High Citadel / Landslide (55 page)

‘Don’t think about it too much, Clarry,’ advised Mac. ‘You might sprain your brain. Boyd knows what he’s doing. It’s worrying the Mattersons, isn’t it? So why should it worry you, too?’

‘I don’t know that it does,’ said Clarry, brightening a little. ‘It’s just that I don’t understand what’s going on.’

Mac chuckled. ‘Neither does anyone else,’ he said. ‘Neither does anyone else—but we’re getting there slowly.’ Clarry said, ‘You want to watch out for Howard Matterson, Mr Boyd—he’s got a low boiling-point. When he gets going he can be real wild. Sometimes I think he’s a bit nuts.’

I thought so, too, but I said, ‘I wouldn’t worry too much about that, Clarry, I can handle him.’

When we pulled up in front of Mac’s cabin, Clarry said, ‘Say, isn’t that Miss Trinavant’s station wagon?’

‘It is,’ said Mac. ‘And there
she
is.’

Clare waved as she came to meet us. ‘I felt restless,’ she said. ‘I came over to find out what’s going on.’

‘Glad to have you,’ said Mac. He grinned at me. ‘You’ll have to sleep out in the woods again.’

Clarry said, ‘Your auto going all right, Miss Trinavant?’

‘Perfectly,’ she assured him.

‘That’s great. Well, Mr Boyd, I’ll be getting along home—my wife will be wondering where I am. Will you need me again?’

‘I might,’ I said. ‘Look, Clarry; Howard Matterson saw you with me. Will that make trouble for you? I’m not too popular right now.’

‘No trouble as far as I’m concerned—he’s been trying to put me out of business for years and he ain’t done it yet. You want me, you call on me, Mr Boyd.’ He shook his head. ‘But I sure wish I knew what was going on.’

Mac said, ‘You will, Clarry. As soon as we know ourselves.’

Summerskill went home and Mac shepherded Clare and me into the cabin.

‘Bob’s being awfully mysterious about something,’ he said. ‘He’s got some crack-brained idea that the dam is going to collapse. If it does, you’ll be four million dollars to the bad, Clare.’

She shot me a swift glance. ‘Are you serious?’

‘I am. I’ll be able to tell you more about it when I’ve looked at the cores I’ve got in the jeep. Let’s unload them, Mac.’

Pretty soon the table was filled with the lengths of two-inch cylindrical core. I arranged them in order and rejected those I didn’t want. The cores I selected for inspection had a faint film of moisture on the surface and felt smooth and slick, and a check on the numberings told me that they’d come up from the thirty-foot level. I separated them in three heaps and said to Clare, ‘These came from three borings I
made today on the escarpment between the dam and the powerhouse.’ I stroked one of them and looked at the moisture on my finger. ‘If you had as many sticks of dynamite you couldn’t have anything more dangerous.’

Mac moved away nervously and I smiled. ‘Oh, these are all right here; it’s the stuff up at the escarpment I’m worried about. Do you know what “thixotropic” means?’

Clare shook her head and Mac frowned. ‘I should know,’ he admitted. ‘But I’m damned if I do.’

I walked over to a shelf and picked up a squeeze-tube. ‘This is the stickum I use on my hair; it’s thixotropic gel.’ I uncapped the tube and squeezed some of the contents into the palm of my hand. ‘Thixotropic means “to change by touch”. This stuff is almost solid, but when I rub it in my hands, like this, it liquefies. I brush it on to my hair—so—and each hair gets a coating of the liquid. Then I comb it and, after a while, it reverts to its near solid state, thus keeping the hair in place.’

‘Very interesting,’ said Mac. ‘Thinking of starting a beauty parlour, son?’

I made no comment. Instead I picked up one of the cores. ‘This is clay. It was laid down many thousands of years ago by the action of glaciers. The ice ground the rock to powder, and the powder was washed down rivers until it reached either the sea or a lake. I rather think that this was laid down in a fresh-water lake. I’ll show you something. Got a sharp knife, Mac?’

He gave me a carving knife and I cut two four-inch lengths from the middle of the same core. One of the lengths I put on the table standing upright. ‘I’ve prepared for this,’ I said, ‘because people won’t believe this unless they see it, and I’ll probably have to demonstrate it to Bull Matterson to get it through his thick skull. I have some weights here. How many pounds do you suppose that cylinder of clay can support?’

‘I wouldn’t know,’ said Mac. ‘I suppose you
are
getting at something.’

