Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 61
61
used. Very often the foundation size is restricted by the strength 3.1.7 Major Conclusions
of the concrete, which is a limiting value (10 to 15 tsf) compared
with the rock's strength. Inclination factors are not used because Major conclusions are the following:
no load details are available from the structures group at the
1. In many states, the geotechnical aspects of the founda-
time of the design. When designing foundations for retaining
tion design (bearing capacity, settlement, and sliding) are
wall, the maximum eccentricity is assumed.
being evaluated before all the loading details are avail-
able. As such, load inclination and/or eccentricity cannot
3.1.6.6 Washington--Interview with be directly accounted for. Several approaches are taken
Jim Cuthbertson, Chief Foundations Engineer to resolve the situation including (1) providing effective
Washington's questionnaire response indicated a relatively foundation sizes so that final design sizes will include the
common use of shallow foundations on silts and clay (6%), eccentricity effect (i.e., B = B + 2e); (2) assuming highest
the highest of all responders. It was clarified that those soils eccentricity; and (3) providing unit bearing values, nomi-
are glacier, compacted, highly densified soils, with silts hav- nal and factored.
ing SPT N values of 30 to 40 and clays having SPT N values of 2. The vast majority of the shallow foundations used to sup-
40 to 100. These materials are in some ways IGMs and, hence, port bridges are founded on rock. Only various references
skew the statistics presented of foundations on silt/clay. When are currently available in the specification. A need for
calculating bearing capacity, cohesion is neglected and only a specific, detailed methodology and its calibration was
frictional component is assumed. Foundations on rock and advocated by most states and all those interviewed.
IGM are common (about 30%) and the use of the classical 3. Although most states do not use inclination factors in
bearing capacity analysis leads to unrealistically high values, design, they examine the resistance to sliding, and once
which are then limited to about 80 tsf ultimate capacity based the final foundation size is established (after settlement
on experience. consideration), they check again for bearing capacity with
Similar to the problem presented by Tennessee, in Washing- or without inclination factor (depending on the state).
ton the geotechnical analysis is carried out before eccentricity 4. New foundations on soft, cohesive soils are rarely being
values are available. This is resolved by providing foundation constructed. Some of the statistics in that regard were
dimensions (width and length) that are required to be main- skewed due to referencing highly compacted cohesive soils
tained as effective foundation sizes. When the final design (which border on being IGM) as regular cohesive soils.
accounts for eccentricity, it results in foundation sizes that,
after being reduced for eccentricity, end with the originally
3.2 Assembled Databases
provided effective foundation sizes. This effective foundation
width is used for settlement analysis calculations and sliding 3.2.1 Overview
resistance. As the foundations are cast on grade, a full mobi-
Section 2.1 presents the research plan for establishing data-
lization of the friction angle is assumed.
bases for shallow foundation load tests. Two major databases
were established:
3.1.6.7 Maine--Interview with Laura Krusinski,
Senior Geotechnical Engineer · UML-GTR ShalFound07, which incorporates Databases I
The extensive use of shallow foundations in Maine can be and II. This database is based on a database originally assem-
attributed to rock close to the ground surface (especially in bled for NCHRP Project 12-66 and in its current scope
coastal areas) and economic considerations. The foundations contains 549 case histories of which 409 would conform to
are sized first based on presumptive values and then are checked what is described as Database I and 140 case histories would
against the factored resistance. Maine is making an effort to conform to Database II. UML-GTR ShalFound07 will be
obtain the references mentioned in the code and study them as discussed in Section 3.2.2.
no details are provided in the specifications. Laura Krusinski, · UML-GTR RockFound07, which is presented as Database III
Senior Geotechnical Engineer, finds it useful to provide details and contains 122 case histories, 119 of which were used in
of recommended design methods and calibrate them against the calibration. UML-GTR RockFound07 will be discussed
a database. As with other states, in Maine the foundation in Section 3.2.3.
design is carried out before loading details are available; hence,
eccentricity is assumed not to exist. However, the foundation A summary of the major attributes of each database is pre-
is later checked as part of the structural design. Krusinski also sented below. Additional statistics are presented for relevant
sees a need for guidelines for footing embedment in 100-year analyses (e.g., see Section 3.5 for centric vertical loading on
and 500-year scour events. shallow foundations in/on granular materials).
