SECTION GEOTECHNICAL INSTRUMENTATION

Transcription

1 SECTION GEOTECHNICAL INSTRUMENTATION PART 1 GENERAL 1.1 WORK INCLUDED A. This section covers the work necessary for furnishing and installing new piezometers, movement monuments, and inclinometers (if required), complete. 1.2 QUALIFICATION REQUIREMENTS A. Drilling and logging of borings and installation of piezometers and inclinometers shall be under the full-time supervision of a geotechnical engineer or geologist with at least 3 years previous experience in drilling and installing monitoring wells. The firm and the individuals who actually supervise the work shall be subject to the CONSTRUCTION MANAGER's review and acceptance. All drilling shall be performed by driller licensed by the Utah Office of the State Engineer with a minimum of 5 years experience in drilling, sampling, and piezometer/monitoring well installation. 1.3 SUBMITTALS A. Administrative Submittal: State Agency Permit Submittals. B. Qualifications of firm and personnel installing monitoring wells. C. Submit within 14 days after installation of each instrument: 1. Boring logs for each monitoring well borehole. 2. Construction diagrams for each monitoring well. 3. Initial survey results including horizontal and vertical control data. 1.4 PERMIT REQUIREMENTS A. Monitoring wells shall be installed, constructed, and operated in compliance with current Rules and Regulations of the Utah Administrative Code and especially Section R655-4, Water Well Drillers. B. CONTRACTOR shall be fully responsible for obtaining applicable permits, providing notification of intent to construct monitoring wells, and satisfying reporting requirements of State Engineer's Office GEOTECHNICAL INSTRUMENTATION

2 1.5 DELIVERY, STORAGE, AND PROTECTION A. General: 1. Deliver products and materials in original, unopened containers. 2. Handle products in manner that maintains undamaged conditions. 3. Do not shore products directly on ground. B. Inclinometer Casing: 1. Ship and store casing with suitable wrapping for protection against ultraviolet exposure. 2. Support casing during delivery and storage so that it does not warp or bend. PART 2 PRODUCTS 2.1 GENERAL A. Provide all materials and trained personnel necessary to accomplish the work specified in this Section. All equipment and materials shall be in good operating condition at all times and operated and maintained in strict conformance with manufacturer's recommendations. 2.2 PROTECTIVE CASING A. Galvanized steel pipe of standard wall thickness (ANSI Schedule 40) or as approved by CONSTRUCTION MANAGER. Each length of pipe shall be supplied with lockable cover. B. Commercially available flush mount protective casing and piezometer surface completions for inclinometers/piezometers located in access road, as approved by CONSTRUCTION MANAGER. 2.3 PIEZOMETER/WELL RISER AND SCREE N A. Provide all riser and screen of the types, thicknesses and diameters specified or shown. All riser and screen shall be of new, first quality material, and free of defects in workmanship and handling. B. Riser Pipe: Schedule 40 PVC plastic. Lengths of riser shall be capable of being joined watertight, and the resulting joint shall have the same structural integrity as the riser itself. 1. Piezometers for Groundwater Monitoring in Zone I (Clay) Embankment Fill: 3/4-inch ID. 2. All Other Piezometers: 1-inch ID GEOTECHNICAL INSTRUMENTATION

