Due to weak physical properties of sand, chemical reinforcement methods are widely used to improve sand properties to meet the engineering requirements. However, most of the traditional additives cause environmental problems. Therefore, non-traditional additives such as liquid polymers, enzymes, ions, and lignin derivatives have been studied extensively. In this study, organic polymer is used as a soil stabilizer to reinforce the sand. To evaluate the effectiveness of the organic polymer as soil stabilizer, a series of unconfined compression strength (UCS) tests, direct shear tests, and tensile tests were carried out on reinforced sand with different polymer concentrations and dry densities of sand. The reinforcement mechanism was analysed with scanning electron microscopy (SEM) images. The results indicated that the polymer concentration and dry density of sand had significant effects on the strength characteristics of reinforced sand specimens. The unconfined compressive strength, cohesion, and tensile strength of specimens with the same dry density increased with the increasing polymer concentration. The polymer membranes—formed by the mixture of polymer and water—enwrap the sand particles and interlink them to form a stable structure. The efficiency of this stabilization changed with dry sand density.

Physical and chemical reinforcements are commonly used to improve sand properties for engineering requirements. Many researchers have concluded that composite reinforcement can greatly improve sand property strength. In this paper, polyurethane organic polymer (PU) and polypropylene fiber (PF) were used to reinforce sand. It is found that composite reinforcement has great effects on tensile strength. A series of direct tensile tests were conducted to demonstrate this reinforcement and to investigate the effects of PF content, PU content, dry density, and curing time. Additionally, the reinforcement mechanism was analyzed by scanning electron microscope images. The tensile strength increases with curing time until it reaches a plateau. The composite reinforcement improves the tensile strength exponentially with the increase of PF and PU contents. For the effect due to dry density, the tensile strength first increased and then decreased with the peak at approximately 1.55 g/cm³. Through the interaction force among fibers and sand particles and the bonding force of polymer among sand particles, tensile strength of reinforced sand is greatly improved.

Soil stabilizer can enhance the soil properties, which can improve ecological environmental problems such as soil erosion and slope instability. This study investigates the water-related and mechanical properties of soil stabilization using a polymer soil stabilizer solution synthesized from vinyl acetate polymer. The water properties test, mechanical properties test, durability test and seed growth test were carried out in the laboratory. Also, the effect of vinyl acetate polymer was verified by field tests. The results revealed that vinyl acetate polymer can enhance the water-retaining property, anti-erosion resistance, strength property and durability of soil, all of which increase with the increase of polymer concentration. At the same time, the polymer also has a certain promoting effect on vegetation growth. In addition, field tests proved that vinyl acetate polymer has good effects on soil engineering. These results could be applied as a reference for vinyl acetate polymer-improved soil engineering.

The significant criterion for evaluating the merits of a new type of high molecular polymer lies in its engineering properties and eco-friendliness. The focus of this study was to determine the effects of preparation conditions on the viscosity of the polyvinyl acetate (PVAc) emulsion, including reaction temperature (T_r), initiator concentration (C_APS), monomer concentration (C_VA), pH value, and degree of dilution (D_di). Based on the results of a series of laboratory tests, the range of viscosity value of PVAc was obtained under different conditions, and one set of viscosity values out of these was applied to soil reinforcement tests. Meanwhile, based on the test results, the engineering properties of PVAc solution were evaluated using strength and moisture retention tests, and the reinforcement mechanism was analyzed using scanning electron microscopy (SEM). In addition, it was proven through a vegetation growth test that the PVAc was eco-friendly.

There has been a growing interest in polymer applied for soil reinforcement in recent years. However, there little attention has been paid to the effects of polymer on soil cracking behavior, and cracks significantly change soil strength and hydraulic properties and alter reinforcement effectiveness. This study investigated the desiccation cracking behavior of polyurethane (PU) and polyacrylamide (PAM) admixed clayey soils with different polymer concentrations by performing desiccation cracking tests. Scanning electron microscope (SEM) observation was also carried out to obtain the internal structure of these soils. The results show that PU and PAM addition both prolonged the initial evaporation stage, accelerated later evaporation processes, and the effects were related to polymer concentration. Final cracks morphology analyses show that PAM addition slightly reduced the cracking and crushing degree and kept the soil relatively intact, while PU addition slightly enhanced the cracking and crushing degree of soil. In addition, PU and PAM addition both increased the width and length of cracks. The scanning electron microscopy (SEM) analyses show that the effects of polymer on soil evaporation and cracking could be concluded as: (1) storing water in voids, (2) influencing water immigration channel, (3) providing space for soil shrinkage, and (4) enhancing the connection between aggregates, which did not fully come into play because of the existence of hydrogel form. These achievements provide a certain basis for the research of desiccation cracking behavior of polymer treated soil and make significant sense for the safe and effective running of related projects.

As renewable and environment-friendly materials, coir and sisal natural fibers can be used in soil reinforcement with minimum cost and other benefits. In this study, we focused on their improvements of unconfined compressive properties of polymer treated sand. In total, 36 groups of unconfined compressive strength tests, combined with X-ray diffraction and scanning electron microscope investigations were performed. We had studied the effects of polymer and fiber contents, and fiber types on the reinforcement effectiveness. The results showed that both coir and sisal fiber can improve the mechanical properties and microstructure of treated sand. In terms of strength properties, sisal fiber inclusion was better than coir fiber, while both have a similar reinforcement benefit on soil ductile behaviors. The strength and compressive energy increased with an increment in polymer and fiber content. The reinforced sand can have up to 1 MPa compressive strength and 140 kPa compressive energy for coir fiber inclusion, while 1.2 MPa and 170 kPa, respectively, for sisal fiber. The axial stress-strain characteristics and failure patterns were also improved, and the brittle index decreased toward zero, which suggests an increasing ductile. The polymer membrane enwrapping and bonding sand grains, and the network structure built by fiber crossing and overlapping among sand grains, as well as the interfacial attachment conferred by polymer between sand grains and fiber, all contributed to the reinforcement of treated sand.