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Our Team
R. Kevin Tillis

President / Senior Principal Engineer


M.S. Civil Engineering, University of California, Berkeley, 1986

B.S. Civil Engineering, University of Illinois, Urbana, 1983


Civil Engineer 41180 California

Geotechnical Engineer 2160 California


1993 - Present    Hultgren – Tillis Engineers

1986 - 1993         Harding Lawson Associates

1983 - 1985         Lowney & Associates

Mr. Tillis is responsible for day to day operations, while concurrently managing and overseeing numerous geotechnical engineering projects each year. His experience includes management of complex levee, dam and earthwork projects for local and state agencies. His recent experience includes planning, design and implementation of construction for over 100 miles of levees in the Sacramento-San Joaquin Delta. He has an excellent track record for pushing projects through the design phase into and through the completion of construction. Construction contracts for his levee improvement projects exceed $25 million over the past five years.

Christian P. Muller

Vice President / Principal Engineer


M.S. Civil Engineering, University of California, Berkeley, 1979

B.S. Civil Engineering, University of California, Berkeley, 1978


Civil Engineer 33363 California

Geotechnical Engineer 2036 California


2004 - Present     Hultgren – Tillis Engineers

1979 - 2004          Harding Lawson Associates/

                             MACTEC Engineering and Consulting

Mr. Muller oversees a majority of the firm's heavy industrial projects. He also specializes in deep excavation projects and marine structures. As the firm's resident safety officer, he is well versed in the safety practices and requirements of organizations such as OSHA and DISA Global Solutions. His recent industrial projects include 70 feet tall, 190 foot diameter crude oil storage tanks, both deep and shallow foundations for the associated pipe racks, seismic evaluation of a marine oil terminal with both vertical and battered piles, and a new mixed-use cargo wharf.

Callan J. Yu

Associate Engineer


M.S. Civil Engineering, University of California, Los Angeles, 2010

B.S. Civil Engineering, University of California, Davis, 2007

Civil Engineer 77899 California

Geotechnical Engineer 3117 California


2007 - Present    Hultgren – Tillis Engineers

2006 - 2007         Sacramento Regional County Sanitation District

Callan Headshot.jpg

Mr. Yu provides geotechnical engineering consultation for flood control levees, dams, repair of landslides, marsh restoration projects, seismic hazard evaluations, hydraulic structures, marine and waterfront structures, and commercial development. He has designed several new Bayfront levees for restoration projects including Sears Point and Bel Marin Keys. He is a technical leader and is proficient with the use of analytical methods and modeling related to slope stability, retaining structures, deep foundations, settlement, seepage, and seismic hazards.

Joseph C. Heavin

Associate Engineer


M.S. Civil and Environmental Engineering, Cal Poly State University,

     San Luis Obispo, 2010

B.S. Civil Engineering, Cal Poly State University, San Luis Obispo, 2010


Civil Engineer 79187 California

Geotechnical Engineer 3083 California


2010 - Present    Hultgren – Tillis Engineers

2008 - 2008         Cornerstone Earth Group

Joe Heavin Head shot - cropped2.jpg

Mr. Heavin manages geotechnical engineering projects for rural and urban channels, flood control levees, marsh restoration, landslide remediation, industrial process equipment, and commercial real estate. Mr. Heavin works with numerous clients to evaluate the constructability of their projects with a focus on geotechnical constraints. He assesses erosion damage within restoration projects and designs remediation. He provides observation and testing for earthwork, shallow foundations, spread footings, drilled pier and driven pile foundations and compacted aggregate piers.

Gregory R. Olsen

Senior Engineer


M.S. Civil and Environmental Engineering, Cal Poly State University,

     San Luis Obispo, 2011

B.S. Civil Engineering, Cal Poly State University, San Luis Obispo, 2011


Civil Engineer 82690 California

Geotechnical Engineer 3146 California


2012 - Present    Hultgren – Tillis Engineers


Mr. Olsen performs geotechnical investigations for a variety of public works, flood control, environmental and industrial projects.  He also performs engineering analyses for a variety of projects, including slope stability analysis for landslide remediation, design configurations for levee rehabilitation, and foundation analysis for industrial structures.  He provides observation and testing for grading, shallow foundations, pile and pier foundations, and lime treatment. 

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