Appendix D2: Geotechnical Engineering

Transcription

1 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Appendix D2: Geotechnical Engineering and Geology Fargo Moorhead Metropolitan Area Project Reach 5 Engineering and Design Phase P2# Doc Version: Post FTR Submittal 23 March 2015 DDR_FMM_R5_Appendix_D2_Post_FTR_ docx

2 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology This page is intentionally left blank DDR_FMM_R5_Appendix_D2_Post_FTR_ docx

3 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Appendix D2: Geotechnical Engineering and Geology Table of Contents D.1 PROJECT DESCRIPTION... 1 D.2 REGIONAL GEOLOGY... 1 D.2.1 Physiography... 1 D.2.2 Topography... 1 D.2.3 Geology... 2 D.2.4 Structure... 2 D.2.5 Site Hydrogeology... 2 D.2.6 Seismic Risk and Earthquake History... 4 D.3 SUBSURFACE INVESTIGATION... 4 D.3.1 Exploration... 4 D.3.2 Testing... 5 D.3.3 Design Parameters... 5 D.4 DIVERSION CHANNEL ANALYSIS... 7 D.4.1 Modeling Summary... 7 D Lower Rush Inlet Geometry... 7 D Diversion Channel Geometry... 8 D.4.2 Sections... 9 D.4.3 Seepage D.4.4 Stability D.4.5 Results D.4.6 Future Work D.5 EXCAVATED MATERIAL BERM AND LEVEE ANALYSIS D.6 RIGHT BANK EMEDDED LEVEES D.7 SETTLEMENT AND REBOUND D.7.1 Consolidation Parameters DDR_FMM_R5_Appendix_D2_Post_FTR_ docx D i of D iii

4 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D.7.2 Settlement of typical levee/ Right Bank EMB D.7.3 Rebound in the Channel Excavation D.8 DIVERSION EXCAVATION TYPES D.9 LOCAL DRAINAGE INLETS D.10 RIPRAP AND BEDDING D.11 CONSTRUCTABILITY D.11.1 Excavations D Past Experience D Methods D Stripping and Overexcavation D Dewatering D Sand Pockets / Lenses D.11.2 Access/Maintenance Road Foundations D.11.3 Embankment Construction D.11.4 Winter Conditions D.11.5 Levees and Excavated Material Berms D Net Swelling of Material Used for EMBs D.12 SOURCES OF CONSTRUCTION MATERIALS D.12.1 Levee Material D.12.2 Concrete Aggregate, Riprap, and Bedding D.13 PHASE 1 ENVIRONMENTAL SITE ASSESSMENT D.14 handled properly.references D.15 ATTACHMENTS TABLES Table D2 1: Summary of Soil Exploration for Lower Rush Structure... 5 Table D2 2: Channel Sections Geometry... 9 Table D2 3: Formation Contact Elevations Table D2 4: Summary of Diversion Channel Stability Results Table D2 5: Rock Ramp Stability Results DDR_FMM_R5_Appendix_D2_Post_FTR_ docx D ii of D iii

5 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Table D2 6: Total Stress Parameters Table D2 7: Summary of EMB Maximum Grading Extents Table D2 8: Mean Consolidation Parameters Table D2 9: Settlement Check Analysis Results Table D2 10: Predicted EMB Settlement for Determination of Levee Overbuild Table D2 11: Predicted Ultimate Rebound in Diversion Channel Table D2 12: Summary of Diversion Channel Excavation Types FIGURES Figure D2 1: P Instrumentation Plot... 3 Figure D2 2: P Instrumentation Plot... 4 Figure D2 3 : Brenna Strength Plot... 6 Figure D2 4 : Lower Rush Rock Ramp Configuration Figure D2 6 : EMB Grading Extents Figure D2 6 : EMB Grading Extents Figure D2 7: In situ dry density data compared to standard proctor results ATTACHMENTS Attachment D2 1: Stratigraphy (Included in Reach 5 DDR) Attachment D2 2: Soil Exploration Location Maps (Included in Reach 5 DDR) Attachment D2 3: Boring Log Plates (Included in Reach 5 DDR) Attachment D2 4: Outlet and Diversion Stability Analysis Results Attachment D2 5: Settlement and Rebound Calculations DDR_FMM_R5_Appendix_D2_Post_FTR_ docx D iii of D iii

6 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Appendix D2: Geotechnical Engineering and Geology D.1 PROJECT DESCRIPTION The Lower Rush River Drop Structure is located in the central area of the project where the Lower Rush River will be diverted into the diversion channel, within Reach 5. Within this reach, there are multiple features that require geotechnical design and considerations which are listed below. The reach that will encompass the rock ramp structure is between station and Inlet Structure Multi drop rock ramp o Stability of the excavated slope o Design of riprap and bedding that is used along the rock ramp o Estimate of rebound due to the unloading of the soil Diversion Channel o Stability of the excavated slope, accounting for the excavated material berms and low flow channel o Stability of the excavated slope, accounting for potential erosion of the low flow channel and sedimentation at the bottom of the diversion. o Estimate of rebound due to the unloading of the soil Levees within the Excavated Material Berms along the Diversion Channel o Settlement of the levees and excavated material berms o Minimum vegetation free zone requirements D.2 REGIONAL GEOLOGY D.2.1 Physiography Physiography is discussed in detail in the General Report: Geotechnical Engineering and Geology (Reference D2 1). D.2.2 Topography The topographic profile along the Reach 5 centerline begins at the downstream end at Sta where the ground surface is at typical elevation 890. Along Reach 5 moving upstream, the ground surface elevation rises very gradually to an average of about elevation 894 at Sta The ground surface from this point to the reach s end varies from elevation 893 to 894. A number of small roads and County Road 22 cross the alignment along embankments that are several feet higher than the average ground elevations. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 1 of D2 27

