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小型旋挖钻机影响钻进效果原因分析-打桩机

发表日期:2019-12-07 14:41 文章编辑:admin 所属栏目:旋挖钻机新闻

小型旋挖钻机影响钻进效果原因分析钻进效率是指在正常工作时,所钻桩孔的总深度与所费总时间之比。影响旋挖钻机钻进效率的因素有:孔深、孔径、地层情况、钻具选配及钻杆型式等。

1.孔深对钻进效率的影响

旋挖钻机施工中每当钻头装满土后都要提钻卸土,然后再把钻具下到孔底。显然孔深越小,效率越高。钻进效率V=H1/(t1+t2+2H/V1)(m/h)其中H,为每钻进尺量,m;t1,为钻满一斗所需时间,h;t2为卸土时间,h;H为孔深,m;V,为提、下钻速度,m/h。从上式可知,当其他参数不变时,H越大则V越小,当孔深超过100m后,钻进效率急剧下降,当孔深超过120m时钻进效率会低于其他工法的效率,且事故率大幅升高。因此建议进行超深孔施工时,尽量选用正反循环等其他工法。

2.孔径对钻进效率的影响
目前旋挖钻机最常用的是旋挖钻斗,桶体中空,下部有2个进土斗门。在钻进时,钻碴通过钻齿切削从斗门进人桶体内,在下部钻碴的推力下,上部碴土逐渐上升进入桶内,直至装满桶体。钻孔直径大小影响钻进效率的主要有两点,一是碴土进入斗门的速度,二是碴土在桶体内上升的速度。首先碴土进人斗门速度与斗门进土面积有关,钻孔直径越大,斗门进土面积越大,进土速度越大;
其次碴土在斗体的上升速度与很多因素有关,最主要的是:
(1)碴土的重量;
(2)桶壁与碴土的粘附力。
很显然,钻孔直径越大,碴土的重量越大,但桶壁与碴土的粘附力会减小;当钻头直径减小时,碴土重量减轻,但桶壁与碴土的粘附力则会增大。
当然还有一些其他因素,如钻桶的形状、钻桶表面的摩擦系数、碴土的含水量等,都会影响碴土在桶体的上升速度。综合以上情况,钻孔直径对钻进效率的影响呈现如图2的规律,从图中可以看出,钻孔直径小于1m和大于2m时钻进效率会下降。

.地层对钻进效率的影响
地层对钻进效率的影响主要表现在地层钻进的难易程度(地层的可钻性)和卸土的快慢。
3.1地层的可钻性
地层的可钻性是一个复杂的指标,国内外地质钻探专家把地层按钻进的难易程度进行分级,我国是参照前苏联的分级法,把地层分为12个级别,级别越大可钻性越差。由于在大口径灌注桩孔的施工中对地层的可钻性还没有分级,所以对应不同的地层的钻进工艺就没有统一标准和规范。旋挖钻机桩孔施工的碎岩和携粉的机理与地质钻探还是有区别的,旋挖钻机主要是通过切挖把所钻层分割成大块岩碴,然后装进钻头体内,而地质钻探主要以冲磨把地层磨成细小颗粒,通过冲洗液携带到地面。所以旋挖钻机施工地层的可钻性指标,最主要的是地层的杭压强度,只要钻机所施加的钻压大于地层的抗压强度,钻齿就能压人地层,从而切割成块,作用在钻齿的压强一定要大于地层的抗压强度,即F/S>G式中 F——压力;S——钻齿接触孔底的面积;G——地层的抗压强度。
如果满足以上条件,再优化其他因素,钻进效率就会大大提高,如调整回转速度及钻齿角度等。由上可知,地层越硬,钻进效率越低,因为所需钻压变大,在压力一定时使地层破碎的时间加大。
3.2卸土因素对钻进效率的影响
由于所钻地层的成份、结构、含水量等不同,造成钻碴的粘性不同,当钻碴装满斗体提出地面卸土时,其粘性越大,卸土所需时间就越长。
4.钻具选配对钻进效率的影响
所用钻头种类很多,结构千变万化,对于不同设备机型、不同施工方法和不同地层,要选用不同的钻头。目前旋挖钻机常用的钻头有以下6大类:螺旋钻头、旋挖钻斗、筒式取芯钻头、扩底钻头、冲击钻头和冲抓锥钻头,每一大类中又有很多品种。钻具的选配对旋挖钻机钻进效率影响很大,应根据所钻地层选取最适合的钻头获得钻进效率最大化。
旋挖钻机可根据地层情况配置不同的钻头,在粘性土层可使用长钻筒,加快钻进速度;对于砂卵石含量较大的地层可使用短钻筒,配臵泥浆护壁,控制钻速;对于含孤石、漂石及较硬岩石地层可换用长、短螺旋钻头进行处理,松动后再换上钻筒继续钻进。与常规钻机相比,回转扭矩大,并可根据地层情况自动调整。
5.钻杆的选择对钻进效率的影响
旋挖钻机常用钻杆分为两大类一摩阻式和机锁式,摩阴式钻杆主要是靠钻杆键条的之间的摩擦力产生钻压,此种钊井干的特点是:随钻随加压,无需找加压点,提钻杆时无需解锁,操作方便,提、下钻具速度高,但加压力小,在较软地层钻进中使用该类钻杆效率高;机锁式钻杆是通过钻杆每层之间的加压点,对接后把动力头的加压力传到孔底钻具上形成钻压,此类钻杆的特点是:钻进时只有在各层之间的加压点对接后才能产生最大钻压,提升钻杆时需先解锁,且提、下钻速度慢,适合于较硬地层。

