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HomeMy WebLinkAbout; ; Design of Squires Dam and Appurtenant Structures for Carlsbad Municipal Water District; 1961-02-16C ... ... ... ... ,.. 11111 ,. .. .. ... "" .. "" ' .. ... ... ... .. ... ; ... ,.. .. .. .. .. 11111 ,.. .. C DESIGN OF SQUIRES DAM AND APPURTEMANT STRUCTURES FOR CARLSBAD MUNICIPAL WATER DISTRICT San Diego County, California FEBRUARY, 1961 BOARD OF DIRECTORS Allan o. Kelly, President Mac Carnohan Wesley F. Greek Richard R. Coe Fred W. Maerkle "' .. "' 1111 .. lilt "' .. .. .. .. .. .. 11111 Ill" ... .. I .. .. .. .. 11111 "" 1 .. C "" C TABLE OF Letter of Transmittal SECTION I -General Information A -Introduction B -Design Conclusions C -General Site Conditions D -Hydrology E -Previous Studies SECTION II -Dam Design A -Foundation 1. Foundation Exploration 2. Foundation Conditions CONTENTS 3, Foundation Stripping and Preparation B 4. Earthquake Potential 5, Foundation Design Properties -Embankment Materials 1. Construction Materials Exploration 2. Construction Material Sources 3, Embankment Design Properties 4. Design Criteria 5, Embankment Layout & Design 6, Seepage Analysis 7, Stability Analysis 8, Piezometers and Settlement Markers (Design) 1 3 3 4 5 6 9 10 11 12 12 14 17 19 20 22 23 26 C "' ... "' 1111 "' 1111 ... 1111 Ill 1111 Ill .. ,.. ... ... ... Ill .. ... .. ... .. ... ,.. ... C -Freeboard, Settlement and Camber 1. Freeboard Design 2. Settlement Analysis 3. Camber D -Spillway 1. Location 2. Capacity 3. Design E -Inlet-Outlet Pipe 1. Location 2. Construction Appendix Figure 1 Plan and Location Map Figure 2 Embankment Layout and Details Figure 3 Geologic Profile and Drill Hole Logs Figure 4 Dam Embankment Seepage Analyses Figure 5 Dam Embankment Stability Analysis 27 27 28 28 28 29 29 29 ---------.. -.. ---.. ----------- --------.. .. ARCHITECTS • ENGINEERS 4525 MISSION GORGE PLACE • SAN DIEGO 20, CALIFORNIA • ATWATER 3-5481 February 16, 1961 Board of Directors Carlsbad Municipal Water District P. 0. Box 278 Carlsbad, California Gentlemen: Presented herewith is our report "Design of Squires Dam and Appur- tenant Structures, San Diego County, California" outlining the basis of design for your proposed Squires Dam . The purpose of this report is to give you in some detail our design assumptions and considerations in order that you may be informed re- garding the design characteristics of this structure. This report will be most useful to you in presenting your plans to various State of California agencies for preliminary approval of your proposed con- struction project. Upon receipt of such preliminary approvals, we will be in a position to proceed immediately with the final construc- tion plans and specifications for the project. We have been pleased to perform this portion of the work for you and look forward to an early completion of planning followed by immediate construction. LAC:bhb Respectfully submitted, BOYLE ENGINEER1N· =/·· /) ,, ~< (__;&-,;.;,, L, A. Clayt Project Design W, A, WAHLER AND ASSOCIATES (,,il.7:'j (A.... le' t,_' f., J W. A. Wahler Earth Dam Design ft&Aaoa.c:..1ANA.L ENGINEERING AHO C C C "' .. .. .. C C ,. .. C C C A -INTRODUCTION DESIGN OF SQUIRES DAM AND APPURTENANT STRUCTURES SAN DIEGO COUNTY, CALIFORNIA I. GENERAL The purpose of this report is to present and substantiate the design of the Squires Dam and Appurtenant Structures with special reference to those portions of the design which have a bearing on the public safety of the project. Those features of the project which do not have a bearing on the safety of the dam, spillway, or outlet works are not covered in detail in this report . The proposed Squires Dam project will serve as a regulating and short-term emergency supply reservoir for the Carlsbad Municipal Water District, Carlsbad, California. The water will be supplied by the Metropolitan Water District of Southern California through the San Diego Aqueduct. The site was chosen near Mt. Hinton in San Diego County for its location relative to the District's distribution system and the San Diego Aqueduct, its elevation, and its very small contrib- utary watershed. Since the reservoir drainage basin is only about 60 acres, very little water will originate in this area, thereby minimizing the spillway requirements and water contamination problems. The principal features of this project are the reservoir formed by an earthfill dam across Squires Canyon, a small overflow-type spill- way, an outlet works through the base of the dam, and the feeder pipe- line with chlorination station. The spillway is located in a small ( ( ( C C C "" Ill "" Ill !"' .. "" .. C C C C saddle in the right abutment and the outlet works are located in the bottom of the canyon near the right abutment. The feeder pipe- line is 27 inches in diameter and one mile long, connecting the res- ervoir with the Carlsbad Municipal Water District distribution system near Palomar Airport. The maximum pool water surface is about 14 acres at elevation 505, The capacity of the reservoir at that level is about 450 acre feet. All except 10 acre feet of storage is located above the outlet works intake level. The 10 acre feet of storage below the outlet level are provided for silt storage and can be evacuated as required by portable pumps. The exact surface area and capacity of the res- ervoir will depend on the amount of earth material excavation from that area for construction of the dam. The bulk of the embankment fill materials will be obtained from within the reservoir area. The drain sand and probably the riprap will have to be imported from beyond the reservoir area. Supple- mental core and shell earth fill materials are available at the head of the canyon just above the proposed reservoir water level if they are required. Since the stream in Squires Canyon only flows during and shortly after storms, minimal diversion facilities are all that will be required. Construction of this project is proposed for Summer 1961. The design of the Squires Project was by Boyle Engineering, 4525 Mission Gorge Place, San Diego, California. The earthfill dam design was by W. A. Wahler and Associates, 3850 Middlefield Road, Palo Alto, 2 C C C ,.. ' C ,.. ' ~ ,.. ,.. ,.. ,.. ,.. i ~ California. The field exploration and laboratory testing work was by Benton Engineering, Inc., 4342 Fairmount Avenue, San Diego, California. The geological