Model Test Study on Seepage of Jointed Loess

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EXPERIMENTAL INVESTIGATIONS MODEL TEST STUDY ON SEEPAGE OF JOINTED LOESS UDC 624.131.6:624.131.23 Xiaojun Liu,1* Chuang Lin,2 Xiong Zhang,2 and Qing Kong1 1

Shaanxi Key Laboratory of Geotechnical and Underground Space Engineering, College of Civil Engineering, Xi'an University of Architecture and Technology, China, 2 Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, USA, *Corresponding author Email: [email protected].

This paper focuses on the influence of joints on seepage capacity of a soil mass, the water infiltration range, the area of the wet zone, and water content distributions. Tests were performed using a self-designed seepage device to determine the hydraulic conductivity of loess samples with natural joints. The test results indicate that joints greatly improve the seepage capacity of a soil mass; the depth and quantity of infiltration for the jointed sample are larger than those for the intact sample. The infiltration depths of the jointed sample are about 2.6 times that of intact specimens, and the measured areas of wet zones of the jointed sample are about 2.2 times that of an intact sample. Due to the existence of the joint, higher water content is observed at the joint location. In comparison, the water content distributions are relatively horizontal for the intact sample.

1. Introduction The loess joint is formed on the deposited loess masses under the effect of internal/external forces and neotectonic movements. The loess joints are often observed in the Loess Plateau and have a significant influence on the hydraulic characteristics of loess masses. The loess joint is the major depository and seepage paths for groundwater and is the major factor contributing to the failure of slopes and underground infrastructures in the loess region. In addition, the loess joint is also the major cause of soil erosion, landslide, and earth fissure [1]. Studying the seepage law of loess joints is of great important in evaluating the stability of slopes, tunnels, and highways in the loess region, controlling the geologic hazards such as soil erosions and landslides, and understanding the formation and development of the loess landforms. Joint, as a discontinuous surface within a loess mass, occupies a small volumetric proportion of the entire loess volume but has a very strong seepage capability and is the major flow path. Early studies focused on the hydraulic behavior of a single joint and simplified the seepage issue with a model of the water flow through the spacing between two parallel surfaces. The joint seepage follows the cubic law, meaning that the flow rate is proportional to the cube of the spacing (or opening) of a joint [2]. Therefore, the determination of the spacing is important in calculating the flow rate of joint seepage. Regarding the idealized parallel plate model, the spacing is defined as the distance between the two surfaces in the normal direction. Due to the complex surface formation, the spacing along the joint is no

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