7 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D.2.3 Geology A detailed description of the regional geology can be found in the General Report: Geotechnical Engineering and Geology (Reference D2 1). Generally speaking the Lower Rush Inlet Structure is defined by a sequence of glacio lacustrine deposits (Argusville, Brenna, and Sherack Formations) overlying a dense, overconsolidated glacial till. A layer of alluvial clay and topsoil typically caps the lacustrine sequence. The glacial till is not of great importance on the Lower Rush Inlet Structure, as no pile founded structures are planned. Borings indicate that the top of the glacial till is located at about El Above the till is the Argusville formation, which is approximately 10 to 15 ft thick. The contact between the Argusville Formation and the Brenna Formation is gradational and typically occurs over 10 or more feet. For the purposes of the stability analyses this gradational contact has been assumed as part of the Brenna Formation, which exhibits lower shear strengths than the Argusville Formation. The characterization of the 2012 and 2013 borings, which rely upon liquid limits, have been utilized in the determination of this contact for the Lower Rush analyses, as it is more conservative than the field classifications of the 2010 borings. The contact between the Brenna and Sherack Formations is located at between El. 879 and 884. Typically there is a portion at the top of the Brenna that is oxidized and sometimes desiccated. Testing indicates that this portion of the Brenna, typically several feet thick, is characterized by higher shear strengths, and so it has been broken out as a separate material for stability analyses. The Sherack Formation is typically around 5 ft thick, and its upper limit can range from El. 890 to the ground surface. The Sherack is typically overlain by alluvial clays that are usually several feet thick. The stratigraphy for the Lower Rush inlet structure and Reach 5 is presented in the attachments for the Reach 5 analysis and DDR prepared by the St. Paul District (MVP). D.2.4 Structure Geologic structures are discussed in detail in the General Report: Geotechnical Engineering and Geology (Reference D2 1). D.2.5 Site Hydrogeology The hydrogeology as discussed in the General Report: Geotechnical Engineering and Geology (Reference D2 1) applies to the Lower Rush Inlet Structure. Groundwater levels as measured during soil borings varied. In some borings water could be 2.3 ft from the ground surface after a day, and in other borings the hole would be dry to 20 ft for the same time period. Groundwater assumptions for modeling were made based on instrumentation located at other locations in the Fargo Moorhead area and seepage calibration modeling. Instrumentation consisting of nested vibrating wire piezometers was installed along the proposed alignment in August 2012 and February 2013 to verify groundwater assumptions along portions of the diversion. The nearest instrumentation clusters to Reach 5 are P and P P is located approximately 2.3 miles downstream in Reach P is located just upstream in Reach 6. Readings DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 2 of D2 27

8 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology from these locations indicate that the groundwater depths have fluctuated between 3.5 to 12 feet below the ground surface. The highest groundwater table elevations occurred in June and July of 2013, with the levels dropping afterwards. All piezometers indicate downward gradients through the Lake Agassiz clays into the Unit A Till. Piezometer P indicates a downward gradient of 0.1 to 0.35 (Figure D2 1). Piezometer P indicates a downward gradient of about 0.15 to 0.65 (Figure D2 2). The USGS Fargo gage on the Red River is shown for reference only. Please refer to the General Report: Geotechnical Engineering and Geology (Reference D2 1) for additional information and details concerning the instrumentation. Figure D2 1: P Instrumentation Plot DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 3 of D2 27

9 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Figure D2 2: P Instrumentation Plot D.2.6 Seismic Risk and Earthquake History Seismic Risk and Earthquake History are discussed in the General Report: Geotechnical Engineering and Geology (Reference D2 1). The main conclusion is that the Fargo Moorhead area is one of the least seismically active places in the United States. The estimated peak horizontal ground accelerations are small, g and 0.04g for a mean return time of 2475 years and 4975 years. Considering the low risk, the low ground accelerations, and the fact that the foundation soils are not prone to liquefaction, seismic analysis is not required for the diversion channel and inlet structure. D.3 SUBSURFACE INVESTIGATION D.3.1 Exploration Soil borings and cone penetration test (CPT) soundings were completed within the project area to determine the stratigraphy. The number and type of exploration method is summarized below in the table. The location of the completed soil exploration can be found in Attachment D2 2 for the Reach 5 DDR submitted by MVP. The boring logs can be found in Attachment D2 3 for the Reach 5 DDR DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 4 of D2 27

