Idea Transcript
A REPORT TO VAN KIRK DEVELOPMENTS INC. A PRELIMINARY SOIL INVESTIGATION FOR PROPOSED PROPOSED RESIDENTIAL DEVELOPMENT 6- to 8-STOREY CONDOMINIUM BUILDING WITH 1-LEVEL UNDERGROUND PARKING 1075 QUEEN STREET EAST CITY OF TORONTO
Reference No. 1209-S093 OCTOBER 2012
DISTRIBUTION 3 Copies - Van Kirk Developments Inc. 1 Copy - Soil Engineers Ltd. (Toronto)
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TABLE OF CONTENTS
1.0 INTRODUCTION .................................................................................... 1 2.0 SITE AND PROJECT DESCRIPTION .................................................. 2 3.0 FIELD WORK.......................................................................................... 3 4.0 SUBSURFACE CONDITIONS .............................................................. 4 4.1 4.2 4.3 4.4 4.5 4.6
Existing Pavement Structure ............................................................. 4 Earth Fill ............................................................................................ 5 Silty Clay............................................................................................ 6 Silty Clay Till ..................................................................................... 7 Shale Bedrock .................................................................................... 9 Compaction Characteristics of the Revealed Soils ........................... 11
5.0 GROUNDWATER CONDITIONS......................................................... 14 6.0 DISCUSSION AND RECOMMENDATIONS ...................................... 16 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9
Foundations ........................................................................................ 18 Underground Garage and Slab-On-Grade......................................... 21 Underground Services ....................................................................... 22 Sidewalks, Interlocking Stone Pavement and Landscaping ............. 23 Backfilling in Trenches and Excavated Areas .................................. 24 Pavement Design ............................................................................... 26 Soil Parameters .................................................................................. 28 Excavation.......................................................................................... 29 Further Investigation.......................................................................... 32
7.0 LIMITATIONS OF REPORT ................................................................. 34
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TABLES Table 1 - Existing Pavement Structure............................................................... 4 Table 2 - Estimated Water Content for Compaction ..................................... 11 Table 3 - Groundwater Levels ........................................................................ 14 Table 4 - Founding Levels ............................................................................. 19 Table 5 - Pavement Design (Underground Garage Rooftop) ........................ 27 Table 6 - Pavement Design (On-Grade Parking Lot and Access Road)........ 27 Table 7 - Soil Parameters............................................................................... 29 Table 8 - Classification of Soils for Excavation ............................................ 30 Table 9 - Soil Pressure for Rakers ................................................................. 32
DIAGRAM Diagram 1 - Lateral Earth Pressure (Shoring Structure) ............................... 30
ENCLOSURES Borehole Logs........................................................................ Grain Size Distribution Graphs ............................................. Borehole Location Plan ......................................................... Subdurface Profile .................................................................
Figures 1 and 2 Figures 3 and 4 Drawing No. 1 Drawing No. 2
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1.0 INTRODUCTION
In accordance with written authorization dated September 22, 2012, from Mr. Julian Battiston, Vice-President, of Van Kirk Developments Inc., a preliminary soil investigation was carried out at 1075 Queen Street East in the City of Toronto, for a proposed Residential Development.
The purpose of the investigation was to reveal the subsurface conditions and to determine the engineering properties of the disclosed soils for the preliminary design and construction of the proposed project.
The findings and resulting geotechnical recommendations are presented in this Report.
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2.0 SITE AND PROJECT DESCRIPTION
The site is situated on Iroquois Lake plain where drift has been partly eroded by the water action of the glacial lake and, in places, filled with lacustrine clay, silt, sand and reworked till. The drift beds onto shale bedrock of Georgian Bay Formation at moderate to considerable depths below the prevailing ground surface.
The subject site, at the time of the investigation, was occupied by a 2-storey commercial building and associated parking lot.
Detailed drawings for the proposed development were not available at the time of preparing this report; however, it is understood that the existing building will be demolished to make way for the proposed development which will consist of a 6- to 8-storey condominium building with one-level underground parking. The new development will be provided with municipal services meeting urban standards.
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3.0 FIELD WORK
The field work, consisting of 2 boreholes to depths of 9.4 m and 10.1 m, was performed on October 3 and 4, 2012, at the locations shown on the Borehole Location Plan, Drawing No. 1.
The boreholes were advanced at intervals to the sampling depths by a truckmounted, continuous-flight power-auger machine equipped for soil sampling. Standard Penetration Tests, using the procedures described on the enclosed “List of Abbreviations and Terms”, were performed at the sampling depths. The test results are recorded as the Standard Penetration Resistance (or ‘N’ values) of the subsoil. The relative density of the granular strata and the consistency of the cohesive strata are inferred from the ‘N’ values. Split-spoon samples were recovered for soil classification and laboratory testing.
The field work was supervised and the findings recorded by a Geotechnical Technician.
The elevation at each of the borehole locations was determined with reference to the site bench mark which is the top of the existing stormwater sewer manhole shown on Drawing No. 1. It has been given an assumed elevation of 100.0 m.
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4.0 SUBSURFACE CONDITIONS
Detailed descriptions of the encountered subsurface conditions are presented on the Borehole Logs, comprising Figures 1 and 2. The revealed stratigraphy is plotted on the Subsurface Profile, Drawing No. 2, and the engineering properties of the disclosed soils are discussed herein.
The investigation has disclosed that beneath a pavement structure and, in one location, a layer of earth fill, the site is predominantly underlain by strata of silty clay and silty clay till. The till beds onto shale bedrock of Georgian Bay Formation at depths of 9.2± m and 9.9± m below the pavement surface.
4.1 Existing Pavement Structure (Both Boreholes)
The pavement structure disclosed by the boreholes is presented in Table 1. Table 1 - Existing Pavement Structure Thickness (mm) BH No.