investigation was by Professor Baylor Brooks, San Diego State College, San Diego, California. The project design was prepared for the Carlsbad Municipal Water District of Carlsbad, California. B -DESIGN CONCLUSIONS The basic concept of the design of the Squires Dam, spillway and outlet works was to provide a structure that is adequate beyond any doubt with regard to public safety, and to apply sound engineering and economical Pfincipals throughout the design of the project to make it economical to build, operate and to maintain. On the basis of the design studies, investigations, and data pre- sented herein it is concluded that a safe and economical rolled earth fill type dam can be built at the proposed site using earth materials that are available in the vicinity of the site or within economical haul distances. C -GENERAL SITE CONDITIONS The proposed dam site is located in a well defined canyon adJa- centto and North of Mt. Hinton. The canyon is very short, the drain- age area being limited to about 60 acres. The stream which eroded the canyon is intermittent -having very little flow except for occasional storm periods when the majority of the annual runoff occurs. The general country-side in the area is rolling, varying 3 "" ... "" .. "" 1111 .. Ill' .. .. .. "" .. '"' .. .. "" ... "" .. .. ... .. "" ... "" ... from sea level to about 600 feet in elevation. The site is located just east of the coastal plain underlain by marine sediments and sedimentary rocks, The dam site is in an area underlain by the crystalline igneous rocks which form the local basement complex. This rock classifies as a quartz diorite but is locally referred to as granite. The surface soils are "slope wash" deposits of trans- ported disintegrated quartz diorite material from higher up on the slopes, This material is relatively shallow and overlies in-place weathered and disintegrated quartz diorite which is locally weather- ed to a considerable depth. The rock is extensively jointed, the joint frequency being one of the controlling depth and extent of weathering factors, Major faults are not believed to be present in the immediate dam site area. No unusual or unexpected geological or topographical conditions were found in the area of the dam site. D -HYDROLOGY Intensity duration curves developed for the years of record 1897 to 1941 from San Diego,California,Weather Bureau Records indicate one hundred year storms on the order of the following: Duration in Minutes 10 30 60 12 hour 24 hour Rainfall Intensity Inches Per Hour 3,5 2 1.3 0.3 0,2 The above rainfall intensities would indicate the maximum runoffs in -... -1111 .. .. '"" ... ... ... ... ... '"" .. '"" .. -.. ---11111 .. .. ... -... .. .. ... .. ... - this area on the order of 60 cubic feet per second if reservoir storage is neglected. Taking reservoir storage into account, how- ever, a storm yielding one-inch runoff in one hour would give a re- sulting rise in water level of only 4 inches. This probable rise in water level will be accounted for in the spillway design, E -PREVIOUS STUDIES The project design presented herein is based in part on prelim- inary studies prepared by Boyle Engineering to locate, size, and de- termine the feasibility of the Squires Reservoir. These studies were augmented by specialized studies prepared by consultants to Boyle Engineering and to the Carlsbad Municipal Water District. The most important of these studies are: 1. BOYLE PRELIMINARY REPORTS 2. "GEOLOGICAL CONDITIONS AT SQUIRES DAM SITE, CARLSBAD, CALIFORNIA, 11 July 1960, by Mr. Baylor Brooks, San Diego State College, San Diego, California. 3. "SOIL INVESTIGATION -PROPOSED DAM SITE ADJACENT TO MT. HINTON, SAN DIEGO COUNTY, CALIFORNIA," August 1960, by Benton Engineering, Inc., San Diego, California. 4. "PRELIMINARY DAM DESIGN REPORT," September 1960, Wahler & Associates, Palo Alto, California . 5 .. 11111 .. .. "' .. "' .. .. 11111 .. II .. .. C ,.. 1111, "" 11111 .. .. .. .. .. .. .. .. ... .. "" 11111 II. DAM DESIGN A -FOUNDATION 1. Foundation Exploration. The foundation exploration program was carried out during the sUllllner of 1960. The surface indications at the site were studied by engineering geologists and soils and foundation engineers. The subsurface conditions at the site were investigated by use of diamond drill and bucket auger holes, and by bulldozer trenches . Three deep rotary drill holes were put down somewhat downstream from the present axis of the dam. Continuous NX size diamond cores were obtained of all competent rock materials encountered. Hole lA was extended the last 7,5 feet with a BX size hole, A SUllllnary of the drill hole depth information is presented below: Diamond Core Holes Percent Total Depth Recovery Hole No. Location Depth to Rock in Rock lA Midslope -left abutment* 781 581 83% 2A Midslope -right abutment 80 1 59' 69% 3A Valley bottom 74• 59' 72% *looking downstream The rock encountered in these holes was a crystalline igneous quartz diorite locally referred to as granite. The rock varied from a hard fresh material in the bottom reaches of the holes to a weathered mate- rial with soil like properties. The rock is overlain by insitu weathered 6 C C .. .. - .. I ~ .. - .. .. .. quartz diorite, The degree of weathering of this material varies only indirectly with depth because the weathering has progressed faster along old joint and fracture planes than it has through the blocks of material in between, This results in the formation of in- situ boulders in a matrix of in-place weathered rock of igneous origin, The insitu weathered bedrock is overlain on the surface by a few feet of slope wash debris and a minor amount of stream alluvium in the valley. The bedrock outcrops exhibit a well developed joint pattern. The same general joint pattern is evident in the trench cuts into insitu disintegrated or weathered bedrock, The nature of the bedrock and weathered bedrock materials is such that it has a relatively low pri- mary permeability, Seepage through the joints and cracks in the less weathered rock, however, was considered to be a distinct possibility, Water pressure tests were made in the diamond drill holes to evaluate this problem. The results of these tests are not all-conclusive be- cause water was observed flowing from the top of the hole in some of the tests indicating that water was by-passing the hole packers. The results of the tests which were probably valid along with the observed nature of the rock in the outcrops and cuts indicate that the weathered material is relatively impermeable, or will be when wetted, and that the fresher rocks could exhibit leakage through the joints and cracks. The results of the valid water pressure tests are presented below . 