10 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology submitted by MVP. Details concerning the subsurface investigation can be found in the General Report: Geotechnical Engineering and Geology (Reference D2 1). Table D2 1: Summary of Soil Exploration for Lower Rush Structure Location Machine Borings Undisturbed Borings Hand Auger Topsoil Borings CPT Lower Rush River Drop Structure D.3.2 Testing While conducting the soil borings, samples are collected. Some of these samples are tested to determine the in situ moisture content and Atterberg limits. At less frequency, grain size analysis including hydrometer testing is completed on the samples. The results of these tests are including in the boring log staffs. One undisturbed soil boring (12 162MU) was taken in the vicinity of the Drop Structure, west of the Lower Rush River. Five samples were obtained from this boring and tested for shear strengths and consolidation parameters. D.3.3 Design Parameters Geotechnical design parameters are discussed in detail in the General Report: Geotechnical Engineering and Geology (Reference D2 1). The design parameters presented in the general report were used in the analysis and design of the Lower Rush Structure and Reach 5. Many undisturbed borings were conducted throughout the Fargo Moorhead area. The samples were tested to determine the shear strength and consolidation parameters of the materials. The results were broken up into the different formations and the results combined together to determine the parameters required for design. The results of the undisturbed testing can be found in the General Report: Geotechnical Engineering and Geology (Reference D2 1). During the 35% phase of this project, final changes were made to the project stratigraphic profile by St. Paul District. The changes reflect geologic interpretations based on a review of laboratory testing, contact elevations and selection of most relevant soil borings. The changes in Reach 5 were generally detrimental to the design, lowering the Brenna/Argusville contact and therefore reducing the shear strengths in the lower part of the stratigraphy. In an effort to minimize changes to the layout, MVP performed a thorough review of shear strength testing. An increase in the drained shear strength of the Brenna formation was considered defensible and reduced the impact to layout and schedule. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 5 of D2 27

11 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology The drained shear strength of the Brenna formation was reviewed and it was found that increasing the shear envelope by 20 psf was an acceptable change as the envelope still was within the range of the test results. Additionally it is has been noted that legacy testing performed for the Horace to West Fargo and West Fargo diversions, south of Reach 5, plots well below tests performed for the current project. There is no geologic reason to expect such a discrepancy, and additional investigation is planned to explore potential causes. The updated shear strength data parameters to the Brenna formation is displayed in the below Figure D2 3. Figure D2 3 : Brenna Strength Plot DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 6 of D2 27

12 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D.4 DIVERSION CHANNEL ANALYSIS D.4.1 Modeling Summary This section discusses the basic geometric features of the diversion channel within Reach 5 and the Lower Rush River Rock Ramp as it drains into the diversions channel and as it pertains to geotechnical analysis. D Lower Rush Inlet Geometry The Lower Rush River will empty into the FMM Diversion Channel via a rock ramp which employs rock weirs and a 5% slope to achieve the majority of the elevation change. 1V:8H side slopes are required throughout the ramp to meet stability requirements. Throughout the outlet the base of the excavation will be covered with a layer of rock and bedding material in order to prevent erosion. This erosion protection extends up to the 500 year + 2 feet flood elevation and will be up to five feet thick. In the undrained case it was verified that the additional excavation prior to placing the rock was not detrimental to stability. The geometry of the critical section for the inlet structure is taken at the bottom of the 5% ramp at LRR Station During construction with overexcavation for riprap, this section has the lowest invert elevation within the rock ramp. The invert of the rock ramp at this point is elevation At this location the centerline of the diversion channel low flow channel is about 270 feet away from the rock structure channel centerline. Five feet of riprap are required for erosion protection at this section. Due to the geometry of the rock ramp and corresponding layout of the excavated material berms, the EMBs to the north of the ramp require flatter slopes than those on the EMB to the south of the ramp. The EMB to the north of the ramp is higher in elevation where the critical section occurs at Sta A southern EMB does not exist at this location, and develops very slowly from this point to its maximum elevation much further up the ramp where it has much flatter slopes and a higher invert elevation. To evaluate the stability of the ramp where the southern EMB with slopes 1:8 has a significant height, a section was analyzed at Sta This section has the greatest differential in maximum EMB elevation and invert elevation, and was therefore determined to be a critical location for this analysis. The 1:8 EMB slopes for the EMB south of the Rock Ramp were determined to be stable for this section. Utilizing two different EMB slopes for this reach along the rock ramp optimizes storage area of the excavated material compared to that which would be achieved if both EMBs were constructed at 1:10 slopes. Figure D2 4 displays the location of the two sections. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 7 of D2 27

13 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D Diversion Channel Geometry Figure D2 4 : Lower Rush Rock Ramp Configuration In cross section, the channel features can be divided in three parts: 1) Main channel: The main diversion channel will be described separately from the meandering low flow channel at its base. The main channel provides the vast majority of the channel s capacity and was sized to handle large flows associated with flooding. It is characterized by excavated side slopes of 1V:7H and a 300 ft wide base sloping at 1V:50H (2%) towards the channel centerline. Within Reach 5 the side slopes are typically around 19 ft in height. 2) Meandering Low Flow Channel: A smaller low flow channel at the base of the main channel is required in order to convey the smaller flows anticipated over most of the channel s design life. For environmental reasons, the low flow channel meanders sinuously within the base of the main channel. The geometry of the channel and its spatial relationship to the main channel have been selected in order to meet both hydraulic and geotechnical requirements. The channel itself is 90 ft wide at the top with 5.6 ft high side slopes and a 46 ft wide base sloping at 2% to the low flow channel invert. Side slopes vary with the meander in order to maintain the above dimensions, but are roughly 1V:4H for the stability design case (Case 2, as described in section D.4.4) The low flow channel meanders within a 200 ft wide band centered in the main channel, leaving 50 ft between the toe of the main channel and the top of the low flow channel at its maximum offset from centerline. This was the cross section chosen for stability analysis. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 8 of D2 27

