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- Canadian Foundation Engineering Manual (4th:Edition) - Civil MDC
- Canadian foundation engineering manual free download
- Canadian Foundation Engineering Manual 4th -
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This edition is now only available in English. Work is continuing on developing a new online version of the CFEM with an estimated timeframe for completion of the entire project of approximately 2 years. In the interim, the current 4th Edition with the updated Errata is available for purchase from BiTech Publishers www. As always, CGS members receive preferred pricing. The World Is Flat 3.
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Life of Pi. Anchor Bolts - Concrete Capacity Design. The Perks of Being a Wallflower. Join With us. Today Updates. Moran, Howard N August August 8. July June Duggal Free Download June Charles H. Roth, Larry April Popular Files. Normally, Performance Specifications stipulate the end-results without detailing how to achieve them, whereas Compliance or Prescriptive Specifications detail mandatory methods, materials, etc.
It is incorrect to use formulae requiring insertion of parameters in other dimensions than the base units, because this would require the user to memorize not just the parameter, but also its "preferred" dimension, which could vary from reference to reference. This is a clear improvement over the old system, where every formula had to define whether the parameter was to be input as lb, tons, kips, etc. Therefore, unless specifically indicated to the contrary, all formulae given in the Manual assume the use of parameters given in base SI-units.
The unit kilopascal kPa is commonly used il2- Canadian practice. A prime denotes effective stress e. For symbols indicating force, an upper case letter is used for total force, or force per width or linear length, and a lower case letter is used for force per unit area, i. Normally, when the abbreviating symbols are not used, the units Newton, metre, kilogram, and second are spelled without plural endings e. Table 2. The numeral I in the unit column denotes a dimensionless quantity. For a complete table, see Barsvary et al.
II:i i. An excellent overview of these techniques is provided by Hoek et al. Most of the classificatioIY systems incorporating a number of parameters Wickham et aI. More recently, the systems have been modified to account for the conditions affecting rockmass stability in underground mining situations. While no single classification system has been developed for or applied to foundation design, the type of infonnation collected for the two more common civil engineering classification schemes, Q Barton et aI, and RMR Bieniawski, should be considered.
These techniques have been applied to empirical design situations, where previous experience plays a large part in the design of the excavation in the rockmass.
Empirical techniques are not used in foundation engineering, where a more concentrated expenditure of effort and resources is required and possible, due to the much smaller spatial extent of the work, and the relatively high external loads applied to the rockmass. Values 'range between those of sandstone and those of fine-grained sediments. Values of m; will be significantly different if failure occurs along a weakness plane.
Estimate the average value of the Geological strength index GSI from the contours. Do not attempt to be too precise. Site Investigations 4. The site investigation is one of the most important steps in any foundation design, and should be carried out under the direction of a person with knowledge and experience in planning and executing such investigations.
Drilling crews should be experienced specifically in borings for geotechnical explorations. A valuable guide is provided by ASCE Peck noted that the three factors of most importance to the successful practice of subsurface engineering were: Know ledge of precedents A working knowledge of geology Knowledge of soil mechanics.
A knowledge of precedents in similar ground conditions helps to ensure that no surprises are encountered in the design and construction of the works; knowledge of geology should enable the engineer to anticipate the range of possible variations in ground conditions between the locations of any borings; and knowledge of soil or rock mechanics should minimize the chances of inadequate performance of the ground during and after construction.
A site characterization should be carried out for all projects. The level of detail of any characterization should be appropriate to the proposed site use and to the consequences of failure to meet the performance requirements. The engineer should be able to prepare a design that will not exceed ultimate and serviceability limit states see Chapters 7 and 8 for further discussion. This means that there should be no danger of catastrophic collapse and deformations and other environmental changes should be within tolerable limits.
Depending on the particular nature of the proposed development, the site characterization mayor may not involve field exploration. Once the scope of work has been 'established for the proposed engineering works, the site characterization should comprise three components: Desk Study and Site Reconnaissance Field Exploration , 32 Canadian Foundation Engineering Manual I Reporting. The first component is the most critical.
