FLOOD01986

• County: Bent
• Community: Las Animas
• Stream Name: Arkansas River
• Title: Las Animas Local Protection Project Design Memorandum
• Date: 8/22/1968
• Prepared For: Las Animas
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

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levee centerline. All required borrow will be obtained riverside of levee
alignments. After nominal stripping, 3 inches or less, to remove vegeta-
tion and debris, all material from the borrow areas will be suitable fill
materials for the levees. Foundation investigations for the borrow areas
consisted of auger holes AH-72 thru AH-84 , Location and visual logs of
the auger holes are shown on plate 1. Subsurface exploration was not
made in the upstream borrow areas. The materials from the upstream
, borrow areas will be similar to materials in the downstream borrow areas
- and will provide suitable materials for the random embankment section.
Materials in the borrow areas classify as clay (CH) to clayey silts
(ML-CL) for the upper fine grained layer and clayey sand (SC) to sandy
gravel (GP) for the underlying alluvial materials. The maximum depth of
excavation in any of the borrow areas will be limited by the water table
which varies between 1 and 10 feet.

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8-12. Levees. The total length of levees is approximately 54,735
feet; the south and north levees being 49,300 feet and 5,435 feet,
respectively. Levee fills will be constructed as random fill sections
of material from required excavation and from the borrow areas. The
levee sections, as shown on plate 18, will have a l2-foot crest width,
1 on 3 slopes riverside and 1 on 2.5 lands ide with a maximum height of
about 23.5 feet. Specifications will require that finer grained materials
be placed toward the riverside slopes and coarser materials toward the
landside slope. An inspection trench of 3 foot depth will be excavated
for the entire length of the levees to allow visual inspection of the
surficial foundation materials. The overburden materials after nominal
stripping, 6 inches or less, would provide a suitable foundation for
the levee.

8-13. Stability analyses. Random fill sections will be utilized
throughout all sections of the levee. Maximum height of levee will be
approximately 23.5 feet. Stability analyses for end of construction and
sudden drawdown were made at station 394+50 which is the maximum height
of levee and at station 389+00, which is the maximum height of levee to
be located on a clay foundation layer. Post construction conditions
were evaluated at station 354+00 north levee and station 389+00 south
levee which represent the maximum heights of levee on clay foundation
layers.

8-14. Results of laboratory tests on remolded composite samples
of fill material, undisturbed samples of fine grained foundation
materials, design shear strengths and unit weights of fill and founda-
tion materials are shown on plates 33 and 35. Saturation lines for
sudden drawdown condition were obtained after consideration of embank-
ment permeability and duration of flood.

8-15. Computer and manual solutions for the critical arc for
construction and drawdown condition of analysis are shown on plates 34
and 35. Critical factors of safety for the construction condition
were 1.67 for the riverside

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