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HomeMy WebLinkAboutB16-0243 Geotech Report.pdf· ... ~ JUN 2 3 2016 TOWN OF VAIL ~ CTLITHOMPSON · lflll t'mmtmn:mmuumam TownotYaU OFFICE COPY GEOTECHNICAL CONSULTATION LOT 22, VAIL VILLAGE WEST, FILING NO. 1 1740 SIERRA TRAIL VAIL, COLORADO Prepared For: KEITH NOVICK P. 0. Box 3222 5685 Wildridge Road East Avon, CO 81620 Project No. GS05840-145 April 7, 2014 234 Center Drive I Glenwood Springs, Colorado 81601 Telephone: 970-945-2809 Fax: 970-945-7411 'f!/;; -1~1 ;2 t/-::: f. ll/. -l ·~ I ,J X .. TABLE OF CONTENTS SCOPE ............................................................................................................................................. 1 HISTORICAL PERSPECTIVE ......................................................................................................... 1 EXISTING SUBSURFACE DRAIN AND FOUNDATION WALL. ..................................................... 3 SITE CONDITIONS ......................................................................................................................... 4 PROPOSED CONSTRUCTION ....................................................................................................... 5 SITE EVALUATION ......................................................................................................................... 6 SUBSURFACE CONDITIONS ......................................................................................................... 8 Fill ................................................................................................................................................. 8 Gravel ......................................................................................................................................... 10 Upper Gravel ........................................................................................................................... 1 O Lower Gravel ........................................................................................................................... 11 Clay ............................................................................................................................................. 11 Sandstone Bedrock .................................................................................................................... 11 GROUNDWATER .......................................................................................................................... 12 SLOPE STABILITY ........................................................................................................................ 12 Slope Geometry .......................................................................................................................... 13 Soil Profile .................................................................................................................................. 13 Groundwater ............................................................................................................................... 13 Strength Parameters .................................................................................................................. 14 Slope Stability Analyses ............................................................................................................. 15 Excavation Retainage ................................................................................................................. 16 Excavations ................................................................................................................................ 17 Backfill and Fill ............................................................................................................................ 18 FOUNDATION ............................................................................................................................... 19 Micropiles ................................................................................................................................... 20 FLOOR SYSTEM AND SLABS-ON-GRADE ................................................................................. 21 FOUNDATION WALLS .................................................................................................................. 23 Permanent Excavation Retention ............................................................................................... 23 Temporary Excavation Retention ............................................................................................... 24 No Excavation Retention ............................................................................................................ 24 SUBSURFACE DRAINAGE ........................................................................................................... 25 EARTH RETAINING WALLS ......................................................................................................... 26 SURFACE DRAINAGE .................................................................................................................. 27 ADDITIONAL CONSULTATION, CONSTRUCTION OBSERVATIONS AND MONITORING ...... 27 GEOTECHNICAL RISK ................................................................................................................. 28 LIMITATIONS ................................................................................................................................. 29 FIGURE 1 -APPROXIMATE LOCATIONS OF EXPLORATORY BORINGS AND INCLINOMETER BORINGS FIGURE 2 -APPROXIMATE EXCAVATION DEPTH APPENDIX A-PROJECT GS05050-125 FIGURES, PREVIOUS EXPLORATORY BORING DRILLING, LABORATORY TEST RESULTS AND SLOPE STABILITY ANALYSES KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:\OS05840.000\145\2. Reporta\GS05840 145 R1.doc • ' ,. 1.- SCOPE This report presents results of our geotechnical consultation for the planned residence at 1740 Sierra Trail in Vail, Colorado. We conducted a previous ge- otechnical investigation (Geotechnical Investigation, Solis Residence, Project No. GS05050-125, dated March 13, 2008) to investigate and evaluate subsurface conditions at the site and provide geotechnical engineering recommendations for a previously planned residence. We have utilized research and data from our previous field exploration, laboratory testing and engineering analysis to develop this report. Information from our previous investigation is provided in Appendix A of this report. Unless otherwise identified, figures referred to in this report can be found in Appendix A. This report includes a description of the subsurface condi- tions encountered in our exploratory borings and geotechnical engineering rec- ommendations for design and construction of earth retention, subsurface drains system, foundations, floor systems, below-grade walls and for details influenced by the subsoils for the currently planned residence. The scope of services was described in a Service Agreement, dated March 20, 2014. Our recommendations are based on our understanding of the planned construction. If building plans will differ significantly from the descriptions contained herein, we should be informed so that we can determine if changes to our design criteria are merited. A sum- mary of our findings and conclusions is presented below. HISTORICAL PERSPECTIVE Construction of a single-family home began on the lot in 1979. Extensive excavations were made into the hillside on the lower part of the lot. Records indi- cate that at least one groundwater spring was exposed during the excavation pro- cess and that several slumps occurred. Evidence of larger mass ground move- ment, expressed as undermining of Alpine Drive, were reported. Construction on the site was stopped while several field investigations and engineering analyses were undertaken to evaluate the slope movement and the risk of continued home KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:IGS05840.000\14512. R•por1s\GS05840 145 R1.doc 1 • • building on the lot during 1980 and 1981. A significant scarp