“This electronic communication and its contents may contain confidential information which is the exclusive property of Geotechnical Consultants, Inc. The recipient(s) assumes all liability arising from any alteration, misuse or unauthorized distribution. If you have received this information in error, please notify the sender immediately.”
720 Greencrest Drive Westerville, Ohio 43081-4902
SUBSURFACE EXPLORATION AND PRELIMINARY
GEOTECHNICAL ENGINEERING REPORT PROPOSED
FAIRFIELD COUNTY JUSTICE CENTER-MSMJ SITE 342 WEST WHEELING STREET
LANCASTER, OHIO
Prepared by:
Geotechnical Consultants, Inc. Prepared for:
The Fairfield County Commissioners Wachtel & McAnally Architects/Planners
GCI Project No. 11-G-16121 June 10, 2011 Westerville, Ohio 43081-4902 614.895.1400 Fax: 614.895.1171 www.gci2000.com Branch Offices
INTRODUCTION...1
SITE HISTORY AND PROJECT DESCRIPTION...2
SUBSURFACE CONDITIONS ...3
LABORATORY...5
ANALYSIS AND CONCLUSIONS...5
GEOTECHNICAL EVALUATION BUILDING SUPPORT SEISMIC FACTOR EXCAVATIONS AND GROUNDWATER PAVEMENTS GENERAL SITE PREPARATION AND EARTHWORK CONSTRUCTION MATERIALS ENGINEERNG AND TESTING ...11
FINAL ...12
APPENDIX FOLLOWING PAGE NUMBER...12 General Notes for Soil Classification
General Site Location Map (DeLorme. Street Atlas USA ® 2011) USGS Topographic Map – 1992 Lancaster, Ohio Quadrangle 2009 Aerial Photograph – Fairfield County Auditor
Sanborn ® Fire Insurance Map (May, 1893) Boring Location Plan
Table 1: Summary of Encountered Subsurface Conditions Test Boring Logs
Table 2: Laboratory Test Results ODNR Water Well Logs (2)
INTRODUCTION
As requested and authorized by Mr. Kent Staker of Wachtel & McAnally Architects/Planners, Inc on behalf of the Fairfield County Commissioners, Geotechnical Consultants, Inc. (GCI) has performed a subsurface exploration for a proposed Fairfield County Justice Center building at 342 West Wheeling Street in Lancaster, Ohio. Prior to drilling, the client provided us with a “Scheme E” site plan, dated 6/5/2010, that showed the proposed and existing building footprints and six requested boring locations.
Our study consisted of six standard penetration test borings performed at or near the suggested locations within the proposed structure footprint and limited laboratory testing. A sketch showing the approximate boring locations and copies of the boring logs are included in the appendix of this report. Test hole locations were established from existing site landmarks and general site features. Topographic information was not shown on the plan provided, and GCI did not survey the ground surface elevations at the boring locations.
The intent of this study is to evaluate subsoil conditions and offer preliminary design recommendations relative to foundations, pavements, and earthwork. This report is issued prior to the receipt of final foundation and grading plans. We would suggest that this office review these plans to provide additional recommendations.
This preliminary report has been prepared for the exclusive use of the Fairfield County Commissioners, Wachtel & McAnally Architects/Planners and their consultants for specific application to the proposed Fairfield County Justice Center to be located at 342 West Wheeling Street in Lancaster, Ohio in accordance with generally accepted soil and foundation engineering practices. No warranty, expressed or implied, is made.
SITE HISTORY AND PROJECT DESCRIPTION
The site is comprised of two irregular-shaped parcels totaling about 2.5 acres in size. The property is bordered by retail buildings and Lincoln Avenue (US Route 22) to the south, the tree-lined Hocking River in its current alignment to the west, West Wheeling Street to the north, and a gas station to the northeast. South Memorial Drive (U.S. Route 33) forms the east side boundary. The roadway was constructed over the abandoned Ohio Canal at some time between 1893 and 1899; it was known as Front Street at that time. A foundry and a glass plant were once located east and southeast of the site on the east side of Route 33. A general site location map is appended to this report.
