Practice Periodical on Structural Design and Construction

Background for the lime cement column process is provided and some comparisons with other deep stabilization processes are presented. The specific use to support a vertical mechanically stabilized earth wall between 10 and 12.5 m high is described. This wall, SS-01, was constructed on the weak soils of glacial Lake Bonneville in Salt Lake City, along the alignment of U.S. Interstate 15 (I-15). The soil properties, design of the column support system, and performance of the wall are briefly described. The wall was constructed without the need for “staged” construction and has exhibited no significant shear deformations and only small settlements.

The results of a laboratory load test performed on a particular type of steel sand-jack are presented. A sand-jack is a sand-filled containment frame placed atop falsework to temporarily support abutting concrete bridge-girder segments prior to posttensioning. The girder segments bear directly on a timber “plunger,” which in turn is supported on the sand bed. After construction, the sand is removed, causing the timber plunger to drop, thereby removing support from beneath the finished girder. The falsework may then be easily disassembled. Also presented are the results of a finite-element analysis performed to determine the lateral pressure exerted by the sand bed corresponding to the experimentally obtained displacements of the containment frame. The results provide insight into the capacity and performance of the sand-jack assembly, and guidance to the engineer in determining appropriate design pressures.

At 1:47:12.6 a.m. on September 21, 1999, a 7.3 Richter scale earthquake struck Taiwan at its geographical center, Nan-Tou. The epicenter was located in a mountainous town called Chi-Chi and the focus was 6.9 km below. The maximum seismic accelerations of 9.87 m/s² east-west, 5.63 m/s³ north-south, and 5.20 m/s² vertical were measured at three different seismographic stations near the epicenter. The quake is the strongest one ever recorded in Taiwan. It moved mountains, cut off rivers, caused liquefaction, toppled buildings as well as bridges, cracked highways and concrete dams, and damaged many infrastructures. The quake caused approximately 2,400 deaths, 12,000 injuries, 18,000 totally/partially collapsed buildings, and estimated property loss of U.S. $10 billion. This paper presents postquake fact findings and structural evaluations of the collapsed buildings based on the Taiwan Building Codes. The shocking findings involve an inadequacy of current seismic code provisions, improper design details, faulty construction, and use of poor quality concrete. Most collapsed buildings were designed in accordance with the building codes but constructed with reinforcement inconsistent with the design details and with concrete that had strength of <50% of the code requirement 27.5 MPa. The faulty construction had resulted in the formation of strong-beam/weak-column systems in which the columns failed before any other structural elements. The information presented in this paper will be useful to engineers who design reinforced-concrete structures for earthquake-risk regions.

The road network in Saudi Arabia has experienced remarkable development both in length and standards to become one of the longest and most modern highway networks in the Middle East. Quality of performance of some roads, however, was below a satisfactory level. Various parameters directly and indirectly contribute to the pavement quality performance. The contributing factors are design, specifications, environment (traffic, temperature), and construction-related factors; the indirect factors are managerial-related factors. This paper reviews the factors that contribute to the quality of pavement performance in Saudi Arabia. This review was achieved via both a comprehensive literature review and a highway contractor's survey. The significant performance factors were arranged into three groups: (1) managerial-related factors that include qualification of owner's inspection team, contractor experience, and capability; (2) design and specifications-related factors that include consideration of regional conditions in design, aggregate quality, mix design and composition, and asphalt characteristics; and (3) construction-related factors that include aggregate characteristics, placement and compaction process, uniformity of materials, and mixing operation control. The consideration and improvement of these factors in future pavement construction could lead to better pavement performance, longer service life, and lower maintenance costs.