Asphaltic Concrete
Granular Fill
1
50
200
2
50
600
The natural water content of the granular fill was determined, and the results are plotted on the Borehole Logs; the values are 3% and 6%, indicating that the granular fill is in a moist to very moist condition.
A grain size analysis was performed on 1 representative sample of the granular fill; the result is plotted on Figure 3. The analysis shows that the granular fill generally
Reference No. 1209-S093 satisfies the OPS Gradation Specification Requirements. However, additional testing should be carried out on bulk samples of the salvaged granular fill to determine its suitability for use as road base or sub-base material; otherwise, it can be used for structural backfill and road subgrade stabilization.
4.2 Earth Fill (Borehole 1)
A layer of earth fill was encountered in 1 borehole extending to a depth of 1.5 m below the pavement surface. It is amorphous in structure; it consists of silty clay material with some sand and a variable amount of gravel, construction debris and occasional topsoil inclusions. The original topsoil was not detected beneath the earth fill, but may have been obscured by the augering.
The water content of the earth fill sample was determined, and the result is plotted on the Borehole Log; the value is 14%, indicating that the fill is in a very moist condition.
The obtained ‘N’ value of the earth fill is 13 blows per 30 cm of penetration. The obtained ‘N’ is likely exaggerated due to the presence of construction debris in the fill and does not represent its actual density as determined from tactile testing of the soil sample. The tactile examination indicates that the earth fill is in a loose condition.
As noted, the fill contains topsoil inclusions and other deleterious material, and its consistency is loose; therefore, it is unsuitable for supporting structures. In using the fill for structural backfill, or in pavement and slab-on-grade construction, it should be subexcavated, inspected, sorted free of topsoil inclusions and any deleterious material, and properly recompacted.
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As noted, the fill is amorphous in structure and is generally loose; it will ravel and is susceptible to sudden collapse in steep cuts. Where the earth fill is free of deleterious materials, its engineering properties are generally similar to those of the silty clay described in the following section.
One must be aware that the samples retrieved from boreholes 10 cm in diameter may not be truly representative of the geotechnical and environmental quality of the fill, and do not indicate whether the topsoil beneath the earth fill was completely stripped. This should be further assessed by laboratory testing and/or test pits.
4.3 Silty Clay (Both Boreholes)
The silty clay deposit was encountered beneath the pavement structure or earth fill. It contains a trace of fine sand and is laminated with wet silt and sand seams, indicating that it is a lacustrine deposit.
The obtained ‘N’ values range from 5 to 12, with a median of 6, which indicates that the consistency of the clay is firm to stiff, being generally firm.
The upper layer of the silty clay has been fractured by the weathering process. The weathered zone extends to depths of 1.5± m and 2.0± m below the paved surface.
The water content values range from 18% to 24%, with a median of 19%, showing that the clay is very moist to wet, being generally very moist.
Sample examinations show that the silty clay is a material of medium plasticity.
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Accordingly, the following engineering properties are deduced: •
Highly frost susceptible and high soil-adfreezing potential.
•
Low water erodibility.
•
The clay is virtually impervious. However, due to the silt layers, the lateral permeability is higher than the vertical permeability. The estimated coefficient of permeability is about 10-7 cm/sec, with runoff coefficients of: Slope
•
0% - 2%
0.15
2% - 6%
0.20
6% +
0.28
A cohesive soil, its shear strength is primarily derived from consistency which is inversely dependent on soil moisture.
•
The firm silty clay will consolidate under area surcharge loads. In steep excavations to depths of 2.0 to 3.0 m, the sides may fail and the bottom may heave due to overstressing.
•
A very poor pavement-supportive material, with an estimated California Bearing Ratio (CBR) value of 3% or less.
•
Moderately high corrosivity to buried metal, with an estimated electrical resistivity of 3500 ohm·cm.
4.4 Silty Clay Till (Both Boreholes)
The clay till was encountered in the lower zone of the soil stratigraphy and beds onto the shale bedrock in both boreholes. It consists of a random mixture of soils; the particle sizes range from clay to gravel, with the clay fraction exerting the dominant influence on its soil properties. The till contains some sand to being
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sandy, with a trace of gravel. The structure of the till is generally amorphous, showing that it is a glacial deposit that has been reworked by the past glaciation.
Sample examinations reveal that the clay till is embedded with occasional sand and silt layers, which are often wet.
Hard resistance to augering encountered in places, showing that the till is embedded with occasional cobbles and boulders.
The obtained ‘N’ values range from 9 to 36, with a median of 14, from which the consistency of the till is inferred as firm to hard, being generally stiff. In general, the obtained ‘N’ values decrease with depth; this indicates that the till has been reworked by the water action of the glacial lake.
The Atterberg Limits of 2 representative samples and the natural water content of all the samples were determined. The results are plotted on the Borehole Logs and summarized below:
Liquid Limit
28% and 29%
Plastic Limit
17%
Natural Water Content
12% to 20% (median 14%)
The above results and samples examination indicate that the till is a cohesive material with low plasticity. The natural water content generally lies below its plastic limits, confirming the consistency of the till as determined by the ‘N’ values.
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Grain size analyses were performed on 2 representative samples of the silty clay till and the results are plotted on Figure 4.
Based on the above findings, the soil engineering properties pertaining to the project are given below: •
High frost susceptibility and low soil-adfreezing potential.
•
Low water erodibility.
•
Low permeability, with an estimated coefficient of permeability of 10-7 cm/sec, and runoff coefficients of: Slope
•
0% - 2%
0.15
2% - 6%
0.20
6% +
0.28
A cohesive soil, its shear strength is primarily derived from consistency which is inversely related to its moisture content. It contains sand; therefore, its shear strength is augmented by internal friction.
•
The silty clay till will generally be stable in a relatively steep cut; however, prolonged exposure will allow the weathered layers and the wet sand seams to become saturated, which may lead to localized sloughing.
