|
HOME
SCOPE
STAFF
PROJECTS
PROBLEMS
PUBLICATIONS
CONTACT
US
|
Amarillo
Testing and Engineering, Inc. has performed numerous investigations to
determine the cause and effect of structural or construction defects in
the constructed facility. Over the years, we have observed many of
the problems that have occurred. These problems can be relatively
minor, causing only cosmetic nuisance; or they can be financially and
physically devastating. To the facility owner, any problem is not to
be desired. The purpose of this page is to provide an overview of
the typical construction related problems, why they occur, and how
Amarillo Testing and Engineering, Inc. can contribute to the solution.
The
Problems
This
overview of the common problems encountered on the typical constructed
facility only touches on the issues regarding prudent engineering and
quality control processes. Nevertheless, the nature of premature
failure and defects on all constructed projects have the same thread,
which is the lack of awareness or the lack of attention to the necessary
details that can make the difference. Most failures occur when a
combination of several apparent “minor” short cuts or variance from
accepted standards are used. The purpose of this overview is to
point out the critical nature of prudent and practical engineering and
quality assurance practice on all constructed projects, no matter the
purpose or scope.
Residential
Structures
The
residential structure is typically the lightest duty type construction.
Most new homes are of slab on grade with perimeter grade beam
design. The foundation system must meet minimal local standards, but
local standards only dictate minimum standards. Minimum standards
may be sufficient for some small, simple structures. Since
these minimal standards are commonly practiced, the employment of
dedicated design professionals such as architects and structural design
engineers in the residential structure is less common than other types of
heavier construction. The application of these minimal
standards of the industry may not prevent the commonly observed defects in
the residence such as cracks in walls, ceilings, and floors. The
noted descriptions of typical residential construction problems are the
result of these circumstances.
Most
of the homes built in the Amarillo and Tri-State Area are placed on clayey
topsoil type soil stratum. These clayey soils have a degree of
potential for swelling when wetted and for shrinkage when dried. These
typical soils behave somewhat like a sponge. A sponge will expand in
volume as water is applied from a dry state as the voids in the sponge
fill with water. When the sponge dries, the size of the sponge
reduces. The typical building season in the Area is dry. This
means that the typical home is built on a dry clayey site. As soon
as the home is completed, the landscaping watering begins to change the
foundation soils from a dry state to a wet state. Subsequently, the
initially dry foundation soils are wetted and the clayey soils swell such
as a sponge, and the house experiences uplift, primarily around the
exterior perimeter of the house. This means that the outside walls
are lifted by the wetted, swelling soils. This results in cracks in
walls over adjacent wall doors, cracks in ceilings, and cracks in floor
slabs. In more severe cases, the floor slab can be rendered
significantly out of level.
Severe
plumbing leaks can occur to any home. The aging home is more
susceptible, of course, since the plumbing is older. Plumbing leaks
can cause structural defects by the same process of changed soil moisture
contents beneath the house. The higher the quality and the better
the design of the residence, the less significant the structural damage
resulting from plumbing leaks.
Commercial
Structures
The
typical commercial structure such as office buildings, retail facilities,
and municipal facilities can be considered to be of medium duty construction. Usually,
the structures are heavier than the residential structure, and the
associated foundation system is likewise heavier. The direct
involvement of design professionals such as architects and structural
design engineers often subvert problems commonly associated with
residential structures. This means that the typical commercial
structure's problems with regard to site related structural stress are
less prevalent than as described for the residential structure.
Never-the-less,
commercial and even heavier industrial type structures can suffer similar
problems as described for residential structures. Since commercial
structures often call for more complex foundation and floor systems, the
job site construction procedures call for more intense site preparation
and foundation installation work. A common problem associated with
such structures is the inappropriate or inadequate placement of backfill
soils adjacent to foundation systems and sub-surface utility
installations. These problems can render similar problems with
swelling and/or shrinking soils such as described for residential
structures.
Parking
and Drive Areas
Bituminous
Surface Pavements
Once
the facility has been completed and placed in operation, it can be
expected that the first repairs to the new facility will be somewhere in
the bituminous surfaced parking area. Too frequently, this need for
repair appears in less than five years, and sometimes less than one year.
In most cases, the need for repairs with bituminous surfaced parking
areas are a result of several factors that could have been prevented
during the construction process.
In
pavement failure investigations, it is found that the root of the failure
is typically due to poor drainage of the surface or the underlying
subgrade. It is sometimes difficult to provide for adequate positive
drainage of parking lots and drives. This problem is increased at
the drive entry of the typical parking area because the entry is typically
the lowest elevation in the area and receives the most traffic. It
is not enough to have good surface drainage of the parking area. The
grading of the underlying subgrade is most critical, and had been the
source of many pavement failures. Whenever there exists a low
“swale” area in the subgrade, water will collect. This water
shall act to weaken the subgrade, the base course section, and the
surfacing, itself.
Related
to the grading and drainage of the subgrade is the control of thickness of
the pavement courses. Without good grading control, the base course
thickness can vary and possibly be too thin in the most critical areas
such as low areas in the pavement. The thickness of the bituminous
surfacing, itself, is not as difficult to control, but can be inaccurate
if improper attention is paid during its placement.
