Statistical Correlations between SPT N-Values and ...

Statistical Correlations between SPT N-Values and Soil Parameters Part I: Standard Penetration Tests and Pressuremeter Tests at Victoria Park Station Site

A Project Funded by Natural Sciences and Engineering Research Council of Canada and Supported by SPL Consultants Ltd.

Department of Civil Engineering, Ryerson University

Yankun Liang Laifa Cao Jinyuan Liu

June 2015

Statistical Correlations between SPT N-Values and Soil Parameters: Part I_SPT and PMT

EXECUTIVE SUMMARY An intensive site exploration program was conducted for the Eglinton Crosstown Light Rail Transit (LRT) Project in Toronto, which involved various in-situ testing methods. This offers an excellent opportunity to conduct statistical correlations between the blow count of standard penetration tests (SPT N-value) and other soil parameters. Due to the great number of sites, only the Victoria Park Station site is thoroughly analyzed at this stage. This report focuses on the correlation between SPTs and pressuremeter tests (PMTs). Some basic relationships are established between SPT N-value and PMT data in this report.

DISCLAIMER The contents of this report reflect the views of the author who is responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the views or policies of the Natural Sciences and Engineering Research Council of Canada (NSERC). The author and the NSERC do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the objective of this report.

II

Statistical Correlations between SPT N-Values and Soil Parameters: Part I_SPT and PMT elations between SPT N-Values and Soil Parameters: Part I_SPT and PMT

TABLE OF CONTENTS CHAPTER 1 INTRODUCTION ................................................................................... 1 1.1 INTRODUCTION ........................................................................................... 1 1.2 RESEARCH NEEDS ....................................................................................... 1 1.3 ENGINEERING BACKGROUND ................................................................. 2 1.4 ORGANIZATION OF REPORT ..................................................................... 2 CHAPTER 2 PROJECT SITE CONDITIONS AND GEOLOGY ................................ 4 2.1 PROJECT SITE CONDITIONS ...................................................................... 4 2.2 GEOLOGY CONDITIONS ............................................................................. 4 3.1 STANDARD PENETRATION TEST ............................................................. 7 3.1.1 General Information .............................................................................. 7 3.1.2 Procedures ............................................................................................. 7 3.1.3 Parameters Measured ............................................................................ 9 3.2 PRESSUREMETER TEST ............................................................................ 11 3.2.1 General Information ............................................................................ 11 3.2.2 Procedures ........................................................................................... 12 3.2.2 Parameter Measurements .................................................................... 14 CHAPTER 4 CORRELATIONS BETWEEN SPT N-VALUES AND SOIL PARAMETERS OF VICTORIA PARK STATION ..................................................... 17 4.1 EGLINTON LRT - VICTORIA PARK STATION ........................................ 17 4.2 METHODS OF INVESTIGATION............................................................... 17 4.2 SOIL CLASSIFICATIONS............................................................................ 18 4.3 RELATIONSHIP BETWEEN PARAMETERS ............................................ 24 4.3.1 Soil Profiles of the Boreholes ............................................................. 24 4.3.6 Relationship between SPT N-value and Sensitivity ........................... 32 CHARPTER 5 CORRELATION BETWEEN SPT AND PMT .................................. 33 5.1 EXISTING CORRELATIONS BETWEEN SPT N-VALUES AND PMT DATA ................................................................................................................... 33 5.2 CORRELATION BETWEEN SPT N-VALUES AND PMT DATA FOR GLACIAL TILLS ................................................................................................ 35 5.2.1 Correlation between SPT N-value and EPMT....................................... 35 5.2.2 Correlation between SPT N-values and PL ......................................... 37 5.2.3 Correlation between SPT N-values and Ratio of EPMT/PL .................. 39 CHAPTER 6 MAIN FINDINGS AND FUTURE RESEARCH ................................. 41 III


6.1 MAIN FINDINGS ......................................................................................... 41 6.2 FUTURE RESEARCH .................................................................................. 41 ACKNOWLEDGEMENTS ......................................................................................... 43 REFERENCES ............................................................................................................ 44 APPENDIX A ........................................................................................................... 46 APPENDIX B ........................................................................................................... 52 APPENDIX C ........................................................................................................... 56 APPENDIX D ........................................................................................................... 65

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LIST OF TABLES Table Page Table 3-1 Corrections for SPT N-value (Skempton, 1986) ........................................... 9 Table 3-2 SPT N-value versus friction angle and relative density (Meyerhoff, 1956) 11 Table 4-1 Grain size distributions of various soils....................................................... 24 Table 4-2 Sensitivity of clays (Skempton and Northey, 1952) .................................... 32 Table 5-1 Corrections between SPT N-value and parameters of PMT (Bozbey and Togrol, 2010)................................................................................................................ 34 Table 5-2 Typical Menard pressuremeter values (CFEM, 2006) ................................. 35

