FLOOD05005

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: State Of Colorado Dam Safety Manual
• Date: 6/1/1983
• Prepared By: Colorado State Engineers Office
• Floodplain - Doc Type: Educational/Technical/Reference Information

18

3.5 ROCKFILL DAMS
Most rockfill dams are similar in shape to earth dams.
The difference is that rock fragments make up the
primary material used for construction. The choice of
constructing a rockfill dam versus constructing an
earth dam is usually based on availability of materials.
The sketch below illustrates one configuration of a
rockfill dam.

TRANSITION
ZONE TO
PROTECT CORE
MATERIAL FROM
EROSION

FIGURE 3.S.1
TYPICAL ROCKFILL CROSS SECTION

Because rock fragments alone would leave large open-
ings for seepage flow, a central core, like that in the
zoned earth dam, is required. Also, note that the core
extends into the foundation to help control the flow of
water under the dam. A transition zone is usually
necessary to protect the core from erosion. The transi-
tion zone is designed to keep the fine-grained core
materials from being washed into or through the
rockfill.

3.6 CONCRETE DAMS
Concrete dams are the least common types in Colo-
rado. Concrete is probably the most durable material
for building dams and has a very high resistance to
seepage.

A concrete dam is unique in that it directly transfers
some ofthe pressures created by the stored water to the
foundation and abutments. A concrete dam, therefore,
is very dependent upon the ability of the foundation
and abutments to hold the dam in place.

There are two basic designs for concrete dams: gravity
and arch. The sketches below show how the two are
tied into the foundation and abutments.

3.6-1 CONCRETE GRAVITY DAM
y-~""""'-:: ~~0

I ( I) f / II / ~-~~( f I R~SltT~NCETO

- ~ MOVEMENT BY
KEY IN ABUTMENT
I T

- -

I

PRESSURE
FROM
RESERVOIR

-,".:.-.-.------ ..~

. , '."4 .'-, T - - --- ----
. " RESISTANCE TO MOVEMENT BY
SUPPORT OFFnm
IY FOUNDA.TION ... - .....t \: KEY.IN FOUNDATION
RESISTANCE TO MOVEMENT
(FRICTION BETWEEN DAM & FOVNDA TlONf

FIGURE 3.6-1
CONCRETE GRAVITY DAM

Without a proper key or tie into the abutments
and foundation, and without enough weight, a
gravity dam could tip over or slide downstream
as shown below.

r -.,
I (
I
I \
\
I \ TIPPING
I \
I \
I \
\
\

,
\
,
,
, MOVEMENT
,DOWNSTREAM
,
,
,
,

c
--
--

.. MOVEMENT DOWNSTREAM

b. TIPPING

FIGURE 3.6-2
GRAVITY DAM MUST RESIST RESERVOIR LOADS

The choice of a concrete gravity dam over other
types is based on the available material and the
site conditions.

3.6-2 CONCRETE ARCH DAM
/~--ru ....-:; I I .- / I
/1",' i II RESISTANCE TO MOVEMENT
OFFERED BY ABUTMENT
---;:~, / 'r'

"
,II
I' 1/

I

II I

PRESSURE OF
RESERVOIR

-=--=-----

'.
:i

::.
.'..:

I
'r
'\ :
~

.....
,. .
\~.:

I RESISTANCE TO MOVEMENT
OFFERED BY KEY IN FOUNDATION

SUPPORT OFFERED
BY FOUNDATION
FIGURE 3.6-3 - CONCRETE ARCH DAM