Review of historic (1889 through 1929) Sanborn® maps of the area indicates the site has seen prior development in the form of several buildings used for a slaughter house from at least 1889 to 1919. The 1929 map shows a foundry on the parcel. The Hocking River once crossed through the site, entering the property from the north and then curving to the west; it appears on Sanborn® maps dated 1899 and earlier and is designated as the “old channel” (see attached copy of the 1893 map). We do not know when the river was straightened and realigned to the west end of the site. At some point, fill was placed on the site possibly in connection with the channel rerouting or as a means of dealing with spoils from the on-site or adjacent foundries and glass plant. Review of the 1992 Lancaster, Ohio USGS topographic quadrangle (see attached copy) shows grades ranging from elevation 833 feet near the east site boundary to below elevation 820 feet to the west by the Hocking River. It also shows a building to the east of the existing jail that no longer is present on the site; presumably the existing concrete pavement in this area is the old floor slab, which could account for the significant spalling we observed as it would have consisted of non-air-entrained concrete.
According to the Fairfield County Auditor record, a supermarket was constructed in the northwest portion of the site in 1955. In 1994, this structure was converted to the current minimum security county jail facility. The client indicated that they believe the existing structure is supported on shallow
strip footings and has been subject to some minor settlement that has not impaired its functionality. Conversation with a deputy at the site indicated that the west building wall and adjacent slab were jacked up about 1 to 2 inches through use of grout injections about two years ago, but he repeated that functionality was not impaired prior to that repair. There is concrete pavement at the north end of the site, with asphalt pavement covering the rest of the parcel (see cover photograph). We visually judged the pavements to be in fair to poor condition.
The project consists of constructing a one-story, slab-on-grade prison building with a mezzanine in the central portion of the property. The exterior walls will be 8-inch thick reinforced concrete masonry block with a 4-inch veneer, and the slab will be an 8-inch precast with a 2-inch topping. The structural engineer (Mr. Ray Blinn of Eeman & Blinn, Inc.) provided the following building load information: exterior wall loads will vary from 5.48 to 6.38 kips per lineal foot in the two-story portion and be about 3.03 kips per foot for one-story walls; column loads in the two-story portion will vary from 78 to 89 kips and range from 20 to 30 kips in the one-story area. He estimated about 80% of the loads will be dead loads. A grading plan was not available at the writing of this report, but we anticipate minor grade changes (i.e., 2 feet or less of cuts and fills) will be required to achieve a level building pad and regrade pavement areas. We understand that at least some of the existing building will likely be demolished as part of the project.
SUBSURFACE CONDITIONS
GCI mobilized a truck-mounted drill rig (CME-45 with an automatic sampling hammer) to the site on March 2, 2011 and drilled six standard penetration test borings at or near the requested locations to obtain a generalized profile of existing subsurface conditions. Borings B-1 through B-6 were drilled within the proposed building footprint to depths of either 25 or 30 feet. Specific boring information can be obtained from the boring logs in the appendix. We summarize our boring findings below and in the attached “Summary of Encountered Subsurface Conditions” table.
Surface Cover
The borings were drilled in existing pavement areas. Northern borings B-1 and B-2 encountered a rigid section consisting of 3 to 4 inches of concrete over 3 inches of stone base. The remaining borings found 1 to 3.5 inches of asphalt cast directly on granular fill rather than stone base.
Existing Fill
The six borings encountered existing fill below the pavement section, extending to depths ranging from 9 feet to 17.5 feet below existing grade at the boring locations. The fill consisted primarily of dark brown/black foundry sand (which we would classify as a non-plastic silty fine to medium sand - SM) with varying but generally minor amounts of slag, glass, and brick. Occasional zones of slightly plastic silty, clayey sand (SC-SM) or low plasticity clayey sand (SC) were encountered within the fill. Standard penetration N-values recorded in the fill ranged from 0 to 13 blows per foot (bpf), commonly from 2 to 8 bpf indicating the fill was loose to very loose in cohesionless density.
Natural Soils
We found natural cohesive soils, varying from non-organic to organic and from moderate to high plasticity, immediately below the fill in the five of the six boring locations (east boring B-3 encountered more granular natural soils below the deep fill cover at 17.5 feet below the surface). The cohesive soils were alluvial deposits associated with the former Hocking River channel. In southeast boring B-4, we encountered a non-organic, low to moderate plasticity brown lean clay (CL) that was medium stiff. The other four borings (B-1, B-2, B-5 and B-6) drilled in the north and west portions of the site found heavily stained lean to fat clays (CL to CH/OL to OH) with varying amounts of organics and shells that were very soft (0 to 2 blows per foot commonly recorded).
