Shuji Tamura

Seismic Earth Pressure Acting on Embedded Footing Based on Large-Scale Shaking Table Tests

This paper examines earth pressure acting on an embedded footing and its effects on pile forces, based on both liquefaction and non-liquefaction tests using a large-scale laminar shear box. The following conclusions are drawn: (1) The total earth pressure defined by the difference in earth pressure between passive and active sides in the non-liquefaction tests varies significantly depending on its phase relative to the soil inertia around the embedded footing as well as on the relative displacement between soil and footing; (2) The total earth pressure in the liquefaction test, by contrast, depends mainly on the relative displacement because the soil inertia gets small in liquefied soil; (3) The total earth pressure in the non-liquefaction tests tends to be out of phase by 180 degrees with the superstructure inertia, reducing the shear force and bending moment at the pile head; and (4) The total earth pressure in the liquefaction tests tends to be in phase with the superstructure inertia, making the bending moment at the pile head large. A method for estimating the total earth pressure considering its phase relative to the superstructure inertia as well as the effects of soil inertia has been proposed. The proposed method gives a reasonable explanation of the difference in earth pressure between different tests.

Dynamic Centrifuge Tests to Evaluate Reinforcing Mechanisms of Soil-Cement Columns in Liquefiable Sand

AbstractFour centrifuge tests were performed to investigate the reinforcing mechanisms of soil-cement columns in liquefiable sand. Two unimproved baseline models and two models improved with soil-cement columns were subjected to sine sweep and earthquake base motions of varying intensities to observe acceleration, pore pressure, lateral displacement, and settlement responses. The dynamic records were processed to derive the effective natural frequency of the profiles and to obtain the dynamic stress-strain responses for unimproved and improved soil. It was found that the shear reinforcement mechanisms of columns was not effective in reducing cyclic stress ratios in the treated soil; liquefaction triggering occurred nearly at same time for both unimproved and improved soil cases and the magnitude of the resulting soil settlement was not significantly reduced. When the bases of the columns were free to rotate, the columns rocked within the soil and produced negligible shear stiffening of the soil profile. W...

Pile Stress Estimation Based on Seismic Deformation Method with Embedment Effects on Pile Caps

A pseudostatic analysis, based on the beam on nonlinear Winkler-spring method considering the seismic earth pressure and side friction acting on embedded pile caps, was developed to estimate pile bending moments and shear forces. To verify the proposed method’s effectiveness, the authors conducted six dynamic centrifuge tests on a superstructure-footing model supported by 2×2 piles in sand deposits comprising a dry sand layer over liquefied soil. The seismic earth pressure, vertical wall friction at the active and passive sides, and friction at the sidewalls of the pile caps were separately measured by two-dimensional load cells during shaking. The seismic total earth thrust and side friction estimated by the proposed method showed good agreement with the experimental results for both the amplitude and phase difference to the superstructure and the pile cap inertia forces. The estimated bending moment and shear force in the piles also showed reasonable agreement with the experimental results; they were able to account for differences in the pile rigidity and soil relative density.

Failure behavior of concrete pile and super-structure dynamic response as a result of soil liquefaction during earthquake

In past earthquake disasters, numerous building structure piles were damaged by soil liquefaction occurring during the earthquake. Damage to these piles, because they are underground, is difficult to find. The authors aim to develop a monitoring method of pile damage based on superstructure dynamic response. This paper investigated the relationship between the damage of large cross section cementitious piles and the dynamic response of the super structure using a centrifuge test apparatus. A dynamic specimen used simple cross section pile models consisting of aluminum rod and mortar, a saturated soil (Toyoura sand) of a relative density of 40% and a super structure model of a natural period of 0.63sec. In the shaking table test under a 50G field (length scale of 1/50), excitation was a total of 3 motions scaled from the Rinkai wave at different amplitudes. The maximum acceleration of each of the excitations was 602gal, 336gal and 299gal. The centrifuge test demonstrated the liquefaction of saturated soil ...

Development of the monitoring technique on the damage of piles using the biggest shaking table “E-defense”

