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HomeMy WebLinkAboutGeotechnical Recs CIPCP .' ~ f:!7 A Wholly Owned Subsidiary of The Converse Professional Group Converse Consultants Inland Empire G;!h .?lI1niuerSa~ Celebrating 50 Years of Dedication in Engineering and Environmental Sciences May 1 6. 1996 Mr. Jim Delhamer President - California Region Newland Associates 9404 Genesee Avenue. Ste. 230 La Jolla. CA 92307 Subject: GEOTECHNICAL RECOMMENDATIONS FOR CAST-IN-PLACE CONCRETE PIPE Eastern and Southwestern Portion of "The Meadows" City of Temecula, California CCIE Project No. 96-81-420-01 At the request of Mr. David Shen with Keith Company-Inland Empire, Inc., Converse Consultants Inland Empire (Converse) has prepared this letterlreport to present our evaluations and recommendations for design and construction of cast-in-place (CIP) concrete pipe within the subject project site. The feasibility evaluation presented herein was based on our recently completed preliminary soils investigation for the subject project. The results of the investigation were presented in the following report: . Preliminary Geotechnical Investigation, Eastern and Southwestern Portion of "The Meadows," Temecula, California, dated April 26. 1996. CCIE Project No. 96-81-420-01), prepared for Newland Associates This letterlreport should be considered as an addendum to the above-referenced report. At the time of the preparation of this report, information regarding size, depth and alignment of the CIP concrete pipe was not available. It is our understanding that the proposed C!P concrete pipes will be used as storm drains. Based on our previous experience, it is anticipated that such pipes will range in size from 30 to 84 inches. in diameter. The invert elevation of the. pipes will vary from seven to 20 feet below finish grade. The storm drains will be constructed along proposed roadways. Site preparation for the project will involve cut and fill. The CIP concrete pipes are anticipated to be cast in open-cut trenches excavated within cut and fill areas. Soils to the anticipated storm drain invert level in cut areas within the northern highland (\1""llCd"" ... R.',"-,<k<l P"PCI Converse Consultants Inland Empire 10391 Corporate Drive Redlands, Califomia 92374 Telephone: (909) 796-0544 Facsimile: (909) 796-7675 \ .' area of the project site mainly comprise Pauba Formation material. The Pauba Formation at the invert level should be anticipated to vary and may be composed of dense, nonexpansive sandstone to soft. expansive claystone. The depth of the storm drain invert within the Pauba Valley portion of the site is anticipated to be less than 15 feet from the existing ground surface. Native soils within this depth comprise mainly loose to medium-dense sand, silty sand or clayey sands with lenses of soft, sandy or clayey silt. The fill material at storm drain invert level is anticipated to comprise Pauba Formation material placed and compacted in accordance with the recommendations presented in the above-referenced project soils report. The feasibility of constructing cast-in-place concrete pipe is discussed with respect to the following issues: Foundation Soils at the foundation level should provide full. firm and uniform support throughout continuous sections of the pipe. The "trench form" is defined as that portion of the trench which will serve as the outer form for at least the bottom 120 degrees of the pipe, as is shown in Figure No.1, Typical Section for Cast-in-Place Concrete Pipe. Soils over the trench form provide support to the pipe and should be firm and uniform. The majority of the native soils within the northern highland area and the compacted fill at the anticipated trench form level should be capable of providing such support. We recommend that the trenches for the CIP pipes placed in native soils within the Pauba Valley portion of the area be overexcavated to a depth of at least three (3) feet below the pipe invert. The overexcavation should be backfilled with compacted soils to form a stable trench form. Thin layers of soft and/or loose soils encountered over the trench form within the highland area level should be removed and replaced with compacted fill. Recommendations regarding expansive soils encountered at the foundation level are provided in the following sections. To reduce the potential of pipe distress due to differential settlement, transition sections of pipes from cut to fill and vice versa may should be thickened or retrofitted. Settlement consideration presented in the above-referenced report for the Pauba Valley portion of the site should be considered in the design and construction of the CIP concrete pipe within this area. [il 96-81-420,01 Converse Consultants Inland Empire J:\JOBFILE\ 1996\96-420\96-420- 1 .CIP Z- Exoansive Soils In general, the site soils have a low expansive potential. However. randomly distributed clayey soils with moderate to high expansive potential may be encountered. For the fill areas, clayey soils should be blended during grading with on-site granular soils prior to placement as compacted fill. Storm drain alignment through