块石定向性特征对土-石混合体强度影响的数值模拟

为了探讨土-石混合体的力学强度受块石定向性特征的影响,开发了二维椭圆块石集合体随机模型(2D Elliptic Block Collection Stochastic Model,简称EBCS2D),并在此基础上进行了双轴压缩数值模拟。模拟结果显示土-石混合体的强度受块石定向性特征的影响,该影响规律与含石量显著关联。通过对各向异性屈服面曲线方程和数值模拟结果的拟合分析,验证了该屈服面曲线方程在表达土-石混合体强度方面的适应性。通过引入土-石相互作用单元的概念,阐明了在低、中、高3种含石量下,块石孤立作用和团簇作用交替主导,造成了块石定向性特征对土-石混合体力学强度的不同规律的影响。      

Analysis of raft foundation design based on considering influence of super structure stiffness

The finite element method was used for analysis of raft foundation design in high-rise building. Compared with other conventional methods, this method is more adapted to the practical condition since both superstructure stiffness and soil conditions were considered in calculation. The calculation results by example show that the base reaction is more uniform and the maximum reaction decreases obviously. Accordingly, the raft foundation design is more economic without any loss of security for high-rise building.     

Probabilistic stability analysis of embankment slopes considering the spatial variability of soil properties and seismic randomness

The safety of embankments under seismic conditions is a primary concern for geotechnical engineering societies. The reliability analysis approach offers an effective tool to quantify the safety margin of geotechnical structures from a probabilistic perspective and has gained increasing popularity in geotechnical engineering. This study presents an approach for probabilistic stability analysis of embankment slopes under transient seepage considering both the spatial variability of soil parameters...     

Effect of lithology and structure on seismic response of steep slope in a shaking table test

Studies on landslides by the 2008 Wenchuan earthquake showed that topography was of great importance in amplifying the seismic shaking, and among other factors, lithology and slope structure controlled the spatial occurrence of slope failures. The present study carried out experiments on four rock slopes with steep angle of 60° by means of a shaking table. The recorded Wenchuan earthquake waves were scaled to excite the model slopes. Measurements from accelerometers installed on free surface of the model slope were analyzed, with much effort on timedomain acceleration responses to horizontal components of seismic shaking. It was found that the amplification factor of peak horizontal acceleration, RPHA, was increasing with elevation of each model slope, though the upper and lower halves of the slope exhibited different increasing patterns. As excitation intensity was increased, the drastic deterioration of the inner structure of each slope caused the sudden increase of RPHA in the upper slope part. In addition, the model simulating the soft rock slope produced the larger RPHA than the model simulating the hard rock slope by a maximum factor of 2.6. The layered model slope also produced the larger RPHA than the homogeneous model slope by a maximum factor of 2.7. The upper half of a slope was influenced more seriously by the effect of lithology, while the lower half was influenced more seriously by the effect of slope structure.     

田湾核电站某工程偏移基桩性状分析

用低应变动测法检测基桩结构完整性，其测试结果是可靠的，但在田湾核电站某子项用低应变对因滑坡而倾斜的基桩进行检测时，却发现同样是偏移较大的基桩，有的基桩断裂、破损，有的完整，从低应变测试结果很难与实际情况统一起来。考虑到基桩不是孤立的，是与地基土结合在一起的，通过利用基坑支护理论及滑坡形成的圆弧滑动面原理，并结合施工的一些实际情况，从理论上分析了滑坡后基桩断裂、破损、倾斜的可能性，从而对偏移基桩性状做出了正确判断，为工程桩的处理提供依据。     

Influence of the upper mixed layer depth on Langmuir turbulence characteristics

Journal of Oceanology and Limnology - The upper mixed layer depth (h) has a significant seasonal variation in the real ocean and the low-order statistics of Langmuir turbulence are dramatically...     

Influence of non-dimensional strength parameters on the seismic stability of cracked slopes

Cracks in rock or soil slopes influence the stability and durability of the slopes. Seismic forces can trigger slope disasters, particularly in the cracked slopes. Considering the nonlinear characteristics of materials, the more generalized nonlinear failure criterion proposed by Baker is adopted. The influence of non-dimensional strength parameters on the stability of cracked slopes under earthquakes is performed using the upper bound limit analysis. The seismic displacement is calculated by adopting the logarithmic spiral failure surface according to the sliding rigid block model. Based on the existing studies, two methods for the stability analysis of cracked slopes under earthquakes are introduced: the pseudo-static method(with the factor of safety(Fs) as an evaluation index), and the displacement-based method(with the seismic displacement as an evaluation index). The pseudo-static method can only determine the instantaneous stability state of the cracked slope, yet the displacement-based methodreflects the stability variation of cracked slopes during earthquakes. The results indicate that the nondimensional strength parameters affect the factor of safety and seismic displacement of slopes significantly. The non-dimensional strength parameter(n) controlling the curvature of strength function shapes on the slope stability is affected by other parameters. Owing to cracks, the effect of non-dimensional strength parameters on seismic displacement becomes more significant.     