14 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology 3) Excavated Material Berms (EMBs): Material excavated for the diversion channel will be placed adjacent to the channel in berms that could be a maximum of 20 ft in height. The berms will be offset from the top of excavation by 50 ft and the side slopes facing the channel will be 1V:7H. Side slopes facing away from the channel are currently shown as 1V:6H. Excavation and stability requirements were achieved by maintaining a simple EMB configuration, and, therefore, stepped EMBs analyses were not required. A design envelope was developed in order to help the Civil layout of the EMBs, which provides maximum grading extents for the material that would still remain stable. The results of this process will be presented in section D.5. Models were not updated from the 65% DDR Submittal for the Lower Rush Diversion channel. The parameters chosen and profile assumed in this report were verified by additional borings completed in Formation contact elevations generally varied by less than one foot with all original assumptions being more conservative than those determined by additional exploration. The largest variation was in the contact of the Oxidized Brenna and Brenna formation at Section 8a, which was interpreted to be from 2010 borings and interpreted to be from 2013 boring. This variation was determined to be insignificant in the overall stability of the cross sections, as it did not improve conditions enough to change the required geometry of the cross section. D.4.2 Sections The geometric configurations of the cross sections analyzed for stability are summarized below Table D2 2. Formation contact elevations for each are provided in Table D2 3. Section # Station Ground El. (ft) Channel Side Slopes (V:H) Table D2 2: Channel Sections Geometry EMB Side Slopes (V:H) Section Geometry Toe EL. (ft) Main Channel Base Slope (V:H) Low Flow Slope (V:H) Low Flow Base Slope (V:H) Low Flow invert El. (ft) Ramp invert EL. (ft) :7 1: :50 (2%) 1:4 1:50 (2%) N/A Simple 8A :7 1: :50 (2%) 1:4 1:50 (2%) N/A Simple LRR :8 1:10 (2) :100 (3%) N/A N/A N/A N/A LRR :8 1:8/1:10 (3) :100 (3%) N/A N/A N/A N/A Notes: (1) The EMB configuration and geometry will be detailed in the summary for the stability analysis. (2) Side Slopes for Northern EMB (3) Side Slopes for Southern EMB/Northern EMB EMB (1) DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 9 of D2 27

15 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Table D2 3: Formation Contact Elevations Section 8 8a LRR1 LRR Geologic Unit Top El. (ft) Bottom El. (ft) Top El. (ft) Bottom El. (ft) Top El. (ft) Bottom El. (ft) Top El. (ft) Bottom El. (ft) Alluvium (1) Sherack Ox Brenna Brenna Argusville Till (2) Notes: (1) The top of the Alluvium is considered the Ground Surface Elevation (GSE). (2) The bottom of the Till is equal to the bottom of the model used for stability purposes. D.4.3 Seepage Seepage analysis was conducted according to the MFR 002, Diversion Channel and Low Flow Chanel Design (Reference D2 3), in which the analysis methodology is described in detail. These pore pressures are then used in the long term (drained) slope stability analysis. Briefly, half space models were constructed with a total head condition at the far field boundary, located 2000 ft from the channel centerline. The total head condition is equivalent to 10 ft below the ground surface. This assumes a hydrostatic groundwater condition at the far field boundary, which is thought to be a reasonable assumption based on available instrumentation data. A potential seepage face boundary condition was applied to the face of the channel slope and the base of the low flow channel. Currently the low flow channel is modeled as dry as it is anticipated that the channel could dry up occasionally during the project s design life, and this would represent a critical design condition. Seepage analyses of the were performed similar to the diversion channel analyses. However, the interface between the riprap and the excavated surface was modeled as a zero pressure boundary condition for Section LRR1 at Station This method produced a realistic pore pressure regime while preventing water from ponding in the sizable pore space of the riprap. This was considered a reasonable assumption because the Lower Rush River is known to dry up at times, in which case ponded water below the riprap surface would not be present. Due to the higher elevation of the ramp at Section LRR2, Station 12+00, it is not realistic to assume the piezometric surface will be above the riprap and would pond within its pore space. Therefore, a potential seepage face boundary condition was applied between the riprap and excavated surface. This produced the most realistic ground water conditions for the geometry of this section. A seepage calibration has been performed using piezometer data in the FMM area. The purpose of the calibration was to verify that assumptions regarding boundary conditions and hydraulic conductivities DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 10 of D2 27

