Homework - Construction Dewatering

In this exercise, we will design a dewatering trench using the Dupuit analytical solution and we will design a dewatering system for the Provo City Center Temple excavation site using a Python script in a Google Colab notebook.

Exercise 1 - Dewatering Trench Design

The Los Pollos Hermanos Corporation is planning to build a new manufacturing facility near the Rio Grande River in the outskirts of Albuquerque, New Mexico. The facility will include a hermetically-sealed underground unit with state-of-the-art ventillation and chemical-processing equipment. In order to dewater the site during construction and to ensure that it stays dry while in operation, the company decides to build a french drain between the river and excavation as follows:

A pump will be attached to the drain and the water will be returned to the river. Calculate what capacity will be required (gpm) for the pump. To simplify your calculations, assume that there is a lower permeability layer at the elevation corresponding to the bottom of the excavation. Use a spreadsheet for your calculations.

Exercise 2 - Provo City Center Temple Dewatering

The Provo City Center Temple is a temple of The Church of Jesus Christ of Latter-day Saints in Provo, Utah. The temple is located on the site of the former Provo Tabernacle, which was destroyed by fire in December 2010, leaving only the outer brick facade intact.

The Church of Jesus Christ of Latter-day Saints announced during the October 2011 general conference that the structure woud be rebuilt as the Provo City Center Temple. This is an architect's rendering of the planned temple:

The engineers in charge of the reconstruction faced a difficult task. As a temple, the structure would need to have a basement to house a baptismal font. Furthermore, there was a need to ensure that the reconstructed building is supported by an adequate, modern foundation. This would have to be done without damaging the fragile brick facade. To this they designed an elaborate system of piles:

The excavation went down to a depth of 30 feet below the original ground surface. This presented another challenge because the water table in this region is shallow. In order to accomplish the construction, the site had to be dewatered. This is typically accomplished using a set of shallow wells where each well lowers the water table and creates a "cone of depression" surrounding the well. Multiples wells provide a combined effect resulting in an aggregate zone of drawdown.

Our objective in this exercise is to design a dewatering system using the Google Colab notebook we used for the in-class exercise. The notebook is available at the following link:

Python starter file:

(a) Setup Problem

Before starting, download the following GEOJSON file:

GEOJSON File: temple.geojson (right-click and select "Save Link As")

This represents the footprint of the excavation:

Run the cells to upload the file and visualize the excavation site. You will then interactively create wells by using the point tool to create points corresponding to the well locations. Start by creating 2 wells.

(b) Drawdown Calculations and Manual Design

Assume the following parameters for the problem:

Parameter	Value	units
\(k\)	0.007	cm/sec
\(H\)	30	m
\(R\)	400	m
Design H	25	m
\(Q\)	0.025	m³/s

Enter these values and run the cells to calculate the drawdown at each point in a grid covering the site and visualize the results with the contour plot options.

Now design a dewatering system under three conditions: 2 wells, 4 wells, and 6 wells. In each case, assume that the you can only place the wells outside of the temple footprint. You should change the location of the wells and the total pumping rate. To change the location of the wells, run the optional cell just under the map to delete your prior set of wells and create new wells and then run the following sequence of cells to generate the drawdown map.

Save a copy of each of your designs. Right-click on one of the contour plots showing the water level or head difference inside the excavation and click "Save Image As". Open a Word document and write a short section for each of your three designs (including the contour plots) and discuss the results. Indicate which of the three designs you would suggest using for the actual project.

(c) Rectangular Well System Design

Next, use the algorithm that automatically places a line of wells around the perimeter of the excavation based on an offset distance from the excavation boundary and a specified well spacing. Use an offset of 20m and 8 points along the x-direction.

(d) Pumping Rate Optimization

For the rectangular well system, use the optimization algorithm to find the optimal pumping rate that will dewater the site with the well configuration described above. Save a copy of the contour plot showing the drawdown and include it in your report along with your pumping rate in gpm.

(e) Design Curve

Finally, run the code in the last section of the notebook to generate a design curve for the well system. Save a copy of the plot and include it in your report. Also indicate how many wells you would recommend using, based on the design curve.

Submission

Make a zip archive of your spreadsheet for part 1 and your Word document for part 2. Submit the zip archive on Learning Suite.

Grading Rubric

Total: 30 points

Criteria	Points
Exercise 1: Pump capacity calculation	8
Exercise 2a: Problem setup and file upload	2
Exercise 2b: Manual design - 2 wells	3
Exercise 2b: Manual design - 4 wells	3
Exercise 2b: Manual design - 6 wells	3
Exercise 2b: Design comparison and recommendation	3
Exercise 2c: Rectangular well system results	2
Exercise 2d: Optimized pumping rate	3
Exercise 2e: Design curve and well recommendation	2
Documentation and presentation quality	1