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HomeMy WebLinkAbout001063009 Geotech Assessment 05/23/00 09:20 8360 452 8498 NT! ENG.& SURVEY . [~002 . .. · -. · ' ' 717'.S TH PEABODY sTREET, PORT'ANGELEs, WA/9'36'.~. * '. ' .. ' . ! · ': '.. ~ "* ... · ,~o,~-"2":';J"~Jc°°~*""'"~ ' /~~'"-~ '"'"~ ~ ~' ' · . . . GEOTECHNI.CAL REPORT - .. . .. ' ' .for:' -" " ', -.i'.'.. :. :, . . ,, · · · . ·" Lot J"ofGovernmentlLot:4 .." · ., · · ,. · . . . · , : -' SECTION-6, TOWNSHIP. 30.NORTH, RANGE 1 'wEsT, W:M,. .. JEFFERSON CQUNTY,'WASHINGTON ..-.-. . . . · -, -,. . . · -. Prepared.fOr. .. 'i . .. .. · .. MR.-' & 'MRS..BEN JARvIS. '".. · : " · · - . · .. , · . · . P.r:epared by '-NORTHWESTERN.TERRITORIES,'. 717 South' PeabodY Street Port'Angeles,. Washington. · ,. · .. · . .Ma'y,'i2000 INC · .JEFFERSON COUNTY " ..' - DEPT. OF COMMUNITY.DEVELOPMENT .. ,, · . .. :. · . .. · . . "" COPY.:' 05/23/00 09:20 ~'~360 452 8498 NT! ENG.& SURVEY .. .. · ¥ .- 003 MaY2$; 2000 · Mr. &'Mrs. Ben'Jarvis 6620 "Milano.Court. OlYmPia, WA 9.8.513- 'Subject:. G'eOtechnical 'Report .for Lot. J of GOvernment .Lot. 4 · Dear'M~'. & Mrs; Jarvis:. · . Backgr°-und: .. t ' 'County :requirements. o . _· In response to Mr.' Kevin Bu:rgler's. request .on your behalf, we' co'nducted a site - inspection of the subject, property on .May 19, 2000. Refer' to ..Figure. ii' for scale map' and loCation. This report', addresses the requirements for. a GeotechniCal Report-under. Section 11 of the'Jefferson Cou.nty Critical Areas O'¢dinanCe. The primary focus of the' report is the slope stability Of the north .facing marine blUff as it· relates'to residential home' constructi°n.on the lot.' " ' ...... · .... '. .. Based on the findings-and recommendations of this report, the.undersigned certifies' that: .... '.- .-' . . - . a, · Qther than' normal' bluff recession ("mass wasting"), there'is"minimal landslide hazard as proven by a lack' of evidence of landslide activity, in·t. he vicinity, in the ...past; .. ' ,'-· ' '" · . · b. An analysis of slope Stability-indicates that the Pr0.Posai will'n0t' be subject to risk of landslide Within,the recommended setbacks for the pro.posed 'hOme; ,. . c, The proposal WB not increase surface water discharge Or Sedimentation to ·, adjacent properties beY0n'd.'predevelopment conditions;. . · . , . · , d, The:proposal will nOt' decrease slope Stability'o.n a.,djacent propertieS.." . · · ,. Certificatjo'n of Items` c& d.is Contingent upon PrOpel. conStruction and maintenance.of an .engineered.drainage, erosion and sediment control p!an per.Standard Jefferson 05/23/00 09:21 8360 452 8498 . . .'. .. ... GeOIoqical 'Hisl~on/: NTI ENG.& SURVEY . During the most recent ice age, the cOntinental ice sheet'.moved across this region. The-glaciers, with .their enormouS pressures, ground up the.exiSting-rock units., RoCks not previously found on the Olympic Peninsula were carried" ove!~ on the huge ice sheets coming 'from Canada, and left behind when the ice 'ret'reatedl The, res_ulting'' hodge-pod'ge mixture of rocks and'Soil is known as.."glacial,till",.. -. ,.. . . ... .., .' -. , ,. . . - . 