Study on influence factors of cement-stabilized soil compressive strength

The cement dry jet mixing method has been used to reinforce soft cohesive ground to increase the strength of soft cohesive ground and to decrease its deformation. The study briefly introduces the curing mechanism of cement-soil,presents the factors of influencing on compressive strength,mainly analyses the factors including cement mixing ratio,cement strength grade,curing age,moisture content and soil texture and puts forward some rational proposals at last.

Resilient modulus prediction of soft low-plasticity Piedmont residual soil using dynamic cone penetrometer

Dynamic cone penetrometer（DCP） has been used for decades to estimate the shear strength and stiffness properties of the subgrade soils. There are several empirical correlations in the literature to predict the resilient modulus values at only a specific stress state from DCP data, corresponding to the predefined thicknesses of pavement layers（a 50 mm asphalt wearing course, a 100 mm asphalt binder course and a200 mm aggregate base course）. In this study, field-measured DCP data were utilized to estimate the resilient modulus of low-plasticity subgrade Piedmont residual soil. Piedmont residual soils are in-place weathered soils from igneous and metamorphic rocks, as opposed to transported or compacted soils.Hence the existing empirical correlations might not be applicable for these soils. An experimental program was conducted incorporating field DCP and laboratory resilient modulus tests on "undisturbed" soil specimens. The DCP tests were carried out at various locations in four test sections to evaluate subgrade stiffness variation laterally and with depth. Laboratory resilient modulus test results were analyzed in the context of the mechanistic-empirical pavement design guide（MEPDG） recommended universal constitutive model. A new approach for predicting the resilient modulus from DCP by estimating MEPDG constitutive model coefficients（k;,k;and k;） was developed through statistical analyses. The new model is capable of not only taking into account the in situ soil condition on the basis of field measurements,but also representing the resilient modulus at any stress state which addresses a limitation with existing empirical DCP models and its applicability for a specific case. Validation of the model is demonstrated by using data that were not used for model development, as well as data reported in the literature.

Resilient Modulus of Compacted Lateritic Soils from Senegal at OPM Conditions

Repeated load triaxial tests were performed on five compacted gravel lateritic soils collected from different locations in Senegal: Sébikotane, Dougar, Pa Lo, Mont-Rolland and Ngoundiane. The study revealed that resilient modulus decreases with the increase of the bulk and deviatoric stress in constant confining pressure. In addition, resilient modulus increases with the percentage of cement for appreciably equal contents of moisture. This effect tends to stop for higher stress. Besides, correlations were made with some models of resilient modulus such as the Uzan-Witczack model (Witczack and Uzan, 1988 [1]) and the National Highway Research Program (NCHRP) model (2004 [2]). The study confirms that both models give very good results with the best correlations being obtained with the Uzan-Witczack model.

Soil Subgrade’s Characterization and Classification of Thies (Senegal, West Africa) on a Radius of 2.5 Kilometers along Five Roads

This article explains the results of a study conducted on the characterizations of subgrade soils in the region of Thies. The road platforms are mainly composed of a background soil, which is generally overlapped by a surface layer that plays two roles. Firstly, it protects the soil structure, ensures the leveling, and facilitates the movement of vehicles. Secondly, it brings harmony in the mechanistic characteristics of the materials that compose the soil while improving the long-term life force. The methodology consisted in taking samples of subgrade soil along the roads all over the region of Thies in a 5 km diameter span. The identification tests allowed the Thies-Tivaoune, Thies-Khombole and Thies-Noto axes are characterized by tight sands, poorly graded size. While Thies Pout-axis is characteristic of severe solid particle size and spread well graded and serious to spread and well graded particle size. Finally the Thies-Montrolland axis is characterized by severe to very tight particle size and graduated to spread and serious and well graded particle size. The specific gravity values found Proctor test shows the presence of sand, sandy laterite and laterite. In the target area, polished soils of the A-3 type according to the AASHTO classification system are the most represented with 60%, followed by the A-2-6 type 25%, and the A-2-4 type with 9%, which are typical of gravel, clay, and silty sands. Soils of the A-1-b type (2%) typical of roc fragments, sands and clay are also represented. Polished sands of the A-3 type have a better efficiency on road infrastructures than other types of soil listed above. Finally, we’ve also noted the presence of soils of the A-2-7 and A-4 types with the low percentage of 2%. Subgrade soils of class S4 are the most represented with 58%, followed by those of class S5 with 42%. Samples of the Thies-Montrolland road have a claylike plasticity (CL or CH group), while those of the Thies-Pout road belong to the ML or OL and CL or OL groups with a tendency mostly directed to the CL or OL group. All these results confirm the very nature of soils on the two roads and put the light on the presence of lateritic materials with certain plasticity.

