Soil deformation under slow periodic load is of particular importance to predict the functionality of soil structure in a variety of engineering practices. However, lacking quantification on plastic deformation hinders the deformation analysis of soil subjected to slow periodic load. The axial component of plastic modulus is pivotal and is determined to calculate axial plastic strain and overall soil deformation. In this study, a static triaxial compression system was designed to perform a series of static cyclic triaxial tests and cyclic confined compression tests on a silica sand. The results showed that plastic strain increments decreased gradually, as the loading cycle proceeded, and finally only the elastic strain increment existed. The empirical equation of axial component of plastic modulus was formulated considering the effects of stress states, void ratios, and loading cycles. In combination with the description of elastic modulus, the axial strain increment in each loading cycle was formulated. In addition, in the unloading process of loading cycle, the volume contraction phenomenon was explained by unloading plastic strain and microscopic particle motion based on the present results.

The stresses generated from rock expansion in a confined underground environment will exert additional loads to the existing support system resulting in severe damage during tunnel construction. In this study numerical investigations were carried out for Zagros tunnel in Iran, where swelling has been reported to be an inherent formation property. The presence of expandable clay was investigated using X-ray diffraction mineralogical analyses. The swelling volume strain was used to estimate the amount of stress increased due to swelling. The stress path method is used to obtain the location of swelling stresses. The stress relief zone (SRZ) was considered as the criterion to define the area around the tunnel where swelling stresses exist. In doing so, in the areas where the first stress invariant after excavation becomes lesser than its corresponding value before excavation, the swelling pressure can be built up. Then tunnel stability was investigated by numerical simulations using FLAC2D. The swelling stresses calculated from the free swelling test were applied to those elements around the tunnel within the stress relief zone. A comparison between the results of numerical investigations with field observation indicates that the proposed approach is successful in simulating swelling stress in swelling rocks.

In this study, the effects of weathering on the stiffness characteristics and small strain behaviour of decomposed volcanic rocks were investigated in detail. Few studies exist on the small strain behaviour of weathered materials and the studies on geomaterials resulting from decomposition of volcanic rocks are very scarce. The study investigated the small strain behaviour of decomposed volcanics in the reconstituted and intact states, allowing for the effect of structure. This was achieved by carrying out extensive triaxial tests using multi-directional bender elements and high resolution linear variable differential transformers on the samples of various degrees of weathering from different locations, depths and formations. Elastic model parameters obtained from experimental data are used as stiffness parameters and they are related with engineering indices and depth which is very important from geological point of view. The effect of heterogeneity is much more obvious at small strain. The effect of structure is generally small using bender elements at small strain. Weathering affects the stiffness of decomposed volcanic rocks and more effect is seen particularly for the reconstituted samples. Plasticity and fines content might be controlling parameters for the stiffness of decomposed volcanics.

This study proposes a procedure to evaluate the total cumulative plastic settlement due to repeated train loading for designing embedded railroad track foundations. The approach is based on Li and Selig's method which was developed for ballasted railroads. An illustrative embedded track structure modified from Kaohsiung light rail is analyzed for demonstration. In addition, a parametric study is conducted to investigate the influence of the thickness, stiffness and plastic strain parameters of the subgrade soil and the stiffness of the prepared subgrade on the plastic settlement. The results show that a larger thickness of the subgrade does not necessarily produce larger settlement; the influence of soil strength on the plastic settlement is more significant than that of subgrade modulus; the CL soil can give the largest plastic strain for a low deviatoric stress ratio less than 0.8; the influence of modulus of the prepared subgrade is less significant to the plastic settlement than the thickness of the prepared subgrade.

Studies on active faults in the metropolitan Taipei area have indicated that the Shanchiao fault at the western rim of the Taipei Basin is a highly active normal fault. Fault slip can cause the deformation of shallow soil layers and lead to the destruction of residential building foundations, utility lines, and other infrastructure near the influenced area. The Shanchiao fault is considered a growth normal fault based on geological drilling and dating information. Therefore, a geological structure similar to a growth normal fault was constructed to simulate slip-induced ground deformation after an additional layer of sedimentation formed above the deformed normal fault. We employed a sand box with non-cohesive sands under normal gravity conditions to investigate the shear band propagation and surface deformation of a growth normal fault. In the presence of a sandy sedimentation layer on top of the deformed sandy soil layer caused by a normal fault, a shear band developed along the previous shear band and propagated upward to the sandy surface at a much faster speed compared to the case without a sedimentation layer (i.e., normal fault only). An offset ratio of 1%~ 1.5% (defined as the fault tip offset displacement over the soil layer thickness) for this particular growth fault simulation is required to develop a shear band toward the ground surface. The test results indicated that the shear band of a growth normal fault with sandy material could propagate to the ground surface only under a smaller offset displacement from the fault tip, although the depositional thickness of the upper layer might be very thick. Therefore, a seismic design integrated with the knowledge of near-ground deformation characteristics for this type of fault must be emphasized in current building codes, particularly for critical facilities such as a nuclear power plant.

Non-destructive evaluation techniques have been adopted to provide pile construction quality control for many years. In particular, low strain pile integrity test methods have been used to check lengths and integrity of newly installed pile. The pile integrity testing signals acquired from the receivers on pile heads are complicated by defects and undesired background noise. The continuous wavelet transform (CWT) method with time-frequency distribution is adopted to enhance the characteristics of the testing signal to raise the identification ability in experimental cases. The in-situ tests of drilled shaft indicate that testing signals could be displayed in the time-frequency domain at the same time and then be explored at every single time by CWT. CWT can enhance the signal and make more information visible. Coupling CWT and Sonic Echo (SE) methods to interpret and identify the pile integrity visually, easily and quickly is proven, even for long drilled shafts.

In order to systematically study the scale effect on the shear strength of rock joints, this study used the computer-aided-manufacturing system to reproduce the artificial rock joints for Barton's standard joint profiles of JRC=4~6 and 18~20, natural rock joint profiles, and saw-toothed joints. We divided, enlarged, reduced, and assembled these joint profiles to obtain joint specimens of various sizes ranging from 75 mm to 300 mm in length. Direct shear tests were conducted on these joint specimens to obtain the peak shear strengths under different normal stresses. The surface conditions of the joints at failure were also examined. Based on the test results in this study, it was found that the joint surface geometry configuration rather than the specimen size itself is the main factor in the scale effect on the peak shear strength of rock joints. The geometry configuration or roughness of each individual joint should be evaluated in the use of empirical relations to compute the shear strengths of rock joints of various sizes.

Geotextile filters have been used frequently in revetments for protection of riverbanks, levees, seashores, etc. The filters may be subjected to different flow conditions such as unidirectional or cyclic flows. Besides, the period of flow may vary from short to long due to the fluctuation of water table caused by sea waves, boats, tidal activity, or periodic drawdown of water for irrigation purposes. Due to few literatures on cyclic flow studies, this paper presents the investigation on soil-geotextile filtration mechanisms under long-term cyclic flows using a self-developed apparatus. The soil samples are composed mainly of sand, with 0-20% fines content of silts and clays. The factors taken into account are overburden pressure and cyclic flow periods ranging from long to short, in order to simulate a range of waves. A stereomicroscope is utilized to observe the microstructure of the geotextile filter after testing. The results show that both the overburden pressure and the fine soil content play important roles in the filtration, soil boiling, and settlement behaviors of a soil-geotextile filtration system. Furthermore, the microscopic images of the geotextile show that soil clogging under cyclic flows is not so serious as that under unidirectional flows. Besides, a bridging network can be formed under long-term cyclic flows in the areas near the filter that are not supported by marbles.