A REPORT TO FORTRESS MUNIR 2013 INC. A SOIL … · A REPORT TO FORTRESS MUNIR 2013 INC. A SOIL...

A REPORT TO FORTRESS MUNIR 2013 INC.

A SOIL INVESTIGATION FOR

PROPOSED TOWNHOUSE DEVELOPMENT (PHASE 2)

2055 BROCK ROAD

CITY OF PICKERING

REFERENCE NO. 1603-S066

JULY 2016

DISTRIBUTION 2 Copies - Kohn Partnership Architects Inc. 1 Copy - Fortress Munir 2013 Inc. 1 Copy - Soil Engineers Ltd. (Oshawa) 1 Copy - Soil Engineers Ltd. (Toronto)

Reference No. 1603-S066 ii 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 Topsoil.................................................................................................. 4 4.2 Silty Clay .............................................................................................. 5 4.3 Silty Clay Till ....................................................................................... 7 4.4 Silty Fine Sand ..................................................................................... 9 4.5 Fine to Coarse Sand .............................................................................. 11 4.6 Compaction Characteristics of the Revealed Soils .............................. 12

5.0 GROUNDWATER CONDITIONS ........................................................... 15

6.0 DISCUSSION AND RECOMMENDATIONS ........................................ 17

6.1 Foundations .......................................................................................... 19 6.2 Garages, Driveways and Landscaping ................................................. 22 6.3 Underground Services .......................................................................... 22 6.4 Trench Backfilling ................................................................................ 24 6.5 Pavement Design .................................................................................. 26 6.6 Soil Parameters ..................................................................................... 27 6.7 Preloading Scheme ............................................................................... 28 6.8 Excavation ............................................................................................ 28

7.0 LIMITATIONS OF REPORT .................................................................... 31

Reference No. 1603-S066 iii

TABLES

Table 1 - Estimated Water Content for Compaction ..................................... 12

Table 2 - Groundwater Levels ....................................................................... 15

Table 3 - Pavement Design ............................................................................ 26

Table 4 - Soil Parameters ............................................................................... 28

Table 5 - Classification of Soils for Excavation ............................................ 29

ENCLOSURES Borehole Logs ...................................................................... Figures 1 to 7 Grain Size Distribution Graphs ........................................... Figures 8 to 10 Borehole Location Plan ....................................................... Drawing No. 1 Subsurface Profile ................................................................ Drawing No. 2

Reference No. 1603-S066 1

1.0 INTRODUCTION

In accordance with written authorization dated March 17, 2016, from

Mr. Vince Petrozza, of Fortress Munir 2013 Inc., a soil investigation was carried

out at 2055 Brock Road, in the City of Pickering, for a proposed Townhouse

Development (Phase 2).

The purpose of the investigation was to reveal the subsurface conditions and to

determine the engineering properties of the disclosed soils for the design and

construction of the proposed project.

The geotechnical findings and resulting recommendations are presented in this

Report.


2.0 SITE AND PROJECT DESCRIPTION

The Town of Pickering is situated on Iroquois (glacial lake) plain where, in places,

the glacial till stratigraphy has been partly eroded by the water action of the glacial

lake and filled with lacustrine sands, silts, clays and reworked till.

The subject site is situated at the northeast sector of Finch Avenue and Brock Road,

in the City of Pickering. The investigated area is a weed-covered open field. The

ground surface is relatively flat and level, with minor undulations.

The proposed project consists of the construction of new townhouses, the new

development will be provided with municipal services, landscaped areas, roadways

and paved areas meeting municipal standards.


3.0 FIELD WORK

The field work, consisting of 7 boreholes to depths ranging from 6.6 to 9.6 m, was

performed on April 18, 2016, at the locations shown on the Borehole Location Plan,

Drawing No. 1, enclosed.

The holes were advanced at intervals to the sampling depths by track-mounted,

continuous-flight power-auger machines 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.

In situ vane shear and remoulded vane shear tests were performed using a four-

bladed vane with dimensions of 51 mm in diameter and 150 mm in length. The

tests determine the undrained shear strength of the cohesive soil, and ratio of the

values of the undisturbed and remoulded shear strengths indicates the sensitivity of

the soil.

The field work was supervised and the findings recorded by a Geotechnical

Technician.

The geodetic elevation at each of the borehole locations was obtained by Soil

Engineers Ltd. using a hand-held Global Navigation Satellite System (GNSS)

surveying equipment (Trimble Geoexplorer 6000) having an accuracy of 0.1 m.