The alluvial clays were underlain by a saturated granular formation that was encountered at depths ranging from 12.5 feet (B-4) to 24.5 feet (B-5) below existing grade at the boring locations. These deposits varied from slightly plastic silty, clayey sand with gravel (SC-SM) to non-plastic silty sand with gravel/poorly graded sand with silt and gravel (SM/SP-SM). Trace shells were noted at the top of the granular formation in B-1 and B-6. Standard penetration testing showed the sands to be loose to medium dense. With the exception of B-3, the borings terminated within sand at depths of 25 or 30 feet. East boring B-3 encountered a gray glacial till formation below the upper silty clayey sand with gravel formation at a depth of 26 feet below the surface. Till is a primarily cohesive material comprised of varying amounts of sand and gravel cemented in a lean clay matrix that generally exhibits low to moderate plasticity. We visually classified the soil as gray sandy lean clay with gravel (CL) under the Unified Classification System. Occasional thin layers of silty sand with gravel (SM) were noted within the otherwise cohesive formation. The gray till was very stiff in cohesive consistency. We terminated B-3 in the gray till at a depth of 30 feet below the surface.
Bedrock
Bedrock was not encountered in the borings performed (maximum drilled depth of 30 feet). The USDA
Soil Survey of Fairfield County maps the site as being in an area with bedrock consisting of sandstone
with interbedded shale. We estimate the depth to top of bedrock to be in excess of 100 feet, based on review of logs for water wells in the site vicinity that are registered with ODNR (see attached copies of two of those logs).
Groundwater and Soil Moisture Conditions
We encountered water seepage in the six borings at the time of drilling. In B-2, the groundwater was found within the upper portion of the fill at a depth of 3 feet below the surface; the water level dropped to 8 feet by the completion of drilling. Seepage was encountered within the lower portions of the fill mass in borings B-1, B-3, and B-6 at depths of 7.5 to 9.5 feet below the surface; by the completion of
drilling, the water levels were recorded at depths of 9.5 to 10 feet below grade in these three boreholes. In B-5, groundwater was observed at a depth of 12.5 feet below the surface in the upper portion of the natural dark gray organic clay layer; the water level remained constant at the encountered depth in that borehole at completion. B-4 found seepage within the underlying natural sand formation at a depth of 17.5 feet, with the level rising about a foot in the borehole by the end of drilling.
We generally characterize the retrieved fill samples as moist, with some very moist to wet zones where seepage was encountered within the fill. The natural stained clays and underlying sand deposits were typically described as wet.
Note that groundwater levels and moisture conditions can vary with changes in season and precipitation. It is likely that the underlying sand formation is hydraulically connected to the adjacent Hocking River.
LABORATORY TESTING
We determined the natural moisture content of the first split spoon sample of natural soils obtained in each boring (from depths of 13.5’ to 15’ in five of the borings, from 18.5’-20’ in B-3). East/southeast borings B-3 and B-4 samples were found to have natural moisture contents of 13.5% and 7.7%, respectively, at the time of drilling. The other four samples consisted of stained clays that had much higher moisture contents, ranging from 31.9% in B-2 to 57.5% in B-1. We subjected the two samples with the highest moisture content, B-1 and B-5, to loss-on-ignition testing. Results indicated respective organic contents of 9.2% and 4.3%. From a geotechnical view point, we consider organic contents of above 4% to 5% to be significant.
ANALYSIS AND CONCLUSIONS GEOTECHNICAL EVALUATION
The borings encountered deep deposits of loose fill over the entire building pad. Soft, organic Hocking River channel deposits underlie the north and west portions of the proposed footprint, but may not be present in the southeast part. These subsoil conditions will have a significant impact on foundation and floor slab options, and pavement design to a lesser extent due to both total and differential settlement concerns. We discuss these issues and other concerns below.
The existing structure in the northwest corner of the site was built in 1955. It reportedly was constructed using conventional shallow spread footings and slab-on-grade and has undergone some settlement but of low enough magnitude (1 to 2 inches) to not impair its functionality. The proposed new justice center building will be located southeast of the existing building and over the old Hocking River channel. Our borings showed the existing fill in this area to consist primarily of a silty fine to medium sand in loose to very loose condition that will settle under applied new fill and building loads. Additionally, four of our borings encountered very soft natural alluvial clays with varying amounts of organics and shells. These old
channel deposits combined with the loose fills pose a significant differential settlement potential for the proposed construction. Additionally, the proposed structural loads of the new jail will be about double
those of the existing facility (and therefore will induce a larger magnitude of settlement), and the new building will have reinforced concrete masonry walls, which typically are not flexible enough to accept large movements without cracking. Based on our borings and despite the reported “good” performance of the adjacent existing structure, we feel the site fills and soft clays are not suitable for support of shallow foundations or conventional slab-on-grade for the proposed construction.
