GM44-19 OR-140 MItigation Site Geotech Memo.pdf

158377846

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA 98661

DATE: January 10, 2020

TO: Helen Oppenheimer, PE Project Manager

FROM: Eric Lim, PE, GE Sr. Geotechnical Engineer

SUBJECT: Geotechnical Memo 44-19 Mitigation Site Geotechnical Recommendations Klamath County Boat Marina to Lakeshore Drive

OR DOT 140(1)

Klamath County, Oregon

INTRODUCTION

This memorandum provides geotechnical investigation results and geotechnical recommendations for design and construction of the Mitigation Site of the Klamath County Boat Marina to Lakeshore Drive Project. The project is being designed and delivered by Western Federal Lands Highway Division (WFLHD) for the Oregon Department of Transportation (ODOT). The project site is located just north of the City of Klamath Falls in Klamath County, Oregon as shown in Figure A-1 Site Plan in Appendix A.

This memorandum is supplemental to the Final Geotechnical Report Klamath County Boat Marina to Lakeshore Drive (Lim et al., 2019). The recommendations contained herein are specific to the Mitigation Site conditions and proposed improvements. Assessment of regulated environmental contaminants were not included in our scope of work.

PROJECT DESCRIPTION

The project consists of an approximately 45-acre site that will be developed as constructed wetlands to mitigate impacts from the OR-140 widening project on the other side of Upper Klamath Lake. The proposed mitigation site features will include construction of three cells (or ponds), five drainage ditches, and one new soil berm in the approximate locations shown on Figure A-1. Cell 2 will be used for rearing juvenile sucker fish.

We understand that much of the site is likely reclaimed marshland that was created through dumping waste soil and construction debris. Much of the debris includes large concrete

ERIC

JEEWHAN LIM

Digitally signed by ERIC

JEEWHAN LIM

Date: 2020.01.10 18:56:36 -08'00' rubble up to 5-foot wide slabs with rebar. The current plan is to reuse excavated rubble and other construction debris on-site by encapsulating the waste material within the new berm.

GEOLOGY

According to the Geologic Map of the West Half of the Klamath Falls 1° by 2° Quadrangle, South-Central Oregon (Sherrod and Pickthorn, 1992) the site is mapped as surficial deposits, Qs. These sediments are described as Holocene and Pleistocene age, fine- to coarse-grained sediment deposited in channels, flood plains, marshes, and lakes. The deposits in Klamath Marsh are described as containing rounded pumiceous gravel derived from fluvial and lacustrine reworking of Holocene pumice-fall (Qpf) and ash-flow (Qaf) deposits. Although the Klamath Marsh area is several miles from Upper Klamath Lake, similar pumice and ash deposits are likely to be found within the lake deposits based on our experience.

We also expect diatomaceous silt sediments to be within the lake and mitigation site based on our experience from explorations and research of the widening project on the west side of the lake.

SITE CONDITIONS

The site is a low lying, relatively flat area to the south and west of Lakeport Boulevard on the eastern shore of Upper Klamath Lake. The site is covered in grass, shrubs, and scattered trees. The site is roughly triangular shaped and split into west and east halves by an unpaved access road. A rubble-lined berm is located along the southwest shoreline west of the access road (see Photographs in Appendix A). The east half of the site has a low lying wet area in the southern third. The eastern edge of the site borders a drainage ditch for the adjacent property. These site features are shown on Figures 1 Aerial Photograph and Figure 2 Lidar Map below.

Figure 1 - Aerial Photograph (Map Data: Google 2019)

Figure 2 - Lidar Map (Map Data: DOGAMI, 2019)

Rubble berm

Access Road

Drainage Ditch

SUBSURFACE CONDITIONS

Subsurface conditions were evaluated by excavating eight test pits using a Hitachi Zaxis 130 excavator contracted by ODOT. Test pits TP19-01 to TP19-06 were logged by an ODOT geologist. Test pits TP19-07 and TP19-08 were logged by a WFLHD Geotechnical Engineer.

The test pits generally encountered the following soil types, as summarized in the table below:

Table 1 - Subsurface Materials Summary

Interpreted Material

Test Pits Bottom Depth Observed (ft)

Material Description

Dike Fill TP19-01 to

TP19-03

3 to 4 Silty SAND to Sandy SILT with gravel, cobbles, boulders; Poorly Graded

SAND; Gravelly SILT. Concrete, steel, and wood rubble.

