‘Geotechnical’ Category

Crosslot Bracing

Photo Credit: Alex Mead

Seen here is a textbook example of crosslot bracing of an excavation. Crosslot bracing is used when the horizontal soil pressure of an excavation is simply too high to retained by tiebacks or other method of wall support. One drawback, however, is the need to not hit the braces when working in the excavation. As can be seen at the top right of the excavation an excavator needs to be careful to lower its boom as to avoid striking the steel braces as it compacts fill in the future basement.

Suspension Bridge Cable Embankment

Photo Credit: Alex Mead

Seen here is the cable anchorage for the Ambassador Suspension Bridge over the Detroit River. This large mass of concrete is designed to deliver the opposing forced on the main cables of the bridge after they have passed over the towers. In the concrete mass the seemingly large single cable actually breaks apart into the smaller cables it is made of for anchoring purposes. The length of each cable embedded in the concrete is very important to prevent pull out of the cables and is calculated according to reinforced concrete code ACI 318.

Pile Cap for Driving

Photo Credit: Alex Mead

Seen above is a steel H pile that will be used on a bridge project. The end of the pile is not strong enough to be directly driven into the ground so a protective tip, called a pile point, is welded on the end. Without the pile point the flanges could separate from the web and greatly affect the strength of the pile and make driving it further into the ground very difficult. In soft ground many times pile points are not needed, however, as a precaution some firms use them almost always when driving piles.

Railroad Embankment Failure

Photo Credit: Karl Jansen

Pictured here is the aftermath of an embankment failure. The spring of 2011 has brought record amounts of rain to the midwest, and this rain has to go someplace. This railroad track in Ann Arbor was supported by approximately 30ft of earth and aggregate embankment. Water from rain runoff flows along side the embankment, and slowly infiltrates into the ground. However, with all the rain this spring, the water wasn’t able to infiltrate quickly enough and a pond formed. This pond of water had the strength to push approximately 2000 CYD of earth and trees onto the adjacent Plymouth Rd. It left nearly 200 ft of railroad track suspended like a roller-coaster about 25ft above the washed-out ground. Fortunately, no trains were scheduled to use the track before emergency personnel were notified and responded to the situation.

Pedestrian Tunnel

Photo Credit: Karl Jansen

Pictured here is a pedestrian tunnel under a roadway. Similar to a culvert, a tunnel starts from an open space and ends in an open space. The difference, of course, is that a tunnel allows for the movement of people while a culvert allows for the movement of water. Tunnels such as this one allow for the safe passage of pedestrians under a road.

Steel Retaining Wall

Photo Credit: Karl Jansen

Pictured here is a retaining wall constructed using steel. A retaining wall is used when there is a large elevation difference in a short horizontal distance. In this case, the pond on the left of the photo is much lower than the parking area on the right of the photo. Retaining walls hold back the earth for the higher land to remain stable from erosion.


Photo Credit: Jessie Benaglio

Pictured above is a landslide. Landslides occur when the stability of a slope changes from a stable to an unstable condition. Some natural causes for a landslide are groundwater pressure acting to destabilize the slope, earthquakes, or weakening of a slope from saturation with water. The water source originates from snow or glacier melt or heavy rains. Human activities can also form landslides from vibrations induced by machinery or traffic, blasting, or other construction activities.

Soldier Pile Wall

Photo Credit: Alex Mead

This is a soldier pile and railroad tie retaining wall. These types of walls are common due to their relative ease of construction and the availability of materials. Simply place the vertical members, brown tubes in this case, and stack the railroad ties behind. Then, back fill can be placed behind the wall. One major problem with this wall, however, is the placing of the railroad ties. All joins should be staggered by many inches and secured with large spikes. As you can see on the far right this is not done, and greatly reduces the strength of the wall.

Auger Cast Pile Wall Failure

Photo Credit: Alex Mead

Seen here is the failure of an auger cast pile wall. This type of wall is designed to be a watertight retaining structure for the construction of an underground project. Although it is hard to tell from this photo, the wall appears to have failed due to weak concrete in the piles. One pile broke and released the material it was suppose to keep out of the excavation. This failure formed the mound of dirt seen in the photograph and a “sink hole” approximately 20 ft by 10 ft by 30 ft deep behind the green fence screen. This is what a bad day looks like for a geotechnical engineer.