Forensic Study of Warranty Project on US82

This forensic study is unique in that it involves a pavement warranty specification. Extensive field and laboratory testing was conducted to determine the cause(s) of longitudinal cracks observed on the surface. Four trenches were cut and removed to allow more testing on top of each pavement layer. The tests found that the stiffness of the foamed asphalt base is higher than that of a typical flexible base. However, the subgrade modulus is low compared with the average subgrade modulus in Texas. Water seeped into two trenches (dug into the road where there were surface cracks) within 20 min of digging. No water was observed in the other two trenches, where there were no surface cracks. The two trenches with surface cracks have lower base density and higher base moisture content than the two with no surface cracks. Based on observations of the trenching and coring operations, the same surface cracks have been detected in the base layer. Cracks up to 150 mm into the base layer have been observed. Although cracks have been observed in the base (and they can be related to lower stiffness and higher falling weight deflectometer deflections), it is difficult to determine if the cause of surface cracks is due to the base layer alone. It is difficult to prove if the layer is responsible for the failure, except by properties listed in the specification. One faulty pavement layer can easily cause the failure of other layers. For warranty purposes, layer-specific failure criteria should be clearly outlined. The base did not meet the gradation specification. The field material was substantially finer than specified. While some specifications may have been violated, there is little evidence to show that the cause of the longitudinal cracking is primarily related to the foamed-asphalt-stabilized base.     

Forensic Evaluation of Premature Failures of Texas Specific Pavement Study–1 Sections

The Specific Pavement Study–1 pavement test section on US281 in south Texas comprise the largest Strategic Highway Research Program experimental site in the United States. The project was opened to traffic in 1997, and performance has been poor. Three of these test sections developed deep rutting within 1 year. Their surfaces were milled to restore ride quality. Three years after construction, 14 of the sections had 10 mm or more rutting. A forensic study was initiated by the Texas Department of Transportation to identify the cause of the problem. Nondestructive testing was conducted with both the falling weight deflector and ground penetrating radar. No structural problems were detected with either device, both indicating that the base and subbase layers were strong. A field investigation was initiated; the original plan was to cut nine trenches, however, after four trenches were cut, the problematic layer was identified and the trenching operation was terminated. Dynamic cone penetrometer, stiffness gauge, seismic pavement analyzer, and nuclear density gauge tests were then conducted on top of the base and subgrade layers. The trench profiles indicated that the rutting was coming primarily from the top 50-mm (2-inch) asphalt-concrete layer. Asphalt cores were taken from both rutted and nonrutted sections and bag samples of the base were tested in laboratory. The binder was recovered, and the asphalt content and penetration, aggregate gradation, and type were determined. The cause of the problem was traced to a change in aggregate screening, and also an excess of asphalt in the top layer.     

Detailed Forensic Investigation and Rehabilitation Recommendation on Interstate Highway-30

The main objective of this study is to identify the cause of the punchouts observed on Interstate Highway 30 (IH-30), and to identify possible rehabilitation alternatives. Several nondestructive tests, as well as coring and trenching, were conducted in both distressed and nondistressed areas. Middepth horizontal cracks were found during routine repair and by the trenching performed in this study. It is believed that due to temperature variation at an early stage, horizontal cracks developed at the middepth interface between the steel and concrete. The truck traffic caused the horizontal cracks to deteriorate further. Repetitive truck traffic and thermal loading forced the concrete to crack vertically from the middepth where there were horizontal cracks. The closely spaced transverse and longitudinal cracks, along with the delamination, caused punchouts. Although the problem is not imminent, an immediate seal plus a 75 mm heavy-duty stone matrix asphalt (SMA) overlay will probably provide the most cost-effective remedy for this section of IH-30. Existing distressed areas should be repaired before the rehabilitation. To slow the deterioration, the district should use a latex modified chip seal or asphalt rubber seal (AC15-5TR) followed by a 75 mm heavy duty SMA. This is to provide bonding between the concrete and SMA overlay. If the district chooses to do nothing at this time, it will become costly in 2–3 years if current environmental and traffic conditions hold. The cost to repair a severely deteriorated continuously reinforced concrete pavement (CRCP) would be several times more than the 75 mm heavy duty SMA overlay.     

