KEC Week 9

I have a little catching up to do on this project since the idea to blog about it came to me several weeks into construction.  I will take this time to bring you up to speed with general progress to date.  There is a long and interesting story of the Preconstruction phase that I will get into at another time.  I will also focus many future entries on the sustainable features of this project.

Quick project stats: 31,818sf.  LEED Platinum goal.  Energy Net Zero goal.  Cost not disclosed at client request.  Schedule 15 months (Spring '11 to Summer '12).  Project website with webcam access: http://www.choate.edu/aboutchoate/kohler_environmental_center.aspx

[site prior to start of construction]

We mobilized in late March, starting first with our site erosion control in accordance with the Erosion and Sedimentation Control Plan (ESC) and Storm Water Polution Prevention Plan (SWPPP).  The project was kicked off with a groundbreaking ceremony on April 1, 2011.  Everyone was in good spirits despite the raw weather and snow flurries.

[groundbreaking]

Once the ceremony was complete we continued with erosion control and a small but necessary amount of tree clearing to allow for a new entry drive to access the new building.  Erosion control for this project originally consisted of silt fence and temporary sedimentation traps (TST), along with track pads consisting of crushed stone at the site entries.  LEED requires an ESC plan under one of its prerequisites (SS P1) and the intent is to reduce pollution from construction activities by controlling soil erosion, waterway sedimentation and airborne dust generation.

[silt fence to protect adjacent property from run-off]

[silt fence and hay bales to protect adjacent property from run-off]

[temporary sedimentation trap TST with silt fence and topsoil stockpile]

[silt sock in adjacent catch basin to prevent silt from entry to stormwater system]

[TST]

Topsoil was stripped and stockpiled on site.  Because this site was previously used as a farm years ago, the topsoil depths ranged from 18"-20" which is an unbelievable amount compared to what we would typically see on most sites.  The topsoil stockpile was protected by surrounding it with silt fence and spraying it with grass seed to establish root development and prevent the stockpile from wind or water erosion.  When the project is complete the topsoil will be re-spread to similar depths on site and reseeded with native hay seed to restore the site to its natural state.  This depth of topsoil also helps to establish the native species without the need for a permanent irrigation system.

[topsoil stockpile with silt fence and grass seed to prevent airborne dust and erosion] 

April and May were particularly rainy this year.  These heavy rains coupled with our specific soil conditions, which consists of a very fine clay, presented some challenges with respect to stormwater management.  The SWPPP was modified to include haybales, check damns, detention basins, and the use of a product called Floc Logs.  This was a really very interesting product that we had not used before.  The very fine silts from the red clay on site remained suspended in the stormwater and did not settle out at all resulting in a very high turbidity.  There was a general concern that this high turbidity water could have adverse affects if it left the site and entered nearby streams without first being treated in some way.  Also because of the tight clays and frequency of rains, the TST's were at maximum capacity and took a long time to drain down if at all.  We set up what was best described as a chute, similar to a water slide with jute mesh and Floc Logs.  Stormwater was then pumped down the chute and as the turbid water passed over the Floc Logs, the Floc Logs act to bind the fine silts together so that they settle out of the water and drop to the jute mesh on the bottom of the chute.  The water comes out the low end of the chute crystal clear.  You really need to see it to believe it, but it worked great and helped to alleviate our stormwater management challenges.

[TST with hay bale check dams]

[stormwater detention]

[modified stormwater detention area with pipe chute (center coming straight at the camera) with jute mesh and Flog Log feeding into detention area]

[sample Flog Log photo, Floc Logs are the blue sqaures on the right and are about 18" x 6" and they are like a large cube of Jello]

Our building excavations started on the East wing which is a 2 story structure with a basement.  Prior to construction, a geotechnical engineer uses a drill rig to drill or bore down into the ground to determine what type of soil conditions are present on site.  They may encounter a wide range of materials like gravel, clay, glacial till, or bedrock to name a few.  This information is used by many of the team members to design foundations and plan for site excavations.

[sample drill rig]

The original soil boring logs indicated that we would encounter weathered bedrock while excavating for the basement when we went about 10 feet below grade and these borings proved to be very representative of the actual conditions.  The main excavation was down 14' and the deepest point for the elevator pit and sewerage ejector pit were down about 18', which means we had between 4' and 8' of rock to remove.  Our hopes were that the weathered bedrock would peel up with the excavator and as we got into harder bedrock it would need to be broken up using a hoe ram.  These methods were used and found to be effective.

[excavation for basement foundation]

[bedrock removal]

[bedrock removal (red) and crushed stone (blue) base material for foundations]

This gets us pretty well caught up.  We have just started basement foundations.  We start with formwork and rebar for the basement footings and walls.  We are working the foundation crew long days to make up some of the time lost due to the rains this spring.  We expect to be able to make back the lost time with a combination of crew sizes and overtime over the course of the summer.

[basement foundation footing formwork on crushed stone]