during the road construction phase of the project while MTC provided inspection and testing services to Trico Construction during utility construction and constmction of the pavement section that included the base and subbase courses. 3. A report titled Preliminary Geotechnical Engineering Evaluation, Burlington Hill Road Alignment, by AGRA Earth & Environmental, dated June 11, Two letters by GeoEngineers, Inc. titled Alternative Pavement Section and Cul-de-sac Pavement Section, dated August 4, and August 13, 1999, respectively. 5. The City of Burlington and Leonard, Boudinot & Skodje provided the construction and site photographs, and aerial photographs. At the beginning of this project, we understood that ZZA would receive additional construction observation notes prepared by a Leonard, Boudinot & Skodje field inspector. However, after requesting this information, Leonard, Boudinot & Skodje did not provide it to us. We understand this information may have been transferred to the developer of the project. CONCLUSIONS AND RECOMMENDATIONS Document Review Geotechnical Report by AGRA Earth & Environmental The report by AGRA Earth & Environmental was titled as "Preliminary". However, there were no specific recommendations for further study relative to completing a "final" design report. They also stated that their recommendations were based on a preliminary plan and verbal J-2189,FinalRPT,June06.doc

11 ZZA Hillcrest Drive J June 2006 Page 11 information provided to them, and as such, they might need to modify their conclusions recommendations if any changes were made to the proposed project. We did not observe any records that AGRA was provided the opportunity to review the project design prior to it going to construction. In Section 1.0 of their report, AGRA acknowledged maximum rock cuts and fills of 25 to 30 feet. They stated that new cut and fill slopes could be desi gn ed for the "original" 1: 1 desi gn inclinations. However, in Section 4.1 of their report, AGRA recommended that permanent fill slopes be no steeper than 1.5H: 1 V, due to the risk of excessive raveling and erosion. They also stated that in localized areas, fill slopes as steep as the originally desi gn ed lh: 1 V could be used, but the slope face should be blanketed with small loose riprap to reduce erosion. In Section 4 of their report, AGRA describes the original road section between Stations 0+00 to 7+00 as being of typical cut and fill construction for roadways on a steep slope. The northwest-facing fill slope was described as having a 1 H: 1 V slope which was made up of excavated rock material. They also concluded that the desi gn cut slope angles of 1 H: 1 V would be adequate for minimizing rockfall and raveling. They also note that between Stations and 40+00, the original slope varied from 0.5H: 1 V to 2H: 1 V and that fill thicknesses would be on the order of 10 to 25 feet. They stated again that the desi gn fill slope inclinations of 1 H: 1 V would be adequate provided the recommendations for fill placement described in the report were followed. The structural fill recommendations were very basic in nature and did not address fill placement on slopes. They recommended that a representative of AGRA be present during the placement of all structural fill to observe the work and perform a representative number of in place density tests. We do not have a record of what the AGRA scope of services included. The report states that their study was to evaluate general surface and subsurface conditions at the site in order to formulate geotechnical conclusions and recommendations concerning roadway cuts, fill embankments and general roadway construction considerations. In our opinion, the report by AGRA was preliminary in nature and was not finalized for desi gn purposes. For example, there were no recommendations regarding site preparation that would have addressed grubbing and stripping. Given the nature of the native slopes and soil conditions, as well as the proposed filling and the steep slopes, a slope stability analysis should have been completed. There are no indications that AGRA was involved with the project after submitting their Preliminary Report. Construction Inspection Reports by Advanced Soil Mechanics Advanced Soil Mechanics (ASM) appeared to provide limited construction inspection in the form of density testing and laboratory testing. Only once (May 24, 1999) did ASM note any observation of the subgrade preparation, and then it was only to note that an area had been grubbed. Unless the inspection of the subgrade preparation was the responsibility of another firm, this critical aspect of the project may never have been reported. We did not observe such reports from other firms in the information provided to us. Throughout this project, as well as the repair to Hillcrest Drive, it appears that AGRA was not involved and it is unclear what company, if any, provided the geotechnical engineering oversight. J-2189,Fina1RPT,June06.doc

12 ZZA Hillcrest Drive J June 2006 Page 12 The laboratory testing and construction inspection records provided to us indicated that compaction of the structural fill in the road embankments was completed in general accordance with the project specifications. There are some indications that oversized rock was placed in the fill but it was noted as being broken down into sizes deemed suitable by Advanced Soil Mechanics. The field reports generally describe and record the placement of structural fill while the laboratory testing generally reported the grain-size distribution (sieve analyses), sand equivalent, and Proctor densities. Letters by GeoEngineers Regarding Pavements Although GeoEngineers was involved later in the project, it appears that their involvement was limited to those services provided by Trico during the pavement construction period of the project. However, Trico was reportedly involved with a slide repair within the northwestern area of current road distress that was originally constructed by C&C. It is apparent that the area repaired by Trico has moved since those repairs were completed. There was no documentation provided to ZZA related to the repair work. Given the extent of the repair, we would have expected that a geotechnical engineer would have become involved in order to address the cause of the failure and to develop repair recommendations, which likely would have included a stability analysis. It is unclear if GeoEngineers provided any consulting services relative to this repair. Incomplete Plan Set by Leonard Boudinot & Skodje An incomplete set of plans was provided to ZZA for review. The excerpts received essentially presented the road plans, storm sewer profiles, and Hillcrest Drive Cross Sections. The cross sections do not reference any WSDOT or County Standard Specifications for preparation of the subgrade. The cross sections do not indicate that any benching is necessary when placing fill on slopes. Settlement Monitoring Data by Leonard, Boudinot, & Skodje Settlement monitoring data provided to ZZA by L, B, & S presents distance and elevation measurements for two sets of monitoring lines on the northwest end of Hillcrest Drive. The locations of the sets of monitoring lines are presented on the Exhibit for City of Burlington dated February 7, 2001 by L, B, & S. Lines A through E were established between approximately Stations 3+80 and 4+42 and lines F through J were established between approximately Stations 5+94 and Readings provided to ZZA were taken between December 2001 and July The cumulative horizontal and vertical movements measured at each station are presented on the Table 3 on the following page. In general, it can be seen that the majority of the movements measured are on those monuments west of the curb line and within one point east of the curb line. This correlates well with the cracking observed in the southbound lane of the road. J-2189,FinalRPT,June06.doc