'Req.ional Ge°lO.qical:' ConditionS: ' . . · The. blUff and property are underlain by ancient al'luviai sediments'deposit, ed by outwash streams from-receding, glaciers over' 12,000 years ago.. The se.dimentS contain abundant silts'and fine sands, suggesting deposition in tideland or marshland .: environments; The-generally firm or 'dense consistency of the sediments,..bel0w about 10 or 15.feet in depth as exposed on the'bluff'face, suggests theyhave inthe past been compacted-by thick ice which was present_in the region, This-firm, compact. nature of the sediments a'ccounts 'fo'[ their, ability to remain stable in near'vertical exposures.. '. - ' ' The sediments exPOsed on'the bluff faCe which underlie, the prOPerty consist of tl~ick.'I sequences of fine sandy, silt and Silty Sand which is 'nearly horizOntally bedded... · Irregularly bedded to.lensing sand and gravel. '10 to'l 5 feet thiCk .are.present in'the upper pa.rt, of the bluff. Thinner layers of clayey silt are present i.n.some places near the base of the. bluff. , - 004 , · · . . -. · · - , /~ 'very dense to hard'sand contai, ni. ng gravel and minor'silt is exposed, along the very base of-the bluff. This material appears tO be relatively: resistant to. erosion and .... appears'to underlie th'e broad 'beach which .is present at.t0W tide'along the base:of the · . bi. uff. -' -'" - ' . .. · . . . The blUff has been formed by marine. erosion and underCutting, along the shoreline, . resulting in the Over-Steepening and subsequent :periodic lfailure of the bluff. Resultant slOw landward migration o..f the bluff' haS been primarily in the form. of thin slab failures, · Material accumUlating on'the bea'ch from such masS Wasting is .rapidly dispersed .into the 'Strait.by wave,and· tidal action. Extensive accumulations are not pr. esent at the · base' of this blUff (Photo 2. ). in part, the general lack'of great, volumes of. such debds a't the base of the bluff atteSts to' the limited landward extent o.f irJdi~idual bluff failures.' Individual bluff'failures appear.to tYpically'result i.n losS of several.feet back of the top.of' 'bluff (Photo 3 ), The maximum size of recent failureS appear to have resulted in loss.of three to five feet of the to.p· of bluff in local areas which extend, about 30 to. 50. feet,, along the (o'p edge of the bluff (Photo 3 and Figure 117). Local accumulationS.of soil'debris .. · · . 05/23/00 09:22 ~"360 452 8498 -. NTI ENG.& SURVEY... from such mass wasting is eVident along the base of the bluff. The debris Protects the base of slopes .for'short periods until they are eroded away by tidal currents and.wave action. .. 'The attached Figure 21 is a reprint from "Washington Geology", 'Vol. 25., No. 1, March 1, 1997, which pr0vides' a 'series of sketches illustrating the cyclical process of bluff recession in this region. The.three homes shown, in Figure 17 (attached) are about 1/4 mile northeast of the subject property. Photograph 3 was taken on May 4', 2000, about 1/4 mile soutliwest Of the subject property. .- ... Local Condifiods' Ali of the portion of.the subject property which is above the bluff, areas appears to be stable. No evidence of instability or significant erosion is present. Surface drainage is generally.northwestward toward-the bluff edge. .. The bluff drops about'120 feet at 40 ° to 50.0 from the horizontal to. the' beach below. The face of the bluff is partially vegetated with grasses and: shrubs but few mature - trees.. No evidence of springs or seeps was observ.ed o.n the face of'the-bluff. Evidence ,of a recent shallow slide near the top 'of the bluff was observed, however, this minor scar is now covered with' grass and other Iow growing vegetation.: The Beach: Perhaps the most notable feature'on this section of beach is the accumulation of. ta·rge boulders strewn around (see Photo 2'). These boulders were embedded in the upper. soil strata. They become exposed and fall to the beach as the bluff face recedes. To some degree, these boulders on the beach serve as a natural breakwater to.dissipate energy of the waves and currents that attack and erode the base of the bluff at high tide. ~ ? .. OO5 -Findings:. , . . Overall, the bluff and uplands.at the ·prOperty are "grossly stable". Evidence of normal, ongoing bluff erosion ("wasting") is apparent. 