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Патент USA US2115009

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April 26, 1938.
R E_ DQNCAS'TER
2,115,009
BACKFILL FOR RETAINING WALLS
Filed Aug. 22, 1956
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Patented Apr. 26, 1938
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BACKFILL FOR RETAINING ‘WALLS
Purcell Eli Doncaster, Fort‘ William, Ontario,
'Ganada
7 Application August 22,
2 Claims.
This invention relates to back?lls for retaining
walls and like engineering structures.
There is almost no ?eld of engineering in
which there is less uniformity and less accurate
knowledge of basic factors than in retaining
structures. Structures, which on the basis of
accepted theory of pressure and resistance should
have failed, have proved stable, and others built
strictly in accordance with accepted practice and
10 apparently with liberal factors of safety have
failed.
‘There are few, if any engineering structures in
which factors of safety and liberal allowance for
contingencies are used as generously as in retain
15 ing structures, and yet in general the amount of
materials used in and the costs of the construc
tion of these structures appear unnecessarily
large in comparison to what is considered ade
quate in other engineering structures. One of
the main difficulties is that, under present prac
20
tice, there is no control whatever of the pressure
exerted by the ?ll or backing materials on the re
taining structure, and it is this di?iculty which it
is the object of the present invention to remedy.
According to the invention the back?ll is made
25
up partly of the usual ?lling or backing material
and partly of relatively light hollow members
placed between the retaining structure and the
plane of rupture of the ?ll material. As these
30 hollow members have a much lower weight per
unit of volume than the ordinary ?lling material,
they not only allow the point at which the maxi
mum pressure of the ?ll is exerted on the retain
ing structure to be controlled, but they cause a
reduction in the total outward pressure exerted.
This permits the structure to be made smaller or
of lighter materials than would otherwise be pos
sible, and may permit the use of a different type
of structure than would otherwise be possible,
40 such as steel sheet piling instead of gravity walls
or wooden sheet piling instead of steel. In addi
tion, where piling is used in soft foundation soil,
it permits shorter piles to be used. The hollow
members also present the advantage of reducing
45 the passive resistance required of the earth at the
toe of the structure, which is of importance in the
case of relatively soft or unresistant foundations.
Finally, by reducing the amount of ?ll materials
as to whose actions and pressures there is so
50 little clear knowledge, they reduce the factor of
5
’
1936, Serial No. 91,459
(01. 61—39)
exert an outward pressure against the retaining
structure.
The invention will be more fully understood by
reference to the attached drawing, in which:
Figure l is a perspective view of a back?ll em
bodying the invention.
Figures 2, 3, 4 and 5 are views of various means
for retaining the hollow members in position in
the back?ll.
In the drawing a retaining structure is indi 10
cated at l and the back?ll at 2. The back?ll is
shown as being made up‘ partly of the usual back
?lling material whose plane of rupture is indi
cated at 3 and whose plane of repose is indicated
at 4. Between the plane of rupture 3 and the 15
inner surface of the wall I are placed one or more
relatively light hollow members 5 which may be
either tubular, as shown, or of any other cross
section and may be made of any material which.
is strong enough so that the members will not 20
collapse under the pressure exerted on them. As
examples of suitable materials may be mentioned;
plain or corrugated light steel pipe, such for in
stance as used for culverts; concrete pipe; or‘
wood stave pipe, creosote treated or not accord 25
ing to water conditions.
These light hollow members not only reduce
the total outward pressure exerted on the retain
ing structure but make it possible to lower the
point of maximum pressure on the latter. Grav
ity walls as illustrated are always made heaviest
and their cross section is greatest near their base,
and in the case of sheet piling, in connection with
which the invention has perhaps its most im
portant application, this lowering permits a re
duction in the size of the tie rod and tie rod an
chorages, which are expensive units. The lower
ing of the point of maximum pressure is most
marked in the cases where the hollow members
rest on a stringer supported on piles, since the 40
members and the piles directly support a con
siderable portion of the ?ll directly above the
members.
The hollow members may in certain cases be
provided with holes in their lower are. This may 45
be useful in the case of quay walls and the like
wherethere is water on one side which rises and
falls, since the holes will allow the members to
?ll when the water rises and-empty easily when it
falls, so that extraneous water pressures are 50
uncertainty in connection with the structure.
The hollow members may be left free in the
back?ll or held in any desired position by special
avoided. Moreover, if the water table is high,
the members will act to carry off- the water to
means, in which case they have some effect in
?ll when the latter is open ended.
reducing the tendency of the rest of the back?ll to
weep holes in the structure or on the ends of the
‘
In Figure 1 the members are shown as being 55
2
2,115,009
free in the backfill and this is the way in which
they may usually be arranged. However, in some
cases, such as when the ?ll is in a plastic condi
tion when placed, it may be necessary or desirable
to ?x the members in position in the ?ll in such a
way as to prevent its subsequent movement. Var
ious ways in which this might be done are illus
trated in Figures 2 to 5. When the members are
so retained in position they tend somewhat to re
duce the outward pressure exerted on the retain
ing structure by the rest of the back?ll.
In Figure 2 a hollow member is shown as
being supported on piles and held against out
ward movement by means of a tie member 6 ?xed
to a suitable anchorage 7. In Figure 3 a member
is supported on a cradle bent'8 and in Figure 4 on
a different cradle bent 9, more completely restrict
ing its movement. In Figure 5 a member is
shown as being held against outward movement
by piles driven into the back?ll between it and
the wall and having their upper ends supported
by tie members It] ?xed to a suitable anchor
age “.
'
»
It will be understood that althoughrin Figures
5
2 to 5 only one hollow member has been shown
a plurality of such members might be used.v '
I claim:--- 7
g
'
1. Retaining wall construction comprising a re 10
taining structure, a back?ll therefor, and light
hollow members in said back?ll between the plane
of rupture thereof and said retaining structure.
2. Retaining wall construction as de?ned in '
claim 1,.in which the hollow members are metal 15
pipes.
PURCELL ELI DONCASTER.
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