developed on the upper part of the lot in 1980. Recommendations for slope stabilization were pro- vided to the lot owner and contractor. We understand that very little, if any, seri- ous shoring or anchored earth retention was implemented during the first con- struction attempt. Some slope stabilization was started in March of 1982. On March 8, 1982, a large landslide occurred. The slide mass resulted in the loss of the downhill part of Alpine Drive and portions of a Town water line. The slide mass also pushed the partially completed home off its foundation. Claycomb Engineering Associates, Inc. was hired by the Town to develop a site stabilization and monitoring plan for reconstruction of Alpine Drive and the lot. A requirement of the reconstruction plan was to re-establish the slope geometry that existed prior to excavations for home construction at the site. Implementation of the recommendations provided in the stabilization and reconstruction plan be- gan in May, 1983 and were substantially completed the last week of November, 1983. The plan by Claycomb called for removal of all material above the landslide failure plane, installation of a stepped subsurface drain system and placement of granular structural fill to re-establish grades. We understand that well compacted granular soils were placed from the top of the subsurface drain system to pre- excavation elevations. Figure C-1 shows ground surface profiles before the first construction, the approximate extent of remedial construction and the current sur- face. Daily observation reports by Claycomb and field compaction testing reports by Lincoln Devore were obtained from Town of Vail files. There were some re- ports missing; this is not surprising considering the problem occurred nearly 25 years ago. KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:IGS05840.000\14512. Reports\GS05840 145 R1 .doc 2 f ,. f EXISTING SUBSURFACE DRAIN AND FOUNDATION WALL A critical element of the 1983 slope stabilization and reconstruction effort was the installation of a subsurface drain placed on the natural soils below the slide plane. We understand the drain extends from Alpine Drive to the foundation wall buried below the lower slopes of the lot and daylights below Sierra Trail. We believe, the drain consists of a PVC pipe and 1-1/2 inch minus washed rock wrapped in geotextile fabric. It is critical that the operation of the drain be checked. We recommend the drain system be evaluated by using a camera in- serted in the drain to allow observation of the condition. The drain system may need to be "wet tested". Wet testing involves placing water into a high point of the drain and checking that the water discharges as designed. Water volume should be limited to only that required to check the flow. We believe the slope has been generally stable subsequent to completion of the stabilization and reconstruction project. We also believe that the subsur- face drain is functioning as planned and contributes significantly to the existing stable condition. The buried foundation wall also provides resistance to ground movements. Disturbance to the foundation wall and contamination of the subsur- face drain could adversely affect the existing slope stability. Some disturbance related to home building on the lot will occur, however, new construction should consider the need to minimize disturbance to the foundation wall and drain sys- tem. The drain discharge location needs to be identified and the volume of water being collected and discharged needs to be documented prior to the start of earthwork on the lot. We believe Mr. Bruce Lewis, the engineer who observed fill placement during the remediation, can help locate the discharge location. Mr Lewis is currently a partner in the firm Boundaries Unlimited in Glenwood Springs. Monitoring of the water volume discharged should occur during construction activi- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING N0.1 PROJECT NO. GS05840-145 S:\GS05840.000\14512. Reports\GS05840 145 R1.doc 3 ty on the lot to check that construction activities do not adversely affect the per- formance of the drain. If the drain becomes contaminated with grout during the installation of earth retention, it may become necessary to install horizontal drains and provide an ad- ditional outlet for water currently controlled by the 1983 remedial construction. The construction technique and the required length of each drain will vary depend- ing on the location on the site. SITE CONDITIONS Lot 22 is an approximately one-quarter acre site bounded to the south (up- hill) by Alpine Drive and to the north by a cul-de-sac at the end of Sierra Trail. Residential buildings, estimated at 20 to 25 or more years old, are located to the east and west. A small surface drainage is also located along the west property line. Mature aspen trees are along the east and west property lines. At the time of our site visit to prepare this report, about 3 feet of snow cov- ered the lot. The following description is based on previous site visits. We do not believe significant changes have been made to the lot. Existing site conditions are a result of slope reconstruction performed in 1983. The upper slopes of the lot drop steeply down from the north shoulder of Alpine Drive. These steep slopes transition to less steep slopes from near the center of the lot to the top of a 6-foot high boulder wall adjacent to Sierra Trail. Slopes occurring on the upper part of the lot below Alpine Drive are between 1.4 and 1.5 to 1 (horizontal to vertical) and the lower slopes from the center of the lot to Sierra Trail are between 2 and 4 to 1. Elevations along the shoulder of Alpine Drive are 8197 to 8201 feet; the elevation at the toe of the boulder stacked wall adjacent to Sierra Trail is about 8130 feet. The ground surface is vegetated with a dense ground cover of grass. A 6-inch di- ameter PVC pipe with cap is located near elevation 8160 feet in the central part of KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:\GS05840.000\14512. Reports\GS05840 145 R1.doc 4 (' ' , the lot. We believe this pipe was installed as part of a monitoring system to check for ground movement over time. We were unable to locate and identify the discharge pipe for the installed subsurface drain system. This discharge may be apparent after snowmelt occurs. It is important that the location of the discharge pipe be found. We anticipate in- creased flow from the discharge in the spring and early summer related to snow- melt. PROPOSED CONSTRUCTION We were provided conceptual plans by the Nova Group showing floor ele- vations and building sections. The plans provide sufficient information to provide design-level geotechnical information; however, refinement of the recommenda- tions in this report will be required when building loads and more details of the planned construction are provided. The building will be three levels. The lower level will be completely below- grade on three sides and open to Sierra Trail to the north. The main level will be below-grade to the south and above-grade to the north. The upper level will be partially below-grade to the south and above-grade to the north. Figure 1 of this report shows the extent of the lower level and main level. The lower level floor is shown at elevation 8132.5 feet. The main level floor elevation will be at 8143.5 feet. Excavations will extend an additional 1 to 2 feet to allow foundation and subsurface drain installation. To allow main level construc- tion, a retained "upper'' excavation of+/-20 feet will be required. This excavation will likely be made across the slope at about the location of the existing 8162 foot contour line. Below the retained upper excavation, an excavation of+/-20 to 25 feet below the existing ground surface will be required to step between the lower KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:IGS05840.000\145\2. R•ports\GS05840 145 R1.doc 5 ,, . , and upper excavations. This excavation step will be about 12 feet tall, from about 8142 feet