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HomeMy WebLinkAboutEX08_RS_Geotech_Engineering_Study_CamelliaCourt_220524_v1May 24, 2022 JN 22149 GEOTECH CONSULTANTS, INC. Williams Avenue Ventures LLC 9219 Southeast 33rd Place Mercer Island, Washington98040 Attention: Leon Cohen via email: leon@leongcs.com Subject: Transmittal Letter – Geotechnical Engineering Study Proposed Camelia Court Apartment Building 99-107 Williams Avenue South Renton, Washington Dear Mr. Cohen, Attached to this transmittal letter is our geotechnical engineering report for the proposed Camelia Court Apartment Building to be constructed in Renton. The scope of our services consisted of exploring site surface and subsurface conditions, and then developing this report to provide recommendations for general earthwork and design considerations for foundations, retaining walls, subsurface drainage, and temporary excavations and shoring. This work was authorized by your acceptance of our proposal, P-11138, dated March 25, 2022. The attached report contains a discussion of the study and our recommendations. Please contact us if there are any questions regarding this report, or for further assistance during the design and construction phases of this project. Respectfully submitted, GEOTECH CONSULTANTS, INC. Marc R. McGinnis, P.E. Principal cc: Roger H. Newell Architect – Roger H. Newell via email: roger@rhnewellaia.com MKM/MRM:kg EXHIBIT 8 RECEIVED PLANNING DIVISION 11/01/2023 AVanGordon DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 GEOTECH CONSULTANTS, INC. GEOTECHNICAL ENGINEERING STUDY Proposed Camelia Court Apartment Building 99-107 Williams Avenue South Renton, Washington This report presents the findings and recommendations of our geotechnical engineering study for the site of the proposed Camelia Court Apartment building to be constructed in Renton. Development of the property is in the planning stage, and detailed plans were not available at the time of this study. The preliminary site plans provided to us were prepared by Roger H. Newell Architect, dated February 7, 2022. Based on these plans, and our discussions with Leon Cohen. We understand that a new, six story apartment building is proposed to be constructed at the subject property. The new building will be underlain by one story of underground parking, with a deep elevator pit. Additional parking will be available in the main floor. The remaining second through sixth floors will contain residential apartment units of varying square footage. A courtyard will be located atop the parking garage on the second floor in the western-central side of the building. Entrance to the parking garage will be from the western alley, and pedestrian access is proposed off the eastern street. No elevations have been proposed at this time, but we anticipate that excavations of at least 10 to 12 feet will be needed to reach the basement level foundations, with a deeper local excavation for the central elevator pit/building depending on its final design. Zero lot line setbacks are being proposed for the basement level parking garage on all four sides of the property. If the scope of the project changes from what we have described above, we should be provided with revised plans in order to determine if modifications to the recommendations and conclusions of this report are warranted. SITE CONDITIONS SURFACE The Vicinity Map, Plate 1, illustrates the general location of the site in the northern downtown area of Renton. The site is comprised of three contiguous parcels that form a rectangular-shaped lot with approximate dimensions of 150 feet in the north-south direction, and 115 feet in the east-west direction. The site is bordered to the north by a single-family parcel, to the east by Williams Avenue South, and to the south and west by an alleyway. Multi-story retirement living buildings lie both south and west of the alleyways. The grade across the three parcels is essentially flat, with only gentle declines within localized areas on each parcel. This is consistent with the topography in the surrounding area. The northern two parcels are developed with single-family residences located on the eastern sides of the lots. These residences are older in construction and are one to two stories in height. A one-story, commercial building is located on the southern parcel. Grass lawn and parking areas are set on the western half of he northern two lots, and on the western perimeter of the southern lot. The northern adjacent parcel is developed with a one-story residence that is underlain by a partial footprint basement. This residence appears to be set within 5 feet of the common property line at its closest. While streets and alleys line the remaining eastern, southern, and western sides of the property, newer multi story residential buildings are set south and west of the alley. The southern DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 2 GEOTECH CONSULTANTS, INC. building is six stories in height, and it does not appear that this structure is underlain by a basement. Based on the limited permitting information available online, it would appear that this six-story building was recently constructed in 2018-2019, as older Google Streets images indicate that this building was once a one-story commercial structure similar to the small building on our site’s southernmost lot. The building to the west of the site is five stories in height and appears to contain one level of below grade parking. West of Williams Avenue South is the Fulton Apartments (110 Williams Avenue South). Our firm provided geotechnical services during the construction of this building in 2002. This building is underlain by a basement. Many of the older single-family residences in this area, including the residences on the subject property and adjacent to the north, have undergone variable levels of post-construction settlement over their lifespans. These homes, which do not have strengthened, modern foundations have visible signs to excessive settlement in the form of cracked foundations, dips of moderate in the roof, and out of level building materials. Many of the on-grade structures in the vicinity also show signs of settlement related distress. Some small cracks could also be observed in the exposed walls of the western apartment building. SUBSURFACE The subsurface conditions on the site were explored advancing three Cone Penetration Tests (CPTs) at the approximate locations shown on the Site Exploration Plan, Plate 2. Our exploration program was based on the proposed construction, anticipated subsurface conditions and those encountered during exploration, and the scope of work outlined in our proposal. The Cone Penetration Tests were advanced using a large, truck push rig on May 9, 2022. The data from the CPTs have been used to characterize the subsurface conditions beneath the site using empirical relations obtained from sensors at the tip of the CPT sounding probe. The CPT logs are attached to the end of this report as Plates 3 through 5. Our firm also completed the geotechnical study, as well as observation of the shoring installation, excavation, and foundation construction for the Fulton Apartments located to the east of the site at 110 Williams Avenue South. As a part of this study, we reviewed the explorations conducted for that project. Apparently, it has not been possible to obtain from the City of Renton the explorations that were completed for the retirement living facilities to the west and south of the site. Soil Conditions The CPTs were advanced on the western side of the site, within the gravel parking areas. CPT-1 and CPT-2 were advanced near the northwest and southwest corners of the site, and CPT-3 was advanced in the approximate central-western edge of the site. Beneath the ground surface, loose alluvial silt and sand was revealed, containing scattered organic layers. This upper, loose soil layer continued to a depth of 10 to 16 feet, where medium- dense sand and gravel was revealed. This sand and gravel layer was observed to be highly variable in density, exhibiting a medium-dense