APPENDIX F GEOTECHNICAL MEMORANDUM BY STRATA INC.

Transcription

1 PUD No. 1 of Pend Oreille County Sullivan Lake Cold Water Intake APPENDIX F GEOTECHNICAL MEMORANDUM BY STRATA INC. 95% Draft Design Documentation Report January 19, 2011 Appendix F Geotechnical Memorandum by Strata Inc.

2

3 Sullivan Lake Cold Water Intake Metaline Falls, Washington PREPARED FOR: Mr. Paul Larsen, P.E. McMillen, LLC 835 S. 192nd Street, Building C, Suite 1300 Seatac, Washington PREPARED BY: STRATA, Inc E. Knox Avenue, Suite 200 Spokane, Washington January 14, 2011

4 TABLE OF CONTENTS Page INTRODUCTION... 1 PROJECT UNDERSTANDING... 1 SITE EVALUATION... 2 Research... 3 Site Reconnaissance... 3 Geologic Environment... 4 Subsurface Condition Interpretation... 4 Anticipated Site Conditions... 6 Intake Structure... 6 Pipeline Alignment... 6 GEOTECHNICAL OPNIONS AND RECOMMENDATIONS... 6 Geotechnical Analyses and Assumptions... 8 Foundation System Options and Performance Criteria... 9 Constructability Discussion Geotechnical Continuity and Contractor Submittals LIMITATIONS... 12

5 Sullivan Lake Cold Water Intake Metaline Falls, Washington INTRODUCTION STRATA accomplished this geotechnical foundation evaluation to assess the geologic conditions within the proposed project area and prepare geotechnical recommendations to support structural and civil design and help develop construction documents for the proposed Sullivan Lake Cold Water Intake project to be located near Metaline Falls, Washington. We accomplished the following referencing the authorized scope of geotechnical services dated December 1, STRATA researched available subsurface information such as geologic maps, geotechnical reports and well logs to help us understand the conditions encountered. We also reviewed a dive exploration video and soil samples obtained from the lakebed surface during the dive. 2. STRATA performed site reconnaissance to observe geologic conditions within the outlet channel and the north end of the lake. Our geologic reconnaissance helped identify the extent of glacial outwash sediments or phyllite bedrock as it relates to the intake structure location and outlet channel conditions. A professional geologist performed the reconnaissance and obtained photographs, which are presented in this report. 3. STRATA summarized the above research and site visit in this report, which also provides the following: Geologic environment Anticipated conditions along alignment Geotechnical analyses and assumptions Foundation system options and performance criteria Constructability discussion Geotechnical continuity and contractor submittals STRATA prepared a draft report for review by McMillen, LLC (McMillen). After receiving draft report feedback, we incorporated pertinent review comments into this final report and provided 3 hard copies and 1 electronic copy to McMillen. PROJECT UNDERSTANDING The Sullivan Dam currently exists at the north outlet of Sullivan Lake in Pend Orielle County, Washington. The Pend Orielle County Public Utility District (PUD), retained EES Consulting and McMillen to design a cold water intake structure to support upcoming infrastructure improvements. Current project plans provided by McMillen and reviewed by STRATA include connecting a 48-inch-diameter, high density polyethylene (HDPE) intake

6 Page 2 pipeline to the existing Sullivan Lake Dam structure at STA The pipeline will be buried below the lake bottom near the outlet channel and secured using concrete anchors at the lakebed surface as the pipeline extends to the intake. A steel intake screen system and foundation system will connect to the pipeline and will be constructed over the lakebed at approximately STA The lakebed surface is at elevation 2,450 AMSL at the intake structure. The intake structure will consist of a steel frame connecting to the HDPE pipeline supported by a pile foundation system. McMillen has designed the connection system between the screen system, intake pipe and pile foundations. Two intake screens will be mounted to the steel frame structure and will create slightly eccentric foundation loading conditions. There will be roughly 10 feet of pile between the screen structure and lakebed surface. This free length is required to elevate the screen and intake above the soft silt encountered at the lakebed. The screens are relatively light (approximately 6,300 pounds per screen) and the concrete foundation and steel frame will also be lightly loaded. McMillen reports total structural loads on the order of 20,000 pounds for the entire intake structure that will connect to the pile foundation configuration. The current pile configuration consists of 8 total piles (4 piles per screen in a rectangular configuration) and the piles are currently spaced 5 feet 4 inches to 8 feet 9 inches on center. We understand the concrete intake foundation may be able to accommodate vertical foundation settlement on the order of ½ inch or more. Lateral loading is on the order of 650 pounds per pile. SITE EVALUATION As part of STRATA s authorized scope of service, we evaluated the project site s geologic conditions through a combination of research and a limited site reconnaissance. STRATA reviewed geologic maps, aerial photographs, past geotechnical evaluations performed for the dam and recent lake dive explorations. Our research is described in further detail in the following report sections. Our site reconnaissance was limited by you to a surficial evaluation of the project area and was performed with the goal of estimating the subsurface conditions that may be encountered along the proposed pipeline. At the time of our reconnaissance, snow cover partially obstructed our observation at and near the project site.

