When the world largest shaking table, E-Defense of NIED, is used for geotechnical structures, ‘prototype tests’ are considered as preferable to conventional ‘model tests’. Because this experimental set-up is the only facility that allows faithful reproduction of the various geotechnical investigation techniques and actual geotechnical construction works on artificial geotechnical structures. As a specific example, focuses are placed on embankments of roads and railways, as well as relatively small embankments such as for ponds, levees and dykes. Typical purposes of the projects are experimental verifications of various technologies related to seismic diagnoses and seismic strengthening. In this paper, appropriate sizes of the embankments are examined and optimum designs of the soil container are discussed.

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Slope instability issues due to freeze-thaw action, rainfall and seismicity are common in cold regions like Hokkaido. It is essential to study the varied impacts of temperature difference and infiltration due to rainfall on soil slope stability. The main objective of this study is to find a suitable slope stability assessment method considering the effects of freeze-thaw and rainfall. An embankment slope failure study performed by previous researchers has been numerically simulated. A modelling methodology to perform freeze-thaw, seepage and limit equilibrium slope stability analysis has been adopted and followed. Crucial parameters for slope stability i.e. initial moisture content, moisture content distribution during failure were obtained from the simulation and then compared with the measurement data. The numerical results compared with the measured data provide rational satisfaction and demonstrate the applicability of the software code in order to predict the stability of slope. The numerical modelling approach used in this study is found useful in analysing the rational stability of soil slopes and to simulate the moisture content distribution of slopes subjected to freeze-thaw and rainfall infiltration.

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In Hokkaido, Japan, over 40% area has been covered by volcanic coarse-grained soils. Due to the extreme weather in Hokkaido, snowfall always reaches several meters. After winter, a large amount of snow melts into water simultaneously, and at the same time permeated into ground rapidly and continuously. Fine particles contained in soil, therefore, will be carried out of soil structure by water. Changes in soil structure should be expected. The main purpose of this paper is to examine influences of fine particles run off on the shear behavior and Soil-Water Characteristic Curve, SWCC, which plays a very important role in the determination of unsaturated soil property function, of the volcanic coarse-grained soil under unsaturated condition. A series of triaxial compression tests and soil-water characteristic test were performed for volcanic coarse-grained soil from which fine particles were removed by water flow previously. The experimental results show that the shear strength of volcanic coarse-grained soil decreases a lot under both saturated condition and unsaturated condition when fine content was removed. Fine particles run off also gives a strong influence to soil-water characteristic curve. It causes a right shift in soil-water characteristic curve.

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An early warning monitoring system is one of the most effective ways to reduce disasters induced by slope instabilities. The 2008 Ms 8.0 Wenchuan earthquake that occurred in Sichuan province, China, induced more than 197000 slope failures and landslides. To reduce vulnerability to such slope and landslide hazards, an early warning system becomes important, and for this purpose, a newly developed simple and low-cost early warning system for slope failure and landslides is presented here. The new system is based on a tilt sensor that is easy to install. The sensor can monitor water content and slope deformation with a tilt MEMS (Micro Electro Mechanical Systems) module embedded in the sensor unit, and it can transfer real time data via a wireless network. Since 2010, the monitoring system has been used in seven actual large-scale slope failure and landslide sites to validate field performance. In this paper, we report on one monitoring case to show that the early warning system adequately monitors the stability of slope and debris fields in China. Based on the field site test results, the monitoring method is proposed for regions of increased hazard of earthquake-induced slope failure.

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A full-wavefield imaging detection method is developed and then applied to reveal the defects in the highway embankment. This testing system integrates the point- source/point-receiver scheme with the multi-directional imaging technique to achieve the effect like scanning. It is equipped with an impacting hammer, a series of three-component velocity transducers and a signal capturing unit. To evaluate the feasibility of this system for detecting defect of highway embankment, a full-scaled highway embankment model test with pre-setting defection is conducted. And a 3-D numerical simulation using FEM are performed for comparison and mechanism study. It is paid special attention on the propagation characteristics of full wave field in the model. The characteristics of spectral characteristics derived from Fourier transform are analyzed. Experimental results show agreement with the numerical ones on the processed scanning images. It is concluded that the full-wavefield imaging detection method exhibits high potential in inspecting the defects of highway embankment by imaging.

