Fumio Tatsuoka

Bearing capacity of reinforced horizontal sandy ground

Abstract In order to develop a method of predicting the bearing capacity of horizontal sandy ground reinforced with tensile-reinforcement layers horizontally placed beneath a footing, a series of plane strain model tests with a strip footing was performed. The effects of the length, the arrangements and the rigidity and rupture strength of reinforcement were examined systematically. The strain fields in sand, the tensile forces in reinforcement and the distribution of contact pressure on footing were measured. Even by means of reinforcement layers with a length similar to the footing width, the bearing capacity increased remarkably. Also, the portions of reinforcement layers located outside the footing width contributed to the increase in the bearing capacity only in a secondary way. The bearing capacity of reinforced sand was found equal to the smaller of the following two values; the one controlled by the failure of the reinforced zone immediately beneath the footing and the other by the failure of sand beneath the reinforced zone. Based on the test results, a method of stability analysis by the limit equilibrium method was developed, taking into account the effects of the arrangement and properties of reinforcement and the failure modes of reinforced sand. The predicted values were well in accordance with the measured ones.

A reinforcing method for steep clay slopes using a non-woven geotextile

Abstract The effect of non-woven geotextile reinforcement on the stability and deformation of two clay test embankments is examined based on their performance for about 3 years for the first embankment and about 1 1 2 years for the other. Horizontal planar sheets of a non-woven geotextile are expected to work in three ways: for compaction control; for drainage; for tensile reinforcement. The degree of stability of the steep slopes of the test embankments decreased during heavy rainfall. It is found that the use of non-woven geotextile reinforcement may effectively improve embankment performance. Only the stability analysis in terms of effective stresses can explain the performance of the test embankments. The horizontal creep deformation of the embankments during 2–3 years, which is partly attributed to the creep deformation of the non-woven geotextile, was found to be small. The results of both laboratory bearing capacity tests of a strip footing on a model sand ground reinforced with the non-woven geotextile and plane strain compression tests on sand specimens reinforced with the non-woven geotextile show that the non-woven geotextile gives tensile reinforcement to soils.

SHORT-TERM STRENGTH AND DEFORMATION CHARACTERISTICS OF GEOTEXTILES UNDER TYPICAL OPERATIONAL CONDITIONS

Abstract An apparatus capable of measuring the strength and deformation properties of geotextiles under unconfined conditions and under the confinement of a membrane or a soil was developed. The appratus differed from conventional in-soil test apparatuses in that during the soil-confinement test the soil was allowed to deform with the geotextile while being confined by a prescribed pressure — simulating the predominant operational condition of geotextiles in reinforced soil structures. Three non-woven geotextiles manufactured in different materials and by different bonding processes were used in this study, and their stress-confinement effects were studied. It was shown that the stress-confinement effect existed in the spun-bonded and needle-punched geotextiles but not in the heat-bonded geotextile. The effect of using different materials (membrane and soil) for the confinement was also studied. Under otherwise identical conditions, the results were very similar between the in-membrane and in-soil tests. It was concluded that the in-membrane test is sufficient for evaluating the load-deformation properties of geotextile. Mathematical models were used to represent the measured load-deformation relationships of the geotextiles, and their accuracy was discussed.

Reinforced soil engineering : advances in research and practice

Civil and environmental applications of geosynthetics, Hoe I. Ling performance properties of geogrids, Wim Voskamp unit cell testing of reinforced soils, Hoe I. Ling Modelling the time-dependent behaviour of geosynthetically reinforced soilstructures with cohesive backfill, Victor N. Kaliakin and M. Dechasakulsom issue and nonissue in block walls as implied through computer-aided design, Dov Leshchinsky application of sliding block concept to geosynthetic-constructed facilities, Hoe I.Ling failure of an 8-m-high segmental block wall in the northeast United States, C.M. Reith, G.S. Paxson, and A.W. Cadden displacement monitoring at Verrand high reinforced-soil structure, G. Sembenelli and P. Sembenelli UD case study - BluewaterRetail and Leisure Destination reinforced soil slopes to form steep-sided new lakes, J.H. Dixon state of the practice - past, current and future perspectives of reinforced soil retaining structures in Turkey, Muhannad Ismeik and Erol Guler recentexperiences of reinforced retaining structures in China, Li Guangxin and Wang Zhao large-scale reinforced clay walls backfilled with clay at Cheng Kung University, Ching-Chuan Huang, H.Y. Shan, G.Y. Jean, and A.L. Leu geotextile reinforced abutments onsoft foundation, Ennio M. Palmeira, Andre Fahel, and Luiz E.P. Campos geosynthetic reinforcement in the mitigation of pipeline flotation, Yoshiyuki Mohri, Toshinori Kawabata and Hoe I. Ling practice and research of geosynthetic reinforced soil walls inAustralia, Sik-Cheung Robert Lo geosynthetic reinforced containment dyke constructed over soft foundation - numerical analysis, Hoe I. Ling, Dongyi Yue and Victor N. Kaliakin post-earthquake investigation of several geosynthetic reinforced soilretaining walls and slopes during Ji-Ji earthquake of Taiwan, Hoe I. Ling and Dov Leshchinsky tests on seismic stability of several types of soil retaining walls, Junichi Koseki, Kenji Watanabe, Fumio Tatsuoka, Masaru Tateyama, Kenichi Kojima and YulmanMunaf performance of geosynthetics reinforced soil wall and reinforced earth wall subject to blast loading - experimental and numerical study, Tan Siew Ann shaking table tests of embankment models reinforced with geotextiles, S. Tani, S. Ihara, Y.Yokota, and Y. Okabe centrifuge modelling of seismic performance of reinforced earth structure, Jiro Takemura and Akihiro Takahashi performance analysis of arifiye overpass reinforced earth walls during the 1999 Kocaeli (Turkey) earthquake, C. GuneyOlgun and James R. Martin II dynamic simulation of the reinforced slope failure at the Chi-Nan University during the 1999 Chi-Chi earthquake, Nelson N.S. Chou and Chia-Cheng Fan a compact probabilistic representation -the Chi-Chi earthquake groundmotion, A.W. Smyth, S.F. Masri, and C.H. Loh a critical review of full-scale shaking table tests conducted on reinforced soil retaining walls, Hoe I. Ling.