05/23/00 -3. . . 09:23 '~360 452 8498 NTI ENG.& SURVEY . · . . The typical rate of' recession· for these bluffs has been reported to be six: inches to one..f0ot per year: .'. ... .. .. Under existing conditions, the' average annual rate of recession for this. bluff could be expected to be in the range of 6 to .12 inches or an. aver;age of ~J inches (0.75 fi/yr.) · .. '.. · Once in. 10 to 20' years, a significant slide similar to thOse'shown in Pho.to '3 or Fig. 17 could Occur in a matter of minutes,, resulting in. a .bluff recessio.n of'five feet, more or less in. a single event. , · 006 RecommendatiOns.* . A 1·20-foot minimum setback from' the'top'ed~ge of the bluff i·s recommended for all 'structural bearing, sections of a ·new home On this site. , . A redUction' down to. 100 feet .is possible with more· detailed ·site inveStigation and analysis of a ispecific house plan. · . - , Good. drainage practices and Vegetation management are 'reCommended ~0 prolOng the frequency and magnitude of bluff recession..(Refer to attached publications). Limitations' - . ,. This rePort'is based on'a'viSual inspection O.f the existing site conditions, No scientific measurements., tests or calculations were performed. The findings and report are · limited to the normal standard, of care of the industry for an investigation without benefit of scientific data and calculations. Unless constructiOn plans are reviewed and the cOnstruction work is inspected by the Engineer, no warranty is made by the Engineer concerning conformity of'the ConstruCtion to the conclusions and.recommendations of ! · . this 'report. .'- - ; · Tho'.sole objective bf.this investigation has been to diagnose the· geotechnicai conditions at the.site. The.report has.been prepared for the'exclusive use of Mr."& Mrs. Ben Jarvis and potential purchasers of. the property. It may-be used by others-only with expressed written permission of the Engineer. The report has not been prepared for use by others or other uses. The observations; interpretations, and conclusions herein are based on generally accepted professional engineering .and geologic principles and' practice. This warranty is in 'lieu of all others,either expressed or implied. · .. 05/23/00 09:24 8360 452 8498 Qualifications! *' .. NTI ENG.& SURVEY ~_007 ., · This report has been prepared by or under the direct supervision of Mr. J.R. Jerry Newlin, P.E., licensed by the 'State.of Washington with over 15 years of geotechnical and related ..experience on'the Olympic, Peninsula. · . sincerely, ~ . NORTHWESTERN. TERRITORIES, INC. .. .Newlin, P.E. PrinciPal Engineer. JRNieas C:~JARVlSiwl0d t 05/23/00 09:24 ~360 452 8498 NTI ENG.& S~RVEY ~008 l) OP' 0.50 ~. 0.81 ct, I,PO 209.59' TAX 2 ~ 0.06 a. O<(Z o ~.-,,,c4 I 211 TAX 59 1.40 o. 183.58' 150.40' 135.66' 130.12' 132.70' EASE I"IA? FURA//St-tED BY 001 Wl / 20.~ 132.70' [ 2564.17' (NW 7-30N-1W) 05/23/00 .. · 09:25 .'~360 452 8498 .. NTI ENG.& SURVEY . · · · .. ~ ·-~P H O-T .0 S 4' 009 ., -. · . · . · ;. 05/23/00 09'25 '~360 452 8498 NT~ ENG.