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Experimental Study on the Water Movement of Different Soli-stone Mixtures

Author: WenMingXia
Tutor: ShaoMingAn
School: Northwest University of Science and Technology
Course: Soil
Keywords: soil-stone mixture infiltration and evaporation soil water characteristic curve gravels caliches gangues
CLC: S152.7
Type: Master's thesis
Year: 2011
Downloads: 84
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Abstract


Water scarcity has becoming an important restricted factor of ecological construction, especially on Loess Plateau which is located in arid and semiarid areas of northwest. Due to the soil development processes, soil erosion and the activities of mankind, soils of Loess Plateau always contain rock fragments. The exsitace of rock fragments in soil lead to differences of the movement of water compared to that in homogeneous soil. A large number of researches have been conducted by researchers at home and aboard on water movement of soils containing rock fragments,but the water movement of soil containing rock fragments is a very complex process, involving many factors. Thus, further research is necessary. In this paper, water movements of different stony soil mixture are studied through a large number of soil column experiments, the main conclusions were drawn as follows:1. The cumulative infiltration of stony soils was less than that of homogeneous soils, infiltration could be reduced by rock fragments layer in soils. The infiltration process of soils containing rock fragments in different layer could be described by both Kostiakov model and Philip model excellently. While the wetting front change with time could be described by a power function. The effects of rock fragment positions on cumulative infiltration were related to rock fragment types and sizes. When the size of caliches was 0.2-1cm, gravels was 1-3cm, the cumulative infiltration increased with the decrease of rock fragment position. The rock fragment size was 0.2-1cm, the wetting front of gravels and caliches both reached the lowest level when caliches position at 0-10cm, while that of gangues was at 40-50cm. The cumulative infiltration first decreased to the lowest value for 0-40cm and then increased with the increase of rock fragment thickness. The effects of rock fragment sizes on cumulative infiltration were related to rock fragment types. As for gravels, the cumulative infiltration of different rock fragment sizes as follows: 1-3cm>0.2-1cm>3-5cm. As for caliches, the cumulative infiltration decreased with the decrease of rock fragment sizes. As for gangues, the biggest cumulative infiltration arrived when the size was 0.2-1cm and the smallest one appeared when the size was 1-3cm. There was an inflection point in the effect of rock fragment content on cumulative infiltration which were varied mainly by rock fragment types. As for gravels and gangues, the inflection point arrived when the content Rm=45%, the one of caliches appeared when the content Rm=60%. The effects of rock fragment types on cumulative infiltration were related to rock fragment sizes. When the size was 0.2-1cm, the order of cumulative infiltration of different rock fragment types was as follows: gangue>gravel>caliche. When the size was 1-3cm, the biggest cumulative infiltration arrived when the type was caliche and the smallest one appeared when the type was gangue. When the size was 3-5cm, the biggest one occurred when the type was caliche and the smallest one appeared when the type was gravel. At the same time, the effects of rock fragment types on wetting front were related to rock fragment sizes. The cumulative infiltration with time can be described by Kostiakov model and Philip model. The biggest K、α、A、S arrived at sandy soil and the smallest at Lou soil. At the same time, the order of wetting fronts and infiltration rates of different soil types was as follows: sandy soil>loessial soil>lou soil. In the same soil layer, the order of water content in fine soils was as follows: lou soil> loessial soil>sandy soil.2. The relationship between cumulative evaporation and time could be represented by a second power equation and the evaporation could be efficiently inhibited by rock fragment mulches. The cumulative evaporation decreased with the decrease of rock fragment mulch thickness. It indicated that there was a positive correlation between inhibitory effects on evaporation and rock fragment mulch thickness. The effects of rock fragment mulch thickness on cumulative evaporation were related to rock fragment types and sizes. Under the same type of rock fragment, the decreased rates of cumulative evaporation changed with rock mulch thickness were negatively correlated with rock fragment sizes. Under the same size of rock fragment, the order of decreased rates of different rock fragment types was: gravel> gangue> caliche. As for gravel and caliche, the cumulative evaporation increased with the increase of the rock fragment sizes, but the one of gangue did not change significantly. Under the same rock fragment mulch thickness and the same size, the order of cumulative evaporation of different rock fragment types was: caliche>gangue>gravel. In other words, the biggest inhibitory effects on evaporation arrived at gravel and the smallest appeared at caliche.3. Van Genuchten model、modified Van Genuchten model and Brooks-Corey model could simulat the SWCC of different stony soil. Under the same suction, the water content of stony soils was less than that of homogeneous soil during processes of moisture absorption and adsorption. Under the same suction, the water content of rock fragment with bigger size was more than that with smaller size no matter what kind of rock fragment. As for gravel and caliche, the difference of water content between different rock fragment sizes during absorption process was more obvious than that during adsorption process. As for gangue, when the suction was less than 15KPa during absorption process and suction was more than 60KPa during adsorption process, the difference of water content between different rock sizes became very littler. Under the same suction, the smallest water content of stony soil containing gravles, while the water content of stony soil containing caliche and gangue concerned with the rock fragment content.4. The orthogonal design was adopted to analyze the effects of different factors on infiltration. The influnces of rock fragment types、rock fragment size、rock fragment content and soil texture were first studied. The results indicated that the order of effects of those factors on initial infiltration rate and sorptivety was: soil texture> rock fragment types> rock fragment content> rock fragment size, while the order of effects of those factors on cumulative infiltration was: soil texture> rock fragment content> rock fragment types> rock fragment size. Then, rock fragment types、rock fragment size、rock fragment position and soil texture were taken into account, the results showed that the order of effects of those factors on initial infiltration rate、sorptivety and cumulative infiltration was: soil texture> rock fragment position> rock fragment size> rock fragment type. Finally, the effects of different factors on soil water infiltration under the consideration of rock fragment types、rock fragment thinkness、rock fragment size and soil texture were analyzed. The order of effects of those factors on initial infiltration rate and sorptivety was: soil texture> rock fragment size> rock fragment type >rock fragment thinkness, and the order of effects of those factors on cumulative infiltration was: soil texture> rock fragment thinkness> rock fragment size> rock fragment type.5. The orthogonal design was adopted to analyze the effects of three factors(rock fragment size、rock fragment type and rock fragment mulch thickness ) on evaporation. The results indicated that the order of effects of those factors on evaporation was: rock fragment type> rock fragment mulch thickness> rock fragment size. As for rock fragment type, the order of inhibitory effects on evaporation was: gravel> gangue> caliche. As for rock fragment mulch thickness, the inhibitory effects on evaporation increased with the increase of mulch thickness and the biggest one arrived at 5cm. As for rock fragment size, the inhibitory effects on evaporation decreased with the increase of rock fragment size and the biggest one appeared at 0.2-1cm. The combination of factors beneficial to evaporation showed that the inhibitory evaporation was the most strengthing when the type was gravel with the size of 0.2-1cm, and mulch thickness was 5cm.

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CLC: > Agricultural Sciences > Agriculture as the foundation of science > Soil > Soil physics > Soil moisture
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