Q. What is the products permeability?
A. The Shoreblock® and Shoreloc® products are available in various percentage surface openings. The individual block's percentage opening will dictate its permeability factor.
Q. What product is appropriate for my application?
A. The Hydraulic Engineering Circular 23 (HEC 23) determines block selection by analyzing the hydraulic conditions with the ACBs permissible shear and calculating the safety factor.
Q. What determines block thickness requirements?
Typically, the design hydraulic conditions determine block thickness requirements. Other considerations include vehicle traffic, loading, etc.
Q. What is maximum velocity Shoreblock can handle?
A. Current Federal design procedures utilize bed shear stress for primary stability analysis. This approach takes into consideration: velocity, depth of flow, and energy slope gradient to determine how much hydraulic energy (bed shear) is incident on the ACBs. Block style and thickness are then selected to provide resistance to the design bed shear with appropriate safety factors based on the individual blocks maximum critical shear value as determined by, full scale, hydraulic flume testing.
Q. What filter fabric is best to use?
A. Overall, woven mono-filaments are preferred over non-woven geotextiles because of their high hydraulic conductivity and durability. However, in all cases, the soil's particle size, disbursement and cohesiveness (among other factors) will determine fabric selection. In general, if a fabric exhibits too tight of a weave (or clogs up) sub-structural hydrostatic pressure will build up and force the blocks up and out of the ACB matrix. If the fabric weave is too loose, soil particles will migrate up and trough the ACBs causing sub-structural erosion and consequential ACB failure. Most geotextile suppliers can offer assistance, and in some cases, fabric selection software to enable proper selection of the fabric.
Q. Are cables necessary?
A. Cables can help facilitate installation as well as enhance the overall long-term performance and stability of the system.
Installation - Cabled mats are more easily placed in many cases including steep slope and wet applications. Utilization of cabled mats on large projects can significantly enhance the speed of installation, where a 320 sq. ft. mat can be placed at a rate up to four mats (1,280 sq. ft.) per hour.
Stability and Performance - Loss of a single block in the revetment matrix, either from vandalism, flow of sizable debris, or short-term capacity exceeding hydraulic forces, can significantly increase the likely hood and speed at which the revetment system can fail. Use of cables can help maintain long-term system integrity and significantly reduce these risks.
Q. Do I need to be concerned about cable deteriorating?
A. Cables are typically sized to carry five (5) times the weight of the particular mat, based on breaking strength many times more than the potential load the cable will see in service after mat placement. Cable deterioration rate will depend on cable material (galvanized steel, polyester, etc.) and the service environment. Except for severe chemical environments, cable deterioration should not adversely affect the long-term system performance.
Q. What is the maximum slope Shoreblock can handle?
A. 2:1 slopes are the preferred limit. However, steeper slopes, up to 1:1, can be designed provided a proper slope stability analysis has been performed. Constructability also becomes an issue on steep (1:1) slopes with vertical elevations over 10' and will likely necessitate cables for placement.
Q. How fast can Shoreblock be placed?
A. Production rates vary depending on the type of system being installed, the accessibility of the project and geometries of the bed slope, side slope and overall configuration of the placement. In general, 4" and 6" thick Hand-Placed blocks can be installed at a rate of 40 to 90 square feet per man-hour. Prefabricated cabled mattresses can be installed at a rate of 3 or 4 mats per crane-hour.
Q. Can ACBs be assembled on the jobsite?
A. ACBs can be assembled at the place of manufacture, at a remote site, on the job or even Hand-Placed on the application (provided placement is not submerged or on a steep slope) and then post cabled.
Q. How much does Shoreblock cost?
A. In most markets, ACBs are competitive in cost to 12" diameter (or greater) rock (or riprap) placed in an 18" or greater blanket thickness. In most markets, ACBs are competitive with gabion mattresses and ACBs are typically more cost effective than cast in place concrete.
Q. How do you handle upstream and downstream terminations?
A. If the ACB system does not start and end at an existing structure, typically the blocks (and underlying fabric) are tucked into an anchor trench and backfilled and compacted with the appropriate material. In some cases, the "appropriate material" may be: concrete grout, stone, or grouted riprap instead or soil. Trench depth is typically 1.5 times the potential depth of scour. If the ACB system starts or ends at an existing structure, a reinforced steel grouted interface treatment is typically used to secure the blocks and insure that hydraulic undermining will not occur.
Q. How do you terminate at the top and toe of a slope?
A. Typically termination at the top of an embankment is achieved by tucking the ACBs (and underlying fabric) into a Top Anchor Trench. Top Anchor Trench depth can range from 12" to 36" deep depending on the specific job characteristics and potential for undermining at the top of the embankment.
Q. How do you anchor the system?
A. Anchoring ACBs can be accomplished by several different methods depending on the design objective. Most common methods utilize galvanized steel helical or duckbill anchors. Attachment to the ACB revetment will vary depending on if the system is cabled or non-cabled. If the system is cabled, then a typical method is to thread the cable through the anchor's end eye and secure it by means of compression sleeves or U bolts. The voids around the anchor attachment (whether cabled or non-cabled) are then filled with grout and struck flush with the block top surfaces.
Q. What subgrade compaction is required?
A. 95% standard proctor within +/- 3% of optimum moisture content is the normal requirement for fill embankments. Existing compaction of undisturbed soils is sufficient provided they are stable soils and do not exhibit "yielding" of soft areas.
Q. Can you drive on Shoreblock?
A. When exposing an ACB revetment to traffic, the cross section of the ACB, filter, sub-base and or sub-grade must be checked for load carrying capability. Load bearing capability will depend on the axle load, frequency of the traffic, the thickness of the ACB, the durability of the fabric and the sub-grade material type and thickness of the sub-base or sub-grade. ACB pavements subject to traffic in wet condition must also be analyzed for pore pressure development and potential for loss of fines in the sub-grade or sub-base.
Q. What is the maximum wave height that Shoreblock can handle?
A. Opposition to wave attack is primarily based on unit weight. Studies have been conducted by the Federal Highway Administration indicating ACB stability at wave heights of 11 to 10' depending on the weight of the block. Typically a 4" (30 to 40 lbs) block can withstand wave attacks of 4'. Special care and consideration should be taken when designing ACB applications for wave attack. Wave attack stability data can be obtained through the FHWA.
Q. How do you handle obstructions?
A. Several details are available in our Technical Binder. Typically, the ACB revetment system is placed in full units (full blocks with no miter cutting) until the placement of an ACB will not fit due to an impeding structure. The resulting voids between the ACBs and the structure are then filled with grout to a distance of 18" from the existing structure and struck flush with the block top surfaces.