16 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology correlated reasonably well with field data. The calibration is discussed in detail in the General Report: Geotechnical Engineering and Geology (Reference D2 1). D.4.4 Stability The methodology used to analyze slope stability is described in detail in the MFR 002, Diversion Channel and Low Flow Chanel Design (Reference D2 3), and will be summarized only briefly here. The analyses considered both drained and undrained cases. The pore pressures from the seepage analysis are coupled in the long term (drained) stability analysis. For the drained case, several search zones were identified with varying required factors of safety based on criticality of the slip surface. Two geometric configurations (Case 2 and 5) were analyzed for stability of the diversion channel and have varying required factors of safety depending on the occurrence of each configuration. Two cases analyzed in the 35% DDR (Case 3 and 4) were rendered obsolete in light of the Meander Belt Width Analysis completed by Barr Engineering and the HEC RAS Sediment Transport Analysis completed by USACE St. Paul District. Case 2 represents the design geometry of the low flow channel as described in Section D.4.1. Case 5 represents two vertical feet of erosion at the base of the low flow channel and along the low flow side slopes and sedimentation above the bottom of the diversion channel. The intent of Case 5 is to estimate the stability of the diversion channel throughout the lifetime of the project, considering that erosion of the low flow and sedimentation of the diversion will likely occur. The stability analysis of the inlet structure did not consider the two geometric configurations because the channel was centered within the cut and riprap and bedding is being placed to prevent erosion. It was therefore unnecessary to look at cases in which the inlet channel migrated towards the toe of the main channel. D.4.5 Results Stability results for the Diversion channel are summarized below in Table D2 4. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 11 of D2 27

17 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Table D2 4: Summary of Diversion Channel Stability Results Minimum Required FS General Section Information CASE 2 (1) CASE 5 2 Feet Sedimentation (6) Max crack depth Global Check Left Slope Left Slope EMB Undrained Undrained Global Check Section Station (ft) (3) Global (4) Lower Localized EMB (5) (2) Global (4) Lower Localized a Notes: (1) All factors of safety presented are the optimized factors of safety. The non optimized factors were checked and yield larger values in all cases. (2) The results of the Left Slope EMB analysis stay the same regardless of the low flow case. (3) Tension cracks were started at 1 foot deep and progressively increased until tension forces in the slices were removed. (4) Global Check analysis accounts for the influence of the large EMB. (5) The Undrained analysis has the same entry and exit extents as the Global Check to account for the influence of the EMB (6) Sedimentation was started at 2 feet and increased by 2 feet increments until the factor of safety was not met. Sedimentation greater than 2 feet yielded factors of safety less than those required for all lower and localized analyses. (7) Drained analysis with 5' rock over excavation and riprap in place of soil. Permeability of riprap assumed as 1000 ft/day. Potential seepage face modeled on top of the ramp slopes where riprap is not expected, and zero pressure head placed beneath the riprap material. The diversion stability analysis was performed in accordance with MFR 002, Diversion Channel and Low Flow Chanel Design (Reference D2 3) and also follows the guidance provided in the EMB Regional Webinar presented on June 21 st, The results indicate that benches will not be needed in the diversion slopes along Reach 5 in order to meet stability criteria. Stability results for the Rock Ramp can be summarized in Table D2 5 below. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 12 of D2 27

18 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Section (1) Stationing Max crack depth (ft) Table D2 5: Rock Ramp Stability Results Minimum Required FS Global Global Check Lower Localized LRR Undrained During Construction 1.23 (3) 1.45 (4) Undrained End of Construction (5) LRR Notes: (1) Drained analysis with 5' rock over excavation and riprap in place of soil. Permeability of riprap assumed as 1000 ft/day. Potential seepage face modeled on top of the ramp slopes where riprap is not expected, and zero pressure head placed beneath the riprap material. (2) Temporary excavation for riprap included in the analysis with no material type present. Peak undrained material strengths utilized. (3) Using Ultimate Undrained Material Strengths (4) Using Peak Undrained Material Strengths (5) Riprap in place. Ultimate Undrained Material Strengths utilized. In order to meet stability criteria for the undrained case, the slopes of the Lower Rush Ramp must be 1V:8H. Models of the rock ramp were run with different boundary conditions in the seepage model in order to determine how the difference would be reflected in the stability analysis. These different boundary conditions resulted in a slight variation in Factors of Safety for the drained cases, but utilizing the zero pressure head boundary condition is believed to be the more accurate representation of actual conditions. For the undrained case two conditions were considered, the during construction case in which overexcavation of five feet is modeled for the riprap and the end of construction case in which riprap has been placed within the ramp. For Section LRR1, peak undrained strengths were utilized for the temporary excavation condition, which yielded a Factor of Safety of Utilizing the ultimate undrained strengths resulted in a Factor of Safety of 1.23, which is acceptable for the temporary conditions. Ultimate material strengths are considered when significant deformation may be expected in the soils. The short term, during construction condition is not expected to experience such deformation and can therefore be reasonably expected to attain peak strength characteristics. For Section LRR2, ultimate undrained strengths yielded a Factor of Safety greater than the required 1.3, and therefore, peak strengths were not modeled. End of construction analyses utilized ultimate undrained strengths. A comparison of peak and undrained strengths of foundation materials is displayed in Table D2 6. A typical stress strain relationship obtained from testing of Brenna Formation within the Lower Rush reach is displayed in Figure D2 5. A complete listing of Soil Parameters and testing data is available in the General Report: Geotechnical Engineering and Geology (Reference D2 1) DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 13 of D2 27

