WPC  2"B Z`XArial ItalicArialArial BoldHP LaserJet 4 PlusIIHPLA4PLU.PRS2xCQ\'sZX#|9ND,C2xjAG;X1mC9,  Xm2PG;XP/qC:,cXq2pPG;X2n T|TOO "4^DDV6OOYAOAADDAwDADn6wD66w6RwDwwwuR?ROAnOOODOOOOOOuOAwCCCCCCCCwwwwwwA6AAA6AAgww6A6[6RRRwwwwTDDwuuu6RwDwwDu414WddddddddddddddddddddddddddddddddddddddddNTT~PYVPTO33PPPPTTyuu3OuO"uu~uu"m+^99Ipp.DDNt9D99pppppppppp99tttp̅}9ep}}999\p.ppepp9pp..e.ppppDe9peeeeE5EtD9sZDDD9DDDDDDpD|9pppppȰepppp99999999pppppppppepp|pepppppeeee|pppppppppppp9.999.99Xeep.p:p.pDp.pxppppȼDDDeeee}L}9}9ppppppe}e}e}epp.pDe}9ee|pp8dp,(,WddddddddddddddddddddddddddddddddddddddddNHxxHlpD|pppppLJpDHpD,,DDpDDxppxHxxHsdd,DdD"dxdldtxxd"m+^:D`pp8DDLt8D88ppppppppppDDttt|Đ|8p|||D8Dtp8p|p|pD||88p8||||LpD|pppdL8LtD8ttDDD8DDDDDDpD|8pppppȰppppp88888888|||||||||pp|||p||ppppppppppp||||||||88888888ppp|8|L|8|`|8|||||ȼLLLpppp|`|D|D||||||p|d|d|d||8|Lp|Dpp||:dp,0,WddddddddddddddddddddddddddddddddddddddddNHxxHppD|pppppLHpDPpD88ddpDDxppxHxxHs||8ddD"dxxldtxxd2  P #Xp2PQ XP#e  yxdddy Jicarilla LaJara|'`v(#5Conceptual Design   IV.GEOTECHNICAL/EMBANKMENT DESIGN CRITERIA   R A.` ` Development of Conceptual Improvements(#` XX` ` The geotechnical/embankment concerns for LaJara Lake Dam include lack of erosion protection in the existing spillway, lack of upstream slope protection, poor drainage which inhibits evaluation of foundation seepage, some concern for seismic stability of the upper foundation alluvium and lack of all weather crest access.(#` XX` ` Several geotechnical improvements were studied in the feasibility design report but were not recommended for further investigation in this report. They include; (1) fabric formed concrete protection on the upstream slope, (2) concrete grass pavers protection on upstream slope, (3) wire enclosed stone protection on upstream slope, and (4) compacted soil cement on the upstream slope. These alternatives were all more costly and believed to be less effective than riprap slope protection.(#` XX` ` The following improvements were considered essential for one or more of the conceptual design alternatives. The purpose of each improvement follows:(#`  R XX` ` *X Add rock fill and drain to downstream toe This improvement would improve the static and dynamic stability of the downstream slope, assure drainage between the dam and S.H. 537 and increase the control and permit assessment and measurement of seepage. Improvement of the drainage between S.H. 537 and the dam is essential and a drain system and outfall pipes under S.H. 537 has been designed and will be constructed in the near future.(#  R' XX` ` *X Waste sandstone protection on upstream slope This improvement would protect the upstream slope from wave action using a 24 inch(,)) thick layer of suitable lower grade sandstone, if local quarrying of sandstone is acceptable to the tribe.(#  R XX` ` *X Quarried riprap protection on upstream slope This improvement would protect the upstream slope from wave action using a 12 inch thick layer of graded higher quality riprap over a 6 inch thick bedding layer.(#  R. XX` ` *X All weather surface on crest This improvement would widen the existing dam crest to 10 feet, bring it to a uniform grade and place 6 inches of gravel surfacing for an all weather access. The resulting top of dam would be Elev. 7322.8.(#  R C.` ` Material Properties(#` XX` ` The existing embankment appears to consist of an upper clayey sand and silty, clayey sand layers on the slopes. The interior is generally a lean clay. The upper clayey sand and silty, clayey sand layer is 7 feet thick at crest exploration E2 and thins to approximately 5 feet in explorations E1 and E3. Excavations 12 and 13 indicate that the upper layer is approximately 15 inches thick on both the upstream and downstream slopes. The sandy materials may have been added during a 1963 expansion (raise) of the dam. The lower clay layer is about 18.5 feet thick in exploration E2 and the total embankment thickness at this location is 25.5 feet.