Ballast Rock TP19-04 to

TP19-06

0.5 Poorly Graded GRAVEL with Silt and

Sand

Ballast Base TP19-04 to

TP19-05

1.5 Poorly Graded GRAVEL with Silt and

Sand

Ballast Fill TP19-04 to

TP19-06

7.5+ Sandy SILT; SILT; Sandy FAT CLAY

Fill / Possible Fill

TP19-07 to

TP19-08

5 to 7.1 Weathered Ash or Diatomaceous Elastic SILT with Sand; Elastic SILT with various cinders and sand; Fat

CLAY with sand. Concrete, steel, and wood rubble.

Native Soil TP19-01, TP19-03, TP19-07, TP19-08

4.5+ to 13.6+ SILT; SILT with Sand and interbedded lenses of Silty SAND, SILT, and

SAND; COBBLES/BOULDERS.

Additional details and descriptions are provided in the photographs in Appendix A and on the test pit logs in Append B. Laboratory test results of select samples from the explorations are included in Appendix C. As discussed previously, there are areas of visible rubble including concrete, steel, and wood demolition debris with concrete slabs up to 5 feet wide visible.

There are likely to be other areas of buried rubble and debris not visible from the surface or encountered in the test pits.

Results of electrical resistivity tests of the soils were in the range of 900 to 1,200 ohm-cm.

Soils with resistivities below 2,000 ohm-cm are considered to have a high potential for corrosion to steel.

Groundwater seepage was encountered at depths ranging from approximately 1.8 to 4 feet in test pits TP19-01, TP19-02, TP19-07, and TP19-08 at the time of the explorations.

Groundwater levels should be expected to fluctuate with lake levels, precipitation, seasonal variations, irrigation, changes in grade/adjacent land use, and other on- and off-site factors.

ANALYSIS

The data gathered above was used to perform analyses for embankment stability, settlement, and lateral earth pressures for wall design. In general, the explorations were limited to test pits in scope due to the advantage of being able to view the rubble material in excavations rather than small split barrel samples, as well as limited budget for explorations.

The subsurface conditions were as expected for marshland conditions along the lake shore.

Soils consisted of very soft, very weak, unconsolidated silts to sands with various cobbles, boulders, and concrete/wood/steel rubble and other debris. Groundwater conditions were typically very shallow, especially closer to the lake, and excavations typically caved and sloughed during the short periods they were left open.

The majority of the soils were highly organic, highly wet/saturated, and highly moisture sensitive. The reuse of such soils is not recommended for structural fill applications, such as roadways and below structures. However, we understand that the project will reuse as much of the on-site material as possible, knowing that short-term and long-term settlement and slope failures are risks.

Most of the surface of the mitigation site appears to have been disturbed by filling, regrading, and/or farming. As such, random pockets of rubble, organics, and other debris may be encountered on the site.

DESIGN RECOMMENDATIONS

The following sections present our recommendations for design.

Cut and Fill Slopes

Design and construction of embankment or fill slopes must consider embankment fill material strength, foundation material strength, and surface water and soil pore water conditions.

Generally speaking, the higher the strength of the materials and drier the conditions, the steeper the embankment slopes may be constructed. Strong fill materials are typically inorganic, granular materials, such as well-graded sands and gravels with relatively low amounts of silt and clay. The higher the fraction of silt, clay, and organics (i.e., fine-grained soils), the weaker and more moisture sensitive the soil becomes. Predominantly fine-grained soils become difficult or impossible to compact with increasing moisture content, and placement of fine-grained materials below the water table is not recommended. Further weakening the existing soils on the mitigation site are the ash, organics, and diatomaceous silt materials encountered in the explorations.

Embankment slopes with non-organic, common borrow materials such as silty sand are typically recommended to be designed and constructed with 1V:2H slopes. If the slopes will exposed to running or standing water, such as ditch or pond berms, they are typically designed at slopes of 1V:3H or flatter. However, it is our understanding that steeper slopes are desired on this project to help reduce growth of invasive plant species and reduce predation of the fish in the ditches and ponds. Furthermore, the reuse of the existing site soils and rubble is also desired to reduce cost and environmental impacts of exporting these materials to a landfill.