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15 ZZA Hillcrest Drive J June 2006 Page 15 CONCLUSIONS AND RECOMMENDATIONS It is our opinion that the majority of road distress is likely a result of slope movement with a minor component associated with settlement of the structural fill, all of which is associated with an over-steepened slope fill condition that is not internally stable. Our conclusion is based upon the inclinometer readings that indicate that there is a horizontal component of movement, as well as the settlement monitoring survey data from Leonard, Boudinot, & Skodje. The survey data indicates that there are horizontal and vertical components of movement. Based on the data, we would expect the movement to continue. Some measurements indicated that movement ofup to about 2.5 inches occurs some years. There are several possible contributory factors to the instability of the fill slopes as manifested at the road surface as tension cracks. Cracking was only noticed after the road had been in service for over a year and a relatively wet winter season had begun. Given the introduction of runoff and/or groundwater seepage into the fill soils, the weight of the fill soils increased, thus increasing the driving forces within the overall slope. Groundwater seepage may have created a preferential slip surface along the bedrock contact or within any silty native soils above the bedrock. In our opinion, the report by AGRA does not sufficiently address the geotechnical issues relative to this project and the construction of steep fill on equally steep hillsides. However, this report was titled as preliminary and therefore AGRA should have been given the opportunity to provide additional design and construction recommendations as necessary for final desi gn and construction. We understand that Skagit County had adopted the WSDOT Standard Specifications for Road, Bridge, and Municipal Construction at the time this project was submitted. If this was the case at the time of desi gn ing and developing Hillcrest Drive, we anticipate that Section (14 ), Embankment Construction, would have been applicable for this project. On hillside terraces, the specification states that "Unless otherwise directed by the engineer, the contractor shall terrace the original ground or embankment on hillsides, on the sides of existing embankments, and in transitions from cuts to fills. Each terrace shall penetrate that slope at least 1.5 meters and shall not be more than 1.5 meters high." There is no indication in the geotechnical report or the drawings provided to us that benching of the original slopes was recommended or required. However, Road Cross Section Note 4 on Sheet 24 of 34 of the civil plans indicates that the road subgrade was to have been prepared conforming to Section (1) of the 1998 Standard Specifications and be approved by the soils engineer prior to placement of the structural fill material. Section (1) states that the exposed subgrade is to be compacted to 95 percent of the maximum density. This compaction requirement was also stated in Note 4 of Sheet 24. We did not observe any field reports that indicated the exposed subgrade was prepared in accordance with this specification. We also did not observe any records that AGRA was provided the opportunity to observe the exposed sub gr ades prior to placing structural fill. Based on the records observed, it is difficult to determine what company or agency provided the final geotechnical engineering for the desi gn or was overseeing the J-2189,FinaJRPT,June06.doc

16 ZZA Hillcrest Drive J June 2006 Page 16 geotechnical components of the project. Based on the information provided to ZZA, it appears the L, B, & S was the only engineering company that was involved with the project on a regular basis. Utilities If the northwestern portion of Hillside Drive continues to move, it is probable that the water main and storm sewer will be susceptible to damage given their proximity to the tension cracks in the road and the zone of movement. On the southeastern portion of Hillcrest Drive, the storm sewer is situated within the block of soil that appears to be moving. If the systems are compromised over time due to on-going soil movement, the result of a massive water leak into the unstable soils could initiate a rapid catastrophic failure within the fill that supports the road. We recommend that the City continue to regularly inspect the storm sewer as a means of identifying potential irregularities in pipe grade or water tightness. It has been our experience that the integrity of storm sewer systems can be compromised by relatively small amounts of displacement, and as such, they should be closely monitored. Should the integrity of the storm sewer system be in question based upon the results of inspections, the system should be repaired in a timely fashion. Alternatively, we suggest that the City consider relocating the storm sewer out of the zones that are moving. Drainage We understand that at one time the developer had proposed to pave the area behind the pump station in order to more effectively collect and transport the surficial runoff that is generated from up gradient sources above and to the south of the rock cut. The asphalted surface would reduce the amount of water that would soak into the ground and direct the runoff to a storm pipe just above Station At this time, it is unclear how much of the runoff soaks into the ground, although it is directly upgradient of the affected portions of the roadway. It is our opinion that this measure could have a beneficial impact on the stability of the slope. Long-term maintenance of the asphalt surfacing should be expected due to the rock falls that continue in this area. We recommend a short-term improvement of the surface water drainage system that should be implemented immediately: regularly fill the cracks in the pavement and the gaps between the pavement and the adjacent curb/gutter. This step will reduce the amount of surface water infiltrating into the fill embankments. We recommend that City staff inspect the road at least monthly, and that cracks and gaps be filled with hot tar, or a sand and tar slurry as described in WSDOT Specification (5)C Crack Sealing, as needed and on a regular basis. Repair Options It appears that there are options to consider with respect to re-establishing a stable roadway at the affected areas on Hillcrest Drive. Two would involve leaving the alignment in its current position and one would be to move the roadway off of the unstable portions of the hillsides. For each of these repair options, we have presented conceptual descriptions of the J-2189,FinalRPT,June06.doc

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