Town Hall Meeting June 26, 2014

Transcription

1 Town Hall Meeting June 26, 2014

2 Licensed geotechnical & civil engineer Over three decades of experience Projects ranging from residential development to large earth dams Experienced with construction, instrumentation, analysis, design, landslide stabilization, seismic design and many other aspects of geotechnical engineering Licensed professional geologist & certified engineering geologist with almost 40 years of experience Wide ranging experience providing geologic support for geotechnical projects in southern California Projects include residential development, commercial/industrial sites & infrastructure Strong background with geologic hazards, including mega landslides and seismic evaluations

3 Residential complex covering 277 acres 575 residential lots Northerly 1/3 of site underlain by landslide complex

4 1) Maximize extraction of water from landslide using current manual pumping 2) Obtain necessary permits from Regional Water Quality Control Board to allow discharge of water to either storm drain system or ground surface 3) Convert wells to extraction of water automatic pumping to further maximize 4) Investigate feasibility of hydraugers (horizontal drains) 5) Continue monitoring of piezometers (groundwater level) and slope inclinometers (ground movement) 6) Investigate ground movement related to the Laing Forster Landslide complex.

5 Eight (8) dewatering wells located within the landslide complex Four (4) wells with permanent pumps installed (higher discharge) Four (4) wells pumped with portable pump (lower discharge)

6 Daily pumping W 6&W 7 Weekly pumping W 8 Bi weekly pumping W 2 Monthly pumping W 1, W 3, W 4&W 5

7 Application in progress to the Regional Water Quality Control Board Permit will allow for automatic pumping of the dewatering wells by permitting direct discharge into the storm drain system Automatic pumping will allow for higher pumping rates resulting in substantial lowering of the groundwater level Permit requires sampling and testing of the well discharge water for certain toxic elements and compounds Upcoming changes in the State regulations relating to water quality might ultimately allow direct discharge onto the ground surface (advantage to design of hydraugers)

8 Hydraugers would allow for permanent dewatering of the landslide complex by means of gravity Pumping of the wells within the upper reaches of the site could be eliminated Minimal maintenance would be required (Monthly reading of flow meters & bi yearly purging of the casing screens) Currently meeting with contractors to discuss the feasibility of installing hydraugers with regard to issues such as access, topographic constraints and drain length required RWQCB permit would be required to discharge directly into the storm drain system; however, upcoming changes to State regulations might allow for discharge onto the ground surface

9 Simplified hydrauger diagram Drilling process Completed drains

10 PIEZOMETERS Vertical standpipes used to monitor groundwater levels SLOPE INCLINOMETERS Vertical tubes with grooves used to monitor ground movement at depth

11 Ten (10) piezometers located within and just above the landslide complex Piezometers consist of either one (1) or three (3) standpipes Used to monitor the static groundwater level within the area of concern

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13 Fifteen (15) slope inclinometers located within the development Slope inclinometers consist of a grooved casing installed vertically in the ground to monitor movement at depth An accelerometer probe with alignment wheels is lowered into the casing to measure the tilt during successive readings

14 Inclinometer probe, cable and readout box

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16 Laing Forster Ranch Landslide Area

17 Work In Progress Existing Caisson/Tie Back Repair I 7 I 8

18 Existing Caisson/Tie Back Repair

19 Cross Section Through Repair Slope Inclinometer I 7 Depth of Movement in Inclinometer

20 Inclinometer Movement

21 Tasks: Determine more precise location of existing repair (caissons & tie backs) Necessary to avoid damage from drilling and for proper stability analysis Drill two (2) boreholes upslope of existing repair Down hole log geologic conditions&obtainsamplesofearthmaterialsfortesting Install slope inclinometers in boreholes & monitor along with existing inclinometers Complete geologic surface mapping & prepare cross sections through existing repair with geologic structure determined from exploratory drilling Perform laboratory testing of samples obtained from drilling to determine the engineering properties of the earth materials Perform engineering analysis of the cross sections parameters obtained from laboratory testing using engineering If necessary, design suitable repair(s) to mitigate the existing movement and provide support to the residential lots above Prepare a written report providing findings, conclusions and repair options in sufficient detail to obtain cost estimates from repair contractors and apply for building permits

22 Town Hall Meeting June 26, 2014