& SURVEY ~010 Photo 1 - Subject property viewing southwesterly along Porter Lane. 5/19/00 05/23/00 09'27 8360 452 8498 NTI ENG.& SURVEY ~011 Photo 2 - Marine bluff face viewing westerly. (Note boulders on beach.) 5/19/00 05/23/00 09:29 '~360 452 8498 NTI ENG.& SURVEY ~012 Photo 3 - Recent slide about 1/4 mile southwest of subject property. 5/4/00 05/23/00 09:32 '~360 452 8498 NTI ENG.& SURVEY · ; 013 FIGURES-'17 AND 2i '(Reprinted: from 'M/a'shingt0n Geology'' VOlume 25, No. 1, March,' 1997")' 05/23/00 09:32 '~'360 452 8498 NTI ENG.& SURVEY ~014 Figure '! $, Slide activity such as this in the Useless Bay area of Whidbey island can cause periodic retreat of the bluff edge by as much as 20 feet or so in seconds. During this recent slide, a portion of the fence in front of the large house was lost. Such episodes commonly are preceded ancl foflowed by decades of little ero- sion, making estimates of average bluff retreat rates potentially meaningless. In this location there are multiple impermeable silt layers that perch water, in contrast to conditions like those at Scatchet Head (Fig. 14), where water is con- centrated above one impermeable "perching" layer. Slides here can be triggered by an abun- dance of water (as in the December/January storms) or by wave erosion at the base of the bluff. A rainstorm may simply be the "last slraw". In many locations around the sound, water from winter rains is accumulated inland ol bluffs and may cause landslides to occur months later as it slowly migrates toward the bluff. In Ihe mid- 1970s in the Golden Gardens area of Seattle, slides occurred well into summer after a series of exceptionally wet winters. Figure 16. Severat beach homes on the east side of southern Whidbey island had close calls from debris avalanches. Debris avalanche tracks and deposits here witl soon be colonized by alders. Stripes or patches of aider trees that are all of the same age can indicate areas where slide activity occurred in the past; the age of the trees indicates approximately when the slide(s) occurred, in 'the 1950s and '60s, many beach- level developments like this were constructed on fill behind bulkheads. Material for the fill was commonly hosed off the slopes or bulldozed from the bluffs. This may have contributed to continuing slope instability by destabilizing the toe of the slope. Figure 17. Fortunately, homes here were built with adequate setback-- for these failures. The depth of a failure surface can influence the rate of retreat of the edge of the upland surface; In this slide west of Port Townsend, shallow de- bris avalanching (far left) has caused no signi'fi- cant edge retreat yet. The mid-bluff bench on the right indicates a relative!y deep-seated slide of upper-bluff sediments only. (See Fig. 21B.) The surface of failure for the ~iddle slide is even deeper, "daylighting" at (or below?) beach level (Fig. 21 B, C), and has caused the most re- lreat. At many sites along the coastal bluffs, sedimentary units are not laterally continuous, and conditions can be quite different over a dis- tance of 100 feet or less. Washington Geology, vol. 25, no. I, March 1997 05/23/00 09'34 ~'360 8498 ENG.& SURVEY 015 ? '," z //. , ,_,x. ,_ , : ...... I ...... / 6roo[o~ O~ ground ou~sc~ .