4.0 SUBSURFACE CONDITIONS

Detailed descriptions of the encountered subsurface conditions are presented on the

Borehole Logs, comprising Figures 1 to 7, inclusive. The revealed stratigraphy is

plotted on the Subsurface Profile, Drawing No. 2, and the engineering properties of

the disclosed soils are discussed herein.

This investigation has disclosed that beneath a veneer of topsoil, the site is

underlain by strata of silty clay, silty clay till, silty fine sand and fine to coarse sand

at various depths and locations.

4.1 Topsoil (All Boreholes)

The revealed topsoil ranges from 20 to 61 cm thick. It is dark brown in colour,

indicating that it contains appreciable amounts of roots and humus. These materials

are unstable and compressible under loads; therefore, the topsoil is considered to be

void of engineering value. Due to its humus content, it may produce volatile gases

and generate an offensive odour under anaerobic conditions. Therefore, the topsoil

must not be buried below any structures or deeper than 1.2 m below the finished

grade, so that it will not have an adverse impact on the environmental well-being of

the developed areas.

Since the topsoil is considered void of engineering value, it can only be used for

general landscaping and landscape contouring purposes. A fertility analysis can

determine the suitability of the topsoil as a planting material.


4.2 Silty Clay (All Boreholes)

The silty clay was found to dominate the revealed soil stratigraphy. The clay was

encountered below a layer of silty fine sand and extends to the maximum

investigated depth at Borehole 2. It is laminated with sand and silt seams and

layers, showing it is a lacustrine deposit. The sand and silt seams and layers are

generally wet.

The clay within a depth of 1.5± to 2.0± m from the prevailing ground surface has

generally been weathered.

The obtained ‘N’ values range from weight of hammer to 16, with a median of

4 blows per 30 cm of penetration, indicating that the consistency of the clay is very

soft to stiff, being generally soft. Eighteen in situ shear vane tests were performed

on the very soft to soft clay (with ‘N’ values ranging from weight of hammer to 4).

The obtained shear strength values range from 21.5 to 120 kPa. The sensitivity of

the clay, as assessed by the remoulded shear strength, ranges from 2.8 to 10,

showing that the sensitivity to remoulding of the clay is medium sensitive to

slightly quick.

The Atterberg Limits of 3 representative samples and the water content values of all

of the samples were determined. The results are plotted on the Borehole Logs and

summarized below:

Liquid Limit 33%, 40% and 42%

Plastic Limit 18%, 19% and 21%

Natural Water Content 21% to 41% (median 26%)


The above results show that the clay is a cohesive material with medium plasticity.

The natural water content values generally lie above its plastic limits and below its

liquid limits.

Grain size analyses were performed on 3 representative samples; the results are

plotted on Figure 8.

According to the above findings, the following engineering properties are deduced:

• High frost susceptibility and, due to the high silt content and high moisture

content, it has a high soil-adfreezing potential.

• Low water erodibility.

• Practically impermeable, with an estimated coefficient of permeability of

10-7 cm/sec, an estimated percolation rate of over 80 min/cm, 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 its consistency

which is inversely dependent on soil moisture.

• The very soft to soft clay is highly susceptible to consolidation under surcharge

loads.

• In steep cuts, the very soft to soft clay will slough readily, and a cut face in the

sound clay may collapse as the wet silt slowly sloughs.

• Bottom heaving will occur in trenches cut steeply into the very soft to soft silty

clay. Therefore, the spoil from the excavations should be placed at a


distance from the edge of the excavation at least equal to 3 times the height of

the excavation, and the sides should be cut at 1 vertical:3 + horizontal.

• A very poor material to support flexible pavement, with an estimated

California Bearing Ratio (CBR) value of 3% or less.

• Moderately high corrosivity to buried metal, with an estimated electrical

resistivity of 2500 ohm⋅cm.

4.3 Silty Clay Till (All Boreholes, except Borehole 2)

The silty clay till was found beneath a stratum of silty clay and extends to the

maximum investigated depth at Boreholes 1, 3, 4, 5 and 7. 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. Occasional sand and silt

seams and layers were also detected in the clay till mantle. The till is

heterogeneous in structure, indicating that it is a glacial deposit.

The obtained ‘N’ values range from weight of hammer to 60 blows per 15 cm, with

a median of 33 blows per 30 cm of penetration, indicating that the consistency of

the clay is very soft to hard, being generally hard.

Hard resistance was encountered during augering, showing that the till is embedded

with cobbles and boulders.

