CF-TownC CHC-SY 850628 HII. TOI E & ABBOCIA ,'EB, INC.
8577 MANDERVIL.i.E"RQ DALLAS. TEXAS 75~31 2'L4/361-cJ~11
June 28, 1985
Howard U. FreemanConstruction'Co.
1428 E. Grauwyler
Irving, TX 75060
Attn: Jack Washcitz-~'
Re: Coppell Town Center
Dear Mr. Washcitz:
At the request of Freeman Construction, Shilstone and Associates, Inc. has
undertaken an evaluation of pier conditions at the above referenced project.
The superintendent on the project had noted that some of the piers had very
soft concrete.
CONCLUSIONS
The soft concrete was caused by the intrusion of water into the plastic
concrete. This water either washed the cement out of the concrete matrix or
greatly increased the water cement ratio and so reduced the concrete
strength. Indications are that the "seal" between the removable casing and
the concrete was destroyed at some point. This allowed water standing in the
pier hole to mix in with subsequent layers of concrete and destroy the
concrete's strength. Observers from/ your office .......... .J_III._.L. ',~.,~
_ I~,, state that there was always concrete in the casing during
placement and so the seal was not lost by that method. The other alternative
is that the concrete hung up in the casing while the casing was being
withdrawn and allowed water to intrude without the knowledge of the
observers. The second alternative is unlikely but is the only explanation
which fits all the facts and observations.
The quality of the piers varies greatly. Most of the piers have a layer of
soft concrete starting at the top and ranging down for 18 to 60 inches. Some
of the piers exhibit iow strengths and multiple discontinuities for up to 14
feet. Most of the piers appear to be continuous once they get below the water
table at about 14 feet. Concrete strengths in the piers range from 4600 psi
to nil.
The piers were originally cast with a diameter 4 inches greater than that
specified. Ultrasonic testing identified a reduction in cross section of the
piers ranging from 5 to 30 percent. Considering the cross section reduction
and the increased pier casting size, the effective cross section of the piers
ranges from one half of an inch too small in diameter to three, and one half
inches too large.
It is the responsibility of the Engineer to determine the acceptability of the
piers as they are in place. Two possible deficiencies appear to exist in the
piers: 1) There are multiple lenses or honeycomb in the piers to the depth of
the water table. This condition is evide~t'i~ only a few piers. 2) The top
of the pier may be too soft to support the load to be placed on it. This
condition may exist in many of the piers. In case number one, it may be
necessary to provide alternate means of support for the piers in question. In
case number 2 it is only necessary to remove the soft top concrete until solid
concrete is found and then cap the piers to bring the concrete up to the
design height.
If new piers are to be placed, we feel that ACI 336- "Specification for End
Bearing Drilled Piers" should be followed (copy enclosed). It is not
referenced in the contract specifications but is a good guide to follow.
Paragraph 2.3.4.7 states, "Where casing is removed, provide specially designed
concrete with a minimum slump of 5 in. and with a retarder to prevent arching
of the concrete..." Also, when the bottom of the casing reaches the bottom of
the water table, casing lifts should be confined to small increments such as
two or three feet to reduce the possiblity of a sudden outflow of material to
fill a large void.
PROCEDURE
The softness of the concrete in the piers could have been caused by one of two
types of conditions: 1) Improper batching, mixing or delivery of the concrete
or 2) Improper placement or intrusion of water into the concrete after
placement. A review of the Ready Mix suppliers mix design and batching
operations indicated that the problem was more likely in the second area.
Petrographic analysis of the concrete showed the pressence of fly ash, which
was not permitted in the specifications, but fly ash should not have caused
the problem by itself.
An ultrasonic evaluation of the piers was conducted by Richard Muenow of
Richard Muenow and Associates, Inc. (see attached report). The pulse echo
method of ultrasonic analysis used is recognized by both the National Bureau
of Standards and the Nuclear Regulatory Commission as a valid method of
evaluating the condition of in-place concrete. Pulse echo procedures showed
that almost all piers had soft tops ranging in size from 18 inches to six
feet. Most of the piers showed a reduction of cross section of five to thirty
percent at a depth of about twelve feet. This depth corresponds to the depth
of the water table at the site. Ail of the piers showed good quality concrete
(over 3000 psi) below the cross section reduction. Some of the piers
exhibited multiple lenses, indicating changes in the consistency of the
concrete and probable honeycomb or washout of the cement.
Piers 14, 16, 33, 68 and 69 all exhibited multiple lenses. Piers 69, 16 and
14 were dug out so they could be observed. Each of the piers was extremely
soft to a depth of seven to nine feet, the limit that the back-hoe could
excavate. Pier 16 was cored to a depth of 16 feet. The concrete in the top
two and one half feet had a compressive strength of 1606 psi. The concrete to
a depth of'12 feet either had no cement in it or was so weak that the coring
operation washed out the cement and left only sand and stone. The remaining
concrete to a depth of 16 feet had a compressive strength of 2464 psi.
-2-
Piers t3, 46, 54, 70 and 77 all showed a reduction in cross section of 30
percent at a depth of 9 to 14 feet. These piers were excavated and showed
variable conditions. Piers 13 and 54 were too soft to attach the core
drilling apparatus and remained so for the entire excavated depth. Piers 46,
70 and 77 were cored and showed strengths at the one foot level were 3091,
1370 and 4479 psi respectively. At the three foot level those strengths were
4853, 1935 and 4111 psi.
