本文選題：農(nóng)田土壓實(shí)　切入點(diǎn)：循環(huán)荷載　出處：《河南工業(yè)大學(xué)》2017年碩士論文

【摘要】：近年來,隨著機(jī)械化耕作大規(guī)模普及,農(nóng)業(yè)機(jī)械在提高工作效率的同時(shí),也對(duì)土壤造成了破壞,特別是重型農(nóng)業(yè)機(jī)械的使用。農(nóng)機(jī)作業(yè)時(shí)輪胎對(duì)土壤壓實(shí)產(chǎn)生的影響并不局限于土壤耕作層,也會(huì)影響更深層次土壤的性質(zhì)。以往對(duì)農(nóng)田土壓實(shí)的研究主要集中在短暫,單次的壓實(shí)效果上,這與實(shí)際情況存在差異,本次研究將農(nóng)田土壓實(shí)過程看作是農(nóng)機(jī)長(zhǎng)期、多次碾壓的結(jié)果。普通的翻耕和免耕作并不能從根本上解決壓實(shí)造成的危害,因此需要從土力學(xué)角度對(duì)土壤應(yīng)力狀態(tài)進(jìn)行系統(tǒng)的研究,并找出應(yīng)對(duì)農(nóng)田土壓實(shí)問題的解決辦法。農(nóng)田淺部土層一般可以分為三個(gè)層次:表層土,心層土,底層土。其中表層土又存在土壤性質(zhì)差異較大的兩個(gè)分層:耕作層和犁底層。耕作層由于長(zhǎng)期受到犁鋤作用的影響,與耕作層性質(zhì)存在著明顯的差異,這將對(duì)農(nóng)田土壓實(shí)后土體應(yīng)力狀態(tài)的改變?cè)斐梢欢ǖ挠绊�。由于耕作層造成的壓�?shí)作用可以通過松土緩解,而犁底層、心土層處于地下較深位置,造成的壓實(shí)不易緩解,所以本文在研究耕作層土壤性質(zhì)改變時(shí),也將研究耕作層以下這兩個(gè)層面性狀的改變。在進(jìn)行模擬之前,對(duì)農(nóng)機(jī)作業(yè)時(shí)對(duì)土壤產(chǎn)生的循環(huán)荷載進(jìn)行了合理簡(jiǎn)化,并選取輪胎與土體接觸的橫斷面進(jìn)行研究。通過對(duì)FRIDA載荷分布模型的應(yīng)用,對(duì)農(nóng)機(jī)土壤碾壓時(shí)對(duì)土體表面產(chǎn)生荷載分布進(jìn)行了計(jì)算。并使用ABAQUS用戶自定義程序DLOAD對(duì)農(nóng)田土梯形循環(huán)荷載進(jìn)行了編程與調(diào)用。通過ABAQUS有限元軟件的使用,采用臨界狀態(tài)模型,對(duì)農(nóng)田土在大型農(nóng)業(yè)機(jī)械作業(yè)時(shí)產(chǎn)生的循環(huán)荷載下淺部土層的應(yīng)力狀態(tài)進(jìn)行模擬。結(jié)果顯示,單次壓實(shí)中,加載條件不同,壓實(shí)產(chǎn)生的結(jié)果在應(yīng)力狀態(tài)改變上存在差異,土壤中應(yīng)力的改變同時(shí)會(huì)使孔隙比發(fā)生變化。凹形荷載分布下應(yīng)力較均布荷載與凸型荷載應(yīng)力高。耕作層與犁底層應(yīng)力值大小隨著壓實(shí)次數(shù)的增加而相互接近;隨著輪胎寬度的增加,犁底層與心土層之間應(yīng)力最大值位置逐漸降低。初次碾壓時(shí),耕作層與犁底層孔隙比變化占25次總變化量的59%與47%。隨著壓實(shí)次數(shù)的增多,孔隙比的下降的速率逐漸減小。初次壓實(shí)造成的沉陷量占到了25次壓實(shí)引起的沉陷量的95%以上。多次壓實(shí)后土體性狀的改變較單次壓實(shí)在應(yīng)力狀態(tài)、孔隙比分布、沉陷量、均有提高,其中壓實(shí)效果隨壓實(shí)次數(shù)的增多而不明顯。最后對(duì)農(nóng)業(yè)機(jī)械荷載的控制,作業(yè)模式的選擇、輪胎組數(shù)及膨脹壓的選擇提出了優(yōu)化性建議。
[Abstract]:In recent years, along with the large-scale popularization of mechanized farming, agricultural machinery not only improves the working efficiency, but also causes damage to the soil, especially the use of heavy agricultural machinery.The effect of tire on soil compaction is not limited to the soil tillage layer, but also affects the properties of deeper soil.Previous researches on farmland soil compaction were mainly focused on the transient and single compaction effect, which was different from the actual situation. In this study, the process of farmland soil compaction was regarded as the result of long-term and multiple compaction of agricultural machinery.Ordinary tillage and no-tillage can not fundamentally solve the damage caused by compaction, so it is necessary to systematically study the stress state of soil from the perspective of soil mechanics, and to find out the solution to the problem of soil compaction in farmland.The shallow soil layer of farmland can be divided into three levels: surface soil, core soil and bottom soil.There are two layers in topsoil: ploughing layer and plow bottom layer.Due to the effect of ploughhoe on the cultivated layer for a long time, there are obvious differences between the cultivated layer and the ploughing layer, which will have a certain effect on the change of soil stress state after compaction of farmland soil.Because the compaction caused by tilling layer can be alleviated by loosening soil, and the core soil layer is in the deep underground position at the bottom of the plow, the compaction caused by the compaction is not easy to ease, so this paper studies the change of soil properties in tilling layer.Changes in the traits of the two levels below the tilling layer will also be studied.Before the simulation, the cyclic load generated by agricultural machinery was reasonably simplified, and the cross section of the contact between tire and soil was selected for study.Through the application of FRIDA load distribution model, the load distribution on soil surface during soil compaction of agricultural machinery was calculated.The trapezoidal cyclic load of farmland soil is programmed and called by ABAQUS user defined program DLOAD.Through the use of ABAQUS finite element software, the critical state model is used to simulate the stress state of shallow soil layer under cyclic load caused by large-scale agricultural machinery.The results show that under different loading conditions, the results of compaction are different in stress state change, and the change of stress in soil will make void ratio change at the same time.The stress under concave load distribution is higher than that under uniform load and convex load.The stress values of ploughing layer and plough bottom are close to each other with the increase of compaction times, and the position of maximum stress between plough bottom and core soil gradually decreases with the increase of tire width.During the first compaction, the change of the porosity ratio between the plow bottom and the tilling layer accounts for 59% and 47% of the total change of 25 times.With the increase of compaction times, the decreasing rate of void ratio decreases gradually.The settlement caused by initial compaction accounts for more than 95% of the subsidence caused by 25 compaction.The change of soil properties after multiple compaction is higher than that of single compaction in stress state, void ratio distribution and settlement, and the compaction effect is not obvious with the increase of compaction times.Finally, the optimization suggestions are put forward for the control of agricultural machinery load, the choice of working mode, the selection of tire number and expansion pressure.
【學(xué)位授予單位】：河南工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：S152.9

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