•
A poor pavement-supportive material, with an estimated CBR value of 3%.
•
Moderate corrosivity to buried metal, with an estimated electrical resistivity of 4000 ohm·cm.
4.5 Shale Bedrock (Both Boreholes)
Shale is a laminated, sedimentary, moderately soft rock composed predominantly of clay material. The shale bedrock was encountered at depths of 9.2± m and
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9.9± m below the pavement surface and is grey in colour, showing it is a Georgian Bay Formation. It is thinly to thickly bedded and consists predominantly of mudstone with occasional hard, limy shale and sandstone bands.
The water content values of samples obtained from the sampler and auger are 9% and 12%, showing that the shale within the investigated depth is weathered. The weathered zone generally extends to about 3.0± m below the bedrock surface.
The shale is susceptible to disintegration and swelling upon exposure to air and water, with subsequent reversion to a clay soil, but the laminated limy and sandy layers will remain as rock slabs.
Infiltrated precipitation and groundwater from the overburden soils will often permeate the fissures in the rock and, in places, will be under subterranean artesian pressure. However, because the shale is a clay rock, it is considered to be a material of low permeability and a poor aquifer, and the groundwater yield from the rock will be limited.
The weathered rock can be excavated with considerable effort by a heavy-duty backhoe equipped with a rock-ripper; however, excavation will become progressively more difficult with depth into the sound shale. Efficient removal of the sound shale may require the aid of pneumatic hammering and/or blasting.
When excavating the sound shale, slight lateral displacement of the excavation walls is often experienced. This is due to the release of residual stress stored in the bedrock mantle and the swelling characteristic of the rock. A wider excavation filled with sand fill and lined with compressible Styrofoam (or equivalent) will diminish the load intensity imposed on buried structures by the rock movement.
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The excavated spoil will contain a large amount of hard limy and sandy rock slabs, rendering it virtually impossible to obtain uniform compaction. Therefore, unless the spoil is sorted, or the rock fragments are left for a period of 1 to 2 winters to allow the shale reversion to occur, the excavated shale is considered unsuitable for engineering applications.
4.6 Compaction Characteristics of the Revealed Soils
The obtainable degree of compaction is primarily dependent on the soil moisture and, to a lesser extent, on the type of compactor used and the effort applied.
As a general guide, the typical water content values of the revealed soils for Standard Proctor compaction are presented in Table 2.
Table 2 - Estimated Water Content for Compaction Water Content (%) for Standard Proctor Compaction Soil Type Granular Fill
Determined Natural Water Content (%) 100% (optimum) Range for 95% or + 3 and 6
6
3 to 11
Earth Fill
14
20
16 to 23
Silty Clay
18 to 24 (median 19)
20
16 to 23
Silty Clay Till
12 to 20 (median 14)
16
12 to 21
9 and 12
10
7 to 17
Shale
Based on the above findings, the encountered soils are generally suitable for a 95% or + Standard Proctor compaction. Some of the silty clay is too wet or on the
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wet side of the optimum and will require aeration or mixing with drier soils prior to structural compaction. The aeration can be effectively carried out by spreading it thinly on the ground in dry, warm weather. A portion of the silty clay till is on the dry side of the optimum and will require wetting or mixing with wet soils prior to structural compaction.
The earth fill must be sorted free of topsoil inclusions and other deleterious materials prior to structural use.
The silty clay, silty clay till and inorganic earth fill should be compacted using a heavy-weight, kneading-type roller. The granular fill can be compacted by a smooth drum roller, with or without vibration, depending on the water content of the soils being compacted. The lifts for compaction should be limited to 20 cm, or to a suitable thickness as assessed by test strips performed by the equipment which will be used at the time of construction.
When compacting the very stiff to hard silty clay till on the dry side of the optimum, the compactive energy will frequently bridge over the chunks in the soil and be transmitted laterally into the soil mantle. Therefore, the lifts must be limited to 20 cm or less (before compaction). It is difficult to monitor the lifts of backfill placed in deep trenches; therefore, it is preferable that the compaction of backfill at depths over 1.0 m below the road subgrade be carried out on the wet side of the optimum. This would allow a wider latitude of lift thickness.
If the compaction of the soils is carried out with the water content within the range for 95% Standard Proctor dry density but on the wet side of the optimum, the surface of the compacted soil mantle will roll under the dynamic compactive load. This is unsuitable for road construction since each component of the pavement
Reference No. 1209-S093 structure is to be placed under dynamic conditions which will induce the rolling action of the subgrade surface and cause structural failure of the new pavement. The foundations or bedding of the sewer and slab-on-grade will be placed on a subgrade which will not be subjected to impact loads. Therefore, the structurally compacted soil mantle with the water content on the wet side or dry side of the optimum will provide an adequate subgrade for the construction.
The presence of boulders and/or large limy shale fragments will prevent transmission of the compactive energy into the underlying material to be compacted. If an appreciable amount of boulders and shale fragments over 15 cm in size is mixed with the material, it must either be sorted or must not be used for structural backfill.
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5.0 GROUNDWATER CONDITIONS
Groundwater seepage encountered during augering was recorded on the field logs. The boreholes were checked for the presence of groundwater and the occurrence of cave-in upon their completion, and the data are plotted on the Borehole Logs and listed in Table 3.
Table 3 - Groundwater Levels Measured Groundwater/ Cave-in* Level On Completion
Borehole
Soil Colour Changes Brown to Grey
BH No. Depth (m)
Depth (m)
Depth (m)
Remarks
Depth (m)
El. (m)
Seepage Encountered During Augering
1
9.4
3.0
3.0
Some
3.0
97.3
2
10.1
4.5
1.5
Some
1.5
98.6
As shown above, groundwater was detected at depths of 1.5 m and 3.0 m below the pavement surface (El. 98.6 m and 97.3 m). However, the detected groundwater is likely attributable to perched groundwater derived from infiltrated precipitation trapped in the voids of the fills, the fissures of the weathered soils, and in the sand and silt seams and layers laminated within the soil stratigraphy.