(#` ` ` The alluvial foundation beneath the embankment consists of various thicknesses of lean clays, silty sands, siltyclayey sands, fat clays, poorly graded sands and silty clays. The overburden is the thickest in exploration E2 with a thickness of approximately 86.5 feet. (#` ` ` The rock fill material needed to raise the middle dike, riprap slope and channel protection or diversion dike will probably be obtained from offsite(,)) borrow sources. The upstream slope protection for the embankment, either riprap or waste sandstone, will be properly sized in the final  R design.(#`  Rt D.` ` Static Stability(#` XX` ` Two sections of the existing embankment were reviewed in the Deficiency Verification Analysis (DVA) for both the steady state seepage and rapid drawdown loading conditions. The two sections of the embankment analyzed are at stations 4+40 and 6+00. The rapid drawdown surface for both sections is assumed to drop from elevation 7318.5 to the toe of the upstream slope.(#` ` ` The stability of the downstream slope of the existing embankment for both the tested sections was found to be slightly deficient in the DVA for the steady state seepage loading condition. For the rapid drawdown loading condition, unsatisfactory factors of safety were found for shallow surface sloughs for both of the stations analyzed. The drawdown analysis is overly conservative for a recreation lake which is not subject to drawdown. The addition of riprap or waste sandstone slope protection will improve the upstream slope. Deeper shear surfaces evaluated in the DVA for rapid drawdown resulted in adequate factors of safety. (#` ` ` All of the conceptual design alternatives will include placement of rock fill and a toe drain along the downstream toe. These improvements will load the toe and lower the phreatic surface. The desired factor of safety for the HLSS loading condition is 1.5. Static stability analysis with the improvements will be performed in final design. Addition of RCC overtopping protection on the embankment would also improve the downstream slope stability.(#` (,))Ԍ  R] E.` ` Dynamic Stability ` ` The DVA analyzed the liquefaction potential of the existing embankment and foundation materials during a Maximum Credible Earthquake (MCE) from three possible sources; Transition Zone, Rio Grande Rift and Random earthquake. A MCE is the largest reasonably conceivable earthquake that appears possible along a recognized fault or within a geographically defined tectonic province under the presently known or presumed tectonic framework (USCOLD, 1985). The results of liquefaction studies in the DVA indicate no potentially liquefiable layers are present beneath the embankment. However, it was found that liquefaction at the downstream toe is possible due to a Transition Zone or Random MCE. (#` XX` ` As stated earlier, all of the conceptual design alternatives will include placement of rock fill and a toe drain along the downstream toe, which will  R improve the seismic stability along the downstream toe. xx=(#` ` ` Post earthquake stability analyses will be included in final design using the improved condition of rock fill on the downstream toe. Stability analyses will be performed using UTEXAS3 along with engineering judgement to determine the critical failure surfaces. The post earthquake condition will be psuedostatically modeled by assuming low strength for potentially liquefiable layers. A factor of safety of 1.2 is desirable for the post earthquake case.(#`  Rr# F.` ` Seepage/Piping(#` XX` ` Based on available information and several visual inspections there does not appear to be a serious seepage or potential piping problem except possibly along the existing abandoned outlet pipe and possibly at the north(,)) end of the embankment where it doglegs to tie into S.H. 537 and is probably founded on a weathered and jointed sandstone surface. Installation of the drain system will permit a better evaluation. In any event, the abandoned outlet pipe will need to be plugged and sealed against peripheral seepage as part of the outlet replacement construction. If the north end dogleg of the embankment contact is seeping, the short length of embankment will need to be excavated, the contact surface treated and the embankment replaced. The rockfill over sand filter and toe drain along the toe will further improve seepage control.