3 C. The well screen shall be Schedule 40 PVC in 5-foot lengths. All well screen shall be factory slotted with inch slots. Slot rows shall be spaced parallel, having a slot-to-slot distance of inches, and with approximately 86 slots per row per foot, or as approved by CONSTRUCTION MANAGER. 1. Piezometers for Groundwater Monitoring in Zone I (Clay) Embankment Fill: 3/4-inch ID. 2. All Other Piezometers: 1-inch ID. D. All risers shall be supplied in 5-, 10-, and 20-foot lengths. Have on hand at all times sufficient quantities of each length of pipe to make up any length required. E. Fittings shall be compatible material with riser material. F. Provide all parts of each piezometer riser/screen assembly from a single manufacturer. 2.4 INCLINOMETER CASING (REQUIRED FOR MAIN DAM S CUTOFF WALL OPTION ONLY) A. Provide all inclinometer casing, couplers, and caps of the types, thicknesses and diameters specified or shown. All products shall be of new, first quality material, and free of defects in workmanship and handling. B. The casing shall be a minimum of 3-inch OD, in 5-, and 10-foot lengths. All casing shall have machine cut grooves at 90 degrees inside the casing to allow for monitoring movement in two axis. C. Casing shall be equipped with self-sealing, grout-proof couplings and shall not result in a reduction of the strength or durability of the assembled inclinometer casing. D. Couplings secured with glue, rivets, or tape will not be allowed. E. Snap couplings will not be allowed when the temperature at the time of casing assembly and installation is below 45 degrees F. F. Inclinometer casing, couplings, and caps shall be as manufactured by Durham Geo Slope Indicator, Carson City, Nevada (1-800/ ), or equal and suitable for the installation conditions shown. 2.5 INCLINOMETER PROBE AND DIGITAL INCLINOMETER READOUT A. CONTRACTOR shall supply a new, first quality inclinometer probe and digital inclinometer readout free of defects in workmanship and handling. The GEOTECHNICAL INSTRUMENTATION

4 equipment shall be by the same manufacture producing the inclinometer casing. B. Inclinometer probe shall have the following properties: 1. Wheel Base: 24 inches or greater. 2. Range: Plus or minus 35 degrees from vertical. 3. Resolution foot per 2-foot interval. 4. Temperature Rating: Minus 4 to 122 degrees F. C. Digital Inclinometer readout shall have the following properties: 2.6 CENTRALIZERS 1. Minimum Reading Interval: 1 foot. 2. Readings intervals per survey: > Equipped with software to allow for transferring readings to compute. A. Centering guides shall be fabricated of high-grade, spring stainless steel with ribs on 120-degree centers and adjustable up to 8-inch diameter holes. 2.7 MISCELLANEOUS FITTINGS A. All miscellaneous fittings for piezometer construction shall consist of new, first-quality material, free of defects, and meeting the approval of the CONSTRUCTION MANAGER. Provide fittings as specified or shown. B. Locks shall be commercially available padlocks being keyed alike with the existing piezometer locks. 2.8 FILTER SAND A. The filter sand shall be thoroughly washed, sound, durable, well rounded, siliceous material containing, when delivered, no organic material, soluble materials, calcareous materials, and mica. The filter sand shall be of 16 to 40 mesh sand. The specific gravity of the material shall be not less than BENTONITE PELLETS A. Commercial grade sodium bentonite pellets, as approved by CONSTRUCTION MANAGER CEMENT-BENTONITE GROUT MIX A. Grout shall consist of a cement/sand/bentonite slurry. Proportion one bag of cement to not more than 15 gallons of water. Provide 10 to 12 pounds of powdered bentonite per bag of cement to reduce shrinkage. Mix cement with GEOTECHNICAL INSTRUMENTATION

5 water first and let hydrate for a minimum of 10 minutes, then mix in bentonite. Add sand as appropriate. Consistency and method of mixing shall be approved by the CONSTRUCTION MANAGER. The use of special cements or other admixtures (ASTM C494) to reduce permeability, increase fluidity, and/or control set time, and the composition of the resultant slurry shall be approved by the CONSTRUCTION MANAGER. The density of the slurry mixture for tremie grouting shall be monitored prior to placement (using a standard mud balance). B. Cement: Conform to ASTM Designation C150 Type I or II portland cement. C. Bentonite: High swelling, finely ground, reduced ph, sodium bentonite/montmorillinite. D. Water: Potable water. E. Concrete Sand: Commercially available, washed, silica sand LEAN GROUT A. Lean grout shall be a 1:5 ratio cement-sand mixture by volume. Cement and sand shall be as described in Article CEMENT-BENTONITE GROUT MIX CONCRETE A. Conform to Section 03300, CAST-IN-PLACE CONCRETE REINFORCING STEEL A. Provide rebar conforming to Section 03300, CAST-IN-PLACE CONCRETE. PART 3 EXECUTION 3.1 GENERAL A. Furnish all labor, materials, and equipment necessary to install the geotechnical instrumentation as shown. B. Location of Instrumentation: Install all instrumentation at the locations shown and as established by the CONSTRUCTION MANAGER. The CONSTRUCTION MANAGER will confer with the CONTRACTOR as to the suitability of all planned locations. The CONSTRUCTION MANAGER will make the final decision on instrument locations. During the initial installation of each instrument and during the construction of each instrument, the CONTRACTOR shall perform all surveys to define the initial, intermediate, and final location and elevation of the instruments, and all intermediate surveys to maintain the verticality of the instrument GEOTECHNICAL INSTRUMENTATION

