Proposed Foundation Design for Tenth Line Development
The purpose of this report is to design a foundation for a development proposed at Tenth Line road in Orleans, Ottawa. The foundation should be able to transfer the load of four different columns to a capable sol layer beneath the foundation as well as limit settlement and differential settlement to 25mm and 19mm respectively. A deep foundation is necessary for the development and therefore the piles were designed to transfer the load as well as limit the settlement.
As a result of the ranging column loads, different amount of piles were required per column for economical and practical reasons instead of varying the pile length and diameter for each column loading case.
The columns were arranged from the lowest load C1 to the highest load C3 in the order C1, C2, E4, C3, The columns required 1, 2, 3, and 4 piles in the same order as the column arrangement. Following the design of the foundation, the design was able to transfer all loads to a capable soil layer and also limit the settlement well below 25mm and the differential settlement below 19mm.
Scope of Work
The objective of this project is to design foundations for a proposed commercial development located on Tenth Line in Orleans. The foundations are required to support the load of the 50 x 60 m building area. The dominant soil in the region of Orleans is the clay-type of soil, therefore we will be working with fine-grained soils and we have to take into consideration the cohesion of the soil and the angle of friction as main soil parameters. The provided geotechnical report will allow us to conduct an analysis to ensure that the foundations stresses will not overburden the soil and cause excessive settlement of the building or failure of the soil. The proposed construction of the building will start with an excavation of the construction site, since we are including a basement level for this development. The soils will be excavated and there we will be placing the foundations.
Using the provided information obtained from the Paterson Group geotechnical report, we will be determining if the soil parameters and conditions in order to design the foundations for the columns C1, C2, C3 and E4. The design of the foundations will depends on the soil parameters of the silty clay underneath the surface. Our choice for this development is a shallow foundation, we will be designing the foundation in for the short-term and long-term life of the building according to the ultimate limit state and the serviceability limit state.
Proposed Development
The new project is located near Tenth Line road in Orleans Ottawa. It’s a commercial building in a residential area. The proposed development measured 100 m of length and 100 m of width. The property of the project should be located inside of the limits and 100 m away from Tenth line road and 7m away from the local street. Building footing placement may be measured 60 m in parallel at local street and 50 m in parallel of tenth line road.
Method of Investigation
Site Conditions
A geological survey of the proposed site was conducted by the Geotechnical Division at Patterson Group. Subsurface conditions were determined with a combination of in-situ and laboratory tests involving augers, Shelby tubes, split spoon samplers, and standpipes. Dynamic cone and standard penetration tests were also performed on-site. Information obtained by Patterson Geotechnical is summarized in Appendix A. A Field survey of the site was conducted by Patterson Group and Santec Corporation. The locations and ground surface elevations at each borehole are presented in Appendix A.
Design Parameters
As per recommendations made in the geotechnical report, and the client’s requests, several factors must be considered when designing the building’s foundation.
- Foundation depth must be sufficient to accommodate one underground level.
- Site is 100m x 100m and the building is 50m x 60m. Building can be located anywhere on site.
- Ultimate and Serviceability limit states must be satisfied.
- Some parameters.
- Maximum total settlement: 25mm
- Maximum differential settlement: 19mm
- Maximum lateral deflection: 20mm
- Minimum foundation depth: 3m (below grade)
- Maximum grade raise: 0.3m
- G.F.L 0.00 is at E.L.V. +88.53
- Loading conditions (Column Loads):
Axial Compression Lateral Load C1 235 kN 1.5 kN C2 475 kN 2.5 kN C3 900 kN 5.0 kN E4 700 kN 4.0 kN
Subsurface Conditions
This section entails the subsurface conditions based upon the drilled boreholes at the proposed site location. These soil conditions consist of topsoil overlying silty clay, there is also a layer of glacial till overlying bedrock. The silty clay is inferred from the cone probes and extended up to depths of 20-26m while the bedrock surface had a depth range of 26.67 to 21.79m as it tends to slope upwards from the North to the south. For this project, the main boreholes used in determining the subsurface conditions were Borehole 1 and Borehole 2 which were provided by the Paterson group and were at a distance less than 100m from the chosen site. These boreholes were selected to be representative of the soil beneath the foundation based on the proximity of the selected site. Hence, there was no other reason for looking into other boreholes especially borehole 3, which seemed the most relevant but provided little variation in terms of soil layering when compared to borehole 1 and borehole 2. Shear strength v depth graphs are in appendix
Top Soil
The topsoil encountered at the ground surface at all the borehole test holeshad thickness varying 80mm to 280m. Therefore, it is assumed that the original thickness of the topsoil was 280mm while the rest was naturally stripped away. From the geotechnical report, the recommendation for the poposed site is was to stripp a total of 300mm to completely remove the topsoil and ensure a flat surface.
