Underground Landslide Targets Macon County, NC Homes and Craftsman Village

Big Slow-Moving Landslides

Ask for a description of landslides and most people will characterize them as fast-moving mountain slope events. What they don’t know, is that there is another type of groundbreaking landslide.

These other earth-movement phenomena occur below the surface, are present world wide and slowly destroy everything built on them. Underground landslides have various names: Some call them ancient landslides, engineers use the term deep-seated circular/rotational failures. In Western North Carolina, geologists refer to them as "Big-Slow Movers."

Subterranean landslides can move of their own accord but generally they are prodded into action by changes in the weather or alterations to the landscape. Once these forces are energized, they are difficult to control. The Aldercrest-Banyon Landslide is a classic example of the destructive power of a "Big-Slow Mover."

Aldercrest-Banyon Subdivision Underground Landslide Kelso, Washington (1998-1999)

The Aldercrest-Banyon neighborhood was completed in three phases, 1971 through 1979. When the city of Kelso planning commission granted the permit for the project they knew that a dormant landslide existed on the building site. Nine years later the landslide reactivated. As a consequence 137 homes were condemned.





Photos of Aldercrest-Banyon Neighborhood Landslide Property Damage
Kelso, Washington (1998-1999)


"Big-Slow Moving Landslide"—Craftsman's Village—Macon County, NC

"CONDEMNED: Could this happen to your home? " Macon County News April 1, 2010

The Macon County News reported that a big slow-moving landslide has been identified near the town of Franklin. Rick Wooten, senior geologist with the state Geological Survey calculates this active landslide encompasses 13 acres and is positioned 35 feet below the surface. This landslide is endangering homes and completion of Craftsman’s Village, a commercial/residential development project.



Macon County News Report April 1, 2010


Excavation at the Craftsman’s Village development on Georgia Rd. may have contributed to both a major slope failure on the property (visible above) as well as to the slow-moving slide affecting the property to the south of the development (left side of this picture). Geologist Rick Wooten says the recent clear-cutting above the slide “is not going to help the situation.”


Macon County News Report April 1, 2010


When county officials were first called to investigate cracks in the driveway of Mike Boggan’s property on Blossomtown Drive on February 12, they observed a drop of 2 to 2.5 inches. By the time officials returned a month later, the crack (called the scarp) had increased to 16 to 18 inches.



Macon County News Report April 1, 2010

The crack in Mike Boggan’s driveway is growing by an average of half an inch a day. Boggan, whose house was condemned by the county on March 18, says he is “at a loss.” Excavation at the neighboring Craftsman’s Village development could have contributed to the slow moving slide, say officials. But unpermitted development has continued on the slope.

The Craftsman’s Village, “Big Slow Mover,” is the second underground landslide to result in Western North Carolina mountain real estate property condemnation. The first was documented in Haywood County five years ago.

Case Study: Hunters Crossing Subdivision “Big Slow Moving Landslide” Haywood County, North Carolina

In the fall of 2005 land under the Hunters Crossing Subdivision, a six-unit condominium mountain complex, began to move and so did the homes' structural supports.

Citing safety concerns, emergency management officials cut water to the units.

The cause of the movement under the Hunters Crossing condos was determined by Alpha Environmental Science Inc.'s investigative team. In summary the company's engineers found that the 2001-built subdivision home sites were sitting on a then-dormant, now-active landslide. The following is a reprint of the engineering report provided to Hunters Crossing property owners:

February 10, 2006

Mr. Jeffrey J. Coghill
1490 Devonshire Court
Atlanta, GA 30338

RE: Slope Evaluation for Hunters Crossing in Waynesville, NC AES # 5664.01

The Hunters Crossing slide area involves a side hill slope that extends approximately 250 feet in a north south direction parallel with Lickstone Road and extends approximately 300 feet uphill from the east side of the road. Representatives of Alpha Environmental Sciences Inc. as well as representatives of the North Carolina Geological Survey has visited the site on numerous occasions. During these visits a number of cracks and scarps have been identified in the surface of the failure area. Some of these cracks are in the vicinity of the homes at the top of the failure zone. At least one old apparently inactive slope failure scarp was located downhill in the middle of the zone. Distress in the form of foundation cracks and wall displacement were identified in the homes at the top and bottom of the failure zone. The field observations started in November 2005 and have continued to date. Additional building cracking and ground disturbance have appeared during these visits and new signs of distress have appeared in and around the homes at the bottom of the zone adjacent to Lickstone Road . Slight movement detected by the crack monitors on the foundations of 73 Hunters Crossing on February 8, 2006, reveal that the slope is still in motion.

The two deep (50’) borings progressed at the top of the zone did not encounter rock. A boring taken at bottom of the slope encountered rock at 8.5 feet below existing ground surface. Based on the depth to rock and the type of distress observed in the field, it is our opinion that the slope movement is a deep-seated circular failure. A deep-seated circular failure occurs when the vertical load on the uphill side of the failure zone exceeds the internal soil strength along a failure plane combined with the vertical load on the downhill side of the zone.

