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Home My WebLink AboutCT 73-49; CC and F PALOMAR AIPORT BUSINESS PARK UNIT 2; SOIL INVESTIGATION REPORT; 1976-11-01• Cabot Cabot & Forbes November 1, 1976 114-1 L, 1404 Page 2 grading operations performed in connection with the install ation of an underground conduit for Pacific Telephone & Telegraph Company. Ou'r predecessor fi rm provided earthwork observation and testing services in connection with the previous grading which was performed during the period of March 27 through~May 2, 1975. A summary of the earthwork observation and testing services was presented in a letter dated ,May 8, 1975. The ex{sting fill slope has been ero'ded to a depth of several feet in t,he vicinity of . Sta. 49+50 and there is also some erosion damage and indication of piping in the backfill materials around the existing PT&T vault at Sta. 37+97. The remciining eastern portion of the alignment is relatively flat and low-lying with a natural drainoge channel cross:- ing the alignment at about Sta. 37±. Surface vegetation consists Of a sparse to heavy growth of brush and weeds and a few trees. B. Subsurface A subsurface investigation was performed along the alignment of the proposed street on . March 25, 1975 in connection with an investigation for the previous PT&T improvements. Nine test pits were excavated to a maximum'depth of 10 feet. Copies of the test pit summary and laboratory test results from the previoussoil investigation report are attached. The materials encountered in the exploratory test pits consisted predominantly of loose to dense silty and clayey sands to the maximum depth explored of 10 feet. Loose, wet sandy alluvium was encountered to a depth of 5 feet in Test PHs 1 dnd 5 which were excavated in the bottoms of the two draws. Groundwater seepage was encountered at a depth of 4 feet in Test Pit 5 bu.t was not en- countered in any of the other test pits at the time of our investigation. It must b¢ noted, however, that fluctuations in the level of the groundwater may occur due to variations in rainfall, temperature, and other factors not evident at the time our measurements were made and reportedherei n. The attached summary sheet and relafeQ information depict subsurface conditions only at these specific locations and on the particular date 0f our subsurface exploration. Soil conditions at other locations may differ from conditions occurring at thes~ test pit locations. Also, the passage of time may result in a change in the soil conditions at these test pit locations due to environmental changes. Cabot Cabot & Forbes November 1, 1976 114-1L, 1404 Page 3 CONCLUSIONS AND RECOMMENDATIONS 1. Clearing and Stripping All areas to be graded should be cleared of designated trees, brush, rubble and debris, and stripped to sufficient depth to remove all surface vegetation and organic-laden topsoil. At the time of our field reconnaissance we estimated. that a stripping depth of 3 to 6 inches would be required. The actual stripping depths and extent of the areas requiring stripping should be determined in the field by our representative at the time of construction. Stripped materials should be disposed of as directed by the 9wner's representative. 2. Preparation for Filling After the site has been cleared, stripped and the necessary excavations m9de, the exposed soils in all areas to receive structural fill should be scarified to a depth of 6 inches, . moisture conditioned and compacted to the requirements for structural fill. Where sub- stantial thicknesses of loose soils are encountered, such asin the area where the natural drainpge channel crosses the aHgnment, the loose soils should be excavated down to fi rm ground and recompacted prior to placing overlying fill. Fills constructed on natural slopes having an inclination steeper than 5 horizontal to 1 vertical and fills constructed against the existing fill slopes should be keyed and benched into firm natural ground or well compacted fill below any loose surface soils as illustrated on Figure 1. The toe keys for fills placed in the draws should extend through the loose alluvial soils and at least 2 feet into fi.rm natural ground. The width of the toe keys and extent of removal of loose alluvial soils should be determined by our representative in the fi~ld at the time of construction. Alluvial soils removed from the excavations may be reused as fill or, if unsuitable for compaction because of excessive moisture, should be disposed of as di rected by the owner's representative. 