Forensic Investigation of Ultra-Thin Whitetopping Failures in Taiwan

This paper addresses the causes of the premature failures observed on newly constructed ultra-thin whitetopping (UTW) sections. The key factors contributing to premature failure were high pouring temperature and an insufficient underlying asphalt layer. Severe cracking and deep rutting were observed on sections placed during the daytime when the weather was hot and dry. Pouring temperature was even more critical when river gravel aggregate was used because it has a high thermal coefficient of expansion. Also, a low water-cement ratio magnified the effect of thermal cracking at high pouring temperature. On the basis of field results, it was found that the use of high-strength concrete should be discouraged when the pour temperature is high, since high shrinkage and premature cracking can result. It was concluded that the deep rutting was caused by the pumping of fines from the underlying base layer, in locations where there was no erosion-resistant asphalt layer. Sections poured at temperatures below 30°C with 100?mm of underlying asphalt performed well, and those two criteria are recommended for future UTW application.     

Results from a Forensic Investigation of a Failed Cement Treated Base

After only 2 months in service, the frontage road of US 290 developed a series of depressions that caused a very poor ride. The main cause of the premature failure was attributed to disintegration of the cement treated base (CTB) layer. This was attributed to two primary factors: (1) a very coarse gradation of the aggregate used in the CTB layer which produced a mix that was prone to segregation during placement; and (2) the CTB layer was placed in two lifts, which were not well bonded together. Another contributing factor was the lack of bond between the CTB and the hot mix asphalt (HMA) surface layer. Secondary factors include high air voids in the HMA layer and low HMA layer thickness. The material, when prepared carefully in the lab at the design cement content, passed the strength requirement of 2.07?MPa. But this coarse mix appears to have been difficult to place correctly in the field. The coarsely graded aggregate used on this project appears to be prone to segregation, either during placement or compaction. The ground penetration radar results (with confirmation by core samples) indicated that most of the problems were at the bottom of the upper CTB lift. The CTB was placed in two lifts and very poor condition was found between the two CTB layers. This problem was coupled with a thin, porous, and poorly bonded HMA layer that permitted moisture to enter the CTB layer. Similar failures have also been reported recently on other CTB projects in Houston.     

Forensic Investigation of Ultrathin Whitetopping Pavements in Florida

Developed in the early 1990s, ultrathin whitetopping (UTW) is a relatively new technique for asphalt pavement rehabilitation. To evaluate the applicability of UTW pavement in Florida, in 1997, the Florida Department of Transportation (FDOT) constructed an experimental UTW pavement in a weigh station along I-10, located in north Florida. The performance of these test sections, however, was less than ideal, with the observation of some early cracking on the concrete surface, which developed into severe cracking with time. Therefore, a forensic investigation was conducted to determine the causes of the problems in these UTW sections, so that lessons could be learned from this experimental project, the use of UTW under Florida’s conditions could be adequately assessed, and UTW technology could be properly applied in the future. The scope of work consisted of field evaluation, laboratory testing, and pavement design evaluation. Field evaluation included a pavement condition survey, pavement temperature measurement, nondestructive load testing using a falling weight deflectometer, and slab thickness determination. Laboratory tests were performed to determine concrete and asphalt material properties. Other design and traffic data were also acquired from FDOT. Data collected from the field evaluation and laboratory testing were used in conjunction with a mechanistic UTW pavement design/evaluation procedure to determine the possible causes for premature failure. From this comprehensive evaluation, the primary cause for the failure was found to be inadequate UTW pavement design. The inadequacy of the combination of thickness and slab dimensions contributed to the early cracking of the UTW pavement.     

Dynamic Properties of Chemically Stabilized Sulfate Rich Clay

A series of resonant column tests was conducted on chemically stabilized specimens of sulfate-rich expansive clay from southeast Arlington, Tex. Specimens were tested for different stabilizer types, stabilizer dosages, compaction moisture contents, and confining pressures. Three chemical stabilization methods were used: sulfate resistant type V cement, low calcium class F fly ash, and lime mixed with polypropylene fibers. Results in the small-shear strain amplitude range (<0.0001%) were analyzed to assess the influence of compaction moisture content and confining pressure on the linear shear modulus Gmax and material damping Dmin of stabilized soil. Tests were also conducted at small- to mid-shear strain amplitude levels (0.0001–0.01%) to assess the threshold strain limit γth for each treatment method, and to study the effects of torsional shearing on the rate of degradation of normalized modulus G/Gmax of treated soil. A 10%-by-weight dosage of sulfate resistant type V cement was found to give the highest modulus and lowest damping when compacted at 95% of maximum dry unit weight γd-max on the wet side of Proctor optimum.     