the compacted fill will not require special consideration for expansive soils. In cut areas, thin layers of soft and expansive Pauba Formation comprising mainly claystone, if encountered within the trench form, should be removed and replaced with compacted. nonexpansive, predominantly granular soils. If thick layers of such soft and expansive claystone are encountered within the trench form, we recommend that three (3) feet of soil below the invert elevation be removed and replaced with granular backfill. The bottom of such overexcavations should be thoroughly moistened by ponding to completely expand the soils prior to backfilling. Native soils at the trench form level comprising expansive clayey sand should also be thoroughly moistened by ponding. The moisture should be maintained until the concrete is poured. Localized zones of overly saturated soils may be encountered at the trench form level. Such saturated soils should be removed to a depth of at least three (3) feet below pipe invert. Gravel or crushed rocks. approved by the project soils consultant. may be placed to stabilize the bottom of such overexcavation prior to backfilling with compacted soil. Trench Stabilitv Recommendations regarding stability of temporary sloped trench excavations are presented in the above-referenced report. Cast-in-place construction may require cuts to remain open for long periods. Therefore. there is a potential for ravelling or erosion of cuts due to moisture variations. Surfaces exposed in slope excavations should be kept moist but not saturated to retard ravelling and sloughing during construction. Adequate provisions should be made to protect the slopes from erosion during periods of rainfall. Trenching should comply with all OSHA and local government requirements. No surcharge load should be permitted within at least five (5) feet of the top of slope or within a 1: 1 (horizontal: vertical) line drawn upward from the toe of the slope. [I 96,81-420-01 Converse Consultants Inland Empire J:\JOBFILE\ 1 996\96-420\96-420-'.CIP 2::> Trench Form Cleanuo The trench form should be neatly excavated with vertical sides and a semi-circular bottom. The width of the trench form should equal the diameter of the pipe. This will allow the vertical walls and the trench form bottom to serve as the outside form for concrete placement. The side walls above the top of the pipe may be sloped as recommended above. All debris, foreign objects or material from slide wall sloughing should be removed prior to concrete placement. All trench soils in the trench form that will be coming in contact with concrete should be moistened prior to concrete placement so that no water is drawn from the freshly placed concrete. Groundwater Groundwater was encountered in the exploratory borings drilled within the Pauba Valley portion of the site. Depth to groundwater is generally on the order of 20 feet below existing ground surface. As stated above, the depth of storm drain invert within this area is anticipated to be less than 15 feet from the existing ground surface. Perched water may be encountered locally in other areas. Perched water may result in overly saturated soil conditions. Such saturated soils should be removed in accordance with the recommendations presented above. Feasibilitv Our evaluation and analyses of subsurface conditions for the project site indicate that construction of cast-in-place concrete pipe is feasible, provided that the recommendations included in this letter/report are considered during design and construction. LIMITATIONS The general recommendations provided in this letter/report are based on our preliminary soils investigation. Site grading will result in substantial changes in the soils conditions. Additional consultation regarding design and construction of CIP concrete pipes may be prudent once the information on pipe alignment. diameter and invert depth are available and the site grading is completed. This letter was prepared EI 96-81 -420-01 Converse Consultants Inland Empire J:\JOBFILE\ 1996\96-420\96-420-1 .CIP L\ . .' in accordance with generally accepted professional engineering principles and practice in effect in Southern California at this time. We make no other warranty. either express or implied. Thank you for this opportunity to be of service. If you should have any questions, or if we can be of additional service. please do not hesitate to contact the undersigned. Respectfully submitted. CONVERSE CONSULTANTS INLAND EMPIRE ;/2/~. ~~ (j--- Mohammed S. Islam, Ph.D.. P. E. Project Engineer ~. ~ ~ Quazi S. E. Hashmi, Ph.D., P. E. Senior Vice President/Principal Engineer Encl.: Figure No.1, Typica/ Section for Cast-in-P/ace Concrete Pipe Dist.: 2/ Addressee 3/ The Keith Company-Inland Empire, Inc. MSI/QSH/dmd Cil 96-81-420-01 Converse Consultants Inland Empire J:\JOBFILE\ 1 996\96-420\96-420-1.CIP 5' .. ,.. ~ " e ~ ;; ~ :c , " 2 " . > o a " -< Typical Section For Cast-In-Place Concrete Pipe Eastern and Southwestern Portions of the Meadows City of Temecula. California For: Newland ASSociates @ Converse Consultants Inland Empire Project No. 96-81-420-01 Figure! No. 1 ~