Q. Jacksonville法体積計算(Modification of Jacksonville Post-dredge Method to Compute Boxcuts)[英語]
Fran Woodward of the USACE Jacksonville District recently got in touch with us and requested some changes in the Jacksonville Post-dredge computation method that currently exists in the CROSS SECTIONS program. These changes include:
- The ability to compute the overdepth material using either ALL or Contour dredging methods.
- The ability to exclude the side slope areas from all computations.
- The ability to compute box cuts that provide for side slope material to slough off into voids created beneath the overdepth template around the toes.
There are now two options for the computation of overdepth material. These are "All" and "Contour". Using the "All" option, all material in the area between the design template and overdepth template will be computed. Using the "Contour" option, overdepth material will only be computed where the measured depth is less than the design template. This is identical to the technique used in the Philadelphia Methods of CROSS SECTIONS and the TIN MODEL.
The big change is the revised computation of box cut quantities. Take a look at the figure.
Digging precisely on the side slope is a hard job. In areas where the bottom material is soft, contractors are sometimes allowed to dig deep holes at the toe locations, with the idea that the material on the side slope will fall into the holes created.
In a soon-to-be released version of the CROSS SECTIONS program (it didn't make the 00.5B release), the following quantities will be computed separately for the left side and right side of each pair of survey lines.
A =The remaining side slope material from the after-dredge survey that is above the overdepth template. This will include all material above the design template and between the design and overdepth templates. This material is orange in the above figure.
B =The void present from the toe line outward from the centerline where the after-dredge survey is deeper than the overdepth template. This material is green in the above figure.
C =The void present from the toe line inward towards the centerline a user-specified distance where the after-dredge survey is deeper than the overdepth template.
These areas are computed for each line. [Separate areas are computed for the left and right sides of the channel. The program then uses the Average End Area formula to compute the volume of material contained in the A, B, and C areas between each pair of survey lines.
The Box Cut Volume is then determined by using the following rule:
If A > (B + C) then Box Cut Volume = B + C
If A < (B + C) then Box Cut Volume = A
For example, if I have 80 yd³ of available material remaining on the side slope and I have dug a void of 200 yd³, I'm only going to get credited 80 yd³. [I can't have more material fall into the hole than actually exists.]
Likewise, if I have 150 yd³ of available material on the side slope and I have dug a void of 75 yd³, I'm only going to get credited 75 yd³. I'm only going to get credit until the void is full.