The Stabilizing Granular Soil with Slow-setting and Slight-expansive Cement

According to the characteristics of granular soil,the technological requirements of the special-purpose cement for stabilizing granular soil are put forward to meet the demands of implementation of highway base engineering.A kind of slow-setting and slight-expansive cement is developed by the cross experiment method in slag-clinker-gypsum-alkaline system,the final setting time of the cement can be prolonged to 8h,and it has properties of low dry shrinkage,high flexural strength and good crack resistance.The strength of granular soil stabilized by the cement is increased by 20% compared with that stabilized by Chinese 425-Grade slag cement.

Grain Size Influence on the Compaction Aptitude and the Bearing Strength of the Gravel Lateritic Soils

This study is carried out to appreciate the coarse elements influence of the gravel lateritic soils on the pavement behavior. The material involves not only the 0/20 mm granular particles considered in the specifications and on the laboratory tests, but also all of the material that is actually used in the construction sites. Geotechnical characterization was leaned on five differentiated granular classes of 0/20;0/25;0/31.5;0/40 and 0/63 mm diameters. The sample of 0/40 mm gets the best compaction aptitude, while that of 0/31.5 mm reaches the greatest bearing strength and a good Optimum Moisture Content. According to the requirements and its bearing strengths, the material is usable up to subbase layer and its behavior depends on the grain size.

A Practical Model for Deformation Prediction of Highway Subgrade Soils

This paper reports a practical constitutive relation for highway subgrade soils. The proposed model is derived based on the laboratory repeated load testing of four subgrade soils. Statistical parameters generally used in the power model of subgrade permanent strain are expanded into material constants with engineering significance. The constitutional relation reported in this paper can be used in the mechanistic based pavement design of highway flexible pavements and railroad tracks.

Development of a New Dynamic Lightweight Penetrometer for the Determination of Mechanical Properties of Fine-Grained Soils

Dynamic cone penetrometer is mainly used as an in situ device and laboratory application, in a mould, has rarely been reported due to the confining effect. In this study, a dynamic lightweight cone penetrometer that can be used in a CBR （California bearing ratio） mould in the laboratory as well as in the field, with similar results, was developed. The results show that the influence of the mould confinement can be eliminated when the hammer mass is 2.25 kg. A strong correlation was found between CBR values and the new dynamic lightweight penetrometer index, for six fine-grained soil samples, with different moisture contents, used in this study.

Using Sorghum Stalk as a Partial Replacement of Lime in the Stabilization of Red Clay Soil for Road Sub-Grade Construction

This research aimed at testing the viability of using Sorghum Stalk Ash (SSA) as a partial replacement of lime in the stabilization of red clay soils for road subgrade construction. Red clay soils have been identified as highly expansive soils, which are affected by both climatic conditions and loading patterns. The consideration of both traffic loading patterns and climatic effects on these soils has been taken into account. A penetration test of 2.5 mm has been used on both pure red soils and stabilized soils at 10% and 15% partial replacement of lime with SSA and showed an improvement in the CBR of stabilized red clay soils up to 11.6%. Again, the PI of stabilized soils at 15% partial replacement of lime reduced up to 11.2%. The results obtained on both CBR and PI of these red clay soils are within the recommended values for the effective subgrade required for laying both permanent and flexible pavements. As a result, a recommendation of making use of SSA to lower the quantities of lime and its costs used in the stabilization of highly expansive soils have been tested through this research. However, further research on a more percentage partial replacement of lime to improve the PI of these soils to below 10% while keeping the CBR levels within the road construction regulations is welcomed.