7 Page 3 Research We performed an internet search for documents relating to the Sullivan Lake Dam and the bridge construction. In addition, we searched for available geologic maps and subsurface well logs in the vicinity. We obtained the following documents to support our research. If additional documents are available or we become aware of additional documents that aide in our evaluation, we will include them in our final report. Site Reconnaissance Joseph, Nancy L., July 1990, Geologic Map of the Colville 1:100,000 Quadrangle Washington-Idaho. Department of Ecology, State of Washington Well Logs. Miller, Fred.; Burmeister, Russell; 1983, Preliminary Geologic Map of the Abercrombie Mountain Area, Pend Orielle County Washington. Google Earth Aerial Photo of the Project Site. EES Consulting; Sullivan Lake Cold Water Intake Tech Memo No. 002, McMillen LLC, October 14, Site Plan and Intake Pipe Profile, McMillen LLC, September 21, Engineering Report on Sullivan Lake Project No Washington, prepared by Harza Engineering Company, Chicago, Illinois, January 23, Pend Orielle County Shoreline Master Program Update Reach Scale Inventory and Assessment (Item 56 Sullivan Lake). STRATA performed our site reconnaissance on December 6, We traversed the shoreline along the outlet channel s east bank, south of the existing bridge. We also evaluated the exposed soil conditions below the existing bridge and either side of the dam. We evaluated exposed soil and bedrock outcrops along Sullivan Lake Road, which traverses the west lakeshore. We photographed pertinent conditions during our reconnaissance, which are presented on Plate 1, Site Photographs. Our reconnaissance can be separated into four areas as detailed below. As stated earlier, our site reconnaissance was limited by snow cover and we recommend a follow up site reconnaissance be performed in the spring to observe any additional soil and/or rock exposures that may be exposed and substantiate or alter our opinions and recommendations. Area 1 We began our reconnaissance along the outlet channel s east bank and shoreline south of the existing bridge near the dam. We observed relatively clean sand and gravel near the water s edge and along the bank. As we traversed to the higher

8 Page 4 elevations along the bank, the sand and gravel contained a higher silt content. We observed cobbles throughout the exposed sand and gravel. Area 2 We evaluated conditions below the existing bridge and south side of the dam. We observed relatively clean sand and gravel with cobbles and occasional boulder erratics along the bank edges. We observed surficial silt deposits on the upper bank of the outlet channel. Phyllite riprap had been placed directly below the existing bridge. Area 3 Conditions north of the dam consisted of clean sand, gravel, cobbles and boulders near the water s edge. Area 4 We evaluated two bedrock outcrops to the south and west of the dam along Sullivan Lake Road. The first outcrop was approximately ½ mile from the dam and was located within a rock fall area. We observed phyllite metamorphic bedrock with zones containing tight folds and minor faulting. The second outcrop we observed was approximately ¾ mile south of the dam, along Sullivan Lake Road. We observed phyllite bedrock, which appeared to be dipping at a shallow angle away from the lake, to the west. Geologic Environment The geologic conditions near Lake Sullivan and the dam area are a combination of glacial-scoured metamorphic bedrock and Quaternary-aged glacial sediments. Metamorphic bedrock consisting of phyllite borders the west side of Sullivan Lake and metamorphic quartzite borders the eastern side (Joseph, 1990). The metamorphic bedrock is geologically much older (Precambrian) than the glacial activity and resulting sediments that formed Sullivan Lake. Extensive folding, regional uplift, and faulting of the metamorphic bedrock created the mountainous topography in the project area. Subsequent to regional metamorphism, the entire north portion of Idaho and Washington State was covered by a large glacial ice sheet. Glacial action eroded the bedrock, creating steep and deep valleys in the entire region. When the glaciers regressed north during the end of the last ice age, they deposited glacial sediment. Our opinion is this glacial sediment comprising outwash and moraine sediments dammed the northern end of the lake. Harza (1958) noted the natural glacial dam to be approximately ½ mile wide and as long as ½ mile. Glaciolacustrine and glacial and alluvium material have been mapped in the dam footprint (Burmeister, Miller, 1983). Subsurface Condition Interpretation Our subsurface interpretations along the pipeline are based upon available geologic information, our site reconnaissance and reviewing of topographic and aerial photographs. From our review of the topographic map presented as Plate 2, Topographic Map, and aerial