7 .. 1111 .. 1111 .. ... .. ... .. .. .. ... .. ... .. .. ... .. ... .. ... .. .. ... .. ... WATER PRESSURE TEST DATA Depth Hole Interval water* Time In-Coefficient of No . Tested Loss (cf) terval (min) Permeability (ft/yr) 2A 49,5 1 to 80 1 1.0 4 21 2A 19,5 l to 80 1 4.o 4 52 3A 611 to 74 1 no water loss Impermeable 3A 50,5 1 to 741 no water loss Impermeable 3A 491 to 741 no water loss Impermeable 3A 19,5 l to 74 1 2.6 7 20 *Applied pressure= 50 psi. The near surface soils in the dam foundation were explored by the use of bucket auger holes and bulldozer trenches. Four 24-inch diam- eter bucket auger holes were put down in the valley bottom to depths ranging from 4-1/2 to 6-1/2 feet. Undisturbed and disturbed samples were taken of the representative materials encountered in the holes . These samples were tested in the laboratory to define the state and the physical and mechanical properties of the materials encountered . A summary of these test results is presented below: Bucket Auger Holes -11 C" Series Coefficient of Hole No, ¢ Permeability lC 0.1 ft/yr 2c* 30-1/2° 25 ft/yr Max. Density 127 .1 pcf Opt. Moisture 9% Plasticity Non plastic Non plastic *Tests were performed on samples recompacted at optimum moisture con- tent to 90% of the maximum density reported above . The test procedures used are described in the section of this report on embankment design values . 8 .. .. - .. .. - .. ' • .. .. .. ... .. ... .. ... ... ... The bulldozer trenches were 12 to 16 feet wide, and 3 to 12 feet deep. They afford an excellent opportunity for inspection and appraisal of the dam foundation conditions in-place. Approximately 500 lineal feet of trench within the dam contact area (including access road cut available for this purpose) were excavated in the right abutment, 500 lineal feet in the left abutment, and 700 lineal feet in the valley bottom. The location of the drill holes and trenches is presented on Fig- ure 1 and drill hole logs are presented on Figure 3. An interpreted longitudinal cross section of the Squires Canyon Valley, along the axis of the dam is also presented on this figure. 2. Foundation Conditions. The dam site foundation and abutments consist of in-place weathered and otherwise decomposed quartz diorite. This is locally covered by a relatively thin layer of slope wash or debris consisting of redeposited material of the same general type that it overlays, although it is slightly more weathered. The slope wash or debris originates only a short distance up-hill from where it presently lies. Relatively sound but badly fractured bedrock occurs in spotty outcrops on the right abutment above elevation 420, There is very little alluvial material in the creek bed due to the relatively short distance to the creek head. The insitu weathered quartz diorite will provide a relatively strong and incompressible foundation for the proposed dam. The primary permeability of the foundation material is quite low and the only permeability problems 9 ... 11111 1111 ... 1111 11111 .. 11111 ... ... ... ... .. ... .. .. 11111 ... .. ... .. ... ... ... ... ... .. ,.. 11111 of any consequence are the secondary or joint pattern seepage planes • The altitude of the joint planes is nearly vertical so they are not serious from a structural point of view, only as potential seepage paths . 3, Foundation Stripping and Preparation. The embankment foundation preparation will consist of stripping all organic material and all low density or low strength material from beneath the entire dam contact area and of excavating all alluvial or relatively permeable material from beneath the impervious core contact area. The stripping will in- clude the removal of a minimum of two feet of material from beneath the entire contact area to insure the removal of most of the brush root zones and other undesirable material, The impervious contact excava- tion will be made a minimum of 5 feet into in-place weathered bedrock to insure that all deep roots and animal boroughs have been inter- cepted. A cut-off trench having a bottom width of 20 feet will be excavated beneath the impervious core contact to an average depth of about 15 feet in order to minimize seepage losses through the founda- tion and abutments. Where the impervious core cut-off trench contact is with relatively fresh but fractured rock fragments, they should be removed when they are loose, When a firm base has been prepared, the area will be air and water jet cleaned and all joints and cracks will be concrete packed or slush grouted as required. These areas will be pressure grouted when deemed necessary by visual inspection of the area prepared for placement of impervious core material, If required, pressure 10 .. .. .. ' ... .. .. .. .. .. 1111 .. .. "" 1111 .. .. "'" "'" I,,, "" ii. -... .. .. .. -.. 1111 -... .. .. grouting will follow the surface clean up but precede slush grouting . Foundation pressure grouting will be ineffective in those areas over- lain by deep weathered bedrock and will not be required in those areas, Slush grouting will also not be required in these areas. The first three feet of impervious material placed in the impervious core con- tact area will be the most plastic material available and it will be placed at or slightly above the optimum moisture content of the mate- rial. This layer is designed to be extruded by embankment pressure into any small cracks in the weathered bedrock material that is other- wise not filled by the foundation preparation and thereby prevents seepage and subsequent piping along the core contact . 4. Earthquake Potential, The Squires Dam will be constructed in a geologically stable canyon, and the embankment will contact insitu weathered bedrock along all of its base. The abutments are sound and all of the alluvial valley fill will be stripped from beneath the embankment fill, Spontaneous liquefaction of foundation materials due to seismic shock is impossible at this site. The probable maximum earthquake intensity to be expected in the vicinity of the dam site has been determined on the basis of the seismic regionalization studies prepared by Professor C. F, Richter of the Cal- ifornia Institute of Technology, The results of these studies were published in his paper "Seismic Regionalization, 11 California Institute of Technology, Division of Geological Sciences, Contribution No. 897, December 1958, These studies were made to provide the maximum probable 11 ... .. ... .. ... -.. -11111 -.. ... 