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LIST OF FIGURE Figure Page Figure 1-1 Particle size effect on blow count for sands (Kulhawy and Mayne 1990). ........................................................................................................................................ 2 Figure 2-1 Crosstown route map (http://www.thecrosstown.ca/the-project) ............ 4 Figure 3-1 Equipment used to perform the SPT (Kovacs et al. 1983) ........................ 8 Figure 3-2 Standard split-spoon sampler (ASTM 1984) .......................................... 8 Figure 3-3 TEXAM PMT equipment (http://geotechpedia.com/Equipment/ Show/1255/TEXAM-Pressuremeter) ......................................................................... 12 Figure 3-4 Plot of pressure versus total cavity volume (Braja, 1990) .................... 13 Figure 3-5 Typical pressure-strain curves of soils at Victoria Park Station site (SPL, 2013) ............................................................................................................................ 14 Figure 3-6 Cylindrical cavity expansion ................................................................... 14 Figure 4-1 Borehole location at Victoria Park Station site ....................................... 17 Figure 4-2 Grain size distribution of silty clay till .................................................... 19 Figure 4-3 Grain size distribution of clayey silt till .................................................. 19 Figure 4-4 Grain size distribution of silty clay ....................................................... 20 Figure 4-5 Grain size distribution of clayey silt ....................................................... 21 Figure 4-6 Grain size distribution of sandy silt ........................................................ 21 Figure 4-7 Grain size distribution of silty sand ........................................................ 22 Figure 4-8 Grain size distribution of silt ................................................................... 22 Figure 4-9 Grain size distribution of sand and gravity sand ..................................... 23 Figure 4-10 Grain size distribution of silty sand till ................................................. 24 Figure 4-11 SPT, PMT and soil file at borehole VP01 ............................................. 25 Figure 4-12 SPT and soil file at borehole VP04 ....................................................... 26 Figure 4-13 SPT and soil file at borehole VP07 ....................................................... 26 Figure 4-14 Relationship between SPT N-value and EPMT ....................................... 27 Figure 4-15 Relationship between SPT N-value and EPMT/PL .................................. 28 Figure 4-16 Relationship between SPT N-value and PL ........................................... 28 Figure 4-17 Relationship between SPT N-value and D50 ......................................... 29 Figure 4-18 Relationship between SPT N-value and water content ......................... 30 Figure 4-19 Relationship between SPT N-value and liquid limit ............................. 31 Figure 4-20 Relationship between SPT N-value and plasticity index ...................... 31 Figure 4-21 Relationship between SPT N-value and liquidity index ....................... 32 Figure 4-22 Relationship between SPT N-value and St ........................................... 32 VI


Figure 5-1 Correlation of N60 and EPMT values in sandy soils (Bozbey and Togrol, 2010) ............................................................................................................................ 34 Figure 5-2 Relationship between SPT N-value and EPMT in silt clay ....................... 36 Figure 5-3 Relationship between SPT N-value and EPMT in silty clay till................ 36 Figure 5-4 Relationship between SPT N-value and EPMT in sand ............................ 37 Figure 5-5 Relationship between SPT N-value and PL in silt clay ........................... 38 Figure 5-6 Relationship between SPT N-value and PL in silty clay till .................... 38 Figure 5-7 Relationship between SPT N-value and PL in sand ................................ 38 Figure 5-8 Relationship between SPT N-value and EPMT/PL in silt clay .................. 39 Figure 5-9 Relationship between SPT N-value and EPMT/PL in silty clay till ........... 39 Figure 5-10 Relationship between SPT N-value and EPMT/PL in sand ..................... 40

VII


CHAPTER 1 INTRODUCTION 1.1 INTRODUCTION This report is to fundamentally conduct statistical correlations between the standard penetration test (SPT) blow count (N-value) and the geotechnical parameters of glacial tills in the Greater Toronto Area (GTA). The SPT is an in-situ dynamic penetration test designed to provide information of the geotechnical engineering properties of soils. The SPT has been successfully applied in different ground conditions where it may not be possible to obtain undisturbed soil samples such as gravels, sands, and silts. Due to distribution of cobbles or boulders within the glacial tills, SPT is widely adopted to assess the properties of glacial tills in Ontario, Canada. The main goal of this research is to study possible correlations between SPT N-values and pressuremeter data for glacial tills. The research findings will be valuable to the local geotechnical community and applicable for infrastructure development in the GTA. 1.2 RESEARCH NEEDS In geotechnical engineering, the SPT is one of the most commonly used in-situ tests. The SPT is a dynamic in-situ test, where a sample tube is driven into the ground at the bottom of a borehole by blows from a slide hammer with a mass of 63.5 kg falling through a distance of 760 mm. The sample tube is driven 152 mm (6 in) into the ground and the number of blows is recorded for the tube penetrating each 152 mm (6 in) up to a depth of 457 mm (18 in). The sum of the number of blows required for the second and third 152 mm (6 in) of penetration is termed as the "standard penetration resistance" or the "SPT N-value". There are many parameters of soils which can be correlated with SPT N-value, such as density, undrained shear strength, friction angle, modulus, etc. SPT N-value is accepted as an important indicator and is most widely used to describe soil characteristics. Once the corrections between SPT N-value and soil parameters are established, it is easy to determine soil characteristics through the SPT. There have been some researches to establish the correlation between SPT N-value and shear wave velocity (Vs), and nearly all of the empirical relationships use a power-law relationship (Dikmen, 2009; Akin et al., 2011). A correction has also been established between SPT N-value and relative density, Dr, which included overburden pressure, σv, (Meyerhof, 1957; Skempton, 1986), grain size (Kulhawy and Mayne, 1


1990) or both (Cubrinovski and Ishihara, 2001). Figure 1-1 shows particle size effect on SPT N-value for sands established by Kulhawy and Mayne (1990), where D50 is the particle diameter for 50% finer by weight and (N1)60 is the SPT N-value corrected for field procedures and overburden effects.

