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SS9701-SY 970331 PROJECT NO. 3414 .MARCII, 1997 -- SLOPE STABILITY ANALYSIS GRAPEVINE CREEK AT CRESTVIEXV COURT COPPELL, TEXAS Presented To: CITY OF COPPELL -- COPPELL, TEXAS March 31, 1997 _ Project No. 3414 City of Coppell Engineering Department 255 Parkway Boulevard Coppell, Texas 75019 ATTN: Mr. Garreth Campbell SLOPE STABILITY ANALYSIS GRAPEVINE CREEK AT CRESTVIEW COURT _ COPPELL, TEXAS Gentlemen: -- Transmitted herewith are copies of the referenced report. Should you have any questions concerning our findings or if you desire additional information, please do not hesitate to call. Sincerely, ~UP. INC. .. : t/vt, - -"'?..'" LK' Rona~d r. ~teed. P.E. '&':" 'j~ ".?, Principal Engineer ~" "v '.'.: ': :.' -' '_". '_"-' .} -- ~ ........ ~.- ....... ~ ..._ ~, FWSiRFR/apr t,,~'~.'~.:. ~ ~.~,4 ~;< g'. ~ -..",V~ -- copies submitted' .04/City ofC~J~i~g'E'ngil~rin~, DepartmentMr Garreth Campbell (1) Craig Olden. Inc :Mr Craig Olden TABI.E OF CONTENTS PAGE INTRODUCTION ........................ I Project Description ................................. 1 .~tlthorizalion .......................... I Purpose and Scope .......................... 2 HEI.D AND I.ABOR..~,TORY INVESTIGATIONS General ........... Field Investigation ..... Laboratot?' Investigation . . . 3 GENERAL SITE CONDITIONS ......... 4 Geology and Straligr:q}hy. ............... 4 G,'ound ~,Vater. ........................ 6 Surface Conditions and Landslide Geomorphoh)gy . ....... 6 ANAI),'SIS ....................... 8 Stability Almlyses ........... 8 Cause(s} of I:ailure ..... 10 RECO.M.M EN D.-XTION S ..................... I i General ................ I 1 Remedial Measures ........... 13 Earth,aork ............... 16 (?ozlslruction ()l)serx :ilion I 7 -i- TABLE OF CONTI"-N'I'S (Continued) I LLI'STR-Xl'IONS PI.ATE PLAN OF' BORINGS ................................ I BOltING I OGS '~ ' KEYS -I'O TERMS AND SVMBOI~S USED ........ 58.:6 LABORATORY TES'I' RESI'LTS - CONSOLID.k'I'EI)-DIL'~INEI) I)IRECT SIII-:AR TES'I' RESI'LTS S&9 INTERPRETIVE GEOLOGICAI_(TROSS-SECTIONA-A' . .10 SLOPE STABIIJTY ANALYSIS- INITIAL SI.Ii)E I l SI.OPE STABILITY ANALh'SIS - INITIAL SI.IDE. UPSTREAM PORTION ............. 12 SLOPE STABII.IT'Y ANAI.YSIS- EXISTING SLIDE .13 SLOPE S'I'ABILITY ANAI.YSIS- V(ITII PIERS AND GABIONS 14 IDEALIZED REMEi)IAI. CROSS-SECTION .......... I $ PLAN VIE~V - PROPOSED REMEI)IAL MEASURES .16 INTI~,ODUC'I'ION Project Description This report presents the results of a geotechnical in\ esti_oation of s~ope instahilit? adjacent to --"¥': ...... '776" ' 'z8,5 Creslview Court in Grapevine Creek. The si:c is located behind ~,-.~.,..~e~ a~ ,mc: .... Coppell. Texas .-\ re'.atixelv lar,.'-o_ landslide has occu:Ted x~!:ifin ;he slope between ,ne" residences and the creek Ihe land:,; dc ','.a.-. initially obser,.ed b', Reed Engineering G:-oup. Inc on I)ecember 18. 1996 .-\ second site visit was :nade on Febraar;' 24. ~997 ..\1 ins :!me. a second landslide scarp formed approximatel,, .... to 15 leer fur:her .~...],..,~'.:. The new scarp is located within about three feet of the pool decking behlnfl "'76 ('res:x ie~,~ Ceu< :\t tile direction of B:e City t..l Ct.w[ ..... se'~'era~ incl:es of sholcrete ~ere applied to the head scarps of the land>lide on FeSruarx 25. I,)97 The slkie has continued to :hove as evidenced bv lOC ol'the hmd.-lide b; stream ~-:ction Movements are episocSc, l_,,pica~Jy occu.q-i:m in resp. onse to rainfall e,,enls .-\s oi"5.1arch ZS. ,c:c,- liZe t..+t,~ ..... t head 5,.aq: ~.,,,> on lhe order ofeioJll lo nine feet in heigilt Authorizatiol~ This investitzation ~,~a~ ~,u'horize(i i~', Mr Garretl: C~m:pbe:: of :.i~e Ci:x of Coppell on Fei~ruaD' 17. 1997 Prt~ect No 3414 - I - March 31. 1997 Purpose and Scope -- The purpose of this investigation has been to evaluate the cause or causes of the landslide, and to evaluate alternatixe remedial measures to stabilize the slide The investigation has included drilling sample borings, field geologic studies, topographic sumev of the failure area, laborato~' -- testing, engineering and geologic analyses, and preparation of the report. FIELD AND LABORATORY INVESTIGATIONS General The field and laboratol3' investigations have been conducted in accordance with applicable standards and procedures set £orth in the 1996 Annual Book of ASTM Standards. Volumes -- 04.08 and 04.09, "Soil and Rock. Geosvmhe:ics". These volumes should be consulted for information on specific test procedures. -- Field Investigation Subsurface conditions were evaluated bx- three sample borings drilled to depths of 7-1i2 to 30 feet. Boring B-I was drilled above the landslide. Borings B-2 and B-3 were drilled within the _ slide mass. The approximate location o£each boring is sho;~n on the Plan of Borings, Plate ] of the report Illustrations. Project No. 3414 - .:" - March 31.. 