1111 ... .. ,. I ... ... I,,. ,. .. ... ... .. ... .. ---.. ... .. ... seismic intensity to be expected for long range, long term projects such as dam structures and are not short term insurance types of estimates. Therefore, the seismic recommendations made below are believed to be conservative. The Squires Dam site is situated on the Southern California batholith. Professor Richter classifies this area as having a maxi- mum probable intensity of VI (MM). Where local alluvium or weak sur- face soils are encountered he recommends consideration of an intensity of VII (MM). When expressed in terms of the maximum probable accelera- tion, these intensities are expected to develop forces equivalent to 0.03g and 0,07g respectively. Although the consequences of a failure of the Squires Dam are small at present it was considered to be pru- dent to design the embankment on the basis of a seismic acceleration factor of O.lOg and to require a minimum factor of safety equal to 1.10 for the arc having the minimum factor of safety computed for gravity and seepage forces only, 5, Foundation Design Properties. All of the foundation materials which are less strong, more compressible, or more permeable than the adjacent fill zone material will be removed as part of the foundation and abutment preparation, The insitu weathered bedrock at the dam site is stronger and less compressible than the. same material in a compacted fill state. B -EMBANKMENT MATERIALS 1. Construction Materials Exploration, The construction materials 12 ... 11111 ... ... 11111 -• .. 11111 --... .. ... ... ... ... .. ... .. ... .. ... ... ... ... ... .. ... ... ... ... ... .. exploration program was carried out concurrently with the foundation exploration program during the summer of 1960. Due to the economic importance of obtaining as much material from the reservoir area as practical, exploration for impervious and shell zone materials was confined to the reservoir area and the area immediately adjacent to the upstream end of the reservoir. The exploration program for con- struction materials consisted of a careful surface reconnaissance and two series of bucket auger holes as well as a road cut excavated through the reservoir area . The reconnaissance of the area indicated that there was probably enough coarse grained insitu weathered bedrock economically available within the reservoir limits to construct the shells of the embankment. There is also a possibility that a sufficient amount of finer grained insitu weathered bedrock is economically available within the reservoir area for the constructi,on of the impervious core zone. In order to in- sure that there was enough of both of these types of material within economical haul distance of the dam, the availability of these materials adjacent to and just upstream from the reservoir was investigated . The "B" series of 24-inch diameter bucket auger holes were put down along the dirt road which crosses the head end of the reservoir . There were five holes in this series ranging from 2 to 10 feet deep . Bag samples were taken of representative materials that were encountered in the holes. These samples were tested in the laboratory to define the physical and mechanical properties of compacted fill made using these materials. A summary of these test results is presented below: 13 .. ... .. Ill ,. 1111 -.. -.. .. .. .. .. ' .. ... ... ... ... .. "" ' .. ... .. Bucket Auger Holes -"B" Series Coefficient of Max, Opt. Hole No. ¢ Permeability Density Moisture Plasticity l/B 26° 20 ft/yr 122.0 12.1 Slight 5B 32° 50 ft/yr 126.0 8.9 Non plastic These tests were performed on samples that were compacted at optimum moisture content to 90 percent of maximum density. The test procedures used are discussed individually in connection with the section of this report on embankment design values. The "C" series of bucket auger holes were discussed in the section of this report on foundation exploration. These two series of holes bracket the proposed impervious core and shell zone material source areas. The location of the 11 B11 and "C" series of bucket auger holes are presented on Figure 1 and the logs of those holes are presented on Figure 3. 2. Construction Material Sources. The Squires Dam will be a rolled earth fill zoned-type embankment utilizing four types of mate- rials in five zones. The materials required are rock for riprap, sand for the drain zone, coarse grained insitu weathered bedrock for the shell zones, and fine grained insitu weathered bedrock for the im- pervious core zone . The results of the field exploratory program and the analysis of the material source conditions that form the basis for the dam design are covered in detail below for the various types of material required . The location and approximate limits of the local material source areas are presented on Figure 1. ... ... ... Ill ... Ill -Ill .. 11111 ... "" ,, .. "" .. "" .. ... ... ... .. .. ... .. ... ... ... ... ... ... The impervious core and shell zone materials will be obtained from the same sauce area, namely from the reservoir area and from the area just upstream of the reservoir within the project watershed. Careful material selection will be made on the basis of material grain size gradation to obtain an average permeability difference factor of at least 10 between the upstream shell and the impervious core zone. The permeability of the downstream shell zone will not be important to the design of the dam . The geological conditions within the reservoir area are essentially the same as those at the dam site. The surface material is somewhat more fine grained than the less weathered material at greater depth although this variation is by no means uniform with depth. The sur- face soils in the topographically steeper areas are coarser grained than in the flatter areas due to the effects of erosion and creep. The most probable reliable sources of "impervious" core zone material are therefore the