Pier 78 showed a reduction of cross section of 5 percent and had core
strengths of 4831 and 4762 psi at the one and three foot levels. Pier 63 had
a cross section reduction of 10 percent at the nine to 11 foot level and a
strength of 3620 psi at that level. Pier 83 showed a 20 percent reduction and
a strength of 3686 psi.
ANALYSIS
Two questionable conditions appear to exist in some of the piers, reduced
cross sectional area and softness to a variable depth. One condition does not
necessarily imply the other but the greater the cross sectional reduction, the
greater the propensity to develop a soft top. Any softness probably does not
extend much below the water table,
The cause of the problems are still in question. The immediate cause of the
problem is the presence of too much water in the concrete. This results in
low strength concrete. Observers report that the concrete had a reasonable
slump (indicative of normal water content) when it was being placed in the
pier hole and that the hole itself was free from waterinside the casing.
To understand how water can intrude into the concrete it is necessary to
understand the drilling and placement processes~ When a pier is being placed
in ground that has water im the drilling depth, a casing (steel pipe) is
placed into the hole so that an area can be created that water cannot enter.
Concrete is then placed into the casing and the casing is gradually removed.
As the casing is removed, it should always contain concrete and be in contact
with the concrete below its lower edge. This prevents water from flowing ~
between the concrete previously placed and new concrete being entered. If the
seal is broken, water will intrude and mix with the new concrete. This
weakens the concrete. Gradually the water will migrate to the top of the
pier, weakening concrete as it goes.
According to observers from both your office and the testing lab, the pier
hole was dry at the time of placement. At no point in the laboratory reports
was there an indication that the seal was broken. The superintentent on the
project is experienced in the placement of piers by this method and reports he
was always placing fresh concrete on top of previous concrete and not water.
This condition is hard to confirm when the top of the casing gets above an
immediately accessable position. When the bottom of the casing reached'the
level of the water table, the top of the casing would be at about eight feet.
It would have been impractical and unsafe to have a person riding the concrete
-3-
cket to observe the level of the co~crete in the casing. The only way to
identify that concrete was still in the casing would have been been the sound
of the concrete hitting bottom. Often this method is sufficient for an
experienced contractor.
During the drilling operation before the casing was placed into the hole, the
water table may have washed large quantities of sand and gravel from the sides
~ the hole into the bottom of the hole (see Figure 1). As the casing was
being raised, it would have reached a larger than normal volume of the hole to
be filled. Given the depth of the water table and the height of the top of
the casing, it is conceivable that the casing lost its seal without placement
personnel recognizing the problem. The superintendent does not believe this
occurred.
One explanation which fits the evidence at hand is that the concrete might
have gotten hung up in the casing as it was lifted. This would result in a
broken seal while there was still concrete in the casing. This condition
usually occurs only in smaller diameter casings but is conceivable in this
case. The piers showing the most problem are mostly the smaller 16 and 20
inch piers. One laboratory report shows concrete being placed at a three inch
slump. If iow slump concrete were placed in the casing at the end of one
truck and the casing was left in place for some time and then lifted, the
above condition could occur. The broken seal would not be visible to
placement personnel.
Enclosed is a copy of Richard Muenow's report. Because of the poor quality of
Xerox reproduction of the photographs, original photos are being sent to us
and will be copied to you. A summary of the pier tests in numerical order is
also included.Should you have any questions, please call us.
Yours truly,
SHIL~TONE & ASSOCIATES, INC.
~__ames M. Shilstone, Jr.
Vice President
enc.
-4-
COPPELL TOk'N CENTER
PIER klASHOUT EXAI~PLE
8'
CASING.
CLAY
CLAY
CDPPELL'~'~WN CENTER
PIER TEST RESULTS
Pier Date Depth Diam Seam % $~C. El(. Oi. Off Top Bott.