OCR for page 62
62
3.2.2 UML-GTR ShalFound07 Table 22. Countries
in which tests were
The UML-GTR ShalFound07 database was expanded conducted and number
from its original format of 329 cases (developed for NCHRP of test cases conducted
Project 12-66) to contain 549 load test cases for shallow founda- in each country.
tions, mostly on granular soils, and concentrating on load tests
Country No. of cases
to failure and/or loading other than centric vertical loads. The
Australia 1
database was constructed in Microsoft Access 2003 format. Brazil 19
The bulk of the cases was collected and assembled from four Colombia 1
sources: (1) ShalDB Ver5.1 (updated version of Briaud and Croatia 1
France 60
Gibbens, 1997), (2) Settlement of Shallow Foundations on Gran- Germany 254
ular Soils, a report to the Massachusetts Highway Department India 6
by Lutenegger and DeGroot (1995), (3) a German test database Italy 56
Jamaica 1
compiled by DEGEBO (Deutsche Forschungsgesellschaft für Japan 9
Bodenmechanik) in a set of volumes, and (4) tests carried out Kuwait 10
at or compiled by the University of Duisburg-Essen, Germany. Nigeria 3
Northern Ireland 1
Table 22 lists the countries in which the tests were carried Portugal 6
out and the number of related cases. The majority of cases South Africa 1
were tests carried out in Germany, the United States, France, Sweden 11
UK 14
and Italy. USA 84
Table 23 summarizes the database by classification based on Others 11
the foundation type, predominant soil type below the footing Total 549
base, and country. The foundation type was classified based
on the footing width, which follows the convention utilized
by Lutenegger and DeGroot (1995). The tests on footing widths
less than or equal to 1 m (3.3 ft) were classified as plate load tests, A detailed list of input parameters in the database is presented
widths between 1 m and 3 m (9.8 ft) were classified as small in Appendix D (see Table D-1). See Figure 47 for the site con-
footings, widths between 3 m and 6 m (19.7 ft) were classified dition (e.g., a footing tested in an excavation or a footing on a
as large footings, and widths greater than 6 m were classified as slope, etc.) and Figure 48 for the conventions of footing dimen-
rafts and mats. "Mixed" refers to soil containing alternating sions and loading. Figures D-1 through D-13 in Appendix D
layers of sand or gravel and clay or silt. "Others" refers to cases contain screen images of the UML-GTR ShalFound07 data-
with either unknown soil type or with materials like loamy base in Microsoft Access. SearchModify, listed under Forms,
scoria. The majority of the tests in the database are plate load allows the user to easily search/modify a footing case in the
tests on granular soils. database.
Table 23. Summary of UML-GTR ShalFound07 database.
Foundation type Predominant soil type Total Country
Sand Gravel Cohesive Mixed Others Germany Others
Plate load tests
346 46 -- 2 72 466 253 213
B 3.3 ft (1m)
Small footings
3.3 ft < B 9.8 ft 26 2 -- 4 1 33 -- 33
(3m)
Large footings
30 -- -- 1 -- 31 -- 31
9.8 ft< B 19.7 ft (6m)
Rafts & Mats
13 -- -- 5 1 19 1 18
B > 19.7 ft
Total 415 48 0 12 74 549 254 295
Note:
"Mixed" are cases with alternating layers of sand or gravel and clay or silt
"Others" are cases with either unknown soil types or with other granular materials like Loamy Scoria
1m 3.3 ft
OCR for page 63
63
SiteConditionID 40101 SiteConditionID 40102
SiteConditionID 40103 SiteConditionID 40104
SiteConditionID 40105
Figure 47. Footing dimensions and site details along with the associated SiteConditionID employed in database
UML-GTR ShalFound07.