上硬下软地层中h型桩与滑坡相互作用机理模型试验研究

组合式抗滑桩是加固大型滑坡的有效防护措施,但上硬下软等复合地层中h型抗滑桩的加固机理仍有待深入研究。基于一套自主研发的上硬下软地层滑坡-h型抗滑桩物理模型试验装置,综合应力应变监测、激光测距仪、高速相机与粒子图像测速(PIV)技术研究了上硬下软地层滑坡中h型桩的位移、内力响应规律与滑体变形破坏特征,揭示了上硬下软地层条件下h型桩与滑坡相互作用机理。研究结果表明,在坡顶荷载逐渐增加的条件下,h型桩加固的上硬下软地层滑坡的演化阶段可划分为蠕变阶段、匀速变形阶段、加速变形阶段和破坏阶段4个阶段。受连系梁影响,前排桩与后排桩桩顶位移较小,应变最大值出现在靠近滑面深度处;后排桩弯矩呈“S”型分布,前排桩弯矩呈三角形分布,负弯矩最大值位于连系梁下方20 cm处。随着硬岩体积分数(φ_B)增加,桩顶位移逐渐减小,前、后排桩最大弯矩值也逐渐减小,但硬岩体积分数超过60%后最大弯矩值变化幅度较小。当φ_B=20%和40%时,后排桩土压力总体呈抛物线形式;当φ_B=60%和80%时,土压力总体呈反“S”型,且滑面附近出现第二个土压力峰值;前排桩土...     

Stability analysis of an unsaturated soil slope considering rainfall infiltration based on the Green-Ampt model

Based on the principle of saturated infiltration and the Green-Ampt model, an unsaturated infiltration model for a soil slope surface was established for either constant moisture content, or depth-varying moisture content and the slope. Infiltration parameters in the partially saturated slope were revealed under sustained rainfall. Through analysis of the variation of initial moisture content in the slope, the ponding time, infiltration depth, and infiltration rate were deduced for an unsaturated soil slope subject to rainfall infiltration. There is no ponded water on the surface of the slope under sustained low-intensity rainfall. The results show that the infiltration parameters of an unsaturated slope are influenced by the initial moisture content and the wetting front saturation, the soil cohesion and rainfall intensity under sustained rainfall. More short-term slope failures can occur with the decrease of cohesion of the soil of the slope. The ponding time and infiltration depth differ considering constant or different initial moisture content respectively in the soil slope. Then, best-fit curves of the infiltration rate, ponding time, and infiltration depth to the wetting front saturation were obtained with constant or different initial moisture contents. And the slope failure time is roughly uniform when subject to a rainfall intensity I5 mm/h.     

Slope seismic response monitoring on the aftershocks of the Wenchuan earthquake in the Mianzhu section

Previous investigations have shown that the seismic response of slopes during the Wenchuan earthquake was highly variable.The present study tries to give an answer to the question:Which are the main factors affecting the seismic response degree of slopes? With the support of the China Geological Survey Bureau,we set 3 monitoring sections in Jiulong slope,Mianzhu city,China with the aim to record the site response of the slope during the aftershocks of the Wenchuan earthquake.After the Wenchuan earthquake,which happened on 12 May 2008,30 aftershocks have been recorded in these monitoring points.We analyzed 11 records,with magnitudes ranging from ML = 4.6 to ML = 3.1.The amplification factors of the horizontal compound PGA and 3D compound PGA have been determined for the 3 points at different elevations on the slope.Results showed that the dynamic response of the slope on the earthquake was controlled by factors such as topography and the thickness of the Quaternary overburden.     

Influence factors on the seismic behavior and deformation modes of gravity retaining walls

This study investigated the influence factors on the seismic response and deformation modes of retaining walls using large-scale model shaking table tests. Experimental results showed that the distribution of peak seismic earth pressures along the height of a wall was a single peak value curve. The seismic earth pressures on a gravel soil retaining wall were larger than the pressures on the weathered granite and quartz retaining walls. Also, the peak seismic earth pressure increased with increases in the peak ground acceleration and the wall height. The measured seismic active earth pressures on a rock foundation retaining wall were larger than the calculated values, and the action position of resultant seismic pressure was higher than 0.33 H. In the soil foundation retaining wall, the measured seismic earth pressures were much smaller than the calculated values, while the action position was slightly higher than 0.33 H. The soil foundation retaining wall suffered base sliding and overturning under earthquake conditions, while overturning was the main failure mode for the rock foundation retaining walls.