fabric thickness are intermediate between the two fabrics described above. 

 Normally, they have less permeability and fewer voids. 



4 Combination Bonded . A number of nonwoven fabrics are a 

 combination of two - or more of the above methods to construct a finished 

 product. Due to the variety and numerous combinations available, it is 

 impossible to make an applicable statement regarding pore properties and 

 thickness of this classification of fabrics. 



(c) Combination Fabrics . Fabrics have been produced by combin- 

 ing woven and nonwoven fabrics using one or more of the bonding methods 

 described above. Usually, these combination fabrics are produced to enhance 

 a particular property or performance requirement not found sufficient in 

 either of the singular types of fabric construction. Hundreds of such com- 

 binations are possible with an equal, or greater, number of finished fabric 

 forms and properties. Each must be evaluated in view of the application 

 being considered. 



The 1977 CE Guide Specification CW 02215 (U.S. Army, Corps of Engineers, 

 1977) states that "The fabric should be fixed so that yarns will retain their 

 relative position with respect to each other. The edges of the fabric should 

 be finished to prevent the outer yarn from pulling away from the fabric." 

 Regardless of the fabric construction, this requirement is necessary to 

 ensure continuous acceptable performance. 



(3) Physical Property Requirements . In few other applications is a 

 filter exposed to so many damaging forces as in most types of coastal struc- 

 tures. Consequently, physical property requirements for geotextile filters 

 are more stringent for these applications. Suitable physical (mechanical) 

 properties are not only necessary during the construction process, but in the 

 permanent structure as well. Due to such structure's constant exposure to 

 dynamic loading, from waves and currents, armor and underlayer movement, 

 earth and hydrostatic pressure, and rapid fluctuations, any geotextile used 

 must have sufficient tensile and abrasive strength to retain its integrity 

 throughout the life of the project. 



The test methods used to determine geotextile 1 s physical property re- 

 quirements are primarily textile tests. However, the test methods and re- 

 quirements referred to herein can be related to the field performance of 

 woven geotextile filters. Evaluation has confirmed successful performance of 

 fabrics having a particular character. Many of the required test results 

 have been verified by more than 20 years of field performance. 



If test methods or results and specifications other than those re- 

 quired in this section are employed, they should be thoroughly evaluated to 

 determine if the method and results are applicable to the intended function 

 or performance in the application of interest. Test methods for required 

 physical property determination are described in Appendix C. 



(a) Properties Required for All Applications . 



1 Tensile Strength . Adequate fabric strength is necessary 

 to withstand dynamic forces, prevent the movement of the- geotextile filter 

 through voids in the stone layer above the fabric, as often occurs with 



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