1997 Boring B-1 was advanced xxith an ATV-mounted drilling rig equipped with continuous flight augers. Borings B-2 and B-3 were advanced by means of hand-operated drilling equipment. -- Samples of cohesixe soils and weathered shale were obtained with thin-x,.alled Shelby tube samplers. Delayed water level obser,'ations were made in the open boreholes to evaluate ground water conditions, after which the borings were backfilled to the ground surface Sample depth, description of materials, and soil classification [Unified Soil Classification System -- (USCS)] are presented on the Boring Logs. Plates 2 through 4 Keys to terms and symbols used on the boring logs are included as Plates 5 and 6 Resu',:s ot' water level obse~'ations in the open bore holes are reported on the individual boring logs Field reconnaissance ~as performed in order to evaluate surface geologic and geomorphic -- conditions in the general area of the l'ailure A topographic sur~ey of the failure area was performed by John E. Hawkins & Associates, Inc on February 24. 1997 The survey was revised on March 25. 1997 in response to further landslide movement and to determine boring elevations Cross-sections and topography presented in this report are based on the Haxvkins _ survey. Laboratoo' luvestigation Upon return to the laboratory, all samples were logged in detail by an engineering geologist in accordance with the USCS and standard geologic nnrnenc',ature Samples of cohesive soils were -- evaluated for consistency by use of a pocket pcnetrometer Pocket penetrometer test results are shown on the boring logs Project No. 3414 - 3 - March 31, 1997 Selected samples of the upper soils and weathered shale were subjected to Atterberg Limits, moisture content, and soil suction determinations. Results of these tests are summarized on -- Plate 7. _ Samples of weathered shale and bentonite were subjected to consolidated-drained (C-D) and consolidated-undrained (C-U) direct shear tests in order to evaluate parameters for slope stability analysis. Both peak and residual shear ',~ere evaluated Results of the direct shear tests -- are shown graphically on Plates 8 and 9. GENERAL SITE CONDITIONS Geology and Stratigraphy Site ~,eoloev consists of terraced alluvial soils overlying x~ eathered and unweathered shale of the Cretaceous Eagle Ford Formation The terrace soils are associated with Pleistocene deposition -- within the floodplain of Grapevine Creek and its tributaries In its unweathered state, the Eagle Ford Formation consists of dark gray. soft crock classification), slightly fissile clay shale with occasional very weak bentonitic seams The Eagle Ford weathers to produce highly plastic -- residual deposits of low shear strength. - In general, subsurface conditions encoumcred in the borings consist of fill and alluvial deposits overlying weathered and unweathered shale. The fill is attributed to site grading durina orieinal construction. Interpretive Geologic Cross-Section A - A' has been prepared for visual reference and is presented on Plate 10 The plan location of the cross-section is shown on Plate 1. Project No 3414 - 4- March 31. 1997 Fill encountered in Boring B-I consists of brownish-yellow and grayish-brown, low plasticity. sandy clay w-ith some calcareous fragments, and traces oF gravel and root fragments The consistency of the fill was relatively low. with pocket penetrometer values between about one and two tons per square foot (ts0. Alluvial soils underlying the fill typically consist of grayish-brown to olive-yellow, high plasticity, silty clay x~ ith varying amounts of shale fragments, calcareous gravel and sandy clay at the base. An approximate two-foot layer ofrecendy deposited silty sand overlies the Pleistocene alluvium at Boring B-3. The alluvial soils are underlain by olive-yellow? olive-gray, and gray, very soft to soft (rock classification), completely weathered to slightly weathered shale with iron-stained joints. Completely weathered shale consists of highly plastic residual clay. The degree of weathering generally decreases with depth The weathered shale is underlain by dark gra;,', soft. unx~eathered shale. The unweathered shale extends to the termination depths of the borings A 7- to 12-inch thick bentonite seam was encountered at approximate Elev. 445 feet The bentonite seam is bluish-gray and unweathered in the upper portion of the slope, and reddist:-yellow and ligh: gray as a result of weathering in the lower portion of the slope. The bentonite seam contained numerous slickensided fractures, indicating that it ig at its re.