The Atterberg Limits of 1 representative sample and the natural water content

values of all the samples were determined; the results are plotted on the Borehole

Logs and summarized below:


Liquid Limit 28%

Plastic Limit 16%

Natural Water Content 6% to 24% (median 8%)

The results show that the clay till is a cohesive material with low plasticity. The

natural water content values generally lie below its plastic and liquid limits,

confirming the generally hard consistency of the till as determined by the ‘N’

values.

A grain size analysis was performed on 1 representative sample of the silty clay till.

The result is plotted on Figure 9.

Based on the findings, the engineering properties related to the project are as

follows:

• High frost susceptibility, with low water erodibility.

• Low permeability, with an estimated coefficient of permeability of

10-7 cm/sec, with an estimated percolation rate of 80 min/cm, 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 very soft clay till is highly susceptible to consolidation under surcharge

loads.


• It will generally be stable in a relatively steep cut in the stiff to hard till;

however, prolonged exposure will allow the fissures in the weathered zone

and the wet sand and silt seams and layers to become saturated, which may

lead to localized sloughing.

• Bottom heaving will occur in trenches cut steeply into the very soft to soft

silty clay till. Therefore, the spoil from the excavations should be placed at a

distance from the edge of the excavation at least equal to 3 times the height

of the excavation, and the sides should be cut at 1 vertical:3 + horizontal.

• A very poor pavement-supportive material, with an estimated CBR value of

3% or less.

• Moderately high corrosivity to buried metal, with an estimated electrical

resistivity of 3500 ohm⋅cm.

4.4 Silty Fine Sand (All Boreholes)

The silty fine sand deposit was encountered below a veneer of topsoil and overlying

a stratum of silty clay. Sample examinations show that it is non-cohesive and is

embedded with silt seams. The laminated structure shows the deposit was derived

from a lacustrine environment. The silty fine sand layer is weathered.

The obtained ‘N’ values range from weight of hammer to 5, with a median of

2 blows per 30 cm of penetration; therefore, the relative density of the sand is very

loose to loose, being generally very loose.

The natural water content was determined and the results are plotted on the

Borehole Logs. The values range from 12% to 25%, with a median of 20%,

showing that the sand deposit is in a wet condition. The wet samples are water

bearing and displayed appreciable dilatancy when shaken by hand.


A grain size analysis was performed on 1 representative sample of the silty fine

sand; the result is plotted on Figure 10.

Accordingly, the following engineering properties are deduced:

• Highly frost susceptible with high soil-adfreezing potential.

• Highly water erodible.

• Relatively pervious, with an estimated coefficient of permeability of

10-3 cm/sec, an estimated percolation rate of 30 min/cm, and runoff

coefficients of:

Slope

0% - 2% 0.04

2% - 6% 0.09

6% + 0.13

• A frictional soil, its shear strength is derived from internal friction and is

density dependent. Due to its dilatancy, the shear strength of the wet sand is

susceptible to impact disturbance; i.e., the disturbance will induce a build-up

of pore pressure within the soil mantle, resulting in soil dilation and a

reduction of shear strength.

• In relatively steep cuts, the sand will be stable in a damp to moist condition,

but will slough if it is wet and run with water seepage. The bottom will boil

under a piezometric head of 0.3 m.

• A fair material to support pavement, with an estimated CBR value of at least

8%.

• Moderately low corrosivity to buried metal, with an estimated electrical

resistivity of 5000 ohm·cm.


4.5 Fine to Coarse Sand (Borehole 6)

The fine to coarse sand was encountered below a stratum of silty clay till and

extends to the maximum investigated depth. It is well-graded, with some silt and a

trace of gravel.

The obtained ‘N’ value is 50 blows per 15 cm of penetration, indicating that the

relative density of the sand is very dense.

The natural water content value of the sample was determined, and the result is

plotted on the Borehole Log; the value is 10%, showing the sand is in a wet

condition. Due to the pervious nature of the sand, some of the water may have

drained during sampling, and the determined value may not represent the actual

water content of the deposit. The wet sand sample is water bearing.

The deduced engineering properties pertaining to the project are given below:

• Low frost susceptibility and high water erodibility.

• Pervious, with an estimated coefficient of permeability of 10-3 cm/sec, an

estimated percolation rate of about 10 min/cm, and runoff coefficients of:

Slope

0% - 2% 0.04

2% - 6% 0.09

6% + 0.13

• A frictional soil, its shear strength is derived from internal friction and is soil

density dependent.

• In relatively steep cuts, the sand will be stable in a damp to moist condition,

but will slough if it is wet and run with water seepage. The bottom will boil

under a piezometric head of 0.3 m.


• A fair to good pavement-supportive material, with an estimated CBR value

of 20% to 30%.

• Low corrosivity to buried metal, with an estimated electrical resistivity of

6500 ohm·cm.