The soil changes from brown to grey at depths of 3.0 m and 4.5± m below the pavement surface. The brown colour indicates that the soils have oxidized. The groundwater regime of the site will fluctuate with the seasons.
Reference No. 1209-S093 If groundwater is encountered, its yield from the silty clay and silty clay till will be small and can be controlled by normal pumping from sumps. In some instances, the shale may contain occasional pockets of groundwater trapped in the rock fissures which may be under moderate subterranean artesian pressure. Upon release through excavation, this water will drain readily.
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Reference No. 1209-S093 6.0 DISCUSSION AND RECOMMENDATIONS
The investigation has disclosed that beneath an existing pavement structure and, in one location, a layer of earth fill, the site is predominantly underlain by strata of firm to stiff, generally firm silty clay and stiff to hard, generally stiff silty clay till. The till beds onto shale bedrock of Georgian Bay Formation at depths of 9.2± m and 9.9± m below the pavement surface.
The upper zone of the native clay is weathered. The weathered zone extends to a depth of 2.0± m below the pavement surface.
Groundwater was measured at depths of 1.5 m and 3.0 m below the pavement surface upon completion of the field work. The detected groundwater is likely attributable to perched groundwater derived from infiltrated precipitation trapped in the voids of the tills, the fissures of the weathered soils, and in the sand and silt seams and layers laminated within the soil stratigraphy. The soil changes from brown to grey at depths of 3.0 m and 4.5± m below the pavement surface. The groundwater regime will fluctuate with the seasons.
The yield of groundwater, if encountered, from the clay and clay till, due to their low permeability, will be limited and will generally be controllable by normal pumping from sumps.
If groundwater is encountered during excavation in the shale bedrock, it can be drained readily with a limited yield.
The geotechnical findings which warrant special consideration are presented below:
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Reference No. 1209-S093 1.
The earth fill found at the site extends to a depth of 1.5 m below the pavement surface and appears to be spoil from vicinal construction. The relative density of the fill is generally loose. It contains topsoil inclusions and other deleterious material, rendering it unsuitable for supporting foundations. For structural use, the fill must be subexcavated, inspected, assessed, sorted free of topsoil inclusions and deleterious materials, aerated and properly compacted. If it is impractical to sort the topsoil and other deleterious material from the fill, then the fill must be wasted and replaced with properly compacted inorganic earth fill.
2.
Laboratory analysis shows that the granular fill generally satisfies the OPS Gradation Specification Requirements. If properly salvaged, the granular fill is suitable for use as a pavement base or sub-base material. However, additional testing should be carried out on bulk samples of the salvaged granular fill to confirm the results. Nevertheless, it can be used for structural backfill and road subgrade.
3.
The weathered clay, which extends to a depth of 2.0± m, below the pavement surface is weak and will consolidate under surcharge loads. To upgrade the weathered clay to engineered status suitable for lightly loaded foundations and floor slab construction, it must be subexcavated, aerated and properly compacted.
4.
Due to the presence of earth fill and weathered clay, the footing subgrade must be inspected by a geotechnical engineer, or a geotechnical technician under the supervision of a geotechnical engineer, to assess its suitability for bearing the designed foundations.
5.
The sound silty clay till and shale bedrock are suitable for normal spread and strip footings and drilled caisson foundation construction.
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Reference No. 1209-S093 6.
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Due to the proximity of the proposed building to the existing buildings, special measures will be required in order to ensure that the construction will not impact the structural integrity of the existing buildings.
7.
Perimeter subdrains and dampproofing of the foundation walls will be required for underground parking construction. The subdrains should be shielded by a fabric filter to prevent blockage by silting.
8.
If rock excavation is required for the construction of the underground parking, in general, this can be achieved by using a backhoe equipped with a rock-ripper in the weathered shale which extends to a depth of 3.0± m below the surface of the bedrock; where extensive limy shale or sandstone layers are encountered, pneumatic hammering may be required for efficient rock removal.
The recommendations appropriate for the project described in Section 2.0 are presented herein. One must be aware that the subsurface conditions may vary between boreholes. Should this become apparent during construction, a geotechnical engineer must be consulted to determine whether the following recommendations require revision.
6.1 Foundations
Based on the borehole findings, the foundations should be placed below the earth fill and weathered clay onto the sound natural soils or shale bedrock. The recommended soil pressures for use in the design of the normal spread and strip footings, together with the corresponding suitable founding levels, are presented in Table 4.
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Table 4 - Founding Levels Recommended Maximum Allowable Soil Pressure (SLS)/ Factored Ultimate Soil Bearing Pressure (ULS) and Corresponding Founding Level Sound Natural Soils 150 kPa (SLS) 250 kPa (ULS) BH No. Depth (m)
El. (m)
Weathered Shale
350 kPa (SLS) 560 kPa (ULS)
600 kPa (SLS) 960 kPa (ULS)
Depth (m) El. (m) Depth (m)
1
3.0 or +*
97.3 or -
-
2
3.0 or +
97.1 or -
9.5 or +
-
El. (m)
9.5 or +
90.8 or -
90.6 or - 10.3 or +
89.8 or -
* Due to the decrease in ‘N’ values with depth, the 150 kPa (SLS) soil pressure must be reduced to 100 kPa (SLS) from a depth of 5.0 m below the prevailing ground surface, and the size of the spread and strip footings at this depth should not be greater than 2.0 m and 1.2 m, respectively.