To mitigate settlement concerns, we recommend that the structure be supported on deep foundations that extend through the existing fill and soft, natural alluvial clay deposits to bear in the underlying non-organic, medium dense to dense sand and gravel or stiff glacial till soils. Based on the soil profile and anticipating that groundwater may typically be encountered at depths of 8 to 10 feet below the surface, we suggest using auger-cast piles for the deep foundations. Auger-cast piles are efficient in deep sand and gravel deposits as they gain capacity primarily due to skin friction, and groundwater does not interfere with their installation. Slab support would remain a concern, unless the slab is also supported on these elements. If this option is selected, we recommend that additional final phase borings be performed to finalize design recommendations. Final phase borings should extend to deeper depths on the order of 60 feet to 70 feet to gather sufficient information to analyze auger-cast piles.
Another possible option would be to modify/strengthen the site soils using stone columns such as “Geopiers.” Geopiers® are closely spaced rammed stone columns which, when properly designed and installed, will improve soil bearing conditions enough to allow the use of conventional spread footings and slab-on-grade. In our opinion, soil bearing capacities on the order of 4.000 psf to 5,000 psf would be feasible for the site when properly fortified with stone columns. We recommend that these elements extend through the fill and soft natural clays to bear in the sand formation. Geopiers® are a proprietary system which would be designed by Geopier, Inc.
Caissons (drilled piers) could be considered for the deep foundation element, but they would require casing to prevent cave-in of the loose granular fill soils and careful groundwater control. Groundwater will be encountered near the fill/natural soil interface, which will necessitate the use of casing within the natural as well as the fill site soils. We also anticipated the need to use a tremie during concrete placement. Caissons are a less preferred option due to the concern of their being subject to excessive post-construction downdrag forces and the potential for bearing soils to heave during construction.
Settlement in pavement areas remains a concern regardless of which foundation system is selected, although a flexible pavement system would be much more forgiving when compared to building elements. This is evidenced by the performance of the existing pavement. The need for periodic maintenance as movements occur should be anticipated. We do recommend that existing asphalt be stripped in proposed pavement areas, and the exposed subgrade carefully proofrolled to delineate soft/loose soils requiring stabilization prior to placement of new fill or pavement sections. Unless properly milled, stripped asphalt will not be suitable for re-use as fill. If milled, asphalt fill should not be placed within the proposed building pads.
We understand that the existing building may be partially or totally demolished as part of the project. Additionally, the existing concrete pavement east of the present jail may in fact be an old building slab
with below-grade building elements still in place. As such, we recommend that the existing concrete and asphalt be removed from within the proposed building footprint plus 10 feet laterally beyond the planned exterior walls. Any structural elements (foundations, slabs, walls, etc.) associated with the apparent former structure or the existing jail structure being demolished should be completely removed from within the building pad area. Reroute existing utilities that cross the proposed building footprint, remove the old line(s), and properly backfill excavations. Ends of abandoned lines outside building and pavement areas should be properly capped.
BUILDING SUPPORT
Due to settlement concerns, we recommend wall, column, and possibly floor slab loads be founded on auger-cast piles bearing in the underlying sand and gravel. Grade beams will be necessary to transfer loads. For preliminary pile capacity design purposes, we suggest accounting for a skin friction of 2 kips per lineal foot of embedment into the natural sand and gravel for 16-inch auger cast piles and 2.25 kips per lineal foot for 18-inch auger-cast piles. The loose fill and soft clays will induce downdrag forces on the pile elements, which will need to be accounted for in design. A pile load test will be required for piles designed over 40 tons. Additional final phase borings are recommended. The borings will need to extend to depths on the order of 60 feet to 70 feet to be able to assess soils within anticipated pile depths. As discussed above, Geopiers® are also viable; contact GCI if you wish to pursue Geopiers® for building support.