and denser constancy in CPT-1 and CPT-2. The deepest looser surficial deposits were revealed in CPT-3, located in the center of the site, where medium-dense soils were not revealed until 16 feet. The medium-dense and denser alluvial sand and gravel continued to the base of the three CPTs at depths of 25 to 36 feet where refusal was met. DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 3 GEOTECH CONSULTANTS, INC. The site and surrounding vicinity of Downtown Renton are underlain by a variable layer of unconsolidated, alluvial soils, which are soils that were deposited by flowing water. The alluvium becomes very gravelly and coarse grained typically within 8 to 15 feet of the ground surface. Like most alluvial deposits, the soil beneath the site contains variable soil layers, containing large cobbles and boulders, and occasional organics. As evidenced in the CPTs, it is common to find looser layers within the more alluvial sand and gravel. These layers can be discontinuous and localized depending on the water flow velocities that occurred during the soil’s deposition. Generally similar soil conditions were encountered in our previous borings conducted for the Fulton Apartments to the west. The coarse-grained gravels were 8 to 12 feet below existing grade on the west side of that property, closest to the subject site. Obstructions in the form of cobbles were revealed by our explorations and can be observed by spikes in the CPT readings. These obstructions made advancing the cone rods excessively difficult and led to refusal in all three exploration locations. However, debris, buried utilities, and old foundation and slab elements are commonly encountered on sites that have had previous development. Cobbles and boulders are often found in soils that have been deposited by glaciers or fast- moving water. Groundwater Conditions Groundwater seepage was recorded at a depth of 16 feet in all three exploration locations. This groundwater table is determined by pore pressure measurements on the CPT probe, so can be somewhat inaccurate. However, based on our previous work on the adjacent Fulton Apartments site, we expect seasonal high groundwater to lie at 15 to 16 feet below the ground surface. It should be noted that groundwater levels vary seasonally with rainfall and other factors. We anticipate that groundwater could be found in more permeable soil layers. The stratification lines on the logs represent the approximate boundaries between soil types at the exploration locations. The actual transition between soil types may be gradual, and subsurface conditions can vary between exploration locations. The logs provide specific subsurface information only at the locations tested. The relative densities and moisture descriptions indicated on the CPT logs are empirical correlations based on the conditions observed with the sensory equipment during the explorations. CONCLUSIONS AND RECOMMENDATIONS GENERAL THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY RELYING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. The explorations conducted for this study encountered alluvial silt, sand, and gravel, which is typical for this area of Renton. The surficial 10 to 16 feet of this soil is in a loose/soft state, and the alluvial DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 4 GEOTECH CONSULTANTS, INC. soils generally became medium-dense and coarse grained beneath depths of 10 to 14 feet in CPT- 1 and CPT-2, and not until a depth of 16 feet in CPT-3. These medium-dense soils generally continued with depth, becoming medium-dense and denser in layers with depth. Current structures in the surrounding area that have been supported in typical conventional shallow foundation systems atop the surficial, looser alluvial soils can experience significant amounts of post-construction settlement due to consolidation of these loose soils over time. Furthermore, the soil in this area that is below the groundwater table is susceptible to liquefaction during a large seismic event. Considering the anticipated excavation depths of more than 10 feet, medium-dense sand and gravel should be encountered at, or close to, the base of much of the excavation, and a heavily reinforced mat foundation can be used for the support of the planned building. A mat foundation is essentially a heavily-reinforced, slab foundation that is intended to distribute the building loads, reduce the necessary bearing capacity, bridge over any excessively soft areas of soil or localized soil liquefaction (sand boils) and reduce the amount of differential settlement across the building. The mat foundation can be placed directly on top of the coarse-grained alluvium, after the excavated surface has been recompacted. Where loose/soft soils are encountered at the planned excavation level, they should be removed and be replaced with compacted granular soils. In wet conditions, this structural fill would likely need to consist of clean crushed rock, such as ballast rock, or 2 to 4-inch quarry spalls. This clean, open-graded rock can be easily placed and compacted without the need for vibratory compaction equipment. The construction budget should contain a contingency for the additional potential cost of overexcavation and replacement. The base of the excavation should be assessed by the project geotechnical engineer to assess whether or not unsuitable soils need to be removed and replaced with structural fill. Additional recommendations can be found in the Mat Foundations section of this report. If only a shallow excavation is proposed later in the design, or the anticipated building loads will be too great to spread out across a lightly loaded mat foundation, deep foundation systems will need to be used to support the new building. In this area, augercast concrete piles are typically used to accomplish this. Preliminary augercast pile recommendations are provided below, but we can provide further recommendations regarding this as the design progresses. Excavations of at least 10 feet are anticipated to be needed to reach the basement level parking garage across all four sides of the site. Based on the zero-lot line setbacks, the excavation depth, poor surficial soils, and the presence of nearby structures and roadways, we expect that excavation shoring will need to be utilized on all four sides of the excavation. For this project, the only appropriate shoring method will be to use a rigid, drilled soldier pile shoring system. Some of the adjacent structures, and the adjacent roadways and utilities rest on loose soils and appear to have undergone varying levels settlement in the past. The shoring design must consider the potential risk of causing additional settlement in these existing, at-risk structures. Due to the high variability in the site soils, and the need to limit shoring deflections, the shoring system should be designed as rigid to the point where little to no deflections are anticipated while the excavation is open during construction of the basement. The shoring system should also be designed with the consideration that overexcavations may need to occur in front of the shoring piles to expose competent medium- dense sand and gravel. Where overexcavation is attempted near the perimeter foundations, it will be necessary to excavate the unsuitable soils one-bucket width at a time, immediately backfilling each overexcavated section with compacted quarry spalls or ballast rock. Refer to the section entitled Temporary Shoring for more information regarding design and installation of the proposed shoring. Based on the soil encountered in our explorations, and from previous construction experience in the vicinity, the site soils should not be excavated at an inclination steeper than a 1.5:1 DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 5 GEOTECH CONSULTANTS, INC. (Horizontal:Vertical) extending continuously from top to bottom of a cut. Even at this relatively flat inclination, the loose, uncompressed alluvial soils have an elevated caving potential, and flatter inclinations may be needed where perched seepage, or caving occurs. Vertical