# Study on Filling Material Strength and Dam Failure Characteristics of Loess Dam
## 1 Introduction  
Loess has a wide distribution range and covers a large area in China (Zheng 2019) [1]. [PERSON] (1965) completed the distribution map of loess in China and put forward the \"new wind formation theory\" of loess, which provides a profound theoretical basis for subsequent studies by scholars [2]. In some engineering structures, especially in the Loess Plateau region of China, local materials are taken into account under the consideration of economic cost and other factors, which greatly reduces engineering costs. Loess accumulation dams and siltation dams are built in northwestern China for soil and water conservation. During the service of geotechnical buildings, the shear strength of filling materials is relatively high in their natural state. When rain falls or groundwater flows, the soil inside is soaked by water; therefore, this causes many geological disasters [3]. The change in water content after wetting causes structural changes in the soil [4, 5], which change the matric suction and stress-strain properties of the soil [6, 7]. Loess underwent volume and shear deformations as a result of soaking, which indicated compression and shearing behavior [8]. The linear form of the Mohr-Coulomb strength theory can accurately reflect the failure behavior ofthe loess along a wetting path, which is dependent on the stress level, the loss degree of matric suction, as well as the hydro-mechanical path [9]. Based on this information, the stress level threshold value was determined, which may be used for assessing whether the loess will fail due to moisture. To investigate the degree of matric suction loss from stable conditions to malfunction, the threshold value of matric suction at failure was established. The volumetric water content is a typical indicator of the degree of humidification. Under various volumetric water contents, the equivalent matric suction can be derived in accordance with the soil-water characteristic curve. Experiments can be used to establish the relationship between soil strength and deformation parameters and matric suction [10]. The effective stress parameter can be determined using the CU (consolidated undrained) test to establish the absorption stress curve, which is straightforward to implement in reality, as the measurement of the matric suction is challenging and time consuming [11]. The Duncan-Zhang model is frequently used to investigate the stress-strain properties of unsaturated loess. Many academics examine the characteristics of unsaturated loess and alter the formula, nonetheless, due to its inherent limits [12; 13]. The relationship between shear rate, confining pressure, dry density, and the shear strength index of soil has a strong regularity when the stress-strain characteristics of the soil are obtained through testing [14; 15; 16; 17], and the equation with the good fitting relationship can be established to calculate the strength of multi-dimensional loess. Additionally, as suction increases, the internal friction angle lowers and the shear strength rises, both of which are non-linear changes [18; 19; 20]. Researchers have simulated the accumulation dam's overflow failure process in order to analyze the seepage failure of the dam. [PERSON] (2021) studied the stability of the dam reinforced by a geogrid and geotextiles through a model test of a tailings dam reinforced in the design site, primarily analyzing the change in pore pressure and pressure inside the dam under the action of water pressure, and obtaining the reinforcing mechanism of the two materials [21]. The general design of the dam body and the physical characteristics of dam filling are both factors in the dam's collapse mechanism. A test method created by [PERSON] (2021) can be used to describe the stability of extensive cemented fillings. By gluing large-sized waste rock fragments, the filling accumulation body can be mimicked. In order to successfully replicate the failure of the mine filling body, the direct shear test and three-point bending test were performed on the sample.