to 8130 feet. We anticipate maximum foundation loads of about 4,000 pounds per linear foot of foundation wall and maximum interior column loads of about 100 kips. We should be informed of actual foundation loads when the information is available. We anticipate that several retaining walls will be constructed as part of landscaping. Comparatively large retaining walls will be needed between Sierra Trail and the garage on the lower level. SITE EVALUATION The initial part of our previous site evaluation consisted of a review of pub- lished geotechnical engineering studies, topographic mapping and an interview with Mr. Lewis, who was on-site during remedial grading. We also viewed the plans developed by Claycomb for the slope stabilization and reconstruction sub- sequent to the large slope failure on the site. When developing the soil profile for this study, we considered information from our borings and information from pre- vious studies. Appendix A provides previous exploratory boring drilling infor- mation. We drilled exploratory borings between November 20 and 27, 2007. An inclinometer (1-1) was installed on the lot adjacent to Alpine Drive on December 17, 2007. Approximate boring locations are shown on Figure 1. Drilling opera- tions were directed by our staff engineer who logged subsurface conditions en- countered in our borings and obtained samples for laboratory testing. We drilled four exploratory borings to explore subsurface conditions. Borings TH-1, TH-2 and TH-3 were drilled in the previously planned building footprint. Boring TH-4 was drilled above the lot adjacent to Alpine Drive. We also installed inclinometer cas- ing in a separate boring next to TH-4 to monitor potential slope movement. Ex- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:\GS05840.000\145\2. Reports\GS05840 145 R1.doc 6 • I ploratory borings were drilled with a track-mounted CME 55 drill rig. Borings TH-1, TH-3 and TH-4 were drilled with solid-stem auger. Boring TH-2 was drilled with hollow-stem augers. A soil anchor drill rig with a downhole air hammer capable of penetrating large cobbles and boulders was used to advance the deeper boring for installation of inclinometer casing. The casing was grouted per the suppliers recommendations. Exploratory borings TH-1, TH-2 and TH-4 were generally sampled at 5 to 1 O feet intervals to about 5 feet below the groundwater table. Most of the soil samples from these exploratory borings were obtained with 1-3/8 inch and 2-inch l.D. spoon samplers. The samplers were advanced with blows from a 140-pound hammer falling 30 inches. Samples in boring TH-3 were obtained by pushing 3- inch diameter Shelby tubes to obtain comparatively undisturbed samples of the fill soils. Shelby tubes were also used to obtain samples of the natural "upper" gravel soils in TH-2. The tips of several Shelby tubes were badly damaged, indicating the presence of significant quantities of gravel and cobbles. Caving soils from the lower part of the fill soils and at the groundwater elevation made sampling not practical deeper than about 5 feet below the groundwater surface. Soil samples were returned to our Glenwood Springs laboratory for visual classification and se- lection of samples for testing. We transported soil samples to our Denver laborato- ry where testing was performed. Inclinometer casing was installed in a boring (1-1) above the building site to monitor potential lateral movements of the existing slope. We installed Slope In- dicator Quick-Lock casing into the boring. The casing has a 2.75-inch outside di- ameter (O.D.) and a 2.32-inch inside diameter (l.D.). The casing has factory slot- ted grooves positioned at 90 degrees to each other. One set of grooves are posi- tioned along the fall line of the slope (A axis). The perpendicular set of grooves is defined as the B axis. An inclinometer probe is lowered to the bottom of the hole and then drawn upwards in two foot increments to take a reading. The probe KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:\GS05840.000\145\2. Reports\GS05840 145 R1.doc 7 ' r ) measures horizontal tilt of the casing in two directions. We recommend the incli- nometer be located and checked to determine if usable. We installed piezometers in borings TH-1 and TH-4 to monitor the water table. The piezometers consisted of installing factory slotted PVC pipe into the borings. We also observed the depth to groundwater in a utility trench excavated in Sierra Trail at the time of our field investigation. SUBSURFACE CONDITIONS Subsurface conditions found in our exploratory borings were fill placed to stabilize and reconstruct the slope underlain by natural soils. The upper 10 to 30 feet of the natural soils were removed or displaced as a result of the large slope failure in 1982. Remedial construction as designed by Claycomb consisted of 2 types of granular fill and a stepped gravel drain system. Below the remedial fill and drain system, we found silty to clayey gravels with some cobbles and sandy clay with silty to clayey sand lenses underlain by gravel, cobbles and boulders. Sand- stone bedrock was penetrated below the gravel, cobble and boulders at 72 feet in the boring drilled for inclinometer casing installation. Bedrock below the site is lo- cated at depths that will not affect the construction as currently planned. Sum- mary logs of the borings from our earlier investigation are shown on Figures 3 and 4 of Appendix A. The following paragraphs describe the soils found in our borings and a portion of our laboratory test results. Laboratory test results are provided in Appendix A. Fill was placed as part of the site stabilization and reconstruction plan de- veloped by Claycomb Engineering Associates (CEA). Estimated thickness of fill is shown on Figure 5 of Appendix A. Based on our review of field reports prepared during fill placement and an interview with Mr. Bruce Lewis, the engineer who ob- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS0584D·145 S:\GS05840.000\145\2. Reports\GS05B40 145 R1.doc 8 ' ' served fill placement, we believe the fill generally consisted of well compacted granular soils. We further understand that a stepped blanket drain was installed below the fill and that the existing uphill foundation wall of the destroyed residence was left in place. The drain is reported to be clean, gravel approximately 1 to 2 feet in thickness. A collector pipe system was provided. Fill thickness found in our borings varied from 5 feet at the top of the lot (TH-4) adjacent to Alpine Drive to 16 to 22 feet in our borings TH-1, TH-2 and TH- 3 drilled in the building envelope. We found two types of fill soils. The majority of the fill was a clayey gravel with scattered cobbles. This soil is similar to the fill ma- terial described in field reports and as described by Mr. Lewis. The lower 5 to 6 feet of the fill was sandy clay with gravel. Below the fill soils, we found gravel that we believe is part of the subsurface blanket drain over natural wet clay. We be- lieve the drain thickness was about 1 foot thick. We encountered some caving of soils into the borings near the drain elevation. Based on penetration resistance tests and our observations, the fill was medium dense or medium stiff to stiff. Fill soils were moist to very moist. Atterberg limit testing on samples of fill from our boring TH-2 indicated liquid limits of 24 to 27 percent and plastic indices of 9 to 11 percent. These results are simi- lar to results found by Chen & Associates during an investigation in 1980 on the natural soils on this lot. Two samples of the upper part of the fill selected for gra- dation testing contained 30 and 34 percent gravel, 41 and 42 percent sand and 25 and 28 percent silt and clay size particles (passing the No. 200 sieve). A grada- tion test on a sample from the lower part of the fill contained 6 percent gravel, 52 percent sand and 42 percent silt and clay size particles. We believe the lower fill will exhibit characteristics that are more like a clay than a gravel. Based on subsurface