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Study on ecological protection technology of rice straw reinforced cement soil hollow block slope

Concrete block additive 2021-07-29 14:34 59
0 Introduction As a form of ecological protection, the

concrete hollow grass planting block has good rain erosion resistance and can provide an excellent growth environment for plants. Zhang Hongli [1] took the vegetation growing for 2 years under different protection types as the research object. The results show that the protection effect of hexagonal hollow brick is the best, and its vegetation coverage is significantly higher than that of the slope under the protection of geocell and lattice beam. Xing Zhenxian [2] and others passed the field test of hexagonal brick slope protection. The research results show that the precast concrete hexagonal brick slope protection has good anti scouring stability and strong soil consolidation capacity. Chen Zhiqiang [3] and others monitored the change of soil moisture under four typical slope protection measures along Shen Fu expressway, and studied the change law of soil moisture under each measure. The test results show that the slope protection form of hexagonal hollow brick combined with herbaceous vegetation has better water conservation effect. The above research results show that using concrete grass planting hollow blocks to protect the slope [4-5] can effectively prevent water and soil loss and promote the rapid growth of slope vegetation. However, this method has some defects in engineering application, such as high cost, large consumption of cement and sand, and high transportation cost, which affects the popularization and application of this method. Therefore, it is necessary to study a grass planting hollow block with good protection effect, low economic cost and less resource consumption

in view of the concept of waste utilization and sustainable development [6-10], a grass planting hollow block made of rice straw, waste soil after engineering excavation and a small amount of cement is proposed in this study, which can give full play to the advantages of concrete hollow block against strong rainfall scouring, effectively prevent water and soil loss on slope and promote the rapid growth of slope vegetation, It can also reduce the consumption of natural resources and reduce the project cost

the key problem whether the hollow block made of rice straw reinforced cement soil can be applied to the slope is that its mechanical properties and durability can not meet the requirements of practical engineering application. Therefore, in this study, the unconfined compressive strength test of rice straw reinforced cement soil and its hollow block is used to study its physical and mechanical properties, durability and change law, and the erosion resistance effect of rice straw reinforced cement soil hollow block is verified through indoor heavy rainfall erosion test and field test, It provides a basis for the application of rice straw reinforced cement soil hollow block in slope protection

1 test materials

the soil used in this test is granite residual gravelly cohesive soil after excavation of a slope in Ningxiang section of louyi Expressway in Hunan Province. The main mineral components of the soil sample are mica, kaolinite, potassium feldspar and quartz particles. The basic physical parameters of soil samples are shown in Table 1 and figure 1

Table 1 basic parameters of test soil sample Tab. 1 Basic parameters of test soil sample index Optimum moisture content /% Maximum dry density / (g · proportion Plastic limit /% Liquid limit /% numerical value sixteen point one one point seven nine two point seven three twenty-two point four three thirty-nine point two six Table options Fig. 1 particle grading curve of soil sample Fig. 1 Particle gradation curve of soil sample Graph options

the cement used in this test is ordinary portland cement P.O 42.5 produced by a company in Hunan Province. See Table 2 for the basic performance indexes of cement

Table 2 basic parameters of cement Tab. 2 Basic parameters of cement model Dry density / (g · Fineness /% Initial setting time / min Final setting time / min Compressive strength / MPa P.O.42.5 three point one one point one one hundred and twenty two hundred and twenty forty-three point three Table options The rice straw used in the

test is divided into four grades according to its diameter: thick straw, medium thick straw, medium thin straw and thin straw. The diameter range of thick straw is 4.3 ~ 5.8 mm, medium thick straw is 3.4 ~ 4.2 mm, medium thin straw is 2.2 ~ 3.3 mm and thin straw is 1.4 ~ 2.1 mm, as shown in Figure 2