I 5/15 24-4 20 VS 90 22.77 2.77
2 5/15 18-5 24 12-16 90 26.56 2.56
5 5/15 18-11 24 12-14 80 25.04 1,04
4 5/15 20-8 24 9-11 90 26.56 2.56
5 5/15 24-11 20 9-12 80 21.47 1.47
6 5/15 24-0 24 VS 95 27.29 5.29
7 5/14 27-9 24 9-12 90 26.56 2.56
8 5/14 29-5 24 VS 90 26.56 2.56
9 5/16 27-11 20 11-12 90 22.77 2.77
10 5/16 29-6 20 11-15 80 21.47 1.47
11 5/15 24-0 24 VS 11-15 85 25.81 1.81
12 5/16 20-0 20 11-12 90 22.77 2.77
15 5/14 28-10 24 9-15 70 25.45 -0.57
I 1! 5/15 24-0 20 Numerous
15 5/16 23-5 50 Not t~ken
16 5/16 28-0 24 Numerous 1606 2464
17 5/16 22-10 50 11-12 90 52.26 2.26
18 5/16 20-2 50 VS 11-12 90 52.26 2.26
19 5/16 22-1 20 VS 9-10 90 22.77 2.77
20 5/17 22-1 20 11-12 95 25.59 5.59
21 5/16 2'0-3 20 VS 9-11 95 23.39 J.39
22 5/16 24-11 20 VS 9-10 95 23.59 3.59
23 5/16 24-6 36 11-12 90 37.95 1.95
24 5/17 2&-9 56 9-12 80 55.78 -0.22
25 5/15 25-2 20 11-15 90 22.77 2.77
26 5/15 24-6 20 11-14 90 22.77 2.77
27 not on plan
28 5/15 22-B 24 11-12 95 27.29 3.29
29 5123 26-3 36 9-11 95 38.99 2,99
30 5/16 23-6 Solid 95 3.90 3,90
51 5/17 24-2 56 10-15 80 55.78 -0.22
52 5/17 25-6 20 11-1J 80 21.47 1.47
55 5/17 19-6 20 Numerous
34 5/17 23-6 20 US 10-11 95 23.39 3.39
55 5/28 23-10 20 I0-13 90 22.77 2.77
56 not on plan
57 5/15 27-9 20 9-12 80 21.47 1.47
58 5125 25-5 36 11-14 80 35.78 -0.22
39 5/17 27-0 56 VS 11-12 95 38.99 2.99
40 5116 22-5 20 US 9-11 90 22.77 2,77
41 5/17 22-0 20 US 9-10 95 23.39 5.39
42 5/17 21-9 20 9-12 BO 21.47 1.47
45 5/17 24-4 20 VS 9-10 95 23.39 3.39
44 5/23 26-4 36 VS 11-15 90 37.95 1.95
45 5/24 25-4 36 1-11 90 37.95 1.95
46 5/24 22-~ 20 12 70 20,08 0,08 ~091 4853
47 5/23 25-5 20 NA
48 not on plan
49 5/23 24-3 20 VS 9-11 90 22.77 2.77
50 5/25 28-3 50 9-12 90 52.26 2.26
51 5/24 27-0 56 VS 11-12 95 38.99 2.99
52 5/17 24-6 30 VS 9-12 80 30.41 0.41
53 5/17 22-4 20 US 8-10 90 22.77 2.77
C 0 P P E LI,/,-T,,O W N CENTER
PIER TEST RESULTS
Pier Date Depth Diam Seam % Sec. Elf. Di. Off Top Bott.
54 5/24 28-2 16 11-14 70 16.73 0,73
55 5/24 26-5 16 V8 10-11 95 19.49 3.49
55 5/28 23-1 24 VS 9-i1 BO 25.04 1.04
57 5/24 27-4 24 VS 9-11 90 26,58 2.56
58 5/23 30-5 24 VS 9-13 90 26.56 2,56
59 5/23 27-0 24 ¥S 10-I1 90 26.56 2.56
60 5/17 23-9 24 VS 9-11 80 25.04 1,04
61 5/23 22-5 16 VS 9-10 90 18.97 2.97
62 5/17 22-4 24 VS 11-12 90 26,56 2,56
63 5/23 24-10 24 V$ 9-11 90 26.56 2.56 3620
64 5/23 24-3 24 VS 9-11 90 26.56 2,56
65 5/23 25-5 20 VS 9-12 80 21.47 1.47
66 5/14 24-0 16 VS 9-11 90 18,97 2.97
67 5t14 26-10 16 9-11 85 18.44 2.44
68 5/14 26-4 16 VBAO TT~ V~y' ~
69 5/14 25-0 16 Numerous
70 5/28 23-2 16 11-12 70 16.73 0.73 1370 1935
71 5/25 24-0 24 11-12 90 26.56 2.56
72 5/28 22-2 16 9-11 95 19.49 3.49
73 5/28 24-11 24 11-12 95 27.29 3.29
74 5/14 27-7 20 VSL 90 '22.77 2,77
75 5/14 27-0 20 9-14 BO 21.47 1.47
76 5/14 26-6 20 VS 9-11 90 22,77 2.77
77 5/14 26-0 20 9-14 70 20,08 O.OB 4479 4111
78 5/14 27-10 20 VS 95 23.39 3.39 4831 4762
79 not on plan
BO 5/16 23-0 16 10-12 SO 17.89 1.89
81 5116 22-9 16 11-12 BO 17.8~ 1.89
82 5/16 25-10 16 9-11 90 18.97 2.97
83 5/16 24-3 16 9-12 80 17.89 1.89 3686
MANUAL OF CONCRETE PRACTICE
SPECIFICATION CHECKLIST (cont.)
Section/Parl/Article of ACI 336.1 Notes to the Designer/Specifier
2.3.1.2b Inspection and testing Specify inspection and testing procedures to be
followed (it is recognized that procedures vary
in different parts of country depending on pre-
vailing geology and experience).
Show bells on drawings.
2.3.1.2c Bells Specif.,,. limiting amount of loose material or water
2.3.1.5 Loose material permitted in hole at time of concrete placement.
Specify any other acceptability requirements.
2.3.1.6 Disposal of excavated material Specify where.
2.3.2.1 Void space Specify whether grouting is required of any an-
nular void space outside of permanent casing.
2.3.2.2 Removal of casing Specify removable or permanent Casing.
2.3.4.1 Dewatering Specify specific dewatering criteria.
2.3.4.2 Approval to place concrete Emphasize.
2.3.4.4 Free fall Specify any special concrete placement proced-
ures required.