Heavy building loads can be supported by drilled caisson foundations. A Maximum Allowable Soil Pressure (SLS) of 1200 kPa and a Factored Ultimate Soil Bearing Pressure (ULS) of 2000 kPa can be used for the design of caissons founded into weathered shale. The caissons must be embedded at least 1.0 m into the weathered shale. The ratio of the embedded soil depth to the diameter of the caisson should be at least 2:1.
The centre-to-centre spacing between the caissons must be at least twice the diameter of the largest adjacent caisson base. To facilitate efficient subgrade inspection and cleaning, the size of the caissons should be at least 80 cm in diameter and the excavation should be temporarily lined.
Alternatively, building loads can also be supported by mat foundation designed with a Maximum Allowance Soil Pressure (SLS) of 100 kPa and a Factored Ultimate Soil Bearing Pressure (ULS) of 150 kPa founded at a depth of 3.0 m or + below the pavement surface. A granular base, consisting of 20-mm Crusher-Run
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Limestone, 0.4 m thick, properly compacted to 98% or + of its maximum Standard Proctor dry density can be placed below the mat foundation.
A Modulus of Subgrade Reaction of 20 MPa/m is recommended for use in the design of the mat foundation.
The above-recommended Maximum Allowable Soil Pressures (SLS) for both normal and caisson foundations incorporate a factor of safety of 3 against shear failure of the underlying soils.
The total and differential settlements of the foundations designed with the recommended bearing capacities are estimated to be 25 mm and 15 mm, respectively.
The foundation of the proposed building will be constructed in close proximity to existing buildings. Appropriate precautions must be taken to ensure that the existing footing subgrade is not deprived of lateral support during or after the construction of the new footings; otherwise, the existing buildings footings must be underpinned to the same founding level as the proposed building.
The design of the foundations should meet the requirements specified in the Ontario Building Code 2006. The structure should be designed to resist an earthquake force using Site Classification ‘C’ (soft rock) on the shale bedrock and Site Classification ‘D’ (stiff soil) on the stiff silty clay till.
The foundations exposed to weathering and in unheated areas, such as the air shaft and ramp-down driveway, should have at least 1.2 m of earth cover for protection against frost action, or must be properly insulated.
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Due to the presence of earth fill, reworked till and weathered clay, the foundation subgrade should be inspected by a geotechnical engineer, or a geotechnical technician under the supervision of a geotechnical engineer, to ensure that the revealed conditions are compatible with the foundation design requirements.
As noted, the silty clay is highly frost susceptible and has high soil-adfreezing potential. In order to alleviate the risk of frost damage, the foundation walls must be constructed of concrete, and either backfilled with non-frost-susceptible pit-run granular, or shielded with a polyethylene slip-membrane. The membrane will allow vertical movement of the heaving soil (due to frost) without imposing structural distress on the foundations. The external grading should be such that runoff is directed away from the foundation.
6.2 Underground Garage and Slab-On-Grade
For the underground levels, the perimeter walls should be designed to sustain a lateral earth pressure calculated using the soil parameters given in Section 6.7. Any applicable surcharge loads adjacent to the proposed building must also be considered in the design of the walls of the underground levels.
Depending on the final design of the building, the subgrade for the floor slab for the underground parking will likely consist of stiff to very stiff silty clay till. Accordingly, the slab should be constructed on a granular base, 20 cm thick, consisting of 20-mm Crusher-Run Limestone, or equivalent, compacted to its maximum Standard Proctor dry density. A Modulus of Subgrade Reaction of 20 MPa/m can be used in the design of the floor slab.
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Perimeter subdrains encased in a fabric filter will be required. The perimeter walls of the underground garage should be dampproofed and must be provided with synthetic sheet drains, or backfilled with free-draining granular, to prevent the accumulation of water against the garage walls. The external grading must be such that water is directed away from the building to prevent ponding adjacent to the underground garage.
Depending on the amount of groundwater encountered at the time of construction, a subdrain system consisting of 100-mm filter-sleeved weepers may be required to prevent the build-up of hydrostatic uplift pressure and moisture upfiltration. The subdrain system must be installed at a depth of about 200 mm below the underside of the granular base. All subdrains are to be connected to a positive outlet. A vapour barrier should be provided to prevent moisture upfiltration.
The slab-on-grade subgrade at the building entrances and in unheated areas should be properly insulated with 50-mm Styrofoam, or its thermal equivalent, or the subgrade material should be replaced with 1.2 m of non-frost-susceptible granular material and should be provided with subdrains. This will minimize frost action in these areas where vertical ground movement cannot be tolerated.
6.3 Underground Services
The subgrade for the underground services should consist of sound natural soils or compacted organic-free earth fill. In areas where the subgrade consists of earth fill or soft soils, it should be subexcavated and replaced with organic-free earth fill or bedding material compacted to at least 95% or + of its Standard Proctor compaction.
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Where the sewers are to be constructed using the open-cut method, the construction must be carried out in accordance with Ontario Regulation 213/91. In areas where a vertical cut is necessary, the use of a trench box is considered to be appropriate. In the design of the trench box and/or shoring structure, the recommended lateral earth pressure coefficients presented in Table 7, Section 6.7, can be used
A Class ‘B’ bedding is recommended for the underground services construction. The bedding material should consist of compacted 20-mm Crusher-Run Limestone, or equivalent.
In order to prevent pipe floatation when the sewer trench is deluged with water, a soil cover with a thickness equal to the diameter of the pipe should be in place at all times after completion of the pipe installation.
Openings to subdrains and catch basins should be shielded with a fabric filter to prevent blockage by silting.
Since the silty clay, silty clay till and shale bedrock have moderately high to moderate corrosivity to buried metal, the water main should be protected against corrosion. In determining the mode of protection, an electrical resistivity of 3500 ohm·cm should be used. This, however, should be confirmed by testing the soil along the water main alignment at the time of sewer construction.