flatter areas. The same principle holds true for the coarser grained materials; they are most likely to be readily available in the steeper hillside areas. Many large insitu boulders will also be encountered within the weathered bedrock zone . The design intent is for the finest grained and therefore presum- ably the most impervious materials to be selected for placement in the core zone; for the coarsest grained and therefore presumably the most pervious materials to be selected for placement in the upstream shell zone, The intermediately graded materials and excess materials meeting either of the other zone requirements are intended for placement in the 15 .. .. .. -.. .. .. .. - .. .. largest zone, the downstream shell zone. It is believed that this zoning combination will result in the most satisfactory dam embankment; however, the design analyses assume the zoning to be effective or ineffective de- pending on the consequences of the zoning assumption for the case being analyzed. The selection is made in such a manner as to achieve the most conservative seepage assumption for each case. Excavation within the reservoir will be more difficult than in flatter areas because of the steepness of the topography. A short haul will compensate to some degree for this difficulty. The use of material from the reservoir will develop storage capacity having a much greater value than any added cost that may result due to the topography of the area for excavation purposes. Excavation of in-place weathered material in this area will be hampered by the presence of insitu boulders. Considerable ripping will be required if the use of self loading scrapers is considered; however, the use of power shovels may be necessary in order to obtain the maximum possible amount of material from the reservoir area. Pro- vision has been made in the outer one-half of the upstream shell for the deposition of excess boulders from the reservoir area if it is economical to dispose of these rocks in that manner. If this alternate is selected, riprap will not be necessary in that portion of the zone actually so constructed. Two alternative riprap sources have been considered during the project design although the contractor will be allowed to use material obtained elsewhere if the quality of the material selected is satisfactory. 16 ... --1111 1111 1111 .. 1111 .. 1111 .. 1111 .. 1111 .. .. -1111 ... 1111 ... .. ... "" 1111 ... Ill These alternates are to select and use sound rock having a satisfactory gradation from the boulders encountered in the shell and core material source areas, or to quarry rock from the Calavaras Quarry about 3 miles north of the dam site for this purpose. Since the wave problems will be minimal at this site due to the small size of the reservoir and since freezing and thawing will not occur due to the southerly location of the site, the soundness of riprap required will not be severe provided that the material is well graded, or that a filter zone is placed if larger sized or poorly graded rock is to be used without secondary shooting on the fill . There is no satisfactory drain zone sand at the dam site. This material will be imported to the site. The allowable gradation limits of this material along with its relation to the proposed impervious core and downstream shell zone material gradation limits are shown on Figure 2. 3. Embankment Design Properties. The probable gradation limits of the material available in the reservoir area for impervious and shell zone are shown on Figure 2. The required gradation for the drain zone sand has been determined so as to meet the filter require- ments of the impervious core zone material. Shell zone material will automatically meet the filter requirements of both the impervious core and drain zone materials. The imp.ervious core and shell zone gradation limits were selected to make the most advantageous use of the materials available for the construction of the dam. The design, however, is 17 .. .. -.. - .. - .. -.. -.. -.. -.. .. -.. -- based on the most disadvantageous seepage assumptions for each case considered, therefore these zone gradations are relative, rather than absolute. The gradation test procedure on which these limits are based is A.S.T.M. Test Procedure D 422-54T. The Atterberg Limit tests were performed using A.S.T.M. Test Procedures D 423-54T and D424-54T. The material at the project site was found to be essentially non-plastic and the apparent liquid limits were found to be less than 26 percent . The compaction tests were made using A.S.T.M. Test Procedure D-698 modified to use 26 blows of a 10 pound hammer with an 18-inch drop on each of 3 layers in a I/30th cubic foot mold. This results in a compactive effort of 35,100 foot pounds. The required minimum fill density will be 90 percent of the maximum density so obtained. The compaction moisture will be controlled within the limits of 3 percent dry and 2 percent wet of the optimum moisture content so ob- tained while attempting to compact at optimum. The stability analyses have been.made using a dry unit weight of 113 pcf for all material in the embanl<Jnent and in the foundation. This is a slightly conservative assumption because the unit weight of the core·zone material will prob- ably be lower than this amount and the shell zone material may be heavier . The permeability of the available impervious and shell zone mate- rials was obtained by use of both constant and falling head tests. The coefficient of permeability so obtained varied from about 0.1 to 50 feet per year. Since the tests were run on the more pervious materials at the site both the shells and the core zone will be relatively impervious . 18 • • • • • - r - ... ... .. ,.. • ... .. ... ... The shear strength of the impervious core and shell zone materials was obtained on samples compacted at the optimum moisture content to 90 percent of the maximum density obtained by the compaction test discussed above. The samples weresaturated under a head of one-half of the chamber pressure, The samples were stored for 24 hours. Triaxial shear tests were then run in approximately 15 minutes without permitting sample drainage. Failure was assumed at 12-1/2 percent strain and Mohrs diagrams were plotted to determine the resulting coefficient of internal friction. Cohesion was ignored for stability analysis purposes because it is not considered to be a reliable property of the materials at the project site for long term embankment conditions. The shear strength obtained was an apparent shear strength under near saturated or satura- ted conditions. The Coefficient of Internal Friction of the impervious core zone material is conservatively estimated to be 0.48 and of the shell zone material to be 0,625. 