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가설 설정
- of specific and limited data sets and (ii) rock masses in the Korean Peninsula have many discontinuities and higher weathering than those in other regions, although the strength of intact rock is relatively high.
제안 방법
- After 32 and 40 days had elapsed since construction of the test piles, load tests were performed at the com pletely weathered rock site and the moderat이y weathered rock site, respectively.
- In order to evaluate rock mass properties quantifiably in which test piles would be placed, uniaxial compressive tests (UCT), point load tests (PLT), pressuremeter tests (PMT) were carried o나t, and rock quality designation (RQD), rock mass rating (RMR), rock mass quality (Q-vaiue), and geological strength index (GSI) were estimated. Test results based on site investigations are summarized in Table 2.
- However, most of these methods are difficult to apply to specific cases, such as in boreholes and for measuring micro-objects for roughness. In this study the borehole roughness at each test site was profiled by molding the roughness surface and then measuring with the laser roughness profiler (LRP). Through comparison with the profiling results of this and other studies, the quantification of borehole roughness in rocks was performed.
- In this study, pile load tests were performed on nine drilled shafts under various conditions such as weathering of rock mass, borehole roughness, pile diameter, and loading directions. Also, database was summarized by reviewing various literature and reports of load tests on drilled shafts in rocks of Korean peninsular.
- In this study, therefore, a database on pile load tests was developed by reviewing pertinent literature and reports of load tests performed in rocks of the Korean Peninsula, so that unit ultimate shaft resistance (匸臥)of rock-socketed dnlled shafts was evaluated and proposed. A total of 43 load tests are summarized in Table 4, which gives appropriate information about the load tests, including type of rock, degree of weathering, pile diameter, total pile length, sock아 length, UCS, Em, RQD, RMR, f^ax, and load test method.
- (1996) and Nam (2004) concluded that none of the empirical methods could be considered a satisfactory predictor fbr their database of pile load tests in rock. Their study test sites are mai이y sandstone, mudstone, limestone, and clayshale, so that it is required to develop database of load tests on drilled shafts in weathered granite-gneiss, which occupies the whole Korean peninsula, and evaluate characteristics of ultimate capacities.
대상 데이터
- A total of nine drilled test shafts were installed in the exposed bedrock of two test sites; five shafts were constructed in completely weathered rocks and the others were done in moderately weathered rocks. Construction condition of all test shafts is summarized in Table 3.
- Field test sites lie within the new city of Dongtan, which was formerly Hwaseong Formation of Cambrian age. The Hwaseong Formation, which represents bedrock material, is composed primarily of gneiss.
- Gypsum samples with the molded roughness surface were profiled by using the LRP developed by the Hyundai Institute of Construction. The LRP system was based on the laser triangulation principle.
이론/모형
- Representative design methods were identified in this study that will be summarized below (FHWA design method, 1999; NAVFAC DM-7.2 design method, 1982; AASHTO design method, 1996; Canadian Foundation Engineering Manual, 1992). Generally, Korean standards or guidelines for rock-socketed drilled shafts adopt one of these design methods.
- Static compressive and uplift load tests performed up to the maximum load of 2, 000 kN with four or five unload-reload cycles were designed by the quick-load test method stated in ASTM D1143-81. Figure 6 아lows the entire set of the pile load test results omitting the unload-reload cycles.
- of Construction. The LRP system was based on the laser triangulation principle. The hardware included a laser generator, a position-sensitive device (PSD) as a laser detector, signal processing circuits, laser control circuits, data acquisition, and digital control units.
성능/효과
- (1) Based on the results of pile load tests, it is observed that shaft resistance of rock-socketed drilled shafts increases by an average of 36% and 37% as borehole roughness increases and pile diameter decreases, respectively. However, the influence of borehole roughness and pile diameter decreases, and the initial slope of the Mv relation slows as the degree of weathering increases.
- (2) Through comparing results of load tests on piles subjected to compressive and uplift loading, it is acceptable that the shear behavior of the rock socket is not influenced significantly for the working load level (within 0.1D of displacement) by the loading direction but for the ultimate load level. At failure, the shaft resistance for the rock socket by uplift loading was found to be 70% of tiiose by compressive loading, corresponding to limited fmax in the AASHTO design method (1996).
- (3) Through a developed database of field load tests on drilled shafts in rock of the Korean Peninsula, it is shown that commonly used design methods for cal culating 疆 by using only UCS can substantially overestimate the £谶 in realistic situations. This could be due to the fact that rock masses in the Korean Peninsula have many discontinuities and greater weathering than in many other regions, even though the strength of intact rock is relatively high.
- Among them, test piles of CSRC, CSSU, and MSRU did not reach the ultimate state, so that the maximum test load was applied. It is evident that shaft resistance of test piles, except for CSSC, increases on an average of 36% and 37% as borehole roughness increases or pile diameter decreases, respectively. Also, it is observed that the influence of borehole roughness and pile diameter in moderately weathered rock is larger than in completely weathered rock, owing to stiffness.
- Figures 4 and 5. It is indicated that rock sockets could be artificially roughened by grooving and the borehole roughness of moderately weathered rock was relatively rougher than those of completely weathered rock. This may have been because there were many vertical discon tinuities in moderately weathered rock, so that rock scraps came off the borehole wall.
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