Figure 1-1 Particle size effect on blow count for sands (Kulhawy and Mayne, 1990) Most correlations were established between SPT N-values and various soil parameters based on in-situ tests data for general soil conditions. Currently, there is only very limited information available for glacial tills and more efforts are still being investigated in this area. 1.3 ENGINEERING BACKGROUND Recently, SPL Consultants Limited (SPL) was retained by Metrolinx/TTC for geotechnical investigation for the detailed design and construction of several stations for the proposed Eglinton Crosstown Light Rail Transit (LRT) in Toronto, Canada. There are tremendous amounts of geotechnical data resulting from this intensive investigation program, including grain size analyses, Atterberg limits, groundwater tests, standard penetration tests, pressuremeter tests, shear strength tests, etc. A great amount of useful information can be derived from these tests, which offers an excellent opportunity to conduct statistical correlations between SPT N-values and geotechnical parameters for glacial tills in the GTA. 1.4 ORGANIZATION OF REPORT This report has been organized into six chapters with main contents listed as below:

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Chapter 1 provides a general introduction and research background. Chapter 2 briefly describes the project site conditions and geology. Chapter 3 summaries the procedures and analyses of different in-situ tests, particularly for the SPT and pressuremeter test (PMT). Chapter 4 provides background information of the Eglinton Crosstown LRT project and correlations between SPT N-value with soil index parameters in the Victoria Park Station site, such as Atterberg Limits and D50. Chapter 5 reviews the current research on the relationship between SPT N-value and PMT data and describes the correlations between SPT N-value and PMT of glacial tills in GTA. Chapter 6 summarizes the main findings from this study and the needs for future research.

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CHAPTER 2 PROJECT SITE CONDITIONS AND GEOLOGY 2.1 PROJECT SITE CONDITIONS The proposed Eglinton Crosstown LRT Project is a 33 km long corridor that would link the Pearson International Airport in the west and the existing Kennedy subway station in the east upon completion. Due to the surfacial congestion in the middle section of the existing Eglinton Avenue, the proposed LRT route will include an underground section with twin tunnels that start from a portal in the west near the Black Creek Drive, cross a well developed urban area, and end at a portal near Brentcliffe Drive in the east. The total alignment length of the twin tunnels is about 10 km. The underground section of the Eglinton Crosstown LRT would consist of constructing proposed twin tunnels with an internal diameter about 5.75 m and a total of twelve underground stations along the tunnel alignment. This project includes 24 stations, in which Victoria Park Station is situated in the area of the intersection of Eglinton Avenue East and Victoria Park Avenue in Toronto, Ontario, as shown in Figure 2-1.

Victorica Park Station

Figure 2-1 Crosstown route map (http://www.thecrosstown.ca/the-project) 2.2 GEOLOGY CONDITIONS The existing grade of Eglinton Avenue along the tunnelled section, from west to east, 4


varies from about EL. 110 m near Black Creek to EL. 185 m at the hilltop near Old Forest Hill Road and from this point descends to about EL. 105 m near the West Don River. The existing grade of Victoria Park Station area generally varies between about EL. 159.4 m and EL. 151.1 m, sloping westward. Based on Karrow (1967) and Sharpe (1980), the Toronto area experienced at least three glacial and two interglacial periods, during which time a sequence of glacial and interglacial depositions took place. Towards the end of the last ice age, when Wisconsinan glacier withdrew from the Lake Ontario Basin to the north and to the east, Lake Iroquois, the forerunner of the present Lake Ontario, was established. However, the entire sequence of these glacial, interglacial and lacustrine deposits is seldom found intact and usually at any one location, one or more of these units are absent. The oldest Quaternary deposits are the Illinoian Age represented by the York Till which is overlain by Sangamonian-aged interglacial deposits (sands, silts, and clays) of the Don Formation. The Wisconsinan Age is represented by deposits formed during several glacier advances and retreats. Scarborough, Pottery Road, and Thorncliffe Formations were formed during the glacial retreats, whereas the Sunnybrook Till from the Early Wisconsinan time and Leaside Till (Newmarket Till and Halton Till) from the Late Wisconsinan period were formed during ice advances. Numerous small pockets of lake or pond deposits are found scattered throughout the till plain in depressions at the till surface. These deposits tend to be concentrated along the edges of the major stream valleys. The LRT Project is located within the physiographic region knows as the Peel Plain. Most of the tableland area consists of till partly modified by the former presence of shallow glacial lakes or post-glacial erosion features. The till in the project site is mapped as Halton Till which is generally considered as a fine grained diamicton with minor fine-grained lacustrine sediments incorporated within the body of the unit, likely to form glacial reworking of underlying lacustrine sediments. This till is typically stiff to hard in consistency, though near the ground surface, weathering can result in it being degraded to consistencies ranging from soft to firm. The till consists of a heterogeneous mixture of gravel, sand, silt and clay size particles in varying proportions. Cobbles and boulders are common in the deposits. The bedrock underlying the project site is considered to be the Ordovician Age bedrock of the Georgian Bay Formation which consists of typically highly weathered to fresh, grey, very fine to fine grained fissile, weak to medium strong shale with widely spaced jointing and sub-horizontal bedding planes, interbedded with slightly 5


weathered to fresh grey, fine grained strong to extremely strong calcareous siltstone and limestone layers (hard layers). The shaly bedrock formations are subjected to high in-situ horizontal stresses which can impose significant loads on tunnel liner or excavation wall in a time-dependent manner. The shale bedrock surface is recorded at elevations ranging from EL. 99 m to EL. 105 m between Yarrow Road and Richardson Avenue near the western limit of the proposed tunnel alignment. The bedrock levels are falling steeply to the west into the Humber River valley. The interpreted bedrock contours rise to approximately El. 110 m beneath Dufferin Street and gradually fall to El.60 m near Brentcliffe Road at the eastern limit of the proposed tunnel alignment (Cao et al., 2015).