Hydraulic conductivity of geotextiles under typical operational conditions

Abstract It is well known that granular backfill can account for more than 50% of the total construction cost for typical geosynthetic-reinforced soil structures. It is therefore desirable to investigate the possibility of using low-quality onsite soil, which may be cohesive and near saturated, as backfill. A geosynthetic that possesses adequate drainage capability in addition to having high tensile stiffness and strength would be highly suitable for this purpose. This study was conducted to investigate the cross-plane and inplane hydraulic conductivities of such geotextiles under typical operational conditions. Two types of geotextile, namely, a nonwoven and a woven-nonwoven composite geotextile, were tested by using different methods of confinement in their virgin state. Samples of the geotextiles retrieved from the field were also tested, and the results were compared with the hydraulic conductivity of virgin specimens. An equation is proposed to include the effect of confining stresses on the hydraulic conductivity of geotextiles. A reduction factor, termed the degree of retention (DOR), is introduced to express the long-term reduction in hydraulic conductivity due to soil-particle retention. In addition, a simple performance test is proposed for investigating the flow behavior of a soil-geotextile composite under its typical operational conditions.

Effects of End Conditions on Triaxial Compressive Strength for Cohesionless Soil

Drained triaxial compression tests of Toyoura sand were carried out with conventional triaxial apparatus to evaluate the effects of sample slenderness and end conditions on triaxial compression strength. It was found thatthe maximum difference in the angle of internal friction Φ d for different test conditions employed was about ′1°. At the same time, the effects of the sample slenderness and each end condition on the strength value could be clearly identified.

Shear Banding in a Sedimentary Soft Mudstone Subjected to Plane Strain Compression

A plane strain compression (PSC) testing system to observe shear banding in softrock was developed. The deformation characteristics of shear band in a sedimentary soft mudstone were evaluated by locally measuring axial and lateral deformations of specimens in drained PSC tests. Shear deformation and dilatancy of shear band that occurred between the peak stress state and the start of the residual stress state were on the order of 1 and 0.5 mm. Dilatancy of the shear band continued during the residual stress state, resulting in a high-residual friction angle mobilized along the shear band. Shear band deformation characteristics of two other sedimentary softrocks were obtained from axial strains measured locally in triaxial compression tests based on the stress-state dilatancy relationship obtained from the PSC tests.

Triaxial compressive and extension strength of sand affected by strength anisotropy and sample slenderness

Drained triaxial compressive and extension strengths of air-pluviated sand were evaluated by means of a conventional triaxial apparatus taking into account both strength anisotropy and the effects of sample slenderness, that is, height/width or diameter ratio (HI D). The initial values of HID employed were 2.0, 1.0, 0.5, and 0.25. The direction of the major principal stress σ 1 was either normal to or parallel to the bedding plane. It was found that the triaxial extension strength is greatly influenced by HID. Strengths in the following four stress conditions were compared: (1) triaxial compression where the σ 1 direction is normal to the bedding plane, (2) triaxial extension where one of two σ 1 directions is normal to the bedding plane while the other is parallel to the bedding plane, (3) triaxial compression where the σ 1 direction is parallel to the bedding plane, and (4) triaxial extension where both σ 1 directions are parallel to the bedding plane. It was found that while the relative strength is a complicated function of H/D, generally the strength is the largest for the second case, intermediate for the first and fourth cases, and the smallest for the third case. This result suggests that Φ is not a simple function of b = (σ 2 - σ 3 )/(σ 1 - σ 3 ), which represents the relative magnitude of σ 2 against σ 1 and σ 3 , but the strength anisotropy and failure mode, especially in triaxial extension, should be taken into account in a combined manner.

A new simple method to substantially increase the seismic stability of reinforced soil structures

A preloading and prestressing (PLPS) method has been proposed to substantially decrease the transient and residual vertical compression of geosynthetic-reinforced soil (GRS) structures subjected to long-term traffic load. It is shown that by using a newly developed device (called the ratchet system) in addition to the PLPS procedure, the seismic stability of PLPS GRS structures becomes very high. The ratchet system can not only maintain high prestress when the backfill tends to contract but also prevent the expansion of the backfill, both effectively restraining the shear and bending deformation of the structure subjected to seismic load.

Stiffness of the ground improved to support the pier of Japan National Large Telescope (JNLT) atop Mauna Kea

A 2.5 m-thick cinder layer immediately below the pier of Subaru (Japan National Large Telescope, JNLT) now under construction on the summit of Mauna Kea in Island of Hawaii was improved by recompacting volcanic cinders obtained by excavation at the site mixed with cement. The purpose was to increase the Youngs modulus at very small strains of the supporting ground to 500 MPa so as to make the lowest natural frequency of the pier-ground system in its rocking motion to be more than 4.3 Hz. This requirement is essential for the telescope control system to correct as quickly as possible for external and internal disturbance of the telescope tracking. The results of the field and laboratory geotechnical tests including the measurements of elastic wave velocities and cyclic triaxial tests, which were performed for the design of the ground improvement work and the prediction and evaluation of the Youngs modulus of the constructed layer, are described.