A Simulation of Salt Transport in NaCl-Laden Soil Barrier to Control Subterranean Termites in an Earth Embankment

Abstract

Subterranean termite activity can increase the hydraulic conductivity and water infiltration of filling soil, and therefore affects the stability of an earth embankment and subsequent safety. As a physical barrier for sustainable termite management, NaCl-laden soil barrier (NLSB) is a promising alternative for subterranean termite control in earth embankments. This novel technology can prevent tunneling and penetration of subterranean termites into the interior of an embankment and has been widely employed for more than 20 years in Zhejiang Province, China. The efficacy and longevity of NLSB depend on the long-term presence of NaCl concentration in soil barriers. The aim of this study is to develop an understanding of water flow and salt transport in NLSB based on the two-dimensional Richards’ equation and convection dispersion equation using the HYDRUS software package. Conceptual and numerical models of NLSB are modeled using scenario analysis according to water level fluctuations, saturated hydraulic conductivity, and rainfall infiltration conditions. Furthermore, the center and spread variance of a solute mass over a 100-year period are quantified using moment analysis. As flood frequency, saturated hydraulic conductivity, and rainfall infiltration flux increase, salt desalination in NLSB significantly increases. When the rainfall infiltration flux is 1% of the annual average rainfall, the total amount of salt transport and leaching can increase by 55%. Moreover, these results facilitate better long-term sustainable management of existing sites and optimal design of future NLSBs.

Delving into Earth Dam Dynamics: Exploring the Impact of Inner Impervious Core and Toe Drain Arrangement on Seepage and Factor of Safety during Rapid Drawdown Scenarios

“…Examining the water mass flux data provided further insights into the behaviors of embankment under varying conditions [33]. During steady-state conditions, a discernible water mass flux of 0.022 kg/s/m 2 was observed at the embankment's upstream face, indicating the movement of water through the embankment.…”

Barrier Longevity of NaCl-Laden Soil against Subterranean Termites in an Earth Embankment

“…The overall NaCl migration in the earth embankment was rather limited, especially above the phreatic line. According to a field survey, O. formosanus (Shiraki) nests in the earth embankment are generally located 1.5 m below the crest and above the phreatic line [24]. The phreatic line is an imaginary line separating the saturated zone and unsaturated zone in an earth embankment.…”

“…With over 20 years of popularization and application in Zhejiang Province, China, NaCl-laden soil barriers (NLSBs) have proven to be a promising field technique to control subterranean termites in earth embankments [2,23,24]. NLSBs are an indigenous approach that utilizes NaCl as a mixing agent in cohesive soils, with the aim of preventing subterranean termite penetration and damage to earth embankments and dams.…”

“…Adequate NaCl concentration in the NLSB is a key method for the long-term prevention of subterranean termite infestations. The failure of NLSB-based treatments is often due to environmental factors, such as repeated water level cycles, saturated hydraulic conductivity of the soil matrix and rainfall infiltration [24].…”

“…Some solutes in an NLSB are transported over time by moving water through advection and dispersion. Variations in soil properties such as hydraulic conductivity, clay and organic matter content and water content can also influence the groundwater and salt transportation characteristics of NLSBs in embankments [24]. Numerous field and laboratory methods have been applied to characterize the transport of water and solutes in soil and to monitor the soil moisture content.…”