Placement of new fill in the building area should be completed to approximate finished subgrade prior to excavation of foundations. Exterior foundations should be placed with a minimum exterior cover equal to the local frost code depth (32 inches typical) or extended to acceptable soils, whichever is deeper. This should not be an issue where deep foundation elements are used.
SEISMIC FACTOR
The borings at the site revealed a generalized profile consisting of loose fill overlying very soft to medium stiff natural clay deposits overlying medium dense sand and gravel. In accordance with the Ohio Building Code, we would estimate the site as a Site Class E – “soft soil profile”.
EXCAVATIONS AND GROUNDWATER
Bedrock was not encountered in the borings (up to 30-foot drilled depths) and is not anticipated to impact slab-on-grade, foundation, and utility excavations within the drilled boring depths. The site fill and natural soils can be excavated using conventional hydraulic equipment. The site fills are loose to very loose, and will need to be braced or appropriately sloped to maintain sidewall stability. All excavations must be in accordance with federal, state, and local guidelines (i.e., OSHA requirements).
Groundwater was initially encountered in the six borings at depths ranging from 3 to 17.5 feet below the surface and was measured at depths of 8 to 16.5 feet at the completion of drilling operations. As such, we anticipate that groundwater will be encountered during installation of the recommended deep foundation elements, probably near the fill/natural soil interface. Significant flows are likely as we
believe the underlying sand and gravel formation is hydraulically connected to the adjacent Hocking River. If water is encountered in shallow utility excavations within the existing fills, we recommend the
trench be dewatered to allow for backfilling in dry conditions; portable sump pumps and working mats of crushed stone may be able to handle these more minor groundwater flows.
PAVEMENTS
The site contains loose fill deposits, as well as soft/organic natural soils in some areas of the property; these soils will settle and may cause premature pavement breakup/drainage problems to some degree. As such, we do not recommend installation of rigid sections as the concrete may crack excessively
should movements occur. Provided the site is properly prepared, it is our opinion that a flexible pavement system can be used for site development, with the expectation of periodic maintenance being
required. We recommend that existing asphalt be stripped from proposed pavement areas. Subgrades
should be carefully proofrolled to identify soft/loose soils. These areas should be stabilized prior to additional fil placement or new pavement construction. Particular attention should be paid to areas where the existing pavement experienced distress. Installation of a biaxial geogrid directly below the base course aggregate would mitigate the effects of differential settlements by helping the pavement section to “float” intact over the fill deposits, and their use should be considered in design.
Design of a site-specific pavement design is beyond the scope of this preliminary study; this would require laboratory testing and we would need design traffic information. For this type of project, GCI would normally recommend a typical minimum pavement section of 3 inches of asphalt over 8 inches of aggregate base in light-duty automobile parking areas. Heavy-duty areas subject to occasional truck traffic would consist of a minimum of 4 inches of asphalt over 10 inches of base aggregate.
Providing adequate sub-base drainage is important to future pavement performance. Finger drains connecting to weep-holes in all inlets, proper grading of pavement sub-grades and surfaces to shed run-off, and under-drains in any pavement swales are suggested sub-base drainage methods and should be used by the site civil engineer.
GENERAL SITE PREPARATION AND EARTHWORK
As a general approach to site preparation, we recommend the following:
1. Where the existing structure is to be demolished, completely remove below-grade structural elements, including foundations, slabs, and walls. Similarly, within the proposed building pad limits plus 10 feet beyond the walls, remove the existing concrete pavement and any old below-grade structural elements from the former building. Properly backfill the resulting excavation. Concrete rubble may be incorporated in structural fills if first broken into pieces no larger than 4 inches in maximum dimension and thoroughly mixed with site soils to avoid creation of voids.
If properly crushed to meet gradation requirements, the concrete may be used as new pavement base material or underslab gravel.
2. Existing utilities that cross the proposed building footprint should be rerouted, the old line(s) removed, and the excavation properly backfilled. The ends of abandoned pipes outside the building footprint should be properly capped.
3. Remove existing asphalt. Asphalt may not be re-used as structural fill unless properly milled. We do not recommend asphalt be incorporated in any building pad fills.
4. Strip surface vegetation and topsoil, if present within proposed building or pavement areas. Topsoil may not be re-used as structural fill.
