Hiroyasu Ohtsu

A study on problems associated with finite element excavation analysis by the stress‐flow coupled method

This study attempts to address some problems associated with excavation analysis by means of the stress-flow coupled method. This is done through the investigation of two examples, both of which are excavation analyses modelling a sequential excavation process. The first example is a three-dimensional elastic analysis of a tunnel constructed in soft rock layer. The second example is an axi-symmetric elasto-plastic analysis of a shaft constructed in slightly overconsolidated clay layer. In order to clarify the effect of sequential excavation process on the analysis results, a conventional two-dimensional analysis on each example is also carried out. Through this study, we will demonstrate that it is essential to consider in detail the incremental advance of a tunnel face when one investigates the change of pore water pressure and stresses surrounding a tunnel face during excavation. Additionally, on the basis of the analytical results obtained, a proposal is presented for evaluating the stability of rock mass surrounding a tunnel during construction.

Visualization of Damage in RC Bridge Deck for Bullet Trains with AE Tomography

In recent years, a lot of accidents associated with infrastructures occur in Japan because of the remarkable deterioration of the infrastructures. Considering the expected reduction of construction investment year after year, it is important to repair and reinforce those structures with the limited budget as well as to extend their service life in the future. From the viewpoint of management and maintenance for those ageing infrastructures, preventive maintenance shall be taken rather than the reactive maintenance. In the preventive maintenance, repairing and reinforcing structures shall be implemented before any fatal deterioration to the structures. However, the reasonable diagnostic method for preventive maintenance has not been established so far. NDT approaches to diagnose the early internal damage of structures is thus in high demand. To solve these issues, the authors had proposed “AE tomography” which executes both AE monitoring and elastic wave tomography. The AE tomography enables to provide accurate AE source locations as well as velocity distribution with the tomography simultaneously. In this paper, in order to verify this proposed AE tomography for in situ infrastructures, deteriorated RC bridge deck for bullet trains was investigated.

Influence of the spatial variability of shear strength parameters on rainfall induced landslides: a case study of sandstone slope in Japan

Rainfall-induced landslides frequently occur in humid temperate regions worldwide. Research activity in understanding the mechanism of rainfall-induced landslides has recently focused on the probability of slope failure involving non-homogeneous soil profiles. This paper presents probabilistic analyses to assess the stability of unsaturated soil slope under rainfall. The influence of the spatial variability of shear strength parameters on the probability of rainfall-induced slope failure is conducted by means of a series of seepage and stability analyses of an infinite slope based on random fields. A case study of shallow failure located on sandstone slopes in Japan is used to verify the analysis framework. The results confirm that a probabilistic analysis can be efficiently used to qualify various locations of failure surface caused by spatial variability of soil shear strength for a shallow infinite slope failure due to rainfall.

Damage Evaluation in Consideration of Distance Decay and Frequency Characteristics of Elastic Wave

Such parameters in the conventional elastic wave method, as frequency and velocity, connected to the damage so far, did not take the influence of the attenuation of propagation distance into consideration so that they were not able to directly connect to the index of degradation. This research studies the quantitative damage evaluation of heterogeneous materials by using frequency response characteristics of elastic waves according to the propagation distance for the purpose of establishment of the elastic wave degradation index which is not influenced by the propagation distance and frequency. Several mortar specimens, which were given by two types of styrene material simulating false cavity, were prepared for examination, and elastic waves were excited and propagated through the specimen. As a result, it was clarified that the quantitative damage evaluation of heterogeneous materials could be performed by comparing two detected waveforms in combination with the ratio of a frequency response.

Construction and Development of Social Infrastructure

This chapter proposes that when constructing hard infrastructure it is necessary to develop an urban management concept that takes a broad perspective, extending beyond megacities to include the development of rural areas and a consideration of the links between rural areas and megacities. This chapter includes representative examples that explain approaches for solving problems endemic to megacities, and problems related to links between megacities and rural areas. For problems endemic to megacities: land subsidence caused by excessive groundwater extraction in both Bangkok, Thailand and Osaka, Japan, and a comparison of the measures adopted to mitigate the progress of land subsidence in both cities, are discussed in detail. For problems related to links between megacities and rural areas: landslides in Thailand are examined and the effectiveness of an established early warning system is discussed.