excavations should not be attempted, and instability was encountered in temporary cut slopes attempted at a 1:1 (H:V) inclination for the Fulton Apartments project. Ecology blocks, or similar non-structural shoring, will not be sufficient to hold up the loose near-surface soils in vertical excavations. In general, unshored excavations should not extend beneath a 3:1 (H:V) line drawn extending downward from any adjacent foundation, utility, or right-of-way. We also anticipate that the deep excavation for the elevator pit will also need to be shored to prevent caving within the excavation. The adjacent older buildings, such as the house to the immediate north of the site, are likely supported on conventional foundations that bear on compressible soils. As a result, it is likely that they have undergone excessive settlement already. It will be important to determine the foundation design for the newer building to the south. There is always some risk associated with demolition and foundation construction near structures such as this. It is imperative that unshored excavations do not extend below a 3:1 (Horizontal:Vertical) imaginary bearing zone sloping downward from existing footings. Contractors working on the demolition and construction of the new rowhouses must be cautioned to avoid strong ground vibrations, which could cause additional settlement in the neighboring foundations. During demolition, strong pounding on the ground with the excavator, which is often used to break up debris and concrete, should not occur. Large equipment and vibratory compactors should not be used close to the property lines or during large fill compaction operations due to the potential for sustained vibrations to adversely affect the neighboring structures and utilities. Additionally, in order to protect yourselves from unsubstantiated damage claims from the adjacent owners, 1) the existing condition of the foundation should be documented before starting demolition, and 2) the footings should be monitored for vertical movement during the demolition, excavation, and construction process. These are common recommendations for projects located close to existing structures that may bear on loose soil and have already experienced excessive settlement. We can provide additional recommendations for documentation and monitoring of the adjacent structures, if desired. The loose/soft alluvial soils are highly variable in composition, are fine-grained and silty, and contain varying organics. Based on this, and the size of the building, the onsite soils should not be used for any structural fill application at this site, as they will not be able to be adequately compacted and will be in an elevated moisture state. Fill beneath foundations must consist of an angular, clean rock such as quarry spalls or ballast rock, and free-draining granular fill should be used behind backfilled walls. Infiltration or dispersion systems should also not be explored for feasibility at this project due to the presence of basement spaces on and around the site, the composition of the subsurface soils, and the lack of open space to install such a system. All collected stormwater runoff should be tightlined offsite to the appropriate facilities. The lowest floor slab elevation should be set at least 2 feet above the encountered groundwater seepage level, and should be higher than that if possible. This provides added protection against unexpected high groundwater levels causing seepage into the basement garage. Regardless, underslab drainage should be provided below the mat slab. This is redundant protection to prevent a build-up of groundwater beneath the mat foundation in the event of seasonal groundwater fluctuations, which could impart hydrostatic uplift pressures on the foundations. It is likely that deeper penetrations, such as an elevator pit, would need to be of watertight construction. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas. The need for a silt fence will be eliminated as soon as the DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 6 GEOTECH CONSULTANTS, INC. excavation is below the surrounding grade. Existing pavements, ground cover, and landscaping should be left in place wherever possible to minimize the amount of exposed soil. Rocked staging areas and construction access roads should be provided to reduce the amount of soil or mud carried off the property by trucks and equipment. Trucks should not be allowed to drive off of the rock-covered areas. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Onsite water containment, such as a Baker Tank, or specialty discharge permits may be needed to contain onsite water that accumulates within the excavation. Following clearing or rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. On most construction projects, it is necessary to periodically maintain or modify temporary erosion control measures to address specific site and weather conditions. The drainage and/or waterproofing recommendations presented in this report are intended only to prevent active seepage from flowing through concrete walls or slabs. Even in the absence of active seepage into and beneath structures, water vapor can migrate through walls, slabs, and floors from the surrounding soil, and can even be transmitted from slabs and foundation walls due to the concrete curing process. Water vapor also results from occupant uses, such as cooking, cleaning, and bathing. Excessive water vapor trapped within structures can result in a variety of undesirable conditions, including, but not limited to, moisture problems with flooring systems, excessively moist air within occupied areas, and the growth of molds, fungi, and other biological organisms that may be harmful to the health of the occupants. The designer or architect must consider the potential vapor sources and likely occupant uses, and provide sufficient ventilation, either passive or mechanical, to prevent a build up of excessive water vapor within the planned structure. As with any project that involves demolition of existing site buildings and/or extensive excavation and shoring, there is a potential risk of movement on surrounding properties. This can potentially translate into noticeable damage of surrounding on-grade elements, such as foundations and slabs. However, the demolition, shoring, and/or excavation work could just translate into perceived damage on adjacent properties. Unfortunately, it is becoming more and more common for adjacent property owners to make unsubstantiated damage claims on new projects that occur close to their developed lots. Therefore, we recommend making an extensive photographic and visual survey of the project vicinity, prior to demolition activities, installing shoring, and/or commencing with the excavation. This documents the condition of buildings, pavements, and utilities in the immediate vicinity of the site in order to avoid, and protect the owner from, unsubstantiated damage claims by surrounding property owners. Additionally, any adjacent structures should be monitored during demolition and construction to detect soil movements. To monitor their performance, we recommend establishing a series of survey reference points to measure any horizontal deflections of the shoring system. Control points should be established at a distance well away from the walls and slopes, and deflections from the reference points should be measured throughout construction by survey methods. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical constraints that become more evident during the review process. We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 7 GEOTECH CONSULTANTS, INC. SEISMIC CONSIDERATIONS In accordance with the International Building Code (IBC), the site class within 100 feet of the ground surface would best be represented by Site Class Type F (Failure Prone Site Class), due to its liquefiable nature. However, ASCE 7 allows for an exception from the F classification if the building period is less than 0.5 seconds. If the building period falls beneath this threshold, a Site Class E can be used for this project. As noted in the USGS website, the mapped spectral acceleration value for a 0.2 second (Ss) and 1.0 second period (S1) equals 1.44g and 0.49g, respectively. If the building period is found to be in excess of 0.5 seconds, a site-specific seismic analysis and study would need to be completed by a specialty consultant, as the ASCE does not allow any other exceptions for larger buildings in liquefiable soils. The soils that will support the building are coarse-grained and in a medium-dense to dense condition. The IBC and ASCE 7 require that the potential for liquefaction (soil strength loss) be evaluated for the peak ground acceleration of the Maximum Considered Earthquake (MCE) which has a probability of occurring once in 2,475 years (2 percent probability of occurring in a 50-year period). The MCE peak ground acceleration adjusted for site class effects (FPGA) equals 0.67g. Current geotechnical analysis cannot accurately predict where and to what extent soil liquefaction will occur during a large earthquake. Using procedures developed by Seed, Idress, et al., it is possible that the coarse-grained soils below the groundwater table could liquefy. While the potential for this to occur in very gravelly soils is thought to be lower than for finer-grained sands. Even so, we have calculated the approximate total ground settlement that could result if liquefaction were to occur in the saturated, loose to medium-dense soils as a result of the design earthquake for this site, and for nearby projects in the Renton Valley. Based on these analyses, it is possible that soil liquefaction could occur at the site during the MCE with total calculated ground settlement in the order of up to 4 to 6 inches. The potential for excessive differential settlement across the structure will be mitigated by the mat foundations such that we would predict differential dynamic settlements of 2 to 4 inches across the structure in the event of a large earthquake. Sections 1803.5 of the IBC and 11.8 of ASCE 7 require that other seismic-related geotechnical design parameters (seismic surcharge for retaining wall design and slope stability) include the potential effects of the Design Earthquake. The peak ground acceleration for the Design Earthquake is defined in Section 11.2 of ASCE 7 as two-thirds (2/3) of the MCE peak ground acceleration, or 0.45g. The recommendations for a mat foundation system presented in this report are intended to prevent catastrophic foundation collapse during a large seismic event. By preventing catastrophic settlement of the foundations, the safety of the occupants should be protected. The intent is not to prevent damage or ensure continued function of the structures after the design seismic event. MAT FOUNDATIONS The mat foundation should be supported on the coarse-grained gravelly alluvial after it has been recompacted. As discussed in the General section, some overexcavation and replacement will likely be necessary to remove loose/soft soils remaining after the excavation is completed. An allowable bearing pressure of 2,000 pounds per square foot (psf) should be used for the mat foundation design. A one-third increase in this design bearing pressure may be used when considering short-term wind or seismic loads. DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 8 GEOTECH CONSULTANTS, INC. Mat foundations are typically designed using the appropriate flexible method. Foundations designed using this method are also known as Winkler Foundations. For this analysis, we recommend using a coefficient of subgrade reaction of 90 pounds per cubic inch (lb/in3). Any shallow mat slabs should be thickened a minimum depth of 18 inches below the adjacent finish grade around the perimeter of the mat, and this thickened edge of the structural slabs should have a minimum width of 16 inches. Deflections will depend on the stiffness of the slab, but we anticipate total deflections under static conditions over time to be on the order of 2 to 3 inches and differential settlements across the structure on the order of 1 to 2 inches or less, can be anticipated. Lateral loads due to wind or seismic forces may be resisted by friction between the foundations and the bearing soil, or by passive pressure acting on the vertical, embedded portions of the foundation. For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level, well-compacted fill. We recommend using the following ultimate values for the foundation’s resistance to lateral loading. PARAMETER ULTIMATE VALUE Coefficient of Friction 0.40 Passive Earth Pressure 250 pcf Where: pcf is Pounds per Cubic Foot, and Passive Earth Pressure is computed using the equivalent fluid density. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend maintaining a safety factor of at least 1.5 for the foundation’s resistance to lateral loading when using the above ultimate values. AUGERCAST CONCRETE PILES Augercast piles are installed using continuous flight, hollow-stem auger equipment mounted on a crane. Concrete grout must be pumped continuously through the auger as it is withdrawn. This allows the piles to be installed where caving conditions or significant groundwater are anticipated. We recommend that augercast piles be installed by an experienced contractor who is familiar with the anticipated subsurface conditions. An allowable compressive capacity of 30 tons can be attained by installing a 16-inch-diameter, augercast concrete pile at least 10 feet into the medium-dense and denser sand and gravel. For transient loading, such as wind or seismic loads, the allowable pile capacity may be increased by one-third. We can provide design criteria for different pile diameters and embedment lengths, if greater capacities are required. The minimum center-to-center pile spacing should be three times the pier diameter to prevent a reduction in the individual pile compressive capacity. Based on our subsurface information information, we estimate that pile lengths of about 25 to 35 feet below the existing grade would be required to achieve adequate penetration into the medium-dense and denser sand and gravel. This estimated depth will be influenced by the final foundation elevations and required structural demands of the piles. This above compressive capacity does not include the potential downdrag forces that may occur within the soil located above the groundwater table in the event of a seismic-induced liquefaction. This force will vary depending on the excavation depth as well as the pile depths. We can comment DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 9 GEOTECH CONSULTANTS, INC. on downdrag forces during the preliminary pile design and once a bottom of excavation elevation has been determined. We estimate that the total settlement of single piles installed as described above will be on the order of one inch. Most of this settlement should occur during the construction phase as the dead loads are applied. The remaining post-construction settlement would be realized as the live loads are applied. We estimate that differential settlements between the foundation piles over any portion of the structures should be less than about one-half-inch. We recommend reinforcing each pile its entire length. This typically consists of a rebar cage extending a portion of the pile’s length with a full-length center bar. Each pile can be assumed to have a point of fixity (point of maximum bending moment) at 15 feet below the top of the pile for design of the reinforcing. Passive earth pressures on the grade beams will also provide some lateral resistance. If structural fill is placed against the outside of the grade beams, the design passive earth pressure from the fill can be assumed to be equal to that pressure exerted by an equivalent fluid with a density of 300 pcf. This passive resistance is an ultimate value that does not include a safety factor. Augercast Pile Installation This section provides general, and typically minimum, guidelines for installation of augercast concrete piles. The piles should be installed by a contractor with experience in the successful installation of