19 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Notes: Table D2 6: Total Stress Parameters Formation Total Stress, c (psf) Ultimate (1) Peak (2) Alluvium Sherack Oxidized Brenna Brenna Argusville See Note (3) 825 Unit A Till (1) The ultimate total stress parameters are based on unconsolidated undrained triaxial shear tests with the failure criterion defined at ultimate deviator stress which equates to the deviator stress at 15% axial strain. (2) The peak total stress parameters are based on unconsolidated undrained triaxial shear tests with the failure criterion defined at peak deviator stress. (3) The Argusville formation ultimate undrained shear strength was assumed to be linearly increasing with depth. Initial cohesion was assumed to be 575 psf, with an increase of 10 psf/ft. Figure D2 5 : Boring MU Uncosolidated Undrained Triaxial Test Results The seepage and stability analyses are presented in Attachment D2 4. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 14 of D2 27

20 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D.4.6 Future Work Any changes to the channel geometry or EMB geometry that occur for non geotechnical reasons may require re analysis for stability. For example, on one side of the channel the EMBs will likely be shaped in undulating hills for recreational purposes. This may have stability implications and will require verification as the grading plan moves forward. D.5 EXCAVATED MATERIAL BERM AND LEVEE ANALYSIS In some areas the EMBs will be subject to differential head conditions for the most significant diversion discharges. It has been determined that for the right bank of the diversion channel the EMBs will in some capacity act as levees. The levees will be designed in accordance with the parameters provided in MFR 001, Levees and Excavated Material Berms along the Diversion (5). The MFR outlines slopes for the levee prism, material and compaction requirements and also covers the Vegetation Free Zone and Vegetation Management Zone requirements needed for the levees and EMBs. The levee prism will be completely encapsulated by the larger EMB for the Lower Rush Reach. There is no need for an embedded levee in the left bank EMB. Analyses were conducted to determine the maximum grading extents of the EMBS based on the current design concepts and restrictions. The crown of the EMB must not extend more than 21 feet above existing grade at the time of construction because of viewshed height limitation requirements. In order to accommodate the 2% crown slope, the initial EMB height is less than the EMB crown height. A simple EMB and different configurations of stepped EMBs, with varied stepped height, width and offset, were analyzed in order to establish a design envelope that the civil layout could fall within and still be stable. The results indicate that for both Sections 8 and 8a, the simple would be the most practical and efficient design. The maximum EMB height and width was then determined for the civil layout to be completed. Once the civil layout of the EMB was determined, verification analyses were performed to assure that the section meets stability requirements. Based on the results, the EMB initial height should be limited to 16 feet with a maximum EMB height of 20 feet and width of 400 feet for both Sections 8 and 8a. A summary of the maximum grading extents is below in Table D2 7. The diversion channel stability plates in Attachment D2 4 show the simple EMB Configuration. The results of the maximum EMB grading extents based solely on the geotechnical slope stability concerns are summarized below in Table D2 7. The heights indicated are based on a generalized existing ground surface elevation. If the existing ground surface is higher than the assumed ground surface, then the elevations of the maximum grading extents need to control the layout. The geotechnical analysis was conducted using the left side of the diversion channel centerline. The stratigraphy has been assumed to be symmetrical along the centerline, so the results of the maximum grading extents of the left EMB can be applied to the right EMB. This is of importance when the DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 15 of D2 27

21 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology undulations are being designed for the right bank recreational plan. The undulations shall be designed such that the undulation grading does not exceed the maximum grading extents. Table D2 7: Summary of EMB Maximum Grading Extents Left Bank EMB Maximum Grading Extents based only on Geotechnical Engineering Considerations (2) Existing Ground EMB Width Configuration EMB Height Section Location Section Extents (1) (ELEV) (ft) (ELEV) (ft) Simple a Simple Notes: (1) Simple EMB without a step and top crowned at 2% (2) All stability analyses completed for left bank EMB. The maximum grading extents for the right bank EMB will be the same. Elevation (FT) Fargo Moorhead Metro Project Geotechnical EMB Maxium Gradients Extents Sections 8 and 8a EMB Crown: 2% EMB Slope 1V:6H EMB Width = 400 ft EMB Height = 20 EMB Slope 1V:7H Case 2 Simplified EMB Stationing Figure D2 6 : EMB Grading Extents DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 16 of D2 27

22 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D.6 RIGHT BANK EMEDDED LEVEES As previously mentioned, an embedded levee will be required within the right bank for flood risk reduction reasons. There is no need for a levee on the left bank. The requirements for the right bank embedded levee are summarized below. Additional details concerning the levees and EMBs can be found in MFR 001, Levees and Excavated Material Berms along the Diversion (5). Crest Elevation The crest elevation will be the estimated maximum flood fight flow profile plus overbuild to account for estimated settlement Typical Section The typical cross section will be the St. Paul District typical section for levees within the Red River Valley which has a 10ft top width and a 1V:3H side slopes Construction Requirements The construction requirements are: o o o o o Stripping: All organic materials beneath the footprint of the levee shall be removed. Inspection Trench: An inspection trench will not be required because the diversion channel will act as a large inspection trench. If any pervious layers are encountered during excavation, an analysis should be completed to determine if a cut off trench will be needed Utilities and Drain Tile: If utilities and drain tile are encountered within the diversion channel excavation or they are known to be beneath the footprint of the levee, at a minimum, the utilities and drain tile shall be removed from beneath the footprint of the levee and extending out 15 feet from both toes of the levee. The exception would be utilities relocated as part of this project in compliance with MFR 010, Utility Relocation Requirements (Reference D2 4). Fill Material: Alluvium or Sherack materials shall be used as fill material. These formations will be located in the upper portion of the diversion channel excavation. These materials are identified in the specifications as those with a liquid limit of less than or equal to 90 (LL 90). Placement: The materials shall be placed in lifts of 12 inches or less. o Compaction: The fill material will be required to be compacted to a minimum 90 percent of maximum dry densisty as determined by the standard proctor. o o Moisture Control: Moisture control will not be specified but this will not relieve the contractor from obtaining the required compaction. Testing: Minimum testing will be completed on materials placed. Testing will include proctors, density, Atterberg limits, and grain size analysis. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 17 of D2 27

