基于Kachanov连续损伤变量及Fredlund非饱和土有效应力理论,提出了结构性损伤膨胀土的强度表征方法。以南水北调中线工程南阳膨胀土为研究对象,利用改进型非饱和土三轴仪对不同损伤程度的三组15个重塑试样进行控制净围压分别为50,100,15...基于Kachanov连续损伤变量及Fredlund非饱和土有效应力理论,提出了结构性损伤膨胀土的强度表征方法。以南水北调中线工程南阳膨胀土为研究对象,利用改进型非饱和土三轴仪对不同损伤程度的三组15个重塑试样进行控制净围压分别为50,100,150 k Pa的三轴压缩试验,定量分析荷载作用下初始孔洞损伤基元及裂隙演化形式对膨胀土力学特性的影响。实验表明:考虑结构性及损伤的非饱和土力学表征能够很好地描述土体的力学行为;孔洞损伤对膨胀土强度没有一致的强化或弱化效果,而裂隙发育形态、演化形式对土体结构及强度起主导作用;围压能够一定程度上抑制裂隙的开展,通过裂隙面咬合产生强度。根据破坏机制将该力学关系表示为裂隙发育及残余强度两个阶段,线性硬化破坏、弹塑性破坏、脆塑性破坏、线性软化破坏四种破坏模式。研究可为揭示膨胀土边坡破坏的力学机制及预测提供新的参考。展开更多
In Senegal, particularly in the Senegal River valley, agricultural mechanization remains limited, mainly due to a lack of agricultural equipment, a lack of expertise in agricultural machinery and an apprehension of th...In Senegal, particularly in the Senegal River valley, agricultural mechanization remains limited, mainly due to a lack of agricultural equipment, a lack of expertise in agricultural machinery and an apprehension of the consequences on soil quality. To better understand agricultural mechanization of rice cultivation, this survey study has been carried out in the Senegal river valley. Precisely, this work aimed to characterize farm machinery and its effects on soil and rice cultivation. A questionnaire was administered to 304 out of 1270 farmers, spread over 8 rice-growing areas, 4 of which are located in the Podor department, three in Dagana and one in Saint-Louis. The results showed that 99.3% of farmers used motorized equipment, with 95.7% using tractor and 3.6% a power tiller. Offset tillage, which is a shallow cultivation practice carried out to break up hard soil without turning it over, was most widespread among growers (95.4%). 78.3% of the valley’s farmers felt that the machinery used to carry out tillage operations was inefficient. According to the farmers, the main constraints on the use of agricultural machinery in the valley were: the upkeep and maintenance of equipment (57%), the lack of expertise in mechanization (31%), and issues adapting machinery to local conditions (12%). Those constraints have contributed to a drop in yields in recent years, the spread of weeds on cultivated plots and the gradual degradation of the soil in the area according to 78% of farmers.展开更多
The horizontal to vertical spectral ratio(HVSR)methodology is used here to characterize pumice soils and to image the three-dimensional surface geometry of Guadalajara,Mexico.Similar to other Latin American cities,Gua...The horizontal to vertical spectral ratio(HVSR)methodology is used here to characterize pumice soils and to image the three-dimensional surface geometry of Guadalajara,Mexico.Similar to other Latin American cities,Guadalajara is exposed to high seismic risk,with the particularity of being the largest urban settlement in Latin America built on pumice soils.Methodology has not yet been tested to characterize subsoil depths in pumice sands.Due to the questionable use of traditional geotechnical tests for the analysis of pumice soils,HVSR provides an alternative for its characterization without altering its fragile and porous structure.In this work,resonance frequency(F0)and peak amplitude(A0)are used to constrain the depth of the major impedance contrast that represents the interface between bedrock and pumice soil.Results were compared with borehole depths and other available geotechnical and geophysical data and show good agreement.One of the profiles estimated on the riverbanks that cross the city,reveals different subsoil thickness that could have an impact on different site responses on riverine areas to an eventual earthquake.Government and academic efforts are combined in this work to characterize depth sediments,an important parameter that impacts the regulations for construction in the city.展开更多
文摘基于Kachanov连续损伤变量及Fredlund非饱和土有效应力理论,提出了结构性损伤膨胀土的强度表征方法。以南水北调中线工程南阳膨胀土为研究对象,利用改进型非饱和土三轴仪对不同损伤程度的三组15个重塑试样进行控制净围压分别为50,100,150 k Pa的三轴压缩试验,定量分析荷载作用下初始孔洞损伤基元及裂隙演化形式对膨胀土力学特性的影响。实验表明:考虑结构性及损伤的非饱和土力学表征能够很好地描述土体的力学行为;孔洞损伤对膨胀土强度没有一致的强化或弱化效果,而裂隙发育形态、演化形式对土体结构及强度起主导作用;围压能够一定程度上抑制裂隙的开展,通过裂隙面咬合产生强度。根据破坏机制将该力学关系表示为裂隙发育及残余强度两个阶段,线性硬化破坏、弹塑性破坏、脆塑性破坏、线性软化破坏四种破坏模式。研究可为揭示膨胀土边坡破坏的力学机制及预测提供新的参考。
文摘In Senegal, particularly in the Senegal River valley, agricultural mechanization remains limited, mainly due to a lack of agricultural equipment, a lack of expertise in agricultural machinery and an apprehension of the consequences on soil quality. To better understand agricultural mechanization of rice cultivation, this survey study has been carried out in the Senegal river valley. Precisely, this work aimed to characterize farm machinery and its effects on soil and rice cultivation. A questionnaire was administered to 304 out of 1270 farmers, spread over 8 rice-growing areas, 4 of which are located in the Podor department, three in Dagana and one in Saint-Louis. The results showed that 99.3% of farmers used motorized equipment, with 95.7% using tractor and 3.6% a power tiller. Offset tillage, which is a shallow cultivation practice carried out to break up hard soil without turning it over, was most widespread among growers (95.4%). 78.3% of the valley’s farmers felt that the machinery used to carry out tillage operations was inefficient. According to the farmers, the main constraints on the use of agricultural machinery in the valley were: the upkeep and maintenance of equipment (57%), the lack of expertise in mechanization (31%), and issues adapting machinery to local conditions (12%). Those constraints have contributed to a drop in yields in recent years, the spread of weeds on cultivated plots and the gradual degradation of the soil in the area according to 78% of farmers.
基金Consejo Nacional de Ciencia y Tecnología of Mexico(CONACyT)under Grant No.1000473。
文摘The horizontal to vertical spectral ratio(HVSR)methodology is used here to characterize pumice soils and to image the three-dimensional surface geometry of Guadalajara,Mexico.Similar to other Latin American cities,Guadalajara is exposed to high seismic risk,with the particularity of being the largest urban settlement in Latin America built on pumice soils.Methodology has not yet been tested to characterize subsoil depths in pumice sands.Due to the questionable use of traditional geotechnical tests for the analysis of pumice soils,HVSR provides an alternative for its characterization without altering its fragile and porous structure.In this work,resonance frequency(F0)and peak amplitude(A0)are used to constrain the depth of the major impedance contrast that represents the interface between bedrock and pumice soil.Results were compared with borehole depths and other available geotechnical and geophysical data and show good agreement.One of the profiles estimated on the riverbanks that cross the city,reveals different subsoil thickness that could have an impact on different site responses on riverine areas to an eventual earthquake.Government and academic efforts are combined in this work to characterize depth sediments,an important parameter that impacts the regulations for construction in the city.