Small-Strain Shear Moduli of Chemically Stabilized Sulfate-Bearing Cohesive Soils

An experimental study was conducted to measure small-strain shear moduli of chemically treated sulfate-bearing expansive soils using the bender element test. The bender element test was chosen because it provides reliable and repeatable small strain shear modulus measurements and allows for the periodical monitoring of stiffness property responses of soil specimens under varying curing conditions. Bender element tests were conducted on cement and lime treated soils and the results were then analyzed to study the variations in stiffness properties of soil specimens at different sulfate levels and curing conditions. Both cement and lime treated natural and artificial clays with low sulfate level of 1,000?ppm showed considerable enhancements in small strain shear moduli, whereas the same treated soils at high sulfate level of 10,000?ppm showed less enhancements in shear moduli due to sulfate heaving. Also, enhancements in shear moduli were lower for soil specimens continuously soaked under water compared to those cured in the humidity room. Rates of stiffness enhancements due to stabilizer type, compaction moisture content, type of curing, and sulfate levels are quantified and summarized.     

Forensic Investigation of Pavement Premature Failure due to Soil Sulfate-Induced Heave

Current practice does not recommend stabilizing high sulfate-bearing soils using calcium-based stabilizers due to high potential swell and low retained unconfined compressive strength. In this technical note, a series of tests has demonstrated that a combination of lime and fly ash (Class F) proved to be the most suitable stabilizer for a high sulfate-bearing soil, and a combination of lime and slag seemed to be the most effective stabilizer for a moderate sulfate-bearing soil in terms of retained unconfined compressive strength and three-dimensional free swell potential.     

Forensic Examination of a Noncomposite Adjacent Precast Prestressed Concrete Box Beam Bridge

On the evening of December 27, 2005 the fascia beam supporting the east side parapet wall of the third span of the Lake View Drive Bridge failed under the action of dead load. To gain insight into the potential causes of the failure a series of forensic analyses were conducted on the beams decommissioned from the bridge. The study correlates external observations of surface condition with internal chloride profile, depth of carbonation, and existing corrosion. The forensic investigation indicated that strand cover was reduced due to the construction methods of the time. The chloride level in the concrete at the lower layer of strands was high enough that corrosion would be expected. Chloride attack was identified to have come from the leakage of water between beams from the bridge deck surface above. Based on the research findings recommendations are made for visual inspection, and guidelines are provided for condition rating of noncomposite prestressed concrete box beam bridges.     

Method for Forensic Analysis of Residential Floor-Elevation Data

An analysis of the levelness of three residential floor slabs constructed on-grade in the Phoenix, Arizona, metropolitan area is presented. The slabs were built using typical methods by a trade subcontractor for a large production builder in different subdivisions. Measurements of the elevation of the floor slabs were made at 0.3 m (1 ft) spacing across the entire surface of all three slabs within the first week after concrete placement. The resulting elevation data were then used as input in several different analytical techniques, including the maximum elevation difference, maximum slope, FL local, and FL. Special consideration was given to the sample size effects and the repeatability of the results for different samples. All of these methods were found to exhibit dependency on sample size or location, leading to undesirable characteristics. An analysis based on the three-standard-deviation range of the elevation measured from a sample of about 80 points widely spread across the surface of the slab is shown to provide an effective balance for the minimization of both sampling and nonsampling error terms.     