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CHAPTER 3 GEOTECHNICAL TESTING METHODS One of the first steps in any geotechnical design problem is to develop an understanding and knowledge of the soil materials at the site. The physical and mechanical properties of soils are determined either by in-situ tests or laboratory tests or a combination of both. Most geotechnical engineering textbooks provide information related to how to conduct in-situ tests and laboratory tests, from which the soil parameters can be obtained. In addition, the American Society for Testing and Materials (ASTM) standards provide guidance on specific procedures for performing the in-situ and laboratory tests. This chapter mainly focuses on the two in-situ test methods: 1) standard penetration test (SPT); and 2) pressuremeter test (PMT). 3.1 STANDARD PENETRATION TEST 3.1.1 General Information The SPT method is a rapid, simple and economical test, which is widely adopted to assess the properties of most soil types, and is usually performed using a conventional geotechnical drill rig, as shown in Figure 3-1. The test does provide a rough index of the relative strength and compressibility of the soil in the vicinity of the test. 3.1.2 Procedures The overall equipment and setup for the SPT are shown in Figure 3-1. To perform the test, the drilling crew, after advancing the test and boring to the desired depth, first removes the string of drill rods slowly and cleans out the hole to the desired depth of testing. After the drilling tools are removed, a standard thick-walled split-spoon sampler, as show in Figure 3-2, is attached to the drill rods and is lowered carefully to the bottom of the hole. With the sampler resting at the bottom of the hole, a slide hammer with a standard weight of 63.6 kg (140 lb) is allowed to fall freely 762 mm (30 in) onto a collar that is attached to the top of the drill string until 457 mm (18 in) of penetration has been achieved. The number of blows is recorded for each of three 152 mm (6 in) intervals, the first generally is considered a seating drive, and the number of blows for the final 305 mm (12 in) is reported as the SPT blow count (N) value. After the sampler has been brought back to the surface, the samples are removed and classified, before being placed into jars, labeled, and sealed with wax for transport. 7


Figure 3-2 Equipment used to perform SPT (Kovacs et al., 1983)

Figure 3-3 Standard split-spoon sampler (ASTM, 1984) Since the SPT is highly dependent on the equipment and operator performing the test, it is often difficult to obtain repeatable results. In addition, the SPT should not be relied on soils containing coarse gravel, cobbles, or boulders, because the sampler can become obstructed, resulting in high and unconservative N values. The test should not be relied on for cohesionless silts because dynamic effects at the sampler tip can lead to erroneous strength and compressibility evaluations. The test also has little meaning 8


in soft and sensitive clays (Kulhawy and Mayne, 1990). 3.1.3 Parameters Measured The SPT N-value can be obtained directly in the record of borehole. Due to complex influence from many reasons, it usually needs to be corrected. In the field, the energy delivered to the rods during an SPT expressed as a ratio of the theoretical free-fall potential energy, can vary from about 30 % to 90 %, namely that the energy ratio (ER) can range from 30% to 90%. The practice now in the United States is to express the SPT N-value measured to an average energy ratio of 60% (ER = 60%). The SPT N-values corresponding to 60% efficiency are termed N60. Numerous correction factors to the measured N-value are necessary because of energy inefficiencies and procedural variation in practice. When all factors are applied to the field recorded N-value, the corrected value N60 is calculated using Eq.3-1, as recommended by Skempton (1986). N 60  NC E C B Cs C R

(3-1)

Where: CE - effects of energy CB - borehole diameter correction CS - sampling method correction CR - rod length correction The correction factors are presented in Table 3-1. As can be noted from Table 3-1, values of the correction term for energy CE vary over a relatively wide range. Table 3-1 Corrections for SPT N-value (Skempton, 1986)

SPT N-value is affected by the effective overburden pressure, σo′. Consequently, the 9


corrected value of N60 obtained under different effective overburden pressures should be changed to correspond to a standard value. That is, (N1)60= CN N60

(3-2)

Where: (N1) 60– value of N60 corrected to a standard value CN - correction factor N60 – standard penetration number, corrected for field conditions. A number of empirical relations were proposed for CN .The most commonly cited relationships are those of Liao and Whitman (1986) and Skempton (1986). Liao and Whitman’s relationship (1986):

(3-3) Skempton’s relationship (1986):

(3-4)

Where: σo ′ - effective overburden pressure Pa – atmospheric pressure (or about 100 kPa) Due to many unknown factors used in the field, the correction of the SPT N-value is ignored in this stage and the field SPT N-value is used in this report. Sometimes the distance driven into the ground by hammer is less than 305 mm, when the number of blows are higher than 50. In this case, the SPT N-value (blows/0.3 m) is corrected using Eq. 3-5 in the current study. Nc 

305N s

(3-5)

10


Where: N c - corrected SPT N-value

s - driven depth actually, mm N - actual number of blows

For example, when the sample tube is driven 150 mm into the ground and the number of blows is 50, then the corrected SPT N-value is 102. If it is more than 200, the corrected SPT N-value will be taken as 200. SPT N-value in exploratory borings gives a qualitative guide to the in-situ engineering properties and provides an indication of the relative density and friction angle of the soil as proposed by Meyerhoff (1956) (see Table 3-2). Table 3-2 SPT N-value versus friction angle and relative density (Meyerhoff, 1956) Soil packing

Relative Density [%]

Friction angle [°]

50

Very Dense

> 80

> 45

SPT N [Blows/0.3 m]