6 C. Exercise care during construction so as to avoid damage to instrumentation. All locations shall be flagged and protected during and after construction. Geotechnical instrumentation that is damaged as a result of the CONTRACTOR's operations shall be repaired or replaced by the CONTRACTOR at his own expense. The CONSTRUCTION MANAGER will determine whether repair or replacement is required. D. All installed instruments shall be clearly labeled for easy identification as shown on the Drawings and approved by the CONSTRUCTION MANAGER, and shall be clearly visible. 3.2 DRILLING AND SAMPLING FOR PIEZOMETERS A. Drill borings as necessary for installation of nested piezometers after completion of embankment construction. Drilling of the borings shall be performed under the direct supervision of the CONTRACTOR's geotechnical engineer or geologist, who shall also be responsible for completing a geotechnical log of each borehole. Each boring shall be sampled on regular 5-foot intervals, or as determined by the CONSTRUCTION MANAGER, using a split-barrel sampler and Standard Penetration Test procedure (ASTM D1586). B. Drilling Equipment: 1. All equipment necessary to perform the drilling for this project shall be provided by the CONTRACTOR. The drilling equipment must produce cased holes through the embankment and open holes in bedrock. Casing may be extended into broken and otherwise unstable rock, at the direction of the CONSTRUCTION MANAGER. Drilling with fluids will not be permitted in the embankment. 2. The CONTRACTOR shall furnish all temporary casing required to advance the hole. All temporary casing shall be removed by the CONTRACTOR at the completion of the boring. C. Drilling in Embankment: 1. General: a. The CONTRACTOR shall drill through the embankment and into weathered bedrock by use of a hollow-stem auger. Drill rigs shall be capable of drilling to a minimum depth of 170 feet. The inside diameter of the hollow-stem auger shall be of a size to allow minimum Hw (4-inch-inside diameter) size casing to be installed through the hollow-stem auger. Water not to exceed 5 gallons per 5 feet of auger advancement may be added to the drill hole to facilitate drilling embankment materials. In no case will more than 5 gallons be added for any 5-foot interval GEOTECHNICAL INSTRUMENTATION

7 b. No samples will be required from embankment drilling. 2. Casing: a. Temporary casing shall be installed through the embankment and loose bedrock to prevent caving and shall be tightly seated within the upper 3 feet of bedrock to prevent loss of water or contact of water with the embankment during rock drilling. Casing shall be seated at greater than 3 feet into bedrock at the direction of the CONSTRUCTION MANAGER if a tight seal cannot be accomplished within the upper 3 feet of bedrock. b. The temporary casing installed in cutoff wall depth determination drill holes and instrumentation holes shall be of minimum Hw size (4 inches inside diameter). c. The CONTRACTOR shall furnish all temporary casing required. d. The CONTRACTOR should anticipate possible difficult drilling in embankment foundation materials due to saturated conditions, firm to hard conditions, and the presence of gravel and cobbles. e. All temporary casing shall be removed by the CONTRACTOR from the drill holes at the completion of the boring. D. Drilling Surficial Materials: 1. General: a. Surficial material is defined as nonembankment layers of soil materials beneath the embankment, regardless of nature and depth. b. The CONTRACTOR shall drill through surficial materials by use of equipment capable of producing a drill hole suitable for the installation of temporary casing. No samples will be required from surficial material drilling. 2. Casing: a. A temporary casing shall be installed through surficial materials and loose bedrock to prevent caving and shall be seated within the top 3 feet of bedrock. Casing shall be seated at greater than 3 feet into bedrock at the direction of the CONSTRUCTION MANAGER if a tight seal cannot be accomplished within the upper 3 feet of bedrock. b. The temporary casing installed in cutoff wall depth determination drill holes and instrumentation holes shall be of minimum Hw (4 inches inside diameter). c. The CONTRACTOR shall furnish all temporary casing required. d. The CONTRACTOR should anticipate possible difficult drilling in surficial materials due to caving conditions and the presence of gravel, cobbles, and boulders. e. All temporary casing shall be removed by the CONTRACTOR at the completion of the drill holes GEOTECHNICAL INSTRUMENTATION