济钢新上工程预结算审查中的问题

工程预、结算审查一般是通过套用预算定额的方法来确定其工程造价 ,但随着经济的进步以及建筑市场的发展 ,仅套用现有的定额有一定的局限性并影响工程造价的准确性。针对预结算审查中常见的特殊工程无合适定额子目和常规工程中定额子目缺项的问题 ,分别采取对近似定额子目进行换算和补充相应定额子目的方法给予解决 ,使造价更趋合理。     

提高工程预算编制质量及有效控制工程结算的方法

建设工程造价审核工作是一门专业性、知识性、政策性很强的工作。它不仅需要掌握专业的预结算知识和国家有关政策、法规,还要了解相关的专业、设计、材料设备采购、施工方法与投资控制等多方面的基础知识。提高预结算编制水平,对做好工程造价管理,有效控制工程造价投资,实现企业项目预期经济效益和社会效益起着至关重要的作用。     

Not Making the Grade: Expansive Soils and Higher Education in Texas

Expansive soils are a serious geologic hazard in Texas; accordingly, one would expect Texas engineering colleges to offer a strong educational program on expansive soils at both the undergraduate and graduate levels. However, data from the geotechnical programs within the civil engineering departments of Texas engineering colleges suggest that while Texas educational programs cover the topic of expansive soils in varying degrees, the educational effort is highly skewed toward traditional geotechnical and foundation issues. In most cases, treatment of the expansive soil problem is limited and is not adequate when measured against the scope and extent of expansive soil problems in Texas.     

Performance of Dowel Bar Retrofit Projects in Texas

In Texas, many miles of plain jointed concrete pavement (JCP) were constructed without proper load transfer devices such as dowels. After a number of years of service, some JCP sections without dowels showed distresses in the form of faulting at transverse joints. Some of the sections were designed in accordance with the AASHTO 1986 Guide, which required 50–75?mm thicker slabs in exchange for not using dowels. This pavement design did not work, with faulting at transverse joints that cause poor ride. Dowel bar retrofit (DBR) was performed on four projects to restore the pavement condition. Overall, DBR restored load transfer efficiency and resulted in improvement of ride quality. Even where the subbase stiffness is 5–10 times less than the minimum value required for proper performance of JCPs, properly installed DBR effectively restored pavement condition with minimum faulting after decades of service. Therefore, it indicated that DBR is able to minimize the faulting even where there is poor base/subgrade support. This is significant in that there are no effective and practical methods to improve subbase conditions in existing concrete pavement, whereas DBR can restore pavement conditions at a reasonable cost. However, not all DBR projects were successful. In one DBR project, faulting in the range of 6.4–9.5?mm occurred after less than 2 years of treatment. Forensic investigation revealed voids under the dowel bars, which indicates poor consolidation of the grout material. Efforts are currently underway in TxDOT to improve specifications for grout materials and DBR construction.     

Effectiveness of Preventative Maintenance Treatments Using Fourteen SPS-3 Sites in Texas

Fourteen Texas SPS-3 test sites were studied to determine the effectiveness of preventative maintenance treatments. These sections were built on four highway classifications (IH, US, SH, and FM) in different climates and with different levels of traffic and subgrade support. Almost all 14 SPS-3 sites were given preventative maintenance treatments (thin overlay, slurry seal, crack seal, and chip seal) in Fall 1990. The distress score concept used by the Texas Department of Transportation (TxDOT) was adopted in this study to judge the effectiveness of preventative maintenance treatments. TxDOT has used this concept since the early 1980s, though the utility factors have been revised few times. The distress score quantifies the visible surface wear due to traffic and environmental influences. Only very few sections experienced premature failures on the SPS-3 sites in Texas. In many cases, superior underlying pavement conditions have been found. The chip seal has the most sites in which it is rated the best performer. The chip seals performed well on a wide range of pavement conditions. In fact, chip seals have the highest distress score for both high and low traffic areas. When initial cost is considered, crack seal provides the best alternative for low traffic routes that have a sound underlying pavement structure. For high traffic routes, chip seal is a better choice. However, a thin overlay is the most effective for rut resistance. Since the thin overlay has the highest initial cost, it is best used on high traffic routes where rutting is a major concern. If rutting is not a concern, chip seal is the best choice for a high traffic area. The treatments applied to US84 sections were too late and did not reach seven years of life as normally was expected, which reconfirms that the timing for preventive maintenance treatment is very important.     