3.2 PRESSUREMETER TEST 3.2.1 General Information The PMT is a load test carried out in-situ in a borehole. An inflatable probe is set at testing depth in a pre-drilled borehole within a soil or rock mass or by direct driving into the mass. The method depends on the materials characteristics. The PMT is used to test hard clays, dense sands and weathered rock which cannot be tested with push equipment. There are three different types of pressuremeter tests: Menard-type pressuremeter, Self-boring pressuremeter, and Cone pressuremeter. In this project, TEXAM PMT testing, one of Menard-type PMT, was carried out. The TEXAM PMT is a reliable instrument for the evaluation of most ground engineering problems. The TEXAM PMT utilizes a monocellular hydraulically inflated probe. A mechanical actuator is used to displace a piston which travels within a cylinder filled with the inflation fluid. The pressuremeter has two major components. The first component is the control unit that remains above ground. The second component of the pressure meter is a probe that is inserted into the borehole (ground) to read the pressure, as 11


shown in Figure 3-4.

Figure 3-4 TEXAM PMT equipment (http://geotechpedia.com/Equipment/Show/1255/TEXAM-Pressuremeter) 3.2.2 Procedures The probe of the PMT is inserted into the borehole and supported at test depth. The probe is an inflatable flexible membrane which applies even pressure to the walls of the borehole as it expands. As the pressure increases and the membrane expand, the walls of the borehole begin to deform. The PMT proceeds by incrementally increasing the inflation pressure while monitoring the radial deformation or volume. Pressure increment should be selected to yield accurate results without producing an excessively long test. A total of seven to ten pressure increments of 25 to 200 kPa are typically used, depending upon the anticipated soil conditions. Pressure increments are generally applied at typically one to three minute intervals. Operator judgment and experience are typically used in deciding when it is appropriate to increase or decrease the pressure. In general, the pressure versus deformation response is monitored and when the response stabilizes under a given pressure, the next pressure increment is applied. PMT results are presented generally as a plot of pressure versus volume, as shown in Figure 3-4.

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Figure 3-5 Typical plot of pressure versus total cavity volume (Braja, 1990) It is good practice to perform the PMT using a phase of cycle loading, a phase including a drained creep test, and at least one unload-reload cycle. The purpose of the creep test is to assess the time-dependent deformation behavior of the material. In a creep test, the pressure is maintained constant for each step for the same period of time, such as 60 seconds. The volumetric expansion of the probe is measured at 15, 30, and 60 seconds after each pressure step to determine a creep curve. The test ends when the probe has been expanded to twice its deflated volume or when the pressure limit of the device has been reached. Once the test has been completed, the probe is deflated, and the device is either advanced to a new depth or returned to the surface. A typical test results expressed in terms of applied pressure versus radial strain is shown in Figure 3-5 for the soil in the Victoria Park Ave Station. To use the expand theory of an infinitely thick cylinder, as shown in Figure 3-6. Then translate volume ΔV/V to radical strain ΔR/R0 using the following calculation process: V  V  (r  r ) 2 L R 2   (1  ) 2 V R0 r L

(3-6)

R V  1 1 R0 V

(3-7)

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Figure 3-6 Typical pressure-strain curves of soils at Victoria Park Station site (SPL 2013)

Figure 3-7 Cylindrical cavity expansion

3.2.2 Parameter Measurements The typical pressure versus radial strain curve (Figure3-5) features up to five distinctive portions which characterize the stress-strain behavior of the soil, namely: · The initial stretching of the membrane prior to contacting the borehole wall; · The linear pseudo-elastic stress-strain portion of the deformation curve; · The departure from linear elastic conditions starting at the yield pressure py; · The unload-reload portion of the test; · The development of soil failure, which is represented by the limit pressure pL. Based on these test features the following soil parameters are determined or estimated:

Total Horizontal Stress σho or po: 14


An estimate of the total horizontal stress σho can be obtained at the intersection of the near horizontal portion of the curve (membrane stretching) with the linear pseudo-elastic line. Actual curves typically exhibit curved transitions, with the most likely value of σho located at the point of maximum curvature. It should be noted that there may be a big error in the estimate of σho if the soil is significantly disturbed during pre-drilling.

Pressuremeter modulus EPMT: The EPMT is represented by the slope of the pressure versus radial strain curve along its linear portion, and may be calculated as follows: 2

E PMT

2

  R     R   1      1       R0     R0    2    1   (1   )( p2  p1 )  2 2   R     R   1        1     R0     R0     1   2  

(3-8)

Where: p1 — the beginning pressure of the linear portion of the curve p2 —the end pressure of the linear portion of the curve ν —Poisson ratio ΔR/R0 — radical strain Where, the sub-indices 1 and 2 indicate the beginning and the end of the linear portion of the curve, respectively. These two points are shown in pressuremeter curves with two oversized circles. In this determination a value of the Poisson ratio, typically ν = 0.33 for most soils, must be assumed. For saturated clays a value of ν = 0.45 is suggested. Yield Pressure py

The yield pressure indicates the end of the linear pseudo-elastic deformations and the onset of plasticity. This yield pressure is useful in indicating beyond which pressure significant creep deformations may occur. Unload-Reload Modulus ER:

The reload modulus is represented by the slope of the unload-reload loop, and may be used to determine elastic soil deformations upon unloading conditions such as those typically encountered during excavations. It includes the unload modulus Eu based on the unloading branch of the curve and the 15


reload modulus ER based on a weighted average of volume corresponding to the same unloading pressure (pressure at beginning of unloading stage). Limit Pressure PL

The limit pressure is a measure of the strength of the soil (either under undrained conditions for cohesive soils, or drained conditions for non-cohesive soils). This parameter is defined as the pressure reached when the soil cavity has been extended to twice its original soil cavity volume Vc (minus the initial total contact pressure po). The limit pressure is not always attained during testing. In such cases, the value of PL is inferred by plotting pressure versus 1/V for the plastic phase of the deformations.