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 1.

Table 1 - Estimated Water Content for Compaction

Soil Type

Determined Natural Water Content (%)

Water Content (%) for Standard Proctor Compaction

100% (optimum) Range for 95% or +

Silty Clay 21 to 41 (median 26) 21 and 22 17 to 27

Silty Clay Till 6 to 24 (median 8) 16 12 to 21

Silty Fine Sand 12 to 25 (median 20) 11 6 to 16

Fine to Coarse Sand 10 10 5 to 15

Based on the above findings, the majority of the silty clay till and some of the silty

clay and fine to coarse sand are generally suitable for a 95% or + Standard Proctor

compaction; however, the silty fine sand and the major portion of the silty clay are

too wet and will require aeration prior to structural compaction. Some of the silty

clay till is too dry and will require the addition of water prior to structural

compaction.


The silty clay and silty clay till should be compacted using a heavy-weight,

kneading-type roller. The sands can be compacted by a smooth 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 soils and be

transmitted laterally into the soil mantle. Therefore, the lifts of these soils 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. Wetting of the

sound till will be necessary to achieve this requirement.

One should be aware that with considerable effort, a 90%± Standard Proctor

compaction of the wet sand is achievable. Further densification is prevented by the

pore pressure induced by the compactive effort; however, large random voids will

have been expelled, and with time the pore pressure will dissipate and the

percentage of compaction will increase. There are many cases on record where

after a few months of rest, the density of the compacted mantle has increased to

over 95% of its maximum Standard Proctor dry density.

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 pavement construction since each component of the pavement


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 foundation 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 in the silty clay till will prevent transmission of the

compactive energy into the underlying material to be compacted. If an appreciable

amount of boulders over 15 cm in size is mixed with the material, it must either be

sorted or must not be used for structural backfill.


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. The data are plotted on the Borehole Logs and

summarized in Table 2.

Table 2 - Groundwater Levels

BH No. Borehole

Depth (m)

Soil Colour Changes Brown to

Grey

Seepage Encountered

During Augering

Measured Groundwater/ Cave-In* Level On Completion

Depth (m) Depth (m) Amount Depth (m) El. (m)

1 9.6 4.5 0.5 Some 1.2* 89.5*

2 6.7 3.0 0.5 Some 1.2* 88.6*

3 9.3 3.0 0.5 Some 6.4 82.1

4 6.7 3.0 0.5 Some 4.6 83.6

5 6.7 4.5 0.5 Some 0.5 86.5

6 9.5 3.0 0.5 Some 1.2/8.7* 87.6/80.1*

7 6.6 3.0 0.7 Some 1.2 88.7 * Cave-in level (In wet sand and silt, the level generally represents the groundwater regime at the borehole location at the time of investigation.)

Groundwater was detected at depths ranging from 0.5 to 6.4 m; cave-in was

detected at depths of 1.2 m and 8.7 m below the prevailing ground surface.

Groundwater will fluctuate with the seasons and the measured levels generally

represent the groundwater regime at the time of the investigation.


The soil colour changes from brown to grey at depths of 3.0 m and 4.5 m below the

prevailing ground surface; the brown colour indicates that the soils have oxidized

and the groundwater will fluctuate with the seasons.

The groundwater yield from the silty clay and silty clay till, due to their low

permeability, will be small and limited in quantity. The groundwater yield from the

sands is expected to be appreciable and likely persistent.


6.0 DISCUSSION AND RECOMMENDATIONS

This investigation has disclosed that beneath a veneer of topsoil, the site is

underlain by strata of very soft to stiff, generally soft silty clay; very soft to hard,

generally hard silty clay till; very loose to loose, generally loose silty fine sand and

very dense fine to coarse sand at various depths and locations. The surficial native

soil layer is weathered to depths of 1.5± to 2.0± m below the prevailing ground

surface.

Groundwater was detected at depths ranging from 0.5 to 6.4 m; cave-in was

detected at depths of 1.2 m and 8.7 m below the prevailing ground surface.

Groundwater will fluctuate with the seasons and the measured levels generally

represent the groundwater regime at the time of the investigation.

The groundwater yield from the silty clay and silty clay till, due to their low

permeability, will be small and limited in quantity. The groundwater yield from the

sands is expected to be appreciable and likely persistent.

The geotechnical findings which warrant special consideration are presented below:

1. The topsoil is highly compressible and will generate volatile gases under

anaerobic conditions, and it is not suitable for engineering applications.

Therefore, the topsoil should be placed in the landscaped areas only and

should not be buried below any structures, or deeper than 1.2 m below the

exterior finished grade of the project.

