## 1 Introduction  
Since rapid urbanisation has significantly impacted surrounding environments [1; 2; 3; 4; 5; 6; 7], environment-friendly construction material may ease the impacts despite many advanced technologies available for environmental protection [8; 9; 10; 11; 12]. The strength and microstructure properties of spent coffee grounds (CG) stabilised with rice husk ash (RHA) were investigated, which are organic wastes derived from agricultural products [13; 14; 15]. The results have shown that elevated temperature curing of up to 90 days was deemed the key to secure the strength development of CG-RHA geopolymers. [PERSON] et al. [16] performed an experimental work to assess the influence of the addition of barley straw on the physico-mechanical properties and the microstructure of a concrete consisting only of sand as the main aggregate. The addition of barley straw to the sand concrete greatly improved its thermo-physical properties. On the other hand, significant improvements have also been measured in other properties, such as flexural strength, lightness, deformability, ductility, and toughness, notwithstanding that a decrease in the mechanical strength and an increase in the dimensional variations have been recorded. To solve the problems raised, several treatments were tested for improving the properties of the optimal composition of the studied lightweight concrete, and the barley straws treated with hot water showed good improvements in the flexural strength of the composite. Additionally, the hot water treatment led to acceptable results in the thermal characteristics although the density of the composite did not increase much compared to the concrete containing the untreated barley straws [17]. Loess soils are aeolian deposits containing primarily silt-sized soil particles. The wind-blown depositional process of loess formation, however, promotes development of a relatively loose soil structure prone to changes in hydro-mechanical load conditions [18]. The silt particles are thus easily eroded by seepage or wind. [PERSON] et al. (2018) [19] investigated the effectiveness of the loess stabilisation using nanoclay both in the laboratory and in the field at the Gonbad dam site, considering various fractions of nanoclay ranging from 0.2% to 3% by mass. The field test section with 2% nanoclay showed the highest erosion resistance, while the laboratory specimens exhibited the same general trends in behaviour. The cost for the use of nanoclay, however, may be an issue as it is subjected to a limited budget, which also indicates restricted applicability. More and more natural hazards were associated with the loess soil in northwest of China because of its metastable structure and wetting-induced collapse deformation [20; 21; 22; 23; 24; 25]. Most natural hazards were initiated by soil erosion caused by expansion of agricultural activities resulting from rapid population growth in the region [26; 27]. This widespread engineering problem led to various scales of catastrophic slope sliding including shallow and deep landslides [28; 29]. Recently, plant roots were used for preventing soil erosion [30; 31; 32; 33] and stabilising slopes [34; 35; 36]. A similar idea was also applied to residential houses built with straw bale containing post-harvest waste (termed PHW hereafter), such as wheat straw and corn cob, and loess soil on the Chinese Loess Plateau. Field investigations have shown that the residential houses were utilised over decades under the effect of freeze-thaw cycles (Figure 1) [37]. The phenomena motivate this study to investigate how the addition of PHW to the slightly cemented loess improves its shear strength properties. The direct shear (DS) method has been deemed to be a quick and economic manner for estimating soil shear strength. Previous studies on direct shear have shown that shear boxes of different size may not lead to similar shear stress-horizontal displacement curve, but shear strength [38; 39; 40].