3. Material for Fill An existing on-site soils below the stripped layer with an organic content of tess than 3 percent by volume are suitable for use as fill. Fill material should no.t, however, contain rocks or lumps over 6 inches in greatest dimension aod not more than 15 percent larger than 2.5 inches. . 4. Compaction All structural fill shou.ld be compacted to a minimum. degree of compaction of 90 percent as determined by ASTM Test Designation 01557-70. Fill material should be spread and Cabot Cabot & Forbes November 1, 1976 114-1L, 1404 Page 4 compacted in uniform horizontal lifts not exceeding 8 inches in uncompacted thicknes~. The upper 6 inches of subgrade soil in pavernent areas should be compacted to a minimum degree of compaction of 95 percent. 5. Trench Backfill Pipeline trenches should be backfilled with compacted fill. Backfill material should be placed in lift thicknesses appropriate to the type of compaction equipment utilized and compacted to a minimum degree of compaction of 85 percent by mechanical means. The upper portion of the backfill to a depfh equal to 1.5 times the. trench wid!p"but not less than 3 feet, should be compacted to a minimum degree of compaction of 90 percent. In addition, that portion of the trench backfill within the· pavement section should conform to the material and compaction requirements of the adjacent pavement section. 6. Slopes It is our opinion that the presently proposed maximum cut and fill .slope inclinations of· 1.5 (horizontal) to 1 (vertical) will be safe against mass instability. . . . Fill slopes should be constructed so las to assure that a minimum degree of compaction of 90 percent is attained to within 18 inches of the finished slope face and that a minimum degree of compaction of 85 percent is attained in the outer 18 inches. This may be accomplished by '"backrolUng" with a sheepsfoot roller or other suitable equipment in 5 to 8 foot vertical increments as the fill is raised. Placement of fill near the tops of slopes should be carried out in such a manner as to assure that foose, uncompacted sorts are not sloughed over the tops and allowed to accumulate on the slope face. The sandier portions of the on-site solIs will be moderately susceptible to erosion where exposed on slopes. Therefore, the project plans and specificafions should contain all necessary features and construction requi.rements to prevent erosion of the slopes both during and after construction. Slopes and other exposed ground surfaces should be appropriately planted with a proteG.tive ground cover. 7. Drainage Positive surface gradients should be provided across all graded areas. to assure' proper drainage and to prevent ponding of water. Cabot Cabot & Forbes November 1, 1976 114-1L, 1404 Page 5 8. Reinforced Concrete Box Culvert In the area where the natural drainage channel crosses the alignment it is proposed to construct a reinforced concrete box culvert under the roadway. We anticipate that there may be up to about 3 feet of loose alluvial soils in this area which will be unsuitable for support of the proposed culvert. However, it is anticipated that the roadway fill will be at least partially constnJcted through this area prior to construction of the box culvert and therefore the loose surface soils will have been removed and recompacted previously as recommended in Item 2. "Preparation fC?r Filling". In light oJ this anticipated sequence of construction, the box culvert will be suitably supported on well compacted HII materials. 