2.3.4.9 Tremie concrete Specify specific tremie procedures, such as: Mini-
mum 7 to 9 in. slump, maximum 5~ in. aggregate,
continuous tremie pipe, minimum pipe embed-
ment in concrete at all times, continuous concrete
placement, and static water ]eve] in hole prior to
concrete placement.
Specify coring or other special requirements of
tremie concrete placement.
2.3.4.10 Concrete tests Specify requirements for making test cylinders
and for testing.
SECTION 1 ....GENERAL REQUIREMENTS
1.1--Scope 1.2.2 Allowable service load bearing pressure--
The vertical pressure per unit area that may be
lA.l--This standard specification covers re/luire- applied to the bearing stratum at the level of the
ments for end bearing drilled pier construction, pier bottom. Allowable service load bearing pres-
1.1.2--The provisions of this standard specifica- sure is normally selected by the Gcotechnical En-
tion shall govern unless otherwise specified in the gineer on the basis of samples, tests, and applied
contract documents. In case of conflicting require- soil mechanics, ~vith due regard for the character
merits, the contract documents shall govern, of the loads to be applied and the settlements that
-- can be tolerated.
1.2--Definitions
1.2.3 Architect-Engineer--The authority, such as
The following definitions cover the meanings of the architect, the engineer, the architectural firm,
certain words and terms as used in this standard the engineering firm, the contracting officer, or
specification, other agent of the owner issuing project specifica-
1.2.1wAcceptable or accepted--Acceptable or ac- tions and drawings, and/or authorized by the
- cepted by the Architect-Engineer or Geotechnical owner to administer work under the project doeu-
, END BEARING DRILLED PIERS
· - ~ 336.1-5
' 1.2~4 Bearing stratum--The formations or layers 1.2.19 Specified--Defined in-the contract docu-
of soil or rock that support the pier and the loads merits.
imposed on it.
1.2.5 Bell--An enlargement at the bottom of the 1.2.20 Submitted--Submitted to the Architect-
shaft for the purpose of spreading the load over Engineer for review.
a larger area.
- 1.2.6 Casing--Protective steel casing usually of 1.3---Notation
cylindrical shape, lowered into the excavated hole The following abbreviations are defined for
to protect workmen and inspectors entering the use in this standard specification.
shaft from collapse or cave-in of the sidewalls 1.3.1--ACI: American Concrete Institute
and for the purpose of excluding soft and water
from the excavation. P.O. Box 19150
Detroit, Mich. 46219
1.2.7 Contract documents--Consist of the agree- 1.3.2--ASTM: American Society for Testing
ment, conditions of the contract, contract specifica-
tions, contract drawings, and all addenda thereto and Materials
issued prior to the signing of the contract. 1916 Race Street
Philadelphia, Pa. 19103
1.2.8 Contract drawings--Drawings which ac-
company contract specifications and complete the 1.3.3--AWS: American Welding Society
descriptive information for drilled pier construc- 2501 N.W. 7th Street
tion work required or referred to in the contract Miami, Fla. 33125
specifications.
1.2.9 Contractor--The organization contracted 1.4--Reference standards
with to carry out the work shown on the contract 1.4.l--The standards referred to in this Standard
drawings and specifications. Specification ACI 336.1 are listed in Articles 1.4.2
1.2.10 Contract specifications--The specifications through 1.4.4 of this Section. with their complete
which employ ACI 336.1 by reference and which designation and title including the year of adop-
serve as the instrument for making the mandatory tion or revision and are declared to be a part of
and optional selections available under the speci- this Standard Specification ACI 336.1 the same
fication, as if fully set forth herein, unless otherwise indi-
1.2.11 End bearing drilled pier--Cast-in-place cared in the contract documents.
foundation element with or without enlarged 1.4.2 ASTM standards
bearing area extending downward through weaker
soils or water to a rock or soil stratum capable of A 36-75 Standard Specification for Structural
'supporting the loads imposed on or within it. A Steel
shaft diameter of 2¥~ ft (0.76 m) is the lower A 82-76 Standard Specification for ColdDraw_n
limit for piers covered by these specifications. Steel Wire for Concrete Reinforce-
1.2.12 Geotech~icaI Engineer--The specialized ment
engineer retained by the owner reporting to the A 252-75 Standard Specification for Welded
Architect-Engineer and with responsibilities as
defined herein, and Seamless Steel Pipe Piles
1.2.13 Testing Zaborator.v~The testing agency A444-75 Standard Specification for Steel
retained by the owner to perform required tests Sheet, Zinc Coated (Galvanized)
on the contract construction materials to verify by the Hot Dip Process for Culverts
conformance with specifications, and Underdrains
1.2.14 Owner~Party that pays for approved A615-76a Standard Specification for Deformed
work performed in accordance with drawings and and Plain Billet-Steel Bars for
contract specifications and receives the completed Concrete Reinforcement
work. A 616-76 Standard Specification for Rail-Steel
1.2.15 Permitted--Permitted by the Architect- Deformed and Plain Bars for Con-
Engineer. crete Reinforcement
1.2.16 Qualified~Qualified by training and by A 617-76 Standard Specification for Axle-Steel
experience on comparable projects. Deformed and Plain Bars for Con-
1.2.17 Required~Required by the contract docu- crete Reinforcement
ments.
