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HomeMy WebLinkAbout; La Costa Valley Unit 4; Soils Report Revised; 1967-08-21PHILIP HENKlNG BENTON PIESIDENI ClYlL ENGIHELII BENTON ENGINEERING. INC. *PPL,ED SOlL MECH.AN,CS - FO”ND*TIOH* 5zl.1 EL CAJON BOULEYARD SAN DIEGO. CALIFORNI* 82115 December 20, 1966 Revised August 2 1, 1967 Paradise Homes, inc. - Route 1, Box 2550 Encinitas, California - Attention: Mr. Irv Roston Subject: Project No. 66-3-3 1 D Recommendations for footings - &~~ _ Gentlemen: It is concluded from correlating the laboratory test results presented with our “Final Report on Compacted Filled Ground, la Costa Unit No. 4, San Diego County, California”dated December ‘16, 1966, with visual observations made during grcding, that the soil conditions within the upper 3 feet on the following lots fall into an expansive classification. - Lot Nos. Lot Nos. 154 184 170 188 171 189 Lot Nos. 199 to 206, inclusive 217 to 221, inclusive z/1- 172 176 177 ._ 180 197 - 181 For this expansive condition, it is recommended that special foundation design and precou- tions be used to minimize the possible differential movements in these soils due to moisture - ohange. It is concluded from our past experience in areas where soils fall into this class- .ification that continuous wall footings should be used throughout and that these should be - placed at greater than minimum depths and reinforced to resist differential movements. Also, if concrete slabs are to be placed on the “expansive ” soi Is, it is recommended moisture tests be taken 4 to 5 weeks prior to pouring concrete to verify ,thot 80 percent saturation of the layers exist, to a depth of 3 feet. If less moisture exists, then presaturation would be recom- mended. The reason for this is that concrete slabs are relatively lightly loaded in comparison to continuous wall footings supporting raised wood floors and they are sujject to much greater upward movement if the “expansive” clays go from a relatively dry field condition to near - - - - - - - - - - - - i i : Ryject No. 66-3-31D L,a Costa Valley Unit No. 4 -2- saturation than are the wall footings that are placed atqreater depths below the finished ground surface. Numerous tests ond observations made to date indicate that the “expansive” soils tend to increase in moisture content with time, once these are covered and lawn water- ing, etc. takes place around the perimeter of the foundation. Houses constructed in the spring when the soils hove natural presaturation have been subjected to far less differential movement than houses constructed on air dry soi Is without presaturation in the fall of the year. The following recommendations are made for two types of foundation construction: I . . Type of Construction of Raised Wood Floors on Continuous Wail Foundations. 1. 2. 3:. 4. 5. Use continuous wall footings throughout and place ot o minimum depth of two feet. Reinforce with one #S steel bar placed 3 inches above the bottom of footing and one f.5 steel bar placed 1 l/2 inches below the top of stem wall of the footing. It is recommended that the steel reinforcement of all interior and exterior continuous wall footings be lapped 48 diameters and that the reinforcement of the interior footings be carried into the exterior walls sufficient distance to develop fu I I s neng th . Construct crawl holes with continuous reinforcement as shown on page 17 of the “Minimum Property Requirements for properties of one or two Living Unik, Located in the Southern California District” by the Federal Housing Adminis- trafion Revised May 1952 or by some equivalent design. For concrete slabs on ground in the garages, it is recommended that a 4 inch _.s,_--^_ thickness of sand be placed beneath the concrete slab and that the concrete slabs be separated by 3/S inch thickness of construction joint material from the exterior wall footings. The slabs should also be reinforced with 6” - 6” by 810 - #IO wire mesh.. II. of Concrete Slab Floors on Ground Between Continuous Walli _.,- ,,,. ,~(,-_‘;,._;.,e II ..-. -.- . . . 1. f Use continuouswall footings throughout and place at a minimum depth of two eet. -I 2. .kl?force with one~,2ikdb~p_laced at th.r.e~~)..,~~~~~~~~~~-~~!~~~..~~, LQt. - the continuous wall footings and one a _-. ,,. IK5’sTeeI bar placed at one and one-half (1 l/2) inches below the top of s& wall of the footing, Hh&~ “!7 i ,.- _L .._ “_. 3. It is recommended that the steel reinforcement of oil interior and exterior continuous wall footirls be lapped 48 diameters and that the interior reinforce- ment be carried into the exterior walls sufficient distance to develop full strength, BENTON ENaINEERrNG. INC. -* \ eoject No. 66-3-31 D -3- Cc Costa Valley Unit No. 4 December 20, 1966 - - - - - - - 0 .- 4. For concrete slabs on ground for this condition, it is recommended that field ,’ moisture checks be made to three feet below finished grade to verify 80 per- -‘-’ .~ - --..-- . . .._. cent saturation. lf80 percent saturation is not present, then it is recommended that water be added by panding, “rain birds” or any suitable method to increase moisture as required. After the presaturation moisture content is achieved with- in the upper fhree feet, the soil may be permitted to surface dry so that equip- ment may work on it .and then a 4 inch sand layer should be deposited within one week. The reinforcing with 6” - 6” by #lo - #lo wire mesh and waterproof- ._., ing may then cnstalled to seal the presoturared soi Is under the concrete slabs. t)ACl, -pi :, 5. For concrete slabs on ground in the garages, it is recommeilded that a 4 inch thickness of sand be placed beneath the concrete slab and that the concrete slats be separated by S/8 inch thickness of construction joint materi,al from ,ee exterior &f?pti.ng~. lhe slak should also be reinforced with 6” - 6” by #lo - #10 wire mesh. i r ‘r f .i’, .>.., ‘;* If you jhould have any questions regarding the above, or if you should desire additional information, please contact me. Very truly yours, BENTON ENGINEERING, INC. BY enton, Civil Engineer (25) Addressee BENTON ENGINEERINO. INC.