augercast piles, in similar soil and groundwater conditions. The piles should be installed with continuous-flight hollow stem auger equipment specifically designed for the installation of auger-placed grout-injected piles. The grout injection point should be at the tip of the auger bit, below the cutting teeth. Due to potential variability in soil conditions on any site, the contractor should provide sufficient auger length to extend the piles well beyond the lengths estimated above and/or indicated by the available exploration information. The following are general accepted techniques that are typically used by local experienced contractors: • The grout should be placed under a minimum pressure of 200 pounds per square inch (psi) to provide adequate bonding with the bearing soils. A pressure gauge should be installed on or near the pump to monitor the pressures during the grouting. The gauge should be easily accessible to the field technician. • A mechanical counter should be located on the grout pump to record the number of strokes required for installation of each pile. • The grout pump should be calibrated prior to pile installation by pumping grout into a container of known volume. This procedure should be repeated as often as deemed necessary to provide a reasonable calibration by the field technician. • Each pile should be drilled and completely filled with grout in an uninterrupted operation. The auger hoisting equipment should be capable of withdrawing the auger smoothly and at a constant rate without jumps or stops. The auger should be removed slowly and smoothly to maintain a constant pressure during removal. A positive grout head of at least 5 feet should be maintained at all times to prevent caving of the drilled hole and the formation of voids. If the removal becomes erratic, or if there is a sudden drop in grout pressure, the pile should be redrilled at least 5 feet below the level when the grout pressure dropped prior to resuming withdrawal. DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 10 GEOTECH CONSULTANTS, INC. • Clockwise rotation of the auger should be performed during the grouting process at least until the grout flow is observed out of the top of the drilled hole. This will stabilize the sides and facilitate spoil material removal. • The installation of piles located within 6 pile diameters of each other on the same working day is not recommended, and piles must cure 24 hours before installation of adjacent piles. • The fresh grout will subside, usually within the first 2 hours. If the grout has not set, the pile should be topped off with fresh grout to the cutoff elevation. • Augercast piles may be reinforced with single or bundled steel reinforcing rods or reinforcing bar cages. The reinforcing should be inserted before the grout sets. The reinforcing should be installed plumb and centered in the pile to avoid contact with the soil. Also, each pile should include a full-length, steel rod in the center; this will serve as a probe to determine the continuity of the pile. Pile Installation Observation A representative of project geotechnical engineer should observe the pile installation process on a full-time basis. The monitoring should include collecting and interpreting the installation data and verifying the bearing stratum elevations. FOUNDATION AND RETAINING WALLS Retaining walls backfilled on only one side should be designed to resist the lateral earth pressures imposed by the soil they retain. The following recommended parameters are for walls that restrain level backfill: PARAMETER VALUE Lateral Earth Pressure * At Rest Earth Pressure 45 pcf 60 pcf Passive Earth Pressure 250 pcf Coefficient of Friction 0.40 Soil Unit Weight 130 pcf Where: pcf is Pounds per Cubic Foot, and Lateral and Passive Earth Pressures are computed using the Equivalent Fluid Pressures. * For a restrained wall that cannot deflect at least 0.002 times its height, a uniform lateral pressure equal to 10 psf times the height of the wall should be added to the above lateral equivalent fluid pressure. This applies only to walls with level backfill. The design values given above do not include the effects of any hydrostatic pressures behind the walls and assume that no surcharges, such as those caused by slopes, vehicles, or adjacent foundations will be exerted on the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Where sloping backfill is desired behind the walls, we will need to be given the wall dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. The surcharge due to traffic loads behind a wall can typically be accounted for by adding a uniform pressure equal to 2 feet multiplied by the above lateral fluid density. Heavy construction equipment should not be operated behind retaining and foundation walls within a DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 11 GEOTECH CONSULTANTS, INC. distance equal to the height of a wall, unless the walls are designed for the additional lateral pressures resulting from the equipment. The values given above are to be used to design only permanent foundation and retaining walls that are to be backfilled, such as conventional walls constructed of reinforced concrete or masonry. It is not appropriate to use the above earth pressures and soil unit weight to back-calculate soil strength parameters for design of other types of retaining walls, such as soldier pile, reinforced earth, modular or soil nail walls. We can assist with design of these types of walls, if desired. The passive pressure given is appropriate only for a shear key poured directly against undisturbed native soil, or for the depth of level, well-compacted fill placed in front of a retaining or foundation wall. The values for friction and passive resistance are ultimate values and do not include a safety factor. Restrained wall soil parameters should be utilized the wall and reinforcing design for a distance of 1.5 times the wall height from corners or bends in the walls, or from other points of restraint. This is intended to reduce the amount of cracking that can occur where a wall is restrained by a corner. Wall Pressures Due to Seismic Forces Per IBC Section 1803.5.12, a seismic surcharge load need only be considered in the design of walls over 6 feet in height. A seismic surcharge load would be imposed by adding a uniform lateral pressure to the above-recommended lateral pressure. The recommended seismic surcharge pressure for this project is 9H pounds per square foot (psf), where H is the design retention height of the wall. Using this increased pressure, the safety factor against sliding and overturning can be reduced to 1.2 for the seismic analysis. Retaining Wall Backfill and Waterproofing Backfill placed behind retaining or foundation walls should be coarse, free-draining structural fill containing no organics. This backfill should contain no more than 5 percent silt or clay particles and have no gravel greater than 4 inches in diameter. The percentage of particles passing the No. 4 sieve should be between 25 and 70 percent. The free-draining backfill should be hydraulically connected to the foundation drain system. Free draining backfill should be used for the entire width of the backfill where seepage is encountered. For increased protection, drainage composites should be placed along cut slope faces, and the walls should be backfilled entirely with free-draining soil. The later section entitled Drainage Considerations should also be reviewed for recommendations related to subsurface drainage behind foundation and retaining walls. The purpose of these backfill requirements is to ensure that the design criteria for a retaining wall are not exceeded because of a build-up of hydrostatic pressure behind the wall. Also, subsurface drainage systems are not intended to handle large volumes of water from surface runoff. The top 12 to 18 inches of the backfill should consist of a compacted, relatively impermeable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled walls at one to 2 percent to reduce the potential for surface water to percolate into the backfill. Water