A 706-76 Standard Specification for Low-Alloy
1.2.18 Shaft--Drilled pier above bearing surface Steel Deformed Bars for Concrete'
exclusive of bell, if any. t,
336.1-6 ' MANUAL OF CONCRETE PRACTICE ~
C 39-72 Standard SpecifiCation for Compres- 1.5.2 Subsurface data--A subsurface investiga-
sive Strength of Cylindrical Con- tion has been made by Logs of
crete Specimens borings and test data are available for Contractor's
E329-72 Standard Recommended Practice for information and for his interpretation as to soil
Inspection and Testing Agencies for and water conditions that may be encountered at
Concrete, Steel and Bituminous Ma- the site. Logs and test data are not represented as
terials as Used in Construction complete description of the site soil and water in-
1.4.3 ACI standards formation bus only display what was found in
301-72 Specifications for Structural Concrete borings at the indicated locations. Contractor has
(Revised for Buildings the right to obtain additional information, if neces-
1975) sary in his judgment.
318-77 Building Code Requirements for Re- 1.5.3 Existing underground utilities--Locate all
inforced Concrete existing underground utilities and construction in
322-71 Building Code Requirements for the field by a qualified surveyor so as to deter-
Structural Plain Concrete mine any conflicts with the work. Should conflicts
1.4.4 AWS standards be determined, do not proceed with the work un-
01.1 Structural Welding Code til the Architect-Engineer specifies method(s) to
012.1 Reinforcing Steel Welding Code eliminate the conflict.
1.5.4 Pre-job con~erence--The contract docu-
1.=. -Project conditions meats will specify if a pre-job conference is re-
1.5.1 E~camination o~ site--Visit (prior to sub- quired among the Architect-Engineer, the Con-
mitring bid) to determine exis, ting surface condi- tractor(s), and the Geotechnical Engineer to
tions, review special requirements for the work.
SECTION 2--MATERIALS AND CONSTRUCTION
PART 2.1gGENERAL f. Notification to Architect-Engineer to permit
2.1,1 Description--This section covers require- in-place inspection of reinforcing steel prior to
ments for materials and construction for end bear- placing concrete
lng drilled piers, and includes the following: g. Testing loboratory reports for concrete tests
during construction
2.1.1.1 Excavation and casing, dewatering, gas
testing and probing, h. Reports of actual location, alignment, eleva-
2.1.1.2 Reinforcing steel. - tions, and dimensions of drilled piers
2.1.1.3 Concrete. i. Reports of materials quantities, if specified
2.1.2 Submittals 2.1.3 Quality assurance
2.1.2.1 Geotechnical Engineer--Will submit 2.1.3.1 Geotechnica! Engi~eer--Will provide
test reports to Architect-Engineer and to Con'trac- inspection of all phases of drilled pier construc-
tor concerning allowable service load bearing tion, and request additional soil or rock testing
pressures, elevations, dimensions, and alignment, if needed.
2.1.2.2 Contractor~Submit the following: 2.1.3.2 Contractor
a. Reinforcing steel shop drawings a. Provide the services of a qualified surveyor
b. Certified mill test reports for reinforcing for performing all surveys and layouts and to
Steel determine vertical and horizontal alignments.
b. Protect reinforcing steel from contamination.
c. Evidence that proposed materials and mix
designs conform to all requirements of "Specifi- 2.1.3.3 Testing laboratory~Will provide ser-
cations for Structural Concrete for Buildings (ACI vices conforming to the requirements of ASTM
301-72) (Revised 1975)," except as modified by E 329, for sampling, testing, inspection, and re-.
these specifications porting with respect to casing, reinforcing, and
concrete.
d. Detailed procedures for casing removal, if
any 2.1.4 Constructiott tolerances
e. Detailed procedures for tremie concrete, if 2.1.4.1 Bottom elevation of drilled piers as
any shown are estimated from so/] boring data. Geo~
END BEARING DRILLED PIERS 336. i'~7
technical Engineer will determine actual final drawings call for an allowable service load bear-
bearing level during excavation, ing pressure, extend excavation to suitable ma-
- 2.1.4.2 Maximum permissible variation of lo- terial.
cation--1/24th of shaft diameter or 3 in., which-_ 2.3.1.2 Determine suitability of supporting ma-
ever is less. - terial for drilled piers, as follows:
2.1.4.3 Concrete shafts out of plumb--Not
a. Explore bearing stratum to depth equal to
more titan 1.5 percent of the length nor exceeding the diameter of the bearing area below the bot-
t2.5 percent of shaft diameter or 15 in., whichever tom of the drilled pier with probe hole when dj-
is less. rected by the Geotechnical Engineer.