2. The building site is underlain by a deposit of very soft to soft silty clay that

extends from depths of 1.5 m or 3.0 m to approximately 7.3± m below the

prevailing ground surface. The very soft to soft clay is only suitable to

support lightly loaded foundations. As a result, a raft foundation can be


used to support the building loads. A compacted granular base, 500 mm

thick, can be placed for the raft foundation. In this case, the site needs to

be preloaded. Alternatively, the proposed building foundations can also be

supported by Helical Piles extending into the very stiff to hard silty clay till

stratum, at depths of over 7 m below the prevailing ground surface. In this

case, deeper boreholes will be necessary.

3. The underlying very soft to soft clay and clay till will consolidate under

surcharge loads. If the site grade will be raised or if a raft foundation is

considered, the site will have to be pre-loaded and the ground settlement

should be monitored for at least 9 to 18 months prior to any construction.

This can be determined by the installation and monitoring of settlement

plates. The required surcharge load for the pre-loading program can be

determined once the site grading and townhouse sitings and their loadings

are available.

4. For slab-on-grade construction, any weathered, soft or loose soils, should

be subexcavated, aerated and properly compacted prior to the placement of

the slab. Any new material for raising the grade should consist of organic-

free soil compacted to at least 98% of its maximum Standard Proctor dry

density. 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.

5. For services constructed in saturated soils, the pipe joints should be leak-

proof or wrapped with a waterproof membrane. A Class ‘B’ bedding is

recommended and it should consist of 19-mm Crusher-Run (graded)

Limestone. Where extensive dewatering is necessary, a Class ‘A’ bedding

consisting of concrete may be required. In the very soft to soft clay, the

bedding must be thickened and/or a Class ‘A’ bedding can be considered.


In extreme cases, concrete cradles supported by piles to refusal may be

necessary.

6. The in situ soils with high silt content are considered to be high in soil-

adfreezing potential; therefore, the foundation walls or the perimeter grade

beams must be either backfilled with non-frost-susceptible pit-run granular,

or shielded with a polyethylene slip-membrane.

7. Excavation into the silty clay till containing boulders will require extra effort

and the use of a heavy-duty backhoe equipped with a rock-ripper. Boulders

larger than 15 cm in size are not suitable for structural backfill.

8. Bottom heaving will occur in trenches cut steeply into the very soft to soft

clay. Therefore, the sides should be cut at 1 vertical:3 or + horizontal and

the spoil from the excavation must be placed at a distance from the edges of

the excavation and/or trenches equal to 3 times the depth of the excavation.

Alternatively, proper shoring by sheeting will be necessary.

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

The borehole investigation has revealed that the building site is underlain by a

deposit of very soft to soft silty clay and silty clay till that extends from depths of

1.5 m or 3.0 m to approximately 7.3± m below the prevailing ground surface. The

soft soil is only suitable to support lightly loaded foundations. As a result, a raft

foundation designed with a Maximum Allowable Soil Pressure (SLS) of 30 kPa and


a Factored Ultimate Soil Bearing Pressure (ULS) of 50 kPa can be used to support

the building loads. A compacted granular base, 500 mm thick, can be placed for

the raft foundation.

Alternatively, the proposed building foundations can also be supported by Helical

Piles extending into the very stiff to hard silty clay till stratum, at depths of over

7 m below the prevailing ground surface. In this case, deeper boreholes will be

necessary.

The load carried by the Helical Piles is directly related to the installation torque of

the pile anchor in the underlying competent soil stratum. The founding elevations,

design loads and number of Helical Piles should be determined by the prospective

Helical Piles Foundation Systems contractor.

The recommended soil pressure (SLS) for raft foundation incorporates a safety

factor of 3. The total and differential settlements of the foundation are estimated to

be 40 mm and 25 mm, respectively.

The foundations or grade beams exposed to weathering, and in unheated areas,

should be provided with at least 1.2 m of earth cover for protection against frost.

Due to the shallow groundwater encountered, it is recommended that the floor slab

be at least 0.5 m above the highest level of groundwater fluctuation.

Perimeter and under floor subdrains will be required. The subdrains should be

shielded by a fabric filter to prevent blockage by silting. These subdrains should

drain into a positive outlet or they should be connected to a sump-pit and drained

by pumping. A vapour barrier should be placed above the obvert of the subdrain to


prevent upfiltration of moisture from dampening the floor surface; the requirements

for this should be assessed at the time of footing construction.

Due to the presence of topsoil and weathered soil, the foundation 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.