~idual shear .~treng~h Project No. 3414 - 5 - March 31. 1997 Plate 10 shows that an existing 30-inch diameter sanitav,' sewer line is located within close proximity of the upper landslide limit. It is unknown ~hether the sewer line has been impacted by landslide movement to date However, continued progression of the slide in the upslope direction may rely likely damage the sewer line ]'he existing swimming pool and decking behind 776 Crestview Court would also be impacted Ground Water -- Ground water was encountered at depths of about 2-1 2 to 10 feet (approx. Elev. 460 to 444 feet) at the time of the field investigation (March. 1997) Ground water was observed at the surface within the central por6on of the landslide mass at approx. Elev. 455 feet The ground -- water is perched above the unweathered shale within the overlying weathered shale and soils. The ground water =ra,~,cnt is toward Grapevine Creek. ]'he depth to ground x~ater will fluctuate with variations in seasonal andx~ar,x.'.- ~.' ,~.,n,a.,~: r '~ and creek flow level Surface Conditions and Landslide Geomorphology The slope varies in height from about l g feet at the upstream end to about 29 feet at the _ downstream end. Slopes outside of the landslide are g~n~r..I,5 on the order of 4.5 horizontal to I vertical (4 5H:IV) upstream of thc lands, de and all..\ downstream The site is located on the outside of a meander bend in Grapevine Creek The outside of a meander bend is termed the "cut bank" and is subject to constant erosion associated with stream -- action. Outside the limits of the landslide, the creek channel is approximately 20 feet wide. Landslide movement has resulted in severe constriction of thc creek channel, blocking most of Project No 3414 - 6 - March 31. 1997 the flow. The blockage has essentially formed a landslide dam with water surface elevations on the order of two feet higher upstream of the landslide Elevated stream flow during storm _ events opens the constriction slightly as the toe of the landslide is eroded Erosion of material from lhe toe then results in further landslide movement. The slide is approximately 95 feet long from head scarp to toe, and approximately 240 feet wide from flank to tlank. As seen on Plate 10. two m~or zones of moxement are evidenced by -- observation of the head scarps in the upper slope Several minor scarps are associated with each failure zone Soils exposed in the head scarps are slickensided as a result of movement of the slide. The cumulative vertical displacement observed in the head scarps varies significantly from the -- upstream to downstream ends of the landslide Cumulative vertical displacement is estimated to be about 6 feet in the upstream potion of the slide, and 15 fret in the downstream portion. Cracking and displacement of tile shotcre:e applied to tile head of the slide in Februao'. 1997 is -- significantly greater in the downstream portion of the s'.ide. 1'his indicates that continued slide activity is much greater in this area. The middle portion of the slope is relatively fiat and characterized by several sag ponds Water within the sag ponds is be'.ieved to be indicative of the ground water level in this area Numerous tension cracks are present wi:bin the lox~er poaion of the slide mass. Based on _ geologic constraints, the base of the slide is anticipated to occur at the interface betx~een the Project No. 3414 - 7- March 31. 1997 bentonite seam and the underlying shale throughout most of the slide mass However, buckling of the shale in the channel bottom indicates that the depth of the slide may be somewhat deeper _ at the dov, nstream end. An 18-inch diameter storm sewer discharges on the slope at approx. Elev. 456 feet. The concrete apron and flume have been separated from the storm sewer as a result of downslope translation of the landslide. The storm sewer x~as reportedl>' placed within a pre-existing natural -- drainage feature - A similar landslide occurred ~mh~edmte,> dox~nstream of the existing landslide in 1993 This slide was repaired in 1994 in accordance with recommendations reported in our geotechnical investigation entitled "Slope Stability .Analysis, Grapevine Creek. Beltline at Mockingbird, -- Coppell, Texas", dated September. 