ABSTRACT:

There were few loading test cases for pile socketed into the poorly cemented rock in the world. In this study, one set of compression and tension instrumented pile loading tests was conducted to investigate the load transfer behavior of the reinforced bored pile in the poorly cemented rock. The results show that the end bearing resistance and its related base settlement are significant. The end bearing of compression pile is linearly increased up to about 54% of the maximum test load. The related base settlement and unit end bearing resistance is about 3.5D% and 10.5MPa respectively. Besides, the pile ultimate unit skin friction in compression and in tension are in same range, i.e., about 90kPa to 103kPa.

1. INTRODUCTION

In the foothill of western Taiwan, most rock strata belong to sedimentary rocks formed in Pliocene and Pleistocene. As the function of lithification with particle cementation and perfect lock-up cannot be achieved due to short period of lithification age, the cementation of the rock is quite poor and susceptible to weathering, slaking and erosion. Based on the uniaxial compression strength, the rocks are classified as low to very low strength rock. The Taiwan High Speed Railway route passes through the foothill of western Taiwan. Bridges and viaducts are the main structures in this project. Cast in site reinforced concrete bored piles are used as foundation supports for bridge and viaduct type structures. Determination of the side resistance and end bearing of drilled shaft or bored pile in the poorly cemented rock was one of the important geotechnical topics. Several methods are available to estimate the bearing capacity of a pile. Pile load test is the most accurate method to evaluate the pile bearing capacity[1]. In this study, one set with one instrumented compression (CP) and one tension (TP) pile load tests was conducted to investigate the he load transfer behavior and the magnitude of pile bearing capacity of the pile in the poorly cemented rock.

2. SUBSURFACE CONDITIONS

The site of pile load test was located at Shinchu County, northern Taiwan. The test area is near by the Shinchu Science Based Industrial Park, a high-tech industry center in Taiwan. The major geomorphology feature of local test site is hilly region. The deposits in this local area are Pleistocene Toukoshan Formation. In northern Taiwan, the Toukoshan Formation is characterized mostly by alternating beds of loosely consolidated sandstone and shale (mudstone) [2].

Fig. 1. Geological profile and instrumentation location of the test pile CP.(available in full paper)

Fig. 2. Geological profile and instrumentation location of the test pile TP.(available in full paper)

Two test piles were cast at the test site and the geological condition is similar except for the thickness of each rock layers. The horizontal distance between the two piles is about 330m. In order to obtain the subsurface conditions of the test site, two boreholes at each pile were drilled. The boring logs are briefly shown in Figure 1 and Figure 2. There are three layers in this profile.

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