information from our borings, the site stabilization and reconstruction plan, and planned building elevations, we believe that the planned excavation will remove the majority of the fill below the building footprint. Fill KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:IGS0584Cl.000\145\2. Reports\GS05840 145 R1.doc 9 • • thicknesses of up to 5 to 1 O feet thick should be anticipated in some areas below the bottom of the planned excavations. The majority of the retained excavation will be in the fill soils. Gravel We found two distinct types of natural gravel in our exploratory borings. The "upper gravel" contained a significantly larger amount of silt and clay than the "lower gravel". The lower gravel contained significantly less fines (silt and clay) and had a larger percentage of cobbles and boulders. Our deep boring (1-1) to in- stall inclinometer casing was advanced through the lower gravel to bedrock using a soil anchor drill rig with a downhole air hammer. Upper Gravel Clayey gravels with scattered cobbles were found below the fill soils in all our borings that penetrated the fill layer. Our borings TH-1, TH-2, TH-4 and 1-1 penetrated 11 to 24 feet of these gravels. These upper gravels were medium dense to dense and moist to wet. Atterberg limit testing on selected samples of the upper gravels exhibited liquid limits of 25 to 27 percent and plastic indices of 7 to 1 O percent. These soils contained 24 to 45 percent gravel, 28 to 42 percent sand and 27 to 34 percent silt and clay sized particles. In the planned building area, the gravel was found between elevations 8137 and 8121 feet. Below the upper part of the lot, adjacent to Alpine Drive, these gravels were at elevations 8194 and 8183 feet. The lower part of this clayey gravel layer caved into borings drilled with solid-stem augers. KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:IGS05840.000\145\2. R1ports\GS05840 145 R1.doc 10 Lower Gravel The lower gravel contains a considerable amount of cobbles and boulders. The lower gravel surface was found near elevation 8102 at the planned building envelope. The gravel was found at elevation 8160 feet in our boring TH-4. These gravels were medium dense to dense based on results of field penetration re- sistance tests. Sandy clay was found between the "upper" and "lower" gravels in borings TH-1 and TH-4. The clay soil layer was 24 feet thick in our boring TH-1 and 22 feet thick in our boring TH-4. Clay was penetrated below the upper gravels in our boring TH-2. The surface of the clay layer was found at elevations 8126 and 8125 feet in borings TH-1 and TH-2, respectively. Samples of clay from our borings TH- 2 and TH-4 were selected for strength testing. A direct shear test was performed on a clay sample from a Shelby tube pushed from 29 to 31 feet. The results of the direct shear test are shown on Figure B-5 in Appendix A. Unconfined compres- sion strengths of 2900 psf and 1100 psf were measured on samples of the clay. The clay soils will likely be found near the bottom of the excavation for the lower level. We believe that the foundation support characteristics of the clay is relatively poor and support of the residence foundations on these soils involves a comparatively high degree of risk of foundation movements that may result in damage to the building. Based on penetration resistance tests, the clays are me- dium stiff to stiff and moist to wet. Sandstone Bedrock We encountered sandstone bedrock at a depth of 72 feet in our boring drilled to install Inclinometer 1-1. The bedrock surface is located a significant KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING N0.1 PROJECT NO. GS05840-145 S:\GS05840.000\145\2. ReportslGS05840 145 R1.doc 11 J • depth below the planned building foundation elevation. We do not anticipate bed- rock will be encountered in the planned foundation excavation. GROUNDWATER We encountered groundwater at depths of about 20 to 26 feet (elevations 8133 to 8127) during drilling of borings in the building envelope. Groundwater was found approximately 27 feet deep (elevation 8171) in our boring TH-4. We also observed water entering a utility trench at 6 feet below the road surface in Si- erra Trail. Two distinct groundwater zones may develop at this site during spring snow melt. Shallow, perched groundwater tables will likely develop on layers of clayey fill soils and/or on frozen soils. The large volume of water available from snow melt may result in water perched at several elevations. Water on frozen soil will likely not be found below depths of approximately 1 O to 12 feet below the ground sur- face. A deeper groundwater table appears to occur at about 20 feet below the ground surface in the building envelope. The surface of the deeper groundwater table will likely rise during snowmelt. SLOPE STABILITY In order to evaluate relative slope stability, it is necessary to define the slope geometry, including the general profile of soil and bedrock, estimate the strength of the materials that make up different zones within the soil profile, and determine groundwater conditions. The geologic conditions at a site influence the soil strength and groundwater conditions. The chosen shear strength components and groundwater elevations are major influences on the computed theoretical fac- tors of safety. Our slope stability analyses considered the global stability of the existing slope and the impact of planned excavations to allow construction of the planned building. KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:IGS05840.000\145\2. Reports\GS05140 145 R1.doc: 12 J I No amount of analysis will completely eliminate the risk of some slope movement during construction. We recommend that the client have a contingency in the budget to address additional retention or drainage measures on an "as nec- essary" basis as construction proceeds. Slope Geometry The slope geometry was modeled from 2006 topographic mapping by Al- pine Surveying, Inc. The topographic mapping is considered accurate to plus or minus one contour interval. The existing site topography is described in detail in SITE CONDITIONS and is shown on Figures 2 and C-1 in Appendix A. The topog- raphy is from maps at a scale of 1 inch = 20 feet with a contour interval of 2 feet. Generally, the ground surface in the vicinity of the proposed building footprint slopes at grades of 2:1 to 4:1. Steeper slopes of 1.4 to 1.5:1 based on the topog- raphy that occurs above the building footprint below Alpine Drive. Soil Profile We modeled the subsurface conditions based upon information from our exploratory borings and considering information from borings drilled by others. Subsurface conditions modeled were a 13 to 22 feet thick layer of fill above a sub- surface drain, 13 to 22 feet of natural clayey gravel with scattered cobbles, and 20 to 21 feet of sandy clay above gravel, cobbles and boulders underlain by sand- stone bedrock. The profile used in our analysis is shown graphically on Figure C- 2 in Appendix A. Groundwater Groundwater was modeled for the anticipated high groundwater condition during spring snow melt and runoff. The groundwater found in our exploratory KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:\GS058.C0.000\145\2, Reports\GS05840 145 R1.doc 13 1 ' borings and a utility trench excavation in Sierra Trail were discussed in the GROUNDWATER section. Strength Parameters Selection of appropriate strength parameters for stability analysis requires knowledge of the method and difficulty of exploratory boring drilling, review of la- boratory test data and the application of knowledge from previous experience with the soils and groundwater conditions in the area of the subject site. There are published values based on classification testing and testing for research or case histories. This type of data was considered when selecting the recommended de- sign values. The majority of the fill material and natural gravels include coarse sand, gravel and some cobbles. Laboratory strength testing in these granular soils ex- cludes