1994 In general, repairs consisted ora series ofreinfbrced concrete piers within the slide mass. an in:ernal dra!nage system, and flattening of the slope to 3H:IV. The grade change ~as accommodated by a six-foot high gabion retaining wall with geogrid slope reinforcement The gabion wall also serx'es as erosion protection at the toe of the _ slope. ANALYSIS - Stability Analyses Slope stability analyses were performed in order to ex-aluate the cause or causes of the landslide, and the shear strengths governing at i~.ilure. Slope stabilit>' anal>scs were aided b>' use of a _ computer program. CLARA 2 31 ]'he program utilizes both two- and three-dimensional Pr~ectNo. 3414 - 8 - March 31, 1997 algorithms based on Bishop's Method of Slices In this case, two-dimensional analyses were performed. The initial section selected for the analysis was taken at the apex of the head scarp, _ v-here it is located closest to the swirnrning pool deck _ To evaluate the stability of the slope, approximate topographic conditions existing prior to failure were reconstructed. Subsurface conditions x~ ere estimated based on information from the borings, field geologic mapping, and ueoloc4c interpretation. The shape and location of the failure surface considered for the ahab, sis was based on landslide -- geomorphology, and on the relative streng:h of subsurface materials. Satisfaction of negative pore water pressures associated with rainfall infiltration and ground water tends to reduce effective shear strength The bentonite seam and weathered shale are particularly susceptible to -- rapid strength loss associated with increases in moisture content and relatively small displacements. Initial values of cohesion and friction angle, as well as other pertinent properties, ~.~ere estimated from the results of the laboratoD' testing. Residual strength was utilized for the bentonite seam based on the discussion above. -- The critical shear strength parameters governing at t~4ilure were back-calculated using iterative solutions for the factor of safety The process ~.~as continued until a factor of safety of one (conditions of incipient fhilure~ was obtained Plate I I illustrates the sliding surface modeled. along with the critical shear strengil~ parameters calct::ated from the analysis. Project No. 3414 - 9 - March 31. 1997 .-ks previously noted, continued slide activity has been significant in the downstream portion of the landslide, and almost imperceptible in the upstream portion. A second two-dimensional -- analysis was carried out to evaluate the difference in the factor of safety of the upstream and downstream portions of the slide. Shear strength parameters obtained frorn the previous analysis were used for this purpose {see Plate I I). The results are presented on Plate 12. The -- results show that the downstream portion of the slope was much more stable than the unstream . ~portinn e,;en at critical e, he;ar qlren,~h This can be concluded intuitively b',- the fact that the downstream slope is much higher and steeper than the upstream slope. Cause(s) of Failure Initial failure of the slide is attributed to a combination of excess pore pressures associated with high ground water, and removal of suppor: at the toe of the slope by stream erosion along the cut bank. Also. vertical erosion (do',~ncutting) of the channel bottom exposed the weak bentonite seam. Cut bank erosion and exposure of the bentonite seam likely caused a relatively _ shallow slide to develop near the base of the slope. Movement of the lower portion of the slope led to a reduction in support of the slope above The force imbalance created by the removal of toe support led to development of new~*,lidino__ surfaces. 'l'his process continued to propagate -- progressix ely upslope, ultimately leading to major landsliding -- The higher, steeper downstream slope x,.as less stable than the upstream slope~ This differential in stability caused the entire -" land.,::de to rotate horizontally in a clockwise direction around a "pivot point" located at the upstream end of the slide Project No 3414 - 10- March 31. 