site investigation and geotechnical evaluation

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Jan 31, 2016 - Site Investigation and Boring Layout. ...... furnished with a tentative site plan locating the building(s), often these are still in the stage where.
KING FAHD UNIVERSITY OF PETROLEUM & MINERALS

CE552 FOUNDATION ENGINEERING: LITERATURE REVIEW: SITE INVESTIGATION AND BORING LAYOUT Revision No. Status Date

Rev.1 LITERATURE REVIEW 31st January 2016

PREPARED FOR DR. SAHEL ABDULJAUWAD KFUPM – DHAHRAN

Revision History

Rev.1

31st January, 2016

LITERATURE REVIEW

Hamzah M Beakawi g201552950

Rev.0

25th January, 2016

LITERATURE REVIEW

Hamzah M Beakawi g201552950

Revision No.

Date

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Site Investigation and Boring Layout.

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TABLE OF CONTENTS 1.0 INTRODUCTION .......................................................................................................................3 1.1 GEOTECHNICAL SITE INVESTIGATION..........................................................................3 1.2 IMPORTANCE OF SITE INVESTIGATION ........................................................................3 1.3 BOREHOLE AND BORING ..................................................................................................3 2.0 BORING LAYOUT AND PLANNING .....................................................................................4 2.1 GENERAL...............................................................................................................................4 2.2 SOWERS (1970)......................................................................................................................5 2.3 ASCE (1976)............................................................................................................................5 2.4 NAVFAC DM-7.1 (1982) ........................................................................................................7 2.5 IS: 1892-1979 (1985: REAFFIRMED 2002) ................................................................................8 2.6 JEA (1990) ...............................................................................................................................9 2.7 BOWLES (1991) ......................................................................................................................10 2.8 EM 1110-1-1804 (2001) ........................................................................................................12 2.9 FHWA (2002) ........................................................................................................................12 2.10 SBC 303 (2007)......................................................................................................................12 2.11 EN 7 (2008) ............................................................................................................................13 2.12 DID (2009) .............................................................................................................................15 2.13 QCS (2014) ............................................................................................................................16 LIST OF REFERENCES ................................................................................................................17 List of Tables Table 1: SOWERS (1970) Boring Depth ..........................................................................................19 Table 2: SOWERS (1970) Spacing of Boreholes ..............................................................................19 Table 3: NAVFAC DM-7.1 (1982) Boreholes Spacing and Numbers ..............................................19 Table 4: NAVFAC DM-7.1 (1982) Boring Depth ............................................................................20 Table 5: IS 1892-1979 (1985) Depth of Exploration.........................................................................20 Table 6: JEA (1990): Boring Layout .................................................................................................21 Table 7: EM 1110-1-1804 (2001) Boring Layout .............................................................................23 Table 8: FAHWA (2002) Boring Layout ..........................................................................................25 Table 9: SBC 303 (2007) Boring Layout ..........................................................................................33 Table 10: DID (2009) Boring Layout ................................................................................................34 Table 11: QCS (2014) Minimum Depth of Boreholes ......................................................................35

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List of Figures Figure 1: ASCE (1976): Depth of Boring Criteria ............................................................................37 Figure 2: IS 1892-1979 (1985) Depth of Exploration .......................................................................38 Figure 3: JEA (1990) Boring Layout .................................................................................................39 Figure 4: EN 7 (2008) Depth of Boring - 1 .......................................................................................40 Figure 5: EN 7 (2008) Depth of Boring - 2 .......................................................................................41 Figure 6: EN 7 (2008) Depth of Boring - 3 .......................................................................................42 Figure 7: EN 7 (2008) Depth of Boring - 4 .......................................................................................43 Figure 8: EN 7 (2008) Depth of Boring - 5 .......................................................................................44 Figure 9: EN 7 (2008) Depth of Boring - 6 .......................................................................................45 Figure 10: EN 7 (2008) Depth of Boring - 7 .....................................................................................46 Figure 11: EN 7 (2008) Depth of Boring - 8 .....................................................................................47 Figure 12: EN 7 (2008) Depth of Boring - 9 .....................................................................................48 Figure 13: EN 7 (2008) Depth of Boring - 10 ...................................................................................49 Figure 14: EN 7 (2008) Depth of Boring - 11 ...................................................................................50 Figure 15: DID (2009) Depth of Boring - 1 ......................................................................................51 Figure 16: DID (2009) Depth of Boring - 2 ......................................................................................52 Figure 17: DID (2009) Depth of Boring - 3 ......................................................................................53

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1.0

INTRODUCTION

1.1

GEOTECHNICAL SITE INVESTIGATION Geotechnical site investigations in general are performed usually by either Civil Engineers

(Geotechnical) or Engineering Geologists. Their main purpose is to determine the ground (soil and rock) properties and characteristics (i.e. physical, chemical, etc) for a certain site / project. Geotechnical investigations may be performed into two methods: the first is known as Reconnaissance (Surface Investigation/Exploration), and the second is known as subsurface investigation/exploration.

1.2

IMPORTANCE OF SITE INVESTIGATION Failures of structures which caused due to ground problems are considered the most costly

at the construction field. The average cost of the foundation is approximately 3.0 to 4.0 % of the total project’s budget. Likewise, the average cost of the geotechnical investigation is approximately 0.5 to 1.0 % of the project’s budget. “You pay for a ground investigation whether you have one or not”, to say the least.

1.3

BOREHOLE AND BORING “A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A

borehole may be constructed for many different purposes, including the extraction of water, other liquids (such as petroleum) or gases (such as natural gas), as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement, as a pilot hole for installing piers or underground utilities, for geothermal installations, or for underground storage of unwanted substances, e.g. in Carbon capture and storage.

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While boring is the process of enlarging a hole that has already been drilled (or cast), by means of a single-point cutting tool (or of a boring head containing several such tools), for example as in boring a gun barrel or an engine cylinder. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internaldiameter counterpart to turning, which cuts external diameters”.

2.0

BORING LAYOUT AND PLANNING

2.1

GENERAL “As a rule of thumb; there are no binding rules on either numbers or depths of borings. It

will rely on the Engineering judgment and site discovery”. In general, and to estimate the concept of boring layout planning (the depth specifically), Tomlinson suggest the following: “The depth to which borehole should be sunk in ground is by the depth of soil affected by the foundation bearing pressure”. “It is impracticable to determine the spacing, depth and number of boreholes before an investigation begins because these depend on the type of proposed structure and uniformity of the formations. Ordinarily, a preliminary estimate of boring layout is made based on experience, project detail and site geology”. However, following are different methodologies of boring layout:

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2.2

SOWERS (1970) In 1970, George B. Sowers et al., “Introductory Soil Mechanics and Foundation” provided

wide range of boreholes’ spacing and depth based on type of structure and number of stories. Refer to Table 1 and Table 2. For hospitals and office buildings, Sowers also use the following rule to determine the boring depth: For light steel or narrow concrete buildings: Equation 1

For heavy steel or wide concrete buildings: Equation 2

Where; Db: Depth of boring, in meters. S: Number of stories. # When deep excavations are anticipated; the depth of boring should be at least 1.5 times the depth of excavations.