Analysis of the influence of small rotary drilling rig on drilling efficiency the ratio of the total depth of the drilled pile hole to the total time spent in normal operation. The factors that affect the drilling efficiency of rotary drilling rig include: hole depth, hole diameter, formation conditions, selection and matching of drilling tools and drill pipe type, etc.

1. Effect of hole depth on drilling efficiency

In the construction of rotary drilling rig, every time the bit is full of soil, it is necessary to lift the drill and unload the soil, and then lower the drilling tool to the bottom of the hole. Obviously, the smaller the hole depth, the higher the efficiency. Drilling efficiency v = H1 / (T1 + T2 + 2H / V1) (M / h), where h is the measurement per drilling ruler, m; T1 is the time required to drill a full bucket, h; T2 is the unloading time, h; h is the hole depth, m; V is the lifting and tripping speed, M / h. It can be seen from the above formula that when other parameters remain unchanged, the larger h is, the smaller V is. When the hole depth exceeds 100m, the drilling efficiency drops sharply. When the hole depth exceeds 120m, the drilling efficiency will be lower than that of other methods, and the accident rate will increase significantly. Therefore, it is suggested that other construction methods, such as positive and negative circulation, should be used as much as possible during ultra deep hole construction.

2. Effect of hole diameter on drilling efficiency

At present, the most commonly used rotary drilling rig is the rotary drilling bucket, the barrel is hollow, and the lower part has two earth inlet doors. During drilling, the drilling muck enters the barrel through the bucket gate through the cutting of drilling teeth. Under the thrust of the lower part of the drilling muck, the upper muck soil gradually rises into the barrel until the barrel is full. There are two main factors that affect drilling efficiency, one is the speed of muck entering the bucket door, the other is the speed of muck rising in the bucket body. First of all, the speed of mucking into the bucket door is related to the area of the bucket door. The larger the drilling diameter is, the larger the area of the bucket door is, and the larger the speed of mucking into the bucket door is;

Secondly, the rising speed of ballast soil in the bucket body is related to many factors, the most important is:

(1) weight of ballast soil;

(2) adhesion between bucket wall and ballast soil.

Obviously, the larger the drilling diameter is, the greater the weight of the ballast soil is, but the adhesion between the barrel wall and the ballast soil will be reduced; when the drill diameter is reduced, the weight of the ballast soil will be reduced, but the adhesion between the barrel wall and the ballast soil will be increased.

Of course, there are some other factors, such as the shape of the drilling barrel, the friction coefficient of the surface of the drilling barrel, the moisture content of the muck soil, etc., which will affect the rising speed of the muck soil in the barrel. Based on the above situation, the influence of drilling diameter on drilling efficiency is shown in Figure 2. It can be seen from the figure that when the drilling diameter is less than 1 m or more than 2 m, the drilling efficiency will decrease.

. effect of formation on drilling efficiency

The influence of formation on drilling efficiency mainly lies in the difficulty of drilling (drillability of formation) and the speed of unloading.

3.1 drillability of formation

The drillability of the formation is a complex index. Domestic and foreign geological drilling experts classify the formation according to the degree of drilling difficulty. China divides the formation into 12 levels according to the classification method of the former Soviet Union. The higher the level, the worse the drillability. Since the drillability of the stratum has not been classified in the construction of large-diameter cast-in-place pile hole, there is no unified standard and specification for the drilling technology of different stratum. The mechanism of rock fragmentation and powder carrying in pile hole construction of rotary drilling rig is different from that of geological drilling. Rotary drilling rig mainly divides the drilled layer into large rock ballast by cutting, and then loads it into drill body. While geological drilling mainly grinds the stratum into small particles by flushing, and carries them to the ground by flushing fluid. Therefore, the drillability index of rotary drilling rig construction stratum is mainly the formation's Hangzhou pressure strength. As long as the drilling pressure exerted by the drilling rig is greater than the formation's compressive strength, the drilling teeth can press the stratum, thus cutting into blocks. The pressure acting on the drilling teeth must be greater than the formation's compressive strength, that is, f-pressure in the F / s > G formula; S-the area of the drilling teeth contacting the bottom of the hole; g-The formation's resistance Pressure intensity.

If the above conditions are met and other factors are optimized, the drilling efficiency will be greatly improved, such as adjusting the rotary speed and the angle of the drill teeth. It can be seen from the above that the harder the formation is, the lower the drilling efficiency is, because the required drilling pressure becomes larger, and the time for the formation to be broken increases when the pressure is fixed.3.2 influence of unloading factors on drilling efficiency



 

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