Chemical grouting method can be used in order to improve the loose sand against the earthquake induced liquefaction. Long term stability of chemically stabilized sand is required for the chemical grouting method to be used to prevent the earthquake induced liquefaction. However, it is quite difficult to obtain and predict the long term performance of chemically stabilized sand. Experimental investigation of long term stability of chemically stabilized sand has been carried out by using the promotion of the silica diffusion and leaching within the chemically stabilized sand under the water flow. It is demonstrated that the time dependent variation of the physical properties of chemical stabilized sand is closely related to the silica movement and leaching from the chemically stabilized sand. Silica movement and leaching of the chemically stabilized sand are obtained by the finite element analysis based on the silica diffusion equation. It is concluded that the long term stability of chemically stabilized sand can be quantitatively evaluated using the combination of the flow water promotion test of chemically stabilized sand and the finite element analysis based on the silica diffusion equation.
In order to prevent derailment of a train due to the huge earthquake, it is required to evaluate seismic performance of the different structures using the common index and improve it. In particular, it is important to reinforce embankments because these are highly used in the railway today. In this study, through the model tests mainly, the failure modes and deformation levels of the embankment and the appropriate seismic reinforcement methods are examined. The new findings are as follows; 1) The embankment-ground failure modes, which related to the embankment height, ground motion and the ground properties, are classified into five types. 2) The new classification corresponds to the deformation level as the common index of seismic performance. 3) It proved that the seismic reinforcement using tie rod can be applied to the conventional design, and the appropriate seismic reinforcement methods for embankment are proposed according to the five failure modes.
It is known that the deformation and flow properties of a rock mass are governed by the discontinuities involved in the rock mass. When a tunnel is excavated, the stress around the tunnel changes complicatedly. However, the changes of the deformation and flow properties under the complicated stress remain poorly understood. Thus, in this study, the flow-deformation coupling experiments are conducted, and the effects of the existence or non-existence of discontinuity, the opening of discontinuity and the stress change on the deformation and flow properties are examined. In consequence, it is clarified that the flow property of the discontinuous rock mass changes rapidly in loading or unloading to a specimen with a discontinuity.
Reusing drinking water sludge discharged during water purification is anticipated for a good use of waste materials as geotechnical materials. So far, drinking water sludge engineering properties has been studied by laboratory tests. This study was conducted to inspect the results of laboratory tests were trial construction using drinking water sludge as a backfill material of water pipe construction. Used sample was mountain sand which was widely used as a backfill material of water pipe construction, two types of drinking water sludge difference from dewatering methods which is sun dry and pressure dehydration, and mixed soil of drinking water sludge mountain sand. The settlement of road surface was measured using surveying instrument during 19 months, and field density tests were conducted in trial construction. As a result, the settlement of road surface in the drinking water sludge and mountain sand were not a significantly differences despite degree of compaction is less than 90%. Finally, this study showed the flowchart about control method for quality of drinking water sludge for use as a subgrade material based on the laboratory CBR tests.
Recently, the phenomena which a ground vibration increases by a track irregularity are reported. It is therefore considered that an influence of track irregularity to the ground vibration may be unable to ignore. We examined about the influence of track irregularity to ground vibration by a numerical simulation. The results of numerical simulation indicate that the maximum and minimum amplitude occur at just before the convex point of the irregular track wave form or at the point if the vibration amplitude at evaluation points changes depending on locus state. The average amplitude increased in proportion to the logarithm of track amplitude irrespective of train speed if the average of the vibration amplitude at the all evaluating points increased. It is considered that the contribution rate of the position synchronous ingredient against the train synchronous ingredient effects the changing vibration amplitude depending on the track state and the increasing of average vibration amplitude.
The active earth pressure during earthquake is usually calculated by Mononobe-Okabe or modified Mononobe-Okabe method which makes the same seismic coefficient acting in a soil wedge of backfill. A new application method in consideration of the reduction effect of horizontal seismic coefficient is proposed in the paper. The method enables expression which does not cause rapid increase of the active earth pressure and the reduction of angle of slip surface with increasing in a seismic coefficient. The object retaining wall is a cantilever retaining wall with heel base, and the setting method of the angle acting of earth pressure on the virtual back is also proposed.
There exists a large class of crushable geomaterials with weak grains such as crushable ground. In order to research pile bearing capacity characteristics in crushable ground, the model pile tests have been carried out using two kind of crushable soil and Toyoura standard sand. To investigate the detailed characteristics of end bearing capacity acquired from the model pile test, soil particles were observed using oedometer test, sieve test and a microscope, following the model pile test. Samples of Chiibishi sand and Toyoura standard sand were sectioned and photographed. Consequently, it became clear that the pile bearing capacity mechanism is greatly dependent on the grade of particle crushability. Various combinations of stress can exist in a soil adjacent to a pile and a given soil element could be subjected to any number of these during pile driving and final loading. For example the existence of large magnitude stresses at the tip. The mobilization of the strength of crushable soils requires a much higher strain level while at the same time the end bearing pressure on the model piles inducing considerable particle breakage. Foundation design methods can be safely used where stress levels or particle strengths prevent crushing. However, in the case of weak grains or high foundation stresses, consideration should be given to the effects of grain crushing. Also, the corresponding relation-ship of deformation of ground particles, pile bearing capacity, and particle crushability became clear.
This paper examines an importance of mechanical properties of lime stabilized soil with recycled bassanite (CaSO4·1/2H2O) derived from waste plasterboard. In order to clarify the influence of the new soil stabilizer on stabilization effect, four kinds of soil samples mixed with the stabilizer at different mixture rate were investigated by a series of laboratory tests (unconfined compression test, X-ray analysis and scanning electron microscope observation). The following conclusions were obtained from the present study: (1) Even if the stabilized soil is expanded by generating ettringite, the soil material gets to be strong gradually by increasing curing period. (2) The new lime stabilizer is suitable for better fine-grained soils than coarse-grained soils. However, even if coarse-grained soil, necessary strength can be secured by raising moderately the degree of compaction of the specimens. (3) Much ettringite (needle crystal, 3CaO·Al2O3·3CaSO4·32H2O) were generated in the lime stabilized soils, and those were locking soil particles.
This paper describes the stability of improved ground by densification method during and after liquefaction. It is generally known that possibility of liquefaction in the improved ground during earthquake is very low. However, it is concerned that the improved ground tends to be influenced by propagation of excess pore water pressure from liquefied ground surrounding the improvement. Therefore, in this study, a series of triaxial and torsional tests was carried out under various different conditions of effective confining stresses, relative densities, anisotropic effective confining stresses and fine contents, in order to investigate the influence of dissipation of excess pore water pressure to shear modulus and post-liquefaction deformation characteristics of loose-to-dense sands. As a result, it was confirmed that the generation condition of excess pore water pressure lead to the difference of the residual deformation of the improved ground after liquefaction.