23 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D.7 SETTLEMENT AND REBOUND The large scale excavation and placement of soil introduces the potential for significant soil rebound and settlement, respectively. Since the final grade is important for many project features, including the drainage structures, embedded levees, and the low flow invert, rebound and settlement need to be analyzed in order to plan potential mitigation measures. Settlement and rebound calculations are presented in Attachment D 2 5 and explained in this section. Calculations were not updated from the 65% DDR Submittal for the Lower Rush Diversion channel. The parameters chosen and profile assumed in this report were verified by additional borings completed in Formation contact elevations generally varied by less than one foot with all original assumptions being more conservative than those determined by additional exploration. The largest variation was in the contact of the Oxidized Brenna and Brenna formation at Section 8a, which was interpreted to be from 2010 borings and interpreted to be from 2013 boring. This variation was determined to be insignificant in the overall settlement and rebound findings. D.7.1 Consolidation Parameters Soil parameters used for settlement and rebound calculations were taken from consolidation tests performed throughout the Fargo Moorhead metro area for several USACE projects. In situ effective vertical stresses were estimated based on the stratigraphy indicated in the adjacent machine boring and assuming a groundwater table 10 ft below ground surface when no other groundwater data was available. Preconsolidation pressures were determined both by the laboratory and by the Casagrande approach. Generally there was good agreement between laboratory determined values and Corps determined values. The glacial till was assumed to be incompressible for the purposes of estimating settlement. The consolidation parameters selected for the settlement and rebound analyses represent the mean or expected value parameters based on the available data. The mean consolidation parameters are shown below in Table D2 8. Table D2 8: Mean Consolidation Parameters Formation sat (pcf) ' OCR C r C c e o C er C ec Alluvium Sherack OX Brenna Brenna Argusville D.7.2 Settlement of typical levee/ Right Bank EMB Settlement of the right bank EMB was estimated in order to approximate the amount of required overbuild for encapsulated levees in order to maintain the maximum flood fight flow profile of the levee. The final grade of the EMBs is not a concern since overbuild will be applied directly to the encapsulated levee section. The levee and right bank EMB were assumed to be practically DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 18 of D2 27

24 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology incompressible for the purposes of analysis. An analysis considering an infinite surcharge equivalent to the maximum allowable EMB height of 20 ft of compacted clay fill and the mean consolidation parameters resulted in a settlement of roughly 17 inches. This value would decrease somewhat by accounting for the finite nature of the loading. Also, the stripping of the upper several feet of topsoil and replacement with compacted levee fill would further reduce this estimate. Check analyses using the settlement program CSETT and the same consolidation parameters were conducted using both infinite and finite loading for Section 8. The resulting settlement values were in agreement with the results calculated using the spreadsheet developed by MVP. Considering overbuild required throughout the entire Reach 5 extents, recommended overbuild for the right bank levee is 1.5 feet. Settlement analyses results are located in Attachment D2 5. Table D2 9: Settlement Check Analysis Results Sta Section 8 EMB Settlement Material δ CSETT infinite (ft) δ CSETT finite (ft) δ EXCEL (ft) Alluvium Sherack Ox Brenna Brenna Argusville Total (ft) Total (in) D.7.3 Table D2 10: Predicted EMB Settlement for Determination of Levee Overbuild EMB Settlement for Determination of Levee Overbuild Section 8 8a EMB Height (ft) Depth of Compressible Material (ft) Predicted Settlement (ft) Rebound in the Channel Excavation The net change in grade resulting from excavation for the diversion channel the will result in rebound. Analysis considering infinite excavation to the level of the diversion channel invert calculated this rebound to be roughly 15 inches. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 19 of D2 27

25 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology Table D2 11: Predicted Ultimate Rebound in Diversion Channel Rebound at Diversion Invert Section 8 8a Excavation Depth (ft) Depth of Compressible Material beneath Excavation (ft) Predicted Ultimate Rebound (ft) Additional details on time rate of rebound calculations can be found in the General Report: Geotechnical Engineering and Geology (Reference D2 1). Over excavation of the diversion channel to account for rebound is not recommended based on geotechnical and hydraulic analyses it is anticipated that hydraulic capacity will be sufficient even if rebound occurs. If and when changes in grade due to sedimentation and/or rebound become a hydraulic issue, cleanout will be required in order to maintain the necessary flow capacity. MVP will monitor rebound in Reach 1 and determine if adjustments should be made prior to construction of subsequent reaches, including Reach 5. D.8 DIVERSION EXCAVATION TYPES The construction of the diversion channel will require excavation through different materials. The type of equipment used, production rates, and excavation costs will depend on the characteristics of these different material. In order to complete a comprehensive cost estimate, the diversion channel excavation was broken into five different excavation types. A profile was developed along the Reach 5 alignment discerning the five different excavation types in order to estimate quantities. A summary of the excavation types is below in Table D2 12. For diversion excavation types 1 and 2, the groundwater table was based on water level readings in the boring logs or the bottom of the local drainage features and was generally 5 to 7.5 feet below the ground surface. This assumption is different from that which is used in the seepage and stability analysis. Table D2 12: Summary of Diversion Channel Excavation Types DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 20 of D2 27