1997 Landsliding resulted in severe constriction of the creek channel. Constriction of the channel causes a localized increase in stream flow velocity which, in turn. results in an increase in _ erosion rates. As the toe of the slide erodes, support is removed and the slide re-activates. moving into the channel. This process will continue until the effective slope of the landslide reaches a point of quasi-static equilibrium The etTectixe slope is reduced by progression of the -- head scarp in the upslope direction. Continued ups'.ope progression of the head scarp threatens the existing pool and decking behind 776 Crest',iew Court. as v. ell as the 304rich sanitaD' sewer line. RECO.M.M ENDATIONS General -- Remedial measures must address both stabilization of the existing landslide and protection of the toe of the slope i-'rom future erosion Sex'eral alternatives have been considered and ex'aluated to stabilize the landslide. Based on this ex'aluation, stabilizv.:!on o~'the landslide in a manner similar -- to that used on the ad acent landslide appears most feasible This system consists of re-grading the slope to 3H 1\ or fl,,,tc,, and stabilizin~ the landslide by a series of reinforced concrete piers within the slide mass. The grade change can be accommodated by construction ufa low height gabion wall with gcogrid earth reinlbrcement Project No. 3414 - 1 ] - .March 31, 1997 The shear strength parameters governing design of piers will be that of the landslide as it currently exists. Minor slide movements in response to stream erosion at the toe indicate that the slide is in a state of quasi-equilibrium Design shear strength parameters were evaluated by solving iterative solutions until a factor of safety of approximatel.x' 1 (0 99) was obtained. The results are presented on Plate 13 Disturbance of the existing equilibrium, by stream erosion, or -- a rise in ground water level, will result in re-activation of the slide. The same parameters were used to evaluate the stability of the upstream portion of the existing slide. The results show that the upstream portion of the slide is stable, with a factor of safety of 1.37 Slope stability analyses, considering a maximum proposed finished slope grade of 3H'I V, were -- performed in order to evaluate the additional shear resistance required along the sliding plane to provide a factor of safety of at least 1.3. The analysis considered that minimal re-grading of the existing ground would be perfornted prior to placement of fill required to achieve finished grade The analyses indicate that an additional shear resistance of 1S0 pounds per square foot (pst') is required for a factor of safety of 1.3. The next step in the analysis involved ex'aluating the nulr, ber and size of piers required to achieve the necessary increase in shear resistance along the existing slide plane to achieve a minimum factor of safety of 1.3. Based on this analysis, a minimum of 25 piers, each 36 inches in _ diameter, are required. Further slope stability analyses were performed to evaluate the minimum top elevation of the piers required to provide an adequate t~ctor of safety against an overriding slide. Based on this analysis, a minimucn top elevation of 450 will provide a minimum fi~ctor of - safety of 1.3 considering an overriding slide The resu!:s are presented on Plate 14 Project No. 3414 - 12 - Xlarch 31, 1997 Remedial Measures -- General: Based on the analyses and discussions above, it is recommended that the existing landslide be stabilized by re-grading the failed slope to a maximum of 3H IV, coupled with installation of 25 reintbrced concrete piers to provide additional shear resistance, and a drainage -- system to lower the phreatic surface A gabion retaining wall ,~ith ueoorid reinforcement should be constructed at the toe of the slope to accommodate grade changes and to provide erosion protection An idealized remedial cross-section is presented on Plate 15. Piers: The piers should be a minimum of 36 inches in diameter and should penetrate a minimum -- of eight feet into dark gray um~eathered shale, or to an elevation of 436 feet, whichever is deeper. The top elevation of the piers sl:.oald be 450 f~et or ~:igher The piers should be spaced in two rows with a center-to-center spacing of 12 feet be:x~een piers The upper and lower rows should be spaced 10 feet apart (center-to-center). with an offset of 6 feet between rows. The _ piers should be reinforced with a minimmn of I-1 2 percent steel throughout their full depth _ Pier excavations should be dr3_' and free of all loose soils and deleterious materials. Due to the presence of shallow ground wa:er, and ,,~. ~]ua., d~,u,bed nature of the landslide materials, use of temporary casing during pier shaft excaxation should be amicipated In no case should pier -- shaft excavations remain open for more than six hours prior to concrete placement. -- A proposed plan layout of the piers is presented on Plate 16. Considering a top elevation of 448 feet for the gabkm wall at the toe. the upstream portion of the slide can be re-graded to a slope much flatter than .