9. Construction Observation Variations in soil conditions are p.ossible and may be encountered during construction •. In order to permit correlation between the preliminary soil data and the actual plans and specifications as original:ly contemplated, it is essential that we be retai.ned to perform. on-site review during the course of constructicm. All earthwork should be performed under the observation of our representative to assure proper site preparation, selection of satisfactory fill materials, as well as placement and· compaction of the fi lis. Suffi ci entnoti fication prior to earthwork operations is ·essential to make certai n that the work wi II be properly observed. If you have any questions, please call. Very truly yours, ROBERT PRATER ASSOCIATES ~~ Robert Prater, C. E. RP:rcs Attachments Copies: Addressee (2) Rick Engineering Company, Attn: Mr. Hank Worley (4) Existing ground surface Horizontal benches into firm ~atural ground and/or well co;"pacted fill Compac ted fiJ I Toe Key - . 2-ft. min. into firm natu~al ground and/orwell compacted fi II Toe Key -width to be determined by Soil Engineer but not less than 10 ft. surface soil Notes: 1) Fi"s to be keyed and benched as shown into existing ground where the existing slopes are steeper than 5 horizontal to 1 vertical. 2) Finished fill slope inclination to be no steeper than 1".5 horizontal to 1 vertical. SCHEMATIC ONLY NOT TO SCALE RECOMMENDATIONS FOR FILLING ROBERT PRATER ASSOCIATES Consul/lOg So". Foundo//on t Geologicol Engineers SLOP G GROUND AIRPORT BUSINESS PARK Carlsbad, California DATE November 1976 Figure 1 TABLE 1 -SUMMARY OF EXPLORATORY TEST PITS Exploratory Approximate Approximate Approximate Depth of Stratifi cation Test Pit Street Station Offset From Ground Surface Test Pit Interval No. (Feet) ct. (Feet) Elevation (Feet) (Feet) (Feet) Description of Material TP-1 48+90 . 80' South 176 9 0-3 SIL TY SAND, loose (SM) Water Content = 8% at 1 ft. 3-5 CLAYEY SAN D, loose (SC) Water Content = 30% at 4 ft. 5-9 CLAYEY SAND, medium dense (SC), TP-2 49+30 20' South 177 5 0-1 CLAYEY SAN D, loose (SC) e 1-10 CLAYEY SAND, medium dense (SC) TP-3 46+20 40' North 215. 10 0-1 SIL TY SAND, loose (SM) 1-10 CLAYEY SAND, medium dense to dense (SC)' . Water Content = 11% at 4 to 6 ft. TP-4 47+10 180' North 225 10 0-2 SILTY SAND, loose (SM) 2-10 . CLAYEY SAND, medium dense to dense (SC) TP-5 41+80 20' South 170 8 . 0-5 SILTY SAND, loose (SM) Water Content = 25% at 4 ft. 5-8· SIL TY SAND, medium dense (SM) TP-6 42+70 2PO' North 186 7 0-7 SILlY SAND,. medium dense (S. TP-7 38-i{)0 0 7 0-3 SILTY SAND, loose (SM) 3-7 SILTY SAND, medium dense (SM) TP-8 33+00 0 6 0-2 CLAYEY SAND., loos.e (SC) 2-6 CLAYEY SAND, medium dense (SC) TP-9 27+00 O· ·5 0-2 SIL TY SAND, medium dense (SM)(FILL) 2-5 CLAYEY SAND, medium dense (SC) NOTES.: . (1) Test Pits excavated on ·March 25; 1975. (2) Groundwater seepage was encountered at a depth of 4 fEiet in TP-5. No groundwater was . encountered in any of the other te'stpits at the. time'~f our investigation. ~ . '~ ,< .. . . UNIFIED SOIL CLASSIFICATION SYSTEM (ASTM D 422·72) U. S. STANDARD SIEVE SIZES 100 7 , 3 . 2 1 3/" \/2 11" " • 10 20 30 "0 SO 60 10 100 200 32J " z 90 10 70 : 60 < Go I-~ 50 U II: ~ 40 30 20 10 o 100 50 10.0 5.0 1.0 0.5 0.1 .os .01 .005 PARTICLE SIZE IN MILLIMETERS GRAVEL SAND COBBLES ...... ---"""r'----f----.r------r------t SILT AND CLAY COARSE FINE COARSE MEDIUM FINE Test UNIFIED KEY Pft . , SAMPLE ELEV. SOIL SYMBOL DEPTH (feet) CLASSIFICATION SAMPLE DESCRIPTION No. (feet) SYMBOL 0 0 TP-3 4-6 210 SC CLAYEY SAND, fine grained {approx lDwney-Haldueer AssDEiates GRADATION TEST DATA UNIT 2 -IMPROVEMENTS FOR PT&T Carlsbad, California Foundallon 1 Soli 1 Geological Englneera S 114-10 PROJECT NO. DATE 1--------1-----,.,.-----1 FIGURE 1 March 1975 ·0 III 20 30 'D 40 ~ < I-III 50 II: I-Z 60 :'l 10 ·10 100 .001 II: III a.. · , , < " >SA,MPLE DEPTH SPECIFIC LIQUID PlASTIC NO. 1FT.) SAMPLE DESCRIPTION GRAVITY L\~)ol INDEX TP-3 4-6 CLAYEY SAND, fine grained ------ ;-zero Air Voids Curve Specific Gravily = 2.60 125 ~~ \ 120 \ \ -I' 0 \ a. ~ ~r\. >-IJ~ " I-115 \ -(/) I ~. z w ~ , .\ Q V 1,\ >-I) ~, a:: Q I~ 110 [\ , " \ 105 ~ 0 5 10 15 20 25 MOISTURE CONTENT % OPTIMUM WATER CONTENT % 13.8 MAXIMUM DRY DENSITY I pef 116.5 TEST DESI-GNATION ASTM D1557-70 COMPACTION TEST RESULTS LOWNEY· KALDVEER ASSOCIATES Foundation / Soil/Geological Enginee .. UNIT 2 -IMPROVEMENTS FOR PT&T Carlsbad, California PROJECT NO. I DATE DRAWING NO. PALO ALTO. CALIFORNIA Sl14-1D I March 1975 2 ,ct