particles larger than X inch. The field soils contain considerable portions larger than X inch. Effectively, the laboratory test results on those granular soils reflect the characteristics of the matrix materials for the soil profiles found at this site. This tends to not account for the frictional strength provided by the gravel and cobbles in the soils. Classification testing results on the fill soils and the natural gravels were compared with published correlations that relate soil properties and shear strength to strength parameters. Our experience was heavily weighted in determining the appropriate strength values to use in the analysis. We performed a direct shear test and unconfined compression tests to evaluate shear strength values for samples of clay obtained from our exploratory borings. Shear strength is typically defined by two parameters; friction angle and cohesion. The direct shear test evaluates these parameters at both low strain (peak) and high strain (softened). The results were compared with published val- ues and correlated with index properties for the soil type tested to judge the rea- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:\GS05840.000\145\2. Reports\GS05840 145 R1 .doc 14 J ' sonableness of the laboratory strength results. Shear strength parameters cho- sen for our analyses are shown on the table below. SELECTED STRENGTH PARAMETERS Unit Cohesion, c Friction Soil Description Weight, y Angle,~ (psf) (pcf) (degrees) Fill, gravel clayey 130 100 34 Fill, clay, gravelly 130 150 32 Gravel, clayey 130 100 35 Clay, sandy 120 300 27 Gravel, clean to silty 130 0 38 Slope Stability Analyses CTL I Thompson, Inc. performed stability analyses of the existing slope us- ing the computer program SLOPE/W, developed and distributed by GeoSlope In- ternational. CTL I Thompson's stability analyses included the existing slope with- out any excavation and the slope with excavations required to construct the pro- posed building. In discussions that follow, the term "factor of safety" (FOS) is used. This term describes the ratio of the strength available to resist sliding compared to forces tending to cause sliding. A factor of safety of 2.0 means the resisting forc- es exceeds the driving forces by 2.0 times. We believe the slope at the site currently exists at a factor of safety of 1.2 to 1.5. The lower factor of safety represents the steep slopes between Alpine Drive and the back of the building envelope at anticipated high groundwater level. When the upper slope drains and dries through the summer, we believe the fac- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:\GS05840.000\145\2. Reports\GS05840 145 R1.doc 15 I ! tor of safety (FOS) is near 1.4 based on the results of the computer analyses. Because the existing slope is near the angle of internal friction, surface raveling and potentially shallow surface slumps must be expected in response to intense precipitation events. Excavation Retainage Maximum excavation depths of about 20 feet (main level excavation) and 20 to 25 feet (lower level excavation) will be required adjacent to the uphill side of the planned residence to attain planned foundation elevations. Safe sloping of excavation sides is not practical. Global stability and internal stability of retention systems for excavations must be considered. The location of the discharge pipe from the previously installed subsurface drain system needs to be located to allow monitoring of flows. beams and post-tensioned anchors may be required to safely provide lateral re- straint and support to uphill excavations and limit potential movements. Installation of closely spaced grout columns between soldier beams would reduce the likeli- hood of caving of soils in open excavations and ground loss above the excava- tions. The installation of horizontal drains may be required to remove water from behind the upper and lower excavations. The need for drains should be consid- ered prior to the start of excavations. The need for horizontal drains is more likely if excavations are made in spring or early summer. We recommend excavations not be made before elevated groundwater levels from snowmelt recede. If site ex- cavations result in noticeable ground movement in Alpine Drive, a row of micropiles may need to be installed to protect the road. CTL should provide earth retention design services to evaluate potential earth retention systems and devel- op earth retention plans for site development. The discharge of the existing sub- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:IGSOSIM0.000114512. Reports\GS05840 145 R1.doc 16 I ' surface drainage system must be monitored during construction at the site. New construction must avoid adversely affecting the performance of the existing drain system. The existing drain system must remain operable during new construction. There are two general concepts for excavation retention: ••I tention systems (with integrated foundation walls or with separate foundation walls) that are designed for the life of the building; or 2 .... ~sys­ tems (usually with separate foundation walls) that provide a safe and stable exca- vation during building construction. When temporary retention is installed, the foundation wall is located in front of the retained face and must be designed for full lateral earth pressure. Permanent excavation retention systems can reduce lateral earth pressures on foundation walls, and thus reduce the required rein- forcement and thickness of the walls. Permanent retention systems with integrat- ed building foundation walls also typically require less excavation outside the pe- rimeter of a building. Temporary systems generally involve lower construction costs of the retainage system; however, there is no reduction of lateral earth pres- sures applied to building foundation walls. In the FOUNDATION WALLS section, we provide recommended earth pressure loadings for design of foundation walls depending on the excavation re- tention/foundation wall concept chosen. Excavations It may be possible to layback some excavations of limited depth to the east and west of the building. Sides of excavations will need to be sloped or braced to meet local, state and federal safety regulations. Generally, the fill soils at this site will classify as Type C soils based on OSHA standards governing excavations. In general, temporary slopes deeper than 4 feet should be no steeper than 1.5 to 1 (horizontal to vertical) in Type C soils. The natural slope is about 1.5 to 1; there- fore, retainage is required. In our opinion, vertical or near vertical excavations for KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GSOSU0-145 S:IGS05840.000\145\2. Reports\GS05840 145 R1 .doc 17 .. . retainage installation should not exceed 6 to 7 feet. Where excavations encounter groundwater seepage, the soils will tend to slough off to flatter slopes than de- scribed above. Contractors should identify the soils and groundwater encountered in the excavations and refer to OSHA standards to determine appropriate slopes. Contractors are responsible for providing and maintaining safe and stable excava- tions. Backfill and Fill Depending on the excavation retention/foundation wall concept chosen, backfill may be required between foundation walls and the excavation retention facing. Proper compaction of backfill adjacent to foundation wall exteriors, behind retaining walls and in utility trenches is important to reduce subsequent settlement and infiltration of surface water. We believe the excavated soils can generally be used as backfill, provided they are free of rocks larger than 3-inches in diameter, organics, and debris. A COOT Class 6 aggregate base course would be an appropriate backfill import that may expedite fill placement. Backfill should be placed in loose lifts of approxi- mately 8-inch thickness or less, moisture conditioned to within 2 percent of opti- mum moisture content, and compacted. Thickness of lifts will likely need to be 4 to 6 inches if there are small confined areas