The foundation must meet the requirements specified in the latest Ontario Building

Code. As a guide, the structure should be designed to resist an earthquake force

using Site Classification ‘E’ (soft soil).

The in situ soils with high silt content are considered to be high in soil-adfreezing

potential; therefore, the foundation walls or the perimeter grade beams must be

either backfilled with non-frost-susceptible pit-run granular, or shielded with a

polyethylene slip-membrane.

Depending on site grading, where earth fill is required to raise the site or where raft

foundation is being used, the overburden will cause the underlying very soft to soft

clay to consolidate. Therefore, the foundation and project construction must not

commence prior to the completion of soil consolidation, which can be determined

by the monitoring of settlement plates. A preloading program will need to be

implemented prior to the project construction. The requirements for the preloading

program can be determined once the site grading and the townhouse sitings and

their loadings are available.


6.2 Garages, Driveways and Landscaping

As noted, the silty fine sand and silty clay are highly frost susceptible, thus, heaving

of the pavement is expected to occur during the cold weather.

The driveways at the entrances to the garages must be backfilled with non-frost-

susceptible granular material, with a frost taper at a slope of 1 vertical:1 horizontal.

The garage floor slab and the side of the foundation must be insulated with

50-mm Styrofoam, or equivalent.

The slab-on-grade in open areas should be designed to tolerate frost heave, and the

grading around the slab-on-grade must be such that it directs runoff away from the

surface.

Interlocking stone pavement and slab-on-grade to be constructed in areas

susceptible to ground movement must be constructed on a free-draining granular

base, at least 0.3 to 1.2 m thick, depending on the degree of tolerance to ground

movement, with proper drainage which will prevent water from ponding in the

granular base.

6.3 Underground Services

The subgrade for the underground services should consist of natural soils or

compacted organic-free earth fill. Where topsoil and badly weathered soils are

encountered, these materials must be subexcavated and replaced with properly

compacted bedding material. If earth fill is required to raise the site, a preloading

scheme will be necessary prior to underground services construction.


A Class ‘B’ bedding, consisting of compacted 20-mm Crusher-Run Limestone, is

recommended for the construction of the underground services. Where water-

bearing sand occurs, the sewer joints should be leak-proof, or wrapped with an

appropriate waterproof membrane to prevent subgrade migration. Where extensive

dewatering is necessary, a Class ‘A’ bedding consisting of concrete may be

required. This can be assessed by a geotechnical engineer during construction.

In areas where the subgrade consists of very soft clay, the granular bedding should

be thickened to at least 50 cm, or stone immersion techniques should be employed

to stabilize the base for sewer construction. If the recommended measures do not

succeed in stabilizing the subgrade, consideration should be given to supporting the

sewer on concrete cradles resting on piles driven to depths of refusal. The necessity

to implement this measure can best be determined by a geotechnical engineer when

the subgrade is exposed to inspection.

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 has moderately high corrosivity to buried metal, the water main

should be protected against corrosion. In determining the mode of protection, an

electrical resistivity of 2500 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 Trench Backfilling

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 pavement subgrade, the backfill should be compacted

to at least 98% of its maximum Standard Proctor dry density with the moisture

content 2% to 3% drier than the optimum. In the lower zone, a 95% or + Standard

Proctor compaction is considered to be adequate; however, the material must be

compacted on the wet side of the optimum.

Below the floor slab, the backfill must be compacted to 98% or + of its Standard

Proctor dry density.

In normal underground services construction practice, the problem areas of road

settlement largely occur adjacent to manholes, catch basins, services crossings,

foundation walls and columns, and it is recommended that a sand backfill 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 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 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 in a narrow vertical trench section, or when the trench

box is removed. 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 and the slab-on-grade construction.

• 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 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.

6.5 Pavement Design

Based on the borehole findings, the recommended pavement design is given in

Table 3.

Table 3 - Pavement Design

Course Thickness (mm) OPS Specifications

Asphalt Surface 40 HL-3

Asphalt Binder 50 HL-8

Granular Base 150 20-mm Crusher-Run Limestone, or equivalent

Granular Sub-base Light-Duty Heavy-Duty

350 450

50-mm Crusher-Run Limestone, or equivalent

In preparation of the subgrade, the subgrade surface should be proof-rolled; any

soft subgrade, organics and deleterious materials within 1.0 m below the underside

of the granular sub-base should be subexcavated and replaced by properly

compacted organic-free earth fill or granular material.


All the granular bases should be compacted to their maximum Standard Proctor dry

density.

In the zone within 1.0 m below the pavement subgrade, the backfill should be

compacted to at least 98% of its maximum Standard Proctor dry density, with the

water content 2% to 3% drier than the optimum. In the lower zone, a

95% or + Standard Proctor compaction is considered adequate.