I said, ‘The cross-section is a bit over three square inches.’ I put a ten-pound weight on the cylinder and quickly added another. ‘Twenty pounds.’ A five-pound weight went on top of that. ‘Twenty-five pounds.’ I added more weights, building up a tower supported by the cylinder of clay. ‘Those are all the weights I have—twenty-nine pounds. So far we’ve proved that this clay will support a weight of about fifteen hundred pounds a square foot. Actually, it’s much stronger.’

‘So what?’ said Mac. ‘You’ve proved it’s strong. Where has it got you?’

‘Is it strong?’ I asked softly. ‘Give me a jug and a kitchen spoon.’

He grumbled a bit about conjuring tricks, but did what I asked. I winked at Clare and picked up the other clay cylinder. ‘Ladies and gentlemen, I assure you there is nothing up my sleeve but my arm.’ I put the clay into the jug and stirred vigorously as though I were mixing cake dough. Mac looked at me unimpressed, but Clare was thoughtful.

I said, ‘This is the meaning of thixotropic,’ and poured the contents of the jug on to the table. A stream of thin mud splashed out and flowed in a widening pool of liquidity. It reached the edge of the table and started to drip on to the floor.

Mac let out a yelp. ‘Where did the water come from? You had water already in that jug,’ he accused.

‘You know I didn’t. You gave me the jug yourself.’ I pointed at the dark pool. ‘How much weight will that support, Mac?’

He looked dumbfounded. Clare stretched out her hand and dipped a finger into the mud. ‘But where did the water come from, Bob?’

‘It was already in the clay.’ I pointed at the other cylinder still supporting its tower of weights. ‘This stuff is fifty per cent water.’

‘I still don’t believe it,’ said Mac flatly. ‘Even though I’ve seen it.’

‘I’ll do it again if you like,’ I offered.

He flapped his hand. ‘Don’t bother. Just tell me how this clay can hold water like a sponge.’

‘Remember when you looked through the microscope—you saw a lot of little flat chips of rock?’ He nodded. ‘Those chips are very small, each about five-hundredths of a millimetre, but there are millions of them in a cubic inch. And—this is the point—they’re stacked up like a house of cards. Have you ever built up a house of cards, Clare?’

She smiled. ‘I’ve tried, but it’s never got very high. Uncle John was an expert at it.’

I said, ‘Then you know that a house of cards structure is mostly empty space.’ I tapped a core. ‘Those spaces are where the water is held.’

Mac still looked a little bewildered, but he said, ‘Sounds feasible.’

Clare said quietly, ‘There’s more, isn’t there? You haven’t shown us this just as a party trick.’

‘No, I haven’t,’ I said. ‘As I said, when this sediment was first laid down it was at the bottom of the sea or a lake. Any salts in the water tend to have an electrolytic action—they act as a kind of glue to stick the whole structure together. If, however, the salts leach out, or if there were very few salts in the first place, as would happen if the deposit were laid down in fresh water, then the glueing effect becomes less. Clare, what is the most characteristic thing about a house of cards?’

‘It falls down easily.’

‘Right! It’s a very unstable structure. I’d like to tell you a couple of stories to illustrate why this stuff is called quick clay. Deposits of quick clay are found wherever there has
been much glaciation—mainly in Russia, Scandinavia and Canada. A few years ago, round about the middle fifties, something happened in Nicolet, Quebec. The rug was jerked from under the town. There was a slide which took away a school, a garage, quite a few houses and a bulldozer. The school wound up jammed in a bridge over the river and caught fire. A hole was left six hundred feet long, four hundred feet wide and thirty feet deep.’

I took a deep breath. ‘They never found out what triggered that one off. But here’s another one. This happened in a place called Surte in Sweden, and Surte is quite a big town. Trouble was it slid into the Gota river. Over a hundred million cubic feet of topsoil went on the rampage and it took with it a railroad, a highway and the homes of three hundred people.
That
one left a hole half a mile long and a third of a mile wide. It was started by someone using a pile-driver on a new building foundation.’

‘A pile-driver!’ Mac’s mouth stayed open.

‘It doesn’t take much vibration to set quick clay on the move. I told you it was thixotropic, it changes by touch—and it doesn’t need much of a touch if the conditions are right. And when it happens the whole of a wide area changes from solid to liquid and the topsoil starts to move—and it moves damn’ fast. The Surte disaster took three minutes from start to finish. One house moved four hundred and fifty feet—how would you like to be in a house that took off at nearly twenty miles an hour?’

‘I wouldn’t,’ said Mac grimly.

I said, ‘Do you remember what happened to Anchorage?’