These environmental goals conflict with typical geotechnical recommendations for engineered slopes. The use of wet to saturated, organic, fine-grained silt, clay, diatomaceous earth, and ash at steeper than typical slope angles will introduce risks to the constructability, schedule, and cost of the project. However, since the primary goal of the mitigation site is creation of aquatic habitat and not the stability of the ditch, pond, and berm slopes, we understand that ODOT accepts these risks and are willing to attempt to construct the slopes as steep as possible using as much existing on-site material as can be reused.

It should be noted that our standard specifications consider embankments to be engineered fill slopes capable of supporting vehicle loads. However, the berm is not intended to be used for vehicle access, and therefore, should not be considered an embankment or structural fill.

Specific construction methods for berms will need to be incorporated into the project Special Contract Requirements (SCRs); this effort will be led by the Geotechnical team.

Based on the project needs described above, the following slope angles will be used for design:

Table 2 - Design Slope Angles

Site Feature Slope Angle Berms (south edge of site) 1V:2H

Drainage Ditch and Pond Slopes 1V:1.5H Pond Slopes within 20 feet of head-gate 1V:2H

Dry season grading is recommended to help dry out the soils. Since space and time for soil processing will be limited, additional budget should be considered for export of excavated materials and import of granular embankment soils and foundation stabilization rock.

Bearing Capacity Failure Due to the weak, lightweight, and saturated foundation materials, we expect that bearing capacity failures may occur as embankment fill is placed. Therefore, fill placement should be limited to an approximately 3-foot thickness within a 24-hour period to allow excess pore pressure to dissipate.

Berm Settlement It should also be noted that the high organic content and high moisture content will cause total and differential settlements over time resulting in uneven slope and embankment surfaces.

These settlements will require higher than normal levels of maintenance than non-organic and conventional fill soils. Overexcavation and replacement of all the organic soils is not considered economical. Unfortunately, the high organic and diatomaceous silt content of the site soils as well as variability of the disturbance of the materials from previous grading make accurate settlement estimates difficult.

Additional Embankment Quantities Even with limiting fill placement rates, the foundation soils will likely settle and/or be displaced.

ODOT’s experience with filling in the lake on the previous Doak Mountain project resulted in embankment volumes equaling 2.5 times the neat line volume of the embankment. We anticipate that a similar ratio could occur on the mitigation site and recommend that additional quantities be planned for to account for the displacement and settlement of the foundation soils and embankment materials.

Shrink/Swell Percentages The on-site soils are very soft and/or loose and for the most part are expected to be uncompacted or loosely compacted materials. Shrink or swell factors could be near 0 percent when placing this wet materials in a berm, or it could swell as much as 10 percent due to relaxation of the unconfined material in the stockpile. We recommend a swell of 5 percent for design when calculating volumes of in-situ material to in-place berms. It should be noted that shrink/swell percentages are estimates and commonly vary by +/- 5 percent or more.

Rubble and Non-Hazardous Waste Encapsulation

We understand that ODOT has performed a hazardous materials screening of the rubble and waste materials visible at the site, and that the materials (mostly concrete, steel rebar, wood, and other construction demolition debris) should be classified as non-hazardous waste. The non-hazardous designation means that although not considered a hazardous waste, the materials do not meet clean fill standards either. The non-hazardous waste can be reused on-site within the embankment areas, such as access road construction and south berm, as long as they are encapsulated.

We understand that the encapsulation should consist of placement of a geotextile fabric over the rubble/debris along with a minimum 2-foot thick layer of “clean” soils placed over the fabric as shown in Figure 3 Encapsulation Detail. The “clean” soils are to consist of soils free of rubble/debris that meet clean fill standards as set by the Oregon Department of Environmental Quality (DEQ). We understand that the berm is not required to be impermeable. We recommend the geotextile fabric meet specifications for separation-stabilization, Class 1, woven or non-woven, type D. Prior to placing the geotextile fabric over the non-hazardous waste, rebar and other protrusions should be cut off or bent down to reduce tears in the fabric.

Berm material should also be used to choke large voids in the rubble to prevent future settlement and tearing of the fabric.

Figure 3 - Encapsulation Detail

Sheet Pile Wall

We understand that construction of an approximately 12-foot tall wall will be necessary to incorporate a head gate at the Cell 2 (juvenile sucker rearing pond). For constructability in the very soft and saturated subgrade conditions as well as retention of the pond water, we recommend the use of a sheet pile wall.