~--~__~__~~~ - er~vd I ~~ ~ '-, ~~ _~A~~ d~ failure ~u~a~ Al lira beginning o! an Idoalltod cycle. Iho blulf lace solll aod po~cltos above Ute relatively Ira. sequence. Snlu~allon creates poro-wnlo~ pfoa~uroa tirol ~oduco tho oflocllvo sffoflgth ol IIToso Runoff and precipilation introduced by the sources shown in A have infilffaled and weak- ened the sediments, causing failure of the un. consolidated upper sand unit. Once mobilized. Ihe sand moves (sometimes episodically. sometimes continuously) along the contacl with Ihe underlying less permeable unit on l~e mid-slope bench, often cascading as a secon- dary landslide off Ute bluff formed by Ute lower unit. This migration of material across the bench decreases Ute buttressing of Ute upper bluff. Failure surfaces can be deep (those that project into Ute lower, less permeable materi- als) as well as shallow. Benched bluff retreat continues. Movement o! slide debris toward the lower bluff furiher de- stabilizes Ute upper bluff, causing continued sloughing onto' the bench. Either failure of the upper bluff onto the bench or. failure-o! the '-- slide debris off Ihe lower bluff can. ~gger a cy- cle et movement. Movement along a deep- seated surface can reset this sequence of evonls. -- Figure · !. This sequence of sketches shows the idealized, potentially cyclical process by which bluffs in Ute northern Puget Sound area are forming and rob'eating. 05/23/00 09'35 ~360 452 8498 NTI ENG.& SURVEY ~016 LAN DSLI DE ALERT AND HILLSIDE DRAINAGE PROBLEMS Many landslides are triggered by improper drainage of water from different sources uphill from the slide. These sources can cause'concentrations of extremely heavy saturated soils. When the saturated soils become heavier than the soils surrounding them, they can easily trigger a landslide. Seek the assistance of a geotechnical engineer for site specific design or consultation. Before undertaking any construction on your slope, check with your local permitting agency. Filling or dumping of debris can cause excess weight, slope dam- age, disturb and smother vegela- tion, and make access difficult. Large trees at the edge of steep slopes can act as a pry bar in strong winds and "- - - cause the root bali and ad- jacent soil to be loosened. Curved or crooked trees on a slope are usually the Vegetation removal and com- paction of soils increases run- off and surface soil erosion. ImproperlY directed down- spouts can cause concen- trated flows which create sub- slantial gullies over time. result of a slow. gradual Septic systems can soil creep. , . ' ,~ -... u~." ~ ~ ~ ~ contribute additional o ,' · ~ ' ' · ~/4~1 z~ ~~-} I moisture to an already ~ - ~ ' / : /' - ' ~ ~'-~ ~ ~ sa~t~ ama and shoUld _ ' ' ~ ,- -',' ~ ~ ]~ not be placed near ihe Il/'.~ .'.", .' .' ~,~~~,o,~. ~ ~/' ~. -"; ,~7 · Th~ p~..~ or ~ / / / ? ~ ~1~.~ __ cracks in [he slope ~ ~ ' / / I _ F/ ~LI7 ~ . . ~ / / v ', ~ ~n ~nd~te the be ~ / . -/, ~__ '/' ,; ~ , ~ ~~ ~ou.d~,o.-~,n~ ~o~ g~nnmg of a land ~ ~ - ,~ /I dom in ' ' _~. ~ / -. ' f.~, _ ~he hi,~i~e ~.~ ~e .' ~ ~i~. ~ ~ ' - ~ ~"~~ ~::/~a~erout O.~o the s~o.e ~usi.~ /' ~ ~, /;~-~~ ~~o.c~.,~a,~,o~o~h~.w~,. ~ere seeps appear ~ Bare areas may in- ~ / '. saturat~ soils. on blufffa~s, thedis-. ~ dicate recent or ' ' charged water erodes '. active slope failure· the soil below causing - ' ' the upper layers to fall - or slide. Springs and groundwatD'r "daylighting' can cause erosion along the slope and undercut the slope face. Saturated soils are prone to mass soil movement. 05/23/00 09'36 ~'360 452 8498 NTI ENG.& SURVEY ~017 · homeowners for l dslide control hillside flooding debris flows soft erosion Wal~ ~!