2.3

ASCE (1976) American Society of Civil Engineers in 1976 stated the following procedure to determine

the depth, number and spacing of boring: Depth of Boring: Borings or test pits should extend through any unsuitable or questionable foundation materials and sufficiently deep into firm stable soils that significant settlement will not develop from compression of that stratum or deeper lying soils under the load of the structure. A commonly used rough rule of thumb is to carry borings to such depth that the net increase in soil Rev.1-LITERATURE REVIEW

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stress under the weight of the structure is less than 10% of the average load of the structure, or less than 5% of the effective stress in the soil at that depth, whichever gives the lesser depth, unless bedrock or dense soils known to lie on rock are encountered first. Refer to Figure 1. D1: is the depth at which the net increase in soil stress under the weight of the structure is less than 10% of the average load of the structure. D2: is the depth at which the net increase in soil stress under the weight of the structure is less than 5% of the effective stress in the soil at that depth. However, for a square structure / foundation and using (2 vertical: 1 horizontal) stress distribution method for dry homogenous soil; usually the smallest depth is (D2) and can be determined using the equation below: ( (

)

)

Equation 3

Where; Db(min): Minimum depth of the borehole, in meters. Df: Depth of foundation, in meters. B: Width of foundation, in meters. If deep excavations are necessary, the explorations should be carried to at least 1.5 times the depth of excavation in order to locate and determine peizometric levels in any aquifers that may exist below the level of excavation (similar to sowers). This is necessary to permit planning dewatering that may be required in such deep excavations to avoid heave or disturbance to the bottom of the excavations. If there is a possibility of artesian aquifers under the area, explorations should be carried even deeper. Exploration of the bedrock may be necessary where, for example, loads are to be carried to rock, where irregularity in the surface would affect settlement, where there may be solution effects, or where there may be construction problems. This requires extending the borings into the rock by Rev.1-LITERATURE REVIEW

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core boring methods. The minimum depth of core boring into bedrock is usually 10 ft (3 m). This depth may be depended upon only where geological conditions are sufficiently well known, where the rock is readily identifiable, and where it is known that the rock surface is reasonably level and free of boulders or severe weathering effects. Where the character of the rock is not known or where there may be boulders or irregular weathering, the core borings should be carried deeper, the final depth being determined by the conditions found and the method of founding the structure. If rock bearing foundations are planned, core borings should be carried to well below the bottom of founding elements, especially if there are adverse rock conditions such as deep weathering or solution effects. Number and Spacing of Boring: Frequently, borings are made in several stages. In the first stage, drive sample type borings usually are made. Based upon these findings, additional borings may be made between the initial borings to define soil conditions in better detail. Samples in these additional borings may be taken either by drive sampler or may be undisturbed. Samples may be taken continuously or at selected intervals. The selection of sample type and frequency is determined by soil conditions and requirements of the structure. Where soil conditions are favorable, especially for small structures, all borings may be completed in the first phase of the investigation.

2.4

NAVFAC DM-7.1 (1982) In 1982, the Naval Facilities Engineering Command (U.S.) stated in their design manual

(DM-7.1) a wide range of boring spacing & number and depth based on the type of structure and foundation, refer to Table 3 and Table 4 respectivally.

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2.5

IS: 1892-1979 (1985: Reaffirmed 2002) Indian Standard “Code of Practice for Subsurface Investigation for Foundation” stated the

following criteria in order to determine the boring depth, spacing and number. Depth of Boring: The depth of exploration required depends on the type of proposed structure, its total weight, the size, shape and disposition of the loaded areas, soil profile, and the physical properties of the soil that constitute each individual stratum. Normally it should be 1.5 times the width of the footing below the foundation level. In certain cases, it may be necessary to take at least 1.0 borehole or cone test or both to 2.0 times the width of the foundation. If a number of loaded areas are in close proximity the effect of each is additive. In such cases, the whole of the area may be considered as loaded and exploration should be carried out up to 1.5 times the lower dimension. In weak soils, the exploration should be continued to a depth at which the loads can be carried by the stratum in question without undesirable settlement and shear failure. In any case, the depth to which seasonal variations affect the soil should be regarded as the minimum depth for the exploration of sites. But where industrial process affect the soil characteristics this may be more. The presence of fast growing and water seeking trees also contributes to the weathering processes. An estimate of the variation with depth of the vertical normal stress in the soil arising from foundation loads may be made on the basis if elastic theory. The net loading intensity at any level below a foundation may be obtained approximately by assuming a spread load of (2 vertical: 1 horizontal) from all sides of foundation, due allowance being made for the overlapping effects of load from closely spaced footings. The depth of exploration at the start of the work may be decided as given in Table 5 and Figure 2, which may be modified as exploration proceeds, if required. In simple way, the depth of boreholes to be drilled varies from 1.5 to 2.0 times width of foundation below the base of foundation.

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Spacing and Number of Boring: Horizontal spacing between the boreholes to be decided as below: -

Buildings: 10 – 30 meters apart.

-

Roads: 30 – 300 meters apart.

-

Landslides: at least 5.0 boreholes in line for profile.

The number of boreholes may be decided as below: -

1.0 borehole for about 200 – 400 sq.m of area that is to be loaded.

-

For residential house 2.0 boreholes are required, and for a long barrack 3.0 to 4.0 boreholes are advisable.

-

For a rectangular building covering 1000 – 2000 sq.m, 1.0 borehole near each corner and 1.0 borehole in the middle, i.e. 5.0 boreholes are recommended.

2.6

JEA (1990) Jordan Engineers association stated in 1990 the following criteria to determine the number,

spacing and depth of boring. Depth of Boring: the required depth of boreholes based on number of stories and area of the structure are given in Table 6. Spacing and Number of Boring: spacing and number of boreholes can be determined as following: -

For multistory building: 1.0 borehole every 200 – 400 sq.m.

-

For Large plan areas (manufacturing plants): 50.0 m spacing with areas greater than 10,000 Sq.m.

-

Foe highways: 60 – 90 m spacing. In uniform conditions may increase to 300 – 600 m. Or increase the spacing if test pits are used to replace some boreholes.

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-

For bridges: Depending on the width of bridge, 1.0 – 3.0 boreholes per pier or abutment.

-

For high cuts: at least 3.0 boreholes to draw a profile. This profile will be repeated every 20 – 30 m in lateral direction depending on the uniformity.

-

For culverts / retaining walls: 1.0 borehole every 30.0 m spacing.

# The boreholes layout should provide information on the soil strata in at least two perpendicular planes as shown in Figure 3. More details are shown in Table 6.

