Equipment Type

Land Detectives

Travelers along Interstate 55 between St. Louis and Springfield, Ill., will encounter a quick series of about a dozen dips in the road. To the average motorist, it's an imperceptible departure from the contours of flat farmland. To geotechnical specialists, the dips clearly communicate one thing — mine subsidence.

February 13, 2006

Travelers along Interstate 55 between St. Louis and Springfield, Ill., will encounter a quick series of about a dozen dips in the road. To the average motorist, it's an imperceptible departure from the contours of flat farmland. To geotechnical specialists, the dips clearly communicate one thing — mine subsidence.

No one sees the lay of the land quite like geotechnical and environmental engineers. "We're basically land detectives," says Richard Laughlin, president of Midwest Testing, a St. Louis-based environmental and geotechnical engineering consulting firm. "Our job is to thoroughly investigate potential impediments to commercial land development and then develop cost-effective solutions to remediate problems."

Indeed, Midwest Testing operates in the do or die world of site feasibility. Before any large investment is made ... before any dirt is disturbed ... Midwest Testing performs early assessments so that land developers can pinpoint the size and scope of potential impediments to development and their costs. Its work includes phase one and phase two site studies, wetlands delineation, asbestos evaluations, remediation planning, cultural studies of land, permitting, and geotechnical studies.

Solving development quandaries can make for an odd sight. In past years, motorists along Interstate 70 approaching the Blanchette Bridge in St. Louis saw what appeared to be a series of mammoth ant hills neatly placed at intervals on the site of a future warehouse. No sci-fi flick in the making here. Instead Midwest Testing was "preloading" the site by placing a load of dirt, equal to the weight that would be borne in the future, where each footing for the building would go. Preloading compresses the soil to mimic the load of the structure — a useful tactic when building on top of less-than-stable flood plain soil.

Sleuthing The Lay Of The Land

A phase one site study begins the detective work. It includes environmental and geotechnical assessments. "Buying land doesn't mean unfettered ownership," says Dan Greenwood, project engineer for Midwest Testing. "There is a litany of permits, including wetlands and streams, water quality, land disturbance, floodplain, and development and construction. They are all dictated by what is under the ground, what is on ground, streams, nearby wetlands, previous uses, and how altering the land will affect neighboring landowners."

All assessments begin with researching the history of the land. It also includes a phase one walkthrough where the trained eye of an environmental specialist looks for anything that would impact development cost. That includes signs of distressed vegetation from chemical spills and the like; remnants of a gas station island, which could signal the presence of underground storage tanks; subtle signs of industrial use such as manhole covers or vent lines for underground tanks; discolored water or water with an odor indicative of contaminants; odd depressions that may be signs of a sinkhole, mine subsidence or an area where a farmer once buried trash; indications that the land harbors an endangered plant or animal; and a tombstone masked as a weathered rock.

Environmental And Cultural Assessments

"States vary on what is required for early assessment," says Andy McCord, Midwest Testing's environmental specialist who has been evaluating environmental trouble spots for more than 20 years. "Illinois requires intense preliminary studies, including cultural assessments to identify archeological features. It can become a particularly in-depth requirement around places like Cahokia, Ill., the site of a prehistoric native civilization."

In some cases, cultural finds can be handled by getting official approval for relocating a barely perceptible gravesite that may have dated from when the land was first settled. "Other cases are not so simple, especially if a collection of features or artifacts appears historically significant," says McCord. "That triggers a more extensive study of the site. The cost to the developer is time — the time it takes to find a resolution."

Environmental issues can also boost development costs and are not just confined to the site. "We examine all of the surrounding land," says McCord. "An industrial site situated uphill on an adjacent property could raise questions about contaminated run off affecting the land to be developed."

Streams and wetlands on a to-be-developed property may require federal permits from the Army Corps of Engineers — a yearlong process in some cases. Jurisdictional streams that cross many properties cannot be filled in until a complete assessment is done on the proposed impacts and every effort is made to minimize them. In the case of a 450-acre business park in Hazelwood, Mo., the Army Corps permit ultimately required the developer to create or preserve more than 164 acres of wetland habitat, both on and off of the site, to counterbalance the impact of developing fewer than 30 acres of wetlands.

Environmental assessments also include evaluating existing buildings on the property for asbestos contamination and other hazards. A recent urban renewal project in the St. Louis area involved the demolition of over 100 homes and businesses. Each structure had to be investigated for potential contaminants, such as asbestos, prior to demolition. This allowed the developer to accurately predict special demolition costs associated with these materials.