公路土质路基振动压实特性数值模拟

采用ABAQUS有限元软件模拟压路机振动压实过程,研究不同碾压方式、碾压组合、松铺厚度D和压路机碾压速度V下路基土的动力响应与压实度变化规律。结果表明:不同碾压方式下最大竖向应力(S_(33))_(max)和竖向位移(U_(3))_(max)大小顺序为强振>弱振>静压,(S_(33))_(max)随碾压遍数N增加保持不变,而(U_(3))_(max)和压实度K在N=1时急剧增加;碾压组合对不同碾压方式下路基土体积应力p影响极小,碾压组合中碾压方式排列次序对路基土竖向位移U_(3)变化影响较大;组合1下不同松铺厚度的路基土竖向位移百分比P、压实度K值均大于碾压组合2,不同组合下D=40 cm时P、K值均为最大;在确定的松铺厚度下,碾压组合与碾压速度对P、K具有显著影响,碾压速度较小时P、K更大,但组合1条件下P、K关于碾压速度的差异较组合2显著。

乡村水泥路面拼接窄长加宽板受力特性分析

福建省农村公路水泥路面多为4.5m×5m的单板单车道,随着交通量的增加,多加宽2m成为双车道。建立有限元模型,研究新旧板缝间摩擦系数、拉杆间距、土基模量等参数下水泥板加宽2m前后的受力变化,发现新旧路基模量差对板底拉应力影响最大,拉杆间距影响不大,但对板缝两侧弯沉差影响最大。

武汉四环线吴家山至沌口段软土地基病害处置技术研究

武汉四环线吴家山至沌口K81+700~K82+600段两侧鱼(藕)塘密布,软土较厚,地质条件差。软土地基经过清淤回填+土工格栅+碎石垫层+CFG桩方式初步治理后,发生路面裂缝等病害,主要是由于路基填土未得到有效压实、沉降,形成超静孔隙水压力,以及降雨丰沛和重载车辆频繁行驶造成的,因此采用了注浆加固路基+抛石挤淤+反压护坡道的方式对裂缝进行治理。治理监测结果和长期的通车运行表明,路面稳定、软土地基病害得到有效处置。

Composition design and performance evaluation of rubber-particle cement-stabilized gravel

To improve the mechanical properties and durability of the cement-stabilized base,rubber particles of three different sizes and with three different contents were optimally selected,the evolution laws of the mechanical strength and toughness of rubber-particle cement-stabilized gravel(RCSG)under different schemes were determined,and the optimal particle size and content of rubber particles were obtained.On this basis,the durability of the RCSG base was clarified.The results show that with an increase in the rubber particle size and content,the mechanical strength of RCSG gradually decreased,whereas the toughness and transverse deformation ability gradually increased.1%content and 2–4 mm sized RCSG can better balance the relationship between mechanical strength and toughness.The 7 d unconfined compressive strength was 17.7%higher than that of the 4–8 mm RCSG.The 28 d toughness index and ultimate splitting strain can be increased by 9.8%and 6.3 times,respectively,compared with ordinary cement-stabilized gravel(CSG).In terms of durability,compared with CSG,RCSG showed a 3.7%increase in the water stability property of cement-stabilized base with 1%content and 2–4 mm rubber particles,5.5%increase in the frozen coefficient,and 80.6%and 37.9%increase in the fatigue life at 0.70 and 0.85 stress ratio levels,respectively.

海相淤泥资源化制备路基填料试验研究

海相淤泥堆弃占用大量土地资源,二次污染风险高。对瓯海底泥展开单因素试验发现,单一胶凝材料对瓯海底泥固化效果不佳,而混料试验模型表明在水泥∶水渣∶石膏=6.2%∶1.8%∶2.0%的配合比和掺量条件下,固化土7d无侧限抗压强度可达2.12MPa,与实际试验结果2.36 MPa相接近。在该最佳配合比条件下固化土的液塑限、击实性能和CBR值得到显著改善,路用性能优于传统水泥固化土,同时复合固化后瓯海底泥由轻污染等级转变为安全等级,环境安全性可靠。通过微观分析,经复合固化淤泥微颗粒之间的孔隙显著减少,进一步论证了复合固化土性能提升的潜在原因。资源化利用海相淤泥制路基填筑可大规模消纳底泥,经济效益和环保效益显著,本次试验为海相淤泥的道路应用提供了借鉴意义。