of backfill, which limit the size and weight of compaction equipment. The backfill should be compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D 698). Moisture content and density of the backfill should be checked during placement by a representa- tive of our firm. Observation of the compaction procedure is necessary. Testing without observation can lead to undesirable performance. Deep narrow zones of backfill between excavation shoring and foundation walls can be very difficult areas to properly place and compact backfill. Where backfill is required in difficult and confined areas, settlement of 2 to 3 percent of KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:IGS05840.000\14512. Reports\GS05840 145 R1.doc 18 .l ' the thickness of the backfill may occur because of the difficulty in achieving com- paction. We have observed settlements approaching 10 percent of the thickness of the backfill in some narrow zones. We recommend specification of a clean granular material (less than 3 percent passing of the #200 sieve) be used in these zones. The material should be compacted to approximately 70 percent maximum relative density (ASTM D 4253 and 4254). This fill can be densified and settled by moisture conditioning and applying compactive effort with vibratory compaction equipment. Properly placed granular backfill may experience settlement of about 1 percent of the fill thickness. Potential settlement should be considered if struc- tures, such as slabs-on-grade, are planned above deep, narrow zones of backfill. We recommend foundation wall backfill be placed and compacted to re- duce settlement. However, compaction of the backfill soils adjacent to concrete walls may result in cracking of the wall. The potential for cracking can vary widely based on many factors including the degree of compaction achieved, the weight and type of compaction equipment utilized, the structural design of the wall, the strength of the concrete at the time of backfill compaction, and the presence of temporary or permanent bracing. FOUNDATION We recommend constructing the residence *I · IJlll!aill ±!" H Micropiles essentially eliminate the risk of unanticipated settlement caused by loose pockets in the existing fill. Micropiles are considered attractive because of the ability of the drilling equipment to drill through cobbles and boulders and to ac- cess tight, restricted access without the need for wide work platforms (roads). Micropiles may be single elements or designed as groups. Pile caps (footings) will need to be provided unless a single pile is used. The micropiles should extend through existing fill and clay soils and penetrate at least 5 feet into the "lower" gravels. To reduce lateral loads applied from the foundation to the excavation shoring, it may be advantageous to incline alternating micropiles to increase lat- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:\GS05840.000\1C512. Reports\GS05840 145 R1.doc 19 .. { eral load capacity. A distance of about 3 feet is required for installation between the excavation face and the casing of the micropile. Our experience indicates that maximum total settlements will be about 1 inch for foundations supported on micropiles penetrating the lower gravel. Recommended design and construction criteria for micropiles and are presented below. ( Micropiles 1P/ Micropiles shr' be designed and detailed in accordance with Section 1810.3.10 of th · · g Code. Further, construction techniques and procedures contained in the FH icropile Design and Construction Guide- lines Manual", Report No. FHWA-SA-97-070 dated June 2000 should be implement- ed. We can design the micropiles or be available to assist in the designs and specifi- cations developed by others. General recommendations for micropiles are provided below. 1. Four distinct classifications of micropiles have been standardized based on various drilling and grouting techniques. A description of the various micropile types (A, B, C, and D) is provided in the previously referenced FHWA manual. The selection of micropile type should be left to the discretion of the designer and/or contractor. Based on the soil types encountered in our exploration, we anticipate a "Type B" micropile will be utilized. This type of micropile would be temporarily cased full length at the time of drilling. Neat cement grout is placed into the hole under pressure (typically 100 to 200 psi) as the temporary cas- ing is withdrawn. We recommend a minimum micropile hole of 5.25 inches and a total length of at least 30 feet. The reinforcement bar in the micropile should extend full length. 2. Values for the grout-to-ground nominal bond strength are commonly based on experience of local contractors and geotechnical engineers. Table 5-2 on page 5-16 of the "Micropile Design and Construction Guidelines Manual" presents ranges of typical values for various instal- lation methods and ground conditions. For initial design calculations and to allow development of foundation plans, we suggest assuming a grout to ground ultimate bond stress of 30 psi for the gravel and cobble. 3. One tension verification load test to two times the design load should be performed on a pre-production micropile at or near the production KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS051140-145 S:\GS05840.000\14512. Reports\GS05840 145 R1 .doc 20 . . pile locations. This testing is usually performed as the first order of work under the construction contract. The purpose is to verify whether de- sign assumptions concerning bond zone strength are appropriate and the adequacy of the contractor's installation method. Production micropiles are approved only after the design assumptions and the ad- equacy of the contractor's installation method have been verified. 4. We recommend, as a minimum, the upper 5 feet of the micropile con- tain permanent casing to provide a sound connection from the micropile to pile cap. The upper section of permanent casing may also be required for lateral load consideration. 5. The top of micropiles should be capped with an anchor plate designed by the structural engineer to provide an adequate connection between the micropile and pile cap. The structural engineer, contractor, and our firm should collaborate on this design to ensure all elements of the connection are considered. 6. The ability of the foundation to span between micropiles should be checked by the structural engineer. 7. Grout sock and/or grout admixtures that lessen the effect of grout loss during grouting operations may need to be utilized. If grout sock and/or grout admixtures are utilized, additional tension verification tests should be performed to verify design bond stress. FLOOR SYSTEM AND SLABS-ON-GRADE We anticipate slab-on-grade floors are preferred in the garage and the low- er and main levels. Slab thickness and amount of reinforcement normally used for residential slab-on-grade floors will not provide sufficient strength to protect against unanticipated settlement of the existing fill below slabs. We recommend a heavily reinforced stiff floor slab be designed for lower level slabs-on-grade placed on the existing fill soils. An alternative would be the provision of a structural floor supported by the foundation. The building plan dimension is relatively small, which may make the cost of structural floors attractive. A washed rock layer with an embedded PVC drain pipe network should be provided underneath below- grade, slab-on-grade floors and on the floors of crawl spaces to mitigate potential problems resulting from ground water and is discussed in the SUBSURFACE KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:\GS05840.000\14512. Reports\GS05840 145 R1.doc 21 DRAINAGE section. The drain system below the slabs will likely carry water dur- ing spring and early summer months. The slabs will be subject to damp condi- tions. The effects of the dampness on the chosen floor covering should be con- sidered. The slabs will be subjected to street salts brought in from vehicles. Con- crete ad mixtures or surface coating should be considered to protect the concrete slab surfaces. We recommend the following precautions for slab-on-grade construction at this site. 1. Slabs should be separated from exterior walls and interior bearing members with slip joints which allow free vertical movement of the slabs. 