5. Thoroughly proofroll the stripped subgrades in pavement areas prior to filling or finish grading to identify unstable areas. Particular attention should be paid to areas where the existing pavements experienced distress. Stabilize as needed. Unstable subgrades below structural slabs do not need to be stabilized. GCI should be contacted to observe proofrolling procedures. 6. Place and compact new fill in loose lifts (8 inches thick or less) to at least 98% optimum
Standard Proctor dry density (ASTM D-698). Lift thickness should be reduced to 6 inches in confined areas where compactive effort is reduced. Cohesive site soils will be best compacted with a sheepsfoot roller, while cohesionless soils will be best compacted with a vibratory, smooth drum roller. The moisture content of the fill soils should be controlled to within 3% of optimum moisture content. Depending on the time of year of earthwork, moisture adjustment of the fill may be required to achieve compaction. Off site borrow should be reviewed by GCI prior to use.
7. Excavate through the prepared building pad for foundations. Additional borings are needed to design the recommended extended foundation system.
8. Slab and pavement subgrades should be compacted to a flat, smooth, stable surface with a flat drum compactor prior to placement of aggregate base. Subgrade preparation during wet weather may require the use of an engineered fabric or geogrid.
CONSTRUCTION MATERIALS ENGINEERING AND TESTING
GCI provides full service construction materials engineering and testing services. For project continuity throughout construction, we recommend that GCI be retained to observe, test, and document:
earthwork procedures (stripping, fill placement, compaction, utility trench backfill, etc.) foundation and slab preparation (proof-rolling, excavations, undercuts, etc.),
concrete placement (footings, structural concrete, slabs) and compressive strength testing, and structural steel (welds, bolts, etc.).
The purpose of this work is to assess that the intent of our recommendations is being followed and to make timely changes to our recommendations (as needed) in the event site conditions vary from those
encountered in our borings. Please contact our field department to initiate these services. FINAL
This report is preliminary and not sufficient for final design of the recommended extended foundation system. Additional deeper borings will need to be performed.
We recommend that GCI be provided the opportunity for general review of the final foundation and grading plans and project specifications in order to verify that recommendations contained in this report have been properly interpreted and implemented. In the event that any changes in the nature of the development are planned, conclusions and recommendations contained in this report shall not be considered valid unless changes are reviewed and conclusions of this report are modified or verified in writing. The recommendations contained in this report are the opinion of Geotechnical Consultants, Inc. based on the subsurface conditions found in the borings and available development information.
The site has seen prior development and was located within the floodplain of the Hocking River prior to its realignment and the subsequent placement of substantial amounts of fill across the property. As such,
the nature and extent of variations between borings may not become evident until construction. If
variations then appear evident, it will be necessary to re-evaluate the recommendations of this report. This report is prepared for design purposes only and is not considered sufficient to prepare an accurate bid document.
GCI appreciates the opportunity to work with you on this project and we hope to continue service for the project through construction. If you have any questions or the need for additional services, please call.
GENERAL NOTES FOR SOIL SAMPLING AND CLASSIFICATIONS
BORINGS, SAMPLING AND GROUNDWATER OBSERVATIONS:
Drilling and sampling were conducted in accordance with procedures generally recognized and accepted as standard methods of exploration of subsurface conditions. The borings were drilled using a truck-mounted drill rig using auger boring methods with standard penetration testing performed in each boring at intervals ranging from 1.5 to 5.0 feet. The stratification lines on the logs represent the approximate boundary between soil types at that specific location and the transition may be gradual.
Water levels were measured at drill locations under conditions stated on the logs. This data has been reviewed and interpretations made in the text of the report. Fluctuations in the level of the groundwater may occur due to other factors than those present at the time the measurements were made.
The Standard Penetration Test (ASTM-D-1586) is performed by driving a 2.0 inch O.D. split barrel sampler a distance of 18 inches utilizing a 140 pound hammer free falling 30 inches. The number of blows required to drive the sampler each 6 inches of penetration are recorded. The summation of the blows required to drive the sampler for the final 12 inches of penetration is termed the Standard Penetration Resistance (N). Soil density/consistency in terms of the N-value is as follows:
COHESIONLESS DENSITY COHESIVE CONSISTENCY
0-10 Loose 0-4 Soft
10-30 Medium Dense 4-8 Medium Stiff
30-50 Dense 8-15 Stiff
50 + Very Dense 15-30 Very Stiff
30 + Hard
SOIL MOISTURE TERMS
Soil Samples obtained during the drilling process are visually characterized for moisture content as follows:
MOISTURE
CONTENT DESCRIPTION
Damp
Soil moisture is much drier than the Atterberg plastic limit (where soils are cohesive) and generally more than 3% below Standard Proctor “optimum” moisture conditions. Soils of this moisture generally require added moisture to achieve proper compaction.