城市污泥和盾构渣土制备烧结路面砖的性能研究

通过对盾构土、污泥的化学组成分析和XRD物相分析,制定了喷雾造粒法制作烧结路面砖的最佳配合比,确定了烧结路面砖的各工艺参数,并系统研究了吸水率、抗压强度及重金属浸出对烧结砖性能的影响。试验表明,当粉煤灰2.24%、黏土56.22%、污泥41.54%造粒烧制的路面砖抗压强度最好;当含水率(质量分数)为8.67%、成型压力30 MPa、烧结温度1080℃时,制备的烧结砖性能最优,抗压强度80 MPa,符合规范对抗压强度的要求;烧结砖吸水率随着烧结温度和成型压力的增加在逐渐降低;抗压强度随着烧结温度和成型压力的升高在逐渐升高;对烧结砖进行重金属浸出检测,重金属测试值远小于规范规定限制。

公路沥青路面水泥稳定土配比及性能

针对处于不同路面结构层的沥青混凝土的配合比设计,有着各自不同的设计要求。对沥青路面水泥稳定土配比及性能进行了研究分析,确定了沥青混凝土的配合比,从强度、稳定性、耐久性等方面为优化沥青路面的设计和施工提供理论依据。主要介绍了沥青路面水泥稳定强度理论,并对原料配合比的设计原则和方法进行了深入分析,指出要使沥青路面水泥具有良好的耐久性、稳定性,同时又具有良好的公路使用品质,就需要对其进行科学的配比设计及性能分析,从而进一步优化其配比和施工工艺,提高沥青路面的整体性能。

Structural characteristics of cement-stabilized soil bases with 3D finite element method

Cement-stabilized soil bases have been widely used in expressways due to its high strength,appropriate stiffness,good water resistance,and frost resistance.So far,the structural characteristics and mechanical behaviors of cement-stabilized soil bases were not investigated so much.In this paper,the 3D elastic-plastic finite element method(FEM)was used to analyze the mechanical behaviors and structural characteristics of cementstabilized soil bases from construction to operation.The pavement filling and the traffic loading processes were simulated,and a contact model was used to simulate the contact behavior between each layer of the pavement.Considering the construction process,the structural characteristics and mechanical behaviors of cementstabilized soil bases were studied under asphalt-concrete pavement conditions.Furthermore,the general rules of deformations and stresses in cement-stabilized soil bases under different conditions were discussed,and some suggestions were put forward for the design and construction of cement-stabilized soil bases.

通州区马驹桥镇非道路用地条件下农村等外公路提升建设的新思路

随着通州区马驹桥镇社会经济的高速发展,道路交通出行的需求日益增加,然而现有道路不能满足交通需求,亟须对道路交通进行改造升级。论文对通州区马驹桥镇农村等外公路提升建设项目进行详细阐述,通过固化土路面的建设,有效解决了在非道路用地条件下对农村等外公路的提升改造。

基于路基改良设计的土体承载特征及路面结构力学响应研究

为研究路基改良设计下路基土体承载力学及水泥混凝土路面结构层力学响应特征,文章采用了力学试验及动力响应计算方法,分析了改良剂掺量和改良深度对路基、路面结构层的影响。研究表明,围压作用对改良土试样应变的影响效应大于改良剂掺量,需着重考虑围压作用对应变的影响。

盐渍土地区路基路面施工材料盐含量检测方法优化与应用

盐渍土含盐量过高时,用作路基路面施工材料容易出现公路表面裂缝、塌陷等情况。本文选取柳格国高G3011敦煌至当金山口高速公路建设项目的路基路面施工材料作为研究对象,选取优化后的质量法,测定盐渍土浸出液中的易溶盐含量。实验结果表明,优化后的方法有效测定路基路面施工材料中的盐含量。