9 Page 5 photographs, it appears the dam and northern end of the lake is consistent with glacial moraine and outwash geomorphology. Our opinion is the moraine may extend into the lake between the east and west bedrock ridges for an unknown distance extending south from the outlet. We base this opinion, in part, on the lake floor bathymetry data that shows the lake floor gently sloping to the south at a much flatter slope than the adjacent topography where bedrock is near the ground surface. The moraine feature at the lake outlet can be interpreted on Plate 3, Aerial Photograph. The end moraine appears to be large enough to extend into the lake to the end of the proposed pipeline. Our interpretation is that glacial sediments could be encountered for 50 feet or more below the lake floor. Well logs located a few miles north show glacial sediments to depths up to 189 feet. Our opinion is metamorphic bedrock is likely far below the lake bottom based on our interpretation of the moraine and outwash sediment thickness and based on the bedrock s steep topography as compared to the relatively flat topography at the lakebed near the proposed intake structure. As part of our research, we reviewed a dive video and soil and rock samples from the dive exploration along the proposed pipeline. The dive video shows waist-deep sediments at the proposed intake location that are very soft and light. From soil sample review, the sediment consists of non-plastic silt. Our opinion is that these sediments will be the deepest where the water column is the highest, thus, allowing for more accumulation for the fine sediments. This trend is also evident in the dive video as the soft sediments reduce in depth as the water column decreases. Approximately halfway between the dam and proposed intake, gravel sediments begin protruding from the sediment and are coated with the silt. The sediment thickness decreases toward the lake and as the static water column depth decreases. Due to the soft and light nature of the sediments encountered, we believe they consist of deposits from surrounding drainages in geologically recent time. We do not believe the soft, light sediments to be associated with glacial activity because they are not indurated and/or compressed. The artificial damming of the lake approximately 90 years ago probably slowed the lake s drainage somewhat and increased fine sediment precipitation. Harza, 1958, reported that wood-bearing piles were driven at random within the excavation before the placement of the concrete for the Sullivan Lake Dam. However, they reported there is no information available as to the number, size or location of these piles or the exact elevation of the bottom of the concrete structure. They also reported that the existing concrete structure is founded on the sands and gravels of the ancient natural dam. During our