Our evaluation indicates that prior to the current movement the vertical forces combined with the soils internal strength were very close to the balance point. Any event that could momentarily reduce the internal soil strength could cause a rotational failure to occur. The type of events that cause this condition would be the infusion of large amounts of water, either from periods of intense rain or a water line failure. Also, a seismic shock such as the 3.8 magnitude earthquake that occurred on August 25, 2005 two miles southwest of Hot Springs, NC could have caused this change in strength. Unfortunately, the reduction in internal strength can for all practical purposes be permanent or take an extremely long time to return to a balanced point.

Because of the large amount of soil in motion, the standard technique that could possibly arrest the current movement is a stabilizing berm constructed on the flat area east of Lickstone Road. This treatment would require the removal of the homes in this area. The soil berm would be about 70 feet deep perpendicular to the creek and twenty to thirty feet high. Techniques that would attempt to stabilize the slope mechanically would involve anchor tie backs drilled into the soil or rock beyond the failure zone. This type of system has been discussed with contractors that have visited the site. The anchors are estimated to cost at least one million dollars to design and install. However, due to the variable nature of all soil deposits, it has to be stated that an engineered mechanical anchor system might not work.

Should it be practical to construct the berm at the base of the failure, it would still not be feasible to reconstruct the homes at the top of the failure zone. This judgment is based on the nature of the failure including, probable permanent reduction in internal soil strength, the identification of older inactive scarps in the hill side and the limited amount of space available to construct a berm.

It is our recommendation that the homes effected by the slope failure, if they are in a condition where they can be moved, be relocated to sites where slope problems do not exist.

If you have any questions, please contact us.

Respectfully submitted,

Alpha Environmental Sciences, Inc.

James K. Connors, PE
Senior Geotechnical Engineer

Roger D. Moore, PG
Division Manager/Professional Geologist

Western North Carolina Mountain Real Estate

Western North Carolina mountain real estate covers a federally-designated high-risk landslide region. Significant landslide activity is expected in the following counties:

Alleghany, Ashe, Avery, Buncombe, Burke, Caldwell, Cherokee, Clay, Graham, Haywood, Henderson, Jackson, McDowell, Macon, Madison, Mitchell, Rutherford, Surry, Swain, Transylvania, Watauga, Wilkes and Yancey.

The 1998 Federal Emergency Management Agency Western North Carolina hazardous-land assessment was based on geologic findings, historic events and soil surveys.

Since there is no state landslide data base, it is impossible to determine the number of Western North Carolina homes condemned or damaged by earth movement. Financial loss is incalculable due to the fact that homeowners' insurance policies do not cover landslide losses.

What is known is that planning boards throughout Western North Carolina have willfully, and without disclosure, exposed property owners to known and easily identifiable landslide hazards.

The issue of Western North Carolina real estate hazardous-land disclosure was raised in 2007. The merits of the Safe Artificial Slope Construction Act are still being studied.

Those involved in hazardous-land sales: developers, planning boards and real estate agents, understand the financial consequences of a state-mandated Landslide Disclosure Statement. They know that if the public were apprised of landslide risks, it is unlikely that many would choose a Western North Carolina mountain home.

The Hills of Rivermist: A Centex Hazardous-Land Subdivision

Rodolfo Gonzalez/AMERICAN-STATESMAN

Views of The Hills of Rivermist Subdivision Landslide— January 25, 2010

Landside in The Hills of Rivermist Subdivision Endangers Homes

Twenty-seven homes in Rivermist and The Hills of Rivermist Subdivisions have been red-tagged because sections of a landside-prevention retaining wall failed. Centex, the developer of Rivermist and The Hills of Rivermist, has offered to compensate property owners above and below the slide area with buybacks.



The Hills of Rivermist Landslide-Prevention Retaining Wall

On February 4, 2010 Roderick Sanchez, director of the Planning and Development Services Department for the City of San Antonio, stated in his findings memorandum that Centex violated the International Residential Code and the International Building Code by neglecting to obtain a permit for the Hills of Rivermist retaining wall.

Mr. Sanchez noted that there were several factors that likely contributed to the wall's instability:

—Design failure in that wall was never properly designed in the first place.

—Construction failure in that wall was not built in accordance with the engineered plans and specifications (this determination has been made in the portions observed).

—Slip failure of the soil strata below the wall.

The city is holding Centex responsible for creating a public hazard. As a result, Centex has agreed to assume liability for its actions and will build a new safety wall. Plans for the landslide-prevention wall have been approved at a cost of four to five million dollars.

The Hills of Rivermist Homes

Property owners outside the landslide hazard area have told the media that their Rivermist homes are exhibiting signs of earth movement damage such as cracks and pop-out nails. This type of structural distress is caused by unstable soils.

Homeowners' Insurance

The Hills of Rivermist property owners who have experienced structural damage have to depend on Centex for repairs because they have no insurance protection: Homeowners' policies nationwide exclude losses caused by earth movement.

The Hills of Rivermist Soil Survey

Thanks to the efforts of Wayne Caswell, a member of the advocacy group Homeowners of Texas, soils in The Hills of Rivermist Subdivision have been identified.