6.4 Sidewalks, Interlocking Stone Pavement and Landscaping
Interlocking stone pavement and the sidewalks in areas which are sensitive to frostinduced ground movement, such as entrances, must be constructed on a free-
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draining, non-frost-susceptible granular material such as Granular ‘B’. It must extend to 1.2 m below the slab or pavement surface and be provided with positive drainage such as weeper subdrains connected to the storm system. Alternatively, the sidewalk and pavement should be insulated with 50-mm Styrofoam, or equivalent.
6.5 Backfilling in Trenches and Excavated Areas
The on-site inorganic soils are suitable for trench backfill. The backfill in the trenches should be compacted to at least 95% of its maximum Standard Proctor dry density and increased to 98% or + below the floor slab. In the zone within 1.0 m below the road subgrade, the material should be compacted with the water content 2% to 3% drier than the optimum, and the compaction should be increased to at least 98% of the respective maximum Standard Proctor dry density. This is to provide the required stiffness for pavement construction. In the lower zone, the compaction should be carried out on the wet side of the optimum; this allows a wider latitude of lift thickness.
In normal sewer construction practice, the problem areas of road settlement largely occur adjacent to manholes, catch basins and services crossings. In areas which are inaccessible to a heavy compactor, sand backfill should be used. Unless compaction of the backfill is carefully performed, the interface of the native soils and the sand backfill will have to be flooded for a period of several days.
The narrow trenches for services crossings should be cut at 1 vertical: 2 or + horizontal so that the backfill can be effectively compacted. Otherwise, soil arching will prevent the achievement of proper compaction. The lift of each
Reference No. 1209-S093
25
backfill layer should either be limited to a thickness of 20 cm, or the thickness should be determined by test strips.
One must be aware of the possible consequences during trench backfilling and exercise caution as described below: •
When construction is carried out in freezing winter weather, allowance should be made for these following conditions. Despite stringent backfill monitoring, frozen soil layers may inadvertently be mixed with the structural trench backfill. Should the in situ soils have a water content on the dry side of the optimum, it would be impossible to wet the soils due to the freezing condition, rendering difficulties in obtaining uniform and proper compaction. Furthermore, the freezing condition will prevent flooding of the backfill when it is required, such as when the trench box is removed, or when the backfill consists of shale mixture. The above will invariably cause backfill settlement that may become evident within 1 to several years, depending on the depth of the trench which has been backfilled.
•
In areas where the underground services construction is carried out during winter months, prolonged exposure of the trench walls will result in frost heave within the soil mantle of the walls. This may result in some settlement as the frost recedes, and repair costs will be incurred prior to final surfacing of the new pavement.
•
To backfill a deep trench, one must be aware that future settlement is to be expected, unless the side of the cut is flattened to at least 1 vertical: 1.5+ horizontal, and the lifts of the fill and its moisture content are stringently controlled; i.e., lifts should be no more than 20 cm (or less if the backfilling conditions dictate) and uniformly compacted to achieve at least
Reference No. 1209-S093
26
95% of the maximum Standard Proctor dry density, with the moisture content on the wet side of the optimum. •
It is often difficult to achieve uniform compaction of the backfill in the lower vertical section of a trench which is an open cut or is stabilized by a trench box, particularly in the sector close to the trench walls or the sides of the box. These sectors must be backfilled with sand. In a trench stabilized by a trench box, the void left after the removal of the box will be filled by the backfill. It is necessary to backfill this sector with sand, and the compacted backfill must be flooded for 1 day, prior to the placement of the backfill above this sector, i.e., in the upper sloped trench section. This measure is necessary in order to prevent consolidation of inadvertent voids and loose backfill which will compromise the compaction of the backfill in the upper section. In areas where groundwater movement is expected in the sand fill mantle, seepage collars should be provided.
6.6 Pavement Design
Where the pavement is to be built on structural slabs, such as the underground garage rooftop, a sufficient granular base and adequate drainage must be provided to prevent frost damage to the pavement. A waterproof membrane must be placed above the structural slab exposed to weathering to prevent water leakage, as well as to protect the reinforcing steel bars against brine corrosion.
The recommended pavement structure to be placed on the underground garage rooftop is presented in Table 5.
Reference No. 1209-S093
27
Table 5 - Pavement Design (Underground Garage Rooftop) Course
Thickness (mm)
OPS Specifications
Asphalt Surface
40
HL-3
Asphalt Binder
60
HL-8
Granular Base
250
20-mm Crusher-Run Limestone
Granular Sub-base
150
Free-Draining Sand Fill
The recommended pavement structure for the on-grade portion of the parking lot and access road is given in Table 6.
Table 6 - Pavement Design (On-Grade Parking Lot and Access Road) Course
Thickness (mm)
OPS Specifications
Asphalt Surface
40
HL-3
Asphalt Binder
60
HL-8
Granular Base
150
Granular ‘A’ or 20-mm Crusher-Run Limestone
Granular Sub-base
300
Granular ‘B’, Type II or 50-mm Crusher-Run Limestone
Prior to placement of the granular bases, the subgrade surface should be proofrolled, and any soft subgrade should be subexcavated and replaced by properly compacted inorganic earth fill or granular material. All the granular bases should be compacted to their maximum Standard Proctor dry density.
The earth fill in the zone within 1.0 m below the pavement must be compacted to 98% or + of its maximum Standard Proctor dry density, with the moisture content 2% to 3% drier than the optimum.
Reference No. 1209-S093
28
The parking lot subgrade will suffer a strength regression if water allowed to infiltrate prior to paving. The following measures should therefore be incorporated in the construction procedures and parking lot design: •
If the parking lot construction does not immediately follow the trench backfilling, the subgrade should be properly crowned and smooth-rolled to allow interim precipitation to be properly drained.
•
The areas adjacent to the parking lot should be properly graded to prevent the ponding of large amounts of water during the interim construction period.
