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<br /> <br />EM 1110-2-1601 <br />1 July 70 <br />t"'\ <br />\,,-~~ . <br /> <br />except when stone is unusually costly and/or labor unusually cheap. Steeper <br />side slopes can be used with hand-placed riprap than with other placing <br />methods. This reduces the required volume of rock. However, the greater <br />cost of hand placement usually makes machine or dumped placement methods <br />and flatter slopes more economical. Hand placement on steep slopes should <br />'I be considered when channel widths are constricted by existing bridge openings <br />. <br />or oth~r structures and when rights-of-way are costly. In the machine place- <br />ment method, sufficiently small increments of stone should be released as <br />close to their final positions as practical. Rehandling or dragging .opo:rations <br />to smooth the revetment surface tend to r.esu~t in segregation and breakage of <br />stone and rough rev.etment surface. Stone should not be dropped from an ex- <br />cessive height as this may result in the same undesirable conditions. Riprap <br />placement by dumping and spreading is the least desirable method as a large <br />amount of segregation and breakage can occur. In some cases, it may be <br />economical to increase the layer thickness and stone size somewhat to offset <br />".e shortcomings of this placement method. <br />m. Riprap Test Samples. Provisions should be made in the specifica- <br />tions for testing an in-place sample of riprap material as soon as a repre- <br />sentative section of revetment has been completed. Additional sample testing <br />of in-place and in-transit rip rap material at the option of the Contracting <br />Officer should be specified. The frequency of sample testing should depend <br />on the ease of producing riprap material that complies with the specifications. <br />The sbe of test samples should be sufficient to be representative of the rip- <br />rap material. Truck-load samples are usually satisfactory for in-transit <br />material. The following tabulation should be used as a guide for the size of <br />in-place samples. <br /> <br />Riprap Layer <br />Thickness, in. <br />12 <br />18 <br />24 <br />30 <br />36 <br /> <br />Size of Samples, <br />cu yd Bulk Volume <br /> <br />1 <br />2 <br />5 <br />10 <br />16 <br /> <br />14m <br /> <br />46 <br /> <br />I <br />1 <br /> <br />''---~ <br /> <br />..... <br />