4. Design Criteria, The design of the Squires Dam is based on the results of economic, seepage, stability, and settlement analyses which include consideration of-all critical conditions that were in- dicated by the site foundation, and construction material source in- vestigations, and the probable reservoir operation. The basic criteria for the design of this dam has been to develop a structure that is adequate beyond any doubt with regard to public safety and to apply sound engineering and economic principles in the design of those as- pects of the project which affect the initial cost and maintenance of the structure . 19 ... ... ... ... ... ... ... ... -... - -• ... 5. Embankment Layout and Design. The most practical and economical development of the subject dam site required a detailed study of the em- bankment quantity-reservoir capacity relationship for several dam heights and axis alignments. The dam axis and crest elevation presented herein was based on the results of this study along with a study of the site topographical, geological, and engineering conditions presented in this report. The final layout, embankment design, and material utili- zation was then again reviewed at the site and the detailed seepage, stability, and settlement analyses presented on Figures 4 and 5 were per- formed on the resulting final embankment section. The embankment section design was based on the economical availa- bility of large quantities of in-place weathered rock material which is both fine grained enough to be relatively impervious, and strong and incompressible enough to support the water tight core with reason- able side slopes as well as on the geological and foundation engineer- ing aspects of the site. The Squires Dam will be a zoned type compacted earth fill embank- ment with a 20 foot wide, 802 foot long crest at Elevation 510. The emergency spillway crest will be at Elevation 505 with the maximum de- sign flood water surface at Elevation 507 resulting in a reservoir sur- charge of 2 feet and a net freeboard under design spillway discharge conditions of 3 feet. The embankment will be approximately 125 feet high above natural stream bed below the crest and 185 feet above the downstream toe of the embankment. The dam will be approximately 150 feet above the bottom of the cut-off trench. The layout and details 20 .. -.. .. .. .. -.. .. 1111 .. 1111 - 1111 .. 1111 .. 1111 .. .. 1111 .. of the embankment are presented on Figure 2 . The dam embankment section consists of an off-center impervious core zone which is drained on the downstream side by a vertical sand drain zone. The impervious core zone is supported on the upstream side by a semi-pervious shell zone and on the downstream by a random permeability shell zone. The downstream shell is underlain by a hori- zontal sand drain zone which is warped up the abutments to prevent pressure build-up due to abutment and foundation seepage as well as to serve as a conduit to carry the vertical sand drain seepage water to the downstream toe of the embankment. The upstream slope of the embankment will be protected against wave erosion by a riprap zone, The downstream slope will have a 15 foot wide berm at Elevation 440 and the slope will be planted with a suitable grass cover to minimize erosion maintenance due to rain runoff. The downstream groins will be protected with a ten-foot wide, 2-foot deep layer of well graded riprap to prevent erosion in this vulnerable area where the abutment runoff will drain down the embankment slope. The embankment slopes are one vertical on three horizontal up- stream and one vertical on two and one-half horizontal downstream with a 15-foot wide berm at Elevation 440. The embankment slopes were selected on the basis of the strength of the available shell construction materials and the site foundation conditions. The stability analyses discussed later in this report present the com- puted minimum factor of safety for each condition studied, These studies were made for major failure sections only. Local, shallow 21 - - -i.. -- -.. --.. -.. .. .. -... -.. arc stability consideration involving only maintenance problems will yield slightly lower factors of safety which, however, are also generally above the required minimums. 6. Seepage Analyses. Steady state and rapid draw down flow nets have been drawn for the dam using the procedures set forth for graphical analysis by Arthur Casagrande in his paper, "Seepage Through Dams," Journal of the New England Water Works Association, June 1937, and by Harry R. Cedergren in discussion of a paper by F. H. Kellogg on "In- vestigation of Drainage Rates Affecting Stability of Earth Dams," Transaction ASCE, Vol. 113, 1948. An anisotropic ratio of 9 to 1 was used in the construction of the flow nets for the embankment fill because of the nature of the construc- tion materials and the specified method of embankment construction. For the zoned dam steady state seepage analyses, the upstream shell wasassumed to be at least 10 times more permeable than the core which for all practical flow net purposes is equivalent to making the ratio infinite. In the zoned dam drawdown analysis, the core was assumed to be relatively impervious and the upstream shell was assumed to be pervious. Where the embankment was assumed to be homogeneous, the permeabil- ity of the upstream shell and impervious core zones are considered to be equal. In all of the seepage studies, the downstream sand drainage zone was assumed to be effective . The foundation was assumed to be impervious because it is believed 22 ... ,.. ,.. I • ,.. ,.. ,.. L .. ... -.. -.. -.. ... "" ,.. - that it will actually be relatively impervious and because it is more conservative for the drawdown and downstream drainage considerations to do so . The seepage losses through the embankment under full reservoir seepage conditions is expected to be less than 2 gpm. Abutment and foundation seepage are believed to be minimal. Any seepage which occurs through these areas will be localized to open joints or cracks which can not be appraised prior to construction. The flow nets are presented on Figure 4. An examination of these flow nets indicates that for the steady seepage case, the zoned dam assumptions are the most conservative because no head loss is assumed in the upstream shell and that for the drawdown case, the vertical equipotential assumption for the homogeneous dam is the most critical case, Since all of the other cases will give much higher factors of safety, these cases were selected for stability analysis. 