•
If the parking lot is to be constructed during the wet seasons and extensively soft subgrade occurs, the granular sub-base may require thickening. This can be further assessed during construction.
A subdrain system should be installed along the perimeter of the pavement and in the paved areas to prevent infiltrating precipitation from seeping into the granular bases (since this may inflict frost damage on the pavement). The subdrains should consist of filter-sleeved weepers and backfilled with free-draining granular material. They should be connected to catch basins and storm manholes.
6.7 Soil Parameters
The recommended soil parameters for the project design are given in Table 7.
Reference No. 1209-S093
29
Table 7 - Soil Parameters Unit Weight and Bulk Factor Estimated Bulk Factor
Unit Weight (kN/m3) Bulk
Loose
Compacted
Earth Fill
20.0
1.20
0.98
Silty Clay
20.5
1.30
1.05
Silty Clay Till
21.5
1.30
1.05
Weathered Shale Bedrock
23.5
1.50
1.10 to 1.15
Lateral Earth Pressure Coefficients Active Ka
At Rest Ko
Passive Kp
Earth Fill and Silty Clay
0.50
0.65
2.00
Silty Clay Till
0.45
0.55
2.22
Weathered Shale Bedrock
0.15
0.25
6.00
Coefficients of Friction Between Concrete and Sound Natural Soils or Shale Bedrock
0.40
Between Concrete and Granular Base
0.60
Maximum Allowable Soil Pressure (SLS) For Thrust Block Design Sound Natural Soils and Engineered Fill
50 kPa
6.8 Excavation
Excavation should be carried out in accordance with Ontario Regulation 213/91.
The sides of the excavation should be cut at 1 vertical:1 or + horizontal, and the spoil from the excavation and/or trenches must be placed at a distance from the
Reference No. 1209-S093
30
edge of the excavation equal to twice the depth of the excavation. Alternatively, interlocking sheeting can be used for the excavation. This must be determined by a qualified engineer.
For excavation purposes, the types of soils are classified in Table 8.
Table 8 - Classification of Soils for Excavation Material
Type
Shale Bedrock
1
Stiff to hard Silty Clay and Clay Till
2
Firm Silty Clay and Earth Fill
3
The groundwater yield from the clay and clay till will be small and can be controlled by pumping from sumps.
Where shoring is required for excavation, the shoring structure should be designed using the lateral earth pressure distribution given in Diagram 1.
Diagram 1 - Lateral Earth Pressure (Shoring Structure)
0.25H
H - Height of Excavation 0.5H
0.25H
g Ka H
H
γ - Bulk Unit Weight For K a and γ refer to Table 7, Section 6.7
Reference No. 1209-S093
31
The overburden load of any adjacent existing structures should also be considered in the design of the shoring structure.
If tiebacks are to be used for the shoring structure, the anchors should be embedded into the very stiff to hard silty clay till or shale bedrock. An average undrained shear strength of 75 kPa can be used for the computation of pull-resistance of the tieback installed in the very stiff to hard silty clay till. For tiebacks installed in the bedrock, a Maximum Allowable Bond Stress of 300 kPa can be used to determine the size and anchorage length of the tieback. All of the tieback anchors should be proof-loaded to at least 133% of the design load and at least 1 full scale test should be carried out on 1 anchor.
If rakers are to be used instead of tiebacks, they should be designed using the recommended Soil Bearing Pressures given in Table 9. The bearing capacity values are based on the assumption that the building will have 1 level of underground parking and the proposed founding level will be at El. 97.2± m.
Reference No. 1209-S093
32
Table 9 - Soil Pressure for Rakers Recommended Soil Pressure (kPa) Angle of Raker
Very Stiff Silty Clay Till
Inclination (α)
Df/B=0
Df/B=1
30°
130
180
45°
120
170
60°
100
150
Df
a
B
Prospective contractors must be asked to assess the in situ subsurface conditions for soil cuts by digging test pits to at least 0.5 m below the intended bottom of excavation. These test pits should be allowed to remain open for a period of at least 4 hours to assess the trenching conditions.
6.9 Further Investigation
As noted, detailed drawings were not available at the time of preparing this report. Given that the scope of the investigation is to reveal the subsurface conditions and determine the engineering properties of the disclosed soils for the general design of
Reference No. 1209-S093 the project, further borehole investigation and rock coring to assess the quality of the bedrock will be required to confirm the findings and recommendations of this investigation.
33
LOG OF BOREHOLE NO: 1
JOB DESCRIPTION: Proposed Residential Development JOB LOCATION: 1075 Queen Street East
METHOD OF BORING: Flight-Auger DATE: October 4, 2012
0.0 100.3
1.5 98.8
Pavement Surface 50 mm ASPHALTIC CONCRETE 200 mm GRANULAR, Fill Brown SILTY CLAY, Fill occ. construction debris and topsoil inclusions Brown, firm weathered
SILTY CLAY a tr. of sand occ. sand and silt seams and layers 3.0 97.3
Grey, stiff to very stiff
N-Value
Type
Elev. (m)
SOIL DESCRIPTION
Number
Depth
Depth Scale (m)
City of Toronto
SAMPLES
FIGURE NO: 1
Atterberg Limits
Shear Strength (kN/m2) 20
40
60
PL
80
Penetration Resistance (blows/30cm) 10
30
50
70
LL
Moisture Content (%) 10
90
20
1
DO 11
2
DO 13
3
DO
3
1
14
24
6 2
4
DO
5
DO 19
19
8 3
16
4
6
DO 12
some sand to sandy, a tr. of gravel occ. wet sand and silt seams and layers, cobbles and boulders
13 5
6 7
DO
9
15
7
8
DO 12
9
DO 50/ 13
13 8
9 Grey, weathered SHALE BEDROCK Refusal to augering END OF BOREHOLE Installed 50 mm Ø monitoring well to 4.6 m with 3.0 m screen at the bottom. Sand backfill from 0.9 to 4.6 m. Bentonite seal from 0.3 to 0.9 m. Concrete from 0.0 to 0.3 m. Provided with flush-mount cover.