~H IX,' Slope --tab...,5 analyses indicate timt this portion of the slide, if -- properly re-graded, will be stable without the addition of piers Project No. 3414 - 13 - March 31, 1997 Drainage System: A drainage blanket should be constructed along the head scarp of the landslide between approximate Elev. 455 and 465. The head scarp should be smoothed and -- graded to a maximum slope of IH-IX,' prior to construction of' the drainage blanket. The proposed extent of the drainage blanket is shown approximately on Plate 16 The drainage blanket should be a minimum of lS inches in width and should consist ora durable crushed stone such as ASTNI C-33. Size 67 or coarser The crushed stone should be separated -- from the surrounding soils by a filter fabric such as ADS 6©0. or equixalent A minimum 6-inch diameter perforated drainage pipe (ADS N-12. or equivalent) should be installed at the base of the drainage blanket. The perforated drainage pipe should be teed into solid drainage pipes -- (ADS N-12, or equivalent) on maximum 12-foot horizontal centers The solid drainage pipes should be sloped to drain {minimum five percent slope) at the toe of the slope The discharge points of the solid pipes should be approxima:ely one foot above the "normal" creek flow level Site Grading: Prior to placement of backfill, the exposed surface of the landslide should be smoothed and proofrolled to identil\' any sol~t zones Soft zones should be over-excavated and _ recompacted in accordance with the Eartha'ork section prior to re-grading Excavated soils should be b'.ended as much as possib'.e to provide a uniform backfill The excavated soils should be replaced and compacted in maximum eight-inch loose lifts in accordance v. ith the Earthv,'ork section. Al! imported fill required to achieve final surface -- grades should consist of a uniformly blended sanely clay as outlined in the Earthwork section. Project No. 3414 - 14- March 31, 1997 The slope should be re-vegetated as soon as possible after completion of grading operations. Consideration should be given to covering the s',ope with an erosion control fabric, such as _ BonTerra S2, during the re-vegetation process. Particular attention should be paid to the upstream and downstream slopes beyond the gabion wall. These slopes should be covered with an erosion control fabric, such as BonTerra C2, and re-vegetated as soon as possible after -- construction. All BonTerra fabrics can be pre-seeded with any mix -- Gabion Wall: The toe of the slope should be protected b.v means of a gabion retaining wall *.vith geogrid slope reinforcement A minimum 6-1~ot high wall is recommended in order to accommodate the required maxin,um .I,.m,c of oH. I \ If poss!ble, the top elevation of the ,,*.'all -- should correspond to the existing gabion wal! located immediately do*.vnstream of the slide (Elev. 448 feet). ]'he trail should extend at least l0 feet be.*.-ond the horizontal limits of the slide in the upstream direction and tied to the existing t~all at the dot~nstream end. ]-he proposed alignment of the gabion wall is shot~ n approximalely on Plate 16. The gabion wall should be founded on undisturbed weathered or unweathered shale A _ minimum six-foot wide gabion mattress should be protided at the toe of the wall to limit the potential for undermining of the $r~undation. The mattress should be anchored, as necessary to prevent uplitL particularly on the up--tream end A minimum oftv. o layers ofgeogrid soil reinforcement (Tensar or Terramesh) is recommended _ The geogrid lavers should be placed between gabions, w!:h the lowermost layer corresponding to. or a maximum of six inches above. ,t ,- '- -" -~.. baa,. of the wa'.l -['he required number and length of Project No 3414 - 15 - March 31, 1997 the geogrid layers will be a function of the actual wall height and on the type of geogrid used. Considering a 6-foot high wall and Tensar UXIS00 geogrid, a minimum geogrid length of 16 _ feet is recommended Regardless of the type ofgeogrid used. each laver should be at least 2.5 times the height of the lhe existing storm drain should be extended to the base of the slope. The storm drain should discharge through the gabion wall if possible Earthwork -- All vegetation and topsoil containim, or~,anic material should be removed at the start of earthwork construction. The surface of the landslide mass should be proofrolled prior to placement of backfill. Any soft or loose zones .