10 Page 6 site reconnaissance, we also observed wood timber piles near the existing bridge. These timber piles must have been driven into glacial sediments, likely consisting of sand and gravel, as opposed to bedrock. Finally, erratic timber is evident along the pipeline alignment several hundred feet from the dam. Anticipated Site Conditions Intake Structure Based on the geologic environment and interpretation stated above, our opinion is the conditions at the intake structure foundation will consist of soft, non-plastic silt overlying sand and gravel outwash or moraine sediments. The silt is of unknown thickness, although the sediments are recent, and gravel and cobbles are evident below the silt layer a few hundred feet from the proposed intake footprint. Our opinion is the silt may be on the order of 3 to 8 feet thick, although this is only an estimate. The underlying sand and gravel will likely contain cobbles and boulders up to 12 inches in diameter, based on the exposed alluvium along the lakeshore and in road cuts. The nature of glacial moraine and outwash sediments suggest the sand and gravel will contain variable silt content and some clean sand layers may be present. Pipeline Alignment From our observations along the lakeshore near the bridge and dam, and our review of the dive video, our opinion is the silt layer near the intake structure will decrease in thickness toward the dam. We expect sand and gravel sediments as characterized above to comprise the majority of the alignment profile near the surface. These sediments are likely deep. The sand and gravel will likely be coarse in the outlet channel since recent geomorphology has likely removed the silt and fine sand sediment in the channel, but the gravel and cobbles remain. GEOTECHNICAL OPNIONS AND RECOMMENDATIONS STRATA accomplished analyses assuming the soil profile described above to provide the following geotechnical opinions and recommendations to assist McMillen in preparing contract documents and to support foundation design for the intake screen structure. The soil profile is based on our research of the data sources listed and has not been confirmed by actual exploration. Our report is also intended to help establish baseline subsurface conditions to assist bidding contractors with respect to foundation design and installation. As we have

11 Page 7 discussed with you, we recommend the proposed foundation system be accepted by the owner on a performance basis. In other words, bidding contractors must select appropriate means, methods, installation procedures, pile systems, installation depths and test actual pile capacities. Ultimately, the foundation design will be provided by the contractor and must be designed by a licensed engineer in the State of Washington. However, we recommend specific parameters be placed on the proposed pile system that will meet the intake systems performance design needs. STRATA and McMillen must work closely together while you prepare plans and specifications that address geotechnical, structural and civil design criteria for the intake structure. Finally, although contractors should review this report to understand the potential subsurface conditions, they must make their own constructability determinations, evaluate the potential conditions independently and incorporate contingency plans for foundation design and construction. The project approach presented herein requires the contractor understand and accept the foundation performance criteria and meet the contract requirements regardless of the actual conditions encountered during construction. Based on our experience, discussions with specialty foundation contractors and assuming the conditions described above are encountered during construction, our opinion is that a slender, drilled-in-place steel pile system is most viable for this project. The pile system must be capable of penetrating cobbles, boulders, sand, gravel and bedrock using drilling fluid to allow installation. The system must allow for lateral load resistance, and as such, must maintain a minimum 5-inch shaft diameter. These systems may include, but are not necessarily limited to micropiles, soil anchors and other drilled-in-place, grouted steel systems. However, to meet lateral load requirements and to maintain strict pile alignment tolerances, any selected foundation system must be carefully designed and installed. Temporary steel casing may be necessary to provide good pile alignment and to help manage cuttings and fluid circulation. Given the above understanding, we recommend McMillen require the foundation system consist of drilled-in anchors with minimum depths, bit diameters and performance criteria as discussed in the following sections. We also recommend project contract documents allow for contractor flexibility to allow for unknown installation conditions and to provide project economy and innovation based on contractor experience with specific project approaches.

12 Page 8 Geotechnical Analyses and Assumptions STRATA assumed the subsurface conditions will consist of an upper layer of soft, nonplastic silt underlain by glacial outwash comprising sand and gravel with cobbles containing some silt and boulders. The extent boulders and silt will be encountered in the subsurface is currently unknown. The upper silt thickness is also unknown. From our research and site characterization presented above, we assumed the following two soil layers for preliminary pile design and to establish realistic pile performance criteria. Upper Layer Soft, non-plastic silt o Buoyant unit weight 30 to 60 pounds per cubic foot (pcf) o Friction angle less than 15 degrees o Soil cohesion less than 200 pounds per square foot (psf) o Assumed thickness approximately 10 feet Lower Layer Dense sand and gravel with cobbles, boulders and silt o Buoyant unit weight 60 to 90 pcf o Friction angle 32 to 36 degrees o Soil cohesion less than 100 psf o Assumed thickness greater than 20 feet Based on the conditions described by the dive team and observed in the video, and the suspected low strength characteristics of the upper silt, we recommend this layer be neglected for pile design. In addition to the unknown silt thickness, there is a low probability bedrock will be encountered within the pile depths. From our review of cobble samples obtained during the exploratory dive, the boulders will be un-weathered and could require rock bits during pile installation. Therefore, contractors must be prepared with equipment capable of penetrating hard phyllite, quartzite bedrock or boulders and removing cuttings with drilling fluid or grout. STRATA assumed the above conditions to perform preliminary pile analyses. We assumed a minimum 5-inch-diameter drill bit and grouted diameter and a minimum installation depth of 10 feet below the lakebed surface. We hereby define the lakebed surface as the elevation at which drilling steel stops moving downward vertically under its own weight. We anticipate this depth would be established during construction when the contractor places the drill bit and steel at the lakebed, and the system stops moving downward vertically under its own weight. This depth can be gauged in advance of placing the pile steel if temporary steel casing is driven into the lakebed prior to advancing piles. To prepare pile performance criteria, we assumed the following:

