AGEC News...

AGEC mentioned in Intermountain Contractor Magazine

The following article was published in the February 2008 issue of Intermountain Contractor magazine.

Sometimes the most important aspects of a project are the ones typically not noticed by the general public. The Montage Hotel site has been a labor of love the past four-plus years for geotechnical engineer Scott Anderson of Applied Geotechnical Engineering Consultants, Inc. (AGEC).

Anderson said the Montage site has several conditions which pose unique engineering challenges. The project site includes an area where up to 40 ft. of mine rock from nearby silver mines was placed. The Daly West and Mears mine shafts are also located on the property. The subsurface soil consists of clayey gravel with occasional clay layers and bedrock at depth. Subsurface water at the site occurs in the spring as the snow melts, and the ground water occurs in a perched condition and follows more permeable channels through the soil. The location and amount of ground water are difficult to estimate. The project site slopes steeply down to the north which requires careful planning of retaining walls. “It’s one of the most challenging sites I’ve ever worked on,” said Anderson.

More than 20 borings and test pits have been drilled/excavated at the site, with many of the borings drilled to depths of 80 to 90 ft. Two of the borings were actually drilled down into the bedrock a depth of more than 130 ft. AGEC also installed monitoring wells to measure groundwater levels for two years. Laboratory testing was performed on many samples of the soil to determine its strength and compressibility.

Other unique services provided by AGEC on this project include:

  • Estimated building settlement – The building is going to be a 13-story concrete structure and will be extremely heavy. Two building cores are supported on mat footings with underlying drilled piers. The mat footings are 6 to 8 ft. thick. The drilled piers are 3 ft. in diameter and up to 100 ft. deep.

  • Mine Rock – Laboratory testing was performed to determine whether the mine rock could be reused as structural fill. The mine rock is being crushed and used as fill in the shoring wall and in other areas.

  • Shoring Wall – A shoring wall is being constructed around the building to retain the lateral earth pressures. The shoring wall is up to 65 feet in height. During early design meetings AGEC suggested the shoring wall consist of an upper mechanically stabilized earth (MSE) retaining wall and a lower soldier pile and tieback anchor wall with a shotcrete facing. AGEC provided consultation during design of the wall.

  • MSE Retaining Walls – MSE retaining walls up to 40 feet in height are being constructed around the hotel. Concrete walls were originally planned. AGEC suggested the use of MSE retaining walls to reduce costs. AGEC provided consultation during design of the retaining walls.

  • Construction Observation – AGEC is observing construction of the building, shoring wall, and retaining walls. Occasionally, the designs have to be modified to fit the conditions encountered. AGEC is providing consultation to help keep construction going and making sure that the construction follows the plans and specifications.