7, Stability Analysis. Stability analyses were performed to check the factor of safety which the embankment section will have for the most critical conditions that it will undergo as a result of the proposed reservoir operations. These analyses were made on the basis of saturated shear strength tests. The apparent shear strength of the soil was obtained by a quick undrained triaxial shear test. This shear strength was used in the stability analyses as the effective stress strength of the soil which is a conservative assumption. Co- hesion, as developed by the laboratory test procedures used for the project, is not a reliable property of the soil so it has been ignored in the stability analyses. 23 ... • ,.. Ill .. Ill "" ... "" l [ .. • .. ... .. .. Ill .. -.. -.. Ill .. ... "" - Three conditions were analyzed for the upstream slope of the dam and two conditions were analyzed for the downstream slope, The upstream conditions were the full reservoir steady seepage case, with and without seismic forces, and the rapid drawdown case. The downstream slope was analyzed for full reservoir seepage conditions with and without seismic forces, The results of these analyses are presented on Figure 5. The minimum factor of safety required for each of the stability cases studied for Squires Dam was selected with consideration given to the method of analysis, the basis for the adopted soil properties, the severity of the seepage assumptions, the nature and consequence of the associated type of failure, and the probability of occurrence of the conditions assumed in each case. The minimum factor of safety required for the full reservoir steady seepage analyses for both slopes is 1.50, The minimum factor of safety for the drawdown case using vertical equipotentials for the upstream slope is 1.00, The minimum factor of safety required for the seismic cases was 1.10, The trial arc method of analysis was used to analyze the upstream slope of the dam. This procedure was applied, using graphical pro- cedures, to determine the arc having the least factor of safety against sliding. This factor of safety is reported in tabulation on Figure 5 as the factor of safety for the case studied, This method considers the resistance of a major segment of the embankment as a whole against failure by shearing along the circular arc upon which 24 "" 111111 ... .. ... .. "'" 11111 ... 111111 ... .. ""' .. ... "" .. ... ... ... .. ... .. ... ... I"" .. the accumulated stresses are the most critical, In this analysis, the centers for each trial arc were selected by judgment and the factor of safety was computed. This process was continued until the arc with the least factor of safety was found. The downstream slope of the dam was analyzed using infinite slope procedures. This is conservative for this dam design because the im- pervious core is too far within the embankment to produce a critical effect on the slope stability, the internal drain prevents seepage forces from developing in the vicinity of the downstream slope, and the foundation strength is greater than that of the embankment fill. The seepage conditions used in the computation of the "seepage forces II for the full reservoir steady seepage case were determined by the use of a flow net seepage analysis. The drawdown "seepage forces" are based on an assumption that the pressures are represented by "vertical equipotentials.11 Both of these seepage force determina- tions were made'with the most critical zoning assumptions. The draw- down seepage assumptions are believed to be very conservative . Seismic forces were applied to the arcs found to be the most critical when acted upon by gravity and seepage forces only. Al- though the addition of seismic forces would shift the location of the critical arc slightly, this simplified method of application of these complex forces is considered to be adequate . The results of the stability analyses for the dam slopes are pre- sented on Figure 5, The seepage assumptions, and all of the pertinent data for each case are shown on this figure. The results of the 25 .. ... ... ... r ... ( C r .. ... I.. ... .. ... l .. .. .. .. .. .. ... .. stability analyses on the dam section indicate that the slopes for the structure will be stable for the conditions analyzed which in- clude all critical conditions that can now be anticipated, A review of the results of the analyses indicates that the de- sign of the upstream slope of the embankment is controlled by the conditions obtained by two-thirds drawdown (with the assumption of vertical equipotentials) with both gravity and seepage forces act- ing. The computed factor of safety for this case is 1,08 as com- pared with the minimum required design value of 1.00. The most critical conditions for the downstream slope exist dur- ing an earthquake with seismic forces acting on the dam slope. The computed factor of safety for this condition is 1.16 as compared with the required minimum design value of 1.10 . 8. Piezometers and Settlement Markers. Piezometers and surface settlement markers will be installed within and on the embankment respectively as shown on Figure 2. The piezometers gages will be read periodically during and following construction of the embank- ment. The settlement markers will be measured periodically follow- ing construction. The purpose of the piezometers and settlement markers is to pro- vide a basis for the systematic evaluation of the stability and gen- eral condition of the embankment during and after its construction on a routine basis . 