As discussed in the SUBSURFACE CONDITIONS section, resistivity testing of the site soils were in a range considered to be highly corrosive to steel. Therefore, we recommend the use of fiberglass reinforced polymer (FRP) sheet piles as the material type. The sheet piles should be designed to resist the lateral earth pressures discussed in the paragraphs below.

Lateral Earth Pressures

Lateral Loading Design of the sheet pile walls should be based on “active” lateral earth pressures, assuming that some deformation of the walls that can be tolerated. Walls which are free to deform on the order of 0.001 to 0.002 times the exposed height are considered to be capable of mobilizing active earth pressures. This lateral deformation is likely to be accompanied by vertical settlement of up to roughly 0.005 times the height of the wall, which may extend back from the side of the cut a distance equal to roughly the height of the cut. Lesser degrees of settlement may also occur within a setback extending twice as far back. A greater amount of lateral deformation could allow greater vertical settlements. We have assumed that no structural elements are located within this zone, or that any structural elements within the zone are considered to be insensitive to this degree of settlement.

For the case of a cantilevered wall system, or a wall with only one level of internal bracing, the applied lateral pressure would be represented by a triangular pressure distribution termed an equivalent fluid density. Figure 4 illustrates the recommended pressure distribution. We recommend a nominal active pressure equivalent fluid densities as shown in Table 3 for level

) backslope conditions. For continuously interlocked sheet piles, the active pressures should be assumed to act on the projected planar wall area of the sheet piles above and below the excavation base. Water pressure is assumed to be balanced on both sides of the sheet piles due to the limited length of the wall and relatively slow lake level changes.

Figure 4 - Lateral Earth Pressure Diagrams

Table 3 - Lateral Earth Pressure Summary

Anchorage Type

Nominal Active Pressure

Nominal Passive Resistance -

Backfill

Nominal Passive Resistance –

Submerged Toe

Uniform Lateral Traffic

Surcharge Cantilever or One Row of

Tiebacks 52 H psf 300 Dbf psf 125 Dtoe psf 100 psf

An additional lateral pressure should be added to the above active pressure loads to account for traffic and construction loading. The traffic loading can be modeled as a uniform or rectangular horizontal load equivalent to 100 psf acting against the back of the wall above the excavation base.

The above active pressures are based on an effective friction angle of 22 degrees, backfill total unit weight of 130 pcf, and no cohesion. Seismic surcharges are not considered necessary for this site and project usage, in our opinion.

The values in Table 3 are unfactored. Load factors from Table 3.4.1-2 Load Factors for Permanent Loads of the AASHTO Bridge Design Specifications (AASHTO, 2017) should be applied. For cantilever walls, a load factor of 1.5 should be used; for anchored walls a load factor of 1.35 should be used.

Lateral Resistance Lateral resistance for the walls could be provided by passive pressure on the buried portion of the sheet piles and a bracing system of deadman anchors, where needed. Figure 4 illustrates the recommended truncated triangular pressure distribution for passive resistance. We recommend a nominal passive pressure, in units of pounds per square foot (psf), equivalent to 125 times the embedded depth of the soldier pile. For continuously interlocked sheet piles, the passive pressure should be applied over projected planar area of the piles, neglecting the upper 2 feet below the ground surface. Per AASHTO Bridge Design Specifications (BDS) (AASHTO, 2017) Table 11.5.7-1 Resistance Factors for Permanent Walls, a reduction factor of 0.75 should be applied for passive resistance of vertical elements.

The above passive pressure is based on an effective friction angle of 22 degrees, effective (submerged) unit weight of 38 pcf, and no cohesion.

Deadman Anchors The anchor block of the deadman must be fully located a sufficient distance behind the retained excavation face to develop resistance within the stable soil mass. As shown on Figure 4, we recommend the anchorage be attained behind a plane that is formed by a 22 degree angle from horizontal from the estimated point of zero moment in the wall. Anchors located in the front of this plane will not achieve full resistance. The passive pressures presented above for lateral resistance should be used, with the anchor block buried at least 2 feet below the ground surface.

The no-load portion of the anchor should also be a minimum length of 15 feet. All anchor block excavations should be backfilled with select granular backfill. Anchor tie rod trenches should be backfilled with unclassified borrow. The tie rods should be specified for Class I Corrosion Protection for tieback anchors as recommended by the Post-Tensioning Institute (PTI) for permanent anchors (PTI, 2014).