The road subgrade will suffer a strength regression if water is allowed to infiltrate

prior to paving. The following measures should therefore be incorporated in the

construction procedures and road design:

• If the road 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.

• Lot areas adjacent to the roads should be properly graded to prevent the

ponding of large amounts of water during the interim construction period.

• Curb subdrains will be required. The subdrains should consist of filter-

sleeved weepers to prevent blockage by silting.

• If the roads are to be constructed during the wet seasons and extensively soft

subgrade occurs, the granular sub-base may require thickening. This can be

assessed during construction.

6.6 Soil Parameters

The recommended soil parameters for the project design are given in Table 4.


Table 4 - Soil Parameters

Unit Weight and Bulk Factor

Unit Weight (kN/m3)

Estimated Bulk Factor

Bulk Loose Compacted

Weathered Soil and Silty Clay 20.5 1.20 1.00

Sound Till 22.0 1.33 1.05

Sands 20.0 1.20 0.95

Lateral Earth Pressure Coefficients

Active Ka

At Rest Ko

Passive Kp

Weathered Soil and Silty Clay 0.50 0.65 2.00

Sound Till 0.40 0.50 2.50

Sands 0.35 0.45 2.86

6.7 Preloading Scheme

The overburden for building construction or grade raise will consolidate the

underlying very soft to soft silty clay and clay till strata; therefore, if the site is to be

raised or if a raft foundation is considered, the site will have to be pre-loaded and

the ground settlement should be monitored for at least 9 to 18 months prior to any

construction. This can be determined by the installation and monitoring of

settlement plates. The required surcharge load for the pre-loading program can be

determined once the site grading and townhouse sitings are available.

6.8 Excavation

Excavation should be carried out in accordance with Ontario Regulation 213/91.


Excavations should be sloped at 1 vertical:1 horizontal for stability.

The till contains occasional boulders. Extra effort and a properly equipped backhoe

will be required for excavation.

For excavation purposes, the types of soils are classified in Table 5.

Table 5 - Classification of Soils for Excavation

Material Type

Sound Till 2

Silty Clay, Weathered Soil and Sand above groundwater 3

Very soft to soft Clay and Sands below groundwater 4

Bottom heaving will occur in trenches cut steeply into the very soft to soft silty

clay. Therefore, the sides should be cut at 1 vertical:3.0 + horizontal and the spoil

from the excavation must be placed at a distance away from the edge of the

excavation at least equal to 3 times the depth of the excavation. Alternatively, the

excavation can be stabilized by proper shoring. It must be extended to a sufficient

depth below the bottom of the excavation to support the earth pressure, hydrostatic

pressure and all the applicable surcharge loads. This must be properly designed by

a structural engineer.

The yield of groundwater from the silty clay and silty clay till, due to their low

permeability, is expected to be small and limited and can generally be controlled

by pumping from sumps.

When excavating into the water-bearing sand at a shallow depth, groundwater

should be controlled by vigorous pumping from closely spaced sump-wells for

Reference No. 1603-S066 30 excavations to a depth of 0.3 m or less below the groundwater level. For

excavation deeper than 0.3 m below the groundwater level, a well-point

dewatering system will be required. This should be assessed by test pits and/or

test pumping prior to the project construction.

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 and the means to control

groundwater, if encountered.

LIST OF ABBREVIATIONS AND DESCRIPTION OF TERMS The abbreviations and terms commonly employed on the borehole logs and figures, and in the text of the report, are as follows: SAMPLE TYPES

AS Auger sample CS Chunk sample DO Drive open (split spoon) DS Denison type sample FS Foil sample RC Rock core (with size and percentage

recovery) ST Slotted tube TO Thin-walled, open TP Thin-walled, piston WS Wash sample PENETRATION RESISTANCE

Dynamic Cone Penetration Resistance:

A continuous profile showing the number of blows for each foot of penetration of a 2-inch diameter, 90° point cone driven by a 140-pound hammer falling 30 inches. Plotted as ‘ • ’

Standard Penetration Resistance or ‘N’ Value:

The number of blows of a 140-pound hammer falling 30 inches required to advance a 2-inch O.D. drive open sampler one foot into undisturbed soil. Plotted as ‘’

WH Sampler advanced by static weight PH Sampler advanced by hydraulic pressure PM Sampler advanced by manual pressure NP No penetration

SOIL DESCRIPTION

Cohesionless Soils:

‘N’ (blows/ft) Relative Density

0 to 4 very loose 4 to 10 loose

10 to 30 compact 30 to 50 dense

over 50 very dense

Cohesive Soils:

Undrained Shear Strength (ksf) ‘N’ (blows/ft) Consistency

less than 0.25 0 to 2 very soft 0.25 to 0.50 2 to 4 soft 0.50 to 1.0 4 to 8 firm 1.0 to 2.0 8 to 16 stiff 2.0 to 4.0 16 to 32 very stiff

over 4.0 over 32 hard

Method of Determination of Undrained Shear Strength of Cohesive Soils:

x 0.0 Field vane test in borehole; the number denotes the sensitivity to remoulding

Laboratory vane test

Compression test in laboratory

For a saturated cohesive soil, the undrained shear strength is taken as one half of the undrained compressive strength

METRIC CONVERSION FACTORS 1 ft = 0.3048 metres 1 inch = 25.4 mm 1lb = 0.454 kg 1ksf = 47.88 kPa

Reference No: 1603-S066

U.S. BUREAU OF SOILS CLASSIFICATION

COARSE

UNIFIED SOIL CLASSIFICATION

COARSE

Project: Proposed Townhouse Development (Phase 2) BH./Sa. 1/7 4/6 6/6

Location: 2055 Brock Road, City of Pickering Liquid Limit (%) = 40 33 42

Plastic Limit (%) = 21 18 19

Borehole No: 1 4 6 Plasticity Index (%) = 19 15 23

Sample No: 7 6 6 Moisture Content (%) = 41 27 33

Depth (m): 6.3 4.7 4.7 Estimated Permeability

Elevation (m): 84.4 83.5 84.1 (cm./sec.) = 10-7 10-7 10-7

Classification of Sample [& Group Symbol]: SILTY CLAY

a tr. of fine sand

GRAIN SIZE DISTRIBUTION

SAND

V. FINE

GRAVELSILT

COARSE FINEFINE

SILT & CLAY

Figure: 8

COARSE

MEDIUM

FINE

CLAY

SAND

MEDIUMFINE

GRAVEL

3" 2-1/2" 2" 1-1/2" 1" 3/4" 1/2" 3/8" 4 8 10 16 20 30 40 50 60 100 140 200 270 325

0

10

20

30

40

50

60

70

80

90

100

0.0010.010.1110100

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Grain Size in millimeters

BH.6/Sa.6

BH.1/Sa.7

BH.4/Sa.6

Soil Engineers Ltd. Reference No: 1603-S066


COARSE


COARSE

Project: Proposed Townhouse Development (Phase 2)

Location: 2055 Brock Road, City of Pickering Liquid Limit (%) = 28

Plastic Limit (%) = 16

Borehole No: 3 Plasticity Index (%) = 12

Sample No: 7 Moisture Content (%) = 19

Depth (m): 6.3 Estimated Permeability

Elevation (m): 82.2 (cm./sec.) = 10-7

Classification of Sample [& Group Symbol]: SILTY CLAY, Till

sandy, a tr. of gravel


SAND

V. FINE

GRAVELSILT

COARSE FINEFINE

SILT & CLAY

Figure: 9

COARSE

MEDIUM

FINE

CLAY

SAND

MEDIUMFINE

GRAVEL

3" 2-1/2" 2" 1-1/2" 1" 3/4" 1/2" 3/8" 4 8 10 16 20 30 40 50 60 100 140 200 270 325

0

10

20

30

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0.0010.010.1110100

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Soil Engineers Ltd. Reference No: 1603-S066


COARSE


COARSE

Project: Proposed Townhouse Development (Phase 2)

Location: 2055 Brock Road, City of Pickering Liquid Limit (%) = -

Plastic Limit (%) = -

Borehole No: 1 Plasticity Index (%) = -

Sample No: 2 Moisture Content (%) = 22

Depth (m): 1.0 Estimated Permeability

Elevation (m): 89.7 (cm./sec.) = 10-3

Classification of Sample [& Group Symbol]: SILTY FINE SAND

a tr. of clay


SAND

V. FINE

GRAVELSILT

COARSE FINEFINE

SILT & CLAY

Figure: 10

COARSE

MEDIUM

FINE

CLAY

SAND

MEDIUMFINE

GRAVEL

3" 2-1/2" 2" 1-1/2" 1" 3/4" 1/2" 3/8" 4 8 10 16 20 30 40 50 60 100 140 200 270 325

0

10

20

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0.0010.010.1110100

Perc

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A REPORT TO FORTRESS MUNIR 2013 INC. A SOIL … · A REPORT TO FORTRESS MUNIR 2013 INC. A SOIL...

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