The three predominate soils in The Hills of Rivermist building site are Anhalt clay (map symbol Ca), Crawford and Bexar stony soils (Cb) and Brandon clay (HtA). These soil compositions are classified "expansive" and are not recommended as a support for home construction.



United States Department of Agriculture—The Hills of Rivermist Soil Survey Map

Mr. Caswell notes that according to the USDA's Web Soil Survey, 94.6% of the selected Area of Interest representing Hills of Rivermist is “Very Limited” for residential construction.

Hazardous-Soil Findings

Bexar County, Texas Soil Survey 1966

The Bexar County Soil Survey, a cooperative endeavor by the U. S. Department of Agriculture, the Texas Agricultural Experiment Station, and the City of San Antonio was undertaken to prevent costly mistakes in land use planning for agriculture and residential development.

Soil identification serves two purposes:

Suburban residential development and the accompanying extension of public utilities and establishment of business and recreational facilities create a need for soils information somewhat different from the information needed for purposes of agriculture. Land appraisers, realtors, city planners, builders, and others need to have facts that will help them to know what sites are suitable for homes or other buildings and what areas should be reserved for other uses.

Sites for houses, industrial buildings, and public utilities need to be carefully studied before construction is begun.

Some of the soils in Bexar County shrink and swell enough to crack foundations and walls.

FHA: Building on Expansive Soils will Result in Severe Structural Damage

In 1974 the Federal Housing Authority warned that buyers should be made aware of the consequences of building homes and other structures on expansive soils:

Severe damage to building foundations can result from "swelling" or "expansive" soils. These soils, usually cohesive clays, can swell or shrink as they go from the dry to the wet state or vice versa. This alteration in moisture can cause a volume change which creates large differential movements within the structure and thus causes excessive cracking of floors, walls, and foundations. Soils with expansive characteristics must be recognized in order to evaluate properly their stability as foundation material.

Studies commissioned by the FHA in the 70s determined that expansive soils were common in Bexar County, Texas.

“Department of the Army USA, Technical Manual TM 5-818-7, Foundations in Expansive Soils, 1 September 1983.”

For the reasons cited below government buildings are not constructed on expansive soils:

b. Occurrence of damages. Damages can occur within a few months following construction, may develop slowly over a period of about 5 years, or may not appear for many years until some activity occurs to disturb the soil moisture.

c. Structures susceptible to damages. Types of structures most often damaged from swelling soil include foundations and walls of residential and light (one-or two-story) buildings, highways, canal and reservoir linings, and retaining walls. Lightly loaded one- or two-story buildings, warehouses, residences, and pavements are especially vulnerable to damage because these structures are less able to suppress the differential heave of the swelling foundation soil than heavy, multistory structures.

Fraudulent Concealment of Hazardous-Soil Conditions

It is clear from the referenced documents that the San Antonio Planning and Development Services Department and the developer Centex knew that home sites throughout The Hills of Rivermist Subdivision were threatened by hazardous-soil conditions.

The San Antonio Planning and Development Services Department has received queries about soil conditions in The Hills of Rivermist Subdivision. The city's response:

The department does not require a builder to submit soil information. Instead, at the time a builder submits its application for a residential building permit, the Code allows the builder the option to hire a licensed professional engineer to design the foundation system for your home in accordance with the Residential Building Code.

Complicity

Because Planning and Development does not require soil analysis as a prerequisite for building permits, hazardous-land data is not recorded on plats. If this pertinent information is not disclosed on plats, it does not appear on real estate sales contracts.

The Hills of Rivermist Hazardous-Land Real Estate Disclosure
Statement

Centex failed to reveal a material fact—unstable soil conditions—on their Hills of Rivermist sales contracts. If purchasers had received the following risk disclosure statement, it is unlikely that they would bought homes in this subdivision.

The Hills of Rivermist Hazardous-Land Disclosure Statement

Please be advised that you are buying a home that has been built on unstable soils. The Federal Housing Authority advises that homes built on expansive soils are likely to experience severe structural damage.

Hutto Parke Hazardous-Land Conditions

The Hills of Rivermist Subdivision is not the only Texas residential community to be affected by hazardous-land conditions. Lennar, the developer of Hutto Parke, exposed their clients to two significant undisclosed risks: arsenic-contaminated land and expansive soils. For additional information please visit the Hutto Parke Web site.

Binding Arbitration

Those purchasing new homes in Texas and numerous other states are denied judicial review of builder-caused defects because of binding arbitration clauses in new home real estate sales contracts. Questions of real estate fraud remain under court purview.

Federal Action

Texas lawmakers have failed to force disclosure of hazardous-land conditions for the usual reasons. Contractual disclosure would have a disastrous impact on real estate development and sales.

Earth movement events: landslides and unstable soils affect property owners in all states. A conservative estimate of the uninsurable losses caused annually by hazardous soils is several billion dollars. Comprehensive, indisputable risk data is available through various state and federal agencies but this information is not communicated to purchasers.

The only solution to the industry's country-wide practice of selling high risk real estate is passage of a federal Hazardous-Land Disclosure Law.