2.7

Bowles (1991) Joseph E. Bowles, “Foundation Analysis and Design” in 1991 stated the following criteria

for number, spacing and depth of boring. There are no clear-cut criteria for determining directly the number and depth of borings (or probings) required on a project in advance of some subsurface exploration. Spacing and Number of Boring: -

For buildings a minimum of 3.0 borings, where the surface is level and the first two borings indicate regular stratification, may be adequate.

-

5.0 borings are generally preferable (at building corners and center), especially if the site is not level.

-

On the other hand, 1.0 boring may be sufficient for an antenna or industrial process tower base in a fixed location with the hole made at the point.

-

4.0 – 5.0 borings are sufficient if the site soil is nonuniform (both to determine this and for the exploration program). This number will usually be enough to delineate a layer of soft clay (or a silt or peat seam) and to determine the properties of the poorest material so that a design can be made that adequately limits settlements for most other situations.

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Additional borings may be required in very uneven sites or where fill areas have been made and the soil varies horizontally rather than vertically. Even though the geotechnical engineer may be furnished with a tentative site plan locating the building(s), often these are still in the stage where horizontal relocations can occur, so the borings should be sufficiently spread to allow this without having to make any (or at least no more than a few) additional borings. In practice, the exploration contract is somewhat open as to the number of borings. The drilling operation starts. Based on discovery from the first holes (or CPT, DMT, etc.) the drilling program advances so that sufficient exploration is made for the geotechnical engineer to make a design recommendation that has an adequate margin of safety and is economically feasible for the client. Sometimes the exploration, particularly if preliminary, discloses that the site is totally unsuitable for the intended construction. Depth of Boring: Borings should extend below the depth where the stress increase from the foundation load is significant. This value is often taken as 10 percent (or less) of the contact stress qo. For the square footing of the vertical pressure profile shows this depth to be about 2B. -

Since footing sizes are seldom known in advance of the borings, a general rule of thumb is 2.0 times the least lateral plan dimensions of the building or 10 m below the lowest building elevation. Where the 2 times width is not practical as, say, for a one-story warehouse or department store, boring depths of 6 to 15 m may be adequate.

-

On the other hand, for important (or high-rise) structures that have small plan dimensions, it is common to extend one or more of the borings to bedrock or to competent (hard) soil regardless of depth.

-

It is axiomatic that at least one of the borings for an important structure terminates into bedrock if there are intermediate strata of soft or compressible materials. Summarizing, there are no binding rules on either the number or the depth of exploratory soil borings. Each site must be carefully considered with engineering judgment in combination with site discovery to finalize the program and to provide an adequate margin of safety.

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2.8

EM 1110-1-1804 (2001) Earth Manual, EM 1110-1-1804 in 2001 (after Dunlap 1980) suggested different criteria to

determine and select the boring number, spacing and depth. Details are shown in Table 7.

2.9

FHWA (2002) Federal Highway Administration (FHWA), suggested different criteria to determine and

select the boring number, spacing and depth. Details are shown in Table 8.

2.10 SBC 303 (2007) Saudi Building Code 303, suggested different criteria to determine and select the boring number, spacing and depth. Details are shown in Table 9. Taking into consideration the following notes: -

If possible, standard penetration test SPT shall be performed in all sites.

-

If questionable soils do exist underneath the building, a minimum of 1.0 borehole shall penetrate all layers containing this soil.

-

Seasonal changes in groundwater table and the degree of saturation shall be considered.

-

If sufficient data is available, a registered design professional may use number and depth of boreholes that are different from the tabular values.

-

For foundation of pole and towers, a minimum 1.0 borehole with sufficient depth shall be located in the center of the foundation.

-

Depth is measured from level of foundation bottom.

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-

Number of boreholes shall be selected by a registered design professional based on variations in site conditions, and contractor shall advice if additional or special tests are required.

2.11 EN 7 (2008) Euro-Code 7 stated the following strategies to determine number, spacing and depth of boring based on type of structure. Number and Spacing of Boring: The following spacing of investigation points should be used as guidance: -

For high-rise building and industrial structures, a grid pattern with points at 15 – 40 m distance.

-

For large-area structure, a grid pattern with points at not more than 60 m distance. For linear structure (roads, railways, channels, pipelines, dikes, tunnels and retaining wall), a spacing of 20 – 200 m is adequate.

-

For special structure (e.g. bridges, stacks and machinery foundation), 2.0 – 6.0 investigation points (boreholes) per foundation will be suitable.

-

For dams and weirs, 25 – 75 m distance along vertical sections is required.

Depth of Boring: For the investigation depth Za (in meters) the following values should be used as guidance. The reference level for Za is the lowest point of the foundation of the structure or structural element, or the excavation base. Where more than one alternative is specified for establishing Za, the one which yields the largest value should be applied. -

For high-rise structures and civil engineering projects, the largest value of the following should be applied:

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Equation 4

Where; bf: Smallest side length of the foundation. Refer to Figure 4. -

For raft foundations and structures with several foundation elements whose effects in deeper strata are superimposed on each other: Equation 5

Where; bB: Smallest side length of the Structure. Refer to Figure 5. -

For embankments and cuttings, the larger value of following conditions should be met: -

For dams: Equation 6

Where; h: embankment height. Refer to Figure 6. -

For Cuttings: Equation 7

Where; h: dam height or depth of cut. Refer to Figure 7. -

For roads and airfields: Equation 8

Refer to Figure 8. -

For trenches and pipelines, the larger value of: Equation 9

Where; hAh: Width of excavation. Refer to Figure 9. -

For small tunnels and caverns: Equation 10

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Where; bAb: Width of excavation. Refer to Figure 10. The groundwater conditions should be taken into account. -

For excavations where the piezometric surface and the groundwater tables are below the excavation base, the larger value of the following conditions should be met: (

)

Equation 11

Where; t: embedded length of the support; and h is the excavation depth. Refer to Figure 11. -

For excavations where piezometric surface and the groundwater tables are above the excavation base, the larger value of the following should be met: (

)

(

)

Equation 12

Where; H: Height of the groundwater level above the excavation base. Refer to Figure 12. -

For cut-off walls: Equation 13

Refer to Figure 13. -

For piles, the following three conditions should be met: Equation 14

Where; Df: Pile base diameter; and bg is the smallest side of the rectangle circumscribing the group of piles forming the foundation at the level of pile base. Refer to Figure 14.

2.12 DID (2009) Department of Irrigation and Drainage (Government of Malaysia) provided in 2008, different criteria to determine the boring number, spacing and depth. Refer to Table 10 and Figure 15 through Figure 17. Rev.1-LITERATURE REVIEW

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2.13 QCS (2014) Qatar National Construction Standards (QCS) 2014, suggested different criteria to determine and select the boring number, spacing and depth. Details are shown in Table 11. Taking into consideration the following notes: -

The depth of boreholes is measured from foundation level.

-

S is the number of floors.

-

For structures small in plan area, exploration should be made at minimum of 3.0 boreholes, unless other reliable information is available in the immediate vicinity. Where a structure consists of a number of adjacent units, 1.0 exploration borehole per unit may suffice.