2.1.4.4 If tile tolerances of Articles 2.1.4.2 and b. Inspection and testing at the bottom of each
2.1.4.3 are exceeded, furnish and pay for correc- pier will be by the Geoteehnieal Engineer.
rive design and construction that may be required.
c. Excavate for drilled pier bells (if required)
2.1.4.5 Concrete cut-off elevation tolerance-- immediately upon confirmation of the allowable
Plus 1 in. to minus 3 in. service load bearing value by the Geotechnical
2.1.5 Delivery. handling, and storage of perma- Engineer.
nentcasing d. If test results indicate the stratum is not
2.1.5.1 Deliver casing to site in undamaged capable of providing the required service load
condition, bearing pressure, notify the Arehitect-Engineei'
2.1.5.2 Handle and protect casing to maintain for a determination of adjustments to be made.
round within ±2 percent. These may include, but not be limited to. advanc-
ing the shaft length as directed by the Geotechni-
cal Engineer and repeating the above steps, or
PART 2.2~MATERIALS
enlarging the bell diameter as determined by the
2.2.1 Stee[casing Architect-Engineer for the appropriate bearing
2.2.1.1 ASTM A 252, Grade 2, or ASTM A 36, pressure as determined by the Geotechnical Eh-
or ASTM A 444 corrugated steel, as specified, or gineer.
as shown on the contract drawings. 2.3.1.3 Provide gas testing equipment, protec-
2.2.1.2 Furnish 100 percent penetration welds tire cage, or temporary casing of proper diameter,
for vertical joints in noncorrugated permanent length, and thickness and other safety equipment
casings, called for by law for inspection and testing of
2.2.1.3 For permanent casing requiring hard- drilled piers and to protect workmen during hand
ened steel teeth for seating into rock, face weld belling or other operations necessitating entry into
teeth with AWS electrodes, shaft.
2.2.2 Reinforcing steel~ASTM A 615, A 616, 2.3.1.4 Check each drilled pier for toxic and
A 617 or A 706, as specified, or as shown on the explosive gases prior'to personnel entering. If gas
contract drawings, is found, ventilate with forced air until safe for
2.2.3 Concrete--Concrete work shall conform to entry.
all requirements of "Specifications for Structural 2.3.1.5 Remove from bottom of drilled piers,
Concrete for Buildings (ACI 301-72) (Revised loose material or free water in quantities sufficient
1975)," except the following: to cause settlement or affect concrete strength as
Sections 3.83, 3.84, Chapter 9 determined bx- the Geotechnical Engineer. Exca-
and 3.85 Chapter 10 rate pier bottoms to a level plane. If bottoms are
Chapter4 Chapter 11 sloping rock. excavate to a level plane or step
Section 5.4 Chapter 12 with maximum step height less than one-quarter
Sections 6.2, 6.3, Chapter 13 the width or diameter of the bearing area.
6.4 and 6.5 Chapter 14
2.3.1.6 Remove excavated material from site or
Section 7.4 Chapter 15 as otherwise directed by the Architect-Eneineer.
2.2.4 Sand-cement 9rout~As specified for filling
annular void outside permanent casing. 2.3.2 Steel casin.q
2.3.2.1 Provide steel casinff for shaft excava-
PART 2.3~CONSTRUCTION tion where required. Provide casin~- of sufficient
strength to withstand handlin~ stresses, concrete
2.3. l Excavation. soil testing, and inspection pressure, and surroundin~ earth and/or fluid
2.3.1.1 Excavate drilled piers to dimensions and pressures. Make diameter of excavation in rela-
~6.1-8 ' MANUAL OF CONCRETE PRACTICE
permanent casing with minimum outside diameter gineer has verified allowable service load bearing
equal to nominal outside diameter of shaft, capacity. Do not leave uncased or belled excava-
2.3.2.2 Casing may be removed at option of lions open overnight.
Contractor unless otherwise specified. If casing is 2.3.4.4 Free fall concrete may be used pro-
removed during or after concreting, follow special vided it is directed through a hopper, or equiva-
requirements specified in Article 2.3.4. lent. such that fall is vertical down center of shaft
2.3.3 Reinforci)~.o steer without hitting sides or reinforcing. Vibrate top
2.3.3.1 Place reinforcement for drilled piers in 5 fl of concrete, but only after casing has been
accordance with the contract documents, pulled or when casing is permanent.
2.3.3.2 Use reinforcement at time of placement 2.3.4.5 Place concrete in pier in one continuous
which is free of mud. oil. or other coatings that operation. If a construction joint is unavoidable,
adversely affec! bon(~ level, roughen, and clean surface prior to recom-
2.3.3.3 Reinforcement with rust, scale, or a mencement of concrete placement. Provide rein-
combination of both may be used provided the forcing dowels or a shear key when required by
minimum dimensions, including height of defor- the Architect-Engineer.
mations and weight of wire brushed specimens. 2.3.4.6 If casing is withdrawn, the Geoteehnica]
are not less than required by applicable ASTM
Engineer wilt provide inspection during the re-
specifications. Architect-Engineer will determine
moral of easing and placing of concrete. With-
acceptability of such reinforcement.
draw casing only as shaft is filled with concrete.
2.3.3.4 Use metal reinforcement without kinks
Maintain adequate head of concrete to balance out-
or nonspecified bends. Straighten or repair bars in
side soil and water pressure above the bottom of
a manner that will not damage the bars or adja- the casing at all times during withdrawal. Specific
cent construction, procedures that the Contractor will follow to ac-
2.3.3.5 Place bars as shown on contract draw- complish this objective shall be submitted for
ings with cover of not less than 3 in. where ex- approval.
posed to soil.