percolating through pervious surfaces (pavers, gravel, permeable pavement, etc.) must also be prevented from flowing toward walls or into the backfill zone. Foundation drainage and waterproofing systems are not intended to handle large volumes of infiltrated water. The compacted subgrade below pervious surfaces and any associated drainage layer DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 12 GEOTECH CONSULTANTS, INC. should therefore be sloped away. Alternatively, a membrane and subsurface collection system could be provided below a pervious surface. It is critical that the wall backfill be placed in lifts and be properly compacted, in order for the above-recommended design earth pressures to be appropriate. The recommended wall design criteria assume that the backfill will be well-compacted in lifts no thicker than 12 inches. The compaction of backfill near the walls should be accomplished with hand- operated equipment to prevent the walls from being overloaded by the higher soil forces that occur during compaction. The section entitled General Earthwork and Structural Fill contains additional recommendations regarding the placement and compaction of structural fill behind retaining and foundation walls. The above recommendations are not intended to waterproof below-grade walls, or to prevent the formation of mold, mildew, or fungi in interior spaces. Over time, the performance of subsurface drainage systems can degrade, subsurface groundwater flow patterns can change, and utilities can break or develop leaks. Therefore, waterproofing should be provided where future seepage through the walls is not acceptable. This typically includes limiting cold-joints and wall penetrations and using bentonite panels or membranes on the outside of the walls. There are a variety of different waterproofing materials and systems, which should be installed by an experienced contractor familiar with the anticipated construction and subsurface conditions. Applying a thin coat of asphalt emulsion to the outside face of a wall is not considered waterproofing and will only help to reduce moisture generated from water vapor or capillary action from seeping through the concrete. As with any project, adequate ventilation of basement and crawl space areas is important to prevent a buildup of water vapor that is commonly transmitted through concrete walls from the surrounding soil, even when seepage is not present. This is appropriate even when waterproofing is applied to the outside of foundation and retaining walls. We recommend that you contact an experienced envelope consultant if detailed recommendations or specifications related to waterproofing design or minimizing the potential for infestations of mold and mildew are desired. TEMPORARY SHORING Given the poor soil conditions, excavation depths, zero-lot line setbacks, and presence of nearby settlement sensitive structures, shoring will be needed on all four sides of the excavation. For this project, the only appropriate shoring method that will provide the necessary rigidity to limit deflections in the excavation will be to use drilled, soldier piles. These soldier piles will need to be designed to limit the magnitude and occurrence of any deflections within the retained height of the cut to prevent adversely impacting the adjacent streets, utilities, and buildings. This will be particularly important near the adjacent northern residence. In general, we recommend a maximum 6-foot center-to-center pile spacing, in order to reduce the potential for excessive caving in the loose near-surface soils during excavation and lagging placement. Soldier pile walls would be constructed after making planned cut slopes, and prior to commencing the mass excavation, by setting steel H-beams in a drilled hole and grouting the space between the beam and the soil with concrete for the entire height of the drilled hole. Wet, caving conditions will be encountered in the holes, and the contractor should be prepared to case the holes and/or use the slurry method if caving soil is encountered. Excessive ground loss in the drilled holes must be DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 13 GEOTECH CONSULTANTS, INC. avoided to reduce the potential for settlement on adjacent properties. If water is present in a hole at the time the soldier pile is poured, concrete must be tremied to the bottom of the hole. Augercast or Continuous Flight Auger (CFA) drilling methods may also be used if the contractor has these methods available to them. As the excavation proceeds downward, the space between the piles should be lagged with timber, and any voids behind the timbers should be filled with Controlled Density Fill (CDF). Treated lagging is usually required for permanent walls, while untreated lagging can often be utilized for temporary shoring walls. Temporary vertical cuts will be necessary between the soldier piles for the lagging placement. The prompt and careful installation of lagging is important, particularly in loose or caving soil, to maintain the integrity of the excavation and provide safer working conditions. Additionally, care must be taken by the excavator to remove no more soil between the soldier piles than is necessary to install the lagging. Caving or overexcavation during lagging placement could result in loss of ground on neighboring properties. Timber lagging should be designed for an applied lateral pressure of 30 percent of the design wall pressure if the pile spacing is less than three pile diameters. For larger pile spacings, the lagging should be designed for 50 percent of the design load. Soldier Pile Wall Design Temporary or permanent soldier pile shoring that is cantilevered should be designed for an active soil pressure equal to that pressure exerted by an equivalent fluid with a unit weight of 45 pounds per cubic foot (pcf). The active pressures should extend to at least 2 feet below the bottom of the excavation to account for the potential need for overexcavations to expose competent soil. If shoring will be located within a 2:1 (H:V) zone of the footings of the neighboring northern house or near any other potentially settlement sensitive structure, roadway, or utility, it should be designed for an at-rest earth pressure of 60 pcf in order to create a stiffer soldier pile system and to minimize the lateral movement of the shoring in these areas. An additional surcharge will need to be incorporated in the shoring design within the extent of this neighboring structure. The design/depth of the foundations for the building to the south need to be determined, in order to assess whether or not a surcharge needs to be included for the effect of that building’s foundations. Traffic surcharges adjacent to pavements travelled by trucks, such as garbage trucks, can typically be accounted for by increasing the effective height of the shoring wall by 3 feet. Heavier loads, such as those from concrete trucks, concrete pump trucks, large excavation equipment, etc. can create larger surcharge pressures on a shoring system. We can provide appropriate surcharge loads once more detailed plans have been developed. Any temporary cut slopes above the shoring walls will exert additional surcharge pressures. These surcharge pressures will vary, depending on the configuration of the cut slope and shoring wall. We can provide recommendations regarding slope and retaining wall surcharge pressures when the preliminary shoring design is completed. It is important that the shoring design provides sufficient working room to drill and install the soldier piles, without needing to make unsafe, excessively steep temporary cuts. Cut slopes should be planned to intersect the backside of the drilled holes, not the back of the lagging. Lateral movement of the soldier piles below the excavation level will be resisted by an ultimate passive soil pressure equal to that pressure exerted by a fluid with a density of 300 DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 14 GEOTECH CONSULTANTS, INC. pcf. No safety factor is included in the given value. This soil pressure is valid only