-

For piles the depth of boreholes is at least below the depth of pile tip by 5.0 meter or 5D (where D is the diameter of the pile at the toe) whichever is greater.

-

For roads, the depth of boreholes shall be greater than 2.0 m below the proposed formation level.

-

For trenches, pipelines and tunnels, the depth of boreholes shall be the larger value of: Equation 15

Where; B: Width of excavation; and D is the diameter or equivalent diameter of the tunnel / underground structures.

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LIST OF REFERENCES 

“Lecture of Foundation Engineering.” CE 552, KFUPM, Saudi Arabia. Dr. Sahel Abduljauwad. 2016.



“NAVFAC DM-7.1”, 1982. .



“IS: 1892-1979”, 1985.



“Foundation Analysis and Design”, Bowles, 1991.



“EM 1110-1-1804”, 2001.



“FHWA”, 2002.



“SBC 303”, 2007.



“EN 7”, 2008.



“DID Manual”, 2009.



“QCS”, 2014.

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TABLES

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Table 1: SOWERS (1970) Boring Depth Building Width 30.5 m

Building Width 61 m

Building Width 122 m

Number of Stories Depth of Boring (m) 1

3.5

3.7

3.7

2

6.1

6.7

7.0

3

10.1

12.5

13.7

4

16.2

20.7

24.7

5

24.1

32.9

41.5

Table 2: SOWERS (1970) Spacing of Boreholes Type of Project

Spacing (m)

Multistory Building

10 – 30

One Story Industrial Plants

20 – 60

Highways

250 – 500

Residential Subdivision

250 – 500

Dams and Dikes

40 – 80

Table 3: NAVFAC DM-7.1 (1982) Boreholes Spacing and Numbers Areas of Investigation

Boring Layout

New Site of Wide Extent

Spacing 60 – 150 m apart so that the area between 4 borings includes about 10% of the total area. For detailed exploration, additional borings to be added in order to establish geological sections.

Development of Site on Soft Compressible Soil

Spacing 30 – 60 m at possible building locations. Add intermediate borings when building site is determined.

Large Structure with Separate Closely Footings

Spacing 15 m in both directions, including borings at possible exterior foundation walls, at machinery and elevators pits.

Low-Load warehouse building of large area

Minimum of 4 borings at corners and intermediate borings at interior foundations.

Isolated Rigid Foundation

For foundation 230 – 930 sq.m in area, minimum of 3 borings around perimeter. Add interior borings depending on initial results.

Isolated Rigid Foundation

For foundation < 230 sq.m in area, minimum 2 borings at opposite corners. Add more for erratic conditions.

Major Waterfront Structures, e.g. dry docks

Spacing = 9.0 m below the lowest part of foundation unless rock is encountered at shallow depth. And depth of boring should also extend to depth where increase in vertical stress for combined foundation is less than 10 % of effective overburden stress.

Isolated Rigid Foundation

>= 9.0 m below the lowest part of foundation unless rock is encountered at shallow depth. And depth of boring should also extend to depth where vertical stress decrease for combined foundation to 10 % of bearing pressure.

Long Bulkhead or Wharf Wall

Extend to depth below dredge line between 0.75 to 1.5 times unbalanced height of wall. Borings should reach top hard stratum if stratification indicates deep stability problem.

Slope Stability

Extend to an elevation below active or potential failure surface and into hard stratum, or to a depth for which failure is unlikely because of geometry of cross section.

Deep Cuts

Extend to depth between 0.75 and 1.0 times base width of narrow cuts. Where cut is above groundwater in stable materials, depth of 1.2 to 2.4 m below base may suffice. Where base is below groundwater, determine extent of previous strata below base.

High Embankment

Extend depth between 0.5 to 1.25 time horizontal length of side slope in relatively homogenous foundation. Where soft strata are encountered, borings should reach hard material.

Dams and WaterRetention Structures

Extend to depth of 0.5 base width of earth dams or 1.0 to 1.5 times height of small concrete dams in relatively homogenous foundation. Borings may terminate after penetration of 3.0 to 6.0 m in hard and impervious stratum if continuity of this stratum is known from reconnaissance.

Table 5: IS 1892-1979 (1985) Depth of Exploration Type of Foundation

Depth of Exploration

Isolated Spread Footing or Raft

1.5 times the width. Refer to Figure 2.

Adjacent Footing with Clear Spacing less than 2 times width.

1.5 times the length. Refer to Figure 2.

Adjacent Rows of Footings

Refer to Figure 2.

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Table 5 (Cont’d): IS 1892-1979 (1985) Depth of Exploration Type of Foundation

Depth of Exploration

Pile and Well Foundations

1.5 times width of structure from the bearing level (toe of pile or bottom of well).

Road Cuts

= bottom width of the cut.

Fill

2.0 m below ground level or equal to the height of the fill whichever is greater.

Table 6: JEA (1990): Boring Layout Minimum Number and Depth of Boring Measured Below Depth of Foundation Number of Floors

250 sq.m; minimum 5 continues samples at each pier. For Cohesionless Soil: Obtain samples or soundings as for cohesive soil. For Competent Rock: Trace formation at each pier, if in doubt of rock quality; drill at least 6.0 m into formation.

Height: 3 – 6 m; space borings at 300 m intervals. Levees

Height: 6 – 12; space borings at 230 m intervals. Height: 12 – 18; space borings at 150 m intervals.

Earth Dams

See Remarks Column

6.0 m. At least equal to height of levee. At least equal to height of levee.

At least equal to height of dam or 2 times the maximum head, whichever is greater. Trace the top of impervious zone.

For Cohesive Soil: Continues undisturbed samples. For Cohesionless Soil: Continues undisturbed samples or soundings. Locate borings along centerline of proposed structures.

For Preliminary Investigation: Maximum stress occurs approximately at midpoint of slope between the centerline and toe of the proposed structure. Establish a square grid pattern of borings located upstream and downstream of dam centerline near midpoint of slope in direction with respect to dam centerline. For Primary Investigation: Trace the limits of various strata, e.g. SAND. Trace power plant, spillways and other control structures as rigid frame structures. Obtain adequate subsurface data to define the character of the abutments. For Cohesive Soil: Continues undisturbed samples. For Cohesionless Soil: Continues undisturbed samples or soundings.

Borrow Pits

Use a 60 m grid spacing

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Maximum depth to water table or working depth of equipment.

Disturbed samples are satisfactory; may use augers to obtain samples.

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Table 7 (Cont’d): EM 1110-1-1804 (2001) Boring Layout Structure Type

Number and Spacing of Boring

Roads

For 2 lane highways: 1 boring per 150 along centerline and at each major change of soil profile. For Multilane highways: 1 boring per 75 m along centerline; borings may be staggered.

Depth of Boring

Remarks

For excavation and level terrain; 3.0 m below level finished grade.