It consists of a review of existing infonnation about the site including the geology. Attention to detail in this phase in conjunction with a site reconnaissance to review existing surface conditions will minimize the potential for surprises during subsequent field exploration and construction. The extent of this phase of the work will depend on the experience ofthe engineer in the particular geological environment and with similar foundation systems or soil structures.
Upon completion of this phase, a preliminary sub-surface model of the site should have been established, enabling consideration of foundation design issues and preliminary selection of foundation options. The engineer may proceed to plan an appropriate field exploration.
The primary objectives offield exploration are to detennine j. Site investigations should be organized to obtain all possible infonnation commensurate with project objectives for a thorough understanding of the subsurface conditions and probable foundation behaviour. Additional infonnation , on the objectives, planning and execution of site investigations is provided by Becker I.
At the very least, the field exploration should confinn the preliminary subsurface model developed during the planning 'phase and should provide sufficient characterization of material properties to allow estimation of the response of the site to the proposed engineering works. In many cases, the macrostructure of the ground such as jointing and fissuring will control the site and foundation perfonnance during and after construction. An understanding of site geology will allow the engineer to anticipate such cases and field exploration should detennine the presence of any layers or zones likely to cause difficulty during construction or operation of the facility.
For example, thin weak layers may be critical for stability or thin penneable layers may be critical in excavations. The selection of an appropriate exploration technique should be based on a clear understanding of the critical failure modes and on the types of layers likely to be present. Upon completion of the stratigraphic logging and material classification, appropriate design parameters can be selected.
It is important that the general character and variability of the ground be established before deciding on the basic principles of the foundation design of the project. The combination of each proj ect and site is likely to be unique, and the following general comments should therefore be considered as a guide in planning the site investigation and not as a set of rules to be applied rigidly in every case.
The depth of exploration is generally determined by the nature of the project, but it may be necessary to explore to greater depths at a limited number of locations to establish the overall geological conditions. The investigation should provide sufficient data for an adequate and economical design of the project. It should also be sufficient to cover possible methods of construction and, where appropriate, indicate sources of construction materials.
The lateral and vertical extent of the investigation should cover all ground that may be significantly affected by the project and construction, such as the zone of stressed ground beneath the bottom of a group of piles, and the stability of an adj acent slope, if present.
The boreholes should be located so that a general geological view of the whole site can be obtained with adequate details of the engineering properties of the soils and rocks and of groundwater conditions. More detailed information should be obtained at the location of important structures and foundations, at locations of special engineering difficulty or importance, and where ground conditions are complicated, such as suspected buried valleys and old landslide areas.
Rigid, preconceived patterns of boreholes should be avoided. In some cases, it will not be possible to locate structures until much of the ground investigation data has been obtained.
In such cases, the program of investigations should be modified accordingly. In the case oflarger projects, the site investigation is often undertaken in stages. A preliminary stage provides general information and this is followed by a second stage and, if required, additional stages as the details of the project and foundation design develop. Reference is made to boreholes as the means of site investigation.
However, in some cases, boreholes can be replaced by, or supplemented by, test pits, test trenches, soundings or probe holes. Regardless of the type of investigation, it is essential that the locations and ground levels for all exploration points be established, if necessary, by survey. Information and recommendations on the extent of site investigations, both depth and number of boreholes, can be found in various references.
Robertson suggested the risk-based approach to characterization shown on Figure 4. Design may then be based qn presumptive bearing pressUres. For medium risk projects, some form of in-situ testing will be necessary. The in-situ testing conventionally consists of penetration testing from which some estimate of the soil properties can be obtained by correlation.
Design methods are also available where in-situ test results are used directly to select design values of bearing pressure. Where the consequences of unexpected ground response result in an unacceptable level of risk, a much more elaborate field and laboratory program should be carried out.
Suggestions for the depth of boreholes and spacing of boreholes are considered in the following sections. The suggestions for minimum depth of boreholes can be more definitive since there is a logical analytical basis. The suggestions for spacing of boreholes are however, more difficult to make and less definitive since much depends on the soil variability, type ofproject, performance requirements, and foundation type selected.
