The purpose of this paper is to comprehensively quantify model error in geotechnical structural design methods, e.g. structural foundations, earth structures and retaining walls. Model errors for structural foundations and earth structures are summarized based on an extensive review of literature, and model errors in retaining walls are quantified in detail by statistical analysis based on collecting actual construction data and model experiment data. From the above, the basic information for conducting a geotechnical reliability analysis is presented. Furthermore, the challenges in geotechnical structural design are indicated from a model error perspective.
In geotechnical structural design, it is very common to transform the measurements obtained in soil investigations, such as SPT-N or CPT-qc, into geotechnical parameters that are directly used in design calculations. The error of these transformations, i.e. transformation errors, is one of the characteristic sources of uncertainty in geotechnical design, and it generally imposes quite a large uncertainty due to its dependence on past experience. The purpose of this paper is to extensively quantify the transformation error in geotechnical structural design through a review of available literature. Furthermore, the practical applicability of these transformation formulas is examined based on a comparison with spatial variability and statistical estimation errors in measurements such as SPT-N.
The collapse of aged embankment has recently occurred owing to torrential rain. To prevent disaster due to such collapse, it is important to check the safety of the embankment. However, it is difficult to examine details of embankments because of cost and time constraints. Therefore, we aim for developing an inspection method which can be easily applied for a lot of embankments. The proposed method utilized dynamic cone penetration test for estimating the degree of compaction in the embankment. This paper describes the scheme of method for evaluating the degree of compaction of decomposed granite used as fill material in Chugoku region. Consequently the practical charts between the penetration resistance measured at a certain depth and the corresponding degree of compaction are established for different levels of compaction energy.
This study discusses on availability of simplified monitoring of slopes for prevention of workers being buried in soil at excavations. A compact strain meter was developed to measure increment of shear strain θ in shallow sub-surface of slopes. A full scale model test was carried out in a model slope composed of soft deposit of Kanto-loam and 45 degrees of inclination and 3.5m of height. The model slope did not fail immediately after a completion of the final excavation, and 24minutes of time lag existed prior to failure. The relationship between θ and the displacement shows good agreement in the increase. Similar reactions to the creep strain curve were observed in θ. A couple of minute time could be provided for escape by identifying either 2nd or 3nd creep. In addition, numerical analyses were performed to investigate the distribution of θ in slopes. A clear increase of θ was confirmed especially at the inside of failure block when the slopes were getting to fail. It was clarified that the potential risk of slope failure is detectable by the monitoring. It is also considered that warning by the monitoring can save workers' lives by escape.
The overlaying mesh method (OMM) is an analytical approach that overlaps two or more independent different-sized-mesh models in the finite element analysis. In the OMM, detailed mesh model is used in the target area under consideration, with coarse mesh model elsewhere, in order to optimize calculation effort. In this study, we first proposed the OMM theory which treats different type elements, i.e., beam elements modeling piles and 2D isoparametric elements modeling surrounding soil. Then, we performed parametric study to investigate the accuracy of the analysis results by changing the mesh sizes, ground properties and pile characteristics in pile-ground interaction system.
It is important to reveal mechanical characteristics of compacted soils in order to ensure stable performance for embankments. However, there may be few experimental studies to verify cyclic shear behavior of embankments. Furthermore, the evaluation of liquefaction potential of embankments has been recently pointed out as well as that of foundation below embankments. On the other hand, in Hokkaido, where many kinds of volcanic soils widely deposit, those soils have been often employed as embankment materials. According to previous researches, coarse-grained volcanic soils have some features of fragility and inner-porosity to cause particle breakage which influence the mechanical characteristics of those soils. In this study, for the purpose to evaluate the influential factors on the cyclic shear behavior of embankments, a series of cyclic undrained triaxial tests was carried out on compacted samples using a coarse-grained volcanic soil deposited in Hokkaido. Each triaxial specimen was made in a different condition based on water content at compaction, dry density and finer content. Experimental results show that compaction conditions such as water content and dry density can affect cyclic strength of compacted soils. However, the tendency to cyclic strength may be quite different depending on the difference of finer content.
The high-pressure injection mixing method is extensively used to improve the ground for higher seismic stability, including the prevention works of soil liquefaction. To design these cement-improved grounds to support permanent structures, evaluation of the strength and deformation characteristics that is much more precise and reliable than the conventional method is required unlike cases of temporary structures. To this end, a methods to accurately evaluate the stiffness at a very small strain, the strain-dependency of stiffness, the confining pressure-dependency of strength and the effects of long ageing period on the strength and stiffness of cement-mixed clayey, sandy and gravelly soils were studied.
This paper describes the three-dimensional (3D) grain shape characteristics of some standard sands and its relation to the granular mechanical properties such as void ratio extent and shear strength. A x-ray micro CT at SPring-8 was employed to obtain CT images of Toyoura sand, Hostun sand, Ottawa sand, Ticino sand, SLB sand and glass ballotini. The CT images were analysed by an originally-developed image processing to identify 3D shape of each grains, and then the identified surface data were converted to STL surface mesh models by a meshing software (MeshLab). Then we calculated some shape indices such as the aspect ratio, the elongation ratio, the flatness ratio, sphericity and Krumbein's sphericity. Two types of indices based on ellipsoidal properties are newly proposed: (1) surface area ratio to ellipsoid, and (2) volume ratio to ellipsoid. The calculated indices are compared by means of their correlation with respect to void ratio characteristics and shear strength. As a result, the void ratio extent showed high correlation with it is found that the void ratio extent, and shear strength were highly correlated with the volume ratio to ellipsoid, and both of the aspect ratio and the volume ratio to ellipsoid, respectively.
On a LNG base, the stability of the structure in case of earthquake is indispensable to reservation of a stable supply and safe operation. Of these, the preservation of bearing performance of “foundation” is one of the most significant at both the ensuring the safety and maintenance of LNG tank especially in the LNG tank foundation classified in large-scale important structure. In this time, in-situ lateral loading test using practical tank foundation was conducted at the opportunity of demolishing LNG tank after 40 years of service. And 3 dimensional elasto-plastic FEM analysis of the test is conducted. From the both results, bearing capacity and corruption level of practical LNG tank foundation were investigated, and the behavior specific to the large-scale group pile foundation was observed.
In this work, the soil-ground solidification by calcium carbonate precipitation has been examined utilizing a urea hydrolysis enhanced by urease. Firstly, a suite of the small cylinder tests (50 mm in diameter and 100 mm in height) was conducted to evaluate the evolution of mechanical properties in the im-proved sand soils mediated by the grout injection. The results show that the strength of the improved samples increases with increase of the amount of calcium carbonate precipitated. Specifically, a uniaxial compressive strength of 3.4 MPa was obtained in the sample with approximately 4 wt.% precipitation against the sand weight. Secondly, drum-can tests (560 mm in diameter and 600 mm in height) were per-formed to examine the validity of this technique. It is concluded that the current technique may be ap-plicable to real fields although the strength of the improved sand should be well-controlled prior to the in-situ application.