For Cohesive Soil: Continues undisturbed samples.

For compacted embankments: treat as for levees.

For Cohesionless Soil: Continues undisturbed samples or soundings.

For rock: extend 0.75 m into rock.

For Preliminary Investigation: Place borings at 300 m intervals in square grid patterns to a depth of 6.0 m. Samples may be disturbed. Site facilities based upon preliminary investigation. Airfields

See Remarks Column

See Remarks Column

Houses

1 boring per 8000 sq.m in new subdivision. 1 boring per individual lot.

To unweathered rock or 4.5 m, whichever is lesser.

Rev.1-LITERATURE REVIEW

For Primary Investigation: For runways; site 2 lines of borings in a square grid pattern at 30 m on either side of runway centerline to a depth of 6.0 m or 1.5 m into rock. For taxiway; place borings at 60 – 76 m intervals along centerline to a depth of 6.0 m. For apron; place borings at 60-75 m in square grid pattern to a depth of 6.0 m

Obtain samples at 1.5 m intervals using undisturbed sampling techniques for cohesive soils or undisturbed soundings techniques for cohesionless soil.

Page 24 of 53

Site Investigation and Boring Layout.

Table 8: FAHWA (2002) Boring Layout

General Notes: It is relatively easy to set guidance for the initial or preliminary stages of the investigation. The final stage of geotechnical design will require greater analysis; each site or case will have specific requirements.

Type of Structure

Study Level or Expected Foundation Type

Preliminary Study 1- Large One-Story Structure, such as warehouses, commercial centers and manufacturing facilities. Footings, Final Report

The Investigation density or effort will depend on the design stage, the size and type of structure and lot size, plus other site-specific factors such as geometry of the site and structures. Thus, these suggestions can only be called “guidelines” and are not standards or rules to be followed; the only standard that can be applied is that the investigation provides the necessary information. The investigation density will depend on specific subsurface conditions and the type of and location of structure.

The purpose of the investigation must be to obtain reliable subsurface information. The investigation is usually performed using borings with SPT or soundings with CPT. In the case of SPT borings; the engineer should include subsurface characterization using undisturbed samples, consolidation tests and atterberg limits; frequent use of continues sampling instead of more-usual 1.5 m intervals is encountered. Use of the CPT will generate much continues data by means of correlations. Other tests within boreholes (e.g. vane shear test) should be considered. Finally, a design-build project might have different requirements than a conventional design-bid-build project. Note: On most jobs it is necessary tp reasonably determine the water level. This task usually requires observations wells that must be read for some time. The client should be made aware of the importance of reliably determining the approximate water level. Be aware that several water levels may exist from perched water tables.

Investigation Density: Suggestion For Study Locations or Boring Density or Frequency of Geophysical Traverses (Double for Slopes)

Suggestions For Depth of Exploration

Every 1394 sq.m, minimum 5 borings, approximately 1.0 boring per 8094 sq.m, maximum spacing 91.5 m.

Take at least 1.0 of the borings or soundings to a depth 10 times the expected width of footings; take the remainder to 4 times this width (measured from bottom of footing). If piles are expected, exploration depth should reach 10 times the pile width below the pile tips.

Every 233 to 650 sq.m, typical spacing 18.3-36.6 m in each direction, 4 corners and at center, 3 to 4 borings per 4047 sq.m. In some locations, consider test pits to substitute for borings.

Borings should extend at least 3.0 footing widths below the expected depth of footing, except for special situations, such as analysis of fills that might induce settlements, where deeper borings and specific tests might be required. In karst regions, additional exploration (geophysics) might be necessary.

Rev.1-LITERATURE REVIEW

Page 25 of 53

Site Investigation and Boring Layout.

Type of Structure

1- Large One-Story Structure, such as warehouses, commercial centers and manufacturing facilities.

2- Isolated Structures such as relatively-small selfstanding buildings within larger commercial lots

3- Two-Story and 3Story Structures, rectangular tanks, multistory commercial centers, walkup apartments, small parking buildings and small industrial buildings

4- Buildings taller than 4 stories, hotels, large parking buildings, large housing apartments or condominiums, structures with footprints greater than 929 sq.m, auditoriums, stadiums or sports centers.

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes)

Suggestions For Depth of Exploration

Piles, Final Report

Every 372 to 836 sq.m, typical spacing 24.4-42.7 m between borings, 4 corners and center; 3 to 4 borings every 3716 sq.m.

Borings should be drilled at least 10 pile diameters below pile tips.

Preliminary

1.0 boring per building - greatly depends on building geometry and site conditions; structures on slopes will require greater investigation density and cross-sections

The boring should be taken to a depth no less than 2.0 times the building width. Any new fill thickness will induce settlements and affect investigation requirements.

Final

3.0 borings lengthwise or diagonal, no less than 1.0 boring per 233 sq.m, maximum spacing 21.3 m; as above, greatly depends on building geometry and site conditions structures on slopes will require greater investigation density and cross-sections.

The depth of final-study borings depends on conditions found while drilling and the geometry of fill to be placed. For pile foundations, take borings at least 10 times the pile width. For footings, borings will typically be 3 to 5 times the footing width, with at least one boring taken to a depth similar to the building width.

On Footings

Every 233 sq.m, minimum 5 borings depending on geometry (e.g., corners and center). Distance between borings should be 15.25 to 30.5 m.

At least one of the borings should be taken to a depth 10 times the footing width; the remaining borings can be taken to 4 times the expected footing width (measured below the footing).

On Piles

Every 464.5 sq.m, minimum 5 borings depending on geometry (e.g., corners and center). Distance between borings should be 30.5 to 45.7 m.

The borings should surpass the pile tips by approximately 10 times the pile diameter.

Mat or Footings

For preliminary studies, do at least 1.0 boring per 1858 sq.m of lot size, or per 929 sq.m of building footprint, if known. For a final investigation, do a boring or sounding every 185.8 to 464.5 sq.m of footprint, with at least 5.0 SPT borings or CPT soundings, or combination. Typical spacing for borings or soundings will be 19.8 to 30.5 m. Concentrated loads require further investigation, depending on footprint geometry.

For preliminary investigation, take at least one of the borings to a depth 10 times the expected footing width, or 3 times the mat width. For a final report, go to 3 times the mat width or 4 times the footing width. If a preliminary report was not done before the final report, also include deep borings as specified for preliminary report.

Rev.1-LITERATURE REVIEW

Page 26 of 53

Site Investigation and Boring Layout.

Type of Structure

4- Buildings taller than 4 stories, hotels, large parking buildings, large housing apartments or condominiums, structures with footprints greater than 929 sq.m, auditoriums, stadiums or sports centers.