‘Worst disaster Alaska ever had,’ said Mac. ‘But that was a proper earthquake.’

‘Oh, there
was
an earthquake, but it wasn’t that that did the damage to Anchorage. It
did
trigger off a quick clay slide, though. Most of the town happened to be built on quick clay and Anchorage took off for the wide blue
yonder, which happened to be in the direction of the Pacific Ocean.’

‘I didn’t know that,’ said Mac.

‘There are dozens of other examples,’ I said. ‘During the war British bombers attacking a chemical factory in Norway set off a slide over an area of fifty thousand square yards. And there was Aberfan in South Wales: that was an artificial situation—the slag heap of a coal mine—but the basic cause was the interaction of clay and water. It killed a schoolful of children.’

Clare said, ‘And you think the dam is in danger?’

I gestured at the cores on the table. ‘I took three samples from across the escarpment, and they show quick clay right across. I don’t know how far it extends up and down, but it’s my guess that it’s all the way. There’s an awful lot of mud appeared down at the bottom. A quick clay slide can travel at twenty miles an hour on a slope of only one degree. The gradient of that escarpment must average fifteen degrees, so that when it goes, it’ll go fast. That power plant will be buried under a hundred feet of mud and it’ll probably jerk the foundations from under the dam, too. If that happens, then the whole of the new Matterson Lake will follow the mud. I doubt if there’d be much left of the power plant.’

‘Or anyone in it,’ said Clare quietly.

‘Or anyone in it,’ I agreed.

Mac hunched his shoulders and stared loweringly at the cores. ‘What I don’t understand is why it hasn’t gone before now. I can remember when they were logging on the escarpment and cutting big trees at that. A full grown Douglas fir hits the ground with a mighty big thump—harder than a pile-driver. The whole slope should have collapsed years ago.’

I said, ‘I think the dam is responsible. I think the quick clay layer surfaces somewhere the other side of the dam. Everything was all right until the dam was built, but then they closed the sluices and the water started backing up and
covering the quick clay outcropping. Now it’s seeping down in the quick clay all under the escarpment.’

Mac nodded. ‘That figures.’

‘What are you going to do about it?’ asked Clare.

‘I’ll have to tell the Mattersons somehow,’ I said. ‘I tried to tell Howard this afternoon but he shut me up. In my report I even told him to watch out for quick clay, but I don’t think he even read it. You’re right, Clare: he’s a sloppy businessman.’ I stretched. ‘But right now I want to find out more about these samples—the water content especially.’

‘How will you do that?’ asked Mac interestedly.

‘Easy. I cut a sample and weigh it, then cook the water out on that stove there, then weigh it again. It’s just a sum in subtraction from then on.’

‘I’ll make supper first,’ said Clare. ‘Right now you’d better clear up this mess you’ve made.’

After supper I got down to finding the water content. The shear strength of quick clay depends on the mineral constituents and the amount of water held—it was unfortunate that this particular clay was mainly montmorillonite and deficient in strength. That, combined with a water content of forty per cent, averaged out over three samples, gave it a shear strength of about one ton per square foot.

If I was right and water was seeping into the quick clay strata from the new lake, then conditions would rapidly become worse. Double the water percentage and the shear strength would drop to a mere 500 pounds a square foot, and a heavy-footed construction man could start the whole hillside sliding.

Clare said, ‘Is there anything that can be done about it—to save the dam, I mean?’

I sighed. ‘I don’t know, Clare. They’ll have to open the sluices again and get rid of the water in the lake, locate where the clay comes to the surface and then, maybe, they
can seal it off. Put a layer of concrete over it, perhaps. But that still leaves the quick clay under the escarpment in a dangerous condition.’

‘So what do you do then?’ asked Mac.

I grinned. ‘Pump some more water into it.’ I laughed outright at the expression on his face. ‘I mean it, Mac; but we pump in a brine solution with plenty of dissolved salts. That will put in some glue to hold it together and it will cease to be thixotropic.’

‘Full of smart answers, aren’t you?’ said Mac caustically. ‘Well, answer this one. How do you propose getting the Matterson Corporation to listen to you in the first place? I can’t see you popping into Howard’s office tomorrow and getting him to open those sluices. He’d think you were nuts.’

‘I could tell him,’ said Clare.

Mac snorted in disgust. ‘From Howard’s point of view, you and Bob have gypped him out of four million bucks that were rightly his. If you tried to get him to close down construction on the dam he’d think you were planning another fast killing. He wouldn’t be able to figure how you’re going to do it, but he’d be certain you were pulling a fast one.’