In case of earthquake damage to buildings, the damage to a superstructure is visible, but the damage to a foundation structure, e.g. the underground pile, is difficult to detect. In this study, the authors aim to develop a monitoring technique for pile damage due to earthquakes. The world’s biggest shaking table, E-Defense, was used to reproduce damage to RC pile models embedded in the soil inside a large scale shear box (8m in diameter and 6.5m in height). The diameter of the RC pile model was 154mm. It consisted of mortar (27.2N/mm2 in compressive strength), 6 main reinforcements (6.35mm in diameter) and shear reinforcement hard steel wire (2mm in diameter at intervals of 20mm). The natural period of the superstructure above the pile models is around 0.12sec. The soil consisted of 2 layers. The lower layer is Albany sand of 80% relative density while the upper layer is only 2m from the surface ground and is Kaketsu sand of 60% relative density. Primary four excitations were scaled from JMA Kobe waves in notification at different amplitudes. The maximum acceleration of each wave is 31gal, 67gal, 304gal, and 458gal, respectively. In the test result, reinforcing steels at the pile head of the RC model yielded when the maximum acceleration was 304gal. After that, mortar of the pile head peeled off and a bending shear failure occurred when the maximum acceleration was 458gal. The peak frequency of rotational spectrum on the foundation did not change in elastic range in the piles. However, the peak frequency fell after the plastic hinge occurred.In case of earthquake damage to buildings, the damage to a superstructure is visible, but the damage to a foundation structure, e.g. the underground pile, is difficult to detect. In this study, the authors aim to develop a monitoring technique for pile damage due to earthquakes. The world’s biggest shaking table, E-Defense, was used to reproduce damage to RC pile models embedded in the soil inside a large scale shear box (8m in diameter and 6.5m in height). The diameter of the RC pile model was 154mm. It consisted of mortar (27.2N/mm2 in compressive strength), 6 main reinforcements (6.35mm in diameter) and shear reinforcement hard steel wire (2mm in diameter at intervals of 20mm). The natural period of the superstructure above the pile models is around 0.12sec. The soil consisted of 2 layers. The lower layer is Albany sand of 80% relative density while the upper layer is only 2m from the surface ground and is Kaketsu sand of 60% relative density. Primary four excitations were scaled from JMA Kobe waves in...

Soil Liquefaction Along the Tokyo Bay Coast Induced by the 2011 Off the Pacific Coast of Tohoku Earthquake

The 2011 Off the Pacific coast of Tohoku earthquake resulted in widespread soil liquefaction along the coast of Tokyo Bay and the Tone River basin, causing extensive damage. This paper reports on cases of damage from soil liquefaction, with a primary focus on the results of investigations performed immediately after the earthquake (13th–17th of March) in mainly Urayasu City, Chiba Prefecture, the damage to detached houses implemented soil cement columns, and the restoration methods of tilting detached houses. Predominant features of liquefaction damage include (1) a long duration of ground motion, (2) expanded liquefaction damage during aftershocks, (3) liquefaction of low-plasticity silt (dredged silt in particular), (4) sinkage and tilting of a majority of detached houses, and (5) an extended period of water and sewage service stoppage. The damage to detached houses complemented soil cement columns depending on the depth of the soil cement column base and the filling soil layer.

Damage to Soils and Foundation

An overview of the geotechnical aspects of the building damage in the 2011 Off the Pacific Coast of Tohoku earthquake is presented based on field reconnaissance made after the quake. It is shown that: (1) extensive soil liquefaction occurred along the coast of Tokyo Bay and around the Tone River floodplain. Liquefaction primarily occurred within relatively new reclaimed area, with large ground settlement up to 60 cm, accompanied by settlement/tilting of wooden and reinforced concrete buildings supported on spread foundations; (2) numerous houses in Sendai’s hilly residential areas constructed with cut-and fill methods were badly damaged not only by simple collapse of retaining walls, but also by slope failures of fill; and (3) several pile-supported buildings tilted and settled not only in the Tohoku region but also in the Kanto plain, implying damage to pile foundations.

EARTHQUAKE RESPONSE OF BUILDING SUPPORTED ON PILES CONSIDERED WITH NONLINEARITY OF PILE-SOIL SYSTEM

To investigate effects of nonlinear soil-structure interaction, we study the influence of the nonlinearity of pile damage on building response. In this paper, it is presented that the results of the centrifuge tests considering elasto-plastic behavior of pile and its simulation analysis. The following conclusions were obtained: (1) The response of the building, which is calculated considering the nonlinear characteristics of pile damage during the main shock, is smaller than that of the building which is calculated without the nonlinearity of pile. (2) In frequency transfer function between the ground and the building, the reduction of predominant frequency is mainly caused by the nonlinearity of the soil around piles. (3) The nonlinearity of pile damage has a very small effect in the building response in aftershock.

LATERAL RESISTANCE OF PILE FOUNDATION ESTIMATED BY CENTRIFUGE AND BLIND TESTS ON SOFT GROUND

The centrifugal model test with the soil-pile-structure system was performed for the dry Toyoura sand layer. In order to investigate the applicability of the seismic deformation method and the Chang equation as the prediction method, the pile response was estimated before the test. The time history response analysis was also carried out. The analysis result was compared with the test. It was found that it may be better to take into consideration the ground displacement caused to an earthquake for evaluation of pile response on the non-liquefying ground.