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A low-cost and simple monitoring method for early warning of rainfall-induced landslides has been proposed by the authors. Tilting angles in the surface layer of slope are mainly monitored in this method. A set of equipment has been developed for practical use, which is equipped with a MEMS (Micro Electro Mechanical Systems) tilt sensor and a volumetric water content sensor. In several case studies with this system, including a slope failure test conducted on a natural slope by applying artificial heavy rainfall, it detected distinct behaviors in the tilting angles in the pre-failure stages. Considering these behaviors, the authors has proposed to issue precaution at a tilting rate of 0.01 degrees per hour, and warning at that of 0.1 degree per hour, for conservative decision.###The development of this system reduced the cost for slope monitoring reasonably. However, the number of available equipment for each slope is still limited due to financial restriction, and therefore, engineers need to select the position of sensors carefully for effective early warning. This paper introduce authors’ recent attempt to develop more low-cost sensor network for slope monitoring. The cost for each sensor node was reduced by around one-third, and consequently, slopes can be monitored at many point, resulting in more meticulous observation of slope behaviors.

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Mechanical stability of embankments such as road embankments and river dykes is significantly influenced by their internal hydraulic states, as represented by phreatic surface location and pore water pressure distribution. The mass transfer across the embankment surfaces through water infiltration and evapotranspiration, and the internal migration of pore water to/from foundation soil layers is considered to play a major role in dictating the evolution of the hydraulic state. This paper reports a case study in which hydraulic state variations in an embankment in Hokkaido were monitored over 9 months, including a winter period with ground surface freezing and a significant snow cover. The studied embankment was a relatively new, constructed with artificially mixed clay and sand which were generated by nearby excavation. The monitoring records indicate a consistent trend of under-drainage to the foundation layer all during the 9 months, with the pore water pressure at deeper parts registering minimum values during winter and reaching maxima during summer. Explanations for this and other observed features were sought by performing unsteady unsaturated seepage flow analysis with some assumed surface input models. Although the adopted models are fairly crude, the analysis results offer important insights into factors that govern the hydraulic state of low-permeability embankment in snowy cold regions.

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The Minxian-Zhangxian Ms6.6 earthquake induced a large number of loess landslides and collapses on July 22, 2013 in Dingxi city, Gansu province. In the center of the quake-hit area, it caused a banding area of landslides dense distribution with 8km wide and 30km long, and which long axis direction is in accordance with the trend of seismo-tectonics of the earthquake. Based on field test pit survey and surface wave investigation, the topography and soil distribution of the west loess landslide at Yongguang village in the landslides dense distribution area was identified. Moreover, the liquefaction probability of loess of the landslide was proven through dynamic triaxial liquefaction tests. The dynamic response characteristics of the landslide were analyzed by combining dynamic finite element method and strength reduction method as well. The results indicate that continuous heavy rain before the earthquake induced moisture content increasing and shear strength reducing in the surface loess layer of the slope. Coupling with the strong quake, tensile stress and liquefaction occurred in the surface soil layer, which caused the loess slope collapse instantaneously and a sliding distance of about 1000m long.

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Landslides due to piping have occurred frequently in rainy season recently. Piping, known as a complex phenomenon of internal erosion, has not been quantitatively studied in laboratory by element experiment. As an attempt to achieve piping effect, artificial pipes both in vertical and horizontal were created by dissolving glucose in Toyoura sand. A series of hollow cylindrical torsional shear tests were conducted for specimens with and without pipes under different confining pressure. Strains during piping propagation were measured locally by clip gauges. Small strain stiffness of sand was investigated by applying small torsional cyclic loading under different principal stress directions. In addition, failure behavior of sand subjected to piping effect was studied. It was observed that shear band propagated partially along the piping plane in specimen with horizontal pipe.

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This article presents a case history of karst cave treatment technique to mitigate possible hazards during shield tunneling in karst region with caves. A field test of shield tunneling excavation was conducted using the karst cave treatment in the karst region of Guangzhou, China. The test site is a tunnel section on Metro line 9. 98 karst caves were found along the tunnel and 13.3% of karst caves are higher than 5 m. Construction program of karst cave treatment is introduced, which includes investigation, treatment determination, grouting and effectiveness check. Field investigation includes unconfined compressive strength (UCS) of borehole samples of grouted materials, standard penetration test (SPT), core recovery (CR). All of the UCS values of the borehole samples are greater than 0.2 MPa, the modified SPT values are more than 10 and the CR values are larger than 90%. These test results demonstrate the applicability of this treatment technology in karst region.

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Among various types of chemical weathering, rainwater is playing a vital role in degradation of soft rock slopes affecting its geotechnical properties. Conducting laboratory tests every year to determine shear strength of widespread mountainous slopes is critical and expensive, thus, a necessity of an empirical relationship is realized. This paper presents a laboratory developed relationship between shear strength and shear wave velocity for the weathering of soft rocks. Acidic nature of rainwater is simulated by laboratory reproduced weathering process on artificial soft rocks made by silica sand, gypsum and CaCO3. Negative ageing effects on the geo-material by deterioration of binding minerals is elucidated from decreasing trends of shear strength and shear wave velocity. It is revealed that the more is the acid contents in rainwater, the more is the decomposition of soft rocks. Moreover, field tests were conducted to acknowledge a general profile of the weathered rock slope.

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