Kazuo Konagai

Single beam analogy for describing soil–pile group interaction

Abstract Most laterally loaded piles are flexible in the sense that they are not deformed over their entire lengths. Instead, pile deflections become negligible below an ‘active pile length’ L a . This L a is an important parameter that governs the overall behavior of a rigidly capped pile group. In the present approach, piles closely grouped together beneath a superstructure are viewed as a single equivalent upright beam whose stiffness matrix determines L a . This idea is verified for different cases of pile spacing, and is further extended for nonlinear behavior of soils surrounding grouped piles.

SIMPLE EXPRESSION OF THE DYNAMIC STIFFNESS OF GROUPED PILES IN SWAY MOTION

A simplified expression is derived for the dynamic stiffness of grouped piles subjected to lateral loading. A computer program, based on the Thin Layered Element Method, is used for this purpose. The results of the program are compared with rigorous solutions. The simplified expression of the dynamic stiffness of grouped piles, where the mass, damping and stiffness parameters are frequency invariant, will be particularly useful for an equivalent linear analysis of the interaction between nonlinear soil and grouped piles in real time.

Simulation of nonlinear soil-structure interaction on a shaking table

A new method to simulate soil-structure interaction effects in shaking table tests has recently been presented by the authors. In this method, analog circuits or digital signal processors are used ...

Analog circuit to simulate dynamic soil–structure interaction in shake table test

Abstract A soil medium at the side of an embedded structure is treated as mutually uncoupled horizontal layers of a unit thickness. A plane strain condition is assumed within each individual layer such that the medium responses do not vary along the thickness. According to previous work by the authors and also a new formulation given herein, the impedance of the above layer at the structure can be produced by frequency-independent simple mechanical models for all three modes of foundation responses. Similar frequency-independent models are also presented for the impedance at the foundation base. These models are made of two different basic elements and a mass interconnected in series. Their arrangements directly indicate the wiring of electric circuits which generate signals corresponding to the transient soil–structure interaction responses. To all intents and purposes, electric circuits do not loose time in responding to the inputs. Therefore, they allow us to simulate the soil–structure interaction response in shake table model tests, which are commonly conducted at relatively high excitation frequencies for earthquake simulation.

Simple evaluation of the effect of seismic isolation by covering a tunnel with a thin flexible material

Abstract Long-term earthquake observations at different tunnel sites within a variety of alluvial soil deposits have clearly demonstrated that a tunnel, which exhibits rather flexible nature within its surrounding soil, follows closely the motion of the soil mass during an earthquake. Therefore, coating a tunnel with a soft material will be a possible measure for minimizing damage to tunnels. This paper provides a clear perspective on the feasibility of this measure by using simple solutions to idealized problems.

Simple formulations of ground impedance functions for rigid surface foundations

A differential equation is formulated for the dynamic response of ground medium by using a simplified ground model. Applying Galerkins procedure for weighted residual, this equation leads to a governing equation only at the ground surface. The equation indicates that the ground surface behavior can be computed even further by a simplified model. By solving the governing equation for the boundary conditions along the surface, expressions in simple closed forms are developed for the dynamic response analysis of a massless rigid foundation that rests on the ground surface. Despite their significant simplicity, the developed expressions compute the values very close to those computed by far more complex rigorous solutions. They are found to be capable of capturing the important characteristics of the dynamic ground behavior well.

Substantiation of debris flow velocity from super-elevation: a numerical approach

The use of super-elevations that a forced vortex flow leaves on the valley walls of a curved flume is a plausible approach toward estimating debris flow velocities in earthquake-induced geo-hazard studies. The centrifugal force of a speeding flow is responsible for a higher flow depth on the outer bend. However, in reality, a flow is not steady, and only the highest flow-marks are left at the outer and inner bends of the flow, which can lead to an inaccurate estimation of the actual velocity. Seeing the real scenario of the field, a series of numerical flume tests using smoothed particle hydrodynamics (SPH) is conducted to validate the estimation of debris flow velocities from flow-marks. Velocities estimated from flow-marks are lower than real velocities near the source region, but they converge to real velocities as the distance to the source increases. Based on several simulations, a best-fit line is proposed for adjusting debris flow velocity from mud-marks, and it is used to estimate flow velocities of the well-documented debris event called “Shiraito river debris flow,” which happened near the rim of the Hakone Crater, Kanagawa Prefecture, Japan, ensuing from the 1923 Great Kanto earthquake.

