Field Work-revised

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The useful field trip Our investigation site, the washed out Old Mt Baldy Road, is located in San Antonio Canyon and can be accessed by the first yellow gate. After being badly damaged, Mt Baldy Road was rebuilt. After visiting the field, we attempt to conduct its topographic, geologic, and hydrologic conditions of the site for analyzing the current conditions and for further engineering improvement. Based on the information obtained, we determine the stability of the new road, propose a solution to enhance its stability, and finally rebuild the washed out Old Mt Baldy Road.

A/ Site Characteristics and Observational Data

The washed out Old Mt. Baldy Road is located at the San Antonio Mountain, Claremont, Los Angeles, California. Its elevation is about 2950ft from the sea level. It was built long a ago on a bedrock named Mesozoic metamorphosed diorite. Due to limited engineering technology at that time, the road was built using as little earthwork as possible, resulting in steep slopes with various rock fractures falling. Later, the new road is rebuilt on the Quaternary landslide deposit with the bedrock beneath. This time, engineers used more cuts to build the new road. As the result, the new road is more stable and durable. Looking down from the Old Mt Baldy Road, we see the San Antonio Creek. Its water is supplied by a stream from San Antonio Mountain or Mount Baldy.

Topographic Map of New and Old Mt Baldy Road

Overview of the existing road and the old road

Topographic Profile with Geologic Features

Geologic Map of San Antonio Canyon Area

At the west side of the Old Mt. Baldy Road, there are many bedrock fractures and wedge failures. First, we have bedrock factures occurred at several locations.

The Fracture Bedrock 1

The Fracture Bedrock 2 Fracture bedrock data: 348 / 67 NE 320 / 68 NE 336 / 73 NE 358 / 77 NE The average dip angle is 71°

Stereo-net of fracture bedrock. Compare with friction angle, there is one fracture bedrock in daylight condition

Friction angle θ = 35° - 45°

We also have wedge failure situation.

The Wedge Failure

Wedge failure data: 339 / 62 NE 225 / 33 SE 274 / 45 SW

Stereo-net of wedge failure. Compare with friction angle, there is one wedge in daylight condition

Friction angle θ = 35° - 45°

Stereo-net of wedge failure

Lay at the east side of the Old Mt. Baldy Road a creek. East edge of the creek is formed by alluvium with 10m wide to 20m to bedrock contact

Detailed geologic map

Two or more cross sections through our site

Location A:

Location B (northern of location A)

Location C (southern of location A)

B/ Analysis and Discussion: 1/ Enhance its stability: At the west side of the road, the dip angle is as high as 71°, but the bedrock is made by Mesozoic metamorphosed diorite (Md), which has a friction angle from 35° to 45°. In addition, there are fracture bedrocks and wedge failures at the west side of the Old Mt. Baldy Road. They could form potential failure surfaces. Therefore, a possible solution is excavating the bedrock and the landslide to reduce the dip angle and remove the fractures and wedge failure. (Insert view of slope at right angles to the line of intersection of wedge failure)

(Insert potential unstable – discontinuities “daylight” in face)

2) Rebuild the Old Mt. Baldy Road How we choose the suitable solution depends on each cross section. For example, at location A, the dip angle that is about 52º, so we need to cut the fracture bedrock at the west side and we reduce the dip angle at the east side.

Before enhancing its stability: SF =

After enhancing its stability:

SF =

Then, at location C, there is a creek alluvium at the east side. For enhancing its stability, we need to cut the fracture at the west side and build a retaining wall at the east side. To reduce the cost of construction, we can use the amount of soil excavating from the west to fill at the east side.

Before enhancing its stability:

SF = After enhancing its stability: SF =

In conclusion, this field trip helps us to apply our knowledge of geology for solving the washed out Old Mt. Baldy Road. Though we have shortcoming of our solution for enhancing its stability, we will our knowledge of geology as our background for our future career