FY98 TARA Briefing

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REMOTE SITE ASSESSMENT
Marian Rollings and Lynette Barna CRREL
FY03 - 225K FY04 - 250K FY05 - 250K FY06 -
200K
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Project Description

• Objective Develop methodology and assemble
  workable models to ascertain structural adequacy
  of a site for aircraft operations as
  environmental conditions change. The system must
  be modular to allow upgraded models to be
  seamlessly incorporated as they develop.
• Scope - This effort concentrates on evaluating
  and assembling existing models into a workable
  methodology. Particular emphasis is placed on
  environmental effects modeling. Other efforts
  are concentrating on specific improvements such
  as enhanced structural modeling and engineering
  property data bases that will be incorporated
  within the methodology as they develop.

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Plan/Progress

• Plan FY03 Assemble methodology and identify
  model and data requirements.
• FY04 Complete evaluation of environmental
  model capabilities
• FY05 Select, refine, verify environmental
  model(s)
• FY06 Assemble final methodology and models
• Progress 1st generation analysis methodology
  assembled and tried on an exercise for a parking
  ramp at Minot, North Dakota. Analysis begun 5
  models to examine environmental effects.

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CONCEPT OF ANALYSIS
Materials Property Data Base
Mission Requirements (traffic)
Revised Structural Assessment As
Environmental Conditions Changes
Structural Assessment
Site Soils or Pavement
Environmental Effects (temp moist)
Site Geometry Clearances
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MINOT NORTH DAKOTA EXERCISE

• Facility 750 x 750 ft parking ramp adjacent to
  Hot Cargo Pad (Feature A-16B)
• Mission 10,000 passes of C-130
• Available Existing Structural Models
• Unsurfaced nomograph
• ACN/PCN for paved areas (access to new ramp via
  Taxiway E and hot cargo pad)

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MINOT SOILS INPUT

• Geology and Geomorphology
• Glaciated upland plain composed of glacial till
• USDA Agricultural Soil Map
• Calcium sulfate present in soil
• Upper 1m typically
• ML or CL
• 60 to 75 fines
• Liquid limit in low 30s, PI 17 to 19
• Finer and more plastic below
• Prairie Pot Holes of wet fine material (can
  avoid)
• AFCESA Pavement Evaluation
• CL soils

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INFERENCES FOR SOIL ASSESSMENT

• Geologic Information
• CBR of 2 to 15
• USDA Soils Map
• CBR of 5 to 10 for most areas
• CBR of 2 to 5 for prairie pot holes which can
  avoid as they are mapped
• Presence of calcium sulfate may preclude
  stabilization
• AFCESA Evaluation
• CBR of 7
• Equilibrium moisture content of 13.0 to 13.6
  under pavements
• ACN/PCN and allowable loads for pavements
• BETTER STRENGTH ESTIMATES POSSIBLE AS INFORMATION
  QUALITY IMPROVES

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UNSURFACED STRUCTURAL CAPACITY FOR MINOT EXERCISE
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STRUCTURAL ASSESSMENT

• Mission cannot be supported
• Unless stabilized (sulfate question unresolved),
  mat, or other structural upgrade
• May be able to operate if soil is frozen
• No existing military criteria for aircraft
  operation on frozen soils
• For this exercise, analyze as a layered elastic
  problem

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FROZEN SOIL ANALYSIS

• Is it a rigid pavement?
• Calculate tensile stresses and compare to some
  fatigue estimate
• Can allow for some cracking in the frozen layer
  by using a cracked modulus analysis method

• Is it a flexible pavement?
• Calculate compressive strain on soil below frozen
  layer and apply standard layered elastic rutting
  criteria

Many frozen fine-grained soils have modulus
values on the order of 80,000 to 500,000 psi (
high-quality base or low to medium quality AC)
and crack at relatively high strain levels.
Probably, a flexible pavement analysis is most
appropriate but will analyze both ways
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REQUIRED DEPTH OF FROZEN SOIL TO SUPPORT MISSION
REQUIREMENTS

• Treat frozen layer as a rigid structure
• 33 to 43 depth depending on modulus for frozen
  soil
• Required thickness reduced about 25 if use
  cracked modulus analysis and analyze for subgrade
  rutting
• Treat as a flexible pavement system (probably
  sounder analysis technique)
• 10 to 20 depth depending on modulus for frozen
  soil
• Results highly dependent on quality of knowledge
  of material properties. Frozen soil properties
  are a function of soil type, moisture content,
  and temperature. They are not a constant.

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ANALYZE ENVIRONMENTAL EFFECTS

• Frost depth calculated by modified Berggren
  equations

Combine structural requirements with climate data
from Minot and predicted frost penetration
Average climate data for Minot AFB
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END RESULT ANALYSIS OF MINOT AFB EXERCISE
Treating as a flexible system
15 December 21 March
June
July
1 15 December
21 March 5 April
Cannot meet mission requirements without
structural upgrade
Marginal
Meets mission requirements
Carrying out this environmental assessment
identifies a 3 month potential window for
operations
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Product

• Description A methodology that will describe
  use of data bases, individual models, and
  criteria for analyzing the structural capacity of
  a site as environmental conditions change.
• FY04 Demonstration Use the NC geometrics and
  soil conditions but translate it to Minot, ND to
  demonstrate how environmental effects impact
  structural capacity.
• Transition Medium Analysis flowchart with
  supporting criteria and models. This work unit
  could all be computerized into a single software
  package but this would require more funding and
  would lose the modular structure that allows
  rapid and easy upgrading.