Determination of Allowable Differential Settlement in Bridge Approach due to Vehicle Vibrations

The differential settlement between the bridge abutment and the approach embankment produces the common “bump at the end of the bridge.” This paper conducts a theoretical study on the determination of the allowable differential settlement. The maximum transient vibration value of the acceleration is recommended as the vibration comfort index. A dynamic response analysis to Man-Vehicle-Road system is carried out by means of the Laplace transform in which the vehicle is modeled as a three-degree-of-freedom system, and the bridge approaches with and without approach-relative slopes are simplified as broken lines model and step model, respectively. Parametric studies are carried out to find out what kind of effects some parameters such as the driving direction and running speed may have on the allowable differential settlement. Finally, the method and computational procedures to determine the allowable differential settlement are presented.     

Performance of a Combined Natural Wastewater Treatment System in West Texas

A study of performance of a combined natural wastewater treatment system was conducted in an arid and semiarid area of West Texas from October 2005 to September 2007. This study investigated the organic matter and nitrogen removal capability in a municipal wastewater land application system following a pond system. Municipal wastewater from the city of Littlefield, Tex. was pretreated by a pond system, and the secondary wastewater effluent from the pond system was surface applied to sprayfield at the wastewater treatment plant and the city farm. The 16 lysimeters were installed in situ to collect the leached water passing the grass root zone. The water samples were taken from the storage pond and the lysimeters for analysis of chemical oxygen demand (COD), total nitrogen, nitrate nitrogen, and ammonia nitrogen. The data show that the pond system played an important role in the treatment. The pond system pretreated COD in the municipal wastewater to the range of 10 to 127 mg/L, total nitrogen to the range of 5 to 19 mg/L, nitrate nitrogen to the range of 2.4 to 8.2 mg/L, and ammonia nitrogen to the range of 0.01 to 6.4 mg/L. The average mass removals and cumulative mass removals were 94 and 96% for total nitrogen, 92 and 93% for nitrate nitrogen, and 96 and 100% for ammonia nitrogen, respectively. There was no potential nitrogen contamination to groundwater found during the research period. The study illustrated that this type of combined natural wastewater treatment system can be used to effectively treat and safely dispose municipal wastewater, and save freshwater used for agricultural irrigation in arid and semiarid area.     

Field Investigation of Soil Heave by a Large Diameter Chilled Gas Pipeline Experiment, Fairbanks, Alaska

A large scale 105-m-long, 0.9-m-diam chilled pipeline experiment was conducted to assess the response of a production pipeline that transits between unfrozen (seasonally frozen) and permafrost soils in discontinuous permafrost regions. Thermal and heave characteristics of the experiment for a three-year monitoring period are reported. In response to the chilled pipeline, the progressive cooling patterns within the permafrost and unfrozen soils were different, resulting in the development of a thermal boundary at the transition zone between the two thermally different soils. The absolute maximum movement of pipeline was 0.197 m near the thermal boundary, resulting in a differential heave of 0.148 m. Three distinct heave phases were identified within the unfrozen soil. Phase 1 of the first 200 days related to penetration and heave above the groundwater table and was characterized by heave rates between 0.211 and 0.237 mm/day. Phase 2 resulted in increased ice segregation due to interaction of the freez-ing front with the groundwater table. This phase lasted from approximately day200 to day 500 and corresponded to a heave rate from 0.206 to 0.313 mm/day. Phase 3 was characterized by a further decrease in the heave rate to about 0.081 mm/day and lasted from approximately day 500 to day 1,056.     

Case History of Damage to a School Building Caused by Differentially Heaving Bedrock

This case study considers the question of whether settlement or heave is the principal cause of damage to a school building near Denver. The building, which was underlain by engineered fill in the center and shallow claystone bedrock beneath the outer wings, experienced progressive deformation and significant damage during a 15-year period. With several millions of dollars of rebuilding costs at risk, the most likely cause of failure needed to be ascertained to arrive at an optimum mitigation solution. The investigation described herein considers the regional geology and its known effect on various types of engineered structures in terms of characteristic damage patterns. The focus progressively narrows to concentrate on the geology and damage patterns of the local area and the site. The findings indicate that the major cause of damage to the building is associated with differential heaving of steeply dipping, expansive bedrock layers. This conclusion was adopted as a basis for subsequent remedial planning and design.