Evaluation of geotechnical risk on the mountain tunnel construction projects considering overburden

In the construction project of the underground structure, such as the mountain tunnels, the construction cost is estimated based on the information obtained by the geological survey.However, it is impossible to understand whole geological condition in a site, since the amount of the investigation is limited because of prior to construction limitation of budget allocated for the project.Especially, the geological investigation using elastic waves, which is common in design phase of mountain tunnels to be excavated in more than 100m depth, involves the uncertainty Therefore, it is important to consider the uncertainty of the ground evaluation at the investigation stage.From such a view point, this study aims to develop the methodology to evaluate cost variation caused by geotechnical risl, in the mountain tunnel construction projects, and attempts to investigate the effect of overburden on cost estimation of the difference between the presumption construction cost and the construction cost is examined.

STUDY ON ROAD SLOPE DISASTER PREVENTION INTEGRATED MANAGEMENT S YSTEM

In order to promote infrastructure management that takes into consideration the challenging social and economic conditions and the occurrence of many natural disasters in recent years, it is necessary to define what infrastructure management should be like from the viewpoints of both risk management and asset management. From these viewpoints, this paper proposes a GIS-based slope risk evaluation system implemented as part of the road slope disaster prevention integrated management system, and shows an example of a system applied to the evaluation of road slopes in a real road network. The slope risk evaluation system is a GIS-based package of analysis systems for a number of tasks including the automatic acquisition of slope data from three-dimensional topographic data, the calculation of the annual probability of rain-induced failure of each slope, and road network risk evaluation based on detour loss. The slope risk evaluation system is a promising tool for assisting in decision making that uses the risk evaluation technique for road slope disaster prevention. This study aims to define the direction of a road slope disaster prevention integrated management system that combines asset management and risk management.

A Proposal on Establishment of Early Traffic Warning Systems against Heavy Rainfall Based on Social Economic Losses

Early traffic warning systems against heavy rainfall carry out traffic regulations before disasters occur in order to reduce risks of slope disasters caused by heavy rainfall. The objective of-the system is prevention of the losses of life and injury caused by the disaster. It has the disadvantage, however, that drivers cannot pass the route, appearing when the slope disaster does not occur under the traffic regulation.In this proposal, we investigate the social economic losses when a slope collapses or early traffic warning systems are carried out, considering the probability of failure of slope. More specifically, social economic losses are classified into direct losses and indirect losses. The direct loss is related to cost of slope restoration and compensation for damages to vehicles, passengers and private properties. On the other hand, the indirect loss is related to losses to road users due to diversions during interruption of road service caused by slope failures or the traffic regulation by the early traffic warning system. Furthermore, we utilize Tank Model in order to consider the ground water level change to calculate a probability of slope failures by a difference of rainfall patterns and continuities.While the conventional early traffic warning system is based on the historical records of slope disasters, the system which we propose is based on the social economic losses. Regarding accumulated rain as a criterion for traffic regulations against heavy rainfall, we propose the method for establishment of the early traffic warning system focuses on socio-economic view points.

Risk Evaluation Method for SPSP Cutoff Walls at Coastal Waste Landfill Sites

An evaluation method that can express the local leakage of leachate from joint sections in steel pipc sheet pile (SPSP) cutoff walls is discussed, in this study. In particular, the evaluation of environmental feasibility (containment of leachates containing toxic substances) considering a three-dimensional arrangement and hydraulic conductivity distribution of the joint sections in the SPSP cutoff wall is compared with an evaluation that generally uses the equivalent hydraulic conductivity. This equivalent hydraulic conductivity assumes that the joint section and the steel pipe are integrated; therefore, the hydraulic conductivity is substituted with a uniform permeable layer. However, in an evaluation that employs the equivalent hydraulic conductivity, it is difficult to consider the local leakage of leachate containing toxic substances from the joint sections in the SPSP cutoff wall. This paper concluded that evaluations of the environmental feasibilities of the SPSP cutoff walls with joint sections must take into account the local leakage of leachates containing toxic substances from the joint section.

LCC EVALUATION OF SLOPS CONSIDERING SENSITITY OF SOCIAL DISCOUNT RATE

This study develops the decision-making model, which made the norm the risk aiming at extending the examination from a viewpoint of the conventional disaster prevention to structure management for a slope among road structures. Specifically in consideration of the performance deterioration about the stability of a slope, the life cycle cost based on the risk assessment result at the time of assuming rain as a natural hazard is calculated. Also, its attention is paid to the performance deterioration resulting from the groundwater counter measurement system by this study. It expresses using a multi-tank model about the groundwater behavior used as the performance deterioration. Furthermore, while making reference about the influence affect the calculation result of the life cycle cost paying attention to a social discount rate, the appraisal method which results in planning of the optimal maintenance repair plan based on risk assessment is proposed.