Fig. 2 classification of rice straw Fig. 2 Classification of rice straw Graph options 2 test method 2.1 strength test of rice straw reinforced cement soil hollow block

first mix the air dried granite residual soil with cement, then add water for mixing, and then add rice straw for mixing. Finally, put the mixture into the standard mortar test mold three times, and scrape the interface of each layer. Based on the research results of fiber reinforced soil [11-12], it is preliminarily determined that the mass reinforcement rate of rice straw is 0.1%, 0.2%, 0.3%, 0.4% and 0.5%; The reinforcement length is 5, 10, 15, 20 mm; The water content of the sample without reinforcement in the water tank is 16%, and then the compressive strength of the sample without reinforcement in the water tank is tested. The overall test process shall be carried out according to the steps specified in the code for design of cement soil mix proportion (jgjt 233-2011)

based on several better rice straw mixing ratios and lengths obtained from the above tests, rice straw reinforced cement soil materials were prepared by adding different cement contents, and the loading size was 20 cm × 20 cm × Fig. 3 rice straw reinforced cement soil hollow block Fig. 3 Rice straw reinforced cement soil hollow block Graph options 2.2 block strength change test under indoor dry wet cycle and outdoor natural environment

in practical engineering, concrete grass planting hollow blocks often encounter dry and wet cycle environment. In the south, due to the concentrated rainfall, high temperature and large temperature difference in summer, the hollow blocks almost inevitably suffer from the scouring of rainstorm and the repeated action of dry wet cycle. Based on this situation, the strength change law of rice straw reinforced cement soil hollow block under dry wet cycle [14] is studied to provide a certain theoretical basis and reference for the engineering application of rice straw reinforced cement soil hollow block

indoor dry wet cycle strength test: it is defined as the immersion saturation process when the test piece is soaked in rain for 12 hours, the dehydration drying process when the test piece is dried in 105 ℃ The mechanical properties of

block will gradually weaken with the increase of time under the action of complex factors such as atmospheric and natural environment. In order to investigate the influence of outdoor natural environmental conditions on the strength development law of rice straw reinforced cement soil hollow block, the block cured for 28 days under indoor conditions was placed on the outdoor exposed slope in Changsha, and the strength change of the block in atmospheric environment was measured every other month

2.3 indoor simulated rainfall scouring experiment

in order to quantitatively compare the anti scouring performance of rice straw reinforced cement soil hollow block slope protection, the simulation test of heavy rainfall scouring is carried out by using rice straw reinforced cement soil hollow block slope protection, three-dimensional geonet slope protection and granite residual soil slope without slope protection [15-18]. The slope ratio is 1:1 and 1:1.75, the rainfall intensity is 6 mm / min, and the scouring time is 1 h. The erosion water sample shall be collected every 5 min after the test, and the sediment quality shall be measured by drying method (see Fig. 4)

Fig. 4 scour test device Fig. 4 Scouring test device Graph options 2.4 grass planting test of field hollow block

in order to verify the vegetation growth effect of rice straw reinforced cement soil grass planting hollow block in atmospheric environment, three-dimensional geonet, natural bare slope and rice straw reinforced cement soil hollow block are respectively used for slope protection on the field slope. After the same grass species ryegrass is sown, the plant growth is regularly observed and recorded, By comparing and analyzing the plant growth height and coverage of different protection forms, the quality of protection forms is evaluated

3 Analysis of test results 3.1 analysis of unconfined compressive strength and influencing factors test results 3.1.1 effect of rice straw content on unconfined compressive strength

Figure 5 shows the change curve of unconfined compressive strength of rice straw reinforced cement soil with rice straw reinforcement rate at different curing ages. It can be seen from Figure 6 that with the increase of the content of rice straw, the unconfined compressive strength increases first and then decreases. When the content of rice straw changes between 0.1% ~ 0.3%, the unconfined compressive strength increases obviously, which is mainly due to the greater mechanical bite force and friction force between rice straw and cement soil interface with the increase of rice straw content and the setting and hardening of cement soil. When there is an external force, through the reinforced soil friction and the tensile properties of rice straw, the development of micro cracks is restrained and the vertical and transverse deformation of cement soil is restrained, so as to improve the integrity and compressive strength of reinforced soil. However, when the content of rice straw exceeded 0.3%, the strength began to decrease gradually. On the one hand, too much rice straw will increase the pores in the soil, reduce the compactness of the soil, and weaken the reinforcement effect of rice straw; On the other hand, too much rice straw is easy to overlap in the soil, weakening the connection between cement soil particles, which will lead to the decline of its compressive strength

Fig. 5 Variation of unconfined compressive strength of reinforced cement soil with the content of rice straw Fig. 5 Unconfined compressive strength of reinforced cement soil varying with rice straw content
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