40
0
SILTY CLAY, Till
9.2 91.1 9.4 90.9
30
WATER LEVEL
1209-S093
10
11
12
Soil Engineers Ltd.
12
W.L. @ El. 97.3 m on completion
JOB NO:
LOG OF BOREHOLE NO: 2
1209-S093
JOB DESCRIPTION: Proposed Residential Development JOB LOCATION: 1075 Queen Street East
METHOD OF BORING: Flight-Auger DATE: October 3, 2012
0.0 100.1
Pavement Surface 50 mm ASPHALTIC CONCRETE 600 mm GRANULAR, Fill
N-Value
Type
Elev. (m)
SOIL DESCRIPTION
Number
Depth
Depth Scale (m)
City of Toronto
SAMPLES
FIGURE NO: 2
Atterberg Limits
Shear Strength (kN/m2) 20
40
60
PL
80
Penetration Resistance (blows/30cm) 10
30
50
70
LL
Moisture Content (%) 10
90
20
30
40
WATER LEVEL
JOB NO:
0 1
DO 32
2
DO
3
DO 12
6
Brown, firm to stiff SILTY CLAY a tr. of sand weathered occ. sand and silt seams and layers
5
20
1
18 2
DO
5
DO 25
6
DO 15
7
DO 18
19
6 3
Stiff to hard
SILTY CLAY, Till
16
20
4
brown grey
14 5
6 some sand, a tr. of gravel occ. wet sand and silt seams and layers, cobbles and boulders
8
13
DO 13
7
9
DO 11
14 8
9
9.9 10.1 90.2 90.0
Grey, weathered SHALE BEDROCK Refusal to augering END OF BOREHOLE
10
DO 36
11
DO 50/ 7.6
12
10
11 Installed 50 mm Ø monitoring well to 4.6 m with 3.0 m screen at the bottom. Sand backfill from 0.9 to 4.6 m. Bentonite seal from 0.3 to 0.9 m. Concrete from 0.0 to 0.3 m. Provided with flush-mount cover.
12
Soil Engineers Ltd.
9
W.L. @ El. 98.6 m on completion
3.0 97.1
4
Soil Engineers Ltd.
GRAIN SIZE DISTRIBUTION
Reference No: 1209-S093
U.S. BUREAU OF SOILS CLASSIFICATION GRAVEL
SAND SILT
COARSE
FINE
COARSE
MEDIUM
FINE
CLAY
V. FINE
UNIFIED SOIL CLASSIFICATION GRAVEL
SAND SILT & CLAY
COARSE 3" 2-1/2" 2"
1-1/2"
FINE 1"
3/4"
1/2"
3/8"
MEDIUM
COARSE 4
8
10
16
20
FINE 30
40
50
60
100
140
200
270 325
100 90 GRANULAR 'A' 80 GRANULAR 'B' 70 60 50 40 30 Percent Passing
20 10 0 100
Grain Size in millimeters
10
Project:
Proposed Residential Development
Location:
1075 Queen Street East, City of Toronto
1
0.1
0.01
0.001
Liquid Limit (%) =
-
Plastic Limit (%) =
-
Borehole No:
1
Plasticity Index (%) =
-
Sample No:
1
Moisture Content (%) =
3
Depth (m):
0.3
Estimated Permeability
100.0
Classification of Sample [& Group Symbol]:
(cm./sec.) = GRANULAR, Fill
10-2
Figure: 3
Elevation (m):
GRAIN SIZE DISTRIBUTION
Reference No: 1209-S093
U.S. BUREAU OF SOILS CLASSIFICATION GRAVEL
SAND SILT
COARSE
FINE
COARSE
MEDIUM
FINE
CLAY
V. FINE
UNIFIED SOIL CLASSIFICATION GRAVEL
SAND SILT & CLAY
COARSE
FINE 4
3" 2-1/2" 2"
100
1-1/2"
1"
3/4"
1/2"
MEDIUM
COARSE 8
10
16
20
FINE 30
40
50
60
100
140
200
270 325
3/8"
90
BH.1/Sa.6
80
BH.2/Sa.8 70 60 50 40
Percent Passing
30 20 10 0 100
Grain Size in millimeters
10
Project:
Proposed Residential Development
Location:
1075 Queen Street East, City of Toronto
1
0.1
0.01
0.001
1/6
2/8
Liquid Limit (%) =
BH./Sa.
29
28
17
17
1
2
Plasticity Index (%) =
12
11
Sample No:
6
8
Moisture Content (%) =
13
13
10-7
10-7
Depth (m):
4.8
6.3
Elevation (m):
95.5
93.8
Classification of Sample [& Group Symbol]:
Estimated Permeability (cm./sec.) = SILTY CLAY, Till sandy, a trace of gravel
Figure: 4
Plastic Limit (%) = Borehole No:
BH. No. Topsoil (cm) Elevation (m) El. (m)
1 100.3
‘W’ ‘N’
‘W’ ‘N’
2 100.1
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
‘W’ ‘N’
101 100 99
·11 ·13 ·6
98 97
·8 ·19
96
·32 ·5 ·12 ·6 ·25 ·15
·12 95 94
·18 ·9
·13
93
·12
·11
92
LEGEND ·36
91
·50/13 cm
PAVEMENT STRUCTURE
·50/7.6 cm
90
SILTY CLAY FILL SILTY CLAY SILTY CLAY TILL SHALE BEDROCK WATER LEVEL
SUBSURFACE PROFILE
SOIL ENGINEERS LTD.
Scale:
Horiz.: N.T.S. Vert.: 1:100
Ref. No.: 1209-S093 Drawing No. 2