13 Page 9 Unit pile shaft friction 1.5 kips per lineal foot (ultimate capacity) Pile end bearing neglect end bearing Pile lateral load capacity 1.5 kips (ultimate capacity) o Measured at the lakebed surface elevation (point at which drill steel stops moving downward vertically under its own weight) o Assumes ¼ inch of lateral deflection at the lakebed surface o Assumes minimum spacing of 4 times the pile diameter (20 inches) Point of fixety 1.0 to 2.0 feet below the lakebed surface o Actual point of fixety will be difficult to determine without actual knowledge of the subsurface conditions Foundation System Options and Performance Criteria We recommend any foundation system proposed for the intake structure meet the following criteria: Continuous, drilled-in steel o Minimum 60 kips per square inch (ksi) yield strength o Minimum cross-sectional area of 1,000 square millimeters o Threaded rod capable of accepting couplers, nuts and plates to accommodate the screen structure Minimum grout bulb or steel shaft diameter of 5 inches We recommend project specifications outline the above requirements with respect to pile systems. STRATA takes no exception to entertaining alternate pile systems or slight deviations from the above criteria, providing the performance criteria recommended below are followed. However, we recommend any substitutions or deviations for the above criteria be discussed after contractor selection. This will allow STRATA, McMillen and the owner to meet with the selected contractor to understand the alternative system s benefits, efficiencies and potential cost savings. We recommend project specifications establish the following pile performance criteria for acceptance purposes: Minimum installation depth below lakebed surface of 10 feet Vertical pile ultimate capacity of no less than 8 kips per pile (4 kips allowable) Each pile must be load tested after installation to verify the above performance criteria are met STRATA provided McMillen with pile system specifications. We recommend a similar version of these specifications be considered for project contract documents and adjusted by McMillen and/or STRATA to meet project needs. The pile specifications provided contain

14 Page 10 specific details of installation requirements, contractor submittals and pile materials. If a foundation system is identified that requires slight deviation from the recommended specifications, STRATA must be contacted to review these specifications and provide recommended revisions prior to installation. Constructability Discussion STRATA reviewed our experience and discussed pile installation procedures with several experienced specialty contractors. From STRATA s and the interviewed contractors experiences, the above pile systems and performance criteria are realistic and constructible. However, we offer the following considerations to McMillen and the selected contractor with respect to constructability issues with the specified pile system: Cobbles, boulders or bedrock may be encountered. Drill bits must be capable of penetrating competent, intact rock during installation. Cobbles, boulders, sand and gravel may create some sway or deviation in the pile alignment during drilling. Larger steel diameters can help reduce the potential for piles to wander during drilling and deviate from the specified alignments. Steel guides or jigs placed at the bottom of the lakebed may be necessary to maintain specified pile alignment. Steel casing may be required and can be incorporated into the foundation design to stiffen the free length of the pile system between the lakebed surface and screen structure. Some difficulties may be encountered based on the substantial unbraced distance of drill steel between the lakebed and water surface. The drill steel may buckle, bend, wander, or sway during drilling, which may impact pile alignments and create other installation difficulties. Larger diameter steel bars with higher stiffness, or using temporary steel casing can help reduce these effects. Contractors must be prepared to address these difficulties during installation and select their means, methods, equipment and pile diameters accordingly. Load testing in tension following installation will be necessary. Load testing piles from a barge at the water surface will require careful consideration to ensure a steady datum for pile deflection measurement is established and that datum is not affected by load testing and barge movement. Measuring gross pile deflections may be necessary to gauge the pile systems effectiveness. The contract will be required to secure the necessary permits to allow drilling into the lakebed. These permit requirements, including erosion control, grout containment and other factors, may create additional constructability challenges and are the contractor s responsibility to address.