2. Underslab plumbing should be pressure tested for leaks before the slabs are constructed. Plumbing and utilities which pass through slabs should be isolated from the slabs with sleeves and provided with flexible couplings to slab supported appliances. 3. Exterior patio and porch slabs should be isolated from the residence. These slabs should be well-reinforced to function as independent units. 4. Frequent control joints should be provided, in accordance with Amer- ican Concrete Institute (ACI) recommendations, to reduce problems associated with shrinkage and curling. 5. KEITH NOVICK . . . ... . .... ,. . : .. or 2003 International ode (IRC) may require a vapor retarder be placed be- tween the base course or subgrade soils and the concrete slab-on- grade floors. The merits of installation of a vapor retarder below floor slabs and PT slabs depend on the sensitivity of floor coverings and building to moisture. A properly installed vapor retarder (10 mil mini- mum) is more beneficial below concrete slab-on-grade floors where floor coverings, painted floor surfaces or products stored on the floor will be sensitive to moisture. The vapor retarder is most effective when concrete is placed directly on top of it. A sand or gravel level- ing course should not be placed between the vapor retarder and the floor slab. The placement of concrete on the vapor retarder may in- crease the risk of shrinkage cracking and curling. Use of concrete with reduced shrinkage characteristics including minimized water content, maximized coarse aggregate content, and reasonably low LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:IGS05840.000\14512. Reports\GS05140 145 R1.doc 22 . ' slump will reduce the risk of shrinkage cracking and curling. Consid- erations and recommendations for the installation of vapor retarders below concrete slabs are outlined in Section 3.2.3 of the 2003 report of American Concrete Institute (ACI) Committee 302, "Guide for Concrete Floor and Slab Construction (ACI 302.R-96)". The most positive method to mitigate potential floor movement is to con- struct structural floors. If the owner wishes to reduce the potential for floor move- ment, we recommend structural floors in living areas. Structural floors are sup- ported by the foundation system. There are design and construction issues asso- ciated with structurally supported floors, such as deeper excavation depths, venti- lation and increased lateral loads which must be considered. FOUNDATION WALLS Earth pressures applied to foundation walls will depend on the excavation retention/foundation wall system chosen. If foundation walls are integrated with a permanent excavation retention system, the lateral loads will be resisted by the excavation retention system (see Excavation Retention). Earth pressures on foundation walls for several other conditions are discussed in the following sec- tions. Permanent Excavation Retention Some permanent excavation retention systems allow one-sided concrete pours to construct foundation walls, and placement of backfill is not required. In some instances where permanent shoring is constructed, however, foundation walls are constructed some distance from the excavation retention system. This is a hybrid condition where pressure on foundation walls is controlled by the width and thickness of backfill between the retainage facing and the foundation wall. Vertical stresses are reduced from friction on both sides of the backfill which can result in a reduction of lateral forces exerted on the foundation wall. This is re- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840·145 S:\GS05840.000\145\2. Reports\GS05840 145 R1.doc 23 . ' ferred to as an arching effect. This condition can be approximated for walls up to 25 feet high and backfill width of 3 feet as a uniform pressure of 500 psf for the full height of the wall. Consideration must be made for drainage and surcharge pres- sures. 1 Temporary Excavation Retention If a temporary excavation retention system is constructed, backfill may or may not be required between foundation walls and the excavation retention facing. In either case, foundation walls must be designed to accommodate earth pres- sures from the full height of backfill. No reduction in earth pressures should be made to accommodate for temporary excavation retention systems. The founda- tion wall should be designed for an equivalent fluid pressure of at least 50 pcf. The design value does not include allowance for surcharge loads or hydrostatic pres- sure. Surcharge loads from Alpine Drive above the site will need to be consid- ered. 1 No Excavation Retention Some shorter foundation walls along the east and west sides of the building may be constructed without shoring. Excavations would need to be laid back to safe and stable configurations. This condition assumes use of granular soil back- fill with slight slopes away from the building. The foundation wall is assumed to be restrained from rotation and drained. The design value does not include allow- ance for traffic, surcharge loads from traffic or adjacent structures or hydrostatic pressure. An equivalent fluid density of 50 pounds per cubic foot is recommended to calculate lateral earth pressure on the wall. Figure 8 in Appendix A shows this condition. If slab-on-grade and structural fill is placed behind foundation walls, we recommend an increased equivalent fluid density be used to accommodate the KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05841J.145 S:\GS05840.000\145\2. Reports\GS05840 145 R1 .doc 24 . ' compactive effort required to place structural fill. The construction sequence should be analyzed to assure that proper bracing exists during placement of struc- tural fill behind foundation walls. The recommended equivalent density assumes deflection; some minor cracking of walls may occur. If very little wall deflection is desired, a higher equivalent fluid density may be appropriate for design. Backfill placed adjacent to foundation wall exteriors should be placed and compacted as outlined in the SITE EARTHWORK section. SUBSURFACE DRAINAGE We anticipate that subsurface water will flow towards the site at elevations above the planned lower level floor. The water will need to be collected in perma- nent dewatering systems (drains). We are providing recommendations for a per- manent drainage system. We have observed occasional incidents of water in basement window wells after construction. We recommend considering a drain pipe to connect the bottom of window wells to the foundation drain. Section R310.2.2 of the 2012 IRC re- quires a drain in the window wells. We recommend an exterior foundation drain be installed around the perim- eter and adjacent to below-grade interior foundation walls where the foundation steps down the slope (if any). A washed rock layer with an embedded PVC drain pipe network should be provided under below-grade floor slabs and in crawl space areas. The exterior foundation drains should consist of 4 inch diameter, rigid, slot- ted PVC pipe encased in free draining gravel. A prefabricated drainage compo- site should be placed adjacent to foundation walls. Care should be taken during backfill operations to prevent damage to drainage composites. The drain should lead to a gravity outlet or a sump pit where water can be removed by pumping. KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GSOS840-145 S:\GS051140.000\14512. Reports\GS051140 145 R1 .doc 25 . ' Gravity outlets should be protected from clogging and freezing. The drain outlets should be checked at least twice each year to verify they are not blocked. Installa- tion of clean outs along the drain pipes is recommended. Slab-on-grade floors should be protected from