Analogue modelling of pre-failure strain accumulation for landslide failure prediction

山体滑坡是最具破坏性的地质灾害之一，在1990年至2006年期间造成了100,000多人死亡。现在有相当多的证据表明，滑坡的影响正在增加。这些影响集中在发展中国家的山区，那里每年的损失可能是GDP的23%。为了对滑坡灾害进行全面评估，需要了解滑坡的可能位置、类型、大小、速度和时间，但最后一个问题仍然知之甚少；2006年2月17日菲律宾莱特的山体滑坡很好地说明了这个问题。这场地震造成1100多人死亡，发生在之前被认定为潜在不稳定的斜坡上。在山体滑坡发生之前，发生了10天的强降雨，在此期间，村子上方的斜坡出现了裂缝。在五天的降雨后，该镇被疏散，但在五天后雨停后，该镇被重新占领。灾难性的是，不久之后发生了山体滑坡。发生大规模山体滑坡的可能性是已知的，观察到了先兆迹象，但对山体滑坡的时机缺乏了解，导致了灾难。在观察了不稳定路堤上的运动或应变后，日本工程师齐藤开发了一种了解失败时机的方法。他观察到，当破坏前变形速度的倒数与时间成反比时，观察到一条直线(Saito，1965)，称为“Saito线性”。这意味着，可以将线性趋势外推到速度达到无穷大的点，从而预测失败。最近，另一些人注意到滑坡中特有的运动模式，称为“三相蠕变”Varnes(1978)，其中一个崩塌的斜坡表现出三个不同的运动周期。最近，为了了解控制这种模式的破坏机制，人们使用了对坍塌斜坡的监测和新颖的岩土测试。这个模型在实际边坡中的应用仍然存在问题，特别是关于边坡几何形状对破坏演化的影响，以及从真实世界监测数据解释应变状态的复杂性。利用一种名为垂直重力加速器的新技术，研究了边坡几何形状和强度变化对破坏前变形机制的影响。在该模型中，由具有弹脆塑性性质的材料形成的斜坡在尺度上与天然斜坡材料的行为相似，通过落在液压冲击器上施加与重力方向相同的快速加速度来承受循环载荷。因此，使用0.4米尺度的模拟来模拟2,000米的斜坡。在一系列模型构型中，将测试坡角、坡长、曲率和强度的影响。变形将使用高精度3D结构光扫描仪进行监测，该扫描仪测量表面变形。在最后一组实验中，将复制在三个仪器良好的真实世界山体滑坡中作用的过程。这些将是英国的塞尔本路基稳定性试验，日本的大田村滑坡，以及马来西亚的波斯塞利姆滑坡。利用3D打印技术对每个边坡进行重建，将破坏模拟和变形结果与监测数据进行对比，以建立对破坏机理和演化的控制。然后将这些数据与从文献中整理的新的滑坡运动数据库进行比较，以揭示滑坡的机制和在大量故障中的运动。确定边坡形态和材料强度对滑坡机制的控制以及由此产生的破坏前地表变形将有助于更好地理解滑坡中观测到的变形趋势、滑坡的触发和运动机制，并将对Saito方法在边坡破坏预测中的应用具有一定的指导意义。

Landslides are one of the most destructive geological hazards, resulting in excess of 100,000 fatalities between 1990 and 2006. There is now considerable evidence that landslide impact is increasing. These effects are focussed upon mountainous areas in developing countries, where losses can be 2 / 3% of GDP per year. To undertake a full assessment of landslide hazard, an understanding of the likely location, style, size, speed and timing of the failure is needed, but the last of these remains poorly understood; a problem well illustrated by the 17th February '06 landslide at Leyte, Philippines. This event killed more than 1,100 people and occurred on slopes previously identified as potentially unstable. Prior to the landslide ten days of intense rainfall occurred, a period during which cracks on the slopes above the village were noted. After five days of rainfall the town was evacuated, but after the cessation of rain five days later, the town was re-occupied. Disastrously, the landslide occurred shortly after. The potential for a large landslide was known, precursory signs observed, but a poor understanding of landslide timing, resulted in catastrophe. One approach to understand failure timing has been developed after observations of movements, or strains, on unstable embankments by Japanese engineer, Saito. He observed that when the inverse of velocity of deformation prior to failure was plotted against time, a straight line was observed (Saito, 1965), termed 'Saito linearity'. The implication was that the linear trend could be extrapolated to a point at which velocity reached infinity, predicting of failure. More recently, others noted characteristic movement patterns in landslides, termed 'three phase creep' Varnes (1978), in which a failing slope exhibits three distinct periods of movement. Recently attempts to understand the failure mechanisms which control this pattern have used monitoring of failing slopes and novel geotechnical testing. Questions remain surrounding the application of this model to real slopes particularly with respect to the influence of slope geometry on the evolution of failure, and the complexity of interpreting strain state from real-world monitoring data. Research is proposed to observe the influence of variations in slope geometry and strength on the mechanisms of pre-failure deformation, using a newly developed technique named a vertical 'gravity accelerator' table. In this model a slope, formed from a material with elasto-brittle-plastic properties, that at scale behaves comparably to natural slope materials, is subject to cyclic-loading by dropping onto a hydraulic ram imposing a rapid acceleration in the same direction as gravity. Hence, a 2,000 m slope is simulated using a 0.4 m scale analogue. In a series of model configurations the influence of slope angle, slope length, curvature and strength will be tested. Deformation will be monitored using a high-precision 3D structured light scanner, which measures the surface deformation. In a final set of experiments the processes acting within three well-instrumented real-world landslides will be replicated. These will be the Selbourne cutting stability experiment, UK, the Ota-Mura Landslide, Japan, and the Pos Selim Landslide, Malaysia. Using 3D printing each slope will be recreated, failure simulated and deformation results compared to monitoring data, to establish the controls on the mechanisms and evolution of failure. These data will then be compared to a new database of landslide movement collated from the literature to exmaine landslide mechanisms and movement in a large number of failures. Determining the controls of slope form and material strength on landslide mechanisms and resulting pre-failure surface deformation will give enhanced understanding of deformation trends observed in landslides, mechanisms for landslide triggering and ovement, and will have implications for the use of Saito methods for slope failure prediction.