5- Initial Review of large land parcels that will be subdivided into large commercial or housing developments, to be followed by subsequent analysis and designs as the properties are developed (e.g. strip malls)

6- For housing developments, with the following exception: In karst areas, alternate supplementary or complementary methods should be considered, in addition to SPT borings or continuous soundings. Resistivity lines are indicated for many cases, although other methodologies also exist and should be considered to improve Interpretations from borings. Consider cross-hole seismic surveys (In karst do not use surface Seismic). Photointerpretation analyses are Essential. In some cases. GPR could be usable. See #8.

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes)

Piles

Conceptual

Predevelopment

Preliminary

Rev.1-LITERATURE REVIEW

Suggestions For Depth of Exploration

For a preliminary investigation, do one boring for each 929 sq.m of building footprint. For a final investigation, do one boring every 464.5 sq.m, minimum 5 borings or soundings, spaced 24.4 to 36.6 m apart. If drilled shafts are used, follow FHWA guidelines: one boring per shaft for shaft diameters (f) greater than 1.83 m; 1.0 boring per 2 shafts for f of 1.22 m to 1.83 m; 1.0 boring per 4 shafts for f < 1.22 m.

The depth of borings should exceed the length of piles by 10 to 20 pile diameters. Although investigation density might be less than for spread footings, beware of false sense of security using piles.

One boring every 1114.8 to 3344.5 sq.m; if site has been previously filled considers other borings with continuous sampling.

The required depth is that which answers important questions at time of lot purchase or before design. Settlements from compression of soft soils, and rippability, are usually important factors to consider. Detailed site reconnaissance and photo interpretation is important.

1.0 boring every 743.2 to 1486.5 sq.m

Once the design of final grades is complete or once the footprint of buildings has been determined, use guidelines shown for other sections of this list. For example, for housing projects, see #6; for industrial projects, see #10.

1.0 SPT boring or CPT sounding every 16187.4 sq.m, minimum 4 borings. Approximate spacing 91.45 to 182.9 m. In karst zones, do at least one geophysical survey, L=91.45 m, every 40468.6 sq.m.

For housing developments, the width and thickness of necessary fills are determining factors in planning of a geotechnical investigation. The borings should be extended below any compressible layer that will be affected or below zones where cavities might be present. Drill borings or take soundings to a depth at least 15 times the expected footing width, or 4.0 times the width of the houses or structures that are being designed, measured from bottom of footing.

Page 27 of 53

Site Investigation and Boring Layout.

Type of Structure

6- For housing developments, with the following exception: In karst areas, alternate supplementary or complementary methods should be considered, in addition to SPT borings or continuous soundings. Resistivity lines are indicated for many cases, although other methodologies also exist and should be considered to improve Interpretations from borings. Consider cross-hole seismic surveys (In karst do not use surface Seismic). Photointerpretation analyses are Essential. In some cases. GPR could be usable. See #8.

7- Multifamily housing in long apartment rows, walkups, 2 storeys or more

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes)

Final

Preliminary

m. In karstic zones, also do a geophysical survey every 20234.3 sq.m, approximately.

Same as above, although shallower borings are feasible if fill width and extent are determined for final stage. Any areas with slopes on fill, or into natural soil, will require at least 2 to 3 borings perpendicular to slope direction, repeating groups of borings every 24.4 to 48.8 m. Consider cross-hole seismic refraction in karst areas.

1.0 CPT sounding or SPT boring every 3 to 6 housing modules. Distance between boreholes no greater than

Take borings or soundings one to 3.0 times the building width.

On relatively flat lots, do a 1.0 boring every 8093.7 sq.m or every 10 to 25 houses (obviously depends on lot sizes). Minimum suggested number of borings is 8 per site. Projects with sloped ground or fill slopes require further analysis. Maximum boring spacing approximately 76.2 to 122

122 m or 3 borings every 1114.8 sq.m.

Final

8- Isolated structures with large loads, e.g., transmission towers, or unspecified loads such as

Suggestions For Depth of Exploration

Footings or Piles

electrical substations, distribution points, transformer pads

Rev.1-LITERATURE REVIEW

One boring every 371.6 sq.m and at least 2.0 per building, spaced 12.2 to 30.5 m apart.

Take borings or soundings at least 2.0 times the building width. For lower buildings with less-intense loading, consider some shorter borings.

Do at least 1.0 boring per location (large structures might require at least 1.0 boring per footing or pad or leg). For narrow transformer banks, drill a boring every 6.0 to 9.1 m along the length of the structure. Do at least 2 borings per structure and 1.0 boring per 232.3 sq.m.

For new or geotechnicallyunknown locations, refer to Case 1. More than 1.0 boring could be required, depending on results and possible foundation problems. Unless it has been established that bearing capacity is not a problem, take borings or soundings below footings 3 times footing width or 5 times below probable tip of piles. Consider seismic refraction at each location if need for rock drilling is suspected. Geologic reconnaissance is highly recommended.

Page 28 of 53

Site Investigation and Boring Layout.

Type of Structure

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes)

Suggestions For Depth of Exploration

Generally

For injection sinkholes, borings should reach the proposed depth of injection. A reasonable number appears to be 3 boreholes per sinkhole, but this will depend on sinkhole size and flows to be injected.

The borings should be complemented with resistivity surveys, cross-hole seismic refraction surveys, or large-scale injection tests as the first injection well is constructed. The depth of injection will depend on the subsurface profile and the presence of nearby structures, and generally will surpass 30.5 m. Borings in fragmented rock should be drilled using NX or larger cores, not SPT.

10- Lots for industrial development, not including

Preliminary Study

1.0 boring every 8093.7 to 16187.4 sq.m (adjust density to include structure types, e.g., warehouses); typical spacing 152.4 m

Not less than 9.1 – 12.2 m into competent layer below any compressible layers.

geotechnical design of each structure

Final Report

2.0 borings per 4046.8 (adjust density if study includes preliminary or final geotechnical analysis for specific welldefined structures); typical spacing 76.2 m.

No less than 9.1 m, including 6.0 m into competent layer and below compressible layers.

See recommendations for industrial developments (#10) and slope stability analyses (#21). Slope stability and effect of settlements on final landfill cover, or new structures over landfill, are crucial aspects of analysis.

Given large size of footprint, for settlement calculations, investigation should reach rock. For hydrogeological analyses, greater depth might be required. Presence of stiff clay or rock quality will be determining factors in establishing the final exploration depth.

Preliminary Study

1.0 sounding or boring at center, or borings at 45.7 m.

Drill center boring to a depth 3.0 times the tank diameter or 6 m in rock with RQD>40%. Consider seismic refraction or resistivity, depending on type of rock.

Final Report

Place borings or soundings at center, along perimeter and intermediate locations (at 0.5 times diameters, or middle of quadrants) so that investigation locations are not spaced more than 30.5 m apart. Investigation density will vary from 1.0 per 185.8 sq.m to 1.0 per 743.2 sq.m for large tanks (diameter ~91.4 m or more).

Perimetral borings could be shorter. The investigation depth depends on subsoil conditions and need for cuts or fills but will likely require a depth of 2 to 3 times the tank radius. Space or distribute borings or soundings evenly within tank area.