for a level excavation in front of the soldier pile; it acts on two times the grouted pile diameter. This passive pressure should not be assumed to begin until at least 2 feet below the bottom of the excavation to account for the potential for overexcavations to be needed in front of the piles. Cut slopes made in front of shoring walls significantly decrease the passive resistance. This includes temporary cuts necessary to install internal braces or rakers. The minimum embedment below the floor of the excavation for cantilever soldier piles should be equal to the height of the "stick-up." EXCAVATION AND SHORING MONITORING As with any shoring system, there is a potential risk of greater-than-anticipated movement of the shoring and the ground outside of the excavation. This can translate into noticeable damage of surrounding on-grade elements, such as foundations and slabs. Therefore, we recommend making an extensive photographic and visual survey of the project vicinity, prior to demolition activities, installing shoring or commencing excavation. This documents the condition of buildings, pavements, and utilities in the immediate vicinity of the site in order to avoid, and protect the owner from, unsubstantiated damage claims by surrounding property owners. Additionally, the shoring walls and any adjacent foundations should be monitored during construction to detect vertical movement. To monitor their performance, we recommend establishing a series of survey reference points to measure any horizontal deflections of the shoring system. Control points should be established at a distance well away from the walls and slopes, and deflections from the reference points should be measured throughout construction by survey methods. At least every other soldier pile should be monitored by taking readings at the top of the pile. Additionally, benchmarks installed on the surrounding buildings should be monitored for at least vertical movement. We suggest taking the readings at least once a week, until it is established that no deflections are occurring. The initial readings for this monitoring should be taken before starting any demolition or excavation on the site. EXCAVATIONS AND SLOPES Appropriate temporary cut slope inclinations for excavations above the water table are discussed in the General section. The recommended temporary slope inclination is based on the conditions exposed in our explorations, and on what has been successful at other sites with similar soil conditions. It is possible that variations in soil and groundwater conditions will require modifications to the inclination at which temporary slopes can stand. Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet weather. It is also important that surface runoff be directed away from the top of temporary slope cuts. Cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that loose soil can cave suddenly and without warning. Excavation, foundation, and utility contractors should be made especially aware of this potential danger. These recommendations may need to be modified if the area near the potential cuts has been disturbed in the past by utility installation, or if settlement-sensitive utilities are located nearby. DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 15 GEOTECH CONSULTANTS, INC. Water should not be allowed to flow uncontrolled over the top of any temporary or permanent slope. All permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce erosion and improve the stability of the surficial layer of soil. DRAINAGE CONSIDERATIONS We anticipate that permanent foundation walls will be constructed against the shoring walls due to the limited lot line setbacks. Where this occurs, a plastic-backed drainage composite, such as Miradrain, Battledrain, or similar, should be placed against the entire surface of the shoring prior to pouring the foundation wall. Weep pipes located no more than 6 feet on-center should be connected to the drainage composite and poured into the foundation walls or the perimeter footing. A footing drain installed along the inside of the perimeter footing will be used to collect and carry the water discharged by the weep pipes to the storm system. Isolated zones of moisture or seepage can still reach the permanent wall where groundwater finds leaks or joints in the drainage composite. This is often an acceptable risk in unoccupied below-grade spaces, such as parking garages. However, formal waterproofing is typically necessary in areas where wet conditions at the face of the permanent wall will not be tolerable. If this is a concern, the permanent drainage and waterproofing system should be designed by a specialty consultant familiar with the expected subsurface conditions and proposed construction. Plate 6 presents typical considerations for foundation drains at shoring walls. These drains should be surrounded by at least 6 inches of 1-inch-minus, washed rock that is encircled with non-woven, geotextile filter fabric (Mirafi 140N, Supac 4NP, or similar material). At its highest point, a perforated pipe invert should be at least 6 inches below the bottom of a slab floor or the level of a crawl space. The discharge pipe for subsurface drains should be sloped for flow to the outlet point. Roof and surface water drains must not discharge into the foundation drain system. A typical footing drain detail is attached to this report as Plate 7. Underdrainage should be used where: (1) crawl spaces or basements will be below a structure; (2) a slab is below the outside grade; or (3) the outside grade does not slope downward from a building. Drains should also be placed at the base of all earth-retaining walls. As noted in the General section, we recommend underdrainage for a basement floor slab, in the event that unexpected rises in the groundwater levels occur. An underslab drainage detail is attached to this report as Plate 8. For the best long-term performance, perforated PVC pipe is recommended for all subsurface drains. Clean-outs should be provided for potential future flushing or cleaning of footing drains. If the structure includes an elevator with an elevator pit, it will be necessary to provide watertight construction for the elevator pit. As a minimum, a vapor retarder, as defined in the Slabs-On-Grade section, should be provided in any crawl space area to limit the transmission of water vapor from the underlying soils. Crawl space grades are sometimes left near the elevation of the bottom of the footings. As a result, an outlet drain is recommended for all crawl spaces to prevent an accumulation of any water that may bypass the footing drains. Providing a few inches of free draining gravel underneath the vapor retarder is also prudent to limit the potential for seepage to build up on top of the vapor retarder. Groundwater was observed during our field work. If seepage is encountered in an excavation, it should be drained from the site by directing it through drainage ditches, perforated pipe, or French DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 16 GEOTECH CONSULTANTS, INC. drains, or by pumping it from sumps interconnected by shallow connector trenches at the bottom of the excavation. The excavation and site should be graded so that surface water is directed off the site and away from the tops of slopes. Water should not be allowed to stand in any area where foundations, slabs, or pavements are to be constructed. Final site grading in areas adjacent to the building should slope away at least one to 2 percent, except where the area is paved. Surface drains should be provided where necessary to prevent ponding of water behind foundation or retaining walls. A discussion of grading and drainage related to pervious surfaces near walls and structures is contained in the Foundation and Retaining Walls section. GENERAL EARTHWORK AND STRUCTURAL FILL All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other deleterious material. It is important that existing foundations be removed before site development. The stripped or removed materials should not be mixed with any materials to be used as structural