2.3.3.6 Make splices in reinforcement as shown 2.3.4.7 Where casing is removed, provide spe-
on contract drawings unless otherwise accepted, cially designed concrete wi,th a minimum slumr~
2.3.3.7 Provide clear distance between bars of of 5 in. and with a retarder to prevent arching
not less than one and one-half times the bar di- ~f"concrete (during casing pulling) or setting of
ameter, nor one and one-half times the maximum concrete until after casing is pulled. Cheek con-
crete level prior to, during and after pulling cas-
aggregate size. lng. Avoid vibrating concrete if casing is pulled.
2.3.4 Co~crete Pull casing before slump decreases below 5 in. as
2.3.4.1 Dewater drilled pier excavation prior to
determined by testing.
placing concrete. Perform pumping in a manner
that will not create ground loss problems that 2.3.4.8 When casing is left in place, fill void
might adversely affect this and existing adjacent space between casing and shaft excavation with
structures as determined by the Geotechnical Eh- concrete or fluid grout by means of grout pipe and
gineer. If during pumping excessive water inflow pump pressure as required.
is noted, use alternative means to reduce inflow' 2.3.4.9 For placing concrete under water,
such as extending casing, outside deep w. etls, or where permitted, use tremie pipe or concrete
grouting, or other acceptable means. If water pumping with special procedures as specified or
seepage still is considered by the Geotechnical Eh- accepted.
gineer to be excessive for safe removal, follow 2.3.4.10 Co~crete tests~Take one set of four
procedure specified in Article 2.3.4.9. cylinders per drilled pier but not more than one
2.3.4.20biain permission of Arehiteet-Engi- set per truck, or less than required by ACI 318-77.
neet prior to placing concrete. Test one sample at 7 days and two at 28 days;
2.3.4.3 Place concrete immediately after eom- keep one sample in reserve for testing in the event
pletion .of excavation and after Geotechnical En- o.f a low break.
MATERIALS ANO NON(~$TRUCllV~ T~STING
~40 HUNT~.IFF. DR.
CHARLOTTE. NORTH CAROUNA Z8211
(704) 377.4041 · (704~ 542,2223
PULSE ECHO NO~TDESTRUCTIVE
EVALUATION OF
PILES AT
COPPELL TOWN CENTER
COPPELL. TEXAS
AND NO~q~ST~t,.~I'rVI~
CO4AJ~OT'TL NO~TJq CAJqO(.#~ 28211
377,40~1 · [70~ ~d2-2223
PULSE-ECHO NONDESTRUCTIVE
EVALUATION OF PILE AT COPPELL
TOWN CENTER BUILDING - COPPELL, TEXAS
BY
RICHARD A. MUENOW P.E.
On June 7, 1985 a series of pulse-echo nondestructive tests (NDT)
were conducted at the Coppell Town Center, Coppell, Texas. The purpose
of our investigation was to determine the insitu condition of concrete
used in approximately 79 pile. It was reported, that due to ground
water flows, some cement matrix wash out may have occurred. This pro-
ject was authorized by Jim Shilstone of Shilstone and Associates, Inc.
of Dallas, Texas. All testing and data reduction was conducted by
Richard Muenow of Muenow and Associates, Inc., of Charlotte, North
Carolina.
TEST TECHNIQUE
The'theory of pulse-echo nondestructive testing for the evaluation of
concrete and concrete structures is based upon Shell's Laws of Reflection
and Refraction. This law states that as mechanical energy (sound waves)
pass through a medium, a portion of the energy will be reflected as changes
in density are encountered. These changes in density can be the opposite
side of the structural member or internal discontinuities such as cracks,
voids, honeycomb or'lack of consolidation associated with the reinforcement
steel system. The pulse-echo NDT system not only identifies these internal '
discontinuities as to nature and characteristics, but will also delineate
aerial extent and depth ~-lthin members. A measure of pulse velocity is
also recorded which is a measure of the speed with which a sound wave
propagates through a medium. This value of pulse velocity is then correlated
to the ~niformity of concrete~ "E" values and the in situ compressive
strengths. See enclosure for test procedure and general illustration of
test method.
TEST LOGISTICS
Prior to our arrival on site most of pile tops had been cleaned off
and concrete exposed. Testing consisted of introducing a stress wave in-
to the pile by means of a spring loaded hammer. Immediately adjacent to
the hammer position is a piezoelectric transducer which receives reflected
energy from within a pile. Personnel from Howard Freeman Construction Co.,
the contractor, assisted in locating and identifying pile for our test
records. Jay Shilstone operated the spring h-mmer and piezoelectric hammer.
TEST DATA
The attached tabulation reflects our test data interpretation; data
includes, pile identification, depth of pile, depth to initial internal
discontinuity and approximate remaining cross sectional area. Common
characteristics to all pile are:
1) Top 6 to 18 inches of each pile appear to contain low
density concrete.
2) Concrete below the 9 to 12 foot elevation is well consolidated
and appears to transmit energy at a rate of 6.4 microseconds
per inch. Propagation times such as these normally indicate
strengths in the range excess of 3000 to 3500 PSI.
3) Concrete from the surface to between the 9 and 12 foot
elevation appears to be of slightly low density, re-
flecting transmission times of 6.8 to 7.6 microseconds
per inch. Propagation times such as these normally in-
dicate strengths in the range of 2500 PSI.