A reduction in the depth can be considered if bedrock or dense soil is encountered within the minimum depth. The net increase in soil stress should appropriately take into account the effect of fill or excavation that may be required for site grading.
The soil stress increase should take into account adjacent foundations since they may increase the soil stress at depth, and the corresponding minimum depth of boreholes. Boreholes should extend below all deposits that may be unsuitable for foundation purposes such as fill ground, and weak compressible soils.
The minimum borehole depth beneath the lowest part of the foundation generally should not be less than 6 m, unless bedrock or dense soil is encountered at a shallower depth. If rock is found the borehole should penetrate at least 3 m in more than one borehole to confirm whether bedrock or a boulder has been found.
Three meters may not be adequate for some geological conditIons; e. No guidance can be given in such cases but where doubt arises, consideration should be given to drilling deeper boreholes. Furthermore, the boreholes or selected number of boreholes should be extended to a sufficient depth to minimize the possibility of weaker strata occurring below the bedrock surface which could affect the performance of piles.
In addition, when weathered rock is present, the boreholes should extend to a sufficient depth into the unweathered rock. Since the foundation type and design is not always finalized at the beginning of the site investigation, it may be prudent to drill holes deeper than originally estimated to allow some variation during project development. Not all boreholes need to be drilled to the same depth since shallower intermediate boreholes may provide adequate information for more lightly loaded foundations.
Also, the level of detailed sampling and in-situ testing may vary considerably from borehole to borehole, depending on the design needs. Pile-supported rafts on clays are often used solely to reduce settlement. In these cases, the depth of exploration is governed by the need to examine all strata that could contribute significantly to the settlement.
The borehole depth should extend to the level at which the soil stress increase from the imaginary raft is small and will not cause significant settlement. In practice, on many occasions, this would lead to an excessive and unnecessary depth of exploration so the engineer directing the investigation should terminate the exploration at the depth where the relatively incompressible strata have been reached.
The entire pile load, possibly with the addition of downdrag, will have to be borne by the stronger strata lying below the weak materials. This will increase the stress at the bottom of the piles and consequently the corresponding depth of boreholes.
General guidance can be provided from previous experience in the area. If any structure is likely to be affected by subsidence due to mining or any other causes, greater exploration depths than those recommended above may be required.
Atterberg limits, grain size distribution, em;n! Generalizedjlow chart to illustrate the likely geotechnical site investigation based on risk after Robertson, 4.
The basis for determining the spacing of boreholes is less logical, and spacing is based more on the variability of site conditions, type ofproject, performance requirements, experience, and judgment.
More boreholes and closer spacing is generally recommended for sites which are located in less developed areas where previous experience is sparse or non-existent. The following comments are given for planning purposes.
For buildings smaller than about m2 in plan area but larger than about m 2, a minimum of four boreholes where the ground surface is level, and the first two boreholes indicate regular stratification, may be adequate. Five boreholes are generally preferable at building comers and centre , and especially if the site is not level.
For buildings smaller than about m2 , a minimum of three boreholes may be adequate. A single ,borehole may be sufficient for a concentrated foundation such as an industrial process tower base in a fixed location with the hole made at that location, and where the general stratigraphy is known from nearby boreholes. The results of one borehole can be misleading, for example, drilling into a large boulder and misinterpreting as bedrock.
Many experienced geotechnical engineers know from direct experience or have personal knowledge that the consequences of drilling a single borehole can be significant. In practical terms, once a drill rig is mobilized to the site, the cost of an additional one or two boreholes is usually not large.
The preceding comments are intended to provide guidance on the minimum number of boreholes for smaller than the suggested structures where the perfonnance of the foundations are not particularly critical. Drilling of minimum number of boreholes should have a sound technical basis. The determination of the number of boreholes and spacing for larger, more complex, and critical projects fonns a very important part of the geotechnical design process, and cannot be covered by simple rules which apply across the entire country.
Establishing the scope of a geotechnical investigation and subsequent supervision requires the direction of an experienced geotechnical engineer. In particular it is good practice, whenever possible, to use both field and laboratory tests for soil strength and compressibility determinations.