15 Page 11 Geotechnical Continuity and Contractor Submittals In authorizing STRATA to provide these preliminary design concepts and performance criteria, you agreed to retain us to observe pile installation and load testing during construction. In addition to our involvement during installation, we recommend McMillen and/or the owner retain STRATA during bidding to evaluate contractor bids and especially contractor submittal requirements. Involving a geotechnical consultant on the owner s behalf for this unique, performance-based foundation system will help reduce potential construction errors, omissions and foundations that do not perform as intended. We recommend each pile be tested in tension to verify the axial capacity as described above and in the specifications. We recommend the selected contractor be required by contract documents to submit a pile design, installation and testing plan. We recommend this submittal comprise the following aspects: Selected foundation system o Design calculations o Installation depths and pile diameters o Steel diameters o Methods to remove cuttings o Bit diameter and nature o Steel specification and mill certificates Installation means and methods o Means of advancing piles o Means of removing drill cuttings o Means and methods of grade control o Method of measuring lakebed surface and installation depths Testing procedures o Method of loading pile in tension o Method of establishing an independent datum for deflection measurement o Load cell and dial gauge calibration records Installation crew o Foreman and anticipated crew members o 3 previous project examples in which the crew has performed similar work o On-site quality control personnel responsible for verify performance criteria is met Permitting o Person responsible to adhere to necessary construction permits o Method of controlling sediment and hazardous substance releases to the lake

16 Page 12 We recommend the plan discussed above and all permits be submitted to McMillen at least 10 business days prior to contractor mobilization. We recommend STRATA and McMillen concurrently review the document for adherence to the specifications and to verify the contractor has addressed the required constructability and performance considerations for the project. In addition, we recommend the pile design, including depths, diameters, unit skin friction and other factors, be designed by a licensed professional engineer in the state of Washington. The calculations should be sealed by the design professional and be included in the contractor s submittal discussed above. LIMITATIONS The above geologic characterization and preliminary geotechnical design were provided without direct exploration and laboratory testing as authorized and limited by our scope. We used prudent, professional judgment in preparing the above preliminary recommendations. McMillen and the owner must be aware that subsurface condition variations may be possible and could impact construction schedules, costs and other considerations. In authorizing STRATA to provide the above services, you understood that exploration was available, but at an additional expense and you hereby agree and accept the level of STRATA s current involvement as meeting your needs for the project, understanding the associated risks of subsurface variations. It must be understood that neither STRATA nor McMillen are responsible as the engineer-of-record for the foundation design. The selected contractor must retain a licensed, qualified professional to design foundations that meet the criteria suggested above and in project contract documents. In authorizing STRATA to provide the above design criteria, you agree to retain us to verify the conditions encountered during construction relative to our preliminary foundation design criteria you referenced to perform structural design. This acknowledgement is in lieu of any express or implied warranties. The following plates accompany this report. Report text and the following visual aids cannot be separated or individually relied upon outside the context of the entire document. Plate 1: Plate 2: Plate 3: Site Photographs Topographic Map Aerial Photograph

17 Photograph 1. Looking upstream from below bridge. Note the gravel sediments along the channel. Photograph 2. Intact sand and gravel sediments near dam. Photograph 3. Gravel sediments below bridge along outlet channel. Site Photographs Sullivan Lake Cold Water Intake Metaline Falls, Washington Photograph 4. Rock cut along west roadway ½-mile from dam. Note the layered gneiss metamorphic rock dipping to the west. Photograph 5. View of outlet channel below dam. Sand and gravel sediments outcrop along outlet channel several hundred yards downstream of dam. Plate 1 MCME01 S10128A

18 Approximate outlet structure location. Topographic Map Sullivan Lake Cold Water Intake Metaline Falls, Washington Plate 2 MCME01 S10128A

19 Note the glacial outwash and moraine structure between ridges at lake outlet. Approximate outlet structure location. Aerial Photograph Sullivan Lake Cold Water Intake Metaline Falls, Washington Plate 3 MCME01 S10128A