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161.
J. A. A. Jones 《地球表面变化过程与地形》1987,12(3):229-248
Natural piping doubles the dynamic contributing area on the upper Maesnant stream in mid-Wales, mainly through linking points well beyond the riparian zones of seepage to the stream. Both discharge and sediment transport rates in the major pipes are closely related to the size of shallow surface microtopographic hollows in which they lie, and which themselves are largely created by piping erosion. However, pipe dischrges are frequently generated by contributing areas larger than these surface depressions and some pipes run counter to the surface topography. The redistribution and acceleration of hillslope drainage processes by piping has implications for theories of hillslope development, especially through plan-form modifications, and also for channel discharge and erosion. 相似文献
162.
In certain tropical slopes it appears possible that soil suction may play a significant role in maintaining stability. This communication outlines a laboratory suction-controlled triaxial test that can be undertaken to validate the threshold suction predicted by resistance envelope methods. It is shown that for two sites examined in St. Lucia, West Indies, the results from such a test confirm results obtained by use of resistance envelopes. 相似文献
163.
164.
Exposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45-year-old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross-sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m-long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long-term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long-term increase in sediment yield caused by the road. The increase amounts to about 2·4 m3/year. This figure, compared to the average annual on-site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion. 相似文献
165.
Mean growing season soil PCO2 data were obtained for 19 regions of the world in nine countries. Bivariate and multiple linear regression analysis with soil log(PCO2) as the dependent variable and TEMP, PRECIP, log(AET), and log(PET) as the four climatic independent variables demonstrated that AET was the best independent predictor of soil PCO2. An improved soil PCO2-AET model was developed by assuming (1) that as AET approaches zero, soil PCO2 approaches the atmospheric value and (2) that there is an upper limit to soil PCO2 at very high AET. This model has the form log(PCO2) = ?3·47 + 2·09 (1 ?e?0·0172 AET) where AET is in mm. It explains 67 per cent of the initial variation in the soil PCO2 data, predicts a soil log(PCO2) of ? 3·47 at AET = 0, and an upper limit of 3·5 per cent (log(PCO2) = ? 1·45) for mean growing season soil PCO2 at AET values of 2000 mm and above. The results of this study suggest that soil PCO2 levels in tropical areas are, on average, higher than those in temperate, alpine, and arctic regions. 相似文献
166.
This paper presents results of meticulous laboratory testing and numerical simulations on the effect of reinforcement on the
low-strain stiffness and bearing capacity of shallow foundations on dry sand. The effect of the location and the number of
reinforcement layers is studied in the laboratory, whereas numerical simulations are used to study the reinforcement-foundation
interaction. Laboratory tests show an increase of 100, 200, and 275% not only in bearing capacity but also in low-strain stiffness
(linear load–displacement behaviour) of a square foundation when one, two, and three layers of reinforcement are used, respectively.
The specimen preparation technique is found to be crucial for the repeatability and reliability of the laboratory results
(less than 5% variability). Numerical simulations demonstrate that if reinforcements are placed up to a depth of one footing
width (B) below the foundation, better re-distribution of the load to deeper layers is achieved, thus reducing the stresses and strains
underneath the foundation. Numerical simulations and experimental results clearly identify a critical zone between 0.3 and
0.5B, where maximum benefits not only on the bearing capacity but also on the low-strain stiffness of the foundation are obtained.
Therefore, soil reinforcement can also be used to reduce low-strain vibrations of foundations. 相似文献
167.
Fadong Li Xianfang Song Changyuan Tang Changming Liu Jingjie Yu Wanjun Zhang 《Environmental Geology》2007,53(3):687-696
The groundwater in headwater region is an important recharge source for the adjacent mountain-front plain. In order to reveal
the relationship among precipitation, soil water and groundwater, from June to September in 2004, stable isotopes (deuterium
and oxygen-18) in precipitation and soil waters at the depths of 10, 20, 30, 50, 70, 90, and 110 cm were analyzed at two sites
covered by black locust (Robinia Pseudoacia L.) (Site A) and grass predominated by Themeda triandra (T. japonica (Willd.) Tanaka) and Bothriochloa ischaemum (B. ischaemum (L.) Keng) (Site B) in an experimental catchment at Taihang Mt., North China, respectively. The δ18O of precipitation in daily rain events shows large variations (−13.3 to −4.3‰) with a mean of 8.1‰. The δ18O and δ D of soil waters along profiles in two sites suggest that the influence of canopy cover was just up to 10 cm in top
soil water. The soil water moved over the zero flux plane at 70 cm in-depth is expected to escape the evaporative effect at
the end of September in both sites. The results show that the stable isotope, instead of tritium as tradition, can be used
to trace the soil water behaviors based on the movement of isotopic peak along the vertical profiles in this semi-arid and
semi-humid mountainous region. The infiltration depths of soil water in Taihang Mt. are 12 and 10 mm/day from June to September
in 2004 in Site A and Site B, respectively. Tracing by stable isotope, recharge fluxes of soil water to local groundwater
are of 3.8 and 3.2 mm/day in Site A and Site B, respectively. The results provide desirable information for assessment of
local groundwater resources.
An erratum to this article can be found at 相似文献
168.
Iodine contents of soils developed over the major rock formations of the northern zone of the Eastern Pontide Tectonic Belt
(Northeastern Turkey) have been investigated with respect to soil-parent rock relationship, effect of topography, elevation,
and climate to construe its effect on the health of the local population. Samples were collected from the A and B horizons
of the soils developed over the major stratigraphic units constituting the eastern Pontides, including the Lower Basic Complex
of Jurassic-Lower Cretaceous age, the Berdiga limestone (Jurassic-lower Cretaceous), the Dagbasi granitoid (Upper Cretaceous),
volcano-sedimentary sequence of Upper Cretaceous age, ore-bearing and barren dacites of Upper Cretaceous age, and Neogene
alkaline basalts. Chemical analyses of soil samples indicate significantly lower iodine abundances for all the soils studied
(5–28 ppm) in comparison to the average abundance of iodine in analogous soils of other parts of the world (22–93 ppm). The
concentration of iodine in soils developed over the same geologic formation decrease with increasing elevation. In certain
cases, this decrease may reach up to 70%. Goiter is highly common throughout this region in Turkey. The results of this study
suggest that the iodine deficiency of region’s soils may be a principal underlying cause for this area of Turkey being an
endemic goiter region. 相似文献
169.
170.
从水泥土的固化机理出发,结合水泥搅拌桩桩身标准贯入试验和水泥土配合比试验,分析讨论了土性指标、土质条件和地层性质对水泥搅拌桩成桩质量的影响。 相似文献