Engineering: Dirty work

The very ground in the Las Vegas Valley is treacherous.

Most of the desert looks innocent enough, just dry, rock-hard stretches of dirt with the occasional patch of ground cover. Underestimating it, however, can invite disaster.

That goes especially for developers. After decades of shifting soil, falling water tables and caliche blasting, developers today take a more cautious approach than ever to building in terms of infrastructure cost and liability, and read the engineering reports on their land more diligently, according to Greg DeSart, president of Geotechnical and Environmental Services, a geo-environmental services firm that produces such reports, among others.

"This has come more to the forefront. Developers really have to pay attention to these (engineering reports) now," DeSart said. "This affects their bottom line."

GES clients are typical of those entities that call for such studies, generally very large land holders. The Clark County Sanitation District, Southern Nevada Water Authority, city of Las Vegas, city of Henderson, public works authorities, Pulte Homes, KB Home, DR Horton and American West are a few.

Geotechnical engineering services are among the first companies called out to a building site, usually before ground is broken and often even before there's a road to take.

Basically, they study dirt.

GES' sister company, Eagle Drilling, owns two trucks armed with long, slender augers used for collecting samples at potential building sites. Drilling anywhere from 10 feet to hundreds of feet, the crews collect bags of dirt or other samples to bring back to the GES laboratory.

GES, in turn, has three basic services: geotechnical engineering, environmental assessment, and testing construction materials ranging from asphalt to building components.

If reams of data on the finer qualities of dirt and asphalt sound like an insomnia cure, ignoring them can be a nightmare. Local examples are plentiful.

Homes and foundations built decades ago along Martin Luther King Boulevard in the Windsor Park subdivision cracked apart as the soil below them subsided, forcing the city of North Las Vegas to help residents move out -- at an enormous cost. Several homes built in the 1970s near Lamb Boulevard and Stewart Avenue tilted as the ground beneath them shifted, enough to allow cans to roll across kitchen floors. The problems at both neighborhoods occured long after residents moved into the homes.

A more expensive problem took shape in recent years on the south end of the Strip. The sheer weight of two properties, Luxor and Mandalay Bay, compressed the soil on which they were built after the resorts were completed. Both remain sound, according to engineers, but required some fixes. A series of jacks were installed under Mandalay Bay to strengthen its footing.

In this light, developers now want all the dirt on their dirt. A sizeable collection of carefully marked soil samples from potential building sites all over the valley amasses in a corner of the engineering firm's lab. Elsewhere in the lab, technicians test other mundane materials: asphalt, concrete and gravel.

It turns out, those unassuming beige granules can be surprisingly diverse, and so is what lies beneath them. In all, there are more than a dozen types of soil in the Las Vegas Valley, according to Bill Hudson of GES. As the firm's lab manager, Hudson oversees the equipment the firm uses to compress, pound, bake, soak, crush and otherwise test the samples they receive from around the valley.

Hudson counts himself among those who never realized how complex sediment could be.

"Before I got into the field, I thought dirt was dirt, asphalt was asphalt, and concrete was concrete," Hudson said. "I was surprised to find out how many types of soil there are in this valley."

Some of the soils are pretty similar -- it is dirt after all -- but as some Southern Nevada residents have learned the hard way, they may react very differently when a building is placed upon them. DeSart classifies five main types that can give property owners fits:

1. Caliche. This is easily the best known soil in the region. It's actually a pretty good thing to build on. It's just a terrible thing to build into, because it's extremely hard and can require explosives to remove. Caliche can be expensive to excavate -- it can add thousands of dollars to the cost of a backyard pool;

2. Clay-like soils. The expansive properties of these soils are revealed when water seeps in from irrigation, often well after the home is completed and the homeowner has moved in;

3. Collapsible soils. It's almost hard to picture now, but the central and southeastern portions of the valley used to contain a lot of water. As the water was pumped dry in some areas, terra not-so-firma was left behind. Much of these areas need to be compressed by weight before building can be started;

4. Soluble soils. Many pockets of the valley contain gypsum (sodium sulfate), which can dissolve in water. For technical reasons, DeSart explains, it's bad to build on ground that dissolves;

5. Corrosive soils. The sulfate content from gypsum and other compounds can be chemically reactive.

Although there is also the occasional fault line or other anomaly, these soil properties constitute "95 percent" of the geological problems developers face.

"Local developers often get burned on these costs, especially caliche," DeSart said.

Some areas of the valley have more than just tricky dirt. Ground water and contaminants -- some in the same place -- are often the legacy of a parcel's previous function.

In downtown Las Vegas, there is contamination where the Union Pacific railroad used to operate, a long-empty parcel now described by one local mayor as a "jewel."

Environmental assessments often reflect past uses and abuses in parts of Henderson as well. Large areas of Nevada's second city contain contaminants from when it was a World War II munitions production center and later when local industry produced volatile chemicals such as rocket fuel over a span of 50 years.

With the remains of a once-vast wetlands and wash on its north, some Henderson land barons also must be wary of endangered species habitats and ground water.

"People see this is a desert, so they think the ground water is hundreds of feet down. Ground water is a surprising issue for a lot of people from out of town. Some of it isn't so deep," DeSart said.

"That's what formed Las Vegas. It was the spring water oozing up from the ground."

For years, ground water was pumped out as the city grew. Ironically, growth is now more likely to cause ground water to occur. DeSart points out that most ground water today is a result of overirrigation.

GES, founded 10 years ago, has about 28 employees. Its sister company, Eagle Drilling, employs five and maintains two drilling vehicles. The companies are based in Las Vegas and perform assessments throughout the state.

Real Estate home