~hou.fl be ox er-excaxated and recompacted as -- outlined below lbr site-excavated soils. -- Excavated soils should be blended to provide as un[form a mix as possible prior to backfilling Backfill using site-excavated soils should be placed in ~naximum loose lifts of 8 inches and compacted to between 92 and 98 percent of the maximum density as determined by ASTM D- 698, "Standard Proctor". The moisture conten: should range from -1 to --4 percentage points __ above optimum. Imported fill required to achieve finished grade should consist ora uniVis, truly blended sandy clay with a Plasticity Index I'PI) of between 10 and 20 Imported fill .hou d be placed and compacted in accordance with the guidelines provided abox e. Project No. 3414 - i6- March 31, 1997 Crushed stone for use in the drainage system should be placed in maximum loose lifts of 8 inches and compacted to a minimum of 60 percent of the relative density as determined by ASTM D- -- 4254. Construction Observation It is recommended that a representative of this office be present to observe all construction actMties in order to confirm a proper bearing stratum and construction procedures. Field -- density tests should be performed at a minimum rate of one test per lift, per 2,000 square feet in all compacted fills. Project No. 3414 - 17 - March 31. 1997 I I ~~L~' ~1'. ', , ~ r~ ~ ~ ~ ~// ./ -'1:-...'--....... ..... .... /'//; ~ .. I '/ /, '"'--::"---.:" ..... ' ............ . ':~./// .' ~ - ~ .............. ~ ' I "'---."- .... :~'C'-~--. "-,~ ~. ~ ~ / ,~-~ ............ ~_ "-- - ...... -"~ ~ ~. /~ * / ~' · ' r ....... ' ............. "-~.m:,~ -- ~ ~ ~ · ~ ~ ...... t ..... '"- "'~ .... Z-~. . ,. '- ~ .... ~' .~ . ~ ~ I ...... / -,-, ~ -, - - - .... z- ......... - ...... ~ --~- ,' .. ,-~ --7 ...... ~'---/: ................. ;'7 ~ ~: .... ~. -~ ~.~~~ ~ z:: ...... --:' ~ ............. - ~?~> ~ .-~ ........... :  '" ...... ' ..... :::-":~ .......... ~;- ' :--~ ' I reed engineering '--' ---r.--'-.--' .-.-'-<--' .- ~-.*.- ~ ..... - ~ A -::~:~-~:-' . ....'~ ~ .-..c-.- PLAN OF BORINGS .~ -<-:--~:-' Slope Stability Analysis ~L~T~ ~ I re~d engi_nee~ing ~....-,, t~ Ar~ly:;s P;oiect No. 3414 Grape~;r,e Cree,~ at C-estview CcJ"t Ca-.e: 03-!O-g? '-'"'-"'"' ~"' Lo:=-~.icn: ~e.~ Pla:e: grsyish-b~owr'. s: fl, w~so'2e ~ i C8':3are.C"JS fra2m-?ts ~ t'sce of ¢/.=vel t'~ ] ~ [Fi:.) ~ .l:i , s~ fra~=e'-,ts :,e!c.w 2.5' - i ' ~J ! S!LTY '~ 'v ' , ., - i {:-'~) " J ~',! ' : i__ \ : 47..2_ -:~ (,....,,:.,l_t=,; ....... '" shae, / . ..... $.~"*~--, ~.=,". s,=;, '"- ~-'='- -~, ~ . , :--_-:_---_-;-m ~ ~ .... = ...... s:'.'.. - ......... : '" ! J ; r_~ n: .... - 23.5' : r'z-----~ bet. tot :e, b.,_,s'-,-;'.~:, -.~,s: '~ 25.C' - i -:--::::: 2e.c' I . .ii' BORING LOG B-I PLATE 2 ~OTEI~NIOJ~. ~I.TANTS reed engin_ee_rjpg_ S ;pe Stap;City An~. y$is PrOlect No. 34,4 Gr~pe-i ne Creek at Crestview Court Date: 03-17-97 Compel', T~xas Lcc3t-3-: See P~a[e i C- S:LTY CL~Y, oli,=-v=~lG~ ~ cra'z, s, ,,, ~ SHSLE, d~r~ gte/, soft. ~- frast~'e, slicker-si:5:, we~the-ed 20- 35; BORING LOG B-2 PLATE 3 ~EOTEO4~ICA[. ~'LTANTS I reed eqgineering~ Project NO. 3414 Grec. evine Gate: 03-13-97 Ccppel,, Tex~s Lo:~ticn: S~e Flare I _> ,,n ~ 0 I S:LTY -~'~ g'ayish-brown, v~ry · "~~ SILTY CLAY,s~=Ii~r,t, O'.ve-ygllow ;;~t gray, *" to med~ stiff :,~ ' S~;~v CLAY, C~tk tray SHALE, c3rk ~r~. (I/2") i To~al Ce2tn = 7.5 w~te- ~ 2.6' & b'=:kec { 2.7' ;n 03-17-97. 25~ 30- BORING LOG B-3 PLATE 4 [~OTEC3"~IIC~. CO~StJLT ~'NTS re~d engineerlpg -5 -~ ' ~-:.-~ -: :.-' :"':':-'.- ~. '1 ' ............ ~ : .,- _[_. ' E--c_E ;-'-:':-. :--;'~-. I :.."- 5'~. s- -;'r..~. ~:':. '~ C_~-~ _=~. ~.__- ...... . ......... E37.,%'3 _CS ~--' = -'-E 2 ; ~%.% Ez ~5-2,E KEYS TO SYMBOLS USED ON BORING LOGS PLATE 5 G~OTEC~IC~. CONSULTANTS reed engineering '2---- SOIL PROPERTIES COHESIC'~LESS SOILS CC'-ES:YE SPT Pocket N-Values Relative P~r,~t: s.'r.,et er (blows/foot) Dersm'.y (T.SmF.) Cs~s:ster. cy 0 - 4 ......................... Very Lo~se <3.25 ................... Very S~fl 4 -lC ......................... L~cse C.2~-9.,~ ........... 10o30 ........................ Ue~u~ DePse C.