One boring every 1858 sq.m of total area or 1.0 boring every 232.3 sq.m of structure area

Short borings will generally be sufficient, say 4.6 m, and 3 times the structure widths. However, the boring depths will also depend on other factors, such as fill thickness and settlements induced.

9- Sinkhole investigations

11- Existing dumps and sanitary landfills (for transfer

Generally

stations, see #1)

12- Circular tanks, steel or concrete

13- Parks, tennis courts or similar, running tracks,

Final Report

community centers

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

Type of Structure

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes) On bedding, solely

14- Major pipelines (~24-inch-diameter, 600 mm, or larger); small or short pipelines require special analysis; culverts; electrical bank stations

based on borings or

Every 76.2 to 182.3 m for final reports; every 457.2 m for preliminary reports. Add a boring or test pit at each vertex or change in direction; try to include manholes.

Take borings to 3 times external pipe diameter. If zone is to be covered with new fill, extend investigation below any compressible zones.

Do seismic refraction survey along pipeline every 76.2 to 182.3 m with borings every 182.3 m, depending on topography. Add a boring per vertex and try to cover each manhole.

Idem

Every 91.4 to 304.8 m; the geological characterization of the site - e.g., presence of faults - will be quite important. Depending on the tunnel size, consider horizontal borings along the tunnel axis.

Vertical borings should be taken at least 1.0 diameter below tunnel floor.

soundings On bedding, but using borings, soundings and geophysical

Suggestions For Depth of Exploration

investigations

Preliminary Study

15- Tunnels Final Report

Every 45.7 m, unless supplemented with seismic refraction lines at ground surface or using cross-hole seismic refraction, or horizontal borings.

Underground structures. Critical 16- Pump stations, dry-docks

factors are uplift or flotation, and excavationdewatering

For a preliminary investigation, do 1.0 borehole towards the proposed center and/or every corner, depending on footprint size; minimum spacing 30.5 m. For a final design, do at least 2.0 borings per 232.3 sq.m of footprint, spaced at 15.2 m. See suggestions for excavations in #17.

issues.

17- Excavation designs, dewatering (Certain situations might require pump tests.)

Open cut excavations

1.0 boring per 232.3 sq.m of excavation footprint for preliminary design, or every 46.5 sq.m for final design. Area is horizontal, calculated at surface level, including additional area required by slopes.

Sheeted excavations

1.0 boring per 92.9 sq.m of footprint for preliminary design, or every 46.5 sq.m for final design, based on structure footprint.

Rev.1-LITERATURE REVIEW

The borings must be taken at least 1.0 diameter below tunnel bottom. Seismic refraction will be of great help. Consider horizontal borings and pilot holes. Tunnel width will impose additional requirements. Proposed bottom elevation is required, since it affects depth of investigation. Even in rock, the investigation must be deep enough to predict flow patterns and excavation methods, although these issues usually require greater analysis during construction. It is suggested to take borings to a depth equal to the foundation level plus 1.5 times the footprint width. Take borings to a depth equal to depth of structure plus 2.0 times the excavation width. Continuous sampling is required given the large impact of minor subsurface details such as thin seams. For preliminary permeability estimates, use falling head tests. For important dewatering and excavation projects, pump tests in wells are highly recommended.

Page 30 of 53

Site Investigation and Boring Layout.

Type of Structure

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes)

Final

Every 22.9 m along wall and 2 or 3 borings or soundings perpendicular to wall (soil profile should extend to cover a length equal to 2.0 times the dredging depth or channel or port depth. Check FHWA guidelines (GEC Number 4 and Soil Nail Manual), which suggest wall borings at 30 meter intervals, plus a line of borings behind the wall at 45.7 spacing. In gentlysloping ground, drill borings to depths equal to 1.0 to 1.5 times the wall height. In sloping ground (assume >20 degrees) go to 2H. FHWA mentions that half of the locations can use CPT instead of SPT. Test pits or test cuts are recommended to document stand-up time and obtain other data.

As indicated in FHWA GEC No. 4, take borings at or behind wall to 2.0 times the wall height; take borings in front of wall to a depth equal to the wall height. Take borings below any potential failure zones. In case of sheet piles, take borings at least 6.0 m below sheet pile tips. For anchored walls (active or passive anchors) the investigation should include the zone of restraint. Deep alluvial deposits will require greater investigation density than shallow alluvial or residual deposits. Drill to cut depth and extract at least 3.0 into rock, if found.

Embankments

1.0 boring every 45.7 to 152.4 m; for viaducts or bridges, considers at least 1.0 boring per pier depending on width of pier. Consider need for transversal sections, minimum 3 per profile or section.

Borings should be taken a depth equal to width of embankment plus 50% (x1.5), at least.

Bridges and viaducts

If drilled shafts are used, follow FHWA guidelines (Standard Specifications 17th Ed. 2002 ): one boring per shaft for pile diameters (f) greater than 1.2 m; one boring per 2 shafts for f of 1.2 to 1.8 m; 1.0 boring per 4 shafts for f < 1.2 m.

For pile caps, borings should be taken at least 10 diameters below the pile tips. As capacity increases, more boreholes or soundings might be required, up to 1.0 per pile. AASHTO requires that boreholes be taken 6.0 m below the pile tips and that they also extend below the pile by 2.0 times width the pile cap width.

Cuts and slopes

In cut areas, need groups of at least 3 borings perpendicular to cut to define profiles. These profiles should be obtained at least every 30.5 45.7 m along cut.

Take boreholes below cut and below potential failure surfaces.

Do borings every 304.8 m for preliminary review. Final report will require investigations points at 30.5 to 91.4 spacing. Keep in mind that river banks will include young heterogeneous deposits and that a detailed investigation is required, no matter how similar initial borings might appear to be.

For structures such as bridges and culverts, see other sections of this table. FOS stability analyses it is usually necessary to reach competent layers. Minimum depth of exploration should exceed 3.0 times width of dike or levee. Consider explorations using both SPT and CPT.

18- Sheet piles, retaining structures, reinforced concrete or mechanicallystabilized earth walls, tieback walls or soil or rock anchors or soil nails

19- Embankments, bridges and highway viaducts, trains

20- Earth dikes or levees

Suggestions For Depth of Exploration

Usually river banks or low-lying areas

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

Type of Structure

21- Slopes (slope failures, isolated or sporadic

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes)

investigations)

Need at least 1.0 longitudinal profile. The minimum investigations should include groups or lines of 2 to 3 borings, every 9.1 to 76.2 m.

22- Airport fields

Need at least 1.0 boring or sounding every 232.3 sq.m.

Emergencies

Generally

25- Quarries

Depth of borings depends on the problem. Slope analyses will require borings taken to a depth at least equal to 1.5 times the slope height. The analysis should consider results from inclinometers, piezometers and continuous sampling. Investigation depth depends on subsoil and need for cuts or fills, presence of compressible soils or possibility of liquefaction. Consider continuous sampling with SPT or CPT with seismic cone.

