Influence of soil density on gas permeability and water retention in soils amended with in-house produced biochar

Biochar has been used as an environment-friendly enhancer to improve the hydraulic properties(e.g.suction and water retention) of soil.However,variations in densities alter the properties of the soil-biochar mix.Such density variations are observed in agriculture(loosely compacted) and engineering(densely compacted) applications.The influence of biochar amendment on gas permeability of soil has been barely investigated,especially for soil with diffe rent densities.The maj or obj ective of this study is to investigate the water retention capacity,and gas permeability of biochar-amended soil(BAS) with different biochar contents under varying degree of compaction(DOC) conditions.In-house produced novel biochar was mixed with the soil at different amendment rates(i.e.biochar contents of 0%,5% and 10%).All BAS samples were compacted at three DOCs(65%,80% and 95%) in polyvinyl chloride(PVC)tubes.Each soil column was subjected to drying-wetting cycles,during which soil suction,water content,and gas permeability were measured.A simplified theoretical framework for estimating the void ratio of BAS was proposed.The experimental results reveal that the addition of biochar significantly decreased gas permeability k_g as compared with that of bare soil(BS).However,the addition of 5%biochar is found to be optimum in decreasing kg with an increase of DOC(i.e.k_(g,65%) k_(g,80%) k_(g,95%)) at a relatively low suction range(200 kPa) because both biochar and compaction treatment reduce the connected pores.     

强夯的物质点法模拟及其能量转化规律分析

提出大应力范围内的密度相关土体本构模型,适用于分析强夯等作用下的土体变形问题。对刚柔接触算法进行了修正,用物质点法结合提出的本构模拟了强夯过程。与其他数值模拟将荷载假设为三角形应力波作为输入荷载不同,通过输入夯锤与土体的碰撞速度实现加载。模拟结果与承德机场4标段某处试验数据进行了对照,吻合较好。提出强夯过程中的能量转化率的概念,对能量转化的规律进行了研究,为研究强夯问题提供了新视角。模拟分析表明,能量转化率的提高不总意味着每击夯沉量的提高,因为能量在较大范围的扩散可能导致高能量转化率下的低夯沉量;剪切变形过程中吸收较多的塑性应变能,可能会使体积压缩变形吸收的塑性应变能向局部集中。通过数值模拟还发现,重锤低落时的能量转化率高于轻锤高落,一般可产生更大的夯沉量。     

Feasible Preparation of a Thin‐Film Composite Nanofiltration (TFC NF) Membrane with Enhanced Skin–Substrate Adhesion and Compaction Resistance: In Situ Construction of Rigid–Flexible Polymer Composited Microspheres (CPs) in the Casting Solution

Novel microspheres (CPs) composited by rigid and flexible polymers are synthesized and embedded in the supporting membranes to enhance both the skin–substrate adhesion and compaction resistance of the thin‐film composite (TFC) nanofiltration membranes. The CPs are in situ formed in the casting solution after the rigid poly(p‐phenylene terephthamide) (PPTA) is produced in the flexible poly(m‐phenylene isophthalamide) (PMIA) solution. Then the PPTA/PMIA in situ blending membranes are prepared by using the NIPs method, and the TFC NF membranes are fabricated via interfacial polymerization on them. The CPs are characterized via polarizing microscopy and TEM. The surface morphology and chemical composition of the blended membranes are characterized by using FESEM, AFM, FTIR, and WCA, respectively. As the results show, the supporting membrane with higher PPTA content exhibits higher permeability, thermal stability, and compaction resistance. Moreover, the adhesion strength between the TFC functional layer and the supporting membrane is improved significantly. It is proposed that this improvement can be attributed to the CPs that are exposed on the top surface of the supporting membrane, which leads to a great enhancement because of the anchoring effect between the functional layer and the CPs.     

Estimating of the Dry Unit Weight of Compacted Soils Using General Linear Model and Multi-layer Perceptron Neural Networks

Compaction of earth fill is a very important stage of construction projects. Degree of compaction is defined by relative compaction. The relative compaction of a compacted earth fill is calculated by dividing the dry unit weight obtained from in situ tests by-into the maximum dry unit weight obtained from laboratory compaction tests. This rate represents compaction quality in the field. Numerous test methods such as sand cone, rubber balloon, nuclear measurements, etc., are available to determine the maximum dry unit weight of soils in the field. It is well known that these methods have disadvantages as well as advantages. This study focused on estimation of dry unit weight of soils depending on water contents and P-wave velocities of compacted soils. The multi-layer perceptron (MLP) neural networks and general linear model (GLM) were used in this study to estimate the dry unit weight of different types of soils. Results of the MLP neural networks were compared with the GLM results. Based on the comparisons, it is found that the MLP generally gives better dry unit weight estimates than the GLM technique. The laboratory experiments and modeling studies showed that a new method for compaction control can be developed depending on P-wave velocity to estimate of the dry unit weight of compacted soils.     

连续分布的粗粒土级配方程与压实性能

以Morgan等人提出的生长曲线为基础,提出了可反映粗粒土"S型"以及"上凸型"颗粒分布的2参数级配方程及参数取值范围;当形状参数a趋向无穷大时,则级配方程转化为分形分布公式。在此基础上,提出了采用相对密度试验手段确定最优压实性能级配的方法。建议级配方程对于长河坝、大石峡、两河口等高坝的填筑级配,具有很好的适用性。利用所得研究成果,对大石峡砂砾料进行室内相对密度试验,结果表明:①对于最大粒径60 mm的不同分布规律的粗粒土而言,随着级配参数的变化,其最大、最小干密度均存在极值点或拐点,且对应的临界P5值都在35%附近。②临界P5值对应粗粒土的极优压实性能级配;颗粒级配越接近分形分布,压实性能越好,临界P5值对应的分形分布级配,即为最优压实性能级配。接近分形分布的长河坝堆石料,较低的现场压实参数却获得了较高的填筑干密度,也佐证了这一结论的合理性。③利用临界分形维数的尺度无关性,可以方便地将室内最优压实性能级配的研究成果推广至现场不同最大粒径的工程级配。结论可用于粗粒土的级配设计以及压实性能评价。     

夯能的传播和夯实柱体的形成（强夯加固机理探讨之三）

本文简要的介绍了波动理论。振动的传播就是能量的传播。沿途各点波的强度及其沿途的变化可用沿途各点的振幅的大小及其变化来表示。夯锤下存在一维波动，它决定了夯坑下夯实体按柱体形状往深部延伸发展。本文讨论对强夯工程夯点布置设计有重要参考价值。     

强夯法在碎石填土地基处理中的应用

简要介绍了强夯法加固岳阳石油化工总厂技改工程碎石填土地基的情况，并对一些有关问题进行了讨论