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CHAPTER 4 CORRELATIONS BETWEEN SPT N-VALUES AND SOIL PARAMETERS OF VICTORIA PARK STATION 4.1 EGLINTON LRT - VICTORIA PARK STATION

This section is to conduct statistic correlation between SPT N-values and geotechnical parameters for Eglinton Crosstown LRT Project – the Victoria Park Station site. The Victoria Park Station site is situated in the area of the intersection of Eglinton Avenue East and Victoria Park Avenue in Toronto, Ontario. There are existing residential buildings at the northwest quadrant of the intersection, detached houses and townhouses at the southwest quadrant, a landscaped area at the southeast quadrant, and a large parking lot at the northeast quadrant. The field investigation consisted of advancing eight (8) boreholes at the locations shown in Figure 4-1 (SPL 2013).

Figure 4-1 Borehole location at Victoria Park Station site 4.2 METHODS OF INVESTIGATION

The boreholes were advanced using truck and all-terrain buggy mounted power drill rigs to depths ranging between 40.0 m and 55.4 m below grade level. The type of drilling method used to advance the boreholes is identified in the respective borehole logs (record of borehole sheets) in report, using hollow-stem augers for the boreholes. The soil stratigraphy was recorded by observing the quality and changes of augered materials which were withdrawn from the boreholes, and by sampling the soils at 0.75 17


m to 1.5 m intervals using a 50 mm O.D. split spoon sampler and an automatic SPT hammer, in accordance with the SPT. SPT tests were carried out in all these eight (8) boreholes. Borehole VP01-PMT for pressuremeter testing was drilled at about 2.5 m east of borehole VP01, the borehole logs sheets attached in Appendix A. Texam pressuremeter testing was carried out by In-Depth Geotechnical Inc. Within the borehole, a total of 11 pressuremeter tests were conducted at depths ranging from 4.37 m to 35.00 m. Soil samples collected during the investigation were visually classified in the field, placed in appropriate containers, labeled and transferred to our laboratory where the samples were re-evaluated by a senior engineer based on the current version of TTC Geotechnical Standards. Representative samples were selected for geotechnical index testing. The testing program consisted of the measurement of the natural moisture content of all samples, the measurement of bulk density of eighty-nine (89) selected samples, grain size and hydrometer analyses of one hundred and three (103) selected samples and consistency (Atterberg) limits for sixty-five (65) plastic soil samples. The grain size analysis curves and results of the consistency (Atterberg) limits tests are shown in Appendix B. Laboratory vane shear tests were conducted in the Shelby tube samples, consolidated undrained triaxial shear tests were carried out on nine (9) samples in Golder Associates’ laboratory. The test results and the effective angle of internal friction interpreted from the triaxial tests are provided in Appendix D. All the test results are provided in SPL report (2013). 4.2 SOIL CLASSIFICATIONS

According to the description of report and borehole logs, the following are the soil encountered in the boreholes: · Topsoil, Pavement Structure and Fill Materials · Silty Clay Till and Clayey Silt Till · Silty Clay and Clayey Silt · Silt, Sandy Silt and Silty Sand · Sand and Gravelly Sand · Silty Sand Till

18


Figure 4-2 Grain size distribution of silty clay till

Figure 4-3 Grain size distribution of clayey silt till 19


Silty Clay Till and Clayey Silt Till: The cohesive tills (silty clay till and clayey silt till) encountered in all boreholes were generally firm to hard, with measured SPT N-values ranging from 5 to more than 50 blows per 300 mm of penetration. A major portion of the cohesive tills were sandy, typically containing 27 to 44% sand. silty clay till samples contain up to 7% gravel, 27 to 38% sand, 37 to 49% silt and 18 to 29% clay size particles. clayey silt till samples contain 1 to 7% gravel, 27 to 44% sand, 37 to 47% silt and 14 to 22% clay size particles. The grain size distribution curves for the samples are shown in Figure 4-2 and Figure 4-3.

Figure 4-4 Grain size distribution of silty clay Silty Clay and Clayey Silt: The silty clay to clayey silt deposits were generally very stiff to hard in consistency, with measured SPT N-values ranging from 16 to more than 50 blows per 300 mm of penetration.

The tested silty clay samples contain up to 6% sand, 46 to 76% silt and 18 to 53% clay size particles, with little gravel particles found. The tested clayey silt samples contain 1 to 9% sand, 68 to 79% silt and 20 to 23% clay size particles, with little gravel particles found in the samples. The grain size distribution curves for the samples are shown in Figure 4-4 and Figure 4-5.

20


Figure 4-5 Grain size distribution of clayey silt

Figure 4-6 Grain size distribution of sandy silt

21


Figure 4-7 Grain size distribution of silty sand

Figure 4-8 Grain size distribution of silt Silt, Sandy Silt and Silty Sand: The relative density of the non-plastic silt, sandy silt 22


to silty sand deposits can be generally described as compact to very dense as attested by the SPT N-values of 15 to more than 50 blows per 300 mm of penetration. The tested silt, sandy silt and silty sand samples typically contain 3 to 66% sand, 26 to 86% silt and 4 to 14% clay size particles, with little gravel particles found in the samples. The grain size distribution curves for the samples are shown in Figure 4-7 and Figure 4-8.