~:.i-t3C ............ ~e::~m St.'f 3C-~C ....................... '2--eP s e ~.CC-2.CC ............ 50 + ......................... Ve-) ~e-se 2.C:?-~.C.~ .......... ROCK PROPERTIES KEY TO DESCRIPTIVE TERNS ON BORING LOGS PLATE 6 ~OTE~:-~I~M. CONSULTANTS SLOPE STABILITY ANALYSIS GRAPEVINE CREEK AT CRESTVIEW COURT COPPELL, TEXAS Summary of Classification and Index Property Tests Liquid Plasticity I',lo[sture Soil Boring Depth Limit Index Content Suction No. (feet~ (%) (Pi) (%) (psf) B-1 1.5- 3.0 ..... 17.1 620 3.0- 4.5 28 14 18.0 ....... 4.5- 6.0 ..... 15.0 3:550 9.0 - 10.0 59 49 25.4 2.250 16.5 - 17.0 70 58 30.9 10,220 25.0 - 26.0 102 84 28.3 12.710 B-2 4.0- 6.0 71 60 30.0 1,900 8 O- 10.0 72 60 32.3 5,070 SUMMARY OF LABORATORY RESULTS PLATE 7 Peed engineering .~ .-~?-?-._- ~ 4000 3000 - CO co 2000 0 1000 2000 3000 4000 5000 $000 NORMAL LOAD 4000 Boring No. B-1 Depth (ft) ls.O-le.5 Unit Dry Weight (pcf) 93.5 ~ 3000 CO POINT NUMBER ----c°' ~..~,~.~.. ~ 2000 Normal Load (psf): 1293 2587 5174 : Moisture Content (%) BEI:ORE: 27.5 27.4 28.9 ~' .',,~, AFTER: 34.1 35.3 33.8 1000 ~ . PEAK RESIDUAL O ~'." : 0 0.1 0.2 0.3 Cohesion (psi): 80 0 Friction Angle (°): 27.5 15.9 SHEAR DISPLACEME_NT (~nche$) CONSOLIDATED-DRAINED DIRECT SHEAR TEST PLATE reed engineering .~:,~,;~-?, 4000 , I o 0 lOOO L~O0 3000 4000 5000 6000 NORMAL LOAD (psf) 4000 Boring No. e-2 Depth (ft) 10.0'- 12.0' Unit Dry Weight (pcf) se.2 ~ 3000 POINT NUMBER Normal Load (psf): 1293 2587 5174 ~i Moisture Content (%) BEFORE: 50.5 ................ ~-~--, PEAK RESIDUAL 0 / o o. 1 0.2 0.3 Cohesion (psf): Friction Angle (o): 76 SHEAR DISPLACEMENT (inches_) CONSOLIDATED-UNDRAINED DIRECT SHEAR TEST PLATE 9 ELEVATION ELEVATION I (feet) (feet) 480- -- 480 470- - ............. -- 470 Sandy Clay (Fill)  _ "~ Silty Clay __ Silty Clay (Alluvium) ~---' ~'- ................ Weathered Shale .'---~_--. Unweathered Shale ~.'.. Unweathered Shale ................... 440 -- ' - I 430 -- -- 430 A A' NOTE__S: 1. Stratigraphic lines are interpretive only. Actual conditions may vary significantly from those shown. ! reed engineering 2. Topographic conditions based on survey by John Hawkins & Associates iRev sed 03-25-97~. i 3. See Plate I for plan location of Cross Section. INTERPRETIVE GEOLOGICAL CROSS SECTION A-A' Slope Stability Analysis I Grapevine Creek @ Crestview Court I .- Coppell, Texas PLATE 10 460 L ~. . ~, I ~so;- J :' , ONE DIVISION = 10 feet CRITICAL SHEAR STRENGTH PARAMETERS LAYER UNIT WEIGHT COHESION FRICTION AHGLE NO. DESCRIPTION (pcf) (psf) (degrees) (~ Unweathered Shale 130 6000 24 ~ Bent(mite Seam 104 O 14 (~) Weathered Shale 12(} 8~ 24 (~ Alluvial Clay 120 5(3 28 Q Sandy Clay (Fill) 125 30 30 SLOPE STABILITY ANALYSIS-INITIAL SLIDE PLATE 11 51(] -- 5oc L _ ONE DIVISION = 10 feet CRITICAL SHEAR STRENGTH PARAMETERS LAYER UNIT WEIGHT COHESION FRICTION ANGLE NO. DESCRIPTION (pcf) (psi) (degrees) (~ Unweathered Shale 130 60(X) 24 ~ Bentonite Seam 104 0 14 (~) Weathered Shale 120 80 24 Q Sandy Clay (Fill) 125 30 30 SLOPE STABILITY ANALYSIS-INITIAL SLIDE, UPSTREAM PORTION PLATE 12 5CC :-- -- ! 490? --T-- -- 480 '-- - \~- ;" CO~RETE P~ER~ ~ ~C~TE ~fl - i~. ~ ~ , , J ONE DIVISION = 10 feet LAYER UNIT WEIGHT COHESION FRICTION ANGLE NO. DESCRIPTION (pcf) (psf) (~) Unweathered Shale 1,30 6(~00 24 ~) Bentonite Seam 104 0 14 (~) Weathered Shale 120 30 24 ~ Alluvial Clay 170 40 26 t,~ Sandy Clay (Fill) 125 20 3(: SLOPE STABILITY ANALYSIS-WITH PIERS 8, GABIONS PLATE 14 4. Ir. stall min. ~'" ~ia..u_r.~- ~_ ~[L~.__4SS~: t~ "~. . equivaleng) i:lt~ .~'erf~raze~ ~r~in~xe_ piu=~ ~ on max. 12' M;~. } ~ischarxe aFFr:.x, i' a~'~e "n:~al~ _reel ~ '~"k.,, section cf ~=-~ Curer re~r_-:ei slupe "!th _rusi~n ~ 4. ~ - ......... L~ ........... ""'-~ , ; 7. C~ = tin. ~' hi~h ~abi~n ---,1 - . ,- APEX. ~ BEN~TE ~M ~ _. _~ ..... UNW~T~D ~ALE EL 43~ * ~30 .................. rood nnflinoorinfl ~ IDEALIZED REMEDIAL I ' o s ,0 ~' CROSS SECTION Slope Stability Analysis I {Idealized Se*fion-~Ol fiO~ Grapevine Greek ~ Crestviow Court i Goppoll, Ioxas PLATE 15 I 9 [ 3±Vgd ' , s~xe/'lleddoo I s~s~l~UV AI!I~q~ls edOlS ~ a~so~o.~-~,,~.w~ ~/~ .--' ..- I I _ ._~ ._. ......... /; ~_,.~.=_~=..r~~ _, ,, _, i · --._- ..... = ..- - ..................... ~'.-'--~. , , _z L --'- *'"------- .... I ._. . .C~ ~ · . .__ - ~ I . .~ --- .... I _ .... I , ~---._._,, ----.__~_ , ..... _ . ---.... . I ~ ..... _ - , .____~ . ..... __-___.___-- -'--. '" ? 'N ~, .u ~:;;-~° ,o,~0o, ............... ~=~ ~....' I ' "'.'- .............. / ~: ~-~~.~ / "-- I