8 E. Drilling in Bedrock: The CONTRACTOR shall drill rock by rotary drilling methods with clear water. F. Occurrences such as sudden changes in consistency, voids, dropping of drill rods, unusual water conditions, and other unanticipated conditions shall immediately be brought to the attention of the CONSTRUCTION MANAGER. Drilling shall be stopped until a determination of the cause and/or effect of such conditions has been assessed by the CONSTRUCTION MANAGER. 3.3 PIEZOMETER INSTALLATION A. Install riser, well screen, centralizers, filter sand, bentonite pellets, and cement-bentonite grout as shown and as otherwise directed by CONSTRUCTION MANAGER. While withdrawing augers/temporary casing during instrument installation, care shall be taken to minimize the increments of auger/temporary casing withdrawal so that collapse of the borehole does not occur. Sand and bentonite pellets shall be placed slowly by tremie so that bridging does not occur in the boring, and so as to prevent the instrument from being lifted as the auger/temporary casing is withdrawn. Hydrate bentonite pellets with clear water before grouting. Grout above the bentonite pellets shall be a bentonite-cement grout, pumped or tremied through a pipe placed at the top of the bentonite seal. B. Install filter sand to completely and uniformly envelope the well screen, and extend 1 foot below and 1 foot above the well screen. Use centralizers to position the piezometer riser and screen in the borehole. C. Instrument installation and backfilling of each piezometer shall, to the extent practical, commence and continue to completion without interruption as soon as possible following drill-hole completion and cleanout. The CONTRACTOR will be responsible for using precautions as necessary during all backfill placement operations to prevent bridging of the backfill material and to ensure compliance with backfill depth requirements by measurement probe checks and placement volume calculations. The CONTRACTOR must be prepared to dislodge all bridged material by vibration of the casing, clearwater jetting, tamping, or other method acceptable to the CONSTRUCTION MANAGER. If clear water has to be introduce into the cased hole during the backfilling operation, any free-water accumulation above the base level of the bentonite seal zone shall be removed by bailing or blowing out with compressed air prior to the placement of bentonite pellet backfill material. D. Install concrete around protective casing as shown and in accordance with Section 03300, CAST-IN-PLACE CONCRETE GEOTECHNICAL INSTRUMENTATION

9 E. Each piezometer shall be developed upon completion of the installation. The method of development that the CONTRACTOR proposes must be acceptable to the CONSTRUCTION MANAGER. The accepted method of development shall be continued until the purge water becomes clear and, in the opinion of the CONSTRUCTION MANAGER, the piezometer has been developed. Development of dry piezometers will not be required. 3.4 DRILLING FOR INCLINOMETER INSTALLATION (REQUIRED ONLY FOR CONCRETE CUTOFF WALL OPTION) A. CONTRACTOR shall install inclinometer casing in Cutoff Wall verification holes as described in Section 02276, PLASTIC CONCRETE CUTOFF WALL. CONTRACTOR shall position verification holes in the locations shown on the Drawings for inclinometer installation. The elevation at which the borehole exits the concrete cutoff wall and enters native sedimentary rock shall be determined and recorded for each boring. Borings for inclinometer installation shall extend through the cutoff wall and into rock a sufficient distance to allow for the bottom of the inclinometer casing to extend 10 feet into rock. Drilling of the borings shall be performed under the direct supervision of the CONTRACTOR's geotechnical engineer or geologist, who shall also be responsible for completing a geotechnical log of each borehole. Requirements for core recovery, logging, and transfer to the OWNER shall be as described in Section 02276, PLASTIC CONCRETE CUTOFF WALL. 3.5 INCLINOMETER CASING INSTALLATION A. General: Inclinometer casing installation shall be in accordance with the recommendations of the inclinometer casing manufacturer. B. Inclinometer Casing Installation in Cutoff Wall: 1. Clear the borehole of debris and obstructions that would prevent or the installation of or damage the casing. 2. Check that the borehole depth is sufficient to meet requirements. Attach the bottom cap, or grout valve if used, to the bottom section of casing and install the casing to the required depth. Keep the casing filled with water to counteract buoyancy. Install the inclinometer casing to align the grooves with the axis of the embankment as shown on the Drawings. Place top cap on the inclinometer casing to prevent entry of grout. 3. Performing grouting in stages so that the grout does not exceed the collapse strength of the casing. Obtain casing manufacturer s recommendation for allowable depth of stage one grouting. Obtain written verification from casing manufacturer if staged grouting is not required for the actual casing installation depths GEOTECHNICAL INSTRUMENTATION