Figure 4-9 Grain size distribution of sand to gravel sand Sand and Gravelly Sand: The relative density of the coarse grained deposits can be described as very loose to very dense as attested by the SPT N-values ranging from 1 to greater than 50 blows per 300 mm of penetration. The tested sand and gravelly sand samples contain up to 34% gravel, 57 to 89% sand, 4 to 18% silt and 3 to 8% clay size particles. The grain size distribution curves for the samples are shown in Figure 4-9. Silty Sand Till: The relative density of the non-plastic tills can be described as compact to very dense as attested by the SPT N-values of 22 to more than 50 blows per 300 mm of penetration. The tested samples contain 2 to 6% gravel, 43 to 58% sand, 25 to 38% silt and 8 to 18% clay size particles. The content of sand is less than silty clay till. The grain size distribution curves for the samples are shown in Figure 4-10.

23


Figure 4-10 Grain size distribution of silty sand till Table 4-1 summarizes the grain size distributions of various soils. Table 4-1 Grain size distributions of various soils Soil Classification

Gravel

Sand

Silt

Clay

Silty clay till

up to 7%

27- 38%

37- 49%

18 - 29%

Clayey Silt Till

Clayey silt till

1- 7%

27- 44%

37- 47%

14 - 22%

Silty Clay and

Silty clay

up to 6%

46 - 76%

18- 53%

Clayey Silt

Clayey silt

1 - 9%

68 - 79%

20- 23%

3- 66%

26- 86%

4 -14%

Silty Clay Till and

Silt, Sandy Silt and Silty Sand Sand and Gravelly Sand

up to 34%

57 - 89%

4- 18%

3- 8%

Silty Sand Till

2 - 6%

43 - 58%

25- 38%

8 - 18%

4.3 RELATIONSHIP BETWEEN PARAMETERS 4.3.1 Soil Profiles of the Boreholes

Figure 4-11 shows the profile of SPT N-values and EPMT values with depth at or close to the location of borehole VP01 at this site. SPT N-values ranged from 5 to 50, and 24


the EPMT values ranged from 15 MPa to 35 MPa in the clayey silt to silty clay till. SPT N-values ranged from 60 to 130, and the EPMT values ranged from 60 MPa to 130 MPa in the silt to silty sand. The SPT N-values are generally greater than 50, especially in the silt to silty sand. It means the silt to silty sand contains coarse gravel, cobbles, or boulders, because the sampler can become obstructed, resulting in high SPT N-values. It is still noted that the EPMT values generally increase as the SPT N-value increased with depth.

Silty clay till/ Clayey silt till Sand / gravelly sand

Silt / Sandy silt/ Silty sand

Figure 4-11 SPT, PMT and soil file at/near borehole VP01 Figure 4-12 shows the profile of SPT N-values with depth in borehole VP04. SPT N-values ranged from 20 to 80 in the silty clay to clayey silt till and from 50 to 200 in the silt to silty sand. Figure 4-13 shows the profile of SPT N-values with depth in borehole VP07, where SPT N-values ranged from 5 to 100 in the silty clay to clayey silt till, from 50 to 150 in the silt to silty sand, and from 40 to 60 in the silty clay to clayey silt. Figure 4-12 and 4-13 show that SPT N-values are generally greater than 50 except at the shallow depths. It should be noted that the higher SPT N-values in the glacial till may be due to the sampler hitting cobbles or boulders. This indicates that SPT is not a good test method for the glacial deposits.

25


Silty clay till/ clayey silt till Silt/sandy silt/silty sand Sand / Gravel sand Silt /sandy silt/ silty sand

Silty clay/ clayey silt

Figure 4-12 SPT and soil file at borehole VP04

Silty clay till/ clayey silt till

Silt/ sand silt/ silty sand

Silt clay/ clayey silt

Figure 4-13 SPT and soil file at borehole VP07 The SPT method often reaches refusal (i.e. N-value greater than 50 for 152 mm increment) when the SPT sampler hits a cobble or boulder within the glacial tills. As the distribution of cobbles or boulders within the glacial tills is random, locally high 26


SPT N-values may not be indicative of the relative density or consistency of glacial tills. The apparent soil parameters estimated from such SPT N-value may be overestimated when the sampler hits cobbles/boulders or underestimated when the sampler penetrates the soil matrix between cobbles/boulders. 4.3.2 Relationship between SPT and PMT data

The EPMT is compared with the SPT N-value, as shown in Figure 4-14. It is found that EPMT generally increases with the SPT N-value; However, there is only very limited correlation available between EPMT and SPT N-value. For the silt to silty sand at borehole VP01, EPMT ranges from 60 to 120 MPa with an average value of 90 MPa. Correspondingly, most SPT N-value of the silt to silty sand are higher than 50.

Figure 4-14 Relationship between SPT N-value and EPMT EPMT/PL can be used as a general guideline for soil identification. For the silt to silty sand of borehole VP01, EPMT/PL ranges from 5 to 15 with an average value of 12. For the silty clay to clayey silt till, EPMT/PL ranges from 5 to 12 with an average value of 8. Due to influence of cobble or boulder within the soils, the range of EPMT/PL is wide, as shown in Figure 4-15. Similarly to relationship between SPT N-value and EPMT and the ratio of EPMT/PL, there is no good relationship between SPT N-value and PL, as shown in Figure 4-16. Due to the influence of cobble or boulder within the soils and a limited number of borehole data, there is only very limited information available about EPMT and no correlation available between EPMT and SPT N-value. Therefore, more data is needed to find the correction between EPMT and SPT N-value.