wetting by installation of an under slab blanket drain. We recommend constructing underslab drains consist- ing of 2-inch diameter slotted PVC pipe installed on 1 O to 12 foot centers and em- bedded in at least 6 inches of washed gravel. The pipes should convey water to perimeter drain collector pipes. Placement of a moisture retarder above the washed rock layer is required in the International Residential Code to mitigate the potential for water vapor transmission through floor slabs. Typical foundation and blanket drain details are shown on Figures 5 and 6 in Appendix A. EARTH RETAINING WALLS Reinforced concrete retaining walls may be constructed. Reinforced con- crete retaining walls can be supported on the natural gravel soils. Design criteria for retaining walls can be provided once the actual locations and bottom of wall locations are known. Retaining walls which can rotate should be designed to resist "active" lat- eral earth pressures calculated using an equivalent fluid density of at least 40 pcf. Retaining walls with reinforcement that is tied into building foundation walls that are not free to rotate should be designed to resist "at rest" lateral earth pressures using an equivalent fluid density of at least 55 pcf. A passive earth pressure of 300 pcf can be used to calculate resistance from sliding for permanent embed- ment depths. These pressures do not include allowances for sloping backfill or hydrostatic pressures. Backfill behind retaining walls and in front of retaining wall footings should be placed and compacted as outlined in the Backfill and Fill sec- tion. KEITH NOVICK I.OT 22, VAii. VII.I.AGE WEST, Fii.iNG NO. 1 PROJECT NO. GS05840·145 S:IGS05840.000\14512. Reports\GS05840 145 R1.doc 26 ' . SURFACE DRAINAGE Surface drainage is critical to the performance of foundations, slabs and exterior flatwork. We recommend the following precautions be observed during construction and maintained at all times after the residence is completed: 1. The ground surface surrounding the exterior of the residence should be sloped to drain away from the residence in all directions. We recommend providing a slope of at least 12 inches in the first 10 feet around the residence, where possible. In no case should the slope be less than 6 inches in the first 5 feet. 2. Backfill around the exterior of foundation walls should be placed and compacted as described in the Backfill and Fill section. 3. The residence should be provided with roof gutters and downspouts. Roof downspouts and drains should discharge well beyond the limits of all backfill. Splash blocks and downspout extensions should be provided at all discharge points. 4. Landscaping should be carefully designed to minimize irrigation. Plants used near foundation walls should be limited to those with low moisture requirements; irrigated grass should not be located within 5 feet of the foundation. Sprinklers should not discharge within 5 feet of the foundation and should be directed away from the residence. 5. Impervious plastic membranes should not be used to cover the ground surface immediately surrounding the residence. These membranes tend to trap moisture and prevent normal evaporation from occurring. Geotextile fabrics can be used to control weed growth and allow some evaporation to occur. ADDITIONAL CONSULTATION, CONSTRUCTION OBSERVATIONS AND MONITORING This report has been prepared for the exclusive use of Keith Novick and the design team for the purpose of providing geotechnical design and construction cri- teria for the proposed project. The information, conclusions, and recommenda- tions presented herein are based upon consideration of many factors including, KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING N0.1 PROJECT NO. GS05840·145 S:IGS05840.000\145\2. Reports\GS05840 145 R1 .doc 27 • • but not limited to, the type of structures proposed, the geologic setting, and the subsurface conditions encountered. The conclusions and recommendations con- tained in the report are not valid for use by others. Standards of practice evolve in geotechnical engineering. The recommendations provided are appropriate for about three years. If the proposed project is not constructed within about three years, we should be contacted to determine if we should update this report. We recommend that CTL I Thompson, Inc. provide construction observa- tion services to allow us the opportunity to verify whether soil conditions are con- sistent with those found during this investigation. If others perform these observa- tions, they must accept responsibility to judge whether the recommendations in this report remain appropriate. Some vertical and horizontal movements of adjacent ground occur when deep excavations are made. The amount of movement depends on the subsur- face conditions, depth of excavations, type of earth retention installed and nature of the adjacent properties. We recommend that a monitor program be developed to check movement during the building construction process. Monitor programs for similar projects consist of survey prisms on adjacent buildings and on ground adjacent to the site. The survey monitor program is normally developed by the project civil engineer. GEOTECHNICAL RISK The concept of risk is an important aspect with any geotechnical evaluation primarily because the methods used to develop geotechnical recommendations do not comprise an exact science. We never have complete knowledge of subsur- face conditions. Our analysis must be tempered with engineering judgment and experience. Therefore, the recommendations presented in any geotechnical eval- uation should not be considered risk-free. We cannot provide a guarantee that the interaction between the soils and a proposed structure will be as desired or in- KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GSD584D-145 S:IGS05840.000\145\2. Raporta\GS05840 145 R1.doc 28 • • tended. Our recommendations represent our judgment of those measures that are necessary to increase the chances that the structures will perform satisfactorily. It is critical that all recommendations in this report are followed during construction. Home owners must assume responsibility for maintaining the structure and use appropriate practices regarding drainage and landscaping. LIMITATIONS Our exploratory borings were located to obtain a reasonably accurate pic- ture of subsurface conditions. Variations in the subsurface conditions not indicat- ed by our borings will occur. A representative of our firm should be called to ob- serve and test fill placement and observe the completed foundation excavation to confirm that the exposed soils are suitable for support of the foundations as de- signed. This investigation was conducted in a manner consistent with that level of care and skill ordinarily exercised by geotechnical engineers currently practicing under similar conditions in the locality of this project. No warranty, express or im- plied, is made. If we can be of further service in discussing the contents of this report, please call. cc: Via email to kanovick@gmail.com KEITH NOVICK LOT 22, VAIL VILLAGE WEST, FILING NO. 1 PROJECT NO. GS05840-145 S:\GS05840.000\145\2. Reports\GS05840 145 R1.doc: -----~--- 29 B & DRILLING, INC. y PO Box 1878 Rifle, Colorado 81650 Phone (970) 625-2608 Fax (970) 625-1502 SUBMITTED TO: ·NOVA GROUP Attention: David Irwin P.O. Box 3342 Vail, Colorado 81658 (970) 94 76-7101 Office (970) 390-0931 Cell Email: snapoutofit2@msn.com JOB NAME & ADDRESS: PROPOSAL May20, 2016 NOVIK RESIDENCE, 1740 SIERRA TRAIL VAIL, COLORADO We hereby propose the installation of: 3,453 SQFT of Temporary Soil Nail Wall and 40 LNFT of Temporary Micro Pile Wall for the excavation of the proposed structure of the Novik Residence at 1740 Sierra Trail in Vail, Colorado. Final shoring design stamped by a Professional Engineer licensed in the state of Colorado will be produced upon receipt of this signed proposal. Estimated construction duration is approximately 27 working days including mobilization (Monday thru Friday). Page 1 ofS