# Strain Rate Effect on Artificially Cemented Clay with Fully Developed and Developing Structure
## 1 Introduction  
Land reclamation projects have been increasingly developed in China for transportation infrastructure [1, 2], and the main works are ground treatment with natural structured clay (e.g., deep cement mixing [3, 4, 5]), backfill works, and imposition of surcharge loads on the treated clay. Consequently, the construction rate is a pivotal determinant influencing the deformation characteristics of reclaimed land featuring structured clay substrates [3, 6]. It is critical to systematically investigate the rate-dependent behaviour and strength properties of both structured and destructed clays in the context of engineering design and analysis. The rate effects on various structured soils have been investigated comprehensively through a series of laboratory experiments [7, 8, 9] and numerical simulations [10, 11], however, the effect of shear rates on clay with varying structural states remains controversial [12, 13, 14]. Especially, the relationship between soil structure and rate sensitivity is still not fully understood. The effect of strain rate on undrained shear strengthwas previously believed to result from a higher excess pore pressure. However, this explanation is only applicable to normally consolidated or less-structured soils and is only one of the contributing factors. [PERSON] et al. [15] investigated the diverse pore pressure responses to strain rate in intact deep marine clays and their constitutive state. For the intact specimen, a higher strain rate caused a higher pore pressure, while a contrary trend was found in the reconstituted specimen. In contrast, [PERSON] et al. [16] suggested that in drained conditions, any rate effect arises from the resistance of pore water to escape from the soil element, while [PERSON] et al. [17] concluded from numerical studies that rate sensitivity is influenced not only by the viscous nature of the soil but also by strain localisation and migration of the pore water within the specimen. [PERSON] et al. [18] investigated the strain rate effects on natural stiff clay with adhesive-bonded structures. Compared to the reconstituted clay, the rate dependency was higher due to the interparticle bonding. However, the evolution of excess pore pressure was independent of the strain rate in the undrained triaxial shearing process. Extensive research has been conducted on the rate effects on residual strength (with a well-formed shear plane) using a ring shear apparatus [19; 20; 21]. The causes of positive rate effects have been attributed to factors such as inherent clay viscosity [22], turbulent shear patterns [23], and particle breakage [24]. Conversely, the negative rate effect can be attributed to the healing stage [25], bond restoration among clay particles [26], and delayed dissipation of excess pore water pressure [27]. The effects of soil structure on the viscous response are not easily defined in natural clays [14; 28], and there are still gaps in the understanding of the rate sensitivity of simpler-structured clays, such as cemented clays [29; 30]. [PERSON] et al. [31] revealed that the calcium silicate hydrates (C-S-H) and calcium aluminate hydrates (C-A-H) were the major reaction product (bond structures) for the mixture of cement and kaolinite clay, and the released oxide colloids and the associated secondary products accumulate at the interface between the primary cementitious paste and clay particles, forming a soft porous phase. This paper aims to investigate the effect of bond structure on the time-dependent behaviour of artificially cemented clays with different curing times. This material serves as a suitable model for simulating natural cemented soil, allowing for controlled experiments to obtain repeatable and reliable results, leading to the establishment of a unified framework. Additionally, this research has practical applications in predicting the behaviour of soil in the field following improvement measures like cement grouting.