27


Figure 4-15 Relationship between SPT N-value and EPMT/PL

Figure 4-16 Relationship between SPT N-value and PL 4.3.3 Relationship between SPT and Particle Size

Figure 4-17 shows the relationship between SPT N-value and D50, where D50 is the grain diameter corresponding to 50% passing by weight. It is found that there is no good relationship between SPT N-value and D50. For the silty clay to clayey silt till, the average value of D50 is 0.03 mm. For sand to gravelly sand, D50 ranges from 0.12 to 0.2 mm with an average value of 0.15mm. Because the value of Dr is unavailable, the relationship between SPT N-value and D50 and Dr cannot be established.

28


Figure 4-17 Relationship between SPT N-value and D50 4.3.4 Relationship between SPT N-value and Water Content

Figure 4-18 shows the relationship between SPT N-value and water content. It is founded that the change in the water content for the same soil is narrow, whereas the SPT N-value varies considerably. For the silty clay to clayey silt till, the water content ranges from 5% to 25% with an average value of 12% for SPT N-value less than 50. For the silty clay to clayey silt, the water content ranges from 15% to 25% with an average value of 20%. There is no good relationship between SPT N-value and the water content.

29


Figure 4-18 Relationship between SPT N-value and water content 4.3.5 Relationship between SPT N-value and Atterberg Limits

Figure 4-19 shows the relationship between SPT N-value and the liquid limit. It is founded that the variation of the liquid limit for same soil is small, whereas SPT N-value varies considerably. For the silty clay to clayey silt till, the liquid limit ranges from 15 to 25with an average value of 18 for SPT N-value less than 50. Figure 4-20 shows the relationship between SPT N-value and the plasticity index. It is founded that the plasticity index has a small range for the same soil, whereas SPT N-value varies considerably. For the silty clay to clayey silt till, the plasticity index is very low, ranging from 5 to 10 with an average value of 18. There is no strong relationship among SPT N-value, liquid limit and plasticity index.

30


Figure 4-19 Relationship between SPT N-value and liquid limit

Figure 4-20 Relationship between SPT N-value and plasticity index Figure 4-21 shows the relationship between SPT N-value and liquidity index. It is founded that liquidity index of the silty clay to clayey silt till is generally less than zero, which means the soil is semi-solid to plastic solid.

31


Figure 4-21 Relationship between SPT N-value and liquidity index 4.3.6 Relationship between SPT N-value and Sensitivity

Figure 4-22 shows the relationship between SPT N-value and sensitivity. Sensitivity, St, is defined as the ratio of the strength of the soil in the undisturbed state to that of the soil in the remolded state. Classes of sensitivity may be defined in Table 4-2 as recommended by Skempton and Northey (1952). Table 4-2 Sensitivity of clays (Skempton and Northey, 1952) Classification

Strength Ratio

Insensitive Low sensitivity Medium sensitivity Sensitive Extra sensitive Quick

16

It is found that there is no good relationship between SPT N-value and St. For silty clay to clayey silt till, the sensitivity ranges from 1 to 5 with an average value of 3, generally corresponding to medium sensitivity.

Figure 4-22 Relationship between SPT N-value and St Through the analysis uses data only from the Victoria Park Station site, there is no good relationship between SPT N-value and other soil parameters, including water content, St, EPMT and Atterberg limits. Therefore, more data is needed to establish the relationships.

32


CHARPTER 5 CORRELATION BETWEEN SPT AND PMT 5.1 EXISTING CORRELATIONS BETWEEN SPT N-VALUES AND PMT DATA

Correlations between the PMT and SPT results for various soils have been reported by Hughes et al. (1977) and Baguelin et al. (1978). According to Ohya et al. (1982), the relationships between pressuremeter modulus EPMT and corrected SPT N-value (N60) for sand to gravelly sand and clay are as follows: Clay: E PMT (kPa)  1930 N 600.63

(5-1)

Sand to gravelly sand: E PMT (kPa)  908 N 600.66

(5-2)

Yagiz et al. (2008) investigated the relationship between the corrected SPT N-value (Ncor) and both pressuremeter modulus, Em, and limit pressure, PL, in Gumusler County, 10 km north of the city of Denizli, Turkey. The statistical program found the best-fit regression between the parameters in a linear combination with a 95% confidence level. The empirical equations expressed by Eq.5-3 and Eq.5-4.

Em  388.67Ncor  4554

pL  29.45Ncor  219.7

r  0.91

(5-3)

r  0.97

(5-4)

where Em and PL are in kPa. However, the SPT and PMT were carried out at depths of 1.5-2 m below ground surface. This paper did not show how to correct the SPT N-values.

33


Table 5-1 Corrections between SPT N-value and parameters of PMT (Bozbey and Togrol, 2010)

Bozbey and Togrol (2010) obtained the correlations between SPT and pressuremeter data measured during an extensive geotechnical investigation conducted in Istanbul, Turkey. Empirical equations were proposed to estimate PL from EPMT Table 5-1 presents Bozbey and Togrol’s results (2010). Figure 5-1 shows the correlation of N60 and EPMT values in sandy soils as recommended by Bozbey and Togrol (2010).

Figure 5-1 Correlation of N60 and EPMT values in sandy soils (Bozbey and Togrol, 2010) Usually, EPMT/PL ratio recommended in the Canadian Foundation Engineering Manual (CFEM) (2006), can be used as a general guideline for soil identification, as follows : For sands 7 < EPMT /PL

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