Silty Clay
Silty clay is the dominant soil type within the proposed location and is located beneath the topsoil at all the test hole locations. The top most layer of the silty clay has been weathered to a to a dark brown dessicated ‘crust leading to a loss of moisture and a depth extension of 2.6m below the original ground surface which was 2.3m below the finished grade. According to the Dynamic Cone Penetration Test DCPT, the silty clay layer has been inferred to extend to depths of between 20m and 27m. This depth extends down to the bedrock within the subject development area. In situ shear vane field tests were carried out within the dessicated layer and relatively high undrained shear strength values were obtained. The silty clay found beneath the dessicated layer appeared to be grey and brown in colour and had depths ranging from 5m to 5.8m below original ground surface and 4.7m and 5.5m below finished grade elevation respectively.
The silty clay yielded peak undrained shear strength values between 20 kpa and 50 kpa indicating a soft consistency. A firm layer of clay was also found under the soft grey and brown clay. A shear profile provided by paterson group was used to read the undrained shear strength values which was determined to be 25 kpa at the top of the firm layer and increasing with depth to values approaching 130 kpa.
Glacial Till
The glacial till layer was inferred beneath the silty clay layer near several boreholes and close to the site of Borehole 1. Glacial till typically consists of a fine soil matrix which is mixed with gravel, cobble, and boulders. It is very important to note that the glacial till will have little impact in this design and the settlement within this thin layer can be considered negligible.
Ground Water
Groundwater table is the top level of an underground surface in which the soil is permanently saturated with water. The water table separates the groundwater from the fringe, or aeration zone, located above it. The water table fluctuates with the seasons and with the year and is affected by climatic variations and the amount of precipitation used by the vegetation. It is also affected by the withdrawal of excessive amounts of water or by artificial recharge. In our project, the Groundwater table is located at the 1.2 m level. The Borehole 2 is the one with the most data available. That's why our point of reference was this one.
Depth of Foundation
Given that groundwater table is located at 1.35m, the boronhole depth is approximately 21.79 m at 26.67 m, taking into account boronhole BH-1 and BH-2. Foundation length is 11.5 m.
Soil Parameters
The soils parameters were obtained by the information of the borehole log in the rapport statement. The soils have 3 layers is especially composed of silty clay. The groundwater table is located at 1.35m. The following figure shows the different layers and their parameters.
Subsurface Profile
Foundation Analysis
Subsurface Profile
Prior to the foundation design, the multiple borehole logs obtained from the Paterson group were analyzed and tabulated to determine the general soil arrangement under the ground surface. As mentioned earlier, the dominating soil in our case is silty clay, a fine-grained type of soil. In the figure below, there is a representation of the general soil distribution in both X-X and Y-Y directions of the proposed development (check Appendix D). The following figures and tables will allow us to determine the profile of our soil and allow us to determine the parameters of the building:
Y-Y Direction Borehole Readings (BH2 to BH1)
| BH-2 | ||
|---|---|---|
| Type of Soil | Elevation (m) | Depth (m) |
| GROUND LVL | 88.53 | 0 |
| TOPSOIL | 88.45 | -0.08 |
| SILTY CLAY | 74.13 | -14.32 |
| Inferred SILTY CLAY | 52.34 | -21.79 |
| BH-1 | ||
| Type of Soil | Elevation (m) | Depth (m) |
| GROUND LVL | 88.53 | 0 |
| TOPSOIL | 88.45 | -0.08 |
| SILTY CLAY | 73.82 | -14.63 |
| Inferred SILTY CLAY | 47.72 | -26.1 |
Representation of Y-Y Direction Soil Profile (BH2 to BH1)
X-X Direction Borehole Readings (BH3 to BH1)
| BH-3 | ||
|---|---|---|
| Type of Soil | Elevation (m) | Depth (m) |
| GROUND LVL | 88.21 | 0 |
| TOPSOIL | 88.06 | -0.15 |
| SILTY CLAY | 73.43 | -14.63 |
| BH-1 | ||
| Type of Soil | Elevation (m) | Depth (m) |
| GROUND LVL | 88.53 | 0 |
| TOPSOIL | 88.45 | -0.08 |
| SILTY CLAY | 73.82 | -14.63 |
| Inferred SILTY CLAY | 47.72 | -26.1 |
Representation of X-X Direction Soil Profile (BH3 to BH1)
In the case of this report, we will be assuming that the soil parameters are uniformly distributed under the soil between BH-2 and BH-1. The parameters are deducted using the results of the soil samples of BH-2 and we assume that those parameters are equally distributed everywhere under the building as mentioned earlier.
