Installation damage is one of the three critical factors in determining T_a, the allowable strength in reinforcement design.

T_a = T_ult / (RF_CR x RF_ID x RF_D)

RF_CR = partial factor for tensile creep;

RF_ID = partial factor for installation damage;

RF_D = partial factor for chemical durability

The untested product default values for creep, RF_CR, installation damage, RF_ID, and chemical durability, RF_D, are established in the 1997 AASHTO Interim Bridge Specifications and, as can be seen in Table 1, default values can be punitive to untested products.

Table 1. Typical Geosynthetic Default and Testing-Derived

Values for ID Partial Reduction Factors

*Per 1997 AASHTO Interims – only acceptable for prelim. Design and non-critical structures.

**PP and PE must have UV Stability > 70%.

***PET must have MW>25,000 and CEG<30.

The Federal Highway Administration Geotechnology Technical Note on Degradation Factors for Geosynthetics published May 1, 1997 cited installation damage as a key issue in determining geosynthetic performance characteristics in reinforcement design and provides ranges of installation damage reduction factors commonly used in design as shown in Table 2.

Table 2.

FHWA Installation Damage Findings

Testing for Installation Damage

Installation damage has generally been shown to affect the ultimate strength of the geosynthetic, rather than its modulus.  Therefore the effects of installation are commonly measured by ultimate strength reductions. 

There is no standardized laboratory simulation of installation damage; however, Watts and Brady of the Transportation Research Laboratory (TRL) in the United Kingdom developed and documented the “Procedure for Installation Damage Test for BBA Assessments”  (CERC.SOIL.TM028, Jan 1997).  This procedure provides a methodology that allows exhumation of test samples without damaging them in the exhumation process.

This procedure as modified by TRI to conform to ASTM D5818  (method for exhuming installation test samples) has proven to be practical, repeatable and produces results within expectations.

TRI’s Installation Damage Procedures

Expertise.  Over 100 different geosynthetic/ soil combinations have been exposed, exhumed, and evaluated at TRI.  TRI conducts the installation damage protocol over a one week period three times a year. Additional special sessions are scheduled on demand. The exhumed samples are then evaluated for retained properties using ASTM D4595, EN ISO 10319 or other protocols as requested by the client.

Apparatus.  The installation damage apparatus consists of steel plates 1.07 meters x 1.32 meters x 12.5 mm thick equipped with lifting chains attached along one side, railroad ties used as retaining walls, soils selected for the test, compaction equipment, geosynthetic specimens and a camera for recording the process and the conditions.

Installation Procedure.  The steel plates are placed on a flat clean rock surface with the 1.32 m sides parallel with the braced retaining walls. Retaining walls are 2 tiers high (approximately 16 inches or 0.4 m).  A layer of soil/aggregate is placed and compacted to not less than 8 inches (0.2 m).  Four geosynthetic coupons per steel plate are placed and covered with a second layer of soil. The second layer is compacted to a lift thickness of 8 inch (0.2m) and 90% proctor.

Exhumation Procedure.  The retaining walls are removed, the plates are lifted by the chains to 45º and soil/aggregate is carefully removed. The geosynthetic specimens are rolled away from the underlying surface. Exhumation damage is minimized.

Evaluating Tensile Properties.  Typically, the second phase of the program is comparative

tensile testing of baseline and exposed specimens.  TRI executes ASTM D4595 or ISO 10319 using capstan grips requiring a specimen of 42 inch (1.07m) length. The test machine is an Instron Model 5583 using Series IX Merlin data acquisition software and an Epsilon extensometer.

Scope of Testing

Characterization of a family of products typically exposes and tests 9 combinations. Each combination consists of one geosynthetic and one soil/aggregate. For each combination, tensile testing is performed on baseline and exhumed geosynthetic materials. A program of 9 combinations would usually consist of 3 styles of geosynthetic – light, medium, and heavy – and 3 soils/aggregates – coarse, medium, and fine.

Testing will be performed to meet the client’s schedule. Generally, multi-client programs lasting approximately one week are arranged in order to spread costs among the participants. Please contact us to find out when the next program will be and to receive current pricing information.

The results of testing are presented in a report that contains a summary of TRI’s Installation Damage procedure, detailed reports of the tensile testing, and pictures.

Sample requirements are a minimum of 7 meters x full roll width.