The accuracy of the stratigraphy, as determined by geophysical methods such as seismic reflection or refraction, or resistivity measurements, should always be checked by borings or other direct observations.
Both approaches have advantages, disadvantages, and limitations in their applicability. The measurement of soil properties by in-situ test methods has developed rapidly during the last two decades. Improvements in equipment, instrumentation, techniques, and analytical procedures have been significant. In-situ test methods can be divided into two groups: logging methods and specific methods.
Commonly, the logging methods are penetration-type tests which are usually and economical. When based on empirical correlations, logging methods provide qualitative values ofvarious geotechnical parameters for foundation design. Specific methods are generally more specialized and often slower and more expensive to perform than the logging methods.
They are normally carried out to obtain specific soil parameters, such as shear strength or deformation modulus. The logging and the specific methods are often complementary in their use. The logging methods are best suited for stratigraphic logging with a preliminary and qualitative evaluation of the soil parameters, while the specific methods are best suited for use in critical areas, as defined by the logging methods, where more detailed assessment is required of specific parameters.
The investigation may include undisturbed sampling and laboratory testing. The logging method should be fast, economic, continuous, and most importantly, repeatable. The specific method should be suited to fundamental analyses to provide a required parameter.
One of the best examples of a combination of logging and specific test methods is the cone penetrometer and the pressuremeter. Common in-situ techniques are listed in Table 4. Between the late s and early s, the test was standardized using a mm O. The blows required to drive the split-barrel sampler a distance of mm, after an initial penetration of mm, is refelTed to as the SPT N value.
This procedure has been accepted internationally with only slight modifications. The number of blows for each of the three mm penetrations must be recorded. Standard Penetration Test results in exploratory borings give a qualitative guide to the in-situ engineering properties and provide a sample of the soil for classification purposes. This information is helpful in determining the extent and type of undisturbed samples that may be required.
TABLE 4. Qualitative comparison of subsoil stratification. See Section 4. Continuous evaluation of undrained shear strength in clays. Qualitative evaluation of compactness Undrained shear strength See Section 4.
Modulus of subgrade reaction. Bearing capacity. Evaluation of coefficient of permeability See Section 4. Results reliable to one order of magnitude are obtained only from long term, large scale pumping tests. Hvorslev Sherard et al. The split-barrel sampler commonly used in the United States often differs from such samplers used elsewhere in that the inner liner is not used.
In addition, it is generally recognized that in granular soils of the same density, blow counts increase with increasing grain size above a grain size of about 2 mm.
F or the foregoing reasons, it is readily apparent that the repeatability ofthe Standard Penetration Test is questiopable. In addition, relationships developed for SPT N value versus an exact density should be used with caution. The Standard Penetration Test is, however, useful in site exploration and foundation design and provides a qualitative Site Investigations 39 guide to the in-situ properties of the soil and a sample for classification purposes. The evaluation of the test results should be undertaken by an experienced geotechnical A detailed discussion of the possible errors in SPT results has been presented by Schmertmann and Skempton Overdrive sampling spoon.
Higher N-values usually result from overdriven sampler. Sampling spoon plugged by gravel. Higher N-values result when gravel plugs sampler, and resistance of an underlying stratum of loose sand could be highly overestimated.
Plugged casing High N-values may be recorded for loose sand when sampling below the groundwater table if hydrostatic pressure causes sand to rise and plug casing. Overwashing ahead of casing. Low N-values may result for dense sand since sand is loosened by overwashing. Drilling method. Not using the standard hammer drop Energy delivered per blow is not uniform European countries have adopted an automatic trip hammer, which currently is not in common use in North America Free fall of the drive hammer is not attained Using more than 1Yi tums of rope around the drum andior using wire cable will restrict the fall of the drive hammer.
The use of wash boring with a side discharge bit or rotary with a tricone drill bit and mud flush is recommended. Using drill holes that are too large Holes greater than mm in diameter are not recommended; use of large diameter-holes may decrease the blow count, especially in sands.
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