OCR for page 64
64
x
edge D =
x2
edge A d = thickness
Se-zz
Ro-xx
Ro-zz
Di-yy edge B th
Di-xx g
Ro-yy len x3 = y
=
b2
edge C
b3 = wid
th
x1 = z
(a)
x
edge D =
x 2
edge A d = thickness
thickless
FzSL
MxxSL
MzzSL
FySL edge B th
FxSL MyySL g
len x3 = y
=
b2
edge C
b3 = wid
th
x1 = z
(b)
Figure 48. Conventions for footing dimensions (a) and applied
loads (b).
3.2.3 UML-GTR RockFound07 and/or square shapes. A majority of the circular footings are
plates. All the rock sockets in the database are circular for which
A database consisting of rock loading by small size inden- the end bearing capacity (tip resistance) could be isolated, sep-
tation, shallow foundations, and drilled shafts (for which the arating it from the shaft resistance of the rock sockets.
tip load-displacement relations were measured) was assembled. Figures 49 to 52 present the distributions of the foundation
The database is composed of a total of 122 case histories from sizes for all cases--non-embedded and embedded footings
10 different countries. Thirty-nine of the cases were obtained and rock sockets, respectively. Table 24 presents a summary
from a study by Zhang and Einstein (1998), and 31 cases were of the database cases used for the determination of the uncer-
obtained from a study by Prakoso (2002) whereas the re- tainty of the bearing capacity analyses of foundations on rock.
maining cases were searched for and found in the literature. Appendix E presents in detail the references that were used to
In a final review, three of the footing cases were found to be build the rock foundation database along with the rock details
tested over a rock that contained a clay seam and, hence, were and the foundation type. All 122 original cases are presented in
excluded from the statistics used in the calibrations. The Appendix E with the three foundations omitted clearly marked.
database developed for the study included footing field load The database has 30 non-embedded shallow foundations,
tests conducted in pseudo rock, hardpan, fine-grained sedi- 28 embedded shallow foundations, and 61 rock sockets. Only
mentary and igneous or volcanic rocks. The shallow foundation four of the shallow foundations have square shapes; the others
case histories were subcategorized according to their embed- are circular. All 61 rock sockets are circular. The width or
ment, differentiating between embedded (embedment depth diameter (B) of the shallow foundations range from 0.07 to
D > 0) and non-embedded (D = 0) footings with circular 23 ft with an average (Bavg) of 1.98 ft. The Rock Sockets have a
OCR for page 65
65
40 25
119 Rock sockets and Footing cases 28 Footing cases with D>0
Mean B = 2.58 ft 0.3 Mean B = 1.18 ft 0.8
COV = 1.594 COV = 0.926
20
30 0.25
0.6
No. of observations
No. of observations
0.2 15
Frequency
Frequency
20
0.15 0.4
10
0.1
10
0.2
5
0.05
0 0 0 0
0 2 4 6 8 10 12 14 16 18 20 22 24 0 1 2 3 4 5
Footing width, B (ft) Footing width, B (ft)
Figure 49. Distribution of B (ft) for 119 case histories Figure 51. Distribution of B (ft) for 28 embedded
in database UML-GTR RockFound07. footing case histories in database UML-GTR
RockFound07.
10
30 Footing cases with D=0 12
Mean B = 4.20 ft 0.3
61 Rock socket cases
COV = 1.799
Mean B = 2.47 ft
8
COV = 0.739
0.25
0.15
No. of observations
6 0.2 8
No. of observations
Frequency
Frequency
0.15 0.1
4
0.1
4
2 0.05
0.05
0 0
0 2 4 6 8 10 12 14 16 18 20 22 24 0 0
Footing width, B (ft) 0 2 4 6 8 10 12
Footing width, B (ft)
Figure 50. Distribution of B (ft) for 30 non-embedded
footing case histories in database UML-GTR Figure 52. Distribution of B (ft) for 61 rock socket
RockFound07. case histories in database UML-GTR RockFound07.
