Here we study the effects of nano clay and polypropylene fiber on the unconfined compression and splitting properties of lime soil. Through a series of unconfined compressive strength (UCS) tests and splitting strength (STS) tests, the mechanical properties of lime soil (LS), nano clay modified lime soil (NLS), fiber modified lime soil (FLS), nano clay and fiber composite modified lime soil (NFLS) are analyzed, and the volume calculation formula of each phase in NFLS is deduced. Nano clay content α_n, porosity volume η and lime volume L_Vi as independent variables, and the prediction models of UCS and STS of NFLS were established. Furthermore, the microstructure of LS, NLS, FLS and NFLS was analyzed by scanning electron microscope (SEM). It can be concluded that (1) with the increase in nano clay content, the UCS and STS of LS and FLS gradually increase. With the increase in fiber content, the UCS of LS first increases and then decreases, while the UCS and STS of NLS and STS of LS increase with the increase in fiber content, and the optimal fiber content is 0.75%. (2) UCS and STS of NFLS and η/L_Vi meet the linear relationship. The empirical formulas of UCS and STS established in this paper have a prediction accuracy of less than 10%. The strength of NFLS can be predicted according to the dry density of the sample and the content of each component material. (3) Nano clay can fill the pores of LS and promote the pozzolanic reaction between lime and soil, while fiber mainly plays a reinforcing role in LS, so as to improve the UCS and STS of LS. In NFLS, nano clay can improve the interfacial properties between fiber and LS, so as to improve its UCS and STS. This study can provide a reference for the modification technology of lime soil.

Using polypropylene fiber (PPF) and nano clay modified lime treated soil (LS), the static and dynamic properties of fiber modified lime treated soil (FLS), nano clay modified lime treated soil (NLS), and fiber nano clay composite modified lime treated soil (NFLS) were studied. Through the unconfined compressive strength (UCS) test and dynamic triaxial test of FLS, NLS, and NFLS, the static and dynamic elastic modulus characteristics at 7 day curing age were explored, and the damage stress–strain model was established. The results show that: (1) Polypropylene fiber and nano clay can significantly enhance the mechanical properties of NFLS. Nano clay can promote the reaction between lime and soil to produce calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), thus improving the strength of NFLS, and UCS can be increased by up to 103%. Polypropylene fiber can enhance the ductility of NFLS and increase the residual ductility strength, and the residual strength can be increased by 827%. (2) Nano clay can enhance the static and dynamic elastic modulus of modified lime treated soil. The static and dynamic elastic modulus of NLS, FLS, and NFLS are linear with the change of polypropylene fiber and nano clay content. The static and dynamic elastic modulus of NLS, FLS, and NFLS are linear, exponential, and logarithmic, respectively. (3) The mesoscopic random damage model can characterize the stress–strain relationship of NFLS. Polypropylene fiber and nano clay can improve the ductility and strength of modified LS, and the composite addition of polypropylene fiber and nano clay can improve the ability of modified LS to resist damage.