Moon S. Nam

Implementation of Noise-Free and Vibration-Free PHC Screw Piles on the Basis of Full-Scale Tests

AbstractNoise and vibration caused by pile driving may disturb surrounding areas to the extent that nearby residents and businesses may file civil complaints, which can bring construction to a halt. To overcome these issues, construction engineers have worked diligently to develop low-noise and low-vibration pile driving methods. One such method, involving noise-free and vibration-free pretensioned spun high-strength concrete (PHC) screw piles, is proposed in this paper. This pile driving method penetrates the ground by rotating and compressing the pile to minimize noise and vibration in addition to maximizing capacity. A noise-free and vibration-free PHC screw pile prototype, the first of its kind, was manufactured and subjected to two pilot tests to determine its production and construction requirements in addition to its performance. In pilot tests, the new noise-free and vibration-free PHC screw pile driving method was found to successfully reduce noise and vibration compared with pile driving involvi...

Determination of Loading Capacities for Bi-directional Pile Load Tests Based on Actual Load Test Results

A bi-directional pile load test (PLT) is regarded as the most reliable method for verifying the design capacity of a large-diameter drilled shaft. The loading capacity is often improperly set while conducting this test, leading to inadequate verification of appropriate design capacities for large-diameter drilled shafts. This problem necessitates a new, rational method for estimating the loading capacity for bi-directional PLTs. In this study, results of numerous bi-directional PLTs conducted by different researchers were analyzed for their failure patterns, load increasing ratios, loading capacity increasing ratios, and sufficiency ratios of the design load. The results indicate that most failure patterns involved a lack of loading capacity. In our assessment, the load increasing and loading capacity increasing ratios were less than 2, confirming that the maximum equivalent test load is not always twice the total bi-directional load. Hence, it is difficult to verify the design capacity using the current planned loading capacity. An analysis of the sufficiency ratios of the design load revealed that 18.6 % of the test results did not satisfy the requirement. To eliminate the uncertainties in verifying the design load, the one-directional loading capacity should be at least 2.5 times the design load.

Structural Resistance Factors for Shear Loading in Drilled Shafts with Minor Flaws Based on Experimental Study

An experimental study was performed to assess the reduction in shear capacity of model drilled shafts having minor flaws, in the form of voids or soil inclusions occupying 15 per cent of the cross-sectional area of the shaft, mispositioned reinforcing steel and corroded reinforcing steel. Such flaws are often produced in construction but either go undetected by NDE or appear as uncertain anomalies on NDE records. Resources did not permit performing large numbers of tests sufficient to investigate the effect of the probability distributions of these factors; however, selected tests were sufficient to develop a general understanding of the phenomena involved and to suggest provisional values of resistance factors to account for the effect on shearing resistance of unknown construction flaws.

Development and Implementation of a High-Pressure, Double-Acting, Bi-Directional Loading Cell for Drilled Shafts

Drilled shaft foundation elements provide a cost-effective foundation alternative for the support of building and bridge superstructure loads. Bi-directional pile loading tests (BDPLTs) to evaluate the capacity of drilled shafts have become popular owing to their capacity to save time and effort as compared to the use of top-down loading tests. However, the use of BDPLTs requires that production shafts be post-grouted following testing in order to assure appropriate in-service performance. Commonly used single-acting loading cells and/or loading cell construction details can pose the potential for the development of voids following post-grouting due to their monotonic jacking action and large footprint. This paper described the development and use of high pressure bi-directional loading cells intended to minimize the possibility of post-test construction defects. First, a comparison was made between the single-acting and double-acting loading cells. Second, the results of laboratory calibrations on the pressurized loading cells were performed, as were component testing of the pumps, hoses, and hydraulic fluid synchronization lines. Then, the use of the new high pressure double-acting loading cells in production testing of instrumented shafts was described, and the efficacy of the new loading cells was illustrated. The new loading cells provided the profession with a load cell alternative for conducting BDLTs and should serve to help reduce the risk of post-test grouting defects in drilled shaft foundations.

Multi-Method Strength Characterization for Soft Cretaceous Rocks in Texas

Modern methods for designing drilled shafts, ACIP piles and similar foundations in soft rock require knowledge of the compressive strength and modulus of the rock. However, jointing at many sites prohibits the recovery of samples of sufficient length and integrity to test rock cores in either unconfined or triaxial compression. Since rational design procedures usually require values of compressive strength, surrogate methods must be employed to estimate the compressive strength of the rock. The surrogate methods considered here are the splitting tension test, the point load index test and the Texas Department of Transportation (TxDOT) dynamic penetrometer test (in which a 76-mm-diameter solid steel cone is driven into rock at the bottom of a borehole in much the same way as a split spoon is driven during the performance of a standard penetration test in cohesionless soil). Soft rock formations typical of those for which such substitutions might be used are the upper Cretaceous formations of North Central Texas, including the Eagle Ford (clay shale) and Austin (limestone) formations. Correlations of the results of the tests listed above with compression strengths of soft rock cores from these formations are provided in the paper. The correlations are formation-dependent, most likely through the degree of cementation present in the geomaterial. The strongest and apparently most reliable correlation was between compressive strength and the TxDOT cone penetration test, although separate correlations were observed in limestone and in clay shale. A clear correlation, but with considerable variance, was found between point load index strength and compressive strength in clay shale. No clear correlations between either point load index or splitting tension strength and compressive strength appeared in the limestone.