Conceptual design

At this stage, should try to perform 1.0 or 2.0 borings at center or deepest section, and at each abutment. For earth dams, test pits at probable borrow sites are needed early. Consider 3 to 8 test pits, with compaction testing and classifications.

Drill to a depth that exceeds probable base width by a factor of 2.0, or drill 4.6 to 6.0 m into rock with RQD>50%.

Preliminary

For earth dams or roller compacted concrete dams, do at least one boring every 106.7 m along main axis. Borings will also be required at shells and abutments. Borings and/or test pits will be required at borrow pits. Number of borings for preliminary analysis will be approximately 3.0, every 106.7 m along main axis.

At least 12.2 into rock with RQD>50%. Need continuous sampling towards surface to define flow zones or liquefiable layers or soft layers. Depth of slurry walls or impervious layers will affect depth of investigation.

Final

Depends on type of dam and potential problems: earth dams will require more exploration towards shells. Final study will require at least 3 borings every 45.7 to 91.4 m along the principal axis. For budget purposes, the final number of borings should be approximately 3 every 45.7 along the main axis, plus numerous test pits.

Depends on potential problems with liquefaction, slope stability or flow that have been identified in the preliminary investigation. In this phase, geophysical investigations will be of great use. Numerous test pits or test trenches will be necessary along potential problem areas or borrow pit areas.

In general

Investigation density will greatly exceed previously-stated suggestions on investigation densities due to concerns regarding differential settlements and quality of previous design and construction.

Follow previous suggestions, depending on specific case. Engineering fees will greatly exceed cost of investigation.

In general

Consider seismic refraction. Borings or trenches, if necessary, should reveal earth cover. Rock fragmentation important. Space at least 2 lines of borings every 61.0 m of cut face.

Take borings below expected cut depth. For seismic refraction, length of survey should generally be 3 to 4 times expected excavation depth.

23- Dams

24- Remodeling and additions to existing structures

Suggestions For Depth of Exploration

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

Type of Structure

26- Parking areas, pavements only

27- Previously-filled areas

28- Marinas

Table 8 (Cont’d): FAHWA (2002) Boring Layout Study Level or Investigation Density: Suggestion For Expected Study Locations or Boring Density or Foundation Frequency of Geophysical Traverses Type (Double for Slopes)

Suggestions For Depth of Exploration

Pavements

One boring every 2322.6 sq.m, depending on specific site Conditions

Boring depths depend on drainage system and settlement allowances. Check width and height of any fill areas, to determine probable settlements.

Deep fill review

Space borings or soundings at least every 45.7 for preliminary study, every 15.2 m for final study.

Boring depths depend on probable depth of fill and type of underlying soils. Use continuous sampling. Require greater boring or sounding density.

In general

Depends on length and width of docks and pile loads. Do boring or sounding every 22.9 to 45.7 m of dock length.

Boring depths will depend on expected loads. Take borings or soundings at least 9.1 m below expected pile tips. A detailed investigation could reduce subsequent pile load test requirements.

Note: Work in Karst zones will probably require double the investigation density stated above.

Table 9: SBC 303 (2007) Boring Layout No. of Stories

= 5

Rev.1-LITERATURE REVIEW

9 – 12

Special Study Special Study

Page 33 of 53

Site Investigation and Boring Layout.

Table 10: DID (2009) Boring Layout Distance Between Borings (m) Location to be Investigated

Horizontal Stratification of Soil

Minimum Number of Borings Required (nos.)

Recommended Minimum Depth of Boring

Uniform

Average

Erratic

New Site of Fairly Wide Extent

-

-

-

5 to 10

-

Low-rise, 1 or 2 storey buildings

60

30

15

1 to 3 for each structure

1.5 times width of loaded or plan area

2 to 4 for each structure

1.5 times width of loaded or plan area or up to 6m into firm or hard layer or 3m into bedrock, whichever encountered earlier

2 to 4 for each structure

Up to 9m into firm or hard layer or 4.5m into bedrock, whichever encountered earlier

Multistory Building

Buildings on Poor or Variable Grounds

Bridge Piers, Abutments

45

-

-

30

-

30

15

-

7.5

1 to 3 for each pier or abutment

Up to 10.5m into firm or hard layer or 6m into bedrock, whichever encountered earlier

Below slip plane or 6m into firm or Stability of Slopes

-

-

-

3 to 5 along each critical section

hard layer or 3m into bedrock, whichever encountered earlier

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

Table 10 (Cont’d): DID (2009) Boring Layout Distance Between Borings (m) Location to be Investigated

Minimum Number of Borings Required (nos.)

Horizontal Stratification of Soil

Uniform

Average

Recommended Minimum Depth of Boring

Erratic 2m to 3m below formation for roads, 6m below

Roads, Runways and Pipelines

250

150

30

-

formation for runways, 0.5m below invert for pipelines

Borrow Pits (for compacted fill)

300 – 150

150 – 60

30 – 15

-

-

Table 11: QCS (2014) Minimum Depth of Boreholes No. of Floors

Depth of Boreholes (m)

8

3 S0.7 (Where S: Number of Floors)

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

FIGURES

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

Figure 1: ASCE (1976): Depth of Boring Criteria

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Site Investigation and Boring Layout.

Figure 2: IS 1892-1979 (1985) Depth of Exploration

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Site Investigation and Boring Layout.

Figure 3: JEA (1990) Boring Layout

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Site Investigation and Boring Layout.

Figure 4: EN 7 (2008) Depth of Boring - 1

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Site Investigation and Boring Layout.

Figure 5: EN 7 (2008) Depth of Boring - 2

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Site Investigation and Boring Layout.

Figure 6: EN 7 (2008) Depth of Boring - 3

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Site Investigation and Boring Layout.

Figure 7: EN 7 (2008) Depth of Boring - 4

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Site Investigation and Boring Layout.

Figure 8: EN 7 (2008) Depth of Boring - 5

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Site Investigation and Boring Layout.

Figure 9: EN 7 (2008) Depth of Boring - 6

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Site Investigation and Boring Layout.

Figure 10: EN 7 (2008) Depth of Boring - 7

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Site Investigation and Boring Layout.

Figure 11: EN 7 (2008) Depth of Boring - 8

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Site Investigation and Boring Layout.

Figure 12: EN 7 (2008) Depth of Boring - 9

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Site Investigation and Boring Layout.

Figure 13: EN 7 (2008) Depth of Boring - 10

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Site Investigation and Boring Layout.

Figure 14: EN 7 (2008) Depth of Boring - 11

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

Figure 15: DID (2009) Depth of Boring - 1

Rev.1-LITERATURE REVIEW

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Site Investigation and Boring Layout.

Figure 16: DID (2009) Depth of Boring - 2

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Site Investigation and Boring Layout.

Figure 17: DID (2009) Depth of Boring - 3

Rev.1-LITERATURE REVIEW

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