26 C C C C C C C C C r I,,. .. L. .. • .. .. .. .. C -FREEBOARD, SETTLEMENT, AND ·CAMBER ANALYSIS The height of the Squires Dam is controlled by the spillway crest elevation to which is added the maximum spillway surcharge and the freeboard. In order to guarantee that the full design height is maintained, the embankment is constructed somewhat higher than re- quired in order to allow for post construction settlement of the dam crest due to consolidation of the fill. In addition, since a perfectly horizontal embankment crest gives the impression of sagging when viewed from the valley floor downstream of the dam, it is custo- mary to increase the height of the center of the embankment in order to counteract the optical illusion which occµrs because of the con- vergence of the valley abutments. 1. Freeboard Design. The maximum spillway surcharge will be about 2 feet, for which an allowance of 3. feet of free board is made. Due to the location and nature of the Squires Canyon reservoir, fre- quency of spill is very low, Due to its size, the crest width, and the provision for upstream slope riprap, the need for freeboard is minimal. A total freeboard of at least five feet will be available most of the time. 2. Settlement Analysis. Consolidation and settlement studies made on materials similar to those in the Squires Dam indicate that the post construction settlement of the dam will be about one percent of its height above the foundation at any point. The post construction settlement of the dam embankment will be roughly proportional to the 27 C C C C C C C C C C C C C C C C C C C height of the dam at that point. This means that the center of the embankment will settle more than the portions of the embankment ad- jacent to the abutments since the abutments and the foundation mate- rials are relatively incompressible. Since the settlement allowance varies across the profile of the dam, it will be provided for along with the camber. 3, Camber. Since public confidence is a function of appearance, camber will be provided to counteract the apparent sag which the shape of the valley will give a perfectly horizontal embankment crest, The camber allowance varies across the profile of the dam, The camber and settlement allowance is presented on Figure 2. D -SPILLWAY 1. Location, The spillway is located at the extremity of the right abutment with the crest at elevation 505,0 in such a position as to discharge down a natural draw at this location, The downstream face of the dam is protected from the natural spillway drainage by a ridge. 2. Capacity, The spillway as designed is an open channel trape- zoidal in cross section, with a 16 foot bottom width, and 1-1/2 to 1 side slopes. Based on a critical depth occurrence at the entrance to the channel, super critical flow in the channel, and a 16 foot width, the computed flow for a water surface elevation of 507 feet is 136 cubic feet per second. Inasmuch as the total drainage area con- tributing to this spillway is only 60 acres, this capacity appears 28 C C C C C C C C C C C C C ~ C C C C C -' .. -----------~ to be more than ample. 3, Design. The spillway is proposed to be an open channel lined with concrete with cutoff walls and side slope protection at the en- trance, At the outlet a cutoff wall is also proposed with necessary natural channel alignment being fixed to protect the downstream face of the dam from any possible erosion. E -INLET-OUTLET PIPE l, Location. The 27-inch diameter inlet-outlet pipe is located to the left of the Squires Canyon drainage channel as indicated on Figure 2, An inlet box at approximate elevation 425 is provided to provide screening if necessary and to prevent silted water from enter- ing the outlet pipe, 2. Construction, The inlet-outlet pipe is 27-inch diameter steel pipe with cement mortar lining and concrete encasement, Cutoff walls have been provided on the outlet conduit where it passes through the impervious core zone of the dam. These walls will serve to lengthen the seepage path, and to change direction of the seepage flow at reg- ular intervals, This may decrease the seepage velocities along the pipe-compacted fill interface. Filter zone cutoffs have been provided at either end of the outlet conduit where it emerges from the core zone into the shell zone in order to prevent piping in the event that seepage does occur along the pipe-soil contact. The outlet valve has been provided at the downstream face of the dam, This has been done for reasons of convenience and economy. The 29 C [ C C [ [ [ C C C [ [ [ C C C [ [ [ design of the outlet conduit minimizes the probability of catestropic pipe failure, and the very small size and regulatory nature of the reservoir makes it possible to assure regular maintenance of the pipe. These factors have indicated practicability of limiting the outlet con- trol to a downstream valve system. 30 . :•"'·' J ._ --'I) ""1: 11.S,C. a G.S. - t_:t,.;;,,. ,, I .,, . ' ---•I'.-----... .. . . " -------------------- PLAN OF DAM AND RESERVOIR ., ,.. ~= .., K&""(: CONTOUR INTERVAL -IQ fl!ET ""' w> :L ,.... .. ..... , -----""".,_'"'u"-PAOJtKT 11_u,-.rno1-1 ---............ ,IA', l"ROJl:~'I Rl>Ql.ll'ol"II~ • """"°"'0 DP.lU. 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STATE OF CALIFORNIA DEPARTMENT OF WATER RESOURCES APPLICATION NO, ____ _ APPAOVEO AS TO SAFETY _;;-:--] DATE REMARKS CARLSBAD UNICIPAL WATER IMPROVEMENT DISTRICT SQUIRES 0.._ DAM EMBANKMENT SEEPAGE ANALYSES W.A.WAHLER a ASSOC¥TES EARTH -0£ ... 11 C-T...-rs -UN. ~ 4 •!t J: ., .. ,_ f -l. I ··'-( ,: ; t;T~ .. UTY ANA.LYC.IC. 4'UAA,._,RV Pt:IOPl!ATllf.-=. Ofll e.AlliANIC.ADl"f.AA'TE.P.IAL._ UWl"'f ~., ... .,... I ""~~-..-.p.TM ! CAl'llr 1 Jl - "Jr T -..c-,n111n,.-y • ('(')N01TIC>N«li, ~·~ ----:-...•--INCUIO• IN<.GIUNl'l'f'_D .... .,.._._..,..,._y_ Clll!CUL--C AWA&.Y414. ~ .. --=c.~: .. ~~ -c•.c.,..- I.IP'I-'4.-: _.,...._ Ql!IAWi,o,,,w TC, C.P.l"TI-\. ---.__ u<;-V~IU,I. 11:QUIIIC)'TIINTIN.. ~ 4°"~1()N4, =t~:~.r~~~'i::~~·-" OOWM4T,.....,._ "',LCM>•: C.P.-IT't ISC>P.CIK °'l"'=\.Y.1N1&-1w1,e-,_.\.nPB!: 6'.t.lAL."'i414'-- ,.,._ \VITW o.,nc. .......... ( PCSP.C.tt. IN - f"1Nrt.4L~-ALY-. OF~.•'t.1-=> l'.'>.•'l.a&O I I I I I I 011.,.•t ... 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A -,:1A.1t1&lC.OTP.OPIC::: RATIO t."l'M&, FL.Ow LIN•~ AIU: 41-10\" M IIIJ,(')LID LIN·~~ .. 6-QUIPO~lst,.:'Tl~I.. AC. OA4~1&D c;c:ALe.: .. ""' ,m• trio' STATE OF CALIFORNIA DEPARTMENT OF WATER RESOURCES ....,..CATION NO .. ___ _ A~ AS TO SAFETY CARLS8AD .I WA"l'rD I DATE •tv1s1oil DATE IIEltARKS DAM EMBANKMENT STABILITY ANALYS1$ W.A.WAHLEJI a ASSOCIAtts EMTM OMI. tiESlal CXIIIIULT..,_TS ~ ----11:CI- I ·i:I I .~ .. ,. 17_!18 ..... 1' ·1