Moist Soil moisture is near the Atterberg plastic limit (cohesive soils) and generally within ±3% of the Standard Proctor “optimum” moisture content. Little to no moisture conditioning is anticipated to be required to achieve proper compaction and stable subgrades.
Very Moist
Soil moisture conditions are above the Atterberg plastic limit (cohesive soils) and generally greater than 3% above Standard Proctor “optimum” moisture conditions. Drying of the soils to near “optimum” conditions is anticipated to achieve proper compaction and stable subgrades.
Wet Soils are saturated. Significant drying of soils is anticipated to achieve proper compaction and stable subgrades.
SOIL CLASSIFICATION PROCEDURE:
Soil samples obtained during the drilling process are preserved in plastic bags and visually classified in the laboratory. Select soil samples may be subjected to laboratory testing to determine natural moisture content, gradation, Atterberg limits and unit weight. Soil classifications on logs may be adjusted based on results of laboratory testing.
Soils are classified in accordance with the ASTM version of the Unified Soil Classification System. ASTM D-2487 “Classification of Soils for Engineering Purposes (Unified Soil Classification System) describes a system for classifying soils based on laboratory testing. ASTM D-2488 “Description and Identification of Soil (Visual-Manual Procedure) describes a system for classifying soils based on visual examination and manual tests.
Soil classifications are based on the following tables (see reverse side):
GENERAL NOTES FOR SOIL SAMPLING AND CLASSIFICATIONS
PARTICLE SIZE DEFINITION CONSTITUENT MODIFIERS
Boulders: >12”
Cobbles: 3” to 12” Trace Less than 5%
Gravel: Coarse: 3/4” to 3” Few 5-10%
Fine: No. 4 (3/16”) to 3/4” Little 15-25%
Sand: Coarse No. 10 (2.0mm) to No. 4 (4.75mm) Some 30-45%
Medium No. 40 (0.425mm) to No. 10 (2.0mm) Mostly 50-100%
Fine No. 200 (0.074mm) to No. 40 (0.425mm)
Silt & Clay <0.074mm; classification based on overall plasticity; in general clay particles <0.005mm.
ASTM/UNIFIED SOIL CLASSIFICATION AND SYMBOL CHART
COARSE-GRAINED SOILS
(more than 50% of materials is larger than No. 200 sieve size)
Clean Gravel (less than 5% fines)
GW Well-graded gravel, gravel-sand mixtures, little or no fines GP Poorly-graded gravels, gravel sand mixtures, little or no fines
Gravels with fines (more than 12% fines)
GM Silty gravels, gravel-sand-silt mixtures
GRAVELS
More than 50% of coarse fraction larger than No. 4 sieve size
GC Clayey gravels, gravel-sand-clay mixtures
Clean Sands (Less than 5% fines)
SW Well-graded sands, gravelly sands, little or no fines SP Poorly-graded sands, gravelly sands, little or no fines
Sands with fines (More than 12% fines)
SM Silty sands, sand-silt mixtures
SANDS
More than 50% of coarse fraction smaller than No. 4 sieve size
SC Clayey sands, sand-clay mixtures
Depending on percentage of fines (fraction smaller than No. 200 sieve size), coarse-grained soils are classified as follows: Less than 5 percent ……….GW, GP, SW, SP Greater than 12 percent ………..GM, GC, SM, SC 5 to 12 percent ………Borderline cases requiring duel symbols: SP-SM, GP-GM, etc.
FINE-GRAINED SOILS
(50% or more of material is smaller than No. 200 sieve size)
ML Inorganic silts and very fine sands, rock flour, silty or clayey fine sands or clayey silts with slight plasticity
CL Inorganic clays or low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays
CL-ML Inorganic silty clay of slight plasticity, P.I. between 4 and 7
SILTS AND CLAYS
Liquid Limit less than 50%
OL Organic silts and organic silty clays of low plasticity
MH Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts
CH Inorganic clays of high plasticity, fat clays
SILTS AND CLAYS
Liquid Limit 50% or greater
OH Organic clays or medium to high plasticity, organic silts
HIGHLY ORGANIC SOILS PT Peat and other highly organic soils
