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November 9, 2013 / Brandon

About Time to go into the Lomita Grading Plan Check – B+W Engineering and Design Blog

About Time to go into the Lomita Grading Plan Check #CivilEngineer

As we are waiting to get back plan checks from other cities, mainly in the South Bay area, we are preparing to submit our Civil Engineered Grading Plan check to the City of Lomita.

We originally bid on the Civil Engineering for this grading plan thinking that the property would be sloped from back to front allowing for gravity flow to drain out through the front. As we started working out the grades, we learned that sloping the proposed grades back to front wasn’t the original concept. The idea of a pump was thrown around for about five minutes.

To start off the process of grading the site we begin in the front to see what grades we are trying to hit. This is one of the rare times that I needed a 3D model from the Architect to understand his concept. Plugging in a few grades and working my way to the back showed we had some options on how to successfully slope the lot. The worst case scenario was a pump in the backyard collecting the rear yard stormwater and pumping over two hundred feet to the front of the property. I wasn’t into this idea and had to figure out a better way to handle the stormwater. The client wasn’t too thrilled about a pump either. So I started to plot place holder grade elevations around the property to tie into the Finished Floors Elevations of the multi-unit building. Once I placed a few drains in the backyard I worked out the drainage pipe system. Now we are onto something, it turns out that it is possible to gravity flow a pipe system to the front if we lifted the backyard ever so slightly from the original Architect’s concept. The only drawback being instead of a planter wall on the backyard, a Civil Engineered retaining wall would take its place. A short retaining wall will always win out over a mechanical pump any day of the week. So now we have a grading plan ready to go. What else is left to do?

Onto my favorite parts of grading, is the Civil Engineer’s Excavation Plan. This is the step of the grading plan process to see how the contractor will dig the lot out to reach the proposed pad elevation. Based on the soils report we can cut out the lot first with a four foot vertical cut and a 1:1 slope above the vertical cut. We want to stay away from shoring if we can, and in this case we are able to. Around the five foot minimum sideyards we can work out the cut without using shoring. As we reach the front yard the four foot vertical cut can transition back into a pure 1:1 slope as there is enough room to daylight the pure 1:1 slope cut. The daylight line is key to the excavation plan as the daylight shows where the limits of grading are located. This is the proof that we can have the site dug out without passing the property line or undermining the surrounding structure. Now that we have working proposed contours and limits of the grading we move onto creating a couple of sections.

The grading plans would not be complete without showing a couple of sections. The excavation plan sections shows views looking through two different angles of the excavation plan. I prefer to cut the sections by hand instead of building a 3D model of the survey and proposed grades. I prefer this method mainly because recreating an existing topography, or survey, with only spot elevations is time consuming and shows more detail than necessary. All we are looking for is where the daylight line hits in relation to the property line and about how deep the Cut or Fill will be relating to the existing grades. We also show the one foot spacing between the toe of the slope and the building outline. In this case the building outline is the subterranean parking garage. We will still build a rough existing surface and proposed surface in order to get estimated earthwork quantities, cut and fill cubic yards.

The final step for these particular grading plans is writing the Hydrology Study. First we map out the existing drainage pattern and calculate the existing flowrates and directions. Ultimately finding the quantity and where the stormwater exits the property. We then break out the proposed grading plan to see where the proposed stormwater will travel and the quantity flowing through area drains and drainage pipes. Last, we calculate the size of the pipes exiting through the curb face and into the street. With the stormwater finding its way to the street storm drain system, leading into the ocean. We break out each proposed area and drainage pattern to size each catch basin. From there as the flow increases we increase the size of the drainage pipes as we work our way to where the stormwater will exit the site. We can then detail out the grading plan with area drain sizing and drainage pipe sizing using construction notes.

I am outlining the steps on a basic site to show current and future Civil Engineering clients our workflow for grading plans.

The post About Time to go into the Lomita Grading Plan Check appeared first on B+W Engineering and Design Blog.
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