Field Measurements and Numerical Simulation of Debris Flows from Dolomite Slopes Destabilized during the 2005 Kashmir Earthquake, Pakistan

A devastating earthquake occurred in Kashmir, Pakistan on October 8, 2005. This earthquake resulted from reactivation of a known active fault later defined as the Balakot–Bagh fault, which caused widespread slope failure throughout its stretch, particularly around Muzaffarabad, the provincial capital of Azad Jammu and Kashmir. This slope failure resulted in a huge amount of debris material which flows in deeply incised creeks during monsoon and hits the inhabitants along the valley in Muzaffarabad. Two GPS measurements are carried out along with channel morphometric parameters and observed changes to investigate the effect of debris flows along these creeks during monsoon. Other than the physical measurements, actual debris flow is simulated using the Depth Average Material Point Method (DAMPM) after carrying out parametric study and calibrating the model for subject topographical and geological settings. The generalized effect of different input parameters of the model on debris flow runout features is studied and discussed in detail. After ensuring validation of the numerical tool, the contribution of a single closed-type check dam to decrease runout intensity to its downstream reach is also investigated for different locations to obtain optimized selection.

Recent Landslide Damming Events and Their Hazard Mitigation Strategies

Earthquakes often strike the vulnerable parts of our society. A 7.0-magnitude earthquake shattered Port-au-Prince, the capital of Haiti. Based on historical records in the Port-auPrince area, the last large earthquake happened in 1770. Therefore, throughout its history, the capital of the country had never experienced any deadly earthquake, but long-lasting political violence. Being the poorest country in the Americas as per the Human Development Index, due attention has never been paid to seismic preparedness, causing the catastrophic devastation with 316,000 casualties to occur (Reuters, 12 January 2010). Even in Japan with advanced technologies in disaster preparedness, the earthquake and tsunami of March 11th 2011 revealed vulnerabilities of disaster prevention schemes/ systems given the tsunami heights exceeding the determined design heights. These devastations often cause long lasting problems. In Haiti 2 million people are managing to get by on food rations. In Japan, huge amount of tsunami debris are just piled up in temporary damp yards with the fear that they might have been radiation-contaminated, thus discouraging all attempts for quick rehabilitations.

Establishment of ICL-Japan for the Kyoto 2020 commitment

The International Consortium on Landslides (ICL), the Global Promotion Committee of the International Programme on Landslides (GPC/IPL), and Slovenian ICL members (University of Ljubljana and Geological survey of Slovenia) organized the Fourth World Landslide Forum in Ljubljana from May 29 to June 2, 2017 (Mikos et al. 2017). The high-level panel discussion consisting of panelists from the signatory organizations of the ISDR-ICL Sendai Partnerships 2015–2025 proposed the 2017 Ljubljana Declaration on landslide risk reduction-contributing to the Sendai Framework for Disaster Risk Reduction (Sassa 2017a) and it was adopted by 588 participants of WLF4 from 52 countries and 7 United Nations and International Organizations. The declaration adopted the organization of the Fifth World Landslide Forum (WLF5) in Kyoto, Japan, 2020 (Sassa 2018c) and the concept to establish the Kyoto 2020 Commitment (KC2020) for global promotion of understanding and reducing landslide disaster risk (Sassa 2018a) as the development of the Sendai Partnerships 2015–2025 (Sassa 2017b). In order to establish and further develop the Kyoto 2020 Commitment at the Fifth World Landslide Forum in 2020, Kyoto, Japan, the Board of Representatives of ICL members decided two new initiatives: (1) creation of a new category of ICL memberships BICL associates^ with 20% of membership fee of the full members and (2) creation of national networks in major landslide countries to strengthen the firm basis for ICL members in each country. The ICL, established in January 2002, is an international organization editing and publishing the Landslides: Journal of the International Consortium on Landslides (Sassa 2018b). However, ICL had never had national platforms/networks. The objective of KC2020 is to establish a global, long-term, and stable framework for understanding and reducing landslide disaster risks (Sassa 2018d). The ICL is a diverse group of members with different backgrounds from government ministries, academia, and private companies. The cooperation of ICL members within each country has been very weak. Soon after 2017 Ljubljana Declaration and ICL Board of Representative meeting in Ljubljana, Italian colleagues who participated in the adoption of the 2017 Ljubljana Declaration during the Fourth World Landslide Forum have worked to establish ICL Italian Network. The progress of ICL Italian network was reported in Landslides (Casagli and Tofani 2018). Japanese members of ICL have also worked to establish its own network, ICL-Japan with the ICL headquarters in Kyoto, Japan, included. The group consists of 17 members as of September 2018, which are three full members, 12 supporters, two associates, and the ICL headquarters. The locations of ICL-Japan members are shown in Fig. 1. The explanation of each member is shown in Table 1 in ANNEX of this issue (Sassa and Konagai 2018e). The ICL-Japan has set up the advisory group for effective activities to support the local organizing committee of the Fifth World Landslide Forum and the launching the Kyoto 2020 Commitment for global promotion of understanding and reducing landslide disaster risk as a host country. The introductions of all members of ICLJapan and priority actions that they are willing to take to contribute to Kyoto 2020 Commitment are listed in Table 2 of Sassa and Konagai (2018e). Currently, the members of ICL Japan network total 17, and headquarter at various locations over the entire nation including Tokyo (8), Yokote, Akita (1), Niigata (1), Kyoto (1), Kanazawa (1), Nagoya (1), Osaka (1), Matsue, Shimane (1), Nishinomiya (1), and Matsuyama (1).