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The Portland Japanese Garden is one of the most highly regarded of its kind in the U.S., and an to help it achieve even more.

The desired effect of a visit to the garden, according to its website, is for the person 鈥渢o realize a sense of peace, harmony and tranquility and to experience the feeling of being a part of nature.鈥� The expansion will enhance that effect, thanks in large part to an intense engineering effort 鈥� a lot of gritty work that will make that sense of tranquility possible.

The $33.5 million project will create the Cultural Crossing: three new buildings 鈥� a cultural education center, a gardening building and a small tea caf茅 鈥� around a large public plaza. In addition, the garden’s entrance will be moved downhill, closer to the parking lot. The structural footprint will increase by 11,328 square feet to 20,191 total square feet of developed area.

At the construction site, trucks and heavy equipment lumber through the muddy terrain. Slabs have been poured for the buildings. Also, 30-foot-high walls to shore up hillsides on either side of the site are being formed via dozens of vertical steel pilings with horizontal layers of wood lagging holding back the hillside.

But it’s more complicated than that, said Josh Faulkner, construction superintendent for the general contractor, Hoffman Construction. First, two hillsides had to be moved.

鈥淭here were two hills that almost touched each other and we had to cut them back to create a giant rectangular space,鈥� he said.

That meant moving thousands of cubic yards of earth off the hillside before structural work could begin.

Next, Faulkner’s crew created a soldier pile wall by inserting 40- to 50-foot steel piles into the ground and securing them with steel tiebacks, said Christopher Pitt of KPFF Consulting Engineers, the engineer of record for the project.

But first, transporting equipment up a narrow roadway to the site was a challenge, Pitt said.

鈥淭hey had to do some selective excavation so they could get the drill rigs up there,鈥� he said. 鈥淎lso, working with the tree canopy above was a challenge since you have to take the auger up high and, once you do dig a hole, you have to drop in a soldier pile up to 70 or 75 feet.鈥�

But the hillsides still put pressure on the walls, and to counteract that force, steel tiebacks were attached to the soldier piles, extending into the earth 30 feet at a 30-degree angle and attached to bedrock, and then filled with grout.

Pitt said the soldier pile wall method is fairly common and most often used in constructing basements, and it was deemed the best solution in this case.

鈥淚nitially there were design options that were less common or more novel that wouldn’t require soldier piles, but those were deemed more challenging and with less comfort level because they’re not common techniques,鈥� he said.

The hillsides, Pitt explained, are in a historic landslide area but the soldier pile wall ensures stability.

鈥淭he whole point is the tieback extends through the part of the hillside that’s wanting to slide and push on the wall and gets anchored solidly in the bedrock,鈥� he said.

All new Cultural Crossing buildings will be rated Leadership in Energy and Environmental Design gold, said Claire Foster, spokeswoman for the Portland Japanese Garden.

鈥淣ow we have two very strong retaining walls and three green-certified buildings that are bolted to each other and bolted to the hilltop,鈥� she said.

Another unseen portion of the project will be construction of 24 geothermal wells — designed by PAE Consulting Engineers — at 300 feet deep. They will provide sustainable heating and cooling for all three Cultural Crossing buildings.

Geothermal energy is not used widely in the Northwest, Faulkner said, but that could change.

鈥淕eothermal is used a lot in Colorado and becoming more so nowadays,鈥� he said. 鈥淟ike any trend, once someone starts designing that, then everyone else wants to do it too.鈥�

Pitt agreed that geothermal is used less in the Northwest than in parts of the country with more extreme temperatures. The system is more expensive to install, he said, but ensures energy savings in the long term.

鈥淕eothermal wells basically run water through and go very deep down to where the temperature of the earth is static,鈥� he said. 鈥淚t is a way to get some passive energy efficiency (by) taking advantage of the temperature of the earth 鈥� it’s very energy-efficient because the earth does the heating and cooling for you.鈥�

The garden expansion was designed by world-renowned Japanese architect Kengo Kuma. He will be in Portland next month for the opening of an exhibition of his work at the Center for Architecture at 403 N.W. 11th Ave. set to run Feb. 4-29.

Pitt said working on the project has been a memorable experience.

鈥淲hat’s exciting for us as structural engineers is working with great local architects like Hacker and Kengo Kuma,鈥� he said. 鈥淭he sky’s the limit for projects they go after.鈥�

Kuma’s design drove the engineering and is 鈥渁 very precise and demanding design,鈥� Pitt said.

鈥淗is structures were very refined and in some cases minimized, with a lot of long roof cantilevers that come down to a very sharp point with very thin edges and straight lines and a very light, fine feel,鈥� he said.