Why Embankments Crack and How to Fix Them

Includes a Live Event on 11/13/2018 at 12:00 PM (EST)

This course is based on 50 years of NRCS experience with investigating and remediating cracked earth embankments.  The presentation consists of two main sections, covering: 1) the nature of soil cracking and the associated internal erosion failure modes; and 2) how to remediate cracked earth embankments.  In the first section, general information is presented on which soils are most susceptible to cracking and which pose the greatest risk for failure by internal erosion.  The most common causes of cracking are identified, along with descriptions of the associated cracking mechanisms and patterns.  In the second section, the two main approaches to repairing cracked embankments are presented: the “cutoff” approach and the “filter” approach.  Real life examples of each are presented.  The use of geotextiles in repairing cracked embankments is discussed, including several case histories and an analytical procedure to design geotextiles to span open cracks.  Finally, the issue of cracking of granular filters is discussed in terms of its incidence, risk, and prevention.

Benjamin C. Doerge

NRCS, Geotechnical Engineer

Benjamin Doerge is a registered professional engineer in Geotechnical, Agricultural, and Environmental Engineering and retired in 2018 from the Natural Resources Conservation Service (NRCS).  He has 39 years of professional experience in the design, construction, and rehabilitation of dams and hydraulic structures.  His most recent position was Geotechnical Engineer at the NRCS National Design, Construction, and Soil Mechanics Center in Fort Worth, Texas.  He has been active in several professional organizations, including ASDSO and ASTM.

I. Why Embankments Crack
 

A. Causes of cracking
  1. Differential settlement
  2. Desiccation*
  3. Collapse of foundation materials*
  4. Expansive soils
  5. Regional subsidence
  6. Seismic shaking
* emphasize
 

B. Soils prone to internal erosion failure modes
  1. Cracking potential
  2. Erodibility
  3. Ability to sustain an open crack
 

C. Failure modes for cracked dams
  1. Internal erosion types
  2. Stages of internal erosion failure modes
  3. Crack flow failure mode
  4. Arizona full-scale test
 

D. Question and answer

II. And How to Fix Them
 

A. Repair approaches
  1. Cutoff approach
  2. Filter approach
  3. Combinations of both
 

B. Issues with both approaches
  1. Cutoff approach – “windows,” deterioration with time
  2. Filter approach – construction issues, cracking of filters, filter compatibility issues
 

C. Case histories of cracked dam repairs
  1. 1986 Arizona Crack Study
  2. Recent case histories
   a. Downstream repair – Texas #1 and #2
   b. Centerline repair – Arizona #1 and #1
   c. Upstream repair – Colorado #1 and #2
 

D. Geotechnical investigations, testing, and analysis for cracked embankments
  1. Purpose of investigations
  2. Investigations
  3. Testing 
  4. Analysis
  5. Case history – Preliminary problem identification

 E. Designing geotextiles to span open cracks
  1. Analytical procedure
  2. Example problem
 

F. Cracking of filters
  1. Relatively few occurrences
  2. Limited documentation
  3. Cementation vs. self-healing
  4. Tests for self-healing behavior
  5. Research on cracked filters
  6. Measures to limit cracking potential of filters
  7. What causes filters to crack?
 

G. Question and answer

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Why Embankments Crack and How to Fix Them
11/13/2018 at 12:00 PM (EST)   |  120 minutes
11/13/2018 at 12:00 PM (EST)   |  120 minutes
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2.00 PDH credits  |  Certificate available
2.00 PDH credits  |  Certificate available