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Liquefaction
Published in Takaji Kokusho, Innovative Earthquake Soil Dynamics, 2017
So far, the particles of granular soils were all fresh (non-weathered), hard in quality and difficult to crush. In nature, particles of some sort of granular soils are easy to crush. One of such crushable soils is decomposed granite, wherein gravel particles are strongly weathered and their angular ends are easy to break. Another typical crushable granular soils is calcareous sands consisting of porous and roundish particles originated from corals. There are still volcanic and other types of crushable granular soils in nature. In the following, some test results on decomposed granite will be addressed to see the effect of particle crushability on the liquefaction resistance in comparison with non-crushable fluvial granular soils of fresh grains.
Forest roads: regional perspectives from around the world
Published in International Journal of Forest Engineering, 2023
C Kevin Lyons, Stelian Alexandru Borz, Campbell Harvey, Muedanyi Ramantswana, Hideo Sakai, Rien Visser
The Chichibu belt is located north of the Shimanto belt. This belt collapsed and once deposited below sea level, the geologic stratum was not formed and the soil is fine-grained. Due to the fine-grained soils, large landslides with long run-outs can result from heavy precipitation. Fine-grained soils limit forest road cut slope height and the ability to construct fill slopes. Keizaburou Oohashi developed log retaining walls to support the cut and fill slopes in decomposed granite; however, they are not recommended for use on public roads (Oohashi 2001). Decomposed granite is sandy, and it is difficult to form a road bed employing only earthwork. The logs used for retaining walls decay as a matter of course. It was reported that the Young’s Modulus of logs buried in the road would be zero within 30 years for sugi (Cryptomeria japonica) and 40 years for hinoki (Chamaecyparis obtusa) (Aizawa et al. 2011). It is supposed that the internal and adhesive friction among the logs and compacted soil makes the road bed stronger like the Terre Armee method. Repeated trafficking and addition of gravel during maintenance can compact and strengthen the road bed even if the logs decay. The log retaining wall structure is effective not only for decomposed granite but also for debris flow deposits.
A methodology for estimation of site-specific nonlinear dynamic soil behaviour using vertical downhole arrays
Published in European Journal of Environmental and Civil Engineering, 2021
E. Ece Eseller-Bayat, Mehmet Ada
The NEES Garner Valley Downhole Array (GVDA) is another site used in this study (Steller, 1996). Figure 2(c) shows the soil layers and S wave velocities measured at the GVDA site. The near-surface stratigraphy beneath GVDA consists of 18–25 m of lake-bed alluvium. The alluvium gradually transforms into decomposed granite at depths of 18–25 m. Decomposed granite which consists of gravelly sand exists from 25 to 88 m. S wave velocities are about 120 m/s near the surface and increase to approximately 480 m/s at a depth of 100 m. Accordingly, the soil profile is classified as silty sand, sand, clayey sand and silty gravel (Steller, 1996). GVDA consists of a set of six triaxial accelerometers located at depths of 6, 15, 22, 50 and 150 m.
Machine learning of geological details from borehole logs for development of high-resolution subsurface geological cross-section and geotechnical analysis
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2022
The delineation of subsurface cross-sections involves determination of geometry and number of soil layers as well as demarcation of the stratigraphic boundaries among different soil layers (Bossi et al. 2016). In practice, subsurface geology of a studied site is investigated via scattered measurements such as borehole logs. The site-specific measurements are normally too sparse to enable a detailed depiction of subsurface geological cross-sections (e.g. Phoon, Ching, and Shuku 2021). Ideally, all the stratigraphic data revealed from limited borehole logs should be incorporated in the development of the subsurface ground model as the sparse measurements are precious. Nevertheless, it is common practice to discard stratigraphic details (e.g. thin seams or apparently discontinuous layers observed in the borehole logs) to facilitate a simplified representation of subsurface stratigraphy (e.g. Vick 2002). For example, Figure 1 illustrates a challenge encountered during the interpretation of detailed stratigraphic boundaries for a typical granitic rock site in Hong Kong (GEO 2006). As shown in Figure 1(a), two borehole logs, namely, log A and log B, were retrieved from a granite weathering site with core stones. From the site-specific boreholes, there are six soil types, namely, residual soil (RS), completely decomposed granite (CDG), highly decomposed granite (HDG), moderately decomposed granite (MDG), slightly decomposed granite (SDG) and fresh granite. Stratigraphy revealed from log B is complex with a stratigraphic alternation of CDG, HDG and MDG. When compared with log B, stratigraphy of log A is more homogeneous with less stratigraphic alternations. It is challenging to determine the thicknesses and dipping directions of different soil strata due to the inconsistencies of the observed soil stratigraphy from borehole logs A and B.