~ & I~ggers ~sl slo~ ~bl~s. Find ~e ~e wal~ ~ ~ing Whal YOU ~ ~ Io prevefll lands~de and sl~ sla~lily ~oBe~: from. ~ out in Ihe rain & check areas like hillslopes, gullies, ddveway & street , drainage, roof gullets & downspouts. Next. see where il i~ & where il 9Des. Conce~traled tlow can cause g~eal damage, · WET., WEAk ,md STEEP - Slope failure problems are caused by any combination d waler salutation and flow; weak. heavy eadh materials; and, steep slopes. Remember. WAI'ER is /he most ~ornmon (n'gger of $1ope fa~lure~ · STEEPS, LOPES - Problems occur on steep slopes, especially when slope of Dee vertical Io two horizontal is exceeded. · DRAINAGE - Channels. streams, gullying, pending and erosion on slopes ali indicate potential slope I~obiems. Road and driveway drains, gutters, down spouls and olher drainage can concentrate and accelerale flow. Ground saturation and ooncenlrated vefodly flow am a major cause of slope problems and landslide Idggedng. · DEBRIS - DeposilJon o! so/Is and vegelation at Ihe base of slopes show erosion, flow and creep from ground cover above. · VEGETATION - Condilion of vegelalion indic, ale slope condilions. Bare slopes may show erosion and sliding. Trees thal bend downhill show creop of upper soils, trees filling uphill may show deep rola(ionaf landsliding. Patches of younger vegetalion may show former slope failure Horsela~l ferns or olhe~we[ loving plants often indicale saturated ground and springs. · 0EFORMED STRUCTURES .~ Foundation cracks; doo~s and windows out of line o~ slicking; I/lied floors: sagging decks: cracks in masonry and chimneys; c~acks in driveways, curbs & roads, gaps belween floors & walls, failing retaining walls & tilted power poles can be warnings of slope instabilily. · LOOSE FILL al lhe lop of a slope due Io yard wasle, cut & fill land grad/rig or olhe~ process can aggravale slope inslabilily. · DIVER[ CONTAIN and safely .DISCHARGE waler around and away !rom unslabte slopes, yards and structures. · Use SANDBAGS to dived water from unconlrolfed spilling, such as over curbs or from gutters and downspouls, or from washing into buildings. · Use GROUND COVER to protecl sensilive and unstable areas with plaslic sheeting or tarps, t~dap or other mmenal. Wood chips and straw may be worked into lhe surface. Sb'aw bales can relard velocily flow and ems!on. Cover ground cracks, such as from sliding or erosion, with plaslic sheeling slaked or loaded down wilh weights. Protect cover Jrom wind damage or other forces. · CONTAIN. FLOW by directing into load gutters, slofm drains or non-eroding stream beds. Flexible plastic pipe can be quickly installed. Redirecl ~ away from slopes and p~es. DO NOT concentrate flow oalo slopes or your neighbors properly, or behind ~etaining wails. · SAFELY, 01SCHARGE~ coocent, rated waler to a safe, non- erodibte site such as a slonn drain, slmet gulter or " rock bed ol' a stream, Coarse rock or bales of slraw can reduce the impact of ~ concenlrated velocity flow~ and can reduce sedimenl'i~. ~ ~ I SAFETY TIPS · Conduct waier to a safe slorm' drain discharge point. \ ,,~ ,PM":... :-"' .'. ' :~ ~ ·, .. I-. ,- ' /.:-;;;. , ..:. ....... ].] c °l~rainage ~b3ted and dischalged O~O loose :fill on lie down slope side of a hou.fe by roof o~ ddveway and road drains is the ~ dominant Uigger of landsliding in areas of residenlial devedopment on steep, weak slopes. 