4) Reduction in cross sectional area, where indicated, appears
to be circumferentially equal.
5) Test data comments indicating "slight seam'' at a particular
depth means that an internal reflector was identified, but
no reduction in cross section could be calculated.
PIER NO. DEPTH COMMENTS
50 28' 0" 9-12 feet seam
90% X section
45 25' 3" 1-11 feet seam
90% X section
47 25' 5" Not Available
46 22' 3" 12 foot seam
70% X section
37 27' 9" 9-12 feet seam
80% X section
70 23' 2" 11-12 feet seam
70% X section
35 23' 0" 10-13 feet seam
90% X section
71- 24~ 0" 11-12 feet seam-
90% X section
28 22~ 8" 12 feet seam
95% X section
25 23~ 2" 12 feet seam
95% X section
26 24' 6" 11-13 feet seam
90% X section
14 24' 0" 11-I4 feet seam
90% X section
15 23' 3" Numerous Lenses
82 23' 10" 9-11 feet seam
90% X section
83 24' ~' 9-12 feet seam
80% X section
PIER NO. DEPTH CO~KENTS
81 22t 9" 11-12 feet seam
80%-90% X section
5 24' 11" 9-12 feet seam
80% X section
80 23' 0" 10-12 feet seam
80%-90% X section
4 20' 8" 9-11 feet
90%-95% X section
3 18' 0" 12-14 feet
80%-90% X section
2 18' 3" 12-16 feet
90% X section
1
. VS seam
90%-95% X section
21 20' 3" VS seam
9-11 feet
95% X section
20 22' 1" VS_seam
11-12 feet
95% X section
IA 23' 6" 11-13 seam
80%-90% x section
73 24' 0" VS seam
11-12 feet
95% X section
34 23' 6" VS seam
10-11 feet
95% X section
33 Numerous Lenes TT.
PIER NO. DEPTH COI~NTS
22' 3" VS seam 9-11 feet
90% X section
72 22' 2" VS seam
9-11 feet
95% X section
43 24' 4" VS seam
9-10 feet
95% X section
42 21' 9" 9-I2 feet seam
80%-90% X section
41 22' 0" VS seam
9-10 feet
95% X section
69 25' 0" Numerous Lenses
67 26' 10" 9-11 feet seam
85% X section
66 24' 0" VS seam
9-11 feet
90% X section
23 24' 6" 11-12 feet seam
90% X section
17 22' 10" 11-12 feet seam
90% X section
12 23' 8" 11-12 feet seam
90% X section
9 27' 11" 11-12 feet seam
90% X section
10 29' 6" 11-13 feet seam
80%-90% X section
PIER NO. DEPTH COMMENTS
39 27' 0" VS seam
11-12 feet
95% X section
44 26' 4" VS seam
11-13 feet
90%-95% X section
38 25' 5" 11-14 seam
80%-90% X section
51 27' 0" VSseam
11-12 feet
95% X section
55 26' 5" VS seam
10-11 feet
95% X section
54 28' 2" 11-14 feet seam
70%-80% X section
31 24' 2" 10-12 feet seam
80%-90% X section
22 24' 11" VS seam
9-10 feet
95% X section
74 27' 0" VSL seam
90%-95%
8 29' 5" VS seam
90%-95%
13 28' 10" 9-13 seam
70%-80% X section
75 27' 0" 9-14 feet
80%-90% X section
76 26' 6" 9-11 feet VS
90%-95% X section
PIER NO. DEPTH COMPIENTS
77 26' 0" 9-14 seam
70X-90X X section
78 27' 10" VS seam
95~ X section
6 25' 5" VS seam
95Z X section
'16 28' 0" Numerous Lenses
24 26' 9" 9-12 feet seam
80% X seciton
29 26' 3" 9-11VS seam
95% X section
30 23' 6" Solid
95Z X section
68 26' 4" VBAO Lenses TT
53 22' 4" VS seam
8-10 feet
90Z X section
52 24t 6" VS seam
9-12 feet
80%-90~ X section
60W
VS seam
9-11 feet
80%-90Z X section
61W 22' 8" VS seam
9-10 feet
90Z X section
59 27' 0" VS seam
10-11 feet
90%-95Z X section
PIER NO. DEPTH COHPIENTS
19 22' 1" VS seam
9-10 feet
90% X section
18 20' 2" VS seam
11-12 feet
90% X section*
11 23' 0" VS seam
11-13 feet
85%-90% X section
7 27' 9" 9-12 feet seam
90% X section
49 24' 3" VS seam
9-11 feet
90% X section
56W 23' 1" VS seam
9-11 feet
80%-90% X section
57W 27' 4" VS seam
9-11 feet
90% X section
65W 25' 5" VS seam
9-12 feet
80%-90% X section
64W 24' 3" VS seam
9-11 feet
90% X section
63W 24' 10" VS seam
9-11 feet
90% X section
PIER NO. DEPTH COUNTS
58W 30~ 5" VS seam
9-13 feet
90Z X section
62W 22t 4" VS seam
11-12 feet
90~ X section
59~ 27t 0" VS seam
11-12 feet
90Z X section
Coppell Town Center
" MUENOW and ASSOCIATES, INC. Jo.-
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