Geotechnical Analysis
The goal of the geotechnical team was to investigate and analyze the current soil conditions in order to design a proper building foundation and retaining wall
Geotechnical Research
Background
Our geotechnical team was provided 7 on-site boring log tables with brief ground information. We conducted further research in order to ensure a detailed and holistic view of the site conditions. The provided information, along with our additional research allowed us to create soil profiles, a foundation design, and a retaining wall design for the project site
Geotechnical Location
The center of the site is located at (Latitude, Longitude) of (33.671110, -117.850306) and falls within the 7.5 Minute Tustin Quadrangle Map
Surficial Units
It lies on alluvial, Qal, soil from the recent quarternary period
Water Table
The boring logs that were collected from our project site showed the water table depth between 55 and 47.5 feet, collected by an spt test
Seismic Hazard
It is unlikely that our site will be impacted by earthquake induced landslide activity. According to the investigation conducted by the United States Geological Survey data, our proposed project is not in a probable landslide hazard zone. In fact, the closest hazard zone is 12.5 km from our project site.
Landslide Hazard
It is unlikely that our site will be impacted by earthquake induced landslide activity. According to the investigation conducted by the United States Geological Survey data, our proposed project is not in a probable landslide hazard zone. In fact, the closest hazard zone is 12.5 km from our project site.
Tsunami Hazard
The site is far enough inland that a potential tsunami inundation hazard is highly unlikely. Therefore, it is not necessary to manage or mitigate this risk.
Geotechnical Analysis
Liquefaction Analysis
According to the Earthquake Zones of Required Investigation quadrangle map, our site is not built in a zone that is susceptible to liquefaction.
Secondly, since our water table is deeper than 50 feet and the N60 values of our soil layers are greater than 30, liquefaction is not a hazard that we have to mitigate.
Settlement Analysis
According to the building code of California, the maximum allowable settlement for a 15-story building is 2 inches.
After performing settlement calculations, it was found that the total settlement for the building structure is 1.88 inches. This falls within the 2 inch maximum and is therefore, code compliant.
Soil Profiles
Soil Profile of Boreholes: 5, 3, 1
Soil Profile of Boreholes: 5, 3, 4
Soil Profile of Boreholes: 2, 3, 1
Soil Profile of Boreholes: 4, 3, 2
Foundation & Retaining Wall Design
Possible Foundation Types
Mat Foundation: Spreads load evenly across the soil
Piles: Columns placed deep into the ground in order to transfer loads to soil/rock layers that have sufficient bearing capacity suitable for settlement requirements
Combination: Best for buildings with large wind or seismic loads, as well as significantly heavy buildings
Factors that Impact Foundation Type Selection
Location and Type of Structure
Magnitude and Distribution of Loads
Ground Conditions
Access for Construction Equipment
Durability Requirements
Effects of Installation Process
Relative Costs
Local Construction Practices
Our Chosen Foundation Design
Our design process was to establish a preliminary mat foundation design and check it against the required design criteria. If it passed, we would keep a mat foundation design; if it didn't then we would move on to pile design.
Given this process, we confirmed that a mat foundation was a sufficient foundation choice. Our calculations determined an embedment depth of approximately 20 feet, with a mat foundation of approximately 7 feet.
Possible Retaining Wall Options
Gravity Retaining Walls: Constructed with plain concrete or stone masonry. The stability depends on their own weight and any soil resting on the masonry. This type of construction is not economical for high walls.
Semi-Gravity: Made using a small amount of steel to minimize the size of the wall.
Cantilever: Made of reinforced concrete that consists of a thin stem and a base slab.
Counterfort: Similar to cantilever walls. However, at regular intervals, they have counterforts that tie the wall and the base slab together.
Factors that Impact Retaining Wall Selection
We need to consider the lateral earth pressure and test the stability of the retaining wall structure.
We need to check the structure for strength and the steel reinforcement required.
Need to check that the structure won't allow overturning, sliding along the base, nor failing bearing capacity.
Our Chosen Retaining Wall Design
Our team went through two renditions of retaining wall design.
Given the considerations to the right, the Geotechnical Team settled on a cantilever retaining wall.