Generally,
the actual quality of the pavement materials such as the base course and
the bituminous surfacing mixture is adequate for most parking areas.
This is because the commercial materials suppliers usually keep tabs
on the quality of materials that they sell. This is not always the
case, though, and poor quality materials have contributed to many pavement
failures in the past. For example, a base course material of poor
quality will contain too much clayey material, and when it becomes wetted,
it weakens. A good quality base course will not weaken when wetted,
and it will be free draining to keep the pavement section from
accumulating moisture over time.
Premature
failure of the bituminous surfacing can occur when the stability strength
of the in-place bituminous mixture is low. This often
has to do with the degree of compaction provided in the placement of the
surfacing and the compaction of the underlying subgrade. The lack of
use of a primer over the base course can result in the loss of effective
asphalt cement in the mixture if the base course absorbs some of the
asphalt at the bottom of the surfacing.
Lack
of consideration of anticipated traffic loadings often leads to premature
pavement failure. For example, the heavily used drive entry ways
often fail first. This is because the traffic loading of these
entries is often very heavy. The drive areas have more traffic than
the parking stalls, but it is common to place the same pavement section
thickness on all areas of parking.
Unusual
weather conditions can create havoc on pavements. New pavements are
particularly susceptible to failure if subjected to heavy conditions of
freeze and thaw soon after the pavement had been placed. Freeze and
thaw can exert terrible stress on any pavement, but new pavement is at
it's most tender before some seasoning occurs, and can be damaged
severely. The placement of pavements during or just before
anticipated inclement weather can lead to possible premature failure.
Concrete
Surfaced Pavements
Many
of the sources of failure of concrete pavements share the same nature as
stated for bituminous surfaced pavements. Poor drainage, poor
subgrade preparation, inadequate base course and concrete thickness can
lead to premature failure.
All
of the control issues as stated for bituminous surfaces can also be a
source of difficulty for concrete surfaced pavements. Common sources
of failure of concrete pavements are the result of improper attention and
quality control of the actual placement and finish of the concrete course.
If the concrete is placed too wet, the surfacing will suffer surface
integrity problems and excessive shrinkage cracking. Improper use of
construction joints and sawn joints can result in excessive cracking.
Premature surface deterioration will occur when the actual quality
of the placed concrete is insufficient.
Subsurface
Structures (Basements)
Seepage
problems in subsurface structures such as basements are often the source
of headaches for the owner. In areas where the sub-surface
static water level is shallow, extensive measures not taken to provide for
a moisture free space result in seepage and possibly flooding. In
areas where no static water level is nearby, seepage problems result
usually from poorly placed soil backfill adjacent to the exterior basement
wall during the construction of the basement. This often occurs, and
it is the result mostly of the lack of awareness of the owner and the
installer of the possible problems that can result from poorly placed
basement wall backfill.
Water
Retention Structures -
The
construction of a pond or a water retention dam structure typically
involves considerable time and expense. Lack of attention to the water
retention capability of the soils that are used in the construction of the
water retention structure is the most common source of failure of such
structures. For example, the installation of a pond in a sandy soil
environment without the placement of some type of moisture barrier liner
assures that the pond shall never efficiently hold water. The
same is true for a dam water retention structure. An earthen
dam constructed all of sandy soils will exhibit excessive seepage that can
lead to eventual dam failure by sub-surface “piping” erosion within
the body of the dam. Dams are particularly susceptible to
catastrophic failure with possible personal hazard if the dam is breached.
Many earthen dams fail because no provisions have been considered
for the possible topping of the dam during a flood occurrence.
Solutions
(During Design/Construction)
The
perfect, defect free structure has yet to be built. However,
awareness of the potential problems related to the typical construction
project during the design and construction of the facility
can help considerably in the minimizing of the aggravation of defective
structures. Several steps can and should be taken, or at least
considered, in the construction of all facilities.
The
initial building site analysis and subsequent site preparation appropriate
to the proposed facility can be crucial to the success of the structure.
Amarillo Testing and Engineering, Inc. offers full services in the
support of the proper engineering analysis of the site and the job-site
quality control of the site preparation construction. We also can
provide foundation design consulting services to help assure that the
foundation and other base construction support is appropriate for the
particular facility. Proper monitoring of the foundation
construction process will help assure that the construction is
accomplished as intended by the job plans and specifications.
Solutions
(After Construction)
Structural
problems can and do occur after the completion of construction or during
the life of the facility. Of course, as with all endeavors, an ounce
of prevention is worth a pound of cure. The solutions rendered prior
to construction are the ounce of prevention. The pound of cure is
typically more expensive and more complex, but not necessarily totally
satisfactory. Cures can be rendered to varying degrees to the above
noted construction-related problems. The variance of the cure is
related, essentially, to how much one wants to spend. It's kind of
like the stranded motorist confronting the tow truck driver who response
to the cost inquiry takes the form of, “How much you got!” Never-the-less,
enough money can effect the cure after the damage has been done. Obviously,
its far better to help insure the damage does not occur in the first
place. We offer structural remediation design and testing services,
and are happy to render such services. We would rather, though, help
one prevent the problems than cure the problems. That's the purpose
of this page!
|