26 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D.9 LOCAL DRAINAGE INLETS The local drainage plan does not call for any drainage inlets at the location of the Lower Rush River Drop/Inlet structure. D.10 RIPRAP AND BEDDING Riprap will be required at several locations where the Lower Rush River meets the Diversion Channel. Riprap gradation R30 and R270 will be used. Further details on the Riprap sizing, gradations, and locations can be found in Appendix C. D.11 CONSTRUCTABILITY D.11.1 Excavations This section discusses several considerations with regards to the constructability of the proposed excavations. D Past Experience MVP has experience with excavations in the Fargo Moorhead area as a result of the Horace to West Fargo and West Fargo Diversion Channels (HWF Diversions) and frequent flood fighting efforts that have required use of borrow material. The HWF Diversions were on the order of 10 feet deep, placing the bottom of the excavation in the Sherack formation or just into the Brenna formation. The side slopes of these channels where excavated at 1V:7H using scrapers. No constructability issues sloughing of the excavated slopes or seepage into the excavation were encountered in the tight clay materials. During flood fights, a substantial amount of borrow is needed to construct emergency levees. The fill is obtained from local borrow pits and have been excavated with very steep to nearly vertical faces with depths ranging from 10 to 20 feet. These steep faces typically show little to no sloughing failures during the time they remain open, which could be up to a couple months. Also, seepage is not a concern as very little water seepages into the excavation. D Methods MVP recognized that the soils change with depth; the materials will become wetter and weaker with depth. Due to the changing nature of the soils with depth, it is anticipated that different excavation techniques will be employed as the excavation increases in depth. Specifically, the stronger upper soils (Alluvium, Sherack) will likely be excavated with a scraper as was the case for the HWF Diversions. As the excavation penetrates into the Brenna Formation the soils may have a reduced capacity to support construction equipment. Therefore, it is likely an excavator will be used and material loaded into offroad haul trucks to transport the excavated materials. DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 21 of D2 27

27 Project and Reach 5 Appendix D2: Geotechnical Engineering and Geology D Stripping and Overexcavation It is anticipated that 1 to 2 feet of topsoil will need to be stripped from the footprint of the project based on the results of the top soil survey. However, localized variations could be encountered along the alignment. This layer should be readily distinguishable as it will be black and contain organics. Topsoil should be stripped from the diversion footprint and stockpiled as needed for placement during final grading. This layer should be readily distinguishable as it will be black and contain organics. It is anticipated that soft surface soils will be encountered at several locations along the alignment and will require special treatment beneath fill areas (EMBs, levees, and other embankments). Slopes of 1V:4H or steeper need to be stepped prior to subgrade preparation. D Dewatering Dewatering prior to the start of excavation will not be required due to the impervious nature of the soils, and the flow of water into the excavation will be minimal. The diversion channel will need to be excavated with a slope such that any precipitation that occurs will runoff towards a low area. If a large amount of precipitation occurs, the contractor may be required to pump this water out of the excavation. D Sand Pockets / Lenses There is the possibility of encountering sand pockets or lenses. If sand pockets or lenses are encountered during excavation and have a perched water table, there could be a large quantity of flow into the excavation. If dewater efforts could not keep up with the flow, an impervious cutoff trench could be constructed adjacent to the diversion channel to reduce flow into the excavation. D.11.2 Access/Maintenance Road Foundations Access and maintenance roads along the project will require adequate foundations in order to minimize surface degradation and associated maintenance over the project lifespan. Aggregate base course will require a minimum 8 thickness, and will be placed atop a separation geotextile. The subgrade shall consist of 3 ft of impervious fill placed in lifts no greater than 9 thick and compacted to 95% of standard proctor with a moisture content between plus 3% and minus 2% of optimum. This design is similar to the standard design used by Cass County. Additionally, calculations following the Giroud and Han design method for unpaved roads (Reference D2 6) were completed as part of the Reach 1 design. The results of the calculations indicate that strong subgrade (undrained shear strength of 1500 psf), geotextile separation fabric, and 9 inches of gravel was needed to support a minimal number of passes (500) of heavy construction traffic (~12,600 lb wheel load). This supports the need to compact the 3 feet of subgrade beneath the aggregate surfacing. D.11.3 Embankment Construction Construction of embankments in the Red River Valley can pose to be problematic due to the weak foundation conditions. Placement of materials along the banks of existing rivers can reactivate existing slides or initiate a new slope failure. Rapid placement of material for embankments can also lead to DDR_FMM_R5_Appendix_D2_Post_FTR_ docx Page D2 22 of D2 27