Geotechnical Assessments

The Leaning Tower of Pisa is eight stories tall, weighs 14,700 metric tons and is the most famous example of an engineering adage: a structure is only as good as the ground it's being built on. When construction began in 1173, no one considered the soft soil upon which the tower was being built. Five years into its construction and only 35 feet tall, the structure began to exhibit its now famous tilt.

"What's interesting is that over the last 60 years or so before there was soil testing, structures were tremendously overbuilt to compensate for unknown subsoil conditions," says Dan Barczykowski, principal with Midwest Testing. "As our body of knowledge increases, along with the cost of construction, we can no longer afford to over design structures to the extent they were 100 years ago."

Finding the most cost-efficient way to transform a plot of land so that it can host a given development is the primary job of a geotechnical specialist. It means developing a comprehensive plan that optimizes site conditions for civil and structural engineering by determining how finished grades will impact surrounding properties; identifying soil conditions, such as soil with high moisture content, which is more costly to move and compact; maximizing site advantages so on-site soil can be used to establish finished grades, minimizing the costly importing of soil; designing retaining walls; helping determine the placement of sewer lines; identifying how the soil will behave under the weight of a building; and defining bedrock and its impact on the project.

In general, ensuring a building's structural integrity on suspect soil is accomplished in one of two ways — modifying the foundation or modifying the soil. In some cases, it is less expensive to modify the soil to accommodate conventional foundations. But weak soils that extend to considerable depths can also require costly deep foundation support, such as drilled piers or driven piles. Preloading a site — as motorists observed near the Blanchette Bridge in St. Louis in the 1990s — is a creative way to compress weak soil deep in the earth so the building can succeed on a conventional foundation system.

Anyone who has seen cracks develop in their lawn only to mysteriously disappear after a rain has experienced high plastic soil conditions. Usually defined by heavy clay, plastic soil contracts in dry weather and expands in wet weather. This "heaving" effect can cause structural distress to buildings. The remedy is usually to remove the soil or amend it with lime or fly ash to control the soil's reaction to wet and dry conditions.

Occasionally, the brutal truth is that a given site may be prohibitively expensive to develop. Bedrock can be the bane of any development project. It requires specialized equipment and blasting which can cost 20 times the amount to remove or amend soil. The information generated by the geotechnical study for the project helps to identify the impact of bedrock on costs and guide changes to reduce its impact on the budget.

Going Deep

Five years ago, an appliance retailer purchased land in Illinois to develop the first of three stores in metro St. Louis. The site offered all the important tangibles — a high-profile location amid a growing sea of homes with easy access from a major thoroughfare. But it also had a hidden danger — the potential for mine subsidence.

"The risk of mine subsidence is really a tough call for any owner or developer," says Greenwood. "Projecting the length of ownership or a building's life span must always factor into evaluating the risk. Mines can remain relatively stable for decades — far longer than any building is owned. But not all mines age gracefully, so it is essential to examine the potential risk of deterioration and its effect on surface conditions."

For geotechnical specialists at Midwest Testing, the telltale signs of sunken land often betray decaying conditions more than 100 feet beneath the surface. But most of the time it's not that obvious. A phase one assessment includes a review of public records to determine the location of long-abandoned mines. If one is present, Midwest Testing breaks out its high tech-video camera.

Drilling a hole 130 or more feet beneath the surface, the camera is lowered into the mine and offers an eerie look at the remnants of a dangerous line of work that flourished in the 19th and early 20th centuries. "It's hard to fathom that people worked down there daily with less than ideal structural supports for the mine," says Greenwood, who comes from a mining family.

"We're looking for signs of decay to the roof and floor of the mine as well as unstable supports," says Greenwood. "Ultimately we want to give the developer a clear picture of risk factors — from low to moderate to high. That's the only way to make an intelligent decision about remediation."

Remediation, which involves filling the mine with a grout-like substance, can cost $500,000 or more. In some instances, that additional investment makes sense. In others, it does not. In the case of the appliance store, the cost of remediation was worth it, but it only protected their site. Across the street, a commercial building built atop the same mine is now showing signs of structural distress.

Insightful, accurate environmental and geotechnical assessment of land is essential to any successful development. Complying with state and federal regulations while engineering the most cost-efficient way to shape the land, use its resources, remediate its problems, and build on it can save developers millions of dollars.

A good detective not only finds clues, but also solves the case.

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