10 4. Stage 1 grouting shall be performed from the bottom of the borehole using a grout tube or a one-way grout valve installed in the bottom cap of the casing. Second stage grouting may be performed by hose or pipe. If a hose is used for Stage 2 grouting, it must be installed with the casing and can be left in place after grouting. If hoses are used for both Stage 1 and Stage 2 grouting, color-code or otherwise distinguish between the two hoses to avoid pumping grout or water through the wrong hose. Perform staged grouting in accordance with the casing manufacturer s recommendations. 5. Counter the buoyancy of the casing during grouting by applying a downward force at the bottom of the casing. Other methods of countering the buoyancy as recommended by the casing manufacturer may be allowed provided that they do not overstress the casing or cause unacceptable deflection of the casing. C. Inclinometer Casing Extension: 1. Extend inclinometer casing above cutoff wall to the top of the dam crest as embankment fill is placed. Protect the inclinometer casing from damage. Cap the top of the inclinometer casing to prevent foreign material from entering casing. 2. Protect inclinometer casing above the top of the concrete cutoff wall using a Schedule 40 PVC sleeve with a minimum ID of 6 inches. Place the sleeve around the inclinometer casing as the casing is extended. Maintain the PVC sleeve at least 12 inches above the top of the casing and cap or otherwise seal the top of the sleeve. 3. Place embankment fill material by hand within 3 feet radius of the PVC sleeve and inclinometer casing. Compact embankment fill material within a 6 feet radius of the inclinometer casing using hand-compaction equipment. 4. CONTRACTOR shall use flagging, ballards, barricades, or other methods to protect the inclinometer casing from damage. 5. After completion of the dam embankment, fill the annular space between PVC protective sleeve and outside of the inclinometer casing with grout. Use the same grout mix as used for the inclinometer installation in the concrete cutoff wall. 6. Install a locking, galvanized steel pipe flush-mount cover at the surface of the embankment as specified and shown. 3.6 MOVEMENT MONUMENTS A. Construct as soon as practicable after completion of the embankment stability berm GEOTECHNICAL INSTRUMENTATION

11 3.7 CLEANUP A. Clean up all waste materials upon completing geotechnical instrument installations. At the completion of the work, dispose all material in accordance with Section 02200, SITE PREPARATION. 3.8 INITIAL SURVEYS A. The CONTRACTOR shall make initial surveys for each new movement monument, new piezometer and raised existing piezometer, and the CONSTRUCTION MANAGER and CONTRACTOR shall jointly agree on appropriate initial readings. Initial surveys shall be performed and certified by a registered Professional Land Surveyor in the State of Utah. B. Initial surveys of instruments shall be made within 7 days after completing each installation. A minimum of three level circuits shall be taken to establish the initial readings for elevation and location. Data shall meet the standards set forth by the National Oceanic and Atmospheric Administration (NOAA) for second order Class 2 precision. At a minimum, initial readings should include a tabulation of instrument type and designation, northing and easting coordinates, elevation, and date surveyed. C. The CONTRACTOR shall make initial readings of the inclinometers to establish a baseline inclinometer position in accordance with inclinometer casing and probe manufacturer recommendations. At a minimum, readings used to establish the baseline shall not be taken until grout has cured for a minimum of 48 hours. Two sets of inclinometer readings, taken a minimum of 24 hours apart and showing no reading discrepancy greater than 1 mm shall be required to achieve the baseline inclinometer position. If sequential inclinometer monitoring events show discrepancies greater than indicated, perform additional surveys as required. END OF SECTION GEOTECHNICAL INSTRUMENTATION