fill, but they could be used in non-structural areas, such as landscape beds. Structural fill is defined as any fill, including utility backfill, placed under, or close to, a building, or in other areas where the underlying soil needs to support loads. All structural fill should be placed in horizontal lifts with a moisture content at, or near, the optimum moisture content. The optimum moisture content is that moisture content that results in the greatest compacted dry density. The moisture content of fill is very important and must be closely controlled during the filling and compaction process. The allowable thickness of the fill lift will depend on the material type selected, the compaction equipment used, and the number of passes made to compact the lift. The loose lift thickness should not exceed 12 inches, but should be thinner if small, hand-operated compactors are used. We recommend testing structural fill as it is placed. If the fill is not sufficiently compacted, it should be recompacted before another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. The following table presents recommended levels of relative compaction for compacted fill: LOCATION OF FILL PLACEMENT MINIMUM RELATIVE COMPACTION Beneath slabs or walkways 95% Filled slopes and behind retaining walls 90% Beneath pavements 95% for upper 12 inches of subgrade; 90% below that level Where: Minimum Relative Compaction is the ratio, expressed in percentages, of the compacted dry density to the maximum dry density, as determined in accordance with ASTM Test Designation D 1557-91 (Modified Proctor). DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 17 GEOTECH CONSULTANTS, INC. LIMITATIONS The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our exploration and assume that the soil and groundwater conditions encountered in the explorations are representative of subsurface conditions on the site. If the subsurface conditions encountered during construction are significantly different from those observed in our explorations, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Unanticipated conditions are commonly encountered on construction sites and cannot be fully anticipated by the limited area of subsurface explorations, especially while the properties are still developed and occupied. Subsurface conditions can also vary between exploration locations. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project. It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects. This report has been prepared for the exclusive use of Williams Avenue Ventures LLC and its representatives, for specific application to this project and site. Our conclusions and recommendations are professional opinions derived in accordance with our understanding of current local standards of practice, and within the scope of our services. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. Our services also do not include assessing or minimizing the potential for biological hazards, such as mold, bacteria, mildew and fungi in either the existing or proposed site development. ADDITIONAL SERVICES In addition to reviewing the final plans, Geotech Consultants, Inc. should be retained to provide geotechnical consultation, testing, and observation services during construction. This is to confirm that subsurface conditions are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction activities comply with the general intent of the recommendations presented in this report, and to provide suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. However, our work would not include the supervision or direction of the actual work of the contractor and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of the contractor. During the construction phase, we will provide geotechnical observation and testing services when requested by you or your representatives. Please be aware that we can only document site work we actually observe. It is still the responsibility of your contractor or on-site construction team to verify that our recommendations are being followed, whether we are present at the site or not. DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Williams Avenue Ventures LLC JN 22149 May 24, 2022 Page 18 GEOTECH CONSULTANTS, INC. The following plates are attached to complete this report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plates 3 - 5 Cone Penetration Test Logs Plate 6 Typical Shoring Drain Detail Plate 7 Typical Footing Drain Detail Plate 8 Typical Underslab Drainage Detail We appreciate the opportunity to be of service on this project. Please contact us if you have any questions, or if we can be of further assistance. Respectfully submitted, GEOTECH CONSULTANTS, INC. 5/24/2022 Marc R. McGinnis, P.E. Principal MKM/MRM:kg DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job No:Date:Plate: 22149 May 2022 GEOTECH CONSULTANTS, INC. 99-107 Williams Avenue South Renton, Washington VICINITY MAP (Source: King County iMap) 1 SITE DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job No:Date:Plate: 22149 May 2022 GEOTECH CONSULTANTS, INC. 99-107 Williams Avenue South Renton, Washington SITE EXPLORATION PLAN 2 No Scale Legend: Cone Penetration Test Location CPT-1 CPT-3 CPT-2 DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job Date:Plate: 22149 GEOTECH CONSULTANTS, INC. CONE PENETRATION TEST LOG May 2022 Logged by: 99-107 Williams Avenue South Renton, Washington 3 DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job Date:Plate: 22149 GEOTECH CONSULTANTS, INC. CONE PENETRATION TEST LOG May 2022 Logged by: 99-107 Williams Avenue South Renton, Washington 4 DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job Date:Plate: 22149 GEOTECH CONSULTANTS, INC. CONE PENETRATION TEST LOG May 2022 Logged by: 99-107 Williams Avenue South Renton, Washington 5 DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job No:Date:Plate: 22149 May 2022 GEOTECH CONSULTANTS, INC. 99-107 Williams Avenue South Renton, Washington 6 SHORING DRAIN DETAIL Foundation wall & Footing Treated lagging Soldier pile Drainage composite Vapor retarder Slab 4" perforated PVC drain (holes turned downward) 2" PVC weep pipe at 6' centers (Pour into footing or wall below slab) Non-woven filter fabric Washed rock or pea gravel Attach weep pipe to drainage composite. Pierce waterproofing and plastic backing of drainage composite. Note - Refer to the report for additional considerations related to drainage and waterproofing. Waterproofing DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job No:Date:Plate: 22149 May 2022 GEOTECH CONSULTANTS, INC. 99-107 Williams Avenue South Renton, Washington 7 FOOTING DRAIN DETAIL Washed Rock (7/8" min. size) Slope backfill away from foundation. Provide surface drains where necessary. 4" min. 4" Perforated Hard PVC Pipe (Invert at least 6 inches below slab or crawl space. Slope to drain to appropriate outfall. Place holes downward.) Tightline Roof Drain (Do not connect to footing drain) Nonwoven Geotextile Filter Fabric NOTES: (1) In crawl spaces, provide an outlet drain to prevent buildup of water that bypasses the perimeter footing drains. (2) Refer to report text for additional drainage, waterproofing, and slab considerations. Backfill (See text for requirements) Vapor Retarder/Barrier and Capillary Break/Drainage Layer (Refer to Report text) Possible Slab DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1 Job No:Date:Plate: 22149 May 2022 GEOTECH CONSULTANTS, INC. 99-107 Williams Avenue South Renton, Washington NOTES: (1) Refer to the report text for additional drainage and waterproofing considerations. (2) The typical maximum underslab drain separation (L) is 15 to 20 feet. (3) No filter fabric is necessary beneath the pipes as long as a minimum thickness of 4 inches of rock is maintained beneath the pipes. (4) The underslab drains and foundation drains should discharge to a suitable outfall. 4-inch perforated PVC pipe (slope to drain) Pea gravel or drain rock L L L 9 to 12 inches Vapor Retarder or Waterproof Vapor Barrier TYPICAL UNDERSLAB DRAINAGE 8 DocuSign Envelope ID: E380154C-A526-42C6-9A09-974E2B481BE1