Standard Penetration Test
Paterson conducted multiples test to allow us to mathematically determine the soil parameters. In this case, an SPT test was conducted. The corrected N value was calculated by determining the following coefficients CE, CR, CS, CB. The following table summarize the calculation of the angle of friction:
SPT Results
| Layer | z (m) | z (ft) | N | Ce | Rod Length (ft) | Cr | Cs | Cb | N(60) | σ'v (kPa) | Cn | N1(60) | φ' |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2.6 | 8.52 | 12 | 1 | 15.5 | 0.85 | 1.12 | 1 | 11.4 | 22.87 | 2.1 | 23.9 | 39 |
| 2 | 6.4 | 20.9 | 5 | 1 | 27.9 | 0.95 | 1.1 | 1 | 5.22 | 36.29 | 1.6 | 8.7 | 32 |
| 3 | 14 | 45.9 | 2 | 1 | 52.9 | 1 | 1.1 | 1 | 2.2 | 69.1 | 1.2 | 2.6 | 26 |
Column and Sheet Pile Design
Columns
With parameters set, column size will be determined. One column will be designed which will have capacity for all loading conditions. The selected pile dimensions will have a FS > 2 for all conditions. Piles will be made of poured concrete with a steel coating.
To accommodate one underground level (2m), foundation start depth will be set to 2.5m. The first pile considered will have a length of 11.5m and a diameter of 0.4m.
Pile Details: Iteration One
| Start Depth [m] | 2.5 |
| Length [m] | 11.5 |
| Diameter [m] | 0.4 |
| GWT Depth [m] | 1.35 |
FS for Axial Loading: Iteration One
| Loading Condition | Axial Load [kN] | FS (TSA) | FS (ESA) |
|---|---|---|---|
| C1 | 235 | 1.59 | 1.28 |
| C2 | 475 | 0.78 | 0.63 |
| C3 | 900 | 0.41 | 0.33 |
| E4 | 700 | 0.53 | 0.43 |
This proposed design is therefore inadequate.
Variations were made to the pile’s diameter and length until a suitable design was found. To keep the depth and diameter of the piles at a reasonable size, groups of piles were considered for the larger loading conditions.
After several iterations, an adequate system of piles was developed for the loading conditions. Results are summarized below. Summarized lateral deflection results in appendix. All designs had lateral deflections within tolerable limits (<10mm).
Selected Designs for Loading Conditions
| Loading Condition | # of Piles, Spacing if Applicable | Diameter [m] | Length [m] | FS (ESA) |
|---|---|---|---|---|
| C1 | 1 | 0.6 | 11.5 | 2.09 |
| C2 | 1 | 1.0 | 11.5 | 2.02 |
| C3 | 4, 0.9m | 0.45 | 11.5 | 2.05 |
| E4 | 3, 1.1m | 0.55 | 11.5 | 2.11 |
Checking Settlement
- The piles will be bored piles, reinforced with steel and made of poured concrete.
- F’c = 40 MPa; Ep = 30 100 MPa
- For medium stiff to stiff clay: Es = 47.85 MPa
- Ep/Es = 629 > 500 ; Elastic deformation is negligible
- As seen in appendix E, for all loading conditions, Rs > Qapp
- Since shaft resistance mobilizes well before toe resistance, for the piles designed, under normal loading conditions: QTA = 0
For group settlement calculations, the Neutral Plane was found to be at a depth of 10.166m. This depth corresponds to two thirds the length of the pile. The compressible layer was assumed to be the layer of stiff to firm clay which extends from the neutral plane to bedrock. Bedrock depth was assumed at 20m. From the geotechnical report, the following information was determined. Borehole two sample TW7 was selected as the reference since its sample depth is 12.6m ≈ 10.166m. Data was obtained from the void-ratio v stress graph and table two: Summary of consolidation test results Avalon West -EVC-N5. Preconsolidation Pressure σ'p = 145 kPa. Ccr = 0.026. eo = 1.45. Settlement of the group piles was determined with this information.
Summary of Pile Settlement
| Loading Condition | Settlement [mm] |
|---|---|
| Single Piles | |
| C1 | 7.72 |
| C2 | 14.10 |
| Pile Groups | |
| C3 | 10.27 |
| E4 | 7.72 |
Since settlement is less than 25 mm for all piles, and ΔSmax = 6.38mm (between C2/E4 and C1) is less than 19mm, the proposed column designs meet settlement requirements.
Sheet Pile Walls
From the strata of the soils parameters, we decided to use for the design sheet pile wall in the foundation. As the soil was composed of silty clay, sheet pile guaranteed to retain the earth and water. It has the function of preventing the risk of landslide during the laying of foundations. Dredge line: 3m. The anchor is placed at 0,675 m below the ground surface. For design calculations see the full version of this report in Appendix.
Soil Profile
Conclusion
The proposed design met all design requirements therefore we can conclude that it is the most effective design option available for the soil and load conditions provided. Our geotechnical team took into consideration the major important details when designing the foundation, column and piles and adjusted our design criteria to fit all economic and safety criteria.
Due to the site location and proposed development, four major designs were made according to the four columns to provide a safe environment as well as transfer the loads in a safest way possible to avoid any failure mechanism.
A future recommendation concerning the project would be to provide additional current data concerning drawings, borehole logs, soil profiles as close as possible to the proposed location.
Appendix
The original report is available from the provided link. It contains all images, tables, and appendicies referenced in the text.