05/23/00 09'37 '~360 452 8498 , EL~II( :~ I'~§ILI~ATIO~ Banks Ihal are sleep and suscopliblo lo landslides, (x are already slougtdng and el~o'oaching upon a slmctum, are in ne~xl el a bank stablflzallon o/led. Many diffor~l levels el ~'olectio~ are posstbio and il Is bos! 1o comuil wtlh a geolecl~ical or slruclural engineer if you a'o in a hazardous area. VEGETATION On geolechnical or slope areas where there is no II~'ea! lo lilo or L/ slruclures a vegelation planting plan may be Ihe mosl ~ ,'",r reasonable apl~oach. The dilferenl lypes of reel syslems -~ Ihal plants have can slrenglhen the c~hesk~ el soils and '~'"' '"'~" bind the soil slmcture Iogether inlo a la'ger unil. This .,~r~ '"'C'5,,'~.. can add resistance Io polenlial landslide areas. · c~,' * .., .,,~..~ Shallow tools can slablize Ihe lop layer ol soil. ....  , while deep lap or laleml root nelwmks can ..~.,.~- ~ ~ . ~ suengthen ~ k~ver base ~ayers. Uany '- '"~ 'I.,t I I? I,.'~.~ planls are parliculady uselul Ior bank be aUe to, p ants i7./' .'m~)l,jr thai grow well in your climale J ~~ and particular soils condi,ions. ~ -]~ / failure l~ane~ INTERCEPTOR ORAIN ~cavale lrer~ i~o impemaeable soil layer. Lay geole,,mle elo trench. Place gravel imo trench and ./Rackre exlefld gravel height Io Ihe maximum anlidpafacl waler level Ovedap geote~le on top of gravel. . 8ack~ with excavafed son. . ._ text~ - . ,;,.:. ?~ Pedora~ drainage pipe placed on 3-6 ind~es otgravel. Pipe midlx~n! should be MORE PERMANENT SOLUTIONS Major problems require major hazard midgatio~ and repairs. The best and easiest cure is Io avoid the hazardous sties. Urban population pressures increase the uses of marginal building sites requiring greater inveslment in stabilization measures. Steep. weak hillslope areas require increased code and ordinance conlrols lo reduce risks Io homeowners. Professional site investigalions by bolh a lechnical engineer and an engineering geologisl have been shown Io reduce landslide damage over 95%. Technical solulions can greally reduce Ihe risks_ Bul. pdvale insurance or governmenl hazard programs DO NOT protect the homeowner at Ibis time. Serious proUems require serious help. Hillside flooding, debris flows, erosion. and sliding ellen generate grealer damage Iha~ lhe homeowner can manage on his/her own. Serious problems require specializes professional expertise of regisle~ed civil engineers with geotechnical specialily and registered enginee~ng geologists. NTI ENG.& SURVEY ~ 018 · CONCRI~TI~ RI~TAININO WALLg C,,o~:mlo r~n~ w~s ~n ~ ~sl~ IO ~lhslW a I~ v~y ~ ~ur~ I~1~ ~l~s, T~y ao p~l~l~y usolM In sl~ ~lu~i~s ~ ~ol~ iS ~ close to l~ I~ ~ ~so N a a~. Tim slro~th of (~ ~Nning wNl Is ~ly ~~l u~ the sk~lh ~ I~ ~s ~ is m~ ~ a~ ~e ~r In ~i~t they ~e ~ t~e~. ~ ~ (ho ~s~n det~ r~lr~ I~ e~ sltuatl~ a S(m~mal ~ g~t~ ~ ~ ~ ~sult~ ~en a ~eie r~alning walt is ~g to ~ u~, _ r / ~ ~ wal~ away ~m ~e of waH ROCK WALLS Rock walls are .essentially gravity walls made of slacked lan:je rock. They pdmadly provide erosion proteclkxl and limited earth supped. ,Slope, rock depth and wall height are ~ to the slability of roc~ walls. Them!ore. they should generally be limited lo 15 feet or less in height and should be installed by professional roc~ety landscape installers. Engineers should design higher walls. :l~r._~=. - o~.,, · . WARNING! I~ your house is in danger of landslide damage, prelect.people first and EVA CUR YE IMMEDIA TEL E/ Danger Signs Include: . Rapid water or sluny flow impacting house. · In steep terrain; if flow stops or is irregular, evacuate fasl! De,s-dam bursts occur very quickly. · House c~acks actively opening. · House making noises. · Walls or floors lilting, - Ground cracks opening under house. · Any potion of house falling away.