CONSTRUCTION CONSIDERATIONS

As discussed previously, there are risks involved when attempting to use the wet to saturated, organic, silt, clay, diatomaceous soils, and ash as steep embankment materials over very soft, saturated subgrade conditions. Bearing capacity failures are highly likely, as well as inability to compact the materials to the proposed slope angles. Failure of slopes may occur and frequent maintenance should be expected during and after construction.

The very soft and wet site conditions will likely preclude the use of wheeled construction equipment, and even conventional tracked equipment, without the use of haul roads utilizing subgrade stabilization geotextiles and coarse aggregate. We understand that temporary site access haul roads and working mats will be up to the contractor to determine with their means and methods.

Fill placement should be limited to an approximately 3-foot thickness within a 24-hour period to allow excess pore pressure to dissipate. This requirement should be added to Section 204 of the Special Contract Requirements. The combination of bearing capacity failure and settlement may result in an increased fill volume equal to approximately 2.5 times neat line fill volume.

It should be noted that soil admixtures, such as cement or lime treatment, for subgrade and embankment stabilization will not be allowed at the Mitigation Site. We understand that the environmental impacts of high pH materials will adversely affect the aquatic habitat.

Temporary dewatering will likely be needed in excavations, especially as the location move toward the lake. The contractor should be prepared to install and provide dewatering as necessary to perform the excavations. A pumping test was not included in our scope of work.

Should the reuse of the site soils be difficult to construct at a relatively steep slope angle, stability could be improved by adding a geotextile reinforcement layer, such as a separation-stabilization, Class 1, woven, type D into the embankment. The reinforcement geotextile should be spaced at a maximum 1.5-foot vertical spacing. The geotextile may terminate at the face; no wrap around is required with the 1V:2H or flatter slope angles.

REFERENCES

AASHTO, 2017, AASHTO LRFD Bridge Design Specifications, 8th Edition, 2017, American Association of State Highway and Transportation Officials, Washington, D.C.

Lim, E., Evan Garich, Nathan Jenks, 2019, Final Geotechnical Report, Klamath County Boat Marina to Lakeshore Drive, OR DOT 140(1), Klamath County, Oregon, Geotechnical Report No. 27-18, Federal Highway Administration - Western Federal Lands Highway Division.

NAVFAC, 1986, Foundations & Earth Structures Design Manual 7.02, Naval Facilities Engineering Command (NAVFAC).

Post Tensioning Institute (PTI), 2014, PTI Recommendations for Prestressed Rock and Soil Anchors.

Sherrod, D.R. and Pickthorn, L.B., 1992, Geologic Map of the West Half of the Klamath Falls 1° by 2° Quadrangle, South-Central Oregon: U.S. Geological Survey, Misc. Investigations Series MAP I-2182, scale 1:250,000.

CLOSING

Please contact Eric Lim at (360) 619-7826 or eric.lim@dot.gov with any questions regarding this memorandum.

CC: John Davis, Lead Designer Melissa J. Hogan, Environmental Protection Specialist Benn Oltmann, Structures Functional Manager Geotechnical File

Attachments: Appendix A: Figure A-1 Site Plan Photos A-1 to A-23

Appendix B: Test Pit Logs TP19-01 to TP19-09

Appendix C: Lab Test Results

APPENDIX A

Figure A-1 Site Plan Photos A-1 to A-23 of TP19-07, TP19-08, TP19-02, and Rubble

Photo A-2, TP19-07

Photo A-1, TP19-07

Photo A-4, TP19-07

Photo A-3, TP19-07

Photo A-6, TP19-07

Photo A-5, TP19-07

Photo A-8, TP19-08

Photo A-7, TP19-08

Photo A-10, TP19-08

Photo A-9, TP19-08

Photo A-12, TP19-08

Photo A-11, TP19-08

Photo A-14, TP19-02

Photo A-13, TP19-08

Photo A-16, TP19-02

Photo A-15, TP19-02

Photo A-18, TP19-02

Photo A-17, TP19-02

Photo A-20, TP19-02

Photo A-19, TP19-02

Photo A-22, Rubble photos

Photo A-21, Rubble photos

Photo A-23, Rubble photos

APPENDIX B

Test Pit Logs

TP19-01

TP19-02

TP19-03

TP19-04

TP19-05

TP19-06

TP19-07

TP19-08

APPENDIX C

Lab Test Results