Loading...
HomeMy WebLinkAboutItem8.3 SlidesJade&Crossridge96-4 (2)CITY CLERK AGENDA STATEMENT CITY COUNCIL MEETING DATE: March 12, 1996 SUBJECT: Slides Above Jade Circle and Crossridge Road Report Prepared by: Lee S. Thompson, Public Works Director EXHIBITS ATTACHED: l) 2) 3) Letter proposal from Berlogar Geotechnical Letter proposal from Santina & Thompson Letter from Naomi and James Shand, residents of Crossridge Road RECOMMENDATION: Provide direction to Staff regarding the following items of work: 1) Expand existing contract for geotechnical work to extend along all of the Crossridge Road slope. ($10,000 to $15,000) 2) Design the repair project and go to bid in this Fiscal Year for award in early July 1996. 3) Investigate to see if the subdrain along the base of the hill is functioning. (DSRSD will lend their TV camera at no charge to the City) 4) Investigate the capacity of the concrete Vee ditch system and redesign and reconstruct as appropriate. ($5,000 to perform a topographic survey of the ditch and recommend solutions, if warranted; $14,000 to design either a brow ditch with retaining wall or a new pipe system) 5) Appropriate funds from unallocated reserves to perform the above work. (Maximum of $39,000) FINANCIAL STATEMENT: To perform the above expanded scope of work, an expenditure in the amount of up to $39,000 would be required in this Fiscal Year. The repair contract work, along with inspection costs of an unknown amount, will be needed in Fiscal Year 1996-97, assuming that the City Council goes forward with this project by approving it in the upcoming Capital Improvement Program. The existing geotechnical contract for investigation and aid in design documents for the slide repairs is up to $27,000. It is possible that the subdivider may be COPIES TO: Property Owners ITEM NO. 8.3 responsible for some or all of the cost of investigation, design and repair work. DESCRIPTION: During the heavy rains of February 1995, two slides developed on the slope above the homes on Crossridge Road and two above the homes on Jade Circle. These slopes are within the City's Dougherty Hills open space. In November 1995, residents of Crossridge Road petitioned the City Council with a request that the City take steps to correct grading and drainage on the slope above their homes in order to avoid any additional landslides. The City Council subsequently directed Staffto conduct a study of the slopes above Crossridge Road and Jade Circle on the east and west sides of the Dougherty Hills open space so that a Capital Improvement Project to repair and mitigate the slides could be developed for the 1996-97 Fiscal Year. In response to Council's directive, Staffissued a Request for Proposal and the City contracted with Berlogar Geotechnical Consultants to conduct this study. Staff subsequently scheduled an informational meeting with property owners of Crossridge Road and Jade Circle to explain the scope of soils investigation work, as well as receive input from the property owners regarding their concerns and experiences. This meeting was held last Thursday evening and was attended by 18 homeowners, 15 along Crossridge Road and 3 along Jade Circle. The property owners expressed the following concerns and requests: 1) The contracted soils investigation work is limited to the existing slide area problems and will not address the entire length of the slopes. There was concern that there may be potential problems with other areas of the hillsides. The request is to extend this soils study to cover all of the Crossddge Road slope. 2) Concern was registered that if the City does not accelerate the timing of the project, the repairs could run into next winter. The request is to do the design work and go to bid this fiscal year with construction beginning in July. 3) Extensive underground water is entering the yards of the homes along the toe of the slopes and that the subdrain may not be working. The request is to check the subdrain for blockage. With respect to this item, the subdrain does run through private property, and it would be the property owner's responsibility to make any needed repairs or work with the developer to make repairs, if needed. 4) There might be a settlement in a portion of the Vee ditch above Crossridge Road, and the capacity of the Vee ditch may be insufficient to carry the runoff because of the length between downdrains. It was requested that further investigation be done on the concrete ditches and that improvements be made to these ditches. Staffhas obtained consultant fee estimates from Berlogar Geotechnical Consultants and from Santina & Thompson for the above work, with the following results: 1) Berlo~:ar Geotechnical Consultants. To extend the geotechnical work to cover the rest of the Crossridge Slope: $10,000 to $15,000 2) Santina & Thompson. Page 2 .~ (a) To provide a study for the Vee ditches: $ 5,000 (b) To provide engineering plans and specifications: $14,000 3) Cost to televise the subdrain $ 0 (DSRSD has agreed to allow us to use their unit at no cost) 4) Stafftime to coordinate this work: $ 5,000 Total: $34,000 to $39,000 · Staffagrees that it would be beneficial as far as timing is concerned if the project could go to bid this fiscal year in order to allow additional time to complete the repair. Staff.will proceed with televising the subdrains, but if they are blocked, it will not be possible to get past the blockage.. Page 3 Via Facsimile and Mail March 8, 1996 Job No. 2090.000 BERLOGAR GEOTECHNICAL CONSULTANTS City of Dublin Attention: Public Works Department 100 Civic Plaza P.O. Box 2340 Dublin, California 94568 Subject: Expanded Scope of Services Dougherty Hills Park Landslides Dublin, California Gentlemen: We understand that you are considering expanding the scope of our investigation to include evaluation of the entire slope along the west side of Crossridge Drive in Dublin California. Our previous scope of services, outlined in a proposal dated January 31, 1996 included evaluation of two recent landslides on the southern portion of this slope. To evaluate the subject slope we anticipate that we would add an additional two days of backhoe exploration to examine subsurface conditions on the slope. Depending on the fmdings of the backhoe exploration, one or more borings also may be needed. Based on the findings of our investigation, we would evaluate the stability of the slope and provide recommendations for areas of slope stability concern that are identified. The findings of this additional investigation would be included in our report addressing the recently active landslides. We estimate the cost of the this additional investigation would be approximately $i0,000 to $15,000. We understand that our consulting service agreement with the City, dated February 5, 1996, would be amended if you decided to proceed with this additional investigation. Please give us a call ff you have any questions regarding our scope of services or fee estimate. Respectfully submitted, BERLOGAR GEOTECI-INICAL CONSULTANTS Principal Geologist RPS :pv SOIL ENGINEERS · ENGINEERING GEOLOGISTS · 5587 SUNOL BOULEVARD · PLEASANTON, CA 94566 o i5102, 484-0220" FAX: [510) 846-9645 THOMPSON . March 11, 1996 Municipal Engineering Surveying lqailroad Engineering Planning Mr. Lee Thompson City of Dublin 100 Civic Plaza Dublin, CA 94568 Subject: Crossridge Road Drainage Improvements Dear Lee: As requested, we have reviewed the referenced site and offer you the following proposal to perform engineering services related to the proposed remedial work. The hillside at the rear of the 36 lots along Crossridge Road consists of a cut slope at approximately 2 to 1 and conforms at the daylight line with the natural slope that is between 3 to 1 and 4 to 1. A vee ditch has been constructed along the cut slope, with a second, higher vee ditch along the northern one half of the area. Some sloughing has occurred above the lower vee ditch. We were advised that the lower vee ditch may have insufficient capacity to convey the hillside run off and two repair alternates were suggested. The first alternate was the construction of an additional "brow' vee ditch along the daylight line. This alternate would probably require a retaining wall in order to construct the necessary bench associated with the vee ditch. The second alternate involved the construction of a pipeline under the existing lower vee ditch with field inlets every I00 feet or so to reduce the flow in the vee ditch. A scaled back combination of the two alternates will probably prove to be the most efficient solution. Santina & Thompson, Inc. could provide a hydraulic and hydrology study of the area along with a field survey in order to provide design alternatives on a time and material basis with a maximum price of $5,000. The studies would also verify and\or establish the extend of the existing drainage problems. Construction contract documents, including detailed design drawings could also be prepared on a time and material basis with a maximum price of $14,000. This work would not include necessary geotechnical studies, slide repair work or construction management services. 1355 Willow Way, Suite 288 Concord, California 94520-5728 510-827-3200 Fax 510-687-1011 Should you have any questions or comments regarding